EFFECTS OF TRAMADOL ON THE MINIMUM ANESTHETIC CONCENTRATION OF ISOFLURANE IN WHITE-EYED PARAKEETS ( PSITTACARA LEUCOPHTHALMUS )

Effects of two continuous infusion doses of lidocaine on isoflurane minimum anesthetic concentration in chickens

OBJECTIVE

To assess the effect of two intravenous (IV) doses of lidocaine on the minimum anesthetic concentration (MAC) of isoflurane in chickens.

STUDY DESIGN

Blinded, prospective, randomized, experimental crossover study.

ANIMALS

A total of six adult female chickens weighing 1.90 ± 0.15 kg.

METHODS

Chickens were anesthetized with isoflurane and mechanically ventilated. Isoflurane MAC values were determined (T0) in duplicate using an electrical noxious stimulus and the bracketing method. After MAC determination, a low dose (LD; 3 mg kg^-1 followed by 3 mg kg^-1 hour^-1) or high dose (HD; 6 mg kg^-1 followed by 6 mg kg^-1 hour^-1) of lidocaine was administered IV. MAC determination was repeated at 1.5 (T1.5) and 3 (T3) hours of lidocaine administration and blood was collected for analysis of plasma lidocaine and monoethylglycinexylidide (MEGX) concentrations. Pulse rate, peripheral hemoglobin oxygen saturation, noninvasive systolic arterial pressure and cloacal temperature were recorded at T0, T1.5 and T3. Treatments were separated by 1 week. Data were analyzed using mixed-effects model for repeated measures.

RESULTS

MAC of isoflurane (mean ± standard deviation) at T0 was 1.47 ± 0.18%. MAC at T1.5 and T3 was 1.32 ± 0.27% and 1.26 ± 0.09% (treatment LD); and 1.28 ± 0.06% and 1.30 ± 0.06% (treatment HD). There were no significant differences between treatments or times. Maximum plasma lidocaine concentrations at T3 were 496 ± 98 and 1200 ± 286 ng mL^-1 for treatments LD and HD, respectively, and were not significantly different from T1.5. With treatment HD, plasma concentration of MEGX was significantly higher at T3 than at T1.5. Physiological variables were not significantly different among times with either treatment.

CONCLUSIONS AND CLINICAL RELEVANCE

Administration of lidocaine did not significantly change isoflurane MAC in chickens. Within treatments, plasma lidocaine concentrations were not significantly different at 1.5 and 3 hours.

Backyard Poultry and Waterfowl Sedation and Anesthesia

The popularity of backyard poultry (chickens, turkey, guinea fowl) and waterfowl (ducks and geese) is increasing in the United States, and these animals frequently present for veterinary care. Like other birds, these species have unique anatomy that should be clinically considered before anesthesia. A balanced approach to an injectable, inhalational, or combination anesthesia protocol must be taken to ensure a safe outcome for the patient and to achieve the procedural needs. A well-informed clinician may use both sedation and general anesthesia to care for backyard bird patients in practice.

Pharmacokinetics and pharmacodynamics of methadone administered intravenously and intramuscularly to isoflurane-anesthetized chickens

OBJECTIVE

To determine the pharmacokinetics and pharmacodynamics of methadone after IV or IM administration to isoflurane-anesthetized chickens.

ANIMALS

6 healthy adult Hy-Line hens.

PROCEDURES

In a randomized crossover-design study, methadone (6 mg/kg) was administered IV and IM to isoflurane-anesthetized chickens with a 1-week washout period between experiments. Blood samples were collected immediately before and at predetermined time points up to 480 minutes after methadone administration. Plasma concentrations were determined by liquid chromatography-mass spectrometry, and appropriate compartmental models were fit to the plasma concentration-versus-time data. Cardiorespiratory variables were compared between treatments and over time with mixed-effect repeated-measures analysis.

RESULTS

A 3-compartment model best described the changes in plasma methadone concentration after IV or IM administration. Estimated typical values for volumes of distribution were 692 mL/kg for the central compartment and 2,439 and 2,293 mL/kg for the first and second peripheral compartments, respectively, with metabolic clearance of 23.3 mL/kg/min and first and second distributional clearances of 556.4 and 51.8 mL/kg/min, respectively. Typical bioavailability after IM administration was 79%. Elimination half-life was 177 minutes, and maximum plasma concentration after IM administration was 950 ng/mL. Heart rate was mildly decreased at most time points beginning 5 minutes after IV or IM drug administration.

CONCLUSIONS AND CLINICAL RELEVANCE

Disposition of methadone in isoflurane-anesthetized chickens was characterized by a large volume of distribution and moderate clearance, with high bioavailability after IM administration. Additional studies are warranted to assess pharmacokinetics and pharmacodynamics of methadone in awake chickens.

Minimum anesthetic concentration of isoflurane and sparing effect of midazolam in Quaker parrots (Myiopsitta monachus)

OBJECTIVE

To determine the effects of midazolam on the minimum anesthetic concentration (MAC) reduction of end-tidal isoflurane concentration (Fe'Iso) measured using an electrical stimulus in Quaker parrots (Myiopsitta monachus).

STUDY DESIGN

Randomized crossover experimental study.

ANIMALS

A group of six adult Quaker parrots, weighing 98-124 g.

METHODS

Birds were anesthetized with isoflurane in oxygen delivered by mask, then tracheally intubated and mechanically ventilated. Three treatments were applied with a 4 day interval between anesthetic events. Each anesthetized bird was administered midazolam (1 mg kg^-1; treatment MID1), midazolam (2 mg kg^-1; treatment MID2) or electrolyte solution (control) intramuscularly. The treatments were administered using a replicated Latin square design and the observers were blinded. Based on a pilot bird, the starting Fe'Iso was 1.8%. After equilibration for 10 minutes, a supramaximal stimulus was delivered using an electrical current (20 V and 50 Hz for 10 ms) and birds were observed for non-reflex movement. The Fe'Iso was titrated by 0.1% until a crossover event was observed. The MAC was estimated using logistic regression.

RESULTS

The MAC of isoflurane (MAC_ISO) was estimated at 2.52% [95% confidence interval (CI), 2.19-2.85] with a range of 1.85-2.65%. MAC_ISO in MID1 was 2.04% (95% CI, 1.71-2.37) and in MID2 was 1.81% (95% CI, 1.48-2.14); reductions in MAC_ISO from control of 19% (p = 0.001) and 28% (p < 0.001), respectively. Heart rate, temperature, sex and anesthetic time were not different among treatments.

CONCLUSIONS

Midazolam (1-2 mg kg^-1) intramuscularly resulted in a significant isoflurane-sparing effect in response to a noxious stimulus in Quaker parrots without observable adverse effects.

CLINICAL RELEVANCE

Midazolam can be used as part of a balanced anesthetic approach using isoflurane in Quaker parrots, and potentially in other psittacine species.

An update on the cecectomy technique in roosters anesthetized with isoflurane used in subsequent amino acid digestibility experiments

This work aims to study an alternative technique of cecectomy in roosters using inhalation anesthesia for subsequent use in digestibility experiments. A total of 30 adult chickens of Leghorn breed were used with an average age of 27 wk. The birds were preoxygenated, and the anesthetic induction was performed using isoflurane diluted in oxygen. After proper muscle relaxation, endotracheal intubation was performed using a Murphy catheter and kept in anesthesia under mechanical ventilation with a constant monitoring of electrocardiography variables, heart rate, oxyhemoglobin saturation, and body temperature during the surgical procedure. An incision of approximately 3 cm was made between keel and cloaca in order to expose and extirpate the cecum followed by a simple ligature. The opening of the peritoneal cavity was closed in 2 ways: Sultan suture technique was used for closing the abdominal wall and modified Cushing intradermic continuous points for closing the skin. The time for anesthesia induction and preoperational period noted to be 10 ± 2 min. Surgical procedures completed in 7 ± 1.5 min. No intraoperatively and postoperatively harm observed in animals. Water was immediately provided after the birds returned to cages and feed offered after 24 h of surgery. In remaining birds, no abnormalities were observed during and after the experimental period (3 mo). The present study describes a promising update on cecectomy technique regarding anesthesia induction and surgical procedures in roosters using potential drugs and safer surgical materials without any trans- and postoperative complications.