Anesthesia is concerning for every patient, this is especially so when the patient has pre-existing conditions. The value of a thorough physical examination and detailed history cannot be underestimated as part of a balanced anesthetic plan because the goal of the plan is to maximize its' effects while minimizing patient complications.
The Anesthesiologist Society of America (ASA) created a physical status scale that is often used in veterinary medicine to rate patients for potential anesthetic risk. The scale is as follows:
ASA status I is a healthy patient
ASA status II is a patient with mild systemic disease with no functional limitations
ASA status III is a patient with severe systemic disease with functional limitations
ASA status IV is a patient with severe systemic disease that is a constant threat to life
ASA status V is a moribund patient that is not expected to survive 24 hours with or without surgery
E denotes an emergency
This section will cover some conditions in which special consideration needs to be given regarding anesthesia.
Puppies and kittens are generally considered neonates for the first 6 weeks of life and pediatrics for the first 12 weeks of life. Compared to adults, neonatal and pediatric patients have immature cardiovascular systems and ventilation muscles, decreased alveolar surface in the lungs, underdeveloped organs, and less body fat. These cause a decreased ability to respond to physiological challenges, exaggerated or prolonged effects of drugs, and a tendency to develop hypothermia, hypoglycemia, and fluid overload.
Successful anesthetic management depends on several actions:
• Careful dosing and administration of drugs.
• Consider using drugs that cause less respiratory depression such as partial opioid agonists (i.e. Buprenorphine instead of Hydromorphone)
• Close monitoring of the cardiovascular status, respiratory rate, and body temperature.
• Ventilate more often for their oxygen consumption is approximately twice that of the adult patient. Also, due to their immature intercostal muscles and diaphragm, pediatrics and neonates must work harder to breathe. This causes a greater potential for respiratory fatigue.
• Include anticholinergics in the anesthetic plan because these patients have less functional contractile tissue and rely on the heart rate for cardiac output.
• It may be prudent to administer a Dextrose CRI depending on the duration of the anesthetic procedure. Do not withhold food if still suckling and fast for no more than four hours if eating solid food. Periodic checks of the patient's blood glucose may be indicated during a lengthy procedure, and post-operatively.
• Hypotension and proper pain management is still a concern as with all anesthetic patients.
• Administer intravenous fluids to maintain cardiovascular support, and use a fluid pump to prevent fluid overload.
• Closely monitor in the post-operative period since they cannot thermoregulate and can become hyperthermic/ hypothermic quickly.
Older patients are less resilient because organ function diminishes with age. It may be difficult for these patients to compensate for physiologic disturbances that can occur from general anesthesia and surgery. They also may have impaired vision and hearing causing them to startle easily. Calming them with compassion along with appropriate sedation may be necessary since stress can increase complications and inhibit recovery.
Several actions are indicated to care for these patients properly:
• Thorough preanesthetic bloodwork and physical exam
• Decreased drug doses to minimize cardiovascular effects and organ elimination
• Monitor closely for hypothermia as most geriatric patients have less body fat, and cannot adequately compensate for heat loss. Also hypothermia's negative effects such as bradycardia, hypotension, fluid overload, and arrhythmias can take a greater toll on these patients.
• Supportive care in the post operative period includes proper fluid administration, lots of bedding, and comforting nursing care.