The effects of nitrous oxide on recovery from isoflurane anaesthesia in dogs

Scoping review of quality of anesthetic induction and recovery scales used for dogs

OBJECTIVE

To compare, describe and assess the level of validation of all instruments measuring quality of induction and recovery from anesthesia in dogs.

DATABASES USED

A search was performed using the electronic database PubMed to find articles containing an induction quality scale, a recovery quality scale or both in dogs. Articles not directly accessible through PubMed were obtained through the Auburn University Library website and Google Scholar. The phrases 'induction scoring systems dogs', 'recovery scoring systems dogs', 'anesthetic induction score dogs', and 'anesthetic recovery score dogs' were used for searches using the 'best match search' function. The time frame searched was from 1980 to May 2020. The search was conducted from March 2020 to May 2020.

CONCLUSIONS

A thoroughly tested and validated scale for measuring the quality of induction and recovery does not exist in the current veterinary literature. A large disagreement exists between studies on the use of induction and recovery scales, and many have reported inconsistent results with current instruments. It is recommended that an induction and recovery scale intended for wide-scale use be constructed and tested extensively for psychometric validation and reliability.

Recovery characteristics of dogs following anesthesia induced with tiletamine-zolazepam, alfaxalone, ketamine-diazepam, or propofol and maintained with isoflurane

OBJECTIVE To compare characteristics of recovery from isoflurane anesthesia in healthy nonpremedicated dogs after anesthetic induction by IV administration of tiletamine-zolazepam with those observed after induction by IV administration of alfaxalone, ketamine-diazepam, or propofol. DESIGN Prospective, randomized crossover study. ANIMALS 6 healthy adult hounds. PROCEDURES Each dog underwent the 4 treatments in random order with a ≥ 7-day washout period between anesthetic episodes. Anesthesia was induced by IV administration of the assigned induction drug or combination (each to effect in 25% increments of calculated dose) and maintained with isoflurane in oxygen for 60 minutes. Cardiorespiratory variables and end-tidal isoflurane concentration (ET_ISO) were measured just before isoflurane administration was discontinued. Dogs were observed and video recorded during recovery. Recovery characteristics were retrospectively scored from recordings by 3 raters. Interrater and intrarater reliability of scoring was assessed by intraclass correlation coefficient calculation. Linear and mixed ANOVAs were used to compare extubation times, recovery scores, and body temperature among treatments. RESULTS Most cardiorespiratory variables, body temperature, ET_ISO, and time to extubation did not differ between tiletamine-zolazepam and other induction treatments. Recovery scores were lower (indicating better recovery characteristics) with propofol or alfaxalone than with tiletamine-zolazepam but did not differ between tiletamine-zolazepam and ketamine-diazepam treatments. Anesthetic episode number and ET_ISO had no effect on extubation time or recovery score. Intrarater and interrater correlations for recovery scores were excellent. CONCLUSIONS AND CLINICAL RELEVANCE Recovery of healthy dogs from anesthesia with isoflurane after induction with tiletamine-zolazepam was uncomplicated and had characteristics comparable to those observed following induction with ketamine-diazepam. However, recovery characteristics were improved when anesthesia was induced with propofol or alfaxalone.

Effect of dexmedetomidine on the minimum infusion rate of propofol preventing movement in dogs

OBJECTIVE

To determine the effect of dexmedetomidine on induction dose and minimum infusion rate of propofol preventing movement (MIR_NM).

STUDY DESIGN

Randomized crossover, unmasked, experimental design.

ANIMALS

Three male and three female healthy Beagle dogs weighing 10.2 ± 2.8 kg.

METHODS

Dogs were studied on three occasions at weekly intervals. Premedications were 0.9% saline (treatment P) or dexmedetomidine (1 μg kg^-1, treatment PLD; 2 μg kg^-1, treatment PHD) intravenously. Anesthesia was induced with propofol (2 mg kg^-1 and then 1 mg kg^-1 every 15 seconds) until intubation. Anesthesia was maintained for 90 minutes in P with propofol (0.5 mg kg^-1 minute^-1) and saline, in PLD with propofol (0.35 mg kg^-1 minute^-1) and dexmedetomidine (1 μg kg^-1 hour^-1), and in PHD with propofol (0.3 mg kg^-1 minute^-1) and dexmedetomidine (2 μg kg^-1 hour^-1). The stimulus (50 V, 50 Hz, 10 ms) was applied to the antebrachium, and propofol infusion was increased or decreased by 0.025 mg kg^-1 minute^-1 based on a positive or negative response, respectively. Data were analyzed using a mixed-model anova and presented as mean ± standard error.

RESULTS

Propofol induction doses were 8.68 ± 0.57 (P), 6.13 ± 0.67 (PLD) and 4.78 ± 0.39 (PHD) mg kg^-1 and differed among treatments (p < 0.05). Propofol MIR_NM values were 0.68 ± 0.13, 0.49 ± 0.16 and 0.26 ± 0.05 mg kg^-1 minute^-1 for P, PLD and PHD, respectively. Propofol MIR_NM decreased 59% in PHD (p < 0.05). Plasma propofol concentrations were 14.04 ± 2.30 (P), 11.30 ± 4.30 (PLD) and 7.96 ± 0.72 (PHD) μg mL^-1 and dexmedetomidine concentrations were 0.68 ± 0.12 (PLD) and 0.89 ± 0.08 (PHD) ng mL^-1 at MIR_NM determination.

CONCLUSIONS AND CLINICAL RELEVANCE

Dexmedetomidine (1 and 2 μg kg^-1) decreased propofol induction dose. Dexmedetomidine (2 μg kg^-1 hour^-1) resulted in a significant decrease in propofol MIR_NM.

Effect of fentanyl on the induction dose and minimum infusion rate of propofol preventing movement in dogs

OBJECTIVE

To determine the effect of fentanyl on the induction dose of propofol and minimum infusion rate required to prevent movement in response to noxious stimulation (MIR_NM) in dogs.

STUDY DESIGN

Crossover experimental design.

ANIMALS

Six healthy, adult intact male Beagle dogs, mean±standard deviation 12.6±0.4 kg.

METHODS

Dogs were administered 0.9% saline (treatment P), fentanyl (5 μg kg^-1) (treatment PLDF) or fentanyl (10 μg kg^-1) (treatment PHDF) intravenously over 5 minutes. Five minutes later, anesthesia was induced with propofol (2 mg kg^-1, followed by 1 mg kg^-1 every 15 seconds to achieve intubation) and maintained for 90 minutes by constant rate infusions (CRIs) of propofol alone or with fentanyl: P, propofol (0.5 mg kg^-1 minute^-1); PLDF, propofol (0.35 mg kg^-1 minute^-1) and fentanyl (0.1 μg kg^-1 minute^-1); PHDF, propofol (0.3 mg kg^-1 minute^-1) and fentanyl (0.2 μg kg^-1 minute^-1). Propofol CRI was increased or decreased based on the response to stimulation (50 V, 50 Hz, 10 mA), with 20 minutes between adjustments. Data were analyzed using a mixed-model anova and presented as mean±standard error.

RESULTS

ropofol induction doses were 6.16±0.31, 3.67±0.21 and 3.33±0.42 mg kg^-1 for P, PLDF and PHDF, respectively. Doses for PLDF and PHDF were significantly decreased from P (p<0.05) but not different between treatments. Propofol MIR_NM was 0.60±0.04, 0.29±0.02 and 0.22±0.02 mg kg^-1 minute^-1 for P, PLDF and PHDF, respectively. MIR_NM in PLDF and PHDF was significantly decreased from P. MIR_NM in PLDF and PHDF were not different, but their respective percent decreases of 51±3 and 63±2% differed (p=0.035).

CONCLUSIONS AND CLINICAL RELEVANCE

Fentanyl, at the doses studied, caused statistically significant and clinically important decreases in the propofol induction dose and MIR_NM.