Glenn R. Pettifer

The cardiopulmonary effects of romifidine in dogs with and without prior or concurrent administration of glycopyrrolate

OBJECTIVE To determine the electrocardiographic and cardiopulmonary effects of romifidine with and without prior or concurrent administration of glycopyrrolate. STUDY DESIGN Randomized crossover experimental study. ANIMALS Six (three male, three female) cross-bred dogs weighing 23 ± 2.4 kg. METHODS Baseline cardiopulmonary measurements were obtained in conscious dogs and one of five treatments was administered. Glycopyrrolate (G) 0.01 mg kg-1, or saline (S) 0.5 mL, were administered IM as premedication (Gp or Sp), or G was administered concurrently (Gc) with romifidine (RO). Treatments were as follows T1, Sp + RO 40 μg kg-1; T2, Gp + RO (40 μg kg-1); T3, Sp + RO 120 μg kg-1; T4, Gp + RO (120 μg kg-1); T5, Sp + Gc + RO (120 μg kg-1). Romifidine or RO + Gc was administered subcutaneously 20 minutes after premedication (time 0), and further measurements were taken 10, 20, 30, 60 and 90 minutes after RO. The main treatment effect was evaluated using two-way anova for repeated measures, followed by one-way anova and a post-hoc least squares difference test with a modified Bonferroni correction (p < 0.02). A Students t-test was used to compare the effect of romifidine at 20 and 60 minutes versus baseline values (p < 0.05). RESULTS Both low- and high-dose RO (T1, T3) significantly decreased heart rate (HR), respiratory rate (RR), cardiac index (CI) and stroke volume index, and increased arterial blood pressure (SAP), systemic vascular resistance (SVR), pulmonary arterial occlusion pressure (PAOP) and central venous pressure. High-dose RO produced greater increases in SVR and SAP measurements. Neither dose of RO produced an alteration in blood gas values or the alveolar to arterial oxygen gradient. Glycopyrrolate significantly increased HR and CI from 10 to 90 minutes between T1/T2 and T3/T4. Increases in SAP were dose related with significant differences between T1/T3 and T2/T4 at 90 and 10 minutes, respectively, and were highest in animals receiving Gp or Gc. High-dose RO groups (T3, T4) had higher values for SVR than low-dose RO groups (T1, T2), unrelated to G administration. There was an increase in PAOP in all treatments. The oxygen extraction ratio was increased with all treatments: larger increases were observed in T1, T3 and T4 compared with only minimal changes in T2. Concurrent G administration was associated with an increased frequency of high-grade second-degree atrioventricular heart block with variable conduction at 10 and 20 minutes. CONCLUSIONS Romifidine produced effects consistent with other selective α2-adrenoreceptor agonists. Glycopyrrolate offset the decrease in HR and partially offset the decrease in CI associated with RO administration. Glycopyrrolate premedication produced an initial tachycardia and added to the increase in SAP associated with RO. Concurrent G administration was associated with a higher frequency of dysrhythmias and is not recommended. Despite the decrease in RR, RO sedation did not alter blood gas values. CLINICAL RELEVANCE It appears likely that G administration prior to or concurrent with RO produces an increase in myocardial workload and oxygen demand suggesting that this combination should not be used in dogs with cardiomyopathy or heart failure. The improvement in oxygen extraction ratio with T2 suggests that G may be beneficial with lower doses of RO, nevertheless, the use of G and RO in cardiovascularly compromised patients is not advised.

The Comparative Cardiopulmonary Effects of Spontaneous and Controlled Ventilation by Using the Hallowell EMC Anesthesia WorkStation in Hispaniolan Amazon Parrots (Amazona ventralis)

Abstract This investigation assessed the cardiopulmonary performance, core body temperatures, and arterial blood gases of Hispaniolan Amazon parrots (Amazona ventralis) during 60 minutes of isoflurane anesthesia, using the Hallowell EMC Anesthesia WorkStation (AWS) in combination with controlled intermittent positive pressure ventilation (C-IPPV) or a nonrebreathing system (Bain circuit) with spontaneous ventilation (SV) (n = 6 birds/group). Direct arterial blood pressures, arterial blood gases, end-tidal carbon dioxide (ETco2), end-tidal isoflurane concentration, heart rates, respiratory rates, and esophageal temperatures were monitored during a 60-minute period of isoflurane anesthesia. Compared with baseline measurements and SV, C-IPPV significantly decreased Paco2 and increased pHa but did not significantly reduce mean arterial blood pressure. No significant difference in esophageal temperature was observed between the birds receiving C-IPPV and those breathing spontaneously on the Bain circuit. The PaCO2-ETco2 gradient was significantly greater in birds receiving SV compared with birds receiving C-IPPV. According to the measured parameters, there were neither deleterious effects nor any apparent advantages associated with positive pressure ventilation. The Hallowell EMC AWS appears to be safe and effective when anesthetizing small birds and will be particularly useful during anesthetic periods when positive pressure ventilation is indicated.