Q: What are your protocol recommendations for sedating and anesthetizing cats that have hyperthyroidism?
The most important anesthetic considerations associated with surgical treatment of feline hyperthyroidism relate to the cardiovascular
status and the corresponding treatment with antithyroid medication or beta-blockers. Minimizing anesthetic risk in these patients
depends on medical treatment before surgery. Patients with severe tachycardia or heart failure should be treated medically
before surgery, and such treatment should not be discontinued before anesthesia. Anesthetic considerations include monitoring
cardiovascular performance, decreased access to the head during neck surgeries, and potential hemorrhage. Postoperative complications
include hypothermia, hypocalcemia, and laryngeal paralysis.
Q: What special type of anesthetic monitoring should be done in patients with organ system dysfunction?
The noninvasive monitoring equipment that is becoming increasingly prevalent in hospitals (e.g. pulse oximetry, capnography, electrocardiography, temperature monitor, blood pressure monitor) can be used in all patients,
not just those with organ system dysfunction. In patients with organ system dysfunction, one type of monitoring may be more
valuable than another, depending on the patient's problems or the type of procedure being performed. Pulse oximetry is more
important to me during bronchoscopy or thoracostomy tube placement. Capnography is difficult to monitor unless the patient
is intubated, and displayed values are more difficult to interpret in spontaneously breathing patients under general anesthesia.
Electrocardiography will be more important in patients predisposed to arrhythmias (e.g. posttrauma patients, patients with splenic tumors or gastric dilatation volvulus).
More invasive monitoring (e.g. direct arterial blood pressure measurement, central venous pressure monitoring, closed urine collection system, arterial
blood gas evaluation) may be reserved for more critically ill patients that may be experiencing organ failure.
Many practitioners think they cannot afford to have all the monitoring equipment now available. I strongly encourage every
practice to consider purchasing this equipment. However, there are no good electrical substitutes for frequent auscultation
with an esophageal stethoscope and frequent evaluation of peripheral pulse quality, palpebral reflex, jaw tone, mucous membrane
color, and capillary refill time. No electrical monitor is as versatile as the anesthetist. So every practice should routinely
use a trained technician devoted to monitoring a patient's depth of anesthesia and physiologic responses to the anesthetic
agents throughout the procedure and into recovery. In some cases, it may be practical to refer patients to practices where
they can be adequately monitored.
Q: Take the case of a young whippet presented 20 minutes after it ingested over 2 lb of chocolate. An arrhythmia was auscultated
that had not been previously noted in the medical record. Sedation before gastric lavage was needed. What is the best way
to proceed when immediate electrocardiography is not practical?
This situation is frequently encountered. The patient's condition will not always wait for the clinician to collect all the
desired information. The goal in this case is to immediately limit absorption of a large amount of theobromine. I suggest
placing an intravenous catheter and administering an intravenous bolus of a balanced electrolyte solution (10 to 20 ml/kg).
Then perform a rapid induction and intubation sequence (to avoid vomiting and aspiration during induction) with an opioid
(e.g. hydromorphone, fentanyl) followed by propofol and an inhalant anesthetic. If electrocardiography is unavailable, frequent
evaluation of the peripheral pulse quality and rhythm may be the best substitute. I would not attempt to treat the arrhythmia
without a diagnosis, but it would be negligent to anesthetize a patient with ventricular tachycardia without making initial
attempts to treat it. If an electrocardiograph is available, I would delay anesthesia for a diagnosis.
If ventricular tachycardia was identified in this or any patient, treatment should be guided by the ECG findings as well as
the patient's pulse rate and quality, mentation, respiratory rate, mucous membrane color, capillary refill time, and, perhaps,
blood pressure to determine the clinical effect of the dysrhythmia. Because anesthetic agents can compromise cardiovascular
performance, ventricular tachycardia may have a greater effect in anesthetized patients. Lidocaine (1 to 2 mg/kg intravenously)
can be administered up to a total dose of 8 mg/kg in a 10-minute period in an awake patient. Eliminating all ventricular ectopy
is desired but not essential. The effect on ventricular tachycardia can be evaluated within two minutes of lidocaine administration,
but the duration of action is short-lived, and readministration is likely to be necessary. Anesthetized patients should receive
no more than about 0.5 mg/kg of lidocaine intravenously at one time because in my experience lidocaine has caused asystole
in susceptible anesthetized patients.