Thermography as an early predictive measurement for evaluating epidural and femoral-sciatic block success in dogs.

OBJECTIVE: To evaluate skin temperature increase as an early predictive measure for evaluating epidural and femoral-sciatic block success in dogs. STUDY DESIGN: Prospective clinical trial. ANIMALS: A total of 29 dogs undergoing orthopaedic surgery on one hindlimb. METHODS: Dogs were anaesthetized and placed into lateral recumbency with the affected limb uppermost and the coat was clipped. Baseline infrared thermographic images (T0) of the affected limb, of the paw pad of the affected leg and of the ipsilateral paw pad were taken. Subsequently, dogs were administered either an epidural (EPI; n=11) or a femoral-sciatic block (FS; n=18) using bupivacaine 1 mg kg-1. Then, 2 minutes after placement of the block, thermographic images were obtained every 3 minutes for a total of four measurements (T1-T4) and surgery was commenced. Rescue analgesia consisting of fentanyl 1 µg kg-1 was administered if needed. A regional block was considered successful if the dose of fentanyl administered was less than the lower 95% confidence interval of the geometric mean of the total fentanyl used in each group. A ≥ 1 °C increase of skin temperature was considered as the minimum increase required for detection of a successful block. RESULTS: A total of 12 out of 18 blocks in the FS and eight of 11 in the EPI group were considered successful based on fentanyl consumption. Out of these, only four of 12 in the FS and one of eight in the EPI group developed an increase in temperature of ≥ 1 °C. Contrarily, four of six of the nonsuccessful cases in the FS and three of three in the EPI group developed an increase in temperature of ≥ 1 °C. CONCLUSIONS AND CLINICAL RELEVANCE: Contrary to reports in humans, thermography did not indicate regional block success prior to surgery in dogs. However further studies under more controlled conditions are needed to determine whether thermography can be used to indicate failure of regional blockade.

Electrocardiographic indicators of excitability in horses for predicting recovery quality after general anaesthesia.

OBJECTIVE: To determine whether preoperative electrocardiographic measurements linked to sympathetic nervous activity could be used to predict recovery quality after general anaesthesia in horses. STUDY DESIGN: Prospective, clinical study. ANIMALS: Eighteen adult client-owned horses. METHODS: The electrocardiogram (ECG) was recorded presurgery in horses under three standard conditions: stabled unattended; with a groom whilst being led along a standard course; alone in the induction box. After surgery, each animal's recovery quality was scored by eight experienced anaesthetists or technicians using Donaldson's scoring system (2000). The digitized ECG recordings were analyzed for T-wave morphology, mean heart rate (HR), HR variability (HRV) and HRV derivatives including mean R-R interval, standard deviation of normal intervals (SDNN) and the root mean square of successive intervals (RMSSD), low (LF) and high frequency (HF) activity and the LF/HF ratio in both fast Fourier transformed and autoregressive spectra. Correlations between ECG variables and recovery score were examined using Spearman's rank correlation. RESULTS: There was no significant correlation between preanaesthetic ECG measurements and recovery quality. CONCLUSIONS: Predictions of recovery quality after general anaesthesia in horses cannot be based on preanaesthetic ECG variables. CLINICAL RELEVANCE: Measures other than those based on the ECG should be investigated as predictors of recovery quality.

Real-time three-dimensional echocardiography for left atrial volume assessment in Thoroughbred racehorses: Observer variability and comparison with two-dimensional echocardiography.

BACKGROUND: Left atrial size predicts cardiac morbidity and mortality in humans and dogs. Real-time three-dimensional echocardiography (3DE) may be reliable for assessing left atrial volume (LAV) in horses. OBJECTIVES: To determine intra- and interobserver variability estimates of 3DE-LAV and compare it to that of 2DE-LAV estimates. STUDY DESIGN: Method comparison. METHODS: 3DE datasets were obtained from 40 horses, then graded for quality, creating a final study population of 22 horses. The 3DE and 2DE maximum LAV (LAVmax ) and minimum LAV (LAVmin ) were measured, and left atrial emptying volume (LA EV) and left atrial ejection fraction (LA EF) were calculated, from the same 3D dataset on four occasions using (a) a semi-automatic surface recognition algorithm and (b) a modified Simpson's method of discs. 3DE LAV measurements were repeated by a second observer. RESULTS: For 3DE, median LAVmax was 596cm3 for observer one, and 852 cm3 for observer two, LAVmin was 373 cm3 for observer one and 533 cm3 for observer two. Low intraobserver measurement variation was observed for LAVmax and LAVmin , with horse-level intraclass correlation coefficients (ICChorse ) for both observers between 76% and 85% (horse added as random effect). The interobserver ICC was 58% for LAVmax and 50% for LAVmin on averaged measurements (with observer added as random effect), indicating consistent differences between observers. While intraobserver variation was similar for 2DE LAVmax measurements, it was greater for LAVmin (ICChorse  = 67%). The intermethod ICC for 3DE vs 2DE was low at 14% for LAVmax and ~0% for LAVmin , indicating less-consistent differences with method. MAIN LIMITATIONS: Small study population, low observer number, use of different imaging modalities (fundamental frequency and octave harmonics). CONCLUSIONS: 3DE assessment of LAV was reliable, suggesting suitability for longitudinal evaluation of clinical cases. Clinicians should be aware of differences in LAV measurements between observers. More defined measurement guidelines may improve repeatability.

The bispectral index during recovery from halothane and sevoflurane anaesthesia in horses.

OBJECTIVE: To record the bispectral index (BIS) when horses moved during either halothane or sevoflurane anaesthesia and when they made volitional movements during recovery from these anaesthetics. STUDY DESIGN: Randomized prospective clinical study. ANIMALS: Twenty-five client-owned horses undergoing surgery aged 8.8 (+/- 5.3; 1-19) years (mean +/- SD; range). METHODS: Baseline BIS values were recorded before pre-anaesthetic medication (BIS(B)) and during anaesthesia (BIS(A)) maintained with halothane (group H; n = 12) or sevoflurane (group S; n =13) at approximately 0.8-0.9 x minimum alveolar concentrations (MAC). Bispectral indices were recorded during the surgery when unexpected movement occurred (BIS(MA)), during recovery when the first movement convincingly associated with consciousness was observed (BIS(M1)) and once sternal recumbency was achieved (BIS(ST)). RESULTS: No significant difference in BIS(M1) was found between halothane- (85 +/- 7; 75-93) and sevoflurane- (87 +/- 10; 70-98) anaesthetized horses although BIS(A) was significantly (p = 0.0002) lower in group S (62 +/- 7; 53-72) than group H (74 +/- 7; 60-84). Differences between BIS(M1) and BIS(A) were significant in sevoflurane (p = 0.00001) and halothane recipients (p = 0.002) but were greater in group S (25 +/- 9; 4-38) compared with group H (12 +/- 10; -9-25). In six of eight horses, BIS(MA) values ranged between those recorded during anaesthesia and at first movement. CONCLUSIONS AND CLINICAL RELEVANCE: Bispectral indices appear to approximate levels of unconsciousness, suggesting that monitoring the BIS may assist equine anaesthesia. However, it does not predict intra-operative movement.

The effects of halothane and isoflurane on cardiovascular function in dorsally recumbent horses undergoing surgery.

OBJECTIVE: To determine the haemodynamic effects of halothane and isoflurane with spontaneous and controlled ventilation in dorsally recumbent horses undergoing elective surgery. STUDY DESIGN: Prospective randomized clinical trial. ANIMALS: Twenty-five adult horses, body mass 487 kg (range: 267-690). METHODS: Horses undergoing elective surgery in dorsal recumbency were randomly assigned to one of four treatment groups, isoflurane (I) or halothane (H) anaesthesia, each with spontaneous (SB) or controlled ventilation (IPPV). Indices of cardiac function and femoral arterial blood flow (ABF) and resistance were measured using transoesophageal and transcutaneous Doppler echocardiography, respectively. Arterial blood pressure was measured directly. RESULTS: Four horses assigned to receive isoflurane and spontaneous ventilation (SBI) required IPPV, leaving only three groups for analysis: SBH, IPPVH and IPPVI. Two horses were excluded from the halothane groups because dobutamine was infused to maintain arterial blood pressure. Cardiac index (CI) was significantly greater, and pre-ejection period (PEP) shorter, during isoflurane compared with halothane anaesthesia with both spontaneous (p = 0.04, p = 0.0006, respectively) or controlled ventilation (p = 0.04, p = 0.008, respectively). There was an association between CI and PaCO(2) (p = 0.04) such that CI increased by 0.45 L minute(-1)m(-2) for every kPa increase in PaCO(2). Femoral ABF was only significantly higher during isoflurane compared with halothane anaesthesia during IPPV (p = 0.0006). There was a significant temporal decrease in CI, but not femoral arterial flow. CONCLUSION: The previously reported superior cardiovascular function during isoflurane compared with halothane anaesthesia was maintained in horses undergoing surgery. However, in these clinical subjects, a progressive decrease in CI, which was independent of ventilatory mode, was observed with both anaesthetic agents. CLINICAL RELEVANCE: Cardiovascular function may deteriorate progressively in horses anaesthetized for brief (<2 hours) surgical procedures in dorsal recumbency. Although cardiovascular function is superior with isoflurane in dorsally recumbent horses, the need for IPPV may be greater.

The risk of death: the confidential enquiry into perioperative small animal fatalities.

OBJECTIVE: To estimate the risks of anaesthetic and sedation-related mortality in companion animals in the UK. (The Confidential Enquiry into Perioperative Small Animal Fatalities, CEPSAF). STUDY DESIGN: A prospective cohort study with nested case-control study. ANIMAL POPULATION: All small animals anaesthetized and sedated at participating centres between June 2002 and June 2004. METHODS: Patient outcomes at 48 hours (alive, dead and killed) were recorded. Anaesthetic and sedation-related death was defined as death where surgical or pre-existing medical causes did not solely cause death. Species-specific risks of anaesthetic-related death and 95% confidence intervals (95% CI) were calculated. Risks were also estimated in the sub-sets of dogs, cats and rabbits that were either healthy or sick (ASA 1-2 and 3-5, respectively). RESULTS: One hundred and seventeen veterinary practices participated in the study and 98 036 dogs, 79 178 cats and 8209 rabbits were anaesthetized and sedated. Overall risks of anaesthetic and sedation-related death in dogs were 0.17% (1 in 601, 95% CI 0.14-0.19%), in cats 0.24% (1 in 419, 95% CI 0.20-0.27%) and in rabbits 1.39% (1 in 72, 95% CI 1.14-1.64%) within 48 hours of the procedure. In healthy dogs, cats and rabbits, the risks were estimated to be 0.05% (1 in 1849, 95% CI 0.04-0.07%), 0.11%, (1 in 895, 95% CI 0.09-0.14%) and 0.73% (1 in 137, 95% CI 0.54-0.93%), respectively. In sick dogs, cats and rabbits, the risks were 1.33%, (1 in 75, 95% CI 1.07-1.60%), 1.40% (1 in 71, 95% CI 1.12-1.68%) and 7.37% (1 in 14, 95% CI 5.20-9.54%), respectively. Postoperative deaths accounted for 47% of deaths in dogs, 61% in cats and 64% in rabbits. Most other small animal species had higher mortality risks. CONCLUSIONS AND CLINICAL RELEVANCE: Small animal anaesthesia appears to be increasingly safe. Greater patient care in the postoperative period could reduce fatalities.

The effects of morphine on the recovery of horses from halothane anaesthesia.

OBJECTIVE: To investigate the effects of peri-operative morphine on the quality and duration of recovery from halothane anaesthesia in horses. STUDY DESIGN: Prospective randomized study. ANIMALS: Twenty-two client owned horses, ASA category I or II. METHODS: Horses undergoing elective surgical procedures were divided into two groups and paired according to procedure, body position during surgery, body mass and breed. Group M+ received morphine by intravenous injection (0.15 mg kg(-1)) before induction of anaesthesia and then by infusion (0.1 mg kg(-1) hour(-1)) during anaesthesia. Group M- received the same anaesthetic agents except that morphine was excluded. At the end of surgery, the horses were placed in a recovery box and allowed to recover without assistance. Recoveries were recorded on videotape, beginning when the anaesthetist left the recovery box, and ending when the horse stood up. Recoveries were assessed from digital video recordings by three observers, unaware of treatment. The time to first movement, attempting and attaining sternal recumbency and standing were recorded. The quality of various aspects of the recovery was assessed to produce a total recovery score; high numerical values indicate poor recoveries. The duration of anaesthesia and the total dose of morphine administered were recorded. RESULTS: The mean morphine dose (95% CI) was 147 (135-160) mg [equivalent to 0.27 (0.25-0.29) mg kg(-1)]. The recovery scores (median, 95% CI) for the M- and M+ groups were 25, 19-41 and 20, 14-26, respectively. Total score increased as duration of anaesthesia increased, independent of treatment. Untreated (M-) horses made more attempts to achieve sternal recumbency: mean number of attempts (95% CI) for M- was 4.5 (2.7-6.2) compared with 2.0 (1.4-2.6) (M+). Untreated horses made more attempts to stand (2.1, 1.6-2.6) compared with the morphine recipients (1.3, 1.1-1.5). Time to standing (in minutes) was significantly (p = 0.0146) longer for the untreated (31.3, 24.3-38.3) compared with treated animals (26.6, 20.9-32.3). The interval between the first movement in recovery to the time at standing was significantly (p < 0.001) longer for M- (14.5, 12.1-16.9 minutes) compared with M+ animals (7.4, 5.0-9.8 minutes). CONCLUSIONS AND CLINICAL RELEVANCE: Recoveries from anaesthesia in the morphine recipients were characterized by fewer attempts to attain sternal recumbency and standing, and a shorter time from the first recovery movement to the time of standing.

Effects of peri-operative morphine administration during halothane anaesthesia in horses.

OBJECTIVE: To study the effects of morphine on haemodynamic variables, blood gas values and the requirement for additional anaesthetic drugs in horses undergoing surgery. STUDY DESIGN: Prospective randomized study. METHODS: Thirty-eight client-owned horses, ASA(American Society of Anesthesiologists) category I or II, undergoing elective surgical procedures, were studied. Horses were divided between two groups, and were paired according to operation, anaesthetist, body position during surgery, mass and breed. Group M+ received morphine by intravenous (IV) injection (0.15 mg kg(-1)) before induction of anaesthesia and then by infusion (0.1 mg kg(-1) hour(-1)) throughout anaesthesia. Group M- received the same anaesthetic technique (pre-anaesthetic medication with romifidine (100 microg kg(-1)) IV; induction with ketamine (2.2 mg kg(-1)) and diazepam (50 microg kg(-1)) IV; maintenance with halothane), except that morphine was excluded. Both groups received flunixin IV (1.1 mg kg(-1)) before surgery. Both groups also received 50% nitrous oxide for the first 10 minutes of anaesthesia. During anaesthesia, end-tidal halothane was maintained at 0.9% (+/-0.1%) in both groups. Heart rate (HR) and respiratory rate (fr), systolic, mean and diastolic arterial pressures were recorded every 5 minutes. Arterial blood samples were analysed every 20 minutes. Additional anaesthetics (ketamine and midazolam) were administered whenever the horse moved. Dobutamine was infused to maintain mean arterial pressure (MAP) > 58 mm Hg, but was discontinued when MAP reached 68 mm Hg. Mechanical ventilation was imposed when PaCO(2) exceeded 9.3 kPa (70 mm Hg). RESULTS: Haemodynamic data (HR and MAP) and blood gas measurements were analysed using repeated measure analysis using a mixed covariance pattern model (SAS version 8.2). A Student's t-test was used to investigate differences between groups in the doses of additional anaesthetics required. There were no significant differences between M+ or M- groups in MAP (p = 0.65), HR (p = 0.74), PaO2 (p = 0.40) or PaCO2 (p = 0.20). Fewer horses in the M+ group received additional anaesthetics (15.8% compared to 21.1% in M- group), and the mean dose of ketamine required was higher in the M- group (mean +/- SD: M-, 0.93 +/- 0.70; M+, 0.45 +/- 0.17). These differences were not statistically significant (p = 0.28). CONCLUSIONS: Pre-anaesthetic and peri-operative morphine administration is not associated with significant haemodynamic or ventilatory changes. Horses receiving morphine tended to receive fewer and lower doses of additional anaesthetic drugs, although this was not statistically significant.

Problems associated with perioperative morphine in horses: a retrospective case analysis.

OBJECTIVE: To identify the incidence of adverse effects caused by morphine 100-170 micro g kg-1 administration during surgery in horses. DESIGN: Retrospective case record analysis (1996-2000). ANIMALS: Eighty-four healthy (ASA 1 or 2) horses, mean age 5.5 +/- 3.1 (SD) years (2 months to 16 years), mean weight 524 +/- 14 kg (100-950). METHODS: Physiological data and evidence of complications were collected from the anaesthetic records of all animals anaesthetized with romifidine, ketamine, diazepam and halothane and undergoing laryngeal surgery or orchiectomy at the Royal (Dick) School of Veterinary Studies. Cases were divided into those receiving (group M+; n = 18) and those not receiving morphine (M-; n = 29), and the data compared. Values for heart and respiratory rate and mean arterial pressure were compared at 15-minute intervals between 30 and 120 minutes after induction using anova for repeated measures. The incidence of intraoperative problems was compared using Fisher's exact test. Recovery scores were compared using Student's unpaired t-test. The records of a further 37 horses undergoing umbilical herniorrhaphy (n = 5), arthroscopy (n = 29) or tarsal arthrodesis (n = 3) were also studied but not analysed statistically due to disparate treatment distribution. RESULTS: There were no significant differences between the M+ and M- groups. The incidence of post-operative complications such as box-walking and colic were similar in each group. CONCLUSIONS: Morphine doses of 100-170 micro g kg-1 do not increase the risk of problems when used to provide perioperative analgesia in horses anaesthetized with romifidine, ketamine, diazepam and halothane. CLINICAL RELEVANCE: Morphine provides an acceptable and relatively inexpensive way to provide perioperative analgesia in horses.