Abstract

Propofol (2,6-diisopropylphenol) (Diprivan, Zeneca Pharmaceuticals, Delaware, USA) is a short acting anesthetic used extensively in humans and domestic animals both as a sole anesthetic and as an adjunct to more complex anesthetic techniques. It is used intravenously, has no cumulative effect and allows a rapid recovery after administration in bolus doses or by continuous infusion. Intravenous injection of phocids is relatively easy due to the size and accessibility of the extradural vein in the posterior lumbar area. The use of propofol was thus evaluated in 12 harbor seal (Phoca vitulina) and three northern elephant seal (Mirounga angustirostris) pups, and two harbor seal adults, as its intravenous administration and short duration of action might overcome problems of unpredictable responses and prolonged apnea observed with some intramuscularly administered anesthetics in phocids.

Propofol was administered as an intravenous bolus into the extradural vein at 2-5 mg/kg. Ten minutes prior to injection, each animal received atropine at 0.01 mg/kg intramuscularly. Time to effect was 0.5-1 minute. Time to recovery was recorded as the time to coordinated skeletal muscle movement, and ability to crawl. It varied between 7 and 15 minutes. A 2 mg/kg bolus caused slight decrease in activity, but no other changes in one harbor seal pup. A 3 mg/kg bolus in four harbor seal pups and two elephant seal pups caused a decrease in activity, mild sedation, skeletal muscle relaxation but no loss of palpebral or swallowing reflexes. A bolus of 4.8-5.0 mg/kg in seven harbor seal pups resulted in loss of withdrawal, palpebral and swallowing reflexes. These animals were intubated, and recovered smoothly in 7-15 minutes. Two of these animals showed complete apnea following injection, spontaneous breathing returning as the effect of the bolus wore off. Arterial P02 measured by peripheral pulse oximetry in these cases was 65% and 80% prior to manual ventilation with oxygen. Heart rate in all animals remained above 100 min7l. In all cases, heart rate was 120-140 min7l as the bolus was administered. In the two adult harbor seals, 3 mg/kg resulted in good muscle relaxation and loss of ocular and swallowing reflexes within I minute of injection. These two animals were then anesthetized for two hours on isoflurane, then recovered uneventfully.

Advantages of use of propofol in phocids in this limited trial was short duration of action but good relaxation and quick, quiet recovery at 5 mg/kg, allowing performance of brief clinical procedures. Disadvantages are the need for restraint for intravenous injection, and the large volume required for animals over 40 kg. It was not possible to determine from this trial whether apnea is more likely following use of propofol than with other anesthetic agents in phocids.