Critical Patient Ahead--How to Avoid Anaesthetic Mishaps with a Critical Patient--Part 2
Recovery begins the moment that the administration of an anaesthetic agent ceases. We usually assume that once the vaporizer is turned off or injectable agent no longer administered that CNS depression reduces and the patient will 'recover' without any further support and monitoring needed. This is often the case but occasionally healthy patients undergoing elective procedures or more commonly debilitated patients undergoing emergency or complicated surgery suffer some type of problem during recovery. To minimise the chances of an untoward event it is necessary to monitor and support these patients as they recover from anaesthesia.
So, how do we go about supporting and monitoring these patients in an appropriate way?
Ideally, oxygen delivery should continue until extubation occurs. This isn't always feasible but provision of oxygen for 5-10 minutes after turning off the vaporizer should be a minimal requirement. After turning the inhalational agent off, the oxygen flow rate should be turned up to at least 1 litre per minute and preferably to 2-3 litres per minute initially to flush anaesthetic agent from the anaesthetic machine and as it is expired by the patient.
Extubation occurs once the patient has adequate control of its airway which is recognised by swallowing, chewing or gagging. Cats may develop laryngospasm if the ET tube is left in place for too long and they should be extubated promptly. Maintenance of an airway until the animal becomes aware is especially important in brachycephalic breeds of dogs. They readily obstruct their airway during recovery and so should be closely monitored during this period. The ET tube should remain in place for as long as possible in these dogs and this often means that the animal may be in sternal recumbency or even mobile before they are extubated. Following extubation the dogs should continue to be closely monitored to ensure that they don't re-obstruct after extubation. They should never be extubated during periods of stimulation as airway obstruction may occur as they fall back into unconsciousness.
Monitoring Following Extubation
Once the animal is extubated and returned to its cage it is all too easy to forget about it. However, a number of parameters should continue to be monitored including temperature, respiratory rate, heart rate, pulse pressure and mucous membrane colour.
Patients commonly arrive from surgery with a low body temperature. This occurs for a number of reasons including the effects of sedative agents, reduced muscle activity, clipping, cold prep solutions, open body cavities and cool fluids (intra-abdominal and parenteral). Without added heat in recovery, body temperature may continue to fall which markedly slows recovery as metabolisation of drugs is impaired. In our practice we place the animal on a heating pad (or heated cage floor) if its temperature is below 37°C and add a heating lamp if temperature is below 35°C.
It is important to check temperature first to make sure that the patient really requires supplementary heat in recovery rather than making the assumption that all patients need heat. Occasionally patients will maintain body temperature during anaesthesia and sometimes even show an elevated temperature. This is especially common in cats that have received ketamine as part of their anaesthetic protocol. It is also important to periodically check body temperature to ensure that temperature is increasing appropriately and to determine the point at which heating should be discontinued.
Respiratory rate and depth are rarely compromised in post-anaesthetic patients but they need to be checked because if abnormal could denote a serious problem. A low respiratory rate may be seen in animals that have become very cold or those that remain deeply anaesthetised. Rapid shallow ventilation may denote pain or difficulty in expanding the chest due to restrictions, e.g., bandaging, chest fluid or pneumothorax. If respiration appears to be severely compromised and it is not possible to determine why within a short period of time, it may be necessary to re-intubate the patient and manually ventilate until the problem can be corrected.
Heart Rate and Rhythm
Heart rate is another parameter that should be checked shortly after the patient arrives in recovery. We expect heart rate to be near normal but it may be elevated in an animal that is hypovolaemic or in pain, or it may be slow secondary to hypothermia or drug administration (opioids, alpha-2-agonists). A markedly abnormal heart rate (either too fast or too slow) reduces cardiac output and tissue perfusion so should be corrected. An analgesic agent may need to be administered to reduce heart rate in a painful animal. Opioids have the additional effect of slowing heart rate as well as providing analgesia. Bradycardia resulting from alpha-2 agonist administration is usually not treated because of the resulting marked hypertension which is produced by the combination of increased heart rate in combination with the intense vasoconstriction induced by the sedative. Bradycardia may also result from hypothermia. Depending upon body temperature, administration of atropine may or may not be successful in elevating the heart rate. In very cold animals, electrical activity cannot physically move through the heart any faster and so atropine has little effect. In close association with checking heart rate, is heart rhythm. Once again, arrhythmias are not expected during recovery but occur occasionally and may be drug induced or secondary to heart disease, gastric dilatation-volvulus or trauma. Lignocaine is the drug of choice for initially treating ventricular arrhythmias. It is readily available in practice, inexpensive and rapidly controls the arrhythmia.
Ideally, blood pressure should be measured but this can't always be achieved in a recovering patient so pulse pressure is often used instead. Pulse pressure is the difference between systolic pressure and diastolic pressure and gives some idea of tissue perfusion. You should be able to feel a strong pulse in the dorsal pedal artery of a dog unless it is cold but it is harder to palpate in cats because of the small size of the artery. If you can't feel the dorsal pedal artery, check the femoral artery--it should be easily palpable in both dogs and cats. A poor peripheral pulse could indicate intense vasoconstriction due to hypothermia, pain or hypovolaemia. Once hypothermia and pain have been ruled out as the cause, it may be necessary to provide a bolus of IV fluids e.g., 10 ml/kg Lactated Ringer's Solution (LRS) to improve blood pressure.
Mucous Membrane Colour and Capillary Refill Time
How useful is mucous membrane colour in estimating tissue oxygenation? Well, it can be quite variable. Mucous membranes may continue to look pink when haemoglobin saturation is too low to maintain tissue oxygenation. If your practice has a pulse oximeter then check the patient's oxygenation if you have any concerns, e.g., patients that have had upper abdominal surgery, airway or thoracic surgery and brachycephalic breeds etc. If you have any concerns about mucous membrane colour or SaO2 from the pulse oximeter, then provide oxygen to the patient via a face mask attached to an anaesthetic machine until you can determine the cause for the problem or the condition resolves.
Frequency of Monitoring
Patients need to be checked frequently initially and the time between checks can be extended with time. At our practice we check the patients every 15 minutes for about the first hour, increasing to 30 minutes or hourly thereafter depending on how well the animal is progressing.
Complications That May Arise During Recovery
Excitement during recovery is not common but may be seen in animals that were not adequately sedated prior to induction and in the sled dog breeds, sight-hounds and Dobermans. Not only can the animal injure itself as it thrashes around in its cage but the noise can agitate other patients and it can be very distracting for staff. Excitement may also be seen in painful animals so it is important to ensure that the animal is pain free before considering giving a sedative. In our practice we routinely provide post-op analgesia to post-surgical patients and if excitement continues we may administer a very low dose of acepromazine (0.01 mg/kg IV) to calm the animal.
It is to be expected that pain will result following a surgical procedure. Analgesia should be provided before the patient becomes aware of the pain if possible. This makes the pain easier to control and reduces the chance of an excited recovery. How do you recognise pain in the recovering animal? Agitation, vocalisation, reluctance to move, aggression are all signs that may reflect pain.
To avoid anaesthetic disaster, mishaps or misadventures be vigilant at all times and anticipate trouble. It rarely occurs to those who expect and have prepared for it!