Anaesthesia Compiled Notes 2022 FC PDF

Nurses Certificate in Medical Nursing NCert(NME) Modular CPD Course Module number 1 Anaesthesia Speaker...

Nurses Certificate in Medical Nursing NCert(NME) Modular CPD Course Module number 1 Anaesthesia Speaker Nicki Grint Note: Copyright on these notes is jointly owned between the Course Speaker and Improve International Ltd and the material must not be copied or distributed without prior permission/authorisation from either party. Improve International Ltd has taken every effort to ensure that the information in these notes and in other taught material is accurate but it cannot take any responsibility for any problems arising from errors therein.  Fluid therapy Fluid compartments in the body Water makes up 60% of the total weight of the body in the adult. In the neonate and paediatric animal it constitutes 80% and 75% of total body water respectively. The body water is initially divided (see figure 1) between fluid within cells (intracellular fluid) and fluid outside of cells (extracellular fluid). This extracellular fluid generally flows in two regions of the body, as plasma in the blood (intravascular volume) and as fluid which bathes the cells in the rest of the body (interstitial fluid). There is a separate category of transcellular fluid (e.g. synovial and csf fluid) which only comprises a very small percentage of the total body water and won’t be considered further. Figure 1 Total body water = 60% of body weight ↓ ↓ Intracellular Extracellular 40% 20% ↓ ↓ Intravascular Interstitial 5% 15% Types of fluid losses Depending on the clinical condition affecting the patient, the type of fluid lost will vary. Animals that have pure dehydration will have lost water from all of the extra cellular and intracellular fluid compartments. Haemorrhagic loss will be entirely from the intravascular space initially. Diarrhoea tends to cause extracellular fluid loss (therefore from the interstitial and intravascular compartment). Hyper, hypo and isotonic solutions. Tonicity is an indication of the concentration of solutes (such as sodium and other electrolytes) in a solution compared to another solution. A fluid is termed hypertonic, isotonic, or hypotonic based on higher, equal, or lower concentrations of electrolytes (usually sodium) compared to normal plasma. 2 NANAES mod 5 N Grint  Hypotonic: Na+ concentration is lower than plasma Isotonic: Na+ concentration is similar to plasma Hypertonic: Na+ concentration is higher than plasma These solutes or electrolytes cannot pass through semi-permeable membranes but water can. Water will try and “follow” solutes to even out concentrations. Hypo-, iso- and hyper-tonic terms can also be used to describe fluid losses. Hypotonic dehydration is when is too little solute (such as sodium) in the body. Isotonic dehydration occurs when you lose equal amounts of water and solutes. Losing too much water while keeping too much sodium in the fluid outside your cells causes hypertonic dehydration. Types of parenteral fluids Crystalloids are any solution of crystalline solids that are dissolved in water eg sodium based or dextrose based. If the electrolyte composition of the solution is similar to extra cellular fluid (ecf), then the fluid is known as a balanced electrolyte solution Extracellular fluid volume replacers If the concentration of sodium is similar to the ecf sodium concentration these fluid stay in the extracellular compartment and therefore these fluids are good at replacing extracellular fluid loss. These fluids can be infused rapidly as they won’t induce changes in electrolyte composition. After IV administration the fluid will redistribute between the intravascular and interstitial compartments; thus for every 1 litre of fluid administered i/v, only about 250-300ml remains in the intravascular space after 1-2hr, so at least 3 times the volume lost is required to make up fluid deficits. Hartmann’s ~131mmol Na+ 5mmol K+ 111mmol Cl- 1.5mmol Ca2+ 29mmol LACTATE Normal Saline (0.9% NaCl) ~150mmol Na+ ~150mmol Cl- Maintenance solutions / water replacers An animal’s maintenance requirement is defined as the amount of water and electrolytes required to replace those lost through normal physiological processes, i.e. through respiration, perspiration and excretion via the alimentary and urinary tracts. 3 NANAES mod 5 N Grint In addition to supplying water, the maintenance fluid should replace electrolytes. In order to meet these specific daily requirements, maintenance solutions have lower sodium and chloride concentrations and an increased potassium concentration when compared with extra cellular fluid. If the K+ concentration in the parenteral solution is less than 20 mmol/L then may need to supplement. These solutions work because they are isotonic. They are isotonic because of the dextrose +/- the small amount of sodium. The dextrose has been metabolised and is no longer osmotically active, only water remains, which can distribute freely throughout the three fluid compartments. It should be noted that the amount of dextrose present in the solutions described provides negligible energy at the concentrations used. We cannot use hypotonic solutions, as this would cause the red blood cell to lyse. Because the sodium concentration is very different from that of the ecf, these fluids should not be given at fast rates, but slowly infused over 24 hours. These fluids are of course no use for restoring circulating volume but are ideal for treating primary water loss. They are also used as maintenance fluids, but if so, should have potassium added to them 4% glucose with 0.18% sodium chloride, (supplemented with 20-30mEq/l of potassium for maintenance) 5% dextrose (supplemented with 20-30mEq/l of potassium for maintenance) ‘Strong KCl’ is the stock solution that you can add to your other bags of fluids. It is a very dense (heavy) solution, so you must ensure that you mix it really well into the fluid bag. Maximum rate for K+ infusion is 0.5mEq/kg/hr. Hypertonic Saline (7.2% NaCl) Hypertonic saline can be used in cases of shock. It causes an increase in blood pressure by several mechanisms, the main one being that it draws water from the interstitial space. Any effect that hypertonic saline has is only transient (30-120 mins). The use of hypertonic saline must be followed by the administration of isotonic crystalloids to replace borrowed water and to provide a long-term increase in circulating volume. The suggested dose is 4ml/kg over 10 4 NANAES mod 5 N Grint mins. The use of hypertonic saline also carries with it some potential side effects; hypernatraemia/hypokalaemia, haemolysis, ventricular arrhythmias, potential for re- haemorrhage. It is because of these problems that repeated doses of hypertonic saline are contra indicate. 5 NANAES mod 5 N Grint Plasma volume expanders Colloids are fluids in which large molecular weight particles are suspended but not visible. Colloids contain large molecules that cannot pass through the vascular endothelium. They increase the colloid osmotic pressure of the plasma and in addition to each litre of fluid staying in the intra vascular compartment, they also ‘pull’ water from the interstitial space into the intra vascular space. To avoid ‘dehydrating’ the interstitium, you should use crystalloids concurrently or just after colloids, to ‘pay back’ the fluid drawn from the interstitial space. Colloids should be used in any case where rapid improvement of circulating volume is necessary. As a general rule no more than 25% (usually 20ml/kg) of circulating volume of an animal should be administered as a colloid at any one time, otherwise the haemodilution will dilute out clotting factors etc. Colloids can be used intra-operatively to help maintain blood pressure, or if an animal has a total protein of less than 35g/litre in order to prevent extravasation of fluid. 6 NANAES mod 5 N Grint Natural colloids include plasma, albumin preparations and whole blood. Artificial colloids, include starches, gelofusin and dextrans. As far as the initial plasma volume expansion goes, it is the number of colloidal molecules per volume of solution administered that are important, and not their size. In fact, the bigger they are, the fewer you can get in unit volume, so the plasma expansion ability is less. But bigger molecules survive longer in the intravascular space. Some disadvantages of colloids include; volume overload, anaphylactic reactions and clotting problems. It is now sometimes difficult to obtain starches as the medical field have reduced their use in certain situations secondary to side effects. TYPES OF PARENTERAL FLUIDS Plasma volume expanders Gelatin based Gelofusin Lasts for maximum 6-8 hours Haemaccel May cause hypersensitivity reaction ranging from mild urticarial lesions to anaphylaxis ?dilutional coagulopathy Dextran based Dextran 40 Lasts approximately 12 hours (D-70) Dextran 70 Hypersensitivity reactions rare ?dilutional coagulopathy Starch based Hetastarch Lasts approximately 24-36 hours Hypersensitivity reactions rare ?dilutional coagulopathy Intravenous fluid therapy calculations Intravenous fluid therapy volumes and rates need to be calculated accurately especially in small animal patients so as not to produce overhydration or insufficient restoration of fluid deficits. With the increased popularity of drip pumps in practice, the administration of fluid therapy can be more accurate, however it may still be necessary to perform calculations and set up fluid therapy plans. www.improveinternational.com | 7 ‘Maintenance’ rates When we talk about maintenance rates we mean the amount of fluid that an average dog needs to take in to match it’s normal. Recommendations from the American Animal Hospital Association include calculating maintenance requirements on an individual basis as the smaller the animal, the higher the maintenance rate; Cats 80 x body weight (kg)0.75 total volume over 24 hours (usually 2-3 ml/kg/hr) Dogs 132 x body weight (kg)0.75 total volume over 24 hours (usually 2-6ml/kg/hr) If an animal was fit and healthy with no fluid deficits that is how much we would have to administer IV to keep the animals fluid balance in equilibrium. However, most of the patients that we put on drips are not fit and healthy, and have fluid imbalances or ongoing losses so we usually end up giving in excess of this rate. Anaesthesia fluid therapy rates Why, when we have animals under anaesthesia do we use ivft far in excess of ‘maintenance’ rates? When an animal is anaesthetised, the agents we use tend to produce hypotension, either via vasodilation or decreasing myocardial contractility. So on top of the ‘maintenance’ rates that the dog needs, we need to give additional fluids to support this blood pressure. In addition, in the case of the bitch spey, the losses may be actually increased from blood loss and evaporative losses from the open abdomen. Fluid therapy rates under anaesthesia can range from 3 to 5ml/kg/hr (the current JAAHA recommendation). You may have to be a little more conservative with fluid rates if the patient suffers from certain cardiac conditions to avoid volume overload. Current fluid therapy recommendations 5ml/kg/hr initial rate in dogs o Reduce by 25% every hour until maintenance rate is reached o Maintenance = 132 x bodyweight(kg)0.75 total volume over 24 hours (approx. 2-6 ml/kg/hr) 3ml/kg/hr initial rate in cats o Reduce by 25% every hour until maintenance rate is reached o Maintenance = 80 x bodyweight(kg)0.75 total volume over 24 hours (approx. 2-3 ml/kg/hr) Hoe to deal with hypotension during anaesthesia Hypotension is a common event during anaesthesia Blood pressure should be measured during an anaesthetic so that hypotension www.improveinternational.com | 8  can be recognised and corrected Fluid therapy boluses should not be used as a sole method of correcting hypotension Evidence suggests that fluid loading of euvolaemic patients with hypotension will not improve blood pressure. Early sympathomimetic treatment should be used instead Below is a plan of how to respond to hypotension Reduce administration of volatile agents if possible Administer a fluid bolus of 3-10 ml/kg crystalloid over 15 minutes Repeat crystalloid bolus if hypotension not resolved Consider trying a colloid bolus of 2-5 ml/kg if blood pressure still low If there is no response to fluid therapy, start sympathomimetic or positive ionotrope therapy Dehydration If an animal is admitted with a pre-existing degree of dehydration, e.g. pyometra, persistent vomiting etc, then this deficit needs to be factored in and compensated for in the fluid therapy plan. First of all, we need to know how dehydrated the animal is by a combination of subjective and objective tests. Subjective tests include moistness of mucous membranes, skin turgor and sunkenness of eyes. When you combine these signs, you can estimate the degree of dehydration using table 1. This is only a rough guide and there are many factors, not just hydration which affect these signs e.g. fat and paediatric animals will have normal skin turgor even when dehydrated, and well hydrated animals which have been panting excessively may have drier mucous membranes. So more objective tests e.g. packed cell volume, total protein, urea, urine specific gravity and sodium levels may give a more accurate picture of the dehydration. The signs of dehydration (where water will be lost from all fluid compartments) should not be confused with signs of hypoperfusion due to inadequate circulating volume i.e. alterations in heart rate, pulse quality, mucous membrane colour, capillary refill time. Severe dehydration will ultimately decrease the intravascular volume and therefore, signs of hypoperfusion will often be seen alongside the signs of dehydration. www.improveinternational.com | 9 Table 1 Signs of dehydration % dehydration Clinical signs 4% No clinical signs 5% Semi dry oral mucous membranes Skin turgor normal Eyes moist 6-7% Dry oral mucous membranes Eyes moist Mild loss of skin turgor 8-10% Dry oral mucous membranes Eyes retracted Considerable loss of skin turgor Signs of hypoperfusion 10% Very dry mucous membranes Severe eyeball retraction Eyes dull Complete loss of skin turgor Altered consciousness Greater signs of hypoperfusion 12% As 10%, moribund 12-15% As 10% but dying Correcting dehydration The % dehydration value from table 1 indicates the amount of water lost as a % of body weight. So if we multiply this % by the animal’s body weight, we can find out how much fluid is owing to the animal, ‘the fluid deficit’ (example 1). This, depending on the severity of the animal’s dehydration, can be given over 12-24 hours (example 2). In more acute situations, deficits may need to be addressed in a shorter time frame, e.g. 1-4 hours. Ongoing losses Usually, when animals are hospitalised with dehydration, losses from vomiting and diarrhoea are still ongoing. Additional boluses of fluids for each episode of vomiting or www.improveinternational.com | 10 diarrhoea the animal has whilst hospitalised should be included. (Example 3). Volumes equalling those lost should be administered, but if you don’t fancy measuring out vomitus, some texts suggest 50ml bolus per vomiting episode and 100ml bolus per episode of diarrhoea in the dog. Assessing response to fluid therapy The patient must be regularly re-assessed and the plan may have to be changed. In addition, it is good practice to administer fluid therapy until certain ‘end-points’ i.e. parameters such as heart rate, mentation, mucous membranes, skin turgor etc have returned to normal. Calculating drip rates So we have got to the stage where we now have a fluid therapy rate, usually represented in ml/kg/hr. To turn that figure into drips per second (example 4) the other pieces of information we need are the animals body weight, and the number of drips per millilitre that the drip set delivers. Whilst most standard drip sets routinely deliver 20 drips per ml of fluid, it is always worth checking on the packet if are using a set that you are not used to. Some larger bore sets deliver 10 drips per ml, and paediatric burettes tend towards 60 drips per ml. Example 1 Fluid deficit (litres) = % dehydration x body weight Therefore a 20kg dog who we assess to be 8% dehydrated Fluid deficit (litres) = 8 x 20 100 Fluid deficit= 1.6 litres Example 2 Fluid plan for the 8% dehydrated 20kg dog in example 2 (assuming no ongoing losses) is fluid deficit over 24 hours in addition to basic maintenance. Maintenance = 132 x 20kg0.75 = 1248ml over 24 hours = 52ml/hr Fluid deficit = 1.6 litres / 24 hours = 66ml/hr Total fluid rate = 52 + 66 = 118 ml/hr www.improveinternational.com | 11  Example 3 If (as is more likely) this animal continues to have extra fluid losses, these must be accounted for as well. 2 bouts of vomiting (10ml and 20ml approx) and 3 bouts of diarrhoea (50ml each) So on top of 118ml/hr, either the (10+20+50+50+50=180ml) can be replaced over the period of the fluid therapy plan (18024= 7.5ml/hr, so total fluid rate of 125.5ml/hr), or preferably boluses equalling the volume lost can be given each time a ‘loss’ is witnessed. Example 4 Calculations for a drip rate are required for a 10kg Terrier undergoing contrast studies in radiography. The drip rate is 5ml/kg/hr and the burrette is a standard 20 drip/ml size. Drip rate = 5ml/kg/hr Drip rate for this dog = 5 x 10 = 50 ml/hr Number of drips per hour = 50 x 20 = 1000 drips/hr Number of drips per minute = 1000 = 17 drops/minute = approx 1 drop every 4 seconds 60 Blood component therapy Blood volumes Total blood volume for dogs = 80-90 ml/kg Total blood volume for cats = 56-60 mll/kg Indications Severe acute haemorrhagic shock, haemolytic anaemia, hypoproteinaemia, coagulopathies, thrombocytopaenia etc. Choosing a donor Dog donors Friendly, clinically normal, large breed dogs (at least 25kg lean weight) with easily www.improveinternational.com | 12 accessible veins and a universal donor blood type. Grey hounds are often used because their PCVs are higher. Dogs with recent bite wounds, acute vomiting and diarrhoea, fever, pregnant, or that have been pregnant should not be used as donors. Avoid using dogs who have been vaccinated within last 10-14 days, or have any parasite burden. Dogs should not be on any medication and should not have received any previous blood transfusions. How to take a canine whole blood donation Put on a sterile pair of gloves. Raise the jugular vein with your non-dominant hand. Using a clean stick (preferably) make a venipuncture with the bevel of the needle facing upwards. The haemostat or clamp should now be released. Blood should flow from the collection line to the bag easily. As soon as the blood starts to enter the collection bag, gently rock the bag to mix the blood with the anti-coagulant. Carry this on regularly (approximately 4 times a minute) during the collection process. Check the weight of the bag intermittently. One full unit is 450ml (which is equivalent to 480g). Once the unit has been collected, stop raising the vein and clamp the collection line again. Remove the needle and apply firm pressure over the venepuncture site with several swabs for two minutes. If required a neck bandage can be applied. If a tube stripper is available, strip the blood in the line into the bag. Stop 5cm from bag, fold the empty tubing and tie a knot behind the fold. Cut the tubing on the needle-side of the knot and discard the needle with tubing into the sharps. Check demeanour, heart rate, mucous membrane colour and pulse quality. If the donor is showing any signs of hypovolaemia, such as tachycardia or pale mucous membrane colour, then crystalloid fluid therapy (at three times the volume removed) can be administered intravenously. Remember that the Pet Blood Bank can provide packed red cells and plasma for canine transfusions. Cat donors Friendly, normal large cat (>5kg) lean weight. The PBB recommend an echo is undertaken to check for occult cardiac disease. A high donor PCV (>30%) is preferred. Don’t use pregnant queens, but previous pregnancy does not exclude queen from donating blood. Cats should be tested routinely for FEL and FIV and FIP. Cats should also be free from for Haemobartonella felis, and bartonella, dirofilaria and babesia. How to take a feline whole blood donation www.improveinternational.com | 13  Sedation will usually be required. The sedation protocol should be chosen based on the temperament and health status of the cat. The author has previously used alfaxalone intramuscularly, or sevoflurane by mask. Others suggest alpha 2 adrenergic agonist based protocols although this class of drugs will prevent any compensatory tachycardia as a response to a loss of blood volume. Flow by oxygen by mask and anaesthetic monitoring should be used for all sedated cats. Their eyes should also be lubricated. A typical ‘unit’ of cat blood is 45ml; but make sure that no more than 12ml/kg donation is taken. A ratio of 1ml of anticoagulant (drawn in a sterile manner from the bag of anti- coagulant) to 7ml of whole blood should be prepared. Clip and aseptically prepare the area over the jugular vein. Put on sterile gloves Attach the butterfly catheter and three way tap to the 60ml syringe (containing anti-coagulant amount described above) and inject some anticoagulant through the three way tap into the butterfly needle. Raise the jugular vein and then insert the butterfly catheter into the vessel, bevel upper most and gently aspirate the blood into the syringe. The blood should be at a rate of 5ml/min or greater. Once the desired volume has been collected into the syringe, turn the three way tap off to the butterfly needle and remove the needle from the vessel. Apply pressure to the venepuncture site. Check demeanour, heart rate, mucous membrane colour and pulse quality. If the donor is showing any signs of hypovolaemia, such as tachycardia or pale mucous membrane colour, then crystalloid fluid therapy (at three times the volume removed) can be administered intravenously. What anti-coagulants are used to stop the blood clotting once collected? Acid Citrate Dextrose Citrate Phosphate Dextrose Adenosine Heparin Canine blood groups Blood groups are defined by inherited antigens on the surface of the red blood cell. If there is an antibody directed against a blood group antigen, we see haemolysis. Of the DEA (dog erythrocyte ( another name for red blood cell) antigens), DEA 1 and 7 www.improveinternational.com | 14 are the most important. Universal donors will be negative for these three DEAs. DEA 1 DEA 3 DEA 4 DEA 5 DEA 6 DEA 7 DEA 8 DEA 9 DEA 10 DEA 11 DEA 12 DEA 13 Ideally you should always cross-match before transfusing, but as dogs rarely have naturally occurring alloantibodies, the first transfusion is unlikely to cause problems. Dogs must be cross matched for any subsequent transfusions though. A typical ‘unit’ of dog blood is 450ml; and a ‘unit’ of packed red cells is around 200ml Feline Blood Groups A = dominant to AB, and most common B = thought to be common in some breeds, e.g. Persian, British shorthair AB = recessive to A; co-dominant with B There is no Universal donor in cats, so you must always cross match – even if you have checked for compatible blood types between donor and recipient. A typical ‘unit’ of cat blood is 45ml; and a ‘unit’ of packed red cells around 20ml Blood administration Must use giving set with in-line filter to ensure microthrombi and debris do not get transfused Blood should be either at room temp not cold straight from the ‘fridge Record recipient’s baseline TPR before start transfusion – this makes it easier to www.improveinternational.com | 15  note reactions. Do not administer blood through lines with Hartmann’s, or other calcium-containing solutions in them, or else clotting of the blood in the line may happen. Packed red cells can be diluted in 0.9% saline to ease administration. Generally you should start administering blood products at 0.5ml/kg/hr, certainly for first 15 minutes to check for acute reactions. If necessary, you can then increase up to 5-20ml/kg/hr. Transfusion reactions Can be immunologic (acute or delayed), and non-immunologic Signs include; o Agitation/restlessness/change in attitude o Nausea, vomiting, salivation o Urticaria with or without pruritus o Anaphylaxis o Pyrexia o Tachypnoea/dyspnoea o Tachycardia o Hypotension o Seizures o Haemolysis, jaundice, haemoglobinuria NB A lot of these will be less obvious under general anaesthesia Others transfusion reactions:- Hypocalcaemia (citrate toxicity) Circulatory overload. Hypervolaemia (volume overload) Hypothermia (blood not warmed prior to infusion) Transmission of infectious diseases If reaction occurs:- STOP infusion and contact the vet. www.improveinternational.com | 16 Corticosteroids +/- antihistamines can be administered. If mild reaction, continue but at SLOW rate If severe, do not continue Types of blood components Whole blood Blood can be stored for up to 4 weeks at +4oC (refrigerator), as long as a closed system was used for its collection. Platelets lose viability within 1-3 days. If aseptic technique was breached, then blood must be used within 24 hours. Packed red cells Usually washed with saline, and re-suspended in minimal saline, so final PCV c. 60-80%. Can be administered, slowly, as packed red cells, especially to patients with chronic anaemic conditions that are normovolaemic. Can be further re-suspended in sterile normal saline to make a less viscous solution for administration. Fresh plasma Blood must be centrifuged and plasma harvested for use within 6 hours to save clotting factors and platelets. Fresh frozen plasma Blood centrifuged and plasma harvested and frozen (-18oC) within 6 hours to save clotting factors. Can be stored for up to 1 year; but after thawing, should be given within 6 hours. Some calculations to estimate how much blood is required to increase a patient’s PCV. 2.2ml/kg of donor blood (pcv approx 40%) will raise recipient’s pcv by 1% 1ml/kg of donor packed red cells (pcv approx 60-80%) will raise recipient’s pcv by 1% We can use this information to calculate the amount of donor blood required: www.improveinternational.com | 17 For whole blood mls donor blood required = desired PCV increase x (2.2 x Recipient BW) For packed red cells mls donor blood required = desired PCV increase x (1 x Recipient BW) An alternative calculation can be used, see below; the benefit of this calculation is that it can be used in different species with different donor PCVs. mls donor blood required = recipient blood volume x desired PCV–recipient PCV donor PCV Blood typing As well as submitting anticoagulated blood to a commercial laboratory for typing there are two commercial blood typing kits available for in-house use. 1. Rapid Vet-H test Interpretation based on agglutination reaction. 2. Alvedia Quick Test DEA 1.1 Interpretation based on immuno-chromatography, whereby test strips are impregnated with monoclonical antibodies. As a result, they work in the presence of agglutination and a low PCV volume Cross Matching Cross-Matching is an in vitro test which investigates for potential reactions between the donor’s blood and the recipient’s blood, which may appear as haemolysis or agglutination. It is the Gold Standard laboratory procedure and to determine the serological compatibility between the donor and recipient. However, this is not always practical and is restricted to patients receiving more than one blood transfusion. Cross-matching should be performed in conjunction with blood typing if: the recipient has received a prior transfusion