The effect of four anaesthetic protocols for maintenance of anaesthesia on trans-diaphragmatic pressure in dogs

Success Rate and Perioperative Complications of Lumbosacral Extradural Anaesthesia in Dogs Undergoing Total Hip Replacement: A Double-Centre Retrospective Study

OBJECTIVE

 The aim of this study was to retrospectively evaluate the success rate and perioperative complications of lumbosacral extradural anaesthesia in dogs undergoing total hip replacement.

STUDY DESIGN

 Records of dogs undergoing total hip replacement in which lumbosacral extradural anaesthesia with 0.5% levo- or bupivacaine combined with either morphine or buprenorphine were retrieved. Success rate was defined as intraoperative fentanyl consumption <1 μg/kg/h with no intravenous infusion of other analgesic drugs and no additional morphine/methadone within the first 3 hours from premedication. Prevalence of intraoperative anaesthetic and postoperative surgical complications was calculated.

RESULTS

 Overall, 206 dogs were included in the study. Success rate was 88.7%. Hypercapnia (75.2%), hypotension (46.1%), hypothermia (27.7%) and regurgitation (6.3%) were recorded during anaesthesia. Within 24 hours post-surgery, urinary retention (17.8%), vomiting/regurgitation/diarrhea (8.2%) and sciatic neurapraxia of the operated limb (5.8%) were recorded. Luxation of the operated hip occurred at 48 and 72 hours after surgery in two dogs and one dog respectively. One dog had cardiopulmonary arrest at 52 hours after surgery.

CONCLUSION

 While hypercapnia, hypotension and hypothermia might develop intraoperatively, the high success rate and the relatively low prevalence of postoperative surgical complications directly associated with lumbosacral extradural anaesthesia justify its use in dogs undergoing total hip replacement.

The functional morphology of the postpulmonary septum of the American alligator (Alligator mississippiensis)

The American alligator (Alligator mississippiensis) has a postpulmonary septum (PPS) that partitions the intracoelomic cavity. The PPS adheres to the capsule of the liver caudally and to the visceral pleura of the lung cranially; the ventrolateral portions of the PPS are invested with smooth muscle, the remainder is tendinous. Differential pressure transducers were used to record the intrathoracic (ITP) and intraperitoneal (IPP) pressures, and determine the transdiaphragmatic pressure (TDP). Each ventilatory pulse resulted in a pulse in ITP and a significantly lower pulse in IPP; meaning that a TDP was established, and that the pleural and peritoneal cavities were functionally isolated. The anesthetized alligators were tilted 30° head-up or head-down in order to displace the liver. Head-up rotations caused a significant increase in IPP, and a significant decrease in ITP (which became negative); head-down rotations produced the opposite effect. During these rotations, the PPS maintained opposite pressures (positive or negative) in the pleural and peritoneal cavities, and established TDPs greater than have been reported for some mammals. Two types of "breaths" were recorded during these experiments. The first was interpreted as a contraction of the diaphragmaticus muscle, which displaces the liver caudally; these breaths had the same effect as the head-up rotations. The second type of breath was interpreted as constriction of the thoracic and abdominal body walls; this type of breath produced pronounced, long-duration, roughly parallel, increases in ITP and IPP. The smooth muscle within the PPS is suggestive of higher-order adjustment or tuning of the PPS's tensile state.

Aminophylline increases parasternal muscle action in awake canines

The traditional theophylline bronchodilator, aminophylline, is still widely used, especially in the treatment of COPD. The effects of aminophylline on ventilation and action of the costal diaphragm have been previously defined, but other respiratory muscles - notably the chest wall, are not well determined. Therefore, we investigated the effects of aminophylline on the Parasternal intercostal, a key obligatory inspiratory muscle, examining muscle length, shortening and EMG. We studied 11 awake canines, chronically implanted with sonomicrometer crystals and fine-wire EMG electrodes in the parasternal muscle. Ventilatory parameters, muscle length (shortening), and moving average muscle EMG activity, were measured at baseline and with aminophylline, during resting and hypercapnic stimulated breathing. Experiments were carried out prior to administration of aminophylline (baseline), and 1.5 h after loading and ongoing infusion. Minute ventilation, tidal volume and respiratory frequency all increased significantly with aminophylline, both during resting breathing and at equivalent levels of hypercapnic stimulated breathing. Parasternal baseline muscle length was entirely unchanged with aminophylline. Parasternal shortening increased significantly with aminophylline while corresponding parasternal EMG activity remained constant, consistent with increased contractility. Thus, in awake, intact mammals, aminophylline, in the usual therapeutic range, elicits increased ventilation and increased contractility of all primary inspiratory respiratory muscles, including both chest wall and diaphragm.