Comparison of plasma propofol concentration for apnea, response to mechanical ventilation, and airway device between endotracheal tube and supraglottic airway device in Beagles.

The relationships between propofol plasma concentrations and the pharmacodynamic endpoints may differ according to a type of airway device. To clarify these relationships in different airway devices would be useful to avoid the complication such as apnea and intraoperative awareness. The aim of this study was to investigate the influence of difference of airway device on propofol requirement during maintenance of anesthesia in dogs. We compared the influence of airway devices on the plasma propofol concentrations for apnea, response to mechanical ventilation, and response to airway device between endotracheal tube (ETT) and supraglottic airway device (SGAD) in Beagles. The pharmacodynamic effects were repeatedly assessed at varying propofol concentrations. The plasma concentrations (mean ± SD) of propofol in the ETT and SGAD groups were 10.2 ± 1.8 and 10.9 ± 2.4 µg/ml for apnea (P=0.438), 7.9 ± 1.2 and 7.4 ± 1.5 µg/ml for response to mechanical ventilation (P=0.268), and 5.2 ± 0.7 and 5.4 ± 1.5 µg/ml for response to airway device (P=0.580), respectively. Required propofol concentration during maintenance of anesthesia may be similar between ETT and SGAD. Without moderate to strong stimuli such as airway device insertion or painful stimulation during surgery, the type of airway device may have little impact on required propofol concentration during maintenance of anesthesia in dogs.

The effect of experience, simulator-training and biometric feedback on manual ventilation technique.

OBJECTIVE: To determine the frequency of provision and main providers (veterinary surgeons, nurses or trainees) of manual ventilation in UK veterinary practices. Furthermore, to determine the variation in peak inspiratory (inflation) pressure (PIP), applied to a lung model during manual ventilation, by three different groups of operators (inexperienced, experienced and specialist), before and after training. STUDY DESIGN: Questionnaire survey, lung model simulator development and prospective testing. METHODS: Postal questionnaires were sent to 100 randomly selected veterinary practices. The lung model simulator was manually ventilated in a staged process over 3 weeks, with and without real-time biometric feedback (PIP display), by three groups of volunteer operators: inexperienced, experienced and specialist. RESULTS: The questionnaires determined that veterinary nurses were responsible for providing the majority of manual ventilation in veterinary practices, mainly drawing on theoretical knowledge rather than any specific training. Thoracic surgery and apnoea were the main reasons for provision of manual ventilation. Specialists performed well when manually ventilating the lung model, regardless of feedback training. Both inexperienced and experienced operators showed significant improvement in technique when using the feedback training tool: variation in PIP decreased significantly until operators provided manual ventilation at PIPs within the defined optimum range. Preferences for different forms of feedback (graphical, numerical or scale display), revealed that the operators' choice was not always the method which gave least variation in PIP. CONCLUSIONS AND CLINICAL RELEVANCE: This study highlighted a need for training in manual ventilation at an early stage in veterinary and veterinary nursing careers and demonstrated how feedback is important in the process of experiential learning. A manometer device which can provide immediate feedback during training, or indeed in a real clinical setting, should improve patient safety.

The effect of two different intra-operative end-tidal carbon dioxide tensions on apnoeic duration in the recovery period in horses.

OBJECTIVE: To compare the effect of two different intraoperative end-tidal carbon dioxide tensions on apnoeic duration in the recovery period in horses. STUDY DESIGN: Prospective randomized clinical study. ANIMALS: Eighteen healthy client-owned adult horses (ASA I-II) admitted for elective surgery. Horses were of a median body mass of 595 (238-706) kg and a mean age of 9 ± 5 years. METHODS: A standardized anaesthetic protocol was used. Horses were positioned in dorsal recumbency and randomly allocated to one of two groups. Controlled mechanical ventilation (CMV) was adjusted to maintain the end-tidal carbon dioxide tension (Pe'CO2 ) at 40 ± 5 mmHg (5.3 ± 0.7 kPa) (group 40) or 60 ± 5 mmHg (8.0 ± 0.7 kPa) (group 60). Arterial blood gas analysis was performed at the start of the anaesthetic period (T0), at one point during the anaesthetic (T1), immediately prior to disconnection from the breathing system (T2) and at the first spontaneous breath in the recovery box (T3). The time from disconnection from the breathing system to return to spontaneous ventilation (RSV) was recorded. Data were analysed using a two sample t-test or the Mann-Whitney U-test and significance assigned when p < 0.05. RESULTS: Horses in group 60 resumed spontaneous breathing significantly earlier than those in group 40, [52 (14-151) and 210 (103-542) seconds, respectively] (p < 0.001). Arterial oxygen tension (PaO2 ), pH, base excess (BE) and plasma bicarbonate (HCO3-) were not different between the groups at RSV, however, PaO2 was significantly lower in group 60 during (T1) and at the end of anaesthesia (T2). CONCLUSIONS AND CLINICAL RELEVANCE: Aiming to maintain intra-operative Pe'CO2 at 60 ± 5 mmHg (8.0 ± 0.7 kPa) in mechanically ventilated horses resulted in more rapid RSV compared with when Pe'CO2 was maintained at 40 ± 5 mmHg (5.3 ± 0.7 kPa).

Apnea and bradycardia due to anaphylaxis to tobacco glycoprotein in the infant rabbit.

Prenatal and postnatal exposure to cigarette smoke is associated with an increased incidence of the sudden infant death syndrome, although the cause(s) for this is unknown. Tobacco glycoprotein (TGP), a group of proteins purified from cured tobacco leaves and present in cigarette smoke, have been shown to cause anaphylaxis in excised hearts and lungs of adult rabbits that were neonatally sensitized to TGP and later rechallenged. We sought to determine whether anaphylaxis occurred in live infant rabbits who were neonatally sensitized to TGP. At the age of 1 day, 12 animals were sensitized to TGP (0.1mg in 0.25 cc alum) via intraperitoneal injection (i.p.i.) followed by a booster ipi at the age of 30 days (TGP-S). Seven animals received i.p.i. of antigen-free alum only (controls). All animals underwent an intravenous TGP challenge at age 42+/-2 days. Heart rate (HR) and respiratory rate (RR) were recorded for 2 min prior to and 5 min after the challenge. Baseline HR (approximately 260) and RR (approximately 120) were similar in all animals. Seven TGP-S animals developed apnea (1.9-4.7s) within 60s of the challenge while none of the controls did. The TGP-S also became bradycardic (the lowest HR over 50 consecutive beats), with the HR decreasing from 260 to 220 vs the controls, whose HR remained constant (approximately 250). We conclude that some rabbits neonatally sensitized to TGP develop apnea and bradycardia upon further intravenous TGP challenge. These studies suggest that cigarette smoke exposure may be associated with a higher rate of SIDS via an anaphylactic mechanism.

Effects of permanent tracheostomy on respiratory reflexes to lung inflation and capsaicin in sevoflurane-anaesthetized dogs.

The aim of this study was to evaluate the effects of permanent tracheostomy on baseline breathing, reflex responses to lung hyperinflation (1.5 kPa) and right atrial capsaicin injection (5 micrograms/kg) before and at 3 and 5 weeks after tracheostomy in sevoflurane-anaesthetized spontaneously breathing dogs (n = 6). In all observation periods, apnoeic responses, represented by an increase in expiration time after lung inflation and right atrial capsaicin injection, were consistently observed to be a result of the Hering-Breuer inflation reflex and the pulmonary C-fibre chemoreflex. Investigation at 3 and 5 weeks after tracheostomy revealed no significant evidence of changing baseline breathing pattern or reflex responses to lung inflation and capsaicin in any ventilatory variable (inspiration time, expiration time, tidal volume, expired ventilation, and end-tidal PCO2) from levels recorded before surgery. These results indicate that permanent tracheostomy, at least up to 5 weeks, does not affect the baseline breathing pattern, the Hering-Breuer inflation reflex or the pulmonary C-fibre chemoreflex. Further, our investigation provides a useful canine model in respiratory physiology.

Naturally occurring nasal obstructions in 11 sheep.

Eleven adult sheep of various breeds were examined due to inspiratory dyspnea. Fiberoptic examinations conducted in 8 of the sheep revealed masses to be obstructing the nasal passages. Identification of the masses through histopathologic examination showed 7 to be adenocarcinomas, 1 a papillary adenoma, and 4 were cases of glandular hyperplasia with lymphoplasmacytic infiltration (nasal polyps). One ewe had both an adenocarcinoma and a polyp. Surgical removal of the masses was attempted on 6 of the sheep. Four of the 6 surgically-treated sheep have survived between 2 mo. - 2 years without recurrence of the obstruction.

Respiratory and cardiac arrest under general anaesthesia: treatment by acupuncture of the nasal philtrum.

The philtrum point VG 26 (Jen Chung) was needled in 69 cases of respiratory depression or apnoea in dogs and cats during induction or maintenance of general anaesthesia. Respiration was restored to normal or near normal rates within 10 to 30 seconds of insertion of the needle in all the cases. In seven cases of anaesthetic apnoea with concurrent cardiac arrest and absence of vital signs, the revival rate was 43 per cent. Those which recovered required four to 10 minutes of acupuncture stimulation. In eight cases of collapse due to other causes, the revival rate was 25 per cent. The cases included five sheep in shock following liver biopsy, two cases of haemorrhagic shock (dog, cat) and one terminal collapse in chronic congestive heart failure (dog).

Surgical anesthesia in turkeys with thialbarbital sodium.

Thialbarbital sodium was found to be a reliable and economical general anesthetic for domesticated turkeys. Despite shortness of action of the initial dose, surgical anesthesia was maintained longer than 2 hours by intermittent infusion via a brachial vein cannula. The drug was reconstituted just before use (66 mg/ml) with sterile 1% saline solution. Rapid smooth induction was produced with an initial dosage of 30 mg/kg for hens and 26.5 mg/kg for toms, when administered within a 30- to 60-second interval. Supplemental infusion of the drug in increments of 0.25 to 1.5 ml was used to sustain the desired level of deep narcosis. The occurrence of respiratory failure was considerably less for thialbarbital than with pentobarbital sodium. Recovery was rapid and smooth.