General anesthesia poses significant risk to small animals, with dogs and cats potentially experiencing anything from minor complications to anesthetic related death. A thorough pre-anesthetic evaluation is crucial for identifying dogs and cats that are at increased risk and also aids in designing the optimal anesthetic protocol for a given patient.
Here are some helpful tips for pre-anesthetic screening.
Pertinent Medical History
A detailed history is important for uncovering clues about the patient’s physical status. For example, a patient with a history of exercise intolerance or difficulty breathing may have underlying cardiac and/or respiratory disease. A patient’s urination and drinking habits can also reveal information about underlying disease, with polyuria and polydipsia potentially being caused by renal dysfunction or an endocrine disease like Diabetes Mellitus or Cushing’s Disease. Special attention should be given to any previous anesthetic episodes and how the patient responded to the drugs that were administered and if any complications were experienced.
A thorough physical exam, with particular focus on the cardiovascular and respiratory systems, is important for recommending additional diagnostics and assessing a patient’s anesthetic risk. For example, if a heart murmur or arrhythmia is auscultated then a cardiac evaluation should be recommended prior to anesthesia so that the anesthetic protocol can be tailored specifically for that patient according to the results of the cardiac evaluation.
A recent biochemistry profile and complete blood count are recommended to screen for metabolic derangements that could increase anesthetic risk. Any abnormalities detected on bloodwork should be addressed if possible or further investigated prior to anesthesia with the appropriate diagnostic tests (i.e. additional blood tests, abdominal ultrasound, urine analysis, etc.).
Additional screening and patient preparation may also be recommended based on a patient’s age. Pediatric patients are animals that are still in the process of developing and they are physiologically immature compared to an adult animal. Dogs and cats less than 6 months of age are considered pediatric patients. Pediatric patients have higher metabolic requirements and lower hepatic glycogen stores compared to adult animals. As a result, it is recommended to only fast pediatric patients for 4 hours (vs. 8 hours for adults) and to check their blood glucose prior to induction and again in recovery. Supplemental dextrose should be administered if indicated.
At the other end of the age spectrum, a patient is considered geriatric when they have achieved an age that is at least 75% of their life expectancy. In general, dogs that are 8 years or older and cats that are 10 years or older are geriatric. Geriatric patients are more likely to have underlying co-morbidities or neoplastic disease that may not be detectable on physical exam or bloodwork, therefore thoracic radiographs and abdominal ultrasound are recommended for additional screening.