Martina Mosing

Use of continuous positive airway pressure (CPAP) to optimise oxygenation in anaesthetised horses – a clinical study

REASONS FOR PERFORMING STUDY Hypoxaemia is a common problem during equine anaesthesia. Continuous positive airway pressure (CPAP) is a ventilation mode routinely employed in man to overcome hypoxaemia but has not been objectively assessed in horses. OBJECTIVES To test the effects of CPAP on oxygenation and its indices in anaesthetised horses in a clinical setting. METHODS Twenty-four healthy horses requiring anaesthesia in dorsal recumbency were anaesthetised using a standard protocol. Following orotracheal intubation and connection to an anaesthetic machine capable of applying CPAP, horses were randomly allocated to ventilate at physiological airway pressure measured at the airway opening (Group PAP) or to receive CPAP of 8 cmH2O (Group CPAP). Arterial blood gas analysis was performed as soon as arterial cannulation was achieved and 30, 60 and 90 min after induction. If PaCO2 increased above 9.31 kPa controlled ventilation was initiated. Groups were compared using a general linear model. RESULTS Horses receiving CPAP had significantly higher PaO2 and calculated oxygen indices than horses receiving PAP. No significant differences in ventilation indices were observed between the 2 groups. Eight horses receiving PAP and 5 receiving CPAP required controlled ventilation. No differences in dobutamine requirements or mean arterial pressures were recorded. CONCLUSIONS Continuous positive airway pressure of 8 cmH2O improved oxygenation indices in dorsally recumbent horses without significantly influencing ventilation. POTENTIAL RELEVANCE Continuous positive airway pressure reduces the incidence of hypoxaemia in anaesthetised horses. Further research is warranted to elucidate the effects of CPAP on the cardiovascular system.

Oxygenation and ventilation characteristics in obese sedated dogs before and after weight loss: a clinical trial.

This prospective clinical study examined the effect of obesity and subsequent weight loss on oxygenation and ventilation during deep sedation in pet dogs. Data from nine dogs completing a formalised weight loss programme were evaluated. Dual-energy X-ray absorptiometry (DEXA) was used to quantify body fat mass prior to and after weight loss. Dogs were deeply sedated and positioned in dorsal recumbency. Sedation was scored using a semi-objective scheme. As part of the monitoring of sedation, arterial oxygen partial pressure (PaO2) and arterial carbon dioxide partial pressure (PaCO2) were measured after 10 min in dorsal recumbency. Oxygen saturation of haemoglobin (SpO2) was monitored continuously using pulse oximetry, starting oxygen supplementation where indicated (SpO2<90%) via a face mask. Morphometric measurements were taken from DEXA images and compared before and after weight loss. Several oxygen indices were calculated and correlated with body fat variables evaluated by DEXA. All body fat variables improved significantly after weight loss. PaO2 increased from 27.9±19.2 kPa to 34.8±24.4 kPa, while FiO2 decreased from 0.74±0.31 to 0.66±0.35. Morphometric measurements improved significantly after weight loss. PaO2/FiO2 (inspired oxygen fraction) and Pa/AO2 (ratio of PaO2 to alveolar PO2) also improved significantly, but there was no change in f-shunt and PaCO2 after weight loss. On multiple linear regression analysis, all oxygen indices were negatively associated with thoracic fat percentage. In conclusion, obesity decreases oxygenation in dogs during deep sedation. Oxygenation status improves with successful weight loss, but ventilation is not influenced by obesity.

Reversal of profound rocuronium block monitored in three muscle groups with sugammadex in ponies

BACKGROUND This clinical study evaluated the speed of reversal of profound rocuronium block in ponies using sugammadex and investigated the differences in onset and recovery from block in three different muscle groups. METHODS Anaesthesia was induced and maintained with isoflurane in oxygen 100% in eight ponies. Neuromuscular monitoring was performed at each site using acceleromyography: in the extensor muscles of the pelvic limb (peroneal nerve) and thoracic limb (radial nerve), and in the orbicularis oris muscle (OOM; facial nerve). Rocuronium 0.6 mg kg(-1) i.v. was administered, followed 5 min later by sugammadex 4 mg kg(-1) i.v. Onset time (onsetROC), maximum block, and time to recovery of the train-of-four ratio to 0.9 (TOFR=0.9) were recorded. The differences between monitored sites were compared using one-way anova followed by a post hoc Dunns test. RESULTS Onset of ROC was significantly delayed in OOM compared with both limbs [pelvic limb, thoracic limb, and OOM: 43.1 (sd 16.9), 50.6 (15.9), and 204.4 (35.8) s, respectively; P<0.001]. Complete block was achieved in the pelvic and thoracic limbs, but in none of the eight ponies in the OOM [mean T1=15.3 (9.4)%; range: 7-36%]. No differences were observed between muscle sites in recovery to TOFR=0.9 [pelvic limb, thoracic limb, and OOM: 2.3 (0.9), 3.4 (1.7), and 2.8 (2.1) min, respectively]. No adverse effects of sugammadex were detected throughout the study period. CONCLUSIONS Sugammadex can be used to reverse profound rocuronium-induced block in ponies during isoflurane anaesthesia. Thoracic limb muscles represent a suitable alternative for monitoring neuromuscular block compared with pelvic limb muscles.

Observations on the muscle relaxant rocuronium bromide in the horse--a dose-response study.

OBJECTIVE To investigate the onset and duration of neuromuscular blockade of rocuronium bromide and its associated haemodynamic effects at three doses in healthy horses. STUDY DESIGN Prospective, randomized experimental study. ANIMALS Seven adult horses aged 3-20 (mean 10.3) years and weighing 466 ± 44 (mean ± SD) kg. METHODS Horses were anaesthetized three times with at least 2 weeks between. They were pre-medicated with 0.6 mg kg-1 xylazine and 0.01 mg kg-1 butorphanol IV. Anaesthesia was induced with 2.2 mg kg-1 ketamine and 0.1 mg kg-1 diazepam IV. Following orotracheal intubation anaesthesia was maintained with isoflurane in 100% oxygen. Intermittent positive pressure ventilation was initiated and the horses were ventilated at a respiratory rate (fr) of 4-8 breaths minute-1. Neuromuscular function was monitored with an acceleromyograph. The peroneal nerve was stimulated with train-of-four (TOF) mode at 2 Hz every 15 seconds. Each horse received, in randomly assigned order, one of the three doses of rocuronium: 0.2 mg kg-1 (D02), 0.4 mg kg-1 (D04) or 0.6 mg kg-1 (D06) IV. Lag time, onset time, time of no response, duration of action and the TOF ratio 0.7 and 0.9 were measured. Recovery time (T125-75) was calculated. Vital parameters were recorded at 5-minute intervals on a standard anaesthetic record form. RESULTS Rocuronium produced a dose-dependent duration of action in isoflurane-anaesthetized horses. 100% block was observed in D04 and D06 but not in D02, in which the maximum decrease of the first twitch of TOF attained was 91.5 ± 16.5%. Time to T125 was 13.1 ± 5.5 minutes, 38.6 ± 10.1 minutes and 55 ± 9.8 minutes in D02, D04 and D06 respectively. There was a significantly shorter time for TOFR 0.9 with 0.2 mg kg-1 compared with 0.4 and 0.6 mg kg-1 rocuronium. T125-75 in D04 and D6 was not statistically significantly different. Heart rate, systolic, diastolic and mean arterial blood pressure increased slightly during the observation period. CONCLUSION Rocuronium is an effective nondepolarizing muscle relaxant in horses under isoflurane anaesthesia. It had a dose-dependent onset and duration of action. Rocuronium did not produce significant changes in the measured cardiovascular parameters.

Clinical evaluation of the v‐gel supraglottic airway device in comparison with a classical laryngeal mask and endotracheal intubation in cats during spontaneous and controlled mechanical ventilation

OBJECTIVE To compare airway management during induction of anaesthesia, in spontaneous ventilation and controlled mechanical ventilation (CMV), using a cat-specific supraglottic airway device (the v-gel), a classical laryngeal mask (LM) or an endotracheal tube (ETT). STUDY DESIGN Prospective, randomized clinical trial. ANIMALS Forty-five healthy cats. METHODS After premedication, cats were randomly allocated to one of three groups to secure the airway: 1) v-gel; 2) LM; or 3) ETT (cuff pressure: 20 cm H2O). Cats were anaesthetized for elective procedures. The dose of propofol necessary to insert the v-gel, LM or ETT, the number of attempts required to achieve insertion and leakage during spontaneous ventilation and CMV at different peak inspiratory pressures (8, 10, 12, 14 and 16 cm H2O) were recorded. Leakage of >20% of tidal volume was considered as a criterion for exclusion. Significance was set at a p-value of <0.05. RESULTS Cats in the v-gel group required a median (range) of 3 mg kg(-1) (2-5 mg kg(-1)) of propofol for successful placement, which was significantly less than the 5 mg kg(-1) (3-7 mg kg(-1)) required for endotracheal intubation (p = 0.005). No significant difference in the total dose of propofol was observed between the v-gel and LM [3 mg kg(-1) (2-7 mg kg(-1))] groups or the ETT and LM groups. Significantly more cats in the ETT group were excluded for leakage of >20% during CMV at all pressure settings. CONCLUSIONS AND CLINICAL RELEVANCE The v-gel is a practical alternative to the LM and ETT for securing the airway after induction of anaesthesia and for CMV up to 16 cm H2O in healthy cats. The v-gel can be inserted at a more superficial level of anaesthesia than the ETT and showed significantly less leakage during CMV than the ETT.

Evaluation of transdermal fentanyl patch attachment in dogs and analysis of residual fentanyl content following removal.

OBJECTIVE To investigate whether the method used to attach matrix-type fentanyl patches influences the degree of skin attachment and the amount of active drug remaining in patches after use. STUDY DESIGN Prospective, randomised clinical study. STUDY POPULATION Fifteen adult dogs of mixed breeds. METHODS Two equally sized matrix-type fentanyl patches were attached to the dorsal third of the lateral thorax of fifteen dogs for 72 hours. The two patches were attached using different techniques: Method AD used an adhesive dressing in combination with a transparent film. Method TG used tissue adhesive applied to the edges of the patch. After 72 hours the patches were removed and the proportion of the patch attached at this time calculated. The residual content of the patches was analysed using a validated gas chromatography-mass spectrometery (GC-MS) analysis technique. RESULTS After 72 hours of continuous attachment, the mean proportion of drug uptake for method AD was 17.2 (SD ± 11.1)% and for method TG this was 16.9 (SD ± 7.3)%. The median proportion of attachment for method AD was 100% and for method TG was 95.6%. CONCLUSIONS The method of attachment did not significantly influence the uptake of fentanyl from matrix-type patches. The method of attachment resulted in a significant difference in the proportion of the patch attached 72 hours after placement, with method AD resulting in a greater median proportion of attachment than TG. CLINICAL RELEVANCE The method used to attach matrix-type fentanyl patches to dogs should not interfere with drug uptake. The residual fentanyl content remaining in these patches after 72 hours of continuous application is significant and could lead to intoxication if ingested by humans.

Pressure profile in the caudal extradural space of standing horses before and after extradural drug administration

The objectives of this study were to measure the pressure in the caudal extradural space of standing horses and to evaluate the usefulness of pressure waves to identify correct needle placement. Caudal extradural pressure was measured in 12 healthy horses. The pressure and any extradural pressure waves were recorded for 3min after puncture, for 1min after testing for lack of resistance (LOR), and for 10min after lidocaine injection. Successful extradural drug administration was confirmed in all horses. The median extradural pressure findings after puncture, after LOR, immediately after injection and 10min after needle placement were -1.60kPa (range -2.27 to 1.33kPa), -0.67kPa (-2.27 to 5.73kPa), 5.00kPa (0.93 to 9.87kPa) and 0.13kPa (-0.67 to 4.53kPa), respectively. Extradural pressure waves were not always present. Extradural space pressure was sub-atmospheric in most horses and extradural injection significantly increased this pressure for up to 10min. Extradural pressure waves had limited usefulness in the confirmation of the correct placement of the needle.

Measurement of respiratory system compliance and respiratory system resistance in healthy dogs undergoing general anaesthesia for elective orthopaedic procedures

OBJECTIVE The aim of this study was to investigate normal values for the dynamic compliance of the respiratory system (Crs) and respiratory system resistance (Rrs) in mechanically ventilated anaesthetized dogs. STUDY DESIGN Prospective clinical study. ANIMALS Forty healthy dogs undergoing elective orthopaedic surgery. Body weight was (mean ± SD) 26.8 ± 10.7 kg (range: 1.9-45.0 kg), age 4.7 ± 2.9 years (range: 0.1-10.6 years). METHODS Dogs were premedicated with acepromazine and methadone administered intramuscularly and anaesthesia induced with propofol intravenously. After endotracheal intubation the dogs lungs were connected to an appropriate breathing system depending on body weight and isoflurane in oxygen administered for maintenance of anaesthesia. The lungs were ventilated mechanically with variables set to maintain normocapnia (end-tidal carbon dioxide concentration 4.7-6.0 kPa). Peak inspiratory pressure, Crs, Rrs, tidal volume, respiratory rate and positive end-expiratory pressure were recorded at 5, 30, 60, 90 and 120 minutes after start of mechanical ventilation. Cardiovascular variables were recorded at time of collection of respiratory data. RESULTS General additive modeling revealed the following relationships: Crs =[0.895 × body weight (kg)] + 8.845 and Rrs=[-0.0966 × body weight (kg)] + 6.965. Body weight and endotracheal tube diameter were associated with Crs (p<0.001 and p=0.002 respectively) and Rrs (p=0.017 and p=0.002 respectively), body weight being linearly related to Crs and inversely to Rrs. CONCLUSION AND CLINICAL RELEVANCE Body weight was linearly related to Crs while Rrs has an inverse linear relationship with body weight in mechanically ventilated dogs. The derived values of Crs and Rrs may be used for monitoring of lung function and ventilation in healthy dogs under anaesthesia.

Evaluation of variables to describe the shape of volumetric capnography curves during bronchoconstriction in dogs

The aim of the study was to investigate changes in volumetric capnography (V(C)) variables during bronchoconstriction in dogs and compare it with total respiratory resistance (R(L)) measured with a Fleisch pneumotachograph. Six dogs were challenged with increasing concentrations of carbachol until obvious signs of bronchoconstriction were seen. All V(C) parameters were obtained before, directly after, 10 and 20 min after maximal bronchoconstriction. The slope of phase III (SIII) and airway and alveolar dead space parameters were significantly different from baseline directly after the challenge. The V(C) curve obtained a typical shape at the time of maximal bronchoconstriction and a trend to return to baseline shape was seen over time. A significant correlation was found for all aforementioned parameters with R(L). We conclude that the shape of the V(C) curve in combination with dead space calculation can be used to verify bronchoconstriction on a breath-to-breath basis.

Influence of the collection and oxygenation method on quantitative bacterial composition in bronchoalveolar lavage fluid samples from healthy dogs

The purpose of the study was to evaluate the effects on quantitative and qualitative microbial content of endoscopic bronchoalveolar lavage fluid (BALF) in healthy dogs using a laryngeal mask airway (LMA). It was hypothesised that oropharyngeal protection might prevent contamination of BALF with oropharyngeal microflora. Ten healthy Beagle dogs were randomly assigned to two groups and underwent endoscopic BAL on two occasions, either via an open unprotected oropharynx with oxygen supply provided via a nasal catheter (NT) or through a sterile LMA. For the second sampling, groups were switched. BALF analysis included quantitative microbial culture, nucleated cell counts and cytology. The mean (+/-SD) number of colony forming units (CFU)/mL found in the BALF using the LMA was 25,610+/-22,943 in the right lung (RL) and 22,510+/-18,779 in the left (LL). With the NT technique, the figures were 21,068+/-19,375 for the RL and 16,060+/-15,523 for the LL, respectively. Nucleated cell counts/microL were 691.0+/-181.6 (RL) and 734.0+/-171.6 (LL) for LMA, and 772.0+/-251.0 (RL) and 748+/-163.2 (LL) for NT. No significant differences were detected either in the number of CFU/mL or in the diversity of bacterial species with the two methods. A significant increase in BALF bacterial counts (with reduced species diversity) was observed on the second compared to the first sampling regardless of the method used. Protection of the oral cavity and oropharynx using an LMA had no significant influence on BALF bacterial counts. The findings suggest that with careful endoscope insertion, the risk of contamination of BALF by resident and transient oropharyngeal microflora can be negligible.