Chapter 33
Anesthetic Considerations for Gastrointestinal Disease
What did that dog eat?
Carrie Schroeder
Department of Surgical Science, School of Veterinary Medicine, University of Wisconsin, USA
- Q. What are the recommendations for fasting of patients prior to anesthesia?
- A. The rationale for pre-operative fasting is to lower the incidence of peri-operative regurgitation and gastroesophageal reflux, thus decreasing the risk of post-anesthetic esophagitis and aspiration pneumonitis or pneumonia. It is generally recommended that food be withheld from adult dogs and cats for 8–12 h prior to surgery while free access to water may be allowed until the time of surgery. Some studies have shown, however, that prolonged fasting may actually increase gastric acidity and gastroesophageal reflux [1,2]. In dogs, the administration of a small meal of canned food 3 h prior to the induction of anesthesia did not significantly increase the volume of gastric contents and actually decreased gastric acidity [2]. This suggests that a very small meal of canned food 3 h prior to anesthetic induction may be of benefit to lower gastric acidity, potentially decreasing the risk of post-anesthetic esophagitis or pneumonitis.
Very young animals (< 12 weeks) should not have food withheld for more than 2 h due to decreased hepatic glycogen stores. Blood glucose should be checked immediately preceding anesthetic induction to verify normoglycemia.
- Q. What are the consequences of gastroesophageal reflux (GER)?
- A. GER reflux may lead to esophagitis, esophageal strictures, and, depending on the severity of reflux, aspiration pneumonitis or pneumonia. Considering that most anesthetic agents decrease the tone of the lower esophageal sphincter, it is not uncommon for patients to have passive or silent GER under anesthesia. Older patients and patients undergoing abdominal surgery have an increased risk of GER as compared to other surgeries, yet patient positioning, surprisingly, has no influence on the incidence of GER [3]. Unfortunately, GER is usually undetectable without the aid of an esophageal pH meter or esphagoscopy. Peri-anesthetic administration of anti-emetics, prokinetics, and antacids are variably effective in preventing GER. The anti-emetic maropitant and the prokinetic metoclopramide were ineffective at reducing GER, while the prokinetic cisapride and proton pump inhibitor omeprazole were both effective in reducing the incidence of peri-anesthetic GER [4–7].
- Q. How do I avoid aspiration pneumonia?
- A. Aspiration of gastric contents does not necessarily cause aspiration pneumonia. The aspiration of regurgitated or refluxed gastric content into the lungs may cause bronchospasm and pneumonitis, which can predispose a patient to bacterial colonization of the lungs and subsequent aspiration pneumonia. The lungs may be damaged by aspiration of greater than 0.3–0.4 ml/kg at a pH less than 2.5 [8]. As discussed previously, GER may be clinically silent and pre-emptive treatments may be ineffective. Prevention of aspiration of gastric contents should be geared towards airway management. It is important to rapidly intubate patients at high risk of GER with a cuffed endotracheal tube and inflate the cuff to properly seal the trachea. The cuff should be generously lubricated prior to insertion of the endotracheal tube to maximize the seal, as the lubricant fills in areas of less than perfect contact between the cuff and the inner wall of the trachea. Prior to extubation, the caudal oropharynx should be suctioned or swabbed if reflux or regurgitated matter are present and the tube should remain in place with the cuff inflated until the patient has regained proper airway reflexes. The nose should be positioned downward so as to allow drainage of regurgitated gastric contents rather than pooling in the caudal oropharynx.
- Q. My patient is obese – how will this affect my anesthetic plan?
- A. There are a number of problems associated with obesity in anesthetic patients. The primary peri-anesthetic concerns involve respiratory compromise, patient positioning, and dosing of anesthetic agents.
- Obesity may lead to rapid desaturation with hypoventilation, as detected by a drop in the measured SpO2.
- This can be managed by thorough pre-oxygenation prior to anesthetic induction: supply 100% oxygen by facemask at 5 l/min for 5 min.
- Following anesthesia, closely monitor SpO2 and supplement oxygen via endotracheal tube or facemask as necessary in order to maintain SpO2 above 94%.
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- This can be managed by thorough pre-oxygenation prior to anesthetic induction: supply 100% oxygen by facemask at 5 l/min for 5 min.
- Q. What are the consequences of gastroesophageal reflux (GER)?
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