Measurement of cardiac output by transoesophageal Doppler echocardiography in anaesthetized horses: comparison with thermodilution

In order to determine if transoesophageal Doppler echocardiography could be used to estimate cardiac output in anaesthetized horses, we have compared the technique with estimations of cardiac output by thermodilution in eight healthy adult thoroughbreds. Measurements of aortic blood flow velocity were made by high pulse repetition frequency (HPRF) and continuous wave (CW) Doppler echocardiography from a 3.5-MHz transoesophageal probe. Cardiac output was increased during the study by administration of dobutamine, providing a range of cardiac output measurements by thermodilution from 15.0 to 64.4 liter min-1. Estimations derived from CW Doppler overestimated cardiac output compared with thermodilution (bias = 4.0 litre min-1). Estimations from HPRF Doppler echocardiography more closely reflected measurements obtained by thermodilution (bias = 0.7 litre min-1). Limits of agreement between the techniques were similar for both modes of insonation (HPRF = -7.7 to 9.1 litre min-1, CW = -4.9 to 12.8 litre min-1). There were significant differences in bias between both Doppler techniques and thermodilution for individual horses. As a result, for any individual horse, limits of agreement between the techniques were closer (HPRF = +/- 6.4 litre min-1, CW = +/- 7.6 litre min-1). We conclude that transoesophageal echocardiography provided an alternative, effective and non-invasive method for measurement of cardiac output in anaesthetized horses.

Experimental evaluation of the Spiegelberg intracranial pressure and intracranial compliance monitor. Technical note

The goal of this study was to compare the Spiegelberg intraventricular intracranial pressure (ICP)/intracranial compliance monitoring device, which features an air-pouch balloon catheter, with existing gold-standard methods of measuring ICP and intracranial compliance. A Spiegelberg intraventricular catheter, a standard intraventricular catheter, and a Codman intraparenchymal ICP microsensor were placed in five sheep, which previously had been given anesthetic and paralytic agents, to allow comparative measurement of ICP at incremental levels (range 5-50 mm Hg). Intracranial pressure measured using the Spiegelberg intraventricular air-pouch balloon catheter displayed a linear correlation with ICP measured using the standard intraventricular fluid-filled catheter (r2 = 0.9846, p < 0.001; average bias -0.74 mm Hg), as well as with ICP measured using the Codman intraparenchymal strain-gauge sensor (r2 = 0.9778, p < 0.001; average bias 0.01 mm Hg). Automated measurements of intraventricular compliance obtained using the Spiegelberg compliance device were compared with compliance measurements that were made using the gold-standard manual cerebrospinal fluid bolus injection technique at ICPs ranging from 5 to 50 mm Hg, and a linear correlation was demonstrated between the two methods (r2 = 0.7752, p < 0.001; average bias -0.019 ml/mm Hg). The Spiegelberg air-pouch ICP/compliance monitor provides ICP and compliance data that are very similar to those obtained using both gold-standard methods and an intraparenchymal ICP monitor over a range of pathophysiological ICPs. The automated closed Spiegelberg system offers practical advantages for the measurement of intraventricular compliance. Assessment of the clinical utility and robustness of the Spiegelberg system, together with the development of an intraparenchymal device, would enhance the clinical utility of automated compliance measurement and expand the range of its applications.

Pain management in pigs undergoing experimental surgery; a literature review (2012-4)

Failure to provide effective analgesia to animals in noxious studies contravenes the obligation to refine animal experimentation and, by increasing 'noise' in physiological data sets, may decrease the scientific validity of results. Pig models of surgical conditions are becoming increasingly important and used for translational work. This review aimed to determine the extent to which the recent biomedical literature describes pain assessment and alleviation in pigs recovering from experimental surgery. Three databases (Medline, Web of Knowledge, and Google Scholar) were searched to find relevant studies published from January 2012 to March 2014. Information on pain assessment and peri- and postoperative analgesia was extracted. The review identified 233 papers meeting selection criteria. Most articles (193/233, 83%) described use of drugs with analgesic properties, but only 87/233 (37%) described postoperative analgesia. No article provided justification for the analgesic chosen, despite the lack of guidelines for analgesia in porcine surgical models and the lack of formal studies on this subject. Postoperative pain assessment was reported in only 23/233 (10%) articles. It was found that the reporting of postoperative pain management in the studies was remarkably low, reflecting either under-reporting or under-use. Analgesic description, when given, was frequently too limited to enable reproducibility. Development of a pain-scoring system in pigs, together with the mandatory description of pain management in submitted articles, would contribute to improved laboratory pig welfare.

A comparison of four systems for scoring recovery quality after general anaesthesia in horses

REASON FOR PERFORMING STUDY

The recovery quality scoring systems (RQSSs) in current use have not been critically reviewed for reliability.

OBJECTIVE

To examine reliability (reproducibility) of 4 RQSSs when applied to a ranked series.

METHODS

A DVD incorporating the recordings of 9 horses recovering from general anaesthesia was evaluated by final year students over 5 days. On Day 1, each evaluator ranked recoveries from 1-9 (1 = best). Over the following 4 days, each evaluator scored the same recoveries using 4 different RQSSs (3 of them in common usage and previously published) applied in random order. The scores from each RQSS were ranked and plotted against the Day 1 ranking of each evaluator to establish the extent of agreement using generalisability theory. The same 9 recoveries were also ranked by 12 experienced equine anaesthetists and the Spearman Rank Correlation coefficient calculated to determine the agreement between experienced and inexperienced evaluators.

RESULTS

The recoveries were evaluated by 117 students. All 4 RQSSs were equally reliable with low (<4%) interobserver variability. The main (80%) source of total variation arose from differences between horses. The overall ranking within each RQSS was strongly correlated with Day 1 ranking. There was strong correlation (r = 0.983) between the students' ranking and that established by experienced anaesthetists. Interobserver reliability was similar with all 4 RQSSs.

CONCLUSION

All 4 RQSSs studied were similarly reliable.

POTENTIAL RELEVANCE

The selection of a universally acceptable RQSS from amongst the 4 examined can be based on criteria other than reliability, e.g. ease of use. This will facilitate wider scale multi-centre studies in recovery quality after anaesthesia in horses.

Post anaesthetic colic in horses: a preventable complication?

REASONS FOR PERFORMING STUDY

There is little information on the prevalence of, and risk factors associated with, post anaesthetic colic (PAC) in horses undergoing nonabdominal operations.

OBJECTIVES

To undertake the first prospective study of prevalence of PAC and identify risk factors in its development in nonabdominal procedures.

METHODS

A multicentre prospective case-control study was conducted, on every horse undergoing anaesthesia for a nonabdominal procedure between April 2004 and June 2005. Colic cases were defined as any horse with recognised signs of abdominal pain within 72 h of general anaesthesia that could not be attributed to any concurrent disease. Five control horses per case were selected randomly from the study population at all hospitals. Multivariable logistic regression analysis was used to examine the relationship between predictor variables and the risk of developing PAC.

RESULTS

The estimated mean prevalence of PAC in the study population was 5.2% (95% CI, 2.8, 8.0). However, the prevalence of colic varied between each centre. The most commonly diagnosed cause of colic was impaction. Multivariable analyses showed that the centre involved and the type of surgery performed were associated with an increased risk of PAC. Preoperative food deprivation and the use of opioid drugs were confounding factors.

CONCLUSIONS

Prevalence of PAC varied significantly between the 4 hospitals studied; there may be hospital-related covariates that account for this. The type of surgery performed influenced the risk of PAC.

POTENTIAL RELEVANCE

Identifying the risk factors for PAC is a prerequisite for its prevention. This study indicates horses at increased risk of PAC that might benefit from a more critical evaluation of post anaesthetic gastrointestinal function and/or the provision of preventative measures. Further investigation is required to explain the variation in prevalence of PAC between centres.

Repair of avulsed cervical nerve roots. An experimental study in sheep

An experimental model was established to investigate the possibility of repairing cervical nerve roots avulsed from the spinal cord, as occurs in traction injuries of the brachial plexus. In five sheep the C6 root was avulsed and the ventral root was reattached using freeze-thawed muscle as a short graft (0.5 cm). Recovery was assessed after one year by electrophysiology and histology. Stimulation of the root produced muscle contractions in four out of five sheep. Action potentials were recorded distal to the grafts in all five sheep. Histological examination showed regenerated fibres in the ventral roots in all cases. These fibres could be traced distally to the brachial plexus. Our study confirms that motor fibres can regenerate out of the spinal cord into the ventral roots and reinnervate muscles, and suggests that reimplantation of avulsed roots is a surgical option in selected cases of traction injury of the brachial plexus.

Comparison of three injectable anaesthetic techniques in pigs

Forty-six near-adult pigs (mean age 10 months, mean weight 156 kg) were anaesthetised for laparoscopy. After intramuscular azaperone (1.0 mg/kg) and ketamine (2.5 mg/kg), 14 of the pigs received intravenous etomidate (200 micrograms/kg) and midazolam (100 micrograms/kg) and 17 were given ketamine (2 mg/kg) and midazolam (100 micrograms/kg). The other 15 pigs were anaesthetised with pentobarbitone (15 to 20 mg/kg) without pre-anaesthetic medication. The duration and adequacy of anaesthesia, recovery rate, and seven physiological variables (ECG, heart rate, indirect arterial blood pressure, respiratory rate, minute volume, mean end-tidal carbon dioxide concentration and percentage oxygen saturation of haemoglobin) were compared. Repeated injections were needed in 29 of the 46 cases. Pentobarbitone was the least satisfactory drug because although the haemodynamic variables were greater, it caused more respiratory depression and a higher overall complication rate than the other methods. Apnoea occurred in two pigs, and was fatal in one, and positive pressure ventilation with oxygen was needed in three others. Intubation conditions were poorer and the times to standing, walking and rooting were longer in the pigs anaesthetised with pentobarbitone.

The early response to major trauma and intramedullary nailing

The stress response to trauma is the summation of the physiological response to the injury (the 'first hit') and by the response to any on-going physiological disturbance or subsequent trauma surgery (the 'second hit'). Our animal model was developed in order to allow the study of each of these components of the stress response to major trauma. High-energy, comminuted fracture of the long bones and severe soft-tissue injuries in this model resulted in a significant tropotropic (depressor) cardiovascular response, transcardiac embolism of medullary contents and activation of the coagulation system. Subsequent stabilisation of the fractures using intramedullary nails did not significantly exacerbate any of these responses.

Haemodynamic effects of a sixty minute infusion of dopamine hydrochloride in horses anaesthetised with halothane

To describe the haemodynamic effects of a 60 min infusion of dopamine 4 microg/kg bwt/min during halothane anaesthesia, 7 mature Thoroughbred horses were studied. The infusion began 1 h after induction of anaesthesia by romifidine (100 microg/kg) and ketamine (2.2 mg/kg bwt). Throughout the period of dopamine infusion and for 30 min after its discontinuation, the horses were ventilated by intermittent positive pressure to maintain PaCO2 between 4.6-5.4 KPa. Inspired halothane concentration was adjusted to maintain an end tidal halothane concentration of 0.9%. Haemodynamic variables were measured using intracardiac strain gauge transducers sited in the left and right ventricle, aorta, and pulmonary artery. Left ventricular pressure was differentiated to obtain maximal rate of increase of intraventricular pressure (LVdp/dtmax). Transoesophageal Doppler echocardiography was performed to measure maximum aortic blood flow velocity (vmax) and acceleration (dv/dtmax), left ventricular velocity time integral (vTI) and cardiac output (CO), and left ventricular pre-ejection period (PEP) and ejection time (ET). Measurements were made during the 60 min infusion, and for 30 min after the infusion was discontinued. Infusion of dopamine 4 microg/kg/min significantly decreased mean aortic pressure, while left and right ventricular end-diastolic pressure and mean pulmonary artery pressure remained unchanged. There was a small, but significant, increase in heart rate during dopamine infusion. Maximum acceleration of aortic blood flow, CO and vTI were also significantly increased by dopamine infusion. Maximal rate of increase of intraventricular pressure (LVdp/dtmax) was significantly decreased 10 min after commencing infusion, but then returned to baseline for the remainder of the study. Left ventricular pre-ejection period (PEP) decreased during dopamine infusion whilst ejection time (ET) significantly increased. All measured variables except LVET had returned to baseline values within 30 min of discontinuing the infusion. This study demonstrated beneficial effects of dopamine infusion upon left ventricular systolic function. However, the therapeutic value of the drug is likely to be limited in clinical anaesthesia due to the simultaneous falls in arterial blood pressure which accompany its administration.

Autonomic and cardiovascular effects of neuromuscular blockade antagonism in the dog

Autonomic and cardiovascular changes were studied when neuromuscular blockade was antagonized in 96 dogs with one of eight anticholinesterase-antimuscarinic drug combinations. Neostigmine (50 or 100 micrograms/kg) was administered before or after atropine (40 micrograms/kg) or glycopyrrolate (10 micrograms/kg). The high dose of neostigmine (100 micrograms/kg) caused bradyarrhythmias, salivation, and signs of bronchosecretion when used with either antimuscarinic agent and irrespective of the administration sequence. The heart rate increased, but not significantly, when atropine was injected before either dose of neostigmine. This did not occur when this administration sequence was reversed. Arrhythmias and cardiovascular and autonomic changes did not occur when glycopyrrolate was injected before or after neostigmine at 50 micrograms/kg.

Clinical evaluation of romifidine/ketamine/halothane anaesthesia in horses

Romifidine, 100 micrograms/kg administered by intravenous injection, was evaluated as a premedicant to ketamine/halothane anaesthesia in 60 horses. Sedation developed within one to two minutes. In three cases mild staggering occurred within two minutes. Anaesthesia was induced after five minutes by the intravenous administration of ketamine (2 to 2.2 mg/kg). A mean time of 79 seconds elapsed before lateral recumbency was adopted. Fifty-four of the horses sank smoothly to the floor, with occasional steps sideways. Jaw tone, limb rigidity and mild muscle tremors often persisted for short periods after induction. Complete relaxation was achieved on average two minutes after the administration of ketamine. The transition to oxygen/halothane anaesthesia was excellent or good in 53 cases. The mean duration of anaesthesia was 79 minutes. Forty-seven of the horses were able to stand after one or two attempts with little or no ataxia. After halothane administration ceased, the mean time to sternal recumbency was 25 minutes and the mean time to standing was 33 minutes. Most horses appeared to be sedated upon standing, but they were able to walk soon after regaining their feet. The characteristics of the induction of anaesthesia were similar to those seen when detomidine/ketamine or xylazine/ketamine are used. The maintenance of anaesthesia with halothane was similar to that following other induction protocols, and the recovery from anaesthesia was smooth and free from excitement.

Are neuromuscular blocking agents being misused in laboratory pigs?

The literature (2012-4) describing experimental pig surgery was reviewed to estimate the extent to which neuromuscular block (NMB) is used, to examine methods for ensuring unconsciousness, and to identify the rationale for use of NMB and establish the anaesthetist's training. In the first stage of a two-stage review, NMB use was estimated using Web of Knowledge to identify articles describing NMB during pig surgeries. In the second stage, PubMed and Google Scholar were used to increase the number of articles for determining measures taken to prevent accidental awareness during general anaesthesia (AAGA). The corresponding authors of screened articles were emailed four times to establish the reason for using NMB and the anaesthetists' backgrounds (medical, veterinary, or technical). The first search revealed NMB use in 80 of 411 (20%) studies. Of the 153 articles analysed in the second stage, two described strategies to reduce AAGA. Some (6%) papers did not provide information on anaesthetic doses; citations supporting anaesthetic efficacy were found in only 13. Five of 69 papers using inhalation agents measured end-tidal anaesthetic concentrations based on human, not porcine, minimal alveolar concentrations. The methods in 13% of articles reporting anaesthetic depth assessment were incomplete or questionable, or both; four described using somatic motor reflexes. Corresponding authors of 121 articles reported that the principal reason for NMB was improved 'surgical visualization' (26%). Medical or veterinary anaesthetists supervised anaesthesia in 70% of studies; non-anaesthetists provided NMB, unsupervised, in 23. Nine respondents prioritized experimental expediency over pig welfare. In laboratory pig studies, AAGA may be prevalent; reported details of its attempted prevention are woefully inadequate.

Spontaneous electroencephalographic changes in a castration model as an indicator of nociception: a comparison between donkeys and ponies

REASONS FOR PERFORMING STUDY

Donkeys are believed to be less demonstrative of pain than ponies. Research into comparative sensory processing between these species is required to elucidate these behavioural differences.

OBJECTIVES

To compare changes in the electroencephalogram (EEG) recorded during castration between donkeys and ponies.

STUDY DESIGN

Prospective clinical study.

METHODS

Six ponies and 6 donkeys were castrated under halothane anaesthesia after acepromazine premedication and thiopental anaesthetic induction. Markers were inserted into the EEG recording at the time of skin incision (skin) and emasculation (emasc) for both testicles (T1 and T2) during a closed castration. Raw EEG data were analysed and the EEG variables median frequency (F50 ), total power (Ptot ) and spectral edge frequency (F95 ) derived using standard techniques. Baseline values of F50 , Ptot and F95 for each animal were used to calculate the percentage change from baseline at T1skin, T2skin, T1emasc and T2emasc.

RESULTS

Decreased F50 values relative to baseline were observed in 4 ponies and 2 donkeys across all castration time points. In the remaining animals, the F50 value increased compared with baseline. Both donkey and pony groups showed an overall decrease in Ptot values compared with baseline at T1skin, but the magnitude of the decrease was significantly less (P = 0.004) in ponies than in donkeys. Donkeys demonstrated an overall greater increase (P = 0.05) in F95 values at T1skin relative to baseline compared with ponies.

CONCLUSIONS

Electroencephalographic responses to the noxious stimulus of castration were noted in both donkeys and ponies. Donkeys demonstrated a greater change in Ptot in response to castration than ponies; thus, donkeys appear to demonstrate a cerebral cortical response to a noxious stimulus that is similar to or greater than that in ponies, suggesting that their subtle behavioural expression of pain is not due to a difference in cortical processing of noxious sensory stimuli.

Alpha-chloralose as a capture and restraint agent of birds: therapeutic index determination in the chicken

The median effective dose for capture (ED50) and the median lethal dose (LD50) of alpha-chloralose given orally to domestic chickens (Gallus domesticus) were determined by probit analysis to be 45 mg/kg and 300 mg/kg, respectively. The therapeutic index (TI = LD50/ED50) was 6.7. This indicates that alpha-chloralose is only a marginally safe capture agent in domestic species and particularly in field applications involving other wild avian species in which the amount of the drug ingested by an individual bird is not controlled.

Factors affecting the perception of recovery quality in horses after anaesthesia

REASONS FOR PERFORMING STUDY

A significant effect of gender, experience and background, i.e. an evaluator's relationship with horses as equine anaesthetists, orthopaedic surgeons, practitioners or owners, on perceptions of recovery quality after anaesthesia would reduce the validity of recovery quality scoring systems.

OBJECTIVES

To determine the effects of evaluator background, experience and gender on their perceptions of recovery quality; and questionnaire response rate as a function of background.

STUDY DESIGN

Cross-sectional survey.

METHODS

A total of 440 potential evaluators were invited to evaluate the video-recorded recoveries of 24 horses using a visual analogue scale (VAS) in which 0 = worst, 100 = best possible recovery. A mean score was generated for each of the 1-24 recoveries within each background group. These were compared using Spearman's rank correlation. The effect of gender and experience on VAS scores were analysed using an ordinal logistic regression after scores were categorised into 'intermediate, 'worst' and 'best' recovery categories based on median, 25th and 75th percentile VAS scores, respectively.

RESULTS

The overall response rate was 35%. The greatest was from the anaesthetists (78%) followed by surgeons (43%). The response rate among owners and practitioners was 26%. Correlation among VAS scores across all background groups was high (Spearman rank > 0.90; P < 0.001). Among the combined veterinarians, there was no significant gender (P = 0.551) or experience (P = 0.103) effect. Among horse owners, the effect of experience was not significant (P = 0.116) although gender was (P = 0.027). Male horse owners awarded significantly greater scores than females.

CONCLUSIONS

When VAS are used to grade recovery quality, neither the background nor the gender of veterinary evaluators affects quality perception. Male owners awarded greater scores than female owners, implying that they are less critical of recovery quality and a gender effect among horse owners must be considered when VAS are used to score recovery quality.

Anaesthesia for lambs undergoing spinal surgery: a case series

Six 1-month-old lambs were anaesthetized for cervical spinal cord surgery. Anaesthesia was induced with intravenous midazolam (0.5 mg/kg) then halothane delivered by mask in an O2-N2O mixture. After endotracheal intubation, the lungs were ventilated mechanically and anaesthesia maintained with halothane and nitrous oxide. Buprenorphine and flunixin were given before and after surgery, and the wound margin was infiltrated with 0.5% bupivacaine solution. Neuromuscular block was produced with repeated injections of atracurium; neuromuscular transmission was restored with edrophonium. Lambs made a rapid recovery without obvious signs of discomfort, sedation, or weakness after operations lasting up to 156 min. Anaesthesia was induced in a seventh lamb using etomidate, which probably contributed to death during recovery from anaesthesia.

Translational toxicological research: investigating and preventing acute lung injury in organophosphorus insecticide poisoning

Poisoning through ingestion of organophosphorus (OP) insecticide is a leading cause of suicide globally. Severe poisoning with OP compounds creates an unconscious, paralysed patient with respiratory failure. These symptoms make pulmonary aspiration of stomach contents highly likely, potentially causing an acute lung injury. To explore this hypothesis, we created a Gottingen minipig pulmonary aspiration model (n=26) to investigate the mechanism and severity of lung injury created through pulmonary instillation of 0.5 mL/kg mixtures of porcine gastric juice (GJ), OP and/or its solvent. Early results show that aspiration of OP and GJ causes pulmonary neutrophil sequestration, alveolar haemorrhage and interstitial oedema, with disruption of the alveolar-capillary membrane. Further measurements will include quantitative CT imaging, histopathology scoring, acute lung injury biomarkers and respiratory function. In order to test the validity of the minipig model, a pilot study in Sri Lanka has been devised to observe signs of lung injury in human patients who have ingested OP insecticide with or without clinical evidence of pulmonary aspiration. Lung injury will be assessed with PaO2/FIO2 ratios and physiological dead space measurement. Blood, bronchoalveolar lavage and urine will be taken at 24 and 48 h after poisoning and at 3-4 h in surgical control patients to measure acute lung injury biomarkers. An unpublished toxicology study from Sri Lanka, 2011-2012, showed that over 40% of unconscious poisoned patients with a GCS <9 were not intubated for ambulance transfer between rural and district hospitals. Delay in intubation leads to aspiration pneumonitis and pneumonia in 38%-45% of unconscious poisoned patients. We hypothesise that non-drug assisted placement of supraglottic airways may be a good tool for use in unconscious poisoned patients requiring transfer from small rural hospitals in Asia. They could confer better airway protection than no airway intervention and reduce both morbidity and mortality.

A comparison of two morphine doses on the quality of recovery from general anaesthesia in horses

Previous studies indicated that perioperative morphine improves recovery quality after general anaesthesia in horses. This clinical trial investigated whether this effect was dose-dependant. Twenty-six horses anaesthetised for surgery were block-randomised to receive one of two intraoperative morphine treatments: Treatment M1 consisted of a constant rate infusion (CRI) of morphine at 0.1mg/kg/h, begun after a loading dose (LD) of 0.15 mg/kg. Treatment M2 was a CRI of 0.2mg/kg/h preceded by an LD of 0.3mg/kg. During recovery, times at the first attempt and at achieving sternal recumbency and standing, and the total recovery duration were not different between groups. Total recovery quality score was not significantly different between groups. Scores for the "sternal phase" were higher (of poorer quality) for M2 but scores in both groups were low. Morphine doses of M2, which are greater than those described previously, do not appear to alter or improve the quality or duration of recovery in horses after surgical anaesthesia.