Generalised neuromuscular blockade after intraurethral administration of atracurium besilate in a male cat with urethral obstruction.

A 4-year-old, entire, male, domestic long-haired cat was presented with an acute history of stranguria and dysuria and diagnosed with urolithiasis causing urethral obstruction. The patient was induced to general anaesthesia and several unsuccessful attempts to flush the uroliths retrogradely towards the bladder were made. An intraurethral administration of the neuromuscular blocking agent atracurium was performed as it has been reported to facilitate urethral catheterisation without any side effects. Respiratory arrest developed after 15 minutes from atracurium administration, which was promptly recognized and treated with mechanical ventilation. The absence of muscle contraction in response to a nerve stimulation confirmed a generalised muscle blockade. Approximately 35 minutes after, a muscle response to nerve stimulation appeared. Neostigmine combined with glycopyrrolate was administered resulting in complete recovery from neuromuscular blockade. In conclusion, the use of intraurethral atracurium can result in systemic absorption of the drug with subsequent generalised neuromuscular blockade.

Stability of dilutions of methadone alone, and in combination with lidocaine and ketamine.

OBJECTIVES: To assess stability and degradation over time, of methadone alone, and mixed with lidocaine and ketamine, using various diluents and storage conditions. MATERIALS AND METHODS: Solutions of methadone diluted in 0.9% NaCl, and methadone-lidocaine-ketamine diluted in 0.9% NaCl or Hartmann's solution, and stored at room temperature with exposure to light, or refrigerated at 4°C and protected from light, were maintained over 10 days. Chemical stability was determined using liquid chromatography immediately after preparation and following 4, 24, 48, 96 and 240 hours of storage. Physical stability of the solutions was evaluated by visual examination and absorbance of ultraviolet/visible light. A linear model assessed the impact of different diluent solutions and storage conditions on drug degradation over time. RESULTS: There was no evidence of physicochemical incompatibility for any solution. Methadone concentration, when diluted alone or in methadone-lidocaine-ketamine with Hartmann's solution at 4°C, did not decline over time. Ketamine and lidocaine decreased to a similar extent over time, regardless of the diluent used or storage method, while methadone in methadone-lidocaine-ketamine diluted with 0.9% NaCl or with Hartmann's solution at room temperature exposed to light, also declined over time; however, all three methadone-lidocaine-ketamine components retained acceptable stability (<10% degradation) for at least 48 hours following preparation, irrespective of diluent or storage conditions. CLINICAL SIGNIFICANCE: Regardless of the diluent or storage method, methadone-lidocaine-ketamine solutions degrade over time, but this only becomes clinically significant after 48 hours. Solutions of 1 mg/ml methadone in 0.9% NaCl are stable for at least 10 days under storage conditions likely to be encountered in general practice.

Cardiopulmonary and sedative effects of intravenous or epidural methadone in conscious dogs.

Cardiopulmonary and sedative effects of intravenous or epidural methadone were compared. Six beagles were randomly assigned to group MIV (methadone 0.5 mg/kg IV + NaCl 0.9% epidurally) or MEP (methadone 0.5 mg/kg epidurally + NaCl 0.9% IV). Cardiopulmonary, blood gas and sedation were assessed at time (T) 0, 15, 30, 60, 120, 240 and 480 min after drug administration. Compared to T0, heart rate decreased at T15-T120 in MIV (p < .001) and T15-T240 in MEP (p < .05); mean arterial pressure was reduced at T15-T60 in MEP (p < .01); respiratory rate was higher at T15 and T30 in both groups (p < .05); pH was lower at T15-T120 in MIV (p < .01) and T15, T30 and T120 in MEP (p < .05); PaCO2 was higher at T15-T60 in MIV (p < .01) and T15, T30 and T120 in MEP (p < .01); sedation scores were higher at T15 and T30 in MIV and T15-T60 in MEP (p < .05). At T120 and T240, sedation score was higher in group MEP compared with group MIV (p < .01) In conclusion, cardiopulmonary and sedative effects of identical methadone doses are similar when administered IV or epidurally to conscious healthy dogs.

Green discolouration of urine following propofol infusion in a dog.

A three-year-old, female neutered Weimaraner was presented with a history of neck pain and tetraparesis. MRI revealed an extradural mass at the level of C3 vertebra, which was thought to be a spinal abscess, and the dog was scheduled for surgical exploration the following morning. Overnight the dog developed an exaggerated ventilatory pattern, with paradoxical inward movement of the thorax on inspiration. Arterial blood gas analysis revealed respiratory acidosis and ventilator support was initiated to prevent excessive respiratory fatigue. During mechanical ventilation, anaesthesia was maintained using a propofol target-controlled infusion system and, subsequently, the dog produced bright green urine in the urine collection system. Although previously documented in humans, this appears to be the first report of green urine in a dog following propofol use.

An evaluation of a target-controlled infusion of propofol or propofol-alfentanil admixture for sedation in dogs.

OBJECTIVES: To evaluate sedation quality and cardiorespiratory variables in dogs sedated using a target-controlled infusion of propofol or propofol-alfentanil admixture. METHODS: A total of 60 dogs undergoing diagnostic imaging were randomly assigned to one of three sedation protocols: propofol alone; propofol with a low concentration of 12 µg of alfentanil per mL of propofol; or propofol with a higher concentration of 24 µg of alfentanil per mL of propofol. Target-controlled infusion was initiated at a propofol target concentration of 1·5 µg/mL and increased until lateral recumbency was achieved. Times to adopt lateral recumbency and recover, pulse rate, respiratory rate, oscillometric mean arterial pressure and oxygen saturation were recorded. Quality of sedation onset and recovery were scored. RESULTS: Propofol target at lateral recumbency differed significantly (P=0·01) between groups with median (range) values of 3·0 (1·5 to 5·5), 2·0 (2 to 4·5) and 2·25 (1·5 to 3·5) µg/mL for propofol alone, propofol with the lower concentration of alfentanil and propofol with the higher concentration of alfentanil groups, respectively. Time to lateral recumbency was longer and quality of onset less smooth for the propofol group. Pulse rate change differed significantly (P<0·001) between groups (mean pulse rate change at onset of sedation: propofol group +2 ±24 bpm, low concentration alfentanil group -30 ±24 bpm, higher concentration alfentanil group -26 ±23 bpm). Hypoxaemia (SpO2 <90%) occurred in 1, 3 and 13 dogs, in the propofol group, the low concentration alfentanil group and the higher concentration of alfentanil group, respectively (P<0·001). CLINICAL SIGNIFICANCE: Addition of alfentanil to propofol target-controlled infusion did not confer cardiovascular benefits and, at the higher concentration, alfentanil increased the incidence of hypoxaemia.

Evoked otoacoustic emissions: an alternative test of auditory function in horses.

REASONS FOR PERFORMING STUDY: Deafness has been reported in horses due to a variety of causes and objective auditory assessment has been performed with brainstem auditory evoked potential testing. Evoked otoacoustic emission (OAE) tests are widely used in human patients for hearing screening, detecting partial hearing loss (including frequency-specific hearing loss) and monitoring cochlear outer hair cell function over time. OAE tests are noninvasive, quick and affordable. Two types of OAE are commonly used clinically: transient evoked OAEs (TEOAEs) and distortion product OAEs (DPOAEs). Detection of OAEs has not been reported and OAE testing has not been evaluated for auditory assessment in horses. OBJECTIVES: To investigate whether TEOAEs and DPOAEs can be recorded in horses, and to evaluate the use of human OAE screening protocols in horses with apparently normal hearing. METHODS: Sixteen systemically healthy horses with normal behavioural responses to sound were included. OAE testing was performed during general anaesthesia using commercially available equipment and the final outcome for each ear for the TEOAE test (after a maximum of 3 runs) and the DPOAE test (after one run) were compared. RESULTS: TEOAEs and DPOAEs can be recorded in horses. Using the chosen TEOAE protocol, 96% of ears achieved a pass. Seventy percent of ears passed DPOAE testing, despite all of these ears passing TEOAE testing. CONCLUSIONS: Using the chosen stimulus and analysis protocols, TEOAEs were recorded from most ears; however, a smaller proportion of ears passed the DPOAE protocol, suggesting that this may be overly stringent and require further optimisation in horses. POTENTIAL RELEVANCE: OAE testing is rapid and easily performed in anaesthetised horses. It provides frequency-specific information about outer hair cell function, and is a promising tool for audiological assessment in the horse; however, it has not been assessed in conscious or sedated animals.