Managing common and uncommon complications of anesthetized patients (Proceedings)
There is no such thing as completely safe anesthesia. Anesthesia complications can occur that can compromise a patient's health and even result in death. Many anesthetic complications and accidents can be minimized or avoided with proper knowledge and avoidance techniques and vigilant patient preparation and monitoring. Early identification of complications is essential so that actions can be taken to minimize their impacts.
Most patients undergoing anesthesia are at risk for 5 common complications associated with anesthesia. They can be termed the "Big 5".1. Hypotension
Hypotension is simply an abnormally low blood pressure. Mean arterial blood pressures of at least 60 mm Hg are necessary for proper perfusion of organs such as the brain, heart, lungs, and kidneys. Hypotension can be a result of hypovolemia, decreased cardiac output, obstructed venous return or vasodilation. Vasodilation is probably the most common cause of hypotension during anesthesia as many sedative, analgesic, and maintenance agents promote vasodilation. Volatile anesthetics are one of the strongest vasodilating agents used and inhalant anesthetic sparing techniques should be used, particularly in those patients where hypotension could be particularly harmful. Treatments for hypotension includes reducing anesthetic agents, intravenous crystalloid and colloid fluid therapy, correction of acid-base and electrolyte abnormalities, and administration of pressor agents.
Hypothermia is the most common complication of use of inhalant anesthetics. Prolonged and/or profound hypothermia can result in decreased wound healing, prolonged recovery time, cardiac arrhythmias, hypotension, prolonged hospital stays, and increased mortality. The use of warming devices before, during, and after anesthesia to maintain a normal temperature is easily done. Forced warm air blankets appear to be the most efficacious especially during long procedures.
Hypoventilation is very common during anesthesia, particularly if opioids are used for analgesia and sedation. Opioids decrease the sensitivity of the central nervous system to elevations in carbon dioxide levels that normally would trigger increased and deeper breathing. Some degree of hypoventilation can be allowed depending on the severity of the patient's condition and their health status. In more critical patients, hypoventilation and a corresponding increase in PaCO2 should not be allowed as this can lead to a respiratory academia which may worsen conditions in a critical patient. Mechanical or assisted ventilation should be performed to keep PaCO2 levels normalized. End tidal carbon dioxide monitoring can be an excellent way to monitor ventilatory effectiveness.
Bradycardia can also be very common during anesthesia. Again, many peri-anesthetic agents including opioids can cause bradycardia either through direct action on the myocardium or enhancement of vagal tone as is the case with opioids. Target goals for appropriate heart rates depend on the individual patient and generally should approximate expected heart rates in sleeping animals. Anti-cholinergic agents such as atropine and glycopyrrolate are the mainstays for treatment of bradycardia. Acceleration of the heart rate can increase cardiac output and blood pressure.
Pain management should be considered in all patients presenting to veterinarians. Because animal patients cannot communicate pain to the practitioner, animals should prove that they do not need analgesic medication rather than prove that they need it. Proper pain management increases healing and reduced infection risks, promotes sleeping, eating, and recovery and reduces hospital stays and convalescent time.
Uncommon complications that occur in anesthetized patients are often related to underlying disease conditions and can be anticipated based on that condition and the stability of the patient. A through physical exam prior to anesthesia and an understanding of the pathophysiology of the underlying conditions can help guide preanesthesia treatment options and minimize complications.
Respiratory complications include dyspnea, hypoxia, respiratory arrest, hyperventilation, and aspiration. Patients with upper airway diseases such as brachycephalic syndrome should be anticipated for potential airway obstruction. Obstruction most often occurs at extubation and close monitoring of these patients in recovery and overnight after surgery is essential. In severe cases, tracheostomy may be necessary. At the very least, an injection of a fast acting corticosteroid can be used to help decrease airway inflammation. Aspiration and subsequent pneumonia can be a very serious complication that can result in prolonged hospitalization, client cost, and even death. Patients at risk include those receiving upper airway procedures, vomiting, and positioning. Those as risk can be treated prior to anesthesia with metaclopramide to promote gastric emptying and marpopitant to reduce vomiting from anesthetic and analgesic drug administration.
Cardiovascular complications that can occur during anesthesia include bradyarrhythmias, tachyarrhythmias, hypotension, and hypertension. Tachyarrhythmias, including ventricular arrhythmias, can be more dangerous than bradyarrhythmias because they increase the myocardium demand for oxygen which can lead to malignant rhythms and can be more refractory to rescue therapy. It is critical to identify preexisting cardiovascular conditions and stabilize patients prior to anesthesia for routine procedures. For patients requiring anesthesia for emergency treatments unstable cardiovascular conditions put them at an increased risk for anesthetic morbitiy and mortality.
Other complications that can occur include postoperative renal insufficiency, electrolyte and acid base abnormalities, hypoglycemia, myopathy and neuropathy, recovery dysphoria, and prolonged recovery. Many of these can be avoided with proper prior work up and anesthetic planning. However, vigilant patient monitoring during anesthesia can help curtail the unexpected problems.
Human and anesthetic machine error can also lead to anesthetic complications. Proper machine maintenance, including monitoring equipment is vital for prevention of avoidable mishaps. Advanced and continued training of staff is also important and can be a wise investment for a veterinary practice. Well trained anesthetist trained in identifying warning signs of impending problems can be exceptionally valuable for patient care and client satisfaction.