Propofol-sparing and hemodynamic effects of guaifenesin in sheep.

OBJECTIVE: To evaluate the propofol-sparing and hemodynamic effects of guaifenesin administered for co-induction of anesthesia in sheep. STUDY DESIGN: Prospective, blinded, two-way crossover experimental study. ANIMALS: Thirteen healthy adult female sheep. METHODS: Anesthesia was induced without premedication with intravenous (IV) guaifenesin 5% at 100 mg kg-1 (GGE) or an equivalent volume of physiologic saline (SAL), followed by IV propofol at a controlled rate (1 mg kg-1 min-1). Heart rate (HR), respiratory rate and oscillometric noninvasive arterial blood pressure (NIBP) were recorded at baseline after co-induction administration, following endotracheal intubation and every 2 minutes thereafter for 10 minutes. Propofol doses required to achieve intubation after each co-induction treatment were compared by independent Student's t-test. Values of p < 0.05 were considered statistically significant. RESULTS: The propofol dose required (mean ± standard deviation) to achieve intubation was significantly lower (p = 0.001) in the GGE treatment (3.40 ± 0.74 mg kg-1) than in the SAL treatment (5.94 ± 1.09 mg kg-1). HR was increased after anesthetic induction compared with baseline in both treatments. HR was generally lower in the GGE treatment than in the SAL treatment. NIBP did not vary between GGE and SAL treatments. CONCLUSIONS AND CLINICAL RELEVANCE: Guaifenesin, when administered as a co-induction agent with propofol in sheep, reduces propofol dose requirements and maintains hemodynamic variables within a clinically acceptable range.

Heart rate, arterial pressure and propofol-sparing effects of guaifenesin in dogs.

OBJECTIVE: To evaluate the heart rate (HR) and systemic arterial pressure (sAP) effects, and propofol induction dose requirements in healthy dogs administered propofol with or without guaifenesin for the induction of anesthesia. STUDY DESIGN: Prospective blinded crossover experimental study. ANIMALS: A total of 10 healthy adult female Beagle dogs. METHODS: Dogs were premedicated with intravenous (IV) butorphanol (0.4 mg kg-1) and administered guaifenesin 5% at 50 mg kg-1 (treatment G50), 100 mg kg-1 (treatment G100) or saline (treatment saline) IV prior to anesthetic induction with propofol. HR, invasive sAP and respiratory rate (fR) were recorded after butorphanol administration, after guaifenesin administration and after propofol and endotracheal intubation. Propofol doses for intubation were recorded. Repeated measures analysis of variance (anova) was used to determine differences in propofol dose requirements among treatments, and differences in cardiopulmonary values over time and among treatments with p < 0.05 considered statistically significant. RESULTS: Propofol doses (mean ± standard deviation) for treatments saline, G50 and G100 were 3.3 ± 1.0, 2.7 ± 0.7 and 2.1 ± 0.8 mg kg-1, respectively. Propofol administered was significantly lower in treatment G100 than in treatment saline (p = 0.04). In treatments G50 and G100, HR increased following induction of anesthesia and intubation compared with baseline measurements. HR was higher in treatment G100 than in treatments G50 and saline following induction of anesthesia. In all treatments, sAP decreased following intubation compared with baseline values. There were no significant differences in sAP among treatments. fR was lower following intubation than baseline and post co-induction values and did not differ significantly among treatments. CONCLUSIONS AND CLINICAL RELEVANCE: When administered as a co-induction agent in dogs, guaifenesin reduced propofol requirements for tracheal intubation. HR increased and sAP and fR decreased, but mean values remained clinically acceptable.

Pharmacokinetics and pharmacodynamics of hydromorphone hydrochloride in healthy horses.

OBJECTIVES: To determine the physiologic and behavioral effects and pharmacokinetic profile of hydromorphone administered intravenously (IV) to horses. STUDY DESIGN: Prospective, randomized, crossover study. ANIMALS: A group of six adult healthy horses weighing 585.2 ± 58.7 kg. METHODS: Each horse was administered IV hydromorphone (0.025 mg kg-1; treatment H0.025), hydromorphone (0.05 mg kg-1; treatment H0.05) or 0.9% saline in random order with a 7 day washout period. For each treatment, physiologic, hematologic, abdominal borborygmi scores and behavioral data were recorded over 5 hours and fecal output was totaled over 24 hours. Data were analyzed using repeated measures anova with significance at p < 0.05. Blood samples were collected in treatment H0.05 for quantification of plasma hydromorphone and hydromorphone-3-glucuronide and subsequent pharmacokinetic parameter calculation. RESULTS: Hydromorphone administration resulted in a dose-dependent increase in heart rate (HR) and systolic arterial pressure (SAP). HR and SAP were 59 ± 17 beats minute-1 and 230 ± 27 mmHg, respectively, in treatment H0.05 at 5 minutes after administration. No clinically relevant changes in respiratory rate, arterial gases or temperature were observed. The borborygmi scores in both hydromorphone treatments were lower than baseline values for 2 hours. Fecal output did not differ among treatments and no evidence of abdominal discomfort was observed. Recorded behaviors did not differ among treatments. For hydromorphone, mean ± standard deviation for volume of distribution at steady state, total systemic clearance and area under the curve until the last measured concentration were 1.00 ± 0.29 L kg-1, 106 ± 21 mL minute-1 kg-1 and 8.0 ± 1.5 ng hour mL-1, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Hydromorphone administered IV to healthy horses increased HR and SAP, decreased abdominal borborygmi and did not affect fecal output.

The effect of midazolam or lidocaine administration prior to etomidate induction of anesthesia on heart rate, arterial pressure, intraocular pressure and serum cortisol concentration in healthy dogs.

OBJECTIVE: To evaluate selected effects of midazolam or lidocaine administered prior to etomidate for co-induction of anesthesia in healthy dogs. STUDY DESIGN: Prospective crossover experimental study. ANIMALS: A group of 12 healthy adult female Beagle dogs. METHODS: Dogs were premedicated with intravenous (IV) butorphanol (0.3 mg kg-1), and anesthesia was induced with etomidate following midazolam (0.3 mg kg-1), lidocaine (2 mg kg-1) or physiologic saline (1 mL) IV. Heart rate (HR), arterial blood pressure, respiratory rate (fR) and intraocular pressure (IOP) were recorded following butorphanol, after co-induction administration, after etomidate administration and immediately following intubation. Baseline IOP values were also obtained prior to sedation. Etomidate dose requirements and the presence of myoclonus, as well as coughing or gagging during intubation were recorded. Serum cortisol concentrations were measured prior to premedication and 6 hours following etomidate administration. RESULTS: Blood pressure, fR and IOP were similar among treatments. Blood pressure decreased in all treatments following etomidate administration and generally returned to sedated values following intubation. HR increased following intubation with midazolam and lidocaine but remained stable in the saline treatment. The dose of etomidate (median, interquartile range, range) required for intubation was lower following midazolam (2.2, 2.1-2.6, 1.7-4.1 mg kg-1) compared with lidocaine (2.7, 2.4-3.6, 2.2-5.1 mg kg-1, p = 0.012) or saline (3.0, 2.8-3.8, 1.9-5.1 mg kg-1, p = 0.015). Coughing or gagging was less frequent with midazolam compared with saline. Myoclonus was not observed. Changes in serum cortisol concentrations were not different among treatments. CONCLUSIONS AND CLINICAL RELEVANCE: Midazolam administration reduced etomidate dose requirements and improved intubation conditions compared with lidocaine or saline treatments. Neither co-induction agent caused clinically relevant differences in measured cardiopulmonary function, IOP or cortisol concentrations compared with saline in healthy dogs. Apnea was noted in all treatments following the induction of anesthesia and preoxygenation is recommended.

Cardiopulmonary effects and recovery characteristics of horses anesthetized with xylazine-ketamine with midazolam or propofol.

OBJECTIVE: To evaluate cardiopulmonary and recovery characteristics of horses administered total intravenous anesthesia (TIVA) with xylazine and ketamine combined with midazolam or propofol. STUDY DESIGN: Randomized crossover study. ANIMALS: A group of eight adult horses, aged 7-22 years, weighing 493-740 kg. METHODS: Horses were administered xylazine (1 mg kg-1) intravenously (IV), and anesthesia was induced with ketamine (2.2 mg kg-1) IV. Anesthesia was maintained for 45 minutes via IV infusion of xylazine (0.016 mg kg-1 minute-1) and ketamine (0.03 mg kg-1 minute-1) combined with midazolam at 0.002 mg kg-1 minute-1 (MKX), propofol at 0.05 mg kg-1 minute-1 (PKXlow) or propofol at 0.1 mg kg-1 minute-1 (PKXhigh). Additional ketamine was administered if a horse moved spontaneously. Cardiopulmonary variables, blood gases, lactate concentration, packed cell volume and total solids were recorded before sedation (baseline), at 10, 20, 30 and 45 minutes during TIVA and 10 minutes after standing. Recovery variables and quantitative recovery scores were compared. Significance was set at p < 0.05. RESULTS: Additional ketamine was required for 50% of MKX horses. Systolic arterial pressure was elevated in MKX at 20 minutes compared with baseline (p = 0.043), at 10 and 20 minutes compared with PKXhigh (p = 0.007, p = 0.024) and at 20 and 30 minutes compared with PKXlow (p = 0.009, p = 0.02). MKX horses (5/8) were hypertensive compared with PKXlow (1/8; p = 0.017). All horses became hypoxemic (PaO2 ≤80 mmHg; 10.7 kPa) during TIVA. Recovery variables did not differ among treatments. CONCLUSIONS AND CLINICAL RELEVANCE: PKXlow and PKXhigh had similar cardiopulmonary and recovery performance compared with MKX. PKX combinations provided superior quality of anesthesia to that of MKX. A combination of propofol, ketamine and xylazine administered as TIVA can be used in horses to provide anesthesia for short procedures. Supplemental oxygen is recommended.