Rocuronium-neuromuscular blockade does not influence the patient state index in anesthetized dogs.

OBJECTIVE: To evaluate the effects of rocuronium and sugammadex on the patient state index (PSI) in dogs anesthetized with propofol. ANIMALS: 6 intact healthy male Beagles. PROCEDURES: Anesthesia was induced with and maintained on a propofol infusion. The estimated plasma propofol concentration (ePC) was recorded. Baseline PSI and train-of-four ratio (TOFR) readings were collected for 2 minutes in stable general anesthesia. Neuromuscular blockade (NMB) was induced with 0.6 mg/kg, IV, rocuronium, and full NMB was confirmed with a TOFR of 0. After 5 minutes, the neuromuscular function was restored with 4 mg/kg sugammadex, IV (reversal), and monitored for 5 minutes. Throughout the data collection, ePC, PSI, and TOFR were recorded every 15 seconds and compared with mixed-effect ANOVA. RESULTS: Baseline ePC, PSI, and TOFR were 3.63 ± 0.38, 41 ± 6, and 0.97 ± 0.08 µg/mL, respectively. There was no difference between the baseline of ePC and PSI from NMB or reversal. Compared to the baseline, the TOFR decreased to 0 with NMB (P < .001) and returned to 0.96 ± 0.08 (P = .721) on reversal. After 5 minutes, sugammadex fully reversed 5 out of 6 dogs to TOFR > 0.90 and partially reversed 1 animal to TOFR = 0.80. CLINICAL RELEVANCE: There was no evidence that NMB with rocuronium and sugammadex-induced reversal interfered with PSI readings under steady-state total intravenous anesthesia with propofol. Further evaluation of PSI is warranted to assess its utility in a clinical population to detect changes in levels of consciousness during NMB.

Pharmacokinetics and pharmacodynamics of meperidine after intramuscular and subcutaneous administration in horses.

OBJECTIVE: To describe the pharmacokinetics and pharmacodynamics of meperidine after IM and subcutaneous administration in horses. STUDY DESIGN: prospective, randomized, blinded, crossover trial. ANIMALS: Six adult horses weighing 494 ± 33 kg. METHODS: Treatments included meperidine 1 mg/kg IM with saline 6 mL subcutaneously, meperidine 1 mg/kg subcutaneously with saline 6 mL IM, and saline 6 mL subcutaneously and 6 mL IM, with a 7-day washout between treatments. Plasma meperidine concentrations and pharmacodynamic values (thermal and mechanical thresholds, physiological variables, fecal production) were collected at various time points for 24 hours. Accelerometry data were obtained for 8 hours to measure locomotor activity. Data were analyzed with a mixed effects model, and α was set at .05. RESULTS: Meperidine terminal half-life (T1/2 ), maximal plasma concentrations, and time to maximal concentration were 186 ± 59 and 164 ± 56 minutes, 265.7 ± 47.2 and 243.1 ± 80.1 ng/mL at 17 ± 6, and 24 ± 13 minutes for IM at subcutaneous administration, respectively. No effect of treatment or time was observed on thermal or mechanical thresholds, heart rate, respiratory rate, locomotor activity, frequency of defecations, or fecal weight (P > .2 for all). CONCLUSION: Maximum meperidine concentrations were achieved quickly with a short T1/2 in both treatment groups. Neither IM nor subcutaneous meperidine influenced thermal or mechanical threshold or physiological variables. CLINICAL SIGNIFICANCE: The short half-life and lack of detectable antinociceptive effect do not support IM or subcutaneous administration meperidine at 1 mg/kg for analgesia in horses.