Cardiopulmonary effects of medetomidine, oxymorphone, or butorphanol in selegiline-treated dogs

Objectives To determine if chronic selegiline HCl administration affects the cardiopulmonary response to medetomidine, oxymorphone, or butorphanol in dogs. Study design Prospective randomized experimental study. Animals Twenty-eight adult, random source, hound dogs weighing 21-33 kg. Methods Dogs were assigned to the following treatment groups: selegiline + medetomidine (MED; n = 6); placebo + MED (n = 6), selegiline + oxymorphone (OXY, n = 6); placebo + OXY (n = 6); selegiline + butorphanol (BUT; n = 7) or placebo + BUT (n = 6). Nine dogs were treated with two of the three premedicants. Dogs were treated with selegiline (1 mg kg(-1) PO, q 24 hours) or placebo for at least 44 days prior to pre-medicant administration. On the day of the experiment, arterial blood for blood gas analysis, blood pressure measurements, ECG, cardiac ultrasound (mM-mode, 2-D, and continuous wave Doppler), and behavioral observations were obtained by blinded observers. An IV injection of MED (750 mug m(-2)), OXY (0.1 mg kg(-1)) or BUT (0.4 mg kg(-1)) was given. Cardiopulmonary and behavioral data were collected at 1, 2,5,15,30, and 60 minutes after injection. Results Selegiline did not modify responses to any of the pre-medicant drugs. Medetomidine caused a significant decrease in heart rate (HR), cardiac output (CO), and fractional shortening (FS). Mean arterial pressure (MAP), systemic vascular resistance (SVR), and central venous pressure (CVP) were increased. Level of consciousness and resistance to restraint were both decreased. Oxymorphone did not affect MAP, CO, CVP, or SVR, but RR and PaCO2 were increased. Level of consciousness and resistance to restraint were decreased. BUT decreased heart rate at 1 and 5 minutes. All other cardiovascular parameters were unchanged. BUT administration was associated with decreased arterial pH and increased PaCO2. BUT decreased level of consciousness and resistance to restraint. Conclusions and clinical relevance Although premedicants themselves altered cardiopulmonary and behavioral function, selegiline did not affect the response to medetomidine, oxymorphone, or butorphanol in this group of normal dogs.