Recovery of horses from general anaesthesia: A systematic review (2000-2020) of risk factors and influence of interventions during the recovery period

The influence of hypoxaemia, hypotension and hypercapnia (among other factors) on quality of recovery from general anaesthesia in horses

OBJECTIVE

To investigate the effect of hypoxaemia, hypotension and hypercapnia, among others, on quality of recovery from general anaesthesia in horses.

STUDY DESIGN

Retrospective, single-centre study.

ANIMALS

A sample of 1226 horses that underwent general anaesthesia between June 2017 and June 2021.

METHODS

Horses and ponies weighing > 200 kg, aged > 6 months, anaesthetized using a xylazine- or medetomidine-isoflurane balanced anaesthesia protocol and presenting a complete anaesthetic record were included. Data were extracted from the clinic record system and from the original anaesthesia records. Recoveries were divided into 'good' and 'bad' based on the available recovery scores. Influence of hypoxaemia [PaO2 < 60 mmHg (7.99 kPa)], hypotension (mean arterial pressure < 70 mmHg for at least 15 minutes) and hypercapnia [PaCO2 > 60 mmHg (7.99 kPa)], anaesthesia protocol, body weight, age, breed, sex, American Society of Anesthesiologists status, type of procedure, emergency or nonemergency, duration of anaesthesia, positioning, times spent in lateral and sternal recumbency during recovery, time until standing and nonassisted or assisted recovery on the assigned recovery score (good/bad) were investigated using generalized linear regression analysis (p < 0.05).

RESULTS

Hypoxaemia and prolonged duration of anaesthesia were significantly associated with a bad recovery score. No other factors had a significant influence on recovery quality.

CONCLUSION AND CLINICAL RELEVANCE

Hypoxaemia and prolonged anaesthesia duration have a negative effect on quality of anaesthetic recovery in horses. Clinically, this highlights the importance of keeping anaesthetic time as short as possible and to monitor oxygenation and treat hypoxaemia as soon as possible.

Open Approach to the Transversus Abdominis Plane in Horses: A Cadaver Feasibility Study

The study's objective was to evaluate the feasibility and dispersion of an open approach to the transversus abdominis plane (TAP) block in eight adult equine cadavers. A ventral midline incision was made, starting 2 cm cranial to the umbilicus and extending 25 cm cranially. In total, 0.5 mL/kg of new methylene blue (NMB) was injected per horse, divided into six injections. Using an 18 g, 8 cm Tuohy needle, three injections were made per side. The needle was guided blindly into the TAP using palpation. A 60 mL syringe was attached directly to the needle, depositing ~0.08 mL/kg at each site. The time to complete the injections was recorded for each cadaver. Following injection, the ventral body wall was dissected to determine if the dye was present within the TAP space as well as to measure the extent of the dispersion of the dye, the cranial to caudal extent, and the width of the dye's spread. Complete deposition of NMB into the TAP (six of six sites) was achieved in 5/8 horses. The median time needed to perform all the injections was 263 s. Increased adiposity (retroperitoneal fat) was associated with unsuccessful injections. This approach to the TAP was easily and quickly performed, though less successful in horses with increased retroperitoneal fat and increased BCS.

Xylazine Infusion during Equine Colic Anesthesia with Isoflurane and Lidocaine: A Retrospective Study

This retrospective study investigated the effect of a xylazine infusion on heart rate; mean arterial pressure; blood gases; anesthetic and dobutamine requirements; recovery quality and duration; percentage of death/survival; and days to die/discharge in horses after colic surgery under partial intravenous anesthesia with isoflurane and lidocaine infusion. Anesthetic records of equine colic surgery were reviewed from similar periods in 2020-2021 and 2021-2022. In both groups, after sedation with xylazine 0.7 mg/kg intravenously (IV) and induction with ketamine 2.2 mg/kg and midazolam 0.06 mg/kg IV, anesthesia was maintained with isoflurane and lidocaine (bolus 1.5 mg/kg IV, infusion 2 mg/kg/h). Group L (2020-2021, n = 45) received xylazine 0.2 mg/kg IV before recovery, group XL (2021-2022, n = 44) received xylazine 0.5 mg/kg/h IV intraoperatively. In group XL, minimal (p = 0.04) and average (p = 0.04) heart rate, intraoperative hematocrit (p = 0.001), minimal (p = 0.002) and maximal (p = 0.04) dobutamine administration rate, animals requiring ketamine top-ups (p = 0.04), and the number of days to discharge (p = 0.02), were significantly lower compared to group L. During recovery in group XL, the time to sternal recumbency (p = 0.03) and time to first attempt (p = 0.04) were significantly longer. This retrospective study suggests that a xylazine infusion may have beneficial effects on horses undergoing colic surgery. Further prospective studies are necessary.