The main aim of treatment is prevention. This requires good anesthetic practice for those patients undergoing general anesthetic and attention to detail for patients in the intensive care unit (ICU). Patients at risk must be identified, including emergency cases, pregnant women, and diabetics. An experienced anesthetist is required for these cases, and regional anesthesia should be considered. For safe intubation patients need to be fasted; thus in emergencies rapid-sequence induction with correct use of cricoid pressure is required. These patients must be preoxygenated, and given an appropriate sedative and muscle relaxant with the application of cricoid pressure from the moment of loss of consciousness until the endotracheal tube is confirmed to be correctly positioned with the cuff inflated. There is debate as to how long patients should be fasted before undergoing elective surgery. The accepted minimum time for solid food to be emptied from the stomach is 6 h. However, evidence initially obtained with children, and now extended to adults, suggests that only a 2-h fasting period is required for clear fluids, and there is no difference in the volume and acidity of gastric contents aspirated from fully fasted patients and those allowed fluids until 2 h preoperatively. This more relaxed fluid regime reduces thirst, improves compliance, reduces hypoglycemia, and allows a better recovery from the anesthetic. It remains essential to identify high-risk cases where standard fasting times will still be needed. The incidence of aspiration during general anesthesia in elective fasted patients where a laryngeal mask was used is negligible. Other approaches to prevention include use of awake intubation and the use of balloon-tipped nasogastric tubes to attempt to occlude the cardia.
Another major arm in prevention is the prophylactic use of antacids. A large number of different methods of alkalinizing the gastric contents have been tried and compared. The best is to use a non-particulate antacid, H2 blocker, or proton pump inhibitor (the most common agents employed include cimetidine, ranitidine, or sodium citrate) in combination with an agent to promote emptying of gastric contents such as metoclopramide or cisapride. A number of agents given preoperatively have been shown both to increase effectively the pH and to reduce the volume of gastric contents ( Table 1).
Unlike antacids, H2 blockers and proton pump inhibitors significantly reduce the volume of gastric contents, and metoclopramide reduces this further. Oral ranitidine at 2 to 3.5 mg/kg is effective in children. Agents employed to promote gastric emptying are not always effective, particularly in diabetics where cisapride has no effect on the volume of gastric aspirates. It is essential to note the fallacy of the common belief that aspiration of less than 25 ml of gastric contents at a pH greater than 2.5 is benign. Many studies have demonstrated a direct pathogenic effect of food particles additional to that of any acid. Acute respiratory distress syndrome has been shown to develop with aspiration of gastric contents at a pH of 6.4 after use of Aludrox ®(aluminum hydroxide). Thus alkalinization of gastric contents is helpful, but is not all that is needed.
In the ICU, similar preventive measures should apply for intubation of patients, many of whom will also have nasogastric tubes inserted. The correct positioning of these tubes is important and can be confirmed by aspiration of acid gastric juice (pH < 4 tested using litmus paper) combined with injection of air and auscultation over the epigastrium. In the absence of aspiration of acid fluid, a confirmatory chest radiograph is essential; auscultation alone is insufficient. Once nasogastric feeding has commenced, preventing gastric dilatation by regular aspiration of gastric contents to determine effectiveness of gastric emptying is essential. If gastric emptying is delayed, as demonstrated by regular gastric aspirates of more than 200 ml every 4 h, agents such as metoclopramide, cisapride, and erythromycin can be employed to promote it. Even a tracheostomy does not completely eliminate the risk of aspiration, as a significant number of patients aspirate some feed over a 48-h period. Finally, safe extubation is also an important factor in the ICU where patients can have an endotracheal tube in position for weeks. The patient must be able to cough and have an adequate gag reflex, the stomach contents must be aspirated, and the patient should be sitting up. The possibility of poor airway protection in the postextubation period must be borne in mind.
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