The Determination of the Minimum Anaesthetic Concentration of Halothane in the Rock Dove (Columba livia) Using an Electrical Stimulus

This study aims to determine the minimum anaesthetic concentration (MAC) of halothane in the Rock Dove using electrical stimulus. Seven Rock Doves are anaesthetised with halothane, and the MAC is determined using the bracketing method. An electrical stimulus (two single pulses and two five-second stimuli, all separated by five-second pauses; 30 Hz, 30 V, 7.5 ms) is applied to the legs via subcutaneous electrodes. A maximum of eight periods of electrical stimulation, each with a preceding 15 min stable phase, is applied to each bird. If the non-reflexive movement occurred following stimulation, the end-tidal halothane (Fe’Hal) is increased by 10% before the next stimulus delivery. If no movement occurred, Fe’Hal is decreased by 10%. The MAC is the average of the highest concentration that allowed movement and the lowest that prevented movement. Physiological variables and ventilatory settings are recorded every five minutes. The current delivered is calculated offline. The mean ± SD MAC of halothane is 1.62 ± 0.29%, calculated from five birds. During the entire anaesthesia, all birds had cardiac arrhythmias —with three having sporadic recurrent periods of prolonged ventricular standstill followed by marked sinus tachycardia. The mean recorded voltage and calculated current and resistance are 27.6 ± 2.7 V, 20.3 ± 7.3 mAmp and 1.6 ± 0.9 kΩ, respectively. The advantage of halothane for prolonged anaesthesia in Rock Doves may be limited when noxious stimulation is used, due to the development of severe ventricular arrhythmias.

Labour analgesia: choice of local anaesthetics

In this chapter, the rationale for the choice of commonly used local anaesthetics—racemic bupivacaine, ropivacaine, and levobupivacaine—is reviewed, particularly with respect to their potency and differential block. Epidural and spinal dosing for labour analgesia and the role of ‘up–down’ studies to determine the minimum local anaesthetic concentration (MLAC) for labour analgesia is explained. Applying the MLAC model has enabled clinical comparisons at equipotent concentrations and doses. It has also quantified what contribution opioids have on the overall effectiveness of the analgesic mixture, provided a means of optimizing combinations of local anaesthetic–opioid solutions, examined the effect of inter-individual and obstetric variables on local anaesthetic potency, and provided a pharmacological-based rationale for analgesia solutions used for labour analgesia.