Cynthia M. Trim

Complications associated with anaesthesia for ocular surgery: a retrospective study 1989–1996

This retrospective study was initiated to identify complications of anaesthesia occurring during ocular surgery. Records of 74 horses anaesthetised for eye enucleation, 65 horses anaesthetised for surgery of the eye and adnexa, and 51 horses anaesthetised for splint bone excision were reviewed. Fifty-three percent of the horses anaesthetised for eye enucleation moved during surgery which was significantly more frequent than in the other groups (P = 0.001). The incidence of moving was significantly reduced by use of an anaesthetic gas analyser for monitoring (P = 0.001). Transient hypertension was measured in 6 horses during removal of the eye. One horse experienced a momentary decrease in heart rate from 36 to 26 beats/min at the start of surgery involving a mass on the third eyelid. The incidence of unsatisfactory recovery from anaesthesia involving multiple attempts to stand was significantly greater after ocular surgery than after splint bone excision (P = 0.036). Our conclusions were 1) the oculocardiac reflex was not active in these horses undergoing ocular surgery, 2) increased attention must be paid to provision of analgesia and adequate depth of anaesthesia, which may be facilitated by use of an anaesthetic gas analyser and 3) horses were at greater risk for unsatisfactory recoveries from anaesthesia after ocular surgery.

Effects of an infusion of dopamine on the cardiopulmonary effects of Escherichia coli endotoxin in anaesthetised horses

Horses with colic may be endotoxaemic and subsequently develop hypotension during anaesthesia for surgical operation. The aim of this study was to evaluate the efficacy of dopamine as a means to improve cardiovascular function in anaesthetised endotoxaemic horses. Nine horses (five in group 1 and four in group 2) were anaesthetised with thiopentone and guaifenesin and anaesthesia was maintained with halothane. After approximately one hour, facial artery pressure, heart rate, pulmonary artery pressure, cardiac output, temperature, pHa, PaCO2, PaO2, base excess, packed cell volume, plasma protein concentration and white cell count were measured (time 0). Escherichia coli endotoxin was infused intravenously over 15 minutes in both groups. Group 2 horses were given an intravenous infusion of dopamine (5 micrograms kg-1 min-1) starting five minutes after the start of the endotoxin infusion and continuing for 60 minutes. Measurements were made at 15 minute intervals for 120 minutes. In group 1, one horse died during the endotoxin infusion and in two other horses mean facial artery pressures decreased to 50 mm Hg. Total pulmonary vascular resistance and packed cell volume were significantly increased. Cardiac output, cardiac index and change in mean arterial pressure were significantly greater in group 2 horses than in group 1 horses. Conversely, diastolic pulmonary artery pressure, total vascular resistance and total pulmonary resistance were significantly less in group 2 than in group 1. PaO2, base excess and white blood cell count were significantly decreased in both groups. It was concluded that dopamine improved cardiovascular function in the presence of endotoxaemia and attenuated the rate of haemoconcentration, but had no effect on the development of decreased PaO2 or metabolic acidosis.

Postanesthetic hemorrhagic myelopathy or myelomalacia.

Hemorrhagic myelopathy or myelomalacia is an uncommon cause of failure to stand after general anesthesia. Affected horses are usually young and have been anesthetized for relatively short times in dorsal recumbency. Clinical signs involve the hind limbs and include loss of deep pain perception. Etiology of this condition is not known. Differentiation from other forms of neuropathy and myopathy is important to the prognosis.

Evaluation of an oscillometric blood pressure monitor for use in anesthetized sheep

OBJECTIVE To determine the accuracy of an oscillometric blood pressure monitor in anesthetized sheep. STUDY DESIGN Prospective study. ANIMALS Twenty healthy adult sheep, 11 males and nine females, weighing 63.6 ± 8.6 kg. METHODS After premedication with buprenorphine or transdermal fentanyl, anesthesia was induced with ketamine-midazolam and maintained with isoflurane and ketamine, 1.2 mg kg(-1) hour(-1), ± lidocaine, 3 mg kg(-1) hour(-1). Invasive blood pressure measurements were obtained from an auricular arterial catheter and noninvasive measurements were from a cuff on the metatarsus or antebrachium. Simultaneous invasive and noninvasive measurements were recorded over a range (55-111 mmHg) of mean arterial pressures (MAP). Isoflurane concentration was increased to decrease MAP and decreasing the isoflurane concentration and infusing dobutamine achieved higher pressures. Invasive and noninvasive measurements were compared. RESULTS Correlation (R(2)) was good between the two methods of measurement (average of three consecutive readings) for systolic (SAP) (0.87), diastolic (DAP) (0.86), and mean (0.90) arterial pressures (p < 0.001). Bias ± SD between noninvasive and invasive measurements for SAP was 3 ± 8 mmHg, for DAP was -10 ± 7 mmHg, and MAP was -7 ± 6 mmHg. There was no significant difference between the average of three measurements and use of the first measurement. Correlations using the first measurement were SAP (0.82), DAP (0.84), and MAP (0.89). Bias ± SD for SAP was 3 ±10 mmHg, for DAP was -11 ± 7 mmHg, and MAP was -7 ± 6 mmHg. The oscillometric monitor slightly overestimated SAP and underestimated DAP and MAP for both average values and the first reading. CONCLUSIONS AND CLINICAL RELEVANCE This oscillometric model provided MAP measurements that were acceptable by ACVIM standards. MAP measurements with this monitor were lower than those found with the invasive technique so a clinical diagnosis of hypotension may be made in sheep that are not hypotensive.

Anesthetic agents and complications in Vietnamese potbellied pigs: 27 cases (1999–2006)

OBJECTIVE To document complications associated with preanesthetic and anesthetic agents used in Vietnamese potbellied pigs and identify predictors of complications. DESIGN Retrospective case series. ANIMALS 27 potbellied pigs (14 female and 13 male) ranging in age from 0.25 to 15 years old and ranging in body weight from 5.9 to 169 kg (13.0 to 371.8 lb) that were anesthetized on 32 occasions between 1999 and 2006. PROCEDURES Data, including perianesthetic management, anesthetic agents and dosages, complications, and outcome, were retrieved from medical records. Patient information, anesthetic agents, and duration of anesthesia were evaluated as predictors for development of complications. RESULTS Anesthesia was maintained with isoflurane or sevoflurane during 30 anesthetic episodes. Commonly used premedicants were butorphanol, atropine, and midazolam administered in combination with xylazine or medetomidine and a combination of tiletamine-zolazepam and butorphanol. Anesthesia was induced with an inhalation agent on 15 occasions, via injection of ketamine on 10 occasions, and via injection of propofol on 3 occasions. Complications included hypoventilation (16/24 [67%]), hypotension (16/25 [64%]), hypothermia (15/31 [48%]), bradycardia (9/32 [28%]), and prolonged recovery time (7/32 [22%]). None of the factors evaluated were associated with development of these complications. All pigs survived anesthesia. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that a variety of anesthetic agent combinations can be used to provide anesthesia in potbellied pigs with satisfactory outcomes. Although there were high incidences of hypoventilation, hypotension, and hypothermia, no specific anesthetic agent was associated with development of these complications.

A survey of the use of arterial catheters in anesthetized dogs and cats: 267 cases

OBJECTIVES To describe the clinical practice of insertion of arterial catheters in anesthetized dogs and cats, to document complications of arterial catheterization, and to determine risk factors associated with the complications. DESIGN Prospective clinical study and retrospective evaluation of medical records. SETTING University teaching hospital. ANIMALS Dogs (n = 251) and 13 cats anesthetized for clinical procedures with arterial catheters inserted for blood pressure monitoring. INTERVENTIONS None. MEASUREMENTS AND MAIN RESULTS Details of the animal and catheter were collected at the time of anesthesia. On the following day, the catheter site was palpated and observed for abnormalities and the medical records of all animals were reviewed retrospectively for complications. Details of catheter placement were available for 216 catheters: 158 catheters in a dorsal pedal artery, 50 catheters in the median caudal (coccygeal) artery, 6 in the median artery, and 1 each in a cranial tibial and lingual artery. Blood pressure was obtained from 200 catheters, and 12 catheters failed before the end of anesthesia. Postoperative observational data obtained from 112 catheters described a palpable arterial pulse at 73 sites and no pulse at 21 sites. No risk factor for arterial occlusion was identified. No complications resulting from arterial catheterization were noted in the medical records. CONCLUSIONS Arterial catheterization resulted in loss of a peripheral pulse postoperatively in 21/94 (22.3%) of animals examined, although no evidence of tissue ischemia was noted in the medical records of any of the patients in this study. These results suggest that insertion of a catheter in the dorsal pedal or coccygeal arteries was not associated with a high risk for complications. However, the course of arterial occlusion postoperatively warrants further investigation.Objectives To describe the clinical practice of insertion of arterial catheters in anesthetized dogs and cats, to document complications of arterial catheterization, and to determine risk factors associated with the complications. Design Prospective clinical study and retrospective evaluation of medical records. Setting University teaching hospital. Animals Dogs (n = 251) and 13 cats anesthetized for clinical procedures with arterial catheters inserted for blood pressure monitoring. Interventions None. Measurements and Main Results Details of the animal and catheter were collected at the time of anesthesia. On the following day, the catheter site was palpated and observed for abnormalities and the medical records of all animals were reviewed retrospectively for complications. Details of catheter placement were available for 216 catheters: 158 catheters in a dorsal pedal artery, 50 catheters in the median caudal (coccygeal) artery, 6 in the median artery, and 1 each in a cranial tibial and lingual artery. Blood pressure was obtained from 200 catheters, and 12 catheters failed before the end of anesthesia. Postoperative observational data obtained from 112 catheters described a palpable arterial pulse at 73 sites and no pulse at 21 sites. No risk factor for arterial occlusion was identified. No complications resulting from arterial catheterization were noted in the medical records. Conclusions Arterial catheterization resulted in loss of a peripheral pulse postoperatively in 21/94 (22.3%) of animals examined, although no evidence of tissue ischemia was noted in the medical records of any of the patients in this study. These results suggest that insertion of a catheter in the dorsal pedal or coccygeal arteries was not associated with a high risk for complications. However, the course of arterial occlusion postoperatively warrants further investigation.