Fluid management theory and practice

Intravenous fluid therapy in adults in hospital theory and practice short lecture

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    Intravenous fluid therapy in adults in hospital theory and practice
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    • 1. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 1 of 35 Objectives Module 1 : Physiology Module 2 : Clinical Assessment Module 3 : Prescribing Module 4 : Case Scenarios Module 5 : OSCE Physiology There are a number of ways in which water can enter and leave the body. For example, drinking fluids increases the amount of water in the body, urination decreases the amount of water in the body .How much water is lost and gained by these different mechanisms is dependent on a number of factors, including age, gender, environmental factors (eg external temperature) and different disease states. In Health In healthy people, the most common forms of water gain and loss are shown below In normal statue Per kg of body weight, a healthy adult is likely to require aprox 30ml of fluid per day. does not apply to estimating paediatric fluid requirements, in which case other estimators are used.
    • 2. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 2 of 35 In Disease In disease states, the body’s ability to maintain fluid homeostasis may be impaired. It is important to note that these losses and gains can be hugely variable, e.g. DKA may involve fluid losses of 10 litres or more (and as such would require equally high volumes of resuscitation fluids)! The human body is very well adapted to maintain homeostasis even in fairly extreme fluctuations in fluid input/output. The kidneys play a vital role in this and can easily handle (and remove) huge volumes of extra fluid in health. However, in disease states (eg Chronic Kidney Disease CKD), the kidneys are much less efficient and these patients are at high risk of fluid overload.
    • 3. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 3 of 35 Fluid Compartments Approximately 60% of body weight is made up of water, although this varies slightly with age and gender. This water can be thought of as distributed across a number of compartments.The approximate fluid distribution between these compartments in health is shown below. The intracellular compartment is sometimes also called the ‘First space’. The extracellular compartment is sometimes also called the ‘Second space’ In Disease States In disease states, the distribution of body water may differ from the standard model shown on the previous page (Physiology : Fluid Compartments), in a number of ways: 1.Global fluid loss – There is water loss from all fluid compartments Eg Dehydration. 2.Global fluid gain – There is water gain in all fluid compartments (most often the majority of fluid excess is in the extracellular space) Eg CKD. 3.Abnormal distribution – This is where fluid losses or gains occur unequally between compartments. This is usually due to changes in hydrostatic or oncotic pressure driving exchange between the extracellular fluid compartments (by Starling’s law). Eg Heart failure causes high hydrostatic pressures in the venous system, leading to extravasation of fluid into the interstitial space, causing oedema. Eg Liver failure causes lowered intravascular oncotic pressure (due to reduced albumin synthesis), again leading to extravasation of fluid causing oedema. Test Yourself ! Why do we examine most carefully for oedema in the feet and sacrum?
    • 4. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 4 of 35 Excess tissue fluid can move relatively freely through the interstitial space. Because people stand and walk on their feet the fluid most often collects here due to gravity. It is often more noticeable towards the end of the day. In patients who are bedbound this gravity 'dependent' fluid will collect in the sacrum instead. A further example of abnormal distribution may be the accumulation of fluid in body spaces where there usually is none (or little), for example bowel, peritoneum and pleural space. These areas are collectively known as the ‘Third space’. Although enormous amounts of fluid may collect in these spaces, it is not ‘available’ for exchange with the rest of the fluid compartment model and so effectively acts as a fluid loss. Patients with large third space losses can be dangerously dehydrated, even though they may have low or normal measurable outputs on the fluid balance chart. Electrolytes Electrolytes are intrinsically linked to fluid homeostasis. Almost all fluids that are lost from the body will contain electrolytes of varying composition and concentrations, and many of the intravenous fluids that are prescribed will contain some form of electrolytes. Electrolytes may be categorised as Cations (positively- charged ions) and anions (negatively-charged ions), and may preferentially distribute to a certain fluid compartment. The main extracellular cation is sodium, the main extracellular anion is chloride. The main intracellular cation is potassium, the main intracellular anion is Phosphate. The most important electrolytes to consider are sodium and potassium.
    • 5. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 5 of 35 In Health The average daily electrolyte loss (and therefore requirement) is: Sodium 1-2mmol/kg/day ((millimole)) Potassium 1mmol/kg/day Therefore, for a 70 kg male the average daily requirements in health are: Sodium ~ 70-140 mmol/day Potassium ~ 70 mmol/day The figures quoted above are a rough guideline only. Sodium and potassium excretion will vary considerably with intake. In addition, sodium excess may be a major contributor to hypertension, so this is something to bear in mind especially in this risk group. What is the normal plasma concentration of potassium? 3.5 - 5.0 mmol/L - Correct! 5.0 mmol/L - no, below 3.5 is hypokalaemia, and above 5.0 is hyperkalaemia. Both can cause dangerous cardiac arrhythmias, which may be fatal if left untreated! Plasma concentrations of > 6.5 mmol/L is a medical emergency and requires urgent intervention. In Disease In some disease states electrolyte losses may be very high. These patients will need careful monitoring and replacement of electrolytes. For example: gastrointestinal losses are often high in potassium, and these patients may require potassium supplementation to levels that would be dangerous to a ‘healthy’ person. The loss of anions in GI disease includes bicarbonate losses in small bowl content. If the losses are high, the bicarbonate should be replaced directly or with a bicarbonate precursor such as lactate. Replacement with sodium chloride (normal saline fluid) in this instance may worsen the acidotic state. However, in other disease states electrolyte losses may be low, or patients may be particularly sensitive to high concentrations of electrolytes, for example patients with ⛺chronic kidney disease or⛺cardiac arrhythmia respectively. These patients may require restriction of certain electrolytes. It is vital to always consider the needs of the individual patient when prescribing fluids or electrolytes, as will be discussed in module 3 : prescribing. Clinical Assessment The learning objectives for this module are: 1. To have an appreciation of the important questions to ask in a patient history in order to guide an impression of fluid status. 2. To be able to recognise clinical signs in the dehydrated and fluid overloaded patient.
    • 6. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 6 of 35 3. Know how to fill out and interpret a fluid balance chart as well as to appreciate its limitations. 4. Understand the benefit of daily weighing of patients prone to retaining fluid. 5. Appreciate which key serum biochemical markers alert clinicians to fluid deficit and overload. To aid assessment of a patient’s fluid status one may look at the following; 1. Patient history 2. Clinical examination of the patient 3. Fluid balance charts 4. Weighing the patient 5. Blood biochemistry Note that more accurate means of assessing fluid balance do exist. These include central venous catheterisation and other invasive monitoring. This tends to be used in critically ill patients and intraoperatively if the patient is at high risk of complications. The methods of assessment discussed here are those you are likely to see on the general medical and surgical wards. Patient history Taking a patient history helps alert to the likelihood of fluid status. Below are some important factors to ascertain in order to guide an impression of fluid status.
    • 7. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 7 of 35 Clinical examination of the patient These signs of fluid deficit or overload may be very subtle until large volumes of fluid have been lost or gained. Often the first sign of fluid deficit is postural hypotension. Other methods of assessing hydration status include axillary moisture which has been observed to be a reliable sign in the elderly. These signs lack sensitivity and specificity, however in combination have greater weighting. It is important to closely monitor patients’ fluid balance to avoid the risk of acute kidney injury. The elderly are at particular risk and if goes unnoticed, permanent kidney damage can result. As a rule of thumb, the minimum acceptable urine output is 0.5-1.0 ml/kg/hr. Less than this, the patient has acute kidney injury (AKI). Test Yourself ! You suspect a patient may be becoming fluid depleted, which of the following should you preferentially carry out as an early indicator? ✅Lying and standing blood pressure ✖Assess skin turgor ✖Look for sunken, dry eyes ✖Assess the JVP Lying and standing blood pressure - Correct! A patient who drops their blood pressure rapidly on standing (postural or orthostatic hypotension) is a good early indicator of fluid depletion. Often the patient will complain of feeling dizzy and unsteady on their feet on rapid standing. With severe dehydration, postural hypotension may induce a temporary loss of consciousness on standing Assess skin turgor - Incorrect. This is generally a late sign of dehydration. In addition this can be an unreliable indicator of dehydration in older people as skin elasticity reduces with age. A good alternative to skin turgor is tongue turgor, as this is not age-dependent. In a well-hydrated individual, the tongue has one longitudinal furrow, but a person with depleted fluids will have additional furrows. X
    • 8. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 8 of 35 Look for sunken, dry eyes - Incorrect. Again a late sign of dehydration. Sunken eyes may also result from starvation or wasting from disease Assess the JVP - Incorrect. Although the JVP is a good indicator of central venous pressure, often the internal jugular vein is very difficult to locate in patients and may only be obvious in grossly fluid overloaded patients. Studies have also shown there to be wide disagreement on JVP measurements between clinicians. With the patient lying at 45 degrees, the JVP is measured indirectly as the internal jugular filling level and should be no more than 3cm vertical distance from the manubriosternal joint (at the level of the second costal cartilages) to the highest level of jugular vein pulsation. If the internal jugular is difficult to locate, the external jugular may be used, although it is not preferred. Distinguishing the jugular venous pulse from the carotid pulse, the jugular venous pulse is: - Decreased with inspiration – On standing the JVP appears lower in the neck Fluid balance chart The nurses will record the daily inputs and outputs of fluid from a patient. In a nil by mouth (NBM) patient this is particularly important as all fluids must be given IV. Below is an example of a daily fluid balance chart showing some of the possible fluid inputs and outputs that may be recorded (click the image to enlarge). The nurses cannot record insensible losses, however bear in mind a ‘healthy’ patient will lose approximately 800-1000ml (See Physiology : Fluid balance in health to revise this). The example fluid balance chart states insensible losses as 800ml of ‘evaporation’ to help remind nurses to include this in their total fluid balance calculation. Although this inclusion depends on the hospital trust. It is important to bear in mind that sick patients e.g. with burns and fever will have much higher insensible losses – appreciation of this will rely on your own clinical judgement. It is important to appreciate however, that fluid balance charts can only be used as a rough guide for what has gone in and out of the body as it is extremely difficult to accurately measure this. In addition an accurate account demands generally unavailable nurse time. Therefore clinical assessment is always more reliable than the fluid balance chart. Only in unusual situations, in which there are very high fluid losses such in the case of a massive diuresis (e.g. sometimes after kidney transplants), is an accurate fluid balance chart an important determinant
    • 9. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 9 of 35 of fluid prescription; often then IV fluids are prescribed as recorded output +30ml per hour, for instance, to account for insensible losses.
    • 10. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 10 of 35
    • 11. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 11 of 35 Weighing the patient Daily patient weighing is particularly useful for patients who are prone to retaining fluid i.e. renal and heart failure, as this allows easy monitoring of changes in fluid balance. Since water has a density of 1g/ml, a 1kg weight loss equates to a water loss of 1 litre. Therefore a 24hr change in weight is a good indicator of an equivalent change in body fluid. This is especially helpful to guide diuretic dosing. A set of chair weighing scales. These are commonly seen on the wards. Blood biochemistry Serum biochemistry results can be used as an adjunct to other clinical observations in order to gain an idea of a patient’s fluid status. Below are some of the urea and electrolyte (‘Us and Es’) changes which may be seen in the fluid depleted or overloaded patient: Urea and creatinine: Levels increase in the dehydrated patient. Urea levels increase proportionately more than creatinine levels. Hyponatraemia: Most commonly caused by water overload either by excessive water drinking or IV fluids - notably glucose solutions. Therefore the ratio of sodium to water in the blood plasma decreases. Hypernatraemia: This occurs in dehydration; simply referring to depletion of water, thus this increases the plasma sodium concentration.Since ‘water follows salt’ and osmoreceptors detect a rise in serum osmolality and trigger thirst and ADH secretion as compensatory measures, it can generally only be seen in the following patients:  In the very old/young or neurologically disabled who have lost the perception of thirst  Too ill to drink  In those with an osmotic diuresis (e.g. caused by glycosuira) in which water is lost disproportionately to sodium. Hypokalaemia: may result from losses of potassium rich GI tract fluid e.g. vomiting and diarrhoea. In such cases, extra potassium supplementation to fluid may be required. See Physiology : Electrolytes in disease states to revise this. Generally, there are no typical serum marker thresholds to signify when a dehydrated patient should be given fluid, or when a fluid overloaded patient should be fluid restricted. This decision is subjective depending on these results and all the other clinical information you have about the patient. Prescribing The learning objectives for this module are:
    • 12. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 12 of 35 1. To appreciate which are some of the most commonly prescribed colloid and crystalloid fluids, their properties and how they distribute in the fluid body compartments. 2. Begin to understand how to calculate a maintenance fluid regimen to match fluid and electrolyte requirements as closely as possible. Appreciate that there is no single correct answer for this. 3. Understand that fluid resuscitation in emergency situations is often concerned with speed of administration of available fluids to maintain blood pressure. 4. Recognise the key patient groups at risk of fluid overload and know to take great care when prescribing fluid for them. 5. Learn how to correctly write up a fluid prescription on a drug chart. Types of Fluid 1.Crystalloid 2.Colloid Colloid Colloid fluids are so named because they all contain large chemicals such as proteins which are incapable of passing across a semi-permeable membrane. Because of this, they increase the colloid oncotic pressure of the intravascular fluid (blood). See Physiology : Fluid compartments in disease states to revise this. Test Yourself ! If you give a patient a litre of a colloid fluid, how would you expect the water content to distribute in the first 15 mins after giving it? The type of colloid you would chose to prescribe in any given situation may depend on a number of properties. Below is a table of some commonly prescribed colloids and their uses:
    • 13. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 13 of 35 Colloids are less frequently prescribed than crystalloids, and they tend to have quite specific uses. Human protein solutions are usually prescribed due to the specific proteins they contain. For example, platelets may be given to a thrombocytopaenic patient to increase their platelet count, or human albumin solution may be given to patients with liver failure who are unable to produce their own albumin affectively. Synthetic colloids are used almost exclusively for their action as a volume expander for patients who are intravascularly depleted.In practice however, it is unclear as to whether synthetic colloids are any better than crystalloid for volume expansion, in that in disease states, the vascular compartment may become ‘leaky’ to colloids, and colloids are known to have other adverse reactions e.g. allergy. This is still the topic of much research. Often, a colloid may be selected for more than one of its properties. For example, blood may be appropriate for a patient who has experienced a large haemorrhage as it will both replace lost haemoglobin and act as a volume expander. More specific indications for some commonly prescribed colloids will be discussed later in this module. Crystalloid Crystalloid fluids all contain chemicals of a simple ionic or crystalline structure, which are capable of passing across a semi-permeable membrane. By osmosis, the water content of these fluids follows this crystalline component.Because crystalloid fluids are able to cross a semi-permeable membrane, they are able to freely move from the intravascular to the extravascular compartment. Depending on their exact composition, they are also able to enter the intracellular compartment to a greater or lesser extent.Below is a table outlining properties
    • 14. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 14 of 35 of three of the most commonly prescribed crystalloids, although it is important to realise that there are a great number of crystalloid products available. Crystalloid fluids are commonly used to provide maintenance water and electrolytes to patients who are dehydrated or nil by mouth. They are well suited to this task as their constituents can move freely from the intravascular compartment into the rest of the body. Glucose solutions These solutions are particularly useful for providing maintenance or rehydrating patients, as they distribute quickly across all fluid compartments in the way that pure water would. At least two-thirds will end up in the intracellular space, helping to hydrate the patient. However, they
    • 15. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 15 of 35 have the disadvantage of containing no electrolytes and so will decrease the patient's blood osmolality by dilution. Test Yourself ! If we want to rehydrate someone, why don't we just give IV water instead of glucose solutions? It is very dangerous to give pure water intravenously, without any additives to increase its tonicity. There is a risk of erythrocyte lysis as the water crosses into these cells by osmosis. Large volumes would also be likely to dilute the electrolyte content of the blood, although electrolyte dyscrasias may occur if large volumes of any fluid are given IV. Interestingly, glucose is actually more efficient at rehydrating the intracellular compartment than pure water alone would be. This is because glucose is metabolised in the cells by the respiration reaction to become carbon dioxide and water. For each molecule of glucose dissolved in solution the cell will generate 6 molecules of water! Note:You may hear some clinicians talking about ‘dextrose’ solutions. This is the old name for glucose solutions, and is not to be confused with dextrans (a type of colloid). The name has now been superseded and you will no longer find dextrose in the ward’s stockroom. Saline solutions Saline contains the important blood electrolyte sodium, of which we need approximately 1-2mmol/day (see Physiology : Electrolytes in health). However, it distributes less evenly across the fluid compartments of the body, and stays mostly in the extravascular space. Test Yourself ! Theoretically, sodium chloride solution should be able to cross the semi-permeable cell membrane into the intracellular space. However in practice much more of this fluid is distributed to the extracellular space compared to glucose solutions. ? Saline will distribute across the extracellular space in the normal proportions of the fluid compartment model (see Physiology : Fluid compartments to revise this). This is because the small sodium chloride and water molecules can move freely across semipermeable membranes and because its tonicity is the same as that of the extracellular fluid. However, for the most part the fluid does not enter the cells because a sodium gradient is established by ion-pumps in the cell membrane. These pumps actively transport sodium out of the cells in exchange for potassium. As the sodium is therefore effectively blocked from entering the cells, the water is unable to follow. Hence the fluid distributes only in the extracellular compartment. NOTE …..Sodium chloride 0.9% solution is often called ‘Normal Saline’. It is important to understand that this expression is used as it has an osmolality similar to that of extracellular fluid (it is ‘isotonic’). It does not contain the same electrolytes in the same concentrations as the extracellular fluid does. It contains a high concentration of sodium and chloride (154mmol/L of each, compared to the normal 135-145mmol/L and 95- 105mmol/L respectively in the extracellular fluid), and none of the other vital electrolytes.
    • 16. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 16 of 35 Although normal saline is a ‘staple’ maintenance fluid, and you are likely to see it prescribed often on the wards, it is important to be aware that it may cause hypernatraemia if used in excess. There is also increasing evidence that it may also lead to a potentially dangerous state of hyperchloraemic acidosis in susceptible patients. In many situations, physiological solutions are now being used as an alternative. Physiological solutions The ‘physiological’ fluids (Hartmanns and Ringer’s being the most common), attempt to provide a greater range of electrolytes, in a composition more similar to that of plasma. They may be safer to use than saline and they are now becoming inexpensive. Like saline, these are ‘isotonic’ fluids and so distribute mostly across the extravascular space. These fluids are used routinely to rehydrate patients in theatres, and are becoming more commonly used as maintenance fluids also. Maintenance Fluids Maintenance fluid is a persons daily necessary fluid requirements to remain healthy and in adequate fluid balance. This may come in the form of oral, enteric or intravascular fluid, although the expression is most often used to mean intravenous crystalloid. There are two main components to consider when prescribing fluids: 1.Water 2.Electrolytes Water Content We require a certain volume of water every day (Typically 2-3L – see physiology). Most people can obtain this from oral intake of food and drinks – this includes hospital in-patients! The human body is much better at judging its own fluid requirements than doctors are, and therefore all patients who can eat and drink should be encouraged to do so. However, there are a number of situations in which we must provide some or all of a patient’s daily fluid requirements (for example, patients who are nil by mouth). In order to determine a patient's daily fluid requirements you should consider: 1.The losses and gains from the previous day (or days) -- Requires careful assessment of their weight and fluid charts.
    • 17. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 17 of 35 2.Anticipated losses today -- Based on the previous days and any changes today. For example, have they developed diarrhoea, are they becoming more pyrexial (see Physiology : Fluid balance in disease) 3.Their current hydration status -- There is little point painstakingly matching todays fluid outputs and inputs if they are already fluid over- or under-loaded. The previous weight and balance charts will help, but clinical and biochemical (blood results) assessment is key. The method above should provide a solid tool for assessing a patient's daily fluid volume requirements. It is important to understand that this may be radically different from the often quoted ‘2-3 L’, especially in unwell patients with altered physiology. It is also helpful to appreciate that in post-operative patients, as a natural consequence of surgical stress, physiological antidiuresis ensues mediated by ADH. This will resolve by itself and so giving too much fluid to these patients should be avoided (particularly to women, and particularly as 5% dextrose) as it can cause severe, life threatening hyponatraemia. Electrolytes As well as water, it is also important to provide daily replacements of the electrolytes lost. Probably the two most important electrolytes to consider when prescribing maintenance fluids are: 1. Sodium 2. Potassium Relatively large amounts of sodium are lost in urine each day and so sodium is present in some concentration in almost all crystalloid fluids. Traditionally, potassium was added to each bag as required in the form of concentrated KCL. However, in order to minimise errors during administration it is now more common to find bags of crystalloid with potassium pre-added. Healthy people need approximately 1-2mmol/kg/day of sodium per day, and 1mmol/kg/day of potassium. As bags of crystalloid contain fixed amounts of these it may be difficult or impractical to exactly match a patient's requirements. This is unlikely to be a problem in the short term, but patients receiving fluids for any prolonged period of time should have their bloods checked daily for derangement. Usually, patients will lose electrolytes through urine and insensible losses, and these can be fairly accurately determined. However, some patients may have higher than normal losses and it is particularly important to monitor electrolytes in these patients. In particular:Vomiting and diarrhoea cause excess potassium loss .Burns, fistulae and surgical drains cause excess sodium loss
    • 18. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 18 of 35 Hyperkalaemia Background  Potassium is vital for regulating the normal electrical activity of the heart.  Increased extracellular potassium reduces myocardial excitability, with depression of both pacemaking and conducting tissues.  Progressively worsening hyperkalaemia leads to suppression of impulse generation by the SA node and reduced conduction by the AV node and His-Purkinje system, resulting in bradycardia and conduction blocks and ultimately cardiac arrest. Definitions  Hyperkalaemia is defined as a potassium level > 5.5 mEq/L  Moderate hyperkalaemia is a serum potassium > 6.0 mEq/L  Severe hyperkalaemia is a serum potassium > 7.0 mE/L What are the ECG signs of potassium excess? There can be many different changes. Here are the main ones you should know about: Bradycardia Flattened P-waves Prolonged PR interval, , flattened P-waves. Wide QRS ST segment sloped Tall T waves ('tented') Effects of hyperkalaemia on the ECG Serum potassium > 5.5 mEq/L is associated with repolarization abnormalities:  Peaked T waves (usually the earliest sign of hyperkalaemia) Serum potassium > 6.5 mEq/L is associated with progressive paralysis of the atria:  P wave widens and flattens  PR segment lengthens  P waves eventually disappear Serum potassium > 7.0 mEq/L is associated with conduction abnormalities and bradycardia:  Prolonged QRS interval with bizarre QRS morphology  High-grade AV block with slow junctional and ventricular escape rhythms  Any kind of conduction block (bundle branch blocks, fascicular blocks)  Sinus bradycardia or slow AF
    • 19. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 19 of 35  Development of a sine wave appearance (a pre-terminal rhythm) Serum potassium level of > 9.0 mEq/L causes cardiac arrest due to:  Asystole  Ventricular fibrillation  PEA with bizarre, wide complex rhythm (Warning! In individual patients, the serum potassium level may not correlate closely with the ECG changes. Patients with relatively normal ECGs may still experience sudden hyperkalaemic cardiac arrest.) Peaked T waves Prolonged PR segment
    • 20. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 20 of 35 Loss of P waves Bradycardia ECG Examples This ECG displays many of the features of hyperkalaemia:  Prolonged PR interval.  Broad, bizarre QRS complexes — these merge with both the preceding P wave and subsequent T wave.  Peaked T waves. This patient had a serum K+ of 9.2. A Worked Example Miss Imaginary is a well 60kg female who is nil by mouth and requires maintenance fluids for the next 24 hours. Assuming this is her first day of maintenance fluids, and she is currently well hydrated with no unusual losses anticipated:
    • 21. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 21 of 35 Required volume of water: approximately 3 litres Requires sodium: 60 x 2 = 120 mmol sodium Required potassium 60 x 1 = 60 mmol potassium Possible regimens: Typically, maintenance fluids are prescribed to be infused over a 24 hour period. This is to minimise the chance of harming a patient by infusing fluids to quickly (more information about this later in Prescribing : Benefits and risks), and to ensure that they stay well hydrated throughout the day. In the case of a 3L total to be infused, each 1 litre ‘bag’ might be set to run for a period of 8 hours. Although both of the regimens suggested above are sensible and provide the patient with approximately her requirements for one day, you should note that neither provide exactly the correct electrolytes. It is very hard in practice to precisely calculate or meet a patient's fluid or electrolyte needs. However, it is important that the patient is constantly clinically and biochemically reassessed, to ensure your regimen is not causing harm. Generally speaking, well patients such as in this worked example should not be kept nil by mouth for periods as long as 24hr e.g. in the lead up to elective surgery, as it is thought to slow recovery and may cause harm. However for the purposes of this simple example you can see how maintenance fluid and electrolyte requirements could be calculated. Fluid Resuscitation As well as being used for ‘maintenance’ (usually crystalloids), and for their physiological effects (usually colloids), fluids may also be used in urgent or emergency situations to resuscitate patients. There are two main ways in which resuscitation fluids are used: 1. To maintain intravascular volume (in order to maintain blood pressure in hypotensive or shocked patients) 2. To replace massive fluid losses Intravascular Repletion In emergency situations patients may become hypotensive (shocked). This may be through blood or plasma loss (hypovolemic shock), blood redistribution (distributive shock) or due to
    • 22. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 22 of 35 failure of the heart to adequately pressurise the blood (cardiogenic shock). The effect of this low pressure is poor tissue perfusion, leading to ischemia and organ failure, which may be fatal. Therefore the aim of emergency fluid resuscitation is simply to provide extra volume to increase the blood pressure. Therefore, unlike in maintenance fluid prescribing, there is little interest in the water or electrolyte content of the fluid (except that it is never a good idea to give patients large volumes of potassium containing fluids quickly, due to the risk of hyperkalaemia). Test Yourself ! Which of the following fluids would be ideal for intravascular repletion in an emergency situation? ❌Colloid ❌Crystalloid ✔Doesn't matter Doesn't matter – Correct answer: Logically, as colloids are designed to stay mostly within the intravascular space, you might expect these to be best fluids in a resus situation. However, large multicentre international trails have shown that there is no difference in mortality in patients resuscitated with colloids over normal saline or other crystalloids. The key in a resus situation is to give whichever fluid is available, as quickly as possible. Initially, any fluid you give a patient will be in the intravascular space, if you gave it intravenously! It takes some time (aprox 20 min) for the fluid to redistribute across the body, by which time hopefully the patient is more stable and in experienced hands. It is also important to note that colloid fluids (especially gelatin based) have a significant rate of allergy and anaphylaxis associated with their use, which may be worth considering in a resus situation. However, the bottom line is to give the most readily available fluid, as quickly as possible (although try to avoid pre-added potassium!) Note that the speed at which you can infuse fluid into a patient depends on two important factors which are within your control: 1.The size of the cannula 2.The pressure under which the fluid is being squeezed into the patient Therefore, it is important to ensure you use the largest cannula possible, in two places, and put pressure on the fluid bags (use pressure bags or get someone to squeeze them!) Which of the following would be the best cannula to use in a resus situation? ✅Brown / Orange 14G - These are the biggest cannula. By the Hagen–Poiseuille law, the rate of infusion increases by the power of four for each unit increase of the cannula radius, and so a bigger cannula can infuse much much more fluid than a small one in a given unit of time. The exact colour of the 14G cannula varies slightly by trust, so check locally. ✖Blue 22G ✖Pink 20G ✖Green 18G Note… Once venous access has been established in these patients, it is useful to take a baseline blood sample for FBC, U+E and group/cross-match, before the fluid infusions start.
    • 23. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 23 of 35 Massive Fluid Losses There are some situations in which patients may have lost huge amounts of fluids and electrolytes, which will need replacing. In these cases it is often important to consider the electrolytes as often the repletion takes some hours or days, and these patients may have severely deranged electrolytes on admission. For example, it is not unusual for patients with diabetic ketoacidosis to require 10 or more litres of fluid over 24 hours, with careful monitoring and supplementation of electrolytes. Patients who have had major blood loss may require significant transfusion with packed red cells (and possibly other blood products). These may serve to help maintain blood pressure, as well as replacing lost haemoglobin or other components. Which one of the following would be a priority in treating DKA? ✅They are likely to require potassium supplementation over the first 24 hours of admission – Correct! Potassium supplementation is commonly required. Acidosis causes cells to release potassium in exchange for hydrogen ions. Due to the high blood glucose, there is a heavy diuresis in which the potassium is lost. As the patient is treated and the acidosis corrects, the remaining potassium in the blood is reclaimed by the cells, often leading to hypokalaemia which requires treatment. ✖They are likely to require potassium restriction over the first 24 hours of admission – Wrong answer. This is unlikely due to potassium loss by diuresis. However patients may present with a normal or high potassium due to the high level of blood acidosis. ✖They are likely to require sodium supplementation over the first 24 hours of admission – although they will have lost some sodium during the diuresis phase which may require some correction, potassium is more of a problem. Patients with DKA require large volumes of intravenous fluid resuscitation and it is important not to prescribe excess saline. It is common to prescribe normal saline in the early phase of fluid replacement in order to replace lost sodium, and avoid administering further glucose to an already very hyperglycaemic patient. As this corrects it is best to switch to glucose solutions. ✖They are likely to require sodium restriction over the first 24 hours of admission – wrong answer. Balancing benefits and risks In general, relatively well patients are probably better given slightly more fluid, rather than less. Patients with well functioning kidneys are able to remove moderate amounts of excess fluid without difficulty, whereas dehydration can predispose to a number of problems including pre-renal failure and venous thromboembolism.
    • 24. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 24 of 35 However, some groups of patients are at significant risk of ‘fluid overloading’, and you should always check for these things before prescribing fluids for a patient: Heart failure In these patients the heart has poor forward-pumping function. Fluid given intravenously is likely to collect in either the systemic or pulmonary venous system and so raise the hydrostatic pressure in these areas. This may cause transudative fluid loss leading to peripheral or pulmonary oedema, the latter of which may be fatal if uncorrected. Liver failure These patients may have low blood albumin and so low colloid oncotic pressure. This also may cause transudative peripheral or pulmonary oedema in susceptible patients if high volumes of fluid are administered. Chronic kidney disease These patients are at risk of fluid overload if large volumes of intravenous fluid are administered, as their ability to excrete excess fluid is impaired. Generally however, up to the point of needing dialysis, most patients with CKD remain in fluid balance, although some require diuretics to maintain this. Only those with established renal failure who are on dialysis produce little or no urine. What would you prescribe for a clinically stable patient with known heart failure who's blood pressure today has dropped to 70/45 (from a baseline of 120/80)? Patients who are taking large amounts of fluid containing medicines It is important to note that a significant proportion of drugs are administered by intravenous infusion. These may be made up in a collectively significant amount of fluid which may be less apparent on the prescription chart, or not appear on the fluid balance chart.
    • 25. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 25 of 35 Principles of fluid prescribing The key to safe and effective prescribing is to have a thorough checklist in your mind. It is vital to remember a number of key principles whenever you pick up your pen to prescribe fluids! 1 Each patient and clinical scenario is unique. There is no place for blanket regimens such as “two sugar one salt”. 2 Each time you prescribe you should:  remember your basic physiology  perform a thorough clinical and biochemical assessment  consider yesterday’s fluid balance, and calculate todays predicted losses and gains 3 Well patients can osmoregulate better than you can do it for them. Patients should eat and drink if they are able to. 4 Remember that fluids can be dangerous. Especially in patients with heart, liver or renal failure. Always start with a small fluid challenge. 5 Never write up for long periods (eg > 24hr). Always review the patient regularly! 6 If in doubt, ask a senior! Practicalities of fluid prescribing You will find a separate fluids prescribing section on almost every hospital drug chart, and it is usually on the back. When you come to prescribe in this section, the chart will ask you to provide certain information. This will include: What fluid? What volume? What rate? What route? Which additives to include? Hopefully having read the rest of this module, you feel confident that you can answer all of these questions. However, as this is a legal prescription there are also a number of other things you must do before you can give your prescribed fluid. You must:  Check the patient's name, date of birth and hospital number is correctly entered on the front of the drug chart. Often it must be re-written on the fluid prescribing sheet on the back also.
    • 26. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 26 of 35  Check the patient has no allergies. Again, this will be on the front of the chart and also often on the fluids section also. It is also important to check with the patient verbally if possible, and check for an allergy wristband.  Provide any other information the chart requires. For example ward, bed number or consultant. Once you have checked all of this information is accurate and you have correctly prescribed the fluids you must date and sign the prescription to make it legal. Most hospitals also require that you write in black ink. Once this has all been done you or the nursing staff may administer the fluid. The image below shows the front of a typical drug card. These vary slightly between trusts
    • 27. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 27 of 35
    • 28. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 28 of 35 An example Below is an example of how you would write up the fluid regimen for the imaginary patient we discussed earlier: Miss Imaginary. Miss Imaginary is a well 60kg female who is nil by mouth and requires maintenance fluids for the next 24 hours. Fluid regimen Important notes by convention nursing staff will not start the next bag of fluid until the previous has finished. If you want to run two bags simultaneously write it on the chart and inform the nursing staff.
    • 29. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 29 of 35 There is a wide degree of acceptable variation as to the way the ‘rate’ is expressed. It may be written as a period of time over which the fluid is to be given (eg 8hrs as written on the drug chart) or as a volume per unit time (eg ml/min). The route is usually IV (intravenous) or IVI (intravenous infusion) but there are others, for example S/C (subcutaneous) Common additives are KCL or drugs such as antibiotics, although on many charts there is a separate place for these. This is a fairly simple prescription for maintenance fluids. Now move on to module 4: practice cases, to try your hand at some more complex scenarios. Module 3 Summary : Prescribing  Prescribed fluids can be classified into two categories; colloid and crystalloids.  Colloids may be used to replace blood components and to expand the intravascular volume by increasing intravascular colloid oncotic pressure. Commonly prescribed colloids include synthetic colloids and human protein solutions.  Crystalloid fluids are commonly used for fluid maintenance and distribute freely from the intravascular compartment to the other compartments. Commonly prescribed crystalloids include glucose, saline and physiological solutions.  When calculating a fluid regimen, it is necessary to see the patient yourself and assess their current hydration status. In addition it is necessary to assess a patient’s fluid balance from the previous day, the current day and predicted future fluid losses and gains. Consider also in this calculation if there are likely to be radical losses or gains in electrolytes e.g. potassium rich GI losses.  In situations of fluid resuscitation in the hypovolaemically shocked patient, there is less concern for the composition of infused fluid but rather the aim is to infuse large volumes fast to maintain blood pressure. However in some cases of massive fluid loss such as DKA, a large derangement in electrolytes can result and so it is necessary to pay careful attention to correcting this.  Certain patient groups are at particular risk of fluid overload and thus exceptional care must be taken when prescribing fluids for them. Starting with a small fluid challenge is recommended. This includes patients with heart failure, liver failure and chronic kidney disease.  When IV fluids are being given it is important to review the patient regularly and never prescribe fluids for more than a 24hr period as fluid requirements are likely to change! Case Scenarios Case 1 : Maintenance fluids A 75 year old lady weighing 70kg is admitted following a stroke. She has a dense left-sided hemiparesis. The A and E SHO has assessed her and found her to have an unsafe swallow. She is apyrexial and otherwise well. Your registrar asks you to make her ‘nil-by-mouth’ and prescribe maintenance fluids. How much fluid will you prescribe for this lady ?
    • 30. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 30 of 35 2.5 L ✅ 3.0 L✅ 4.0 L✅ 2.0 L✖ After assessing the patient and finding her to be euvolaemic, you decide to prescribe 3 litres of fluid over the next 24 hours. Her blood results show that her electrolytes are all within normal limits. What fluid regimen will you prescribe for her? There is a degree of acceptable variation here. As she is euvolaemic with no electrolyte dyscrasias we can assume typical electrolyte and fluid losses will occur over the next 24 hours. As she is 70kg in weight, her sodium needs are 70-140 mmol/day. Ideally, she should be prescribed 1 L of Hartmanns solution, which contains 131mmol Na. However, for one day 1 L of Normal saline (contains 154 mmol) would be acceptable. The rest of the volume should be given as glucose solution, which does not contain further electrolytes. Suggested regimens : 1L 5% Glucose, 1L 0.9% Saline, 1L 5% Glucose (sequentially as '8-hourly bags') 1L 5% Glucose, 1L Hartmanns, 1L 5% Glucose (sequentially as '8-hourly bags'). The nurse who is giving the fluid bleeps you as you have left the ‘drugs to add’ and ‘dose to add’ column of the prescription blank. She would like to know if you wish to add anything to the fluid? The surgical registrar has not asked you to write her up for any pre-operative medication other than maintenance fluids. Would you like to add anything to the fluids, doctor? As well as sodium, it is important to think about replacing potassium losses when prescribing maintenance fluids. As this patient is 70Kg she will need approximately 70 mmol of potassium replacement in 24 hours (often less will be enough). As most crystalloids are now available with potassium pre-added it can be practically difficult to give exactly the ideal amount. Bags tend to come with 20 or 40mmol pre added, so prescribing 20mmol per bag will make administration more practical. This would mean the patient would receive 60mmol of potassium in a glucose, saline, glucose regimen, and 45 mmol potassium in a glucose, Hartmanns, glucose regimen (because heartmanns is not available with extra potassium, although it contains 5mmol as standard). In fact, both of these regimens will probably provide adequate potassium for one day. However, it is vital to check blood results regularly to ensure the potassium level is not becoming deranged, as this can have fatal consequences if uncorrected! Case 2 : Perioperative loss Your registrar calls you to tell you about a 70kg female patient who had an anterior resection 6 hours ago. The registrar says there was intraoperative blood loss of 800ml and that 500ml of Hartmanns was given by the theatre anaesthetist. He says the patient has an abdominal drain in situ which has produced 300ml of blood, but has now stopped draining. He mentions that the patient was euvolaemic prior to the operation. The registrar says the patient is to remain nil-by-mouth in case she needs to go back to theatre. He asks you to prescribe more fluid for the patient, who has had only 500ml of normal saline since the operation.
    • 31. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 31 of 35 What's the first thing that you should do for this patient now? Make sure you physically see the patient. Go to the bedside and examine the patient and check the blood results. Whenever taking a complex handover it is important to get as much information as possible. Speak to the nurse looking after the patient to see if they have any concerns, and speak to the patient / read the notes to find out if they have any important past medical history you should be aware of (eg heart or renal failure) You go to see the patient who is alert but complaining of pain. You examine her and find her to be showing signs of hypovolaemia. What are the clinical signs of hypovolaemia ? You notice that the patient has a catheter in situ. The nurse tells you that this was placed by the anaesthetist pre- operatively. The catheter bag contains 100ml of concentrated urine. How much urine should have collected in the bag in the 6 hours since the operation? What could you do to confirm that the recorded urine output value of 100ml is correct?how did you do The minimum acceptable urine output for adults with normal renal function is 0.5-1 ml/kg/hr. Below this the patient is likely to be in renal failure. In the last 6 hours this patient should have produced: 0.5 x 70 x 6 = 210ml minimum. If a patient has produced less than the minimum obligatory volume of urine this should prompt urgent intervention with a fluid challenge and senior input. However, it is a good idea to first check two things: 1. That the patient is not known to be in end stage renal failure and on dialysis– this could be a normal urine output for them! The place to look for this is in the notes, or ask the patient. 2. That the catheter bag has not simply been drained recently! Look at the fluid balance chart to check if there is any recorded urine output. In this case, the nurse tells you that she recently emptied the catheter bag, which contained 500ml of concentrated urine. The patient tells you that she is still feeling very nauseous. She has a nasogastric tube in-situ, which has produced 300ml since the operation and is still producing large amounts of clear aspirate. Which important electrolyte is commonly lost in vomit and NG aspirate?
    • 32. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 32 of 35 ✅Although many electrolytes are lost, the most problematic may be potassium. The loss of hydrochloric acid from the stomach may induce hypochloraemia and metabolic alkalosis. As a response to this, the kidneys increase the reabsorption of hydrogen ions from the tubules, at the expense of potassium which is exchanged and lost in the urine. ❎Barcarbonate is not usually lost from NG aspirate. More commonly it is lost in diarrhoea which may cause metabolic acidosis. The opposite is usually the case from NG losses. ❎Phosphate loss is not a common problem. ❎Sodium loss is not generally a problem with NG aspirate (see above) The nurse asks you what volume of fluid the patient is likely to need over the next 24 hours. Calculate the approximate fluid requirements for this patient, over the next 24 hrs.??????????? You prescribe adequate replacement and maintenance fluids for the patient, and return regularly to review them. You also prescribe adequate analgesia and antiemetics. The patient's hydration improves and their pain settles.
    • 33. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 33 of 35 Case 3 : Fluid overload While on-call, you are bleeped to see an 82 year old man with known ischaemic heart disease, who was admitted a few hours ago with an episode of chest pain. The nurses looking after him tell you that he has been eating and drinking normally while in hospital, but they are concerned that he has dropped his blood pressure and become increasingly confused in the past 30 minutes. On assessment you find him to be quite confused, with a blood pressure of 83/72 (baseline 115/90). He does not have a catheter in situ and his bed pad is dry. How will you manage this situation? Increasing confusion and a fall in blood pressure is potentially serious. You should recognise that this patient needs attention. In any such situation you should manage the patient following an ABC algorithm, involving senior help early if you feel you are out of your depth! In this case the patient's airway and breathing are normal, but on examination he looks dry.. You decide that the patient may benefit from a fluid challenge, to see if his blood pressure picks up with fluid repletion. Which of the following would you give him: ✅250-500ml Normal Saline STAT “stat” means as fast as you can through a large bore IV cannula or 250-500ml Volplex ((Succinylated gelatin (Modified Fluid Gelatin) 4% w/v in Water for Injections, also containing sodium chloride. ))STAT - Either of these would make for a reasonable fluid challenge. The idea is to watch for a response while the fluid remains intravascular, and so it does not matter greatly weather colloid or crystalloid is used (although glucose is best avoided as it redistributes very quickly). Fluid challenge should be given as a stat dose rather than a slow infusion. NB : 'STAT' comes from the Latin 'statim', meaning 'immediately' . ❌ 1000ml Normal Saline over 2hrs and 1000ml Volplex over 2hrs - A fluid challenge is a quick bolus of a small amount of fluid to encourage a physiological response. This is too much fluid, given over too long. 500-1000ml Normal Saline over 1hr and 500-1000ml Volplex over 1hr in an unknown patient is likely to be too much fluid still. Only small amounts of fluid should be needed to lift the blood pressure. Using large amounts can lead to problems… Before you can prescribe the fluids, your well-meaning SHO (who unfortunately had not read this tutorial) has given the patient a stat dose of 2L Volplex. The patient quickly becomes more unwell. On examination he is now short of breath, with a respiratory rate of 35 and crackles are heard bi- basally. The oxygen saturation is 90 on 2L oxygen via nasal specs (baseline 98% on air) and his lips are slightly blue. What has happened to the patient? How would you go about managing this acute situation? Write down what you would do, and what order you would do it in. Then click the button to reveal the answer. The patient has known ischaemic heart disease which may predispose to heart failure. Large intravenous boluses are dangerous in these patients, as they often lead to fluid overload and pulmonary oedema, as has happened here. Acute heart failure with pulmonary oedema is an emergency. These patients will be very unwell. The patient should again be managed by an ABC algorithm. Turn the oxygen up to 15L, and switch to a non-rebreathing mask. Stop the fluids! (don't forget to do this!) Call for help. The patient will need to be cared for in a monitored bed or transferred to Intensive Therapy Unit (ITU)/High Dependency Unit (HDU).
    • 34. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 34 of 35 You bleep your registrar, who quickly arrives to help stabilise the patient. The registrar asks you to prescribe the ‘acute heart failure drugs’ on the chart, and asks you to keep a close eye on the patient's cardiac function. Make a list of 4 drugs you might need to prescribe for this patient, and the ways in which you can further monitor the patient's cardiac function on the ward. The exact drugs that are used to treat heart failure may vary from case to case. However, most patients in acute heart failure will require: Oxygen – remember this needs to be prescribed on the drug chart! Diamorphine – not all patients will need this, but it acts as a pulmonary venodilator and relieves some of the backpressure from the heart. Nitrates – are also vasodilators, although they work more by reducing the arterial tone so that the heart has to work less hard to pump blood forward. Furosemide – This is a powerful and fast-acting loop diuretic which helps to remove the excess fluid by diuresis. Although HDU/ITU is the ideal place to monitor cardiac function, some simple monitoring can be set up on the ward : Continuous or regular ECG monitoring. Regular blood pressure and heart rate monitoring. Catheterise the patient. Urine output is a good indicator of cardiac output. The patient should have a fluid balance chart started, if they do not already have one. Frequent weighing – Patients' weights should not fluctuate much day-to-day. If a patient gains a lot of weight over the course of the day or night, this may suggest that they are retaining fluid. Summary  Fluid maintenance for otherwise well ‘nill by mouth’ patients undergoing elective surgery, may be a simple calculation of fluid and electrolyte requirement; calculating a rough requirement of sodium and potassium using the patient’s weight.  Sick patients are often far more complicated, with many more fluid and electrolyte losses and gains to consider. In this situation the patient may require large amounts of fluid with extra electrolyte supplementation or restriction. Regular patient reassessment is required including regular blood test results in order to guide electrolyte replacement.  It is paramount to recognise these sick patients and call for senior help early. OSCE During clinical attachments you may have the opportunity to set up an IV fluid infusion for a patient, and certainly by 5th year it is a required practical skill. The video section of this module is a guide to how to set up an IV fluid infusion. It is aimed to teach students earlier on in their clinical training, as well as to consolidate the procedure for those in their later years of study. This video should also cover the main points required of an OSCE station.
    • 35. Copyright 2012 Fluids Tutorial fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Intravenous fluid Page 35 of 35 A print out of an OSCE checklist for setting up an IV fluid infusion is available for student notes and OSCE practice. How to calculate the giving set drip rate Follows is how to calculate the drip rate required to deliver the prescribed rate of fluid: Each giving set states on the back its 'GTT' value (from the latin guttae; drops)- the number of drops in one mL. GTT value allows you to calculate how many drops/min of fluid dropping through the giving set chamber you need to set in order to give the correct amount of fluid in the required time. Here is an easy formula you can use to calculate this: A worked example 1L normal saline given over 8hr using a standard giving set would require a drip rate of: : 1000ml x 20 / 8 x 60 = 42 drops/min (or 7 drops over 10sec) Note that although giving sets are still often used stand alone to deliver a prescribed rate of fluid, electronic infusion devices can also be used when greater accuracy is required. Cannulae All cannulas say on the back of the packaging the maximum flow rate ml/min. Even small cannulas can often support the required infusion rate. e.g. for the example above: 1000ml/ 8 x 60 = 2ml/min required to infuse via the cannula to deliver the fluid over 8 hours. The small Pink 20G cannula can do 50ml/min thus rarely is the cannula the rate limiting step in routine use. However, in emergencies where very large volumes may need to be given over a short period it is vital to use a wide bore cannulae (grey/brown/orange).
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