Gastro-oesophageal reflux in halothane anaesthetized sheep. The effects of feeding and positioning

Effect of the reverse Trendelenburg position on the incidence of gastroesophageal reflux in dogs anesthetized for elective stifle surgery

OBJECTIVE

To determine if a 15° reverse Trendelenburg position decreases the incidence of gastroesophageal reflux (GER) compared with a horizontal position in dogs anesthetized for stifle surgery.

STUDY DESIGN

Prospective, randomized parallel-arm study.

ANIMALS

A total of 44 healthy client-owned dogs were enrolled and data from 36 dogs were analyzed.

METHODS

Dogs requiring preoperative radiographs under anesthesia, or with a history of gastrointestinal signs or administered gastroprotectant therapy within 1 month of surgery were excluded. Anesthesia protocol was standardized to include hydromorphone, dexmedetomidine, ketamine, propofol and isoflurane. Dogs were randomly assigned at enrollment to be positioned in a 15° reverse Trendelenburg or a horizontal position for surgery. Continuous pH monitoring was documented throughout the procedure with a 6.4 Fr (2.13 mm) esophageal pH probe positioned in the distal esophagus via the oral cavity. GER was defined as pH < 4.0 (acidic) or > 7.5 (alkaline) for more than 30 seconds. The proportions of dogs developing GER were compared between groups using Fisher's exact test. Time to reflux was compared using survival curves and the Gehan-Breslow-Wilcoxon test. Statistical significance was set as p < 0.05.

RESULTS

An episode of GER occurred in 11/36 (30%) dogs. Reflux was alkaline in two dogs and acidic in nine dogs. The proportion of dogs with GER was 5/18 (28%) and 6/18 (33%) for dogs in the reverse Trendelenburg position and horizontal position, respectively, and was not statistically significant (p > 0.99). Median (range) time until reflux was 44 (23-135) and 44.5 (9-56) minutes when dogs were positioned in reverse Trendelenburg position and horizontal position, respectively (p = 0.66; two-tailed Mann-Whitney U test).

CONCLUSIONS AND CLINICAL RELEVANCE

Positioning the surgery table in a 15° rostral elevation for dogs anesthetized for elective stifle surgical procedures did not decrease the incidence of GER.

Endotracheal tube obstruction with a blood clot following aspiration of rumen contents in a reindeer

Summary

An apparently otherwise healthy female reindeer was anaesthetised for open reduction and fixation of a hip luxation. The animal developed ruminal bloat which was treated with passage of an orogastric tube that was left indwelling during the procedure. A fluid inspiratory noise was audible two hours after decompression, and clear fluid was suctioned from the airway. It showed no other signs of regurgitation and aspiration of rumen contents intraoperatively, and did not develop obvious respiratory compromise while mechanically ventilated. In recovery, the deer became apnoeic and cyanotic and died suddenly within minutes of being positioned in the recovery box. Just before dying, it coughed a large blood clot out of the endotracheal tube (ETT) . Additional clots were found partially obstructing the ETT lumen once extubated postmortem. Evidence of aspiration was detected at postmortem examination, which also identified pulmonary haemorrhage.

Management and emergency intervention during anesthesia

Proper management and monitoring during anesthesia minimizes the need for emergency intervention. Monitoring of circulation, ventilation, and oxygenation allows for early recognition of problems such as airway obstruction, hypotension, acid-base disturbances, or cardiac arrest, and is discussed. Appropriate therapies are instituted early for best success and are described in this article.

Anesthesia techniques in sheep and goats

A variety of techniques can be used to anesthetize and restrain sheep and goats safely and humanely both in the clinic and in the field. The use of inhalational, injectable, and local anesthetic agents is discussed. Nontraditional agents (opioids and alpha-2 adrenergic agonists) for epidural analgesia also are reviewed because of their promising clinical application.

Motility of the oesophagus and gastro-oesophageal junction during halothane anaesthesia in sheep

Electromanometry and electromyography were used to study gastro-oesophageal motility in two planes of halothane anaesthesia in sheep. Gastro-oesophageal motility when present was greater in light than in deep anaesthesia. The caudal thoracic oesophagus contracted more frequently and for longer than the rostral thoracic oesophagus. In light anaesthesia oesophageal movements were peristaltic in direction with a propagation velocity of 26-29 cm sec-1. Rumen pressures increased throughout anaesthesia and the rate of increase was greatest when the plane of anaesthesia was deep at the start. Gastro-oesophageal reflux (GOR) occurred in both planes of anaesthesia and must occur by passive mechanisms during deep anaesthesia because gastro-oesophageal motility was inhibited. A high pressure zone (HPZ) was demonstrated for a length of 2.9 cm at the gastro-oesophageal junction with a balloon-tipped catheter and a 'pull through' technique. Open-tipped catheters could detect the HPZ but were less sensitive. The pressure in the HPZ was not significantly influenced by the depth of anaesthesia used. In 80% of cases of light anaesthesia an increase in HPZ pressure preceeded the contraction of the cranial sac of the rumen. In deep anaesthesia the HPZ continued to have rhythmic changes in tone. Spontaneous GOR coincided with a maximum gastro-oesophageal pressure gradient in 24% of cases. Rumen insufflation with oxygen provoked GOR at a rumen pressure above 33 mmHg compared with 7.2 mmHg during spontaneous reflux. The study demonstrates that a gastro-oesophageal pressure gradient was not primarily responsible for the initiation of GOR during anaesthesia and that the HPZ at the gastro-oesophageal junction of sheep had some of the properties of a lower oesophageal sphincter and played an important role in the initiation of GOR during anaesthesia.