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Keywords:

  • canine;
  • pain management;
  • respiratory depression;
  • hypoventilation;
  • surgery

Abstract

Objective: To perform blood gas analysis of the respiratory response to transdermal fentanyl in dogs which have experienced an open-chest surgical procedure.

Design: Prospective trial.

Setting: Veterinary Teaching Hospital Surgical Research and Student Laboratory.

Intervention: Dogs were purchased for a surgical laboratory. Students performed a cranial abdominal exploratory and diaphragmatic hernia repair. Sixteen dogs were divided into 2 groups. Dogs received transdermal fentanyl (group F), using an average dose of 4.8 µg/kg/hr, applied to the caudal-lateral abdomen 22 hours before surgery, or intravenous buprenorphine (group B; 0.02 mg/kg) given 1 hour prior to anesthetic induction and every 6 hours postoperatively. All dogs received intravenous acepromazine (0.05 mg/kg) preoperatively and every 6 hours postoperatively. Dogs were instrumented with carotid artery catheters.

Measurements and main results: Arterial blood gas values were analyzed every 2 hours postoperatively. Plasma fentanyl levels were analyzed every 4 hours postoperatively. The mean carbon dioxide tension (PCO2) did not exceed 45 mmHg in either group. The range in mean PCO2 levels was 32.9 (± 3.4)−38.1 (± 3.9) in group B and 34.7 (± 3.25)−43.6 (± 5.5) in group F. At 2 time points, the mean PCO2 was significantly lower in group B compared with normal levels in group F. Hypoxemia occurred in both the groups. The range in mean oxygen tension (PO2) was 76.5 (± 18.3)−91.1 (± 16.3) in group B and 76.0 (± 10.8)−96.6 (± 7.6) in group F. There was no significant difference in PO2 between groups. Levels of fentanyl considered to be analgesic were maintained for the postoperative period.

Conclusions: The use of a relatively high dose of transdermal fentanyl did not induce postoperative hypoventilation as evidenced by serial arterial blood gas analysis in this model.