Preventing Pulmonary Aspiration And The Esophageal Junction Biology Essay

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The esophageal junction or sphincter is an important barrier essential to keeping the stomach contents from regurgitating into the trachea. Anesthesia can affect the tone of this sphincter, causing an increase in aspiration risks for patients. It is therefore necessary to identify predisposing factors and take steps preoperatively to prevent regurgitation of stomach contents.

The esophagus is a muscular tube that connects the pharynx to the stomach. It contains a circular inner layer of muscle and an outer longitudinal layer of muscle.1 The outer layer consists of three distinct areas of musculature. The upper third is composed of voluntary striated muscle, the middle third is a mixture of both striated and smooth muscle, and the lower third is smooth muscle.

The narrowest part of the esophagus occurs at the upper esophageal sphincter (UES), located at the level of the C6 vertebra, immediately posterior to the inferior border of the cricoid cartilage, and stretches across the full width of the cricoid cartilage. This sphincter maintains a resting pressure of 15 to 60 cm H2O and helps to prevent aspiration in healthy, conscious patients.2

The lower esophageal sphincter (LES) is located to the left of the T1 vertebra, on a horizontal plane which passed through the tip of the xiphoid process. The LES is just superior to the stomach and also acts as a barrier to reflux of gastric contents. It maintains a resting pressure of 10 to 30 mm Hg.3 This resting pressure is greater than the 7 mm Hg gastric pressure of the stomach, and it is this difference in pressures, known as the barrier pressure (BP), which prevents reflux of gastric contents. Any change in the UES of LES pressure could result in regurgitation and aspiration.

Anesthesia Implications

Prevention of aspiration starts with a comprehensive preoperative assessment to identify patients at increased risk. Three main categories of risk for aspiration include patients with increased gastric pressures, a tendency to regurgitate, and patients with laryngeal incompetence.

Review of Current Literature

Laryngospasm most commonly occurs as the result of irritation of the airway. Current evidence suggests a correlation between upper respiratory infections (URI) and increased risk of airway obstruction.5 A large prospective study done in 2010 compared multiple preoperative risk factors and identified those that were most likely to increase the incidence of laryngospasm. Children presenting with an active URI suffer from the highest risk; increased airway secretions exacerbate airway inflammation which can produce heightened sensitivity. This sensitivity decreases over 2 to 4 weeks but still poses a significant risk. Therefore, elective surgery should be postponed until 4 weeks have passed. If postponement of the surgical procedure is not possible, adjustment of anesthetic technique is necessary. Recommendations include intravenous use of propofol for induction and maintenance of anesthesia which is less irritating to the airways than the use of sevoflurane. The use of a face mask is the safest airway management tool but may not be practical. An LMA is less likely than use of an endotracheal tube (ETT) to precipitate a spasm though other studies suggest the use of an LMA may increase spasm.

Contrary to the aforementioned study, a retrospective study done of 130 children at the Mayo clinic found that rate of laryngospasm was less with the use of an ETT than face mask or LMA. 6 Due to the retrospective nature of the research there was no way to establish whether removal of an LMA was done during light or deep anesthesia or whether there were secretions associated with removal. If using an LMA, careful suctioning should be done under deep anesthesia, prior to the removal of the device. Further scrutiny of these results did reveal that patients whose airway was managed by ETT were also found to have been neuromuscularly blocked. Regardless of the choice of airway management device, the presence of a current URI statistically increased the risk for an adverse airway event. This study also saw an increase in laryngospasm associated with a recent URI of up to 4 weeks, with risk decreasing over time. As previously discussed, in order to decrease susceptibility to laryngospasm, proper maintenance of an adequate plane of anesthesia is necessary to decrease the effects of stimulation.

An observational study done of 335 children also concluded that incidence of laryngospasm in patients with an URI peaked in a 2 to 4 week period.7 Numerous symptoms were identified but multivariate analysis showed there was no association between specific symptoms and greater risk. A low grade fever or an URI 4 to 6 weeks prior to surgery seemed to afford protection from laryngospasm. The sample size of children that exhibited this protection was weakly correlated so further research is required

In addition to URIs, passive exposure to smoke has been shown to increase the irritability of the airway and is a significant risk factor for laryngospasm.8 Greater risk is seen in patients with a primary care giver who smokes or with 2 or more immediate family members who smoke. In order to reduce respiratory problems, it is recommended that active smokers quit smoking 8 weeks prior to surgery. If a patient cannot comply, it is generally recommended that smoking should cease at least 2 days before surgery. Nonetheless, there is no clear consensus as to what is an appropriate amount of time for cessation to passive exposure to smoke.

Obesity rates in children have increased dramatically over the last 30 years. As of 2006, 15.5% of children and adolescents are considered obese.9 While there is abundant research of adult populations and adverse respiratory events due to obesity, there is a dearth of similar studies in the pediatric population. Comorbidities associated with obesity such as gastroesophageal reflux disease (GERD) have been associated with increased risk of laryngospasm in adults but have not been adequately examined in children. A prospective study done in 2008 did not find a significant increase in laryngospasm in obese children. It is possible that children have less airway irritability than obese adults due to less disease comorbidities or from less time exposed to chronic GERD. However, the authors suggest further research is warranted.

Conclusion

Laryngospasm is a life threatening emergency. A thorough preoperative assessment should be undertaken to identify the risk factors and tailor an anesthesia management plan with those risk factors in mind. Steps that can reduce the risk of laryngospasm include: (1) Use of propofol for induction and maintenance of anesthesia. (2) Selection of the least stimulating airway management device. (3) Maintaining an adequate depth of anesthesia. (4) Limiting passive exposure to smoke for at least 2 days prior to surgery. (5) Suctioning and removal of foreign matter under deep anesthesia. Regardless of known risk, it is necessary for the anesthesia provider to always be vigilant and prepared for adverse events during the delivery of anesthesia.

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