Retrospective computed tomography analysis of endotracheal tube constriction & mispositioning in cats & dogs

Objectives: To discover the prevalence of endotracheal tube (ETT) constriction and rostral and caudal mispositioning in anaesthetised cats and dogs, and to identify associated risk factors. Study Design: Retrospective analysis. Animal population: A total of 146 cats, 670 dogs. Methods: Computed tomography images of the head/neck/thorax from orotracheally intubated cats and dogs were visually assessed for constriction or mispositioning of the ETT. If constriction was present, measurements of the cross-sectional area (CSA) of the ETT lumen at constricted and un-constricted locations were compared. Location and cause of constriction were noted and the expected increase in resistance to gas flow was calculated. Animal information was collected from clinical records. Normality of continuous variables was assessed via the Shapiro-Wilk test. Chi square tests examined associations between variables. Kendall’s tau-b test was performed between measured ETT size and degree of constriction. Results: The ETT extended rostrally beyond incisors in 52% of cases; the connector was within the oral cavity in 19% of cases. The ETT extended beyond the first rib in 25.5% of cases. The prevalence of ETT constriction was 22.7%. Median reduction in CSA was 7.68% (0.14–64.19%). Median increase in resistance assuming laminar and turbulent flow was 16.5% (0.3–680%) and 21% (0.3–1200%), respectively. The most common cause of constriction was the presence of a radiotherapy mouth gag. Significant associations existed between presence of constriction and rostral mispositioning, and caudal mispositioning and extreme brachycephaly. Increased severity of constriction was more likely in smaller ETT. Conclusions: And clinical relevance Constriction and mispositioning of ETT occurred very commonly in this population. Checking the ETT within the oral cavity for constriction and mispositioning is recommended. Radiotherapy mouth gags increase the risk of ETT compression. Smaller ETT are at greater risk of severe constriction. Brachycephalic dogs are at particular risk of caudal mispositioning

Suspected severe post-anaesthetic myopathy or myelopathy in a Clydesdale horse resulting in euthanasia

This case report describes suspected myopathy or myelopathy in a 5-year-old Clydesdale gelding following general anaesthesia for sarcoid removal. The lowest mean arterial pressure was 67 mm Hg. Hyperlactataemia and tachycardia were observed during anaesthesia prompting abortion of surgery. The horse was unable to stand with assistance from a specialised sling. Azotaemia and hyperkalaemia developed in recovery and worsened despite therapeutic interventions. Euthanasia was performed given the grave prognosis. Post-mortem examination was not carried out but could have provided a definitive diagnosis. Specific factors have been identified in the prevention of post-anaesthetic myopathy, including maintenance of adequate tissue perfusion and oxygenation and careful positioning. Potential improvements in the anaesthetic management of this case in relation to these factors are discussed

Effects of midazolam on cardiovascular responses and isoflurane requirement during elective ovariohysterectomy in dogs

Abstract Background A prospective, randomized, placebo-controlled, blinded clinical study was conducted to determine whether a single dose of midazolam affects the cardiovascular response to surgical manipulation of the ovaries during elective ovariohysterectomy. Thirty-nine client-owned dogs undergoing elective ovariohysterectomy were recruited. After scoring cage demeanour, dogs were premedicated with acepromazine (0.03 mg kg-1) and pethidine (3 mg kg-1) intramuscularly into the quadriceps muscle and 20 min later sedation was scored. Anaesthesia was induced with propofol intravenously (IV) to effect. The study treatment (group M: midazolam (0.25 mg kg-1); or group P: placebo (Hartmann’s solution) (0.125 ml kg-1)) was administered IV before the intra-operative manipulation of the first ovary. Anaesthesia was maintained with isoflurane in oxygen. Morphine (0.3 mg kg-1 IV) was administered prior to the start of surgery. The vaporizer setting was adjusted according to the depth of anaesthesia. If an end-tidal isoflurane concentration (FE’Iso) above 1.6% was required additional analgesia was provided with fentanyl (2 μg kg-1). Dogs received meloxicam (0.2 mg kg-1 IV) at the end of procedure. Heart rate, mean arterial blood pressure, respiratory rate and end-tidal partial pressure of carbon dioxide as well as FE’Iso were recorded and analysed. Results A statistical significant difference between groups was detected in FE’Iso, with group M requiring a significantly lower FE’Iso than group P (14.3%) after administration of midazolam. No differences between groups was shown for percentage change in heart rate and mean arterial blood pressure, or end-tidal carbon dioxide and requirement for mechanical ventilation, or rescue analgesia. There was no statistically significant difference in the incidence of complications in group M and P. Group M received significantly more succinylated gelatin solution pre-administration of midazolam than group P, but no differences in fluid administration post-administration of the study treatment (midazolam/placebo) were detected. No statistical significant difference was demonstrated for the use of anticholinergic agents, dobutamine or noradrenaline. Conclusion No significant effect on cardiovascular parameters could be observed with administration of midazolam, but a modest (14.3%) isoflurane-sparing effect was detected

Effect of midazolam on the quality and duration of anaesthetic recovery in healthy dogs undergoing elective ovariohysterectomy or castration

Objective: To determine whether the use of a single dose of midazolam affects quality and duration of the recovery period in healthy dogs undergoing elective castration or ovariohysterectomy. Study design: Prospective, randomized, placebo-controlled, masked clinical trial. Animal population: Seventy-four client-owned dogs undergoing neutering. Methods: Following cage demeanour scoring using a simple descriptive scale (SDS), dogs were premedicated with acepromazine (0.03 mg kg–1) and pethidine (3 mg kg–1) intramuscularly (quadriceps muscle). Twenty minutes later sedation was scored with an SDS. Male dogs were induced with midazolam (0.25 mg kg–1) (group M) or an equivalent amount of Hartmann’s solution (group P) and propofol intravenously (IV). Female dogs were induced with propofol alone and were administered midazolam (group M) or Hartmann’s solution (group P) 5 minutes before intraoperative manipulation of the first ovary. Anaesthesia was maintained with isoflurane in oxygen. Intraoperative analgesia was provided with morphine (0.3 mg kg–1 IV) prior to the start of surgery. Male dogs were administered intratesticular lidocaine (1 mg kg–1). All dogs were administered meloxicam (0.2 mg kg–1 IV) at the end of the procedure, and recovery was scored with an SDS following extubation and 30 minutes later. Time to extubation, head lift, sternal position and standing and complications during recovery were recorded. Data are presented as median (range). Results: Time to standing was significantly longer in animals in group M [56 (13–179) minutes] than in group P [44 (4–137) minutes], and the early recovery score in group M [3 (2–6)] was overall worse than in group P [3 (1–5)]. Significantly more dogs in group M (n = 30) than in group P (n = 22) displayed hypotension. Conclusions and clinical relevance: The administration of midazolam prolonged time to standing and had a mild negative effect on the quality of recovery in a pooled population of healthy male and female dogs undergoing neutering

Severe intraoperative hypoxaemia in a horse due to failure of an oxygen concentrator and auxiliary oxygen supply

A horse with acute colic underwent exploratory laparotomy. Following anaesthetic induction, the inspired fraction of oxygen (FiO2) was found to be 0.23 and severe hypoxaemia (PaO2: 4.12 kPa [30.9 mmHg]) was detected. The terminal oxygen outlet was delivering mostly pressurised room air due to a mechanical fault within the oxygen concentrator, with subsequent failure of the auxiliary oxygen manifold. The oxygen supply in the operating room was switched to a cylinder (FiO2: 0.95) but PaO2 increased to only 12.3 kPa [92.3 mmHg], indicating probable ventilation/perfusion mismatch. Anaesthetic recovery was uneventful, but signs of abdominal pain returned four days later. A second laparotomy revealed perforation of the jejunum and generalised peritonitis, and the horse was euthanased. Failure of both an oxygen concentrator and the backup supply is rare but potentially disastrous. A thorough preanaesthetic equipment check, including the FiO2, and detailed knowledge of all equipment components are essential for the anaesthetist