Complications Of Anaesthesia
Introduction
In every species, anaesthesia carries risks due to the drugs that are used. These risks can sometimes be treatable with appropriate intervention while others may be fatal. For these complications to be detected, careful monitoring is essential both during and after the anaesthetic procedure.
Haemoglobin Desaturation
Many of the complications seen due to anaesthesia are associated with tissue hypoxia. With the use of pulse oximetry and blood gas analysis early detection is possible and allows for correction of falling oxygen levels. However, it is also possible to detect by monitor mucous membrane colour and loking for other signs of cyanosis.
Falls in oxygen can be due to a number of reasons including empty cylinders, kinks in the breathing system and obstructions.
Airway Obstruction
Airway obstructions can occur in both the intubated and non intubated patient. In an intubated patient kinks in the tube and positioning of the patient can both be causes, while in the non intubated patient brachycephalic breeds are at hig risk and again, positioning may also lead to airway obstruction.
Aspiration
A worry in all patients undergoing anaesthesia is the risk of aspirating material that has been refluxed or from the oral cavity in case of dentistry work in some patients. This can lead to the development of aspiration pneumonia. To reduce the incidence of aspiration, patients are commonly starved before a procedure for 8-12 hours depending on the species.
Apnoea
Due to respiratory depression called by a number of the anaesthetic drugs, apnoea is commonly seen in anaesthetised patients. In these cases, the airway should be checked for any obstructions before manual ventilation is performed. Appropriate intervention can then be carried out depending on the underlying cause.
Circulatory Failure
This may be due to a volume insuffiency or a primary cardiac problem. Common causes include haemorrhage and peripheral vasodilation due to the anaesthetic drugs. Treatments include fluid therapy and interventional drugs such as Dobutamine, Dopamine, Ephedrine, Phenylephrine and Vasopressin.
Cardiac Arrhytmias
Many of the anaesthetics commonly used are arrhythmogenic. Changes in cardiac rate and rhythm, therefore, are commonly seen.
Cardiac Arrest
There are a number of causes for cardiac arrest. It is detected via close monitoring of the patient and is when the heart fails to pump, meaning the heart beat is lost and so cardiac auscultation can be the most basic monitoring method to detect an animal in cardiac arrest. The ABC protocol should be started as soon as the patient enters cardiac arrest.
- A - Check that the Airway is patent.
- B - Breathing usually via intermittent positive pressure ventilation.
- C - Circulation usually involving chest compressions either external or internal.
Once the circulation has been recovered, then the risk of tissue hypoxia is reduced and other methods of treatment can be used to try and prevent further cardiac arrests or treat the underlying cause.
If the patient goes into fibrilation, the best treatment is passing an electrical current through the heart, usually performed using defibrillator. However, these are rarely available in practice, although their presence is increasing.
Post Operative Myopathy
One of the most important causes of postoperative complications in horses, postoperative myopathy is commonly seen in well muscled horses. It is usually detected when the horse first tries to stand upon recovery but can take hours to develop. Clinical signs vary from mild lameness to the horse not being able to support its own weight. It is extremely painful. Efforts to prevent development of post operative myopathy include correct positioning and padding on the anaesthetic table. Treatment includes adequate analgesia, fluid therapy and close monitoring of kidney function via serial blood sampling.