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Anesth Analg 2001;93:226-229
© 2001 International Anesthesia Research Society

GENERAL ARTICLES

Resting Esophageal Sphincter Pressures and Deglutition Frequency in Awake Subjects After Oropharyngeal Topical Anesthesia and Laryngeal Mask Device Insertion

Christian Keller, MD*, and Joseph Brimacombe, MB, ChB, FRCA, MD{dagger}

*Department of Anaesthesia and Intensive Care Medicine, Leopold-Franzens University, Innsbruck, Austria; and {dagger}Department of Anaesthesia and Intensive Care, University of Queensland, Cairns Base Hospital, Cairns, Australia

Address correspondence to Prof. J. Brimacombe, Department of Anaesthesia and Intensive Care Medicine, University of Queensland, Cairns Base Hospital, Cairns 4870, Australia. Address e-mail to jbrimacombe{at}austarnet.com.au


   Abstract
Top
 Abstract
Introduction
 Methods
 Results
 Discussion
 References
 
We investigated the effects of oropharyngeal topical anesthesia and placement of the standard (LMA) and the ProSeal (PLMA) laryngeal mask airway on resting gastroesophageal barrier pressure (GEBP), upper esophageal sphincter pressure (UESP), and deglutition frequency in awake subjects. Each subject was studied on 2 consecutive days: 1 day with the LMA and the other with the PLMA, in random order. GEBP and UESP were measured between deglutitions by using a pull-through technique in five sequential conditions: 1) after acclimatization to the manometer, 2) after topical anesthesia, 3) after the LMA or PLMA was self-inserted and the cuff inflated with either 10 or 30 mL of air in random order, 4) after the cuff volume was adjusted to the other randomized volume, and 5) after LMA or PLMA removal. Deglutition frequency was determined between pressure measurements by using a neck microphone. UESP was always larger than GEBP (P < 0.001 for all). Topical anesthesia had no influence on GEBP, UESP, or deglutition frequency. LMA and PLMA placement did not influence GEBP or UESP, but deglutition frequency was higher (P < 0.02 for all). GEBP and UESP did not vary between devices for any condition. Cuff volume did not influence GEBP or UESP. Deglutition frequency was more frequent for the LMA than the PLMA at a 30-mL cuff volume (P = 0.008). We conclude that resting GEBP and UESP are unaffected by oropharyngeal topical anesthesia and the LMA or PLMA in awake subjects, but that deglutition frequency is increased by the LMA or PLMA. This may have implications for the incidence of regurgitation in these situations.

Implications: Resting gastroesophageal barrier pressure and upper esophageal sphincterpressure are unaffected by oropharyngeal topical anesthesia and laryngeal maskdevices in awake subjects, but deglutition frequency is increased by laryngealmask devices. This may have implications for the incidence of regurgitation inthese situations.


   Introduction
Top
 Abstract
 Introduction
Methods
 Results
 Discussion
 References
 
Regurgitation and aspiration of gastric contents continue to be a cause of morbidity and mortality in anesthesia practice (1,2). The major barriers to pharyngeal regurgitation of gastric contents are the upper and lower esophageal sphincters (3). The effects of anesthesia drugs on esophageal sphincter pressures are well known (4,5), but evidence is emerging that airway management techniques also influence the efficacy of these sphincters (6–8). For example, the placement of the laryngeal mask airway (LMA) in anesthetized patients (7) and the application of cricoid pressure in awake subjects (6) reduces lower esophageal sphincter pressure. In addition, placement of a new laryngeal mask device, the ProSealLMA (PLMA) (Laryngeal Mask Company, Henley-on-Thames, UK), is associated with an open upper esophageal sphincter in some anesthetized patients (8). Finally, oropharyngeal topical anesthesia is often applied for awake procedures involving the airway, but there are few published data about its effect on the lower (9) and upper (10) esophageal sphincters. The aim of this study was to investigate the effects of oropharyngeal topical anesthesia and PLMA or LMA placement on resting gastroesophageal barrier pressure (GEBP), upper esophageal sphincter pressure (UESP), and deglutition frequency in awake subjects.


   Methods
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 Abstract
 Introduction
 Methods
Results
 Discussion
 References
 
With hospital ethics committee approval and written, informed consent, we studied 10 healthy, fasted (>6 h), unpaid subjects (ASA grade I). Subjects were excluded if there was a history of gastroesophageal disease or if they were taking medication that might interfere with gastroesophageal function. Each subject was studied on 2 consecutive days: 1 day with the LMA and the other with the PLMA in random order determined by opening a sealed envelope. The LMA was modified to include a drainage tube to provide access to the upper esophagus (Fig. 1).



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  		Figure 1. The laryngeal mask airway modified to provide access to the esophagus. Note that the drainage tube is within the lumen of the airway tube.

 
A standardized esophageal manometry technique was used (11). Esophageal pressures were measured with an 8-lumen manometry catheter (EMC8-R, outer diameter 4 mm; Zinetics EMC, Salt Lake City, UT) that was continuously perfused at a rate of 0.5 mL/min by a pneumohydraulic capillary infusion system (MUI Scientific PIP-4-8; Zinetics EMC) and was connected to a polygraph. The compliance of this system was low, having a pressure increase rate >400 mm Hg/s on total occlusion at the individual catheter opening. This measurement system has been used by other researchers (12). Deglutitions were detected with a neck microphone. Testing in two subjects, each performing 30 voluntary swallows with the PLMA in situ, showed that the microphone had 100% sensitivity and specificity to detect deglutition events. In addition, testing in these same two subjects during various degrees of straining demonstrated that the manometer could detect changes in the lower esophageal sphincter pressure.

Subjects were studied in the supine position with the occiput on a firm pillow 5 cm high. The manometry catheter was introduced orally into the stomach without sedation or topical anesthesia. GEBP and UESP were measured during end-expiration by using a slow pull-through technique (0.5 cm/s) during five consecutive conditions: 1) Baseline GEBP and UESP were measured after a 15-min acclimatization period (baseline/start); 2) the airway was anesthetized with 10 puffs of 1% lidocaine spray and after 5 min, the GEBP and UESP were measured (topical anesthesia); 3) the size 4 LMA or PLMA was self-inserted by the subject with the cuff fully deflated; (the cuff was inflated with either 10 or 30 mL of air in random order, and after 5 min, GEBP and UESP were measured); 4) the cuff volume was adjusted to the other randomized volume and after 5 min, the GEBP and UESP were measured; and 5) the LMA or PLMA was then removed and after 5 min, GEBP and UESP were measured (baseline/end). LMA/PLMA insertion took place without removal of the manometer by threading the proximal end through the drainage tube. After each GEBP/UESP measurement, the catheter was pushed back into the stomach. Subjects were asked to avoid voluntary swallowing other than during placement of the LMA or PLMA. GEBP/UESP measurements were made only between deglutitions. If a deglutition occurred, the measurement was repeated. To provide general information about the anatomic position, the fiberoptic position was recorded at a 10-mL cuff volume by using the following scoring system: 4, only vocal cords visible; 3, vocal cords and posterior epiglottis visible; 2, vocal cords and anterior epiglottis visible; 1, vocal cords not seen (13).

An independent blinded observer using a commercial software program (Gastrosoft Polygram, Upper GI Edition, Version 6.4; Medtronic Synectics, Shoreview, MN) analyzed the data. GEBP was determined by subtracting the intragastric pressure from the average pressure readings from the eight radially orientated ports as they passed through the lower esophageal sphincter. UESP was determined by subtracting the pressure in the drainage tube from the average pressure readings from the eight radially orientated ports as they passed through the upper esophageal sphincter. The lower and upper border of the lower esophageal sphincter was when pressure readings first increased from zero and decreased to a stable value during the pull-through, respectively. The lower and upper border of the upper esophageal sphincter was when pressure readings subsequently increased from a stable value and decreased to zero (drainage tube or pharynx) during the pull-through, respectively. Deglutition frequency was determined for each consecutive condition by averaging the number of swallows during a 5-min interval between pressure measurements.

Sample size was selected to detect a projected difference of 25% in esophageal sphincter pressure between conditions for a type I error of 0.01 and a power of 0.9. The distribution of data was determined with a Kolmogorov-Smirnov analysis. Statistical analysis was performed with a Student’s t-test and a Kruskal-Wallis nonparametric analysis of variance test, followed by Wilcoxon’s test or a one-way analysis of variance, followed by Bonferroni’s corrected multiple-comparisons test. Significance was taken as P < 0.05. Statistical analysis was performed on a personal computer with SYSTAT v 7.0 (SPSS, Chicago, IL).


   Results
Top
 Abstract
 Introduction
 Methods
 Results
Discussion
 References
 
One subject was unable to maintain the LMA or PLMA in position for a sufficient time to collect any data and was replaced with a new subject. The mean (range) age, height, and weight were 32 yr (26–37 yr), 174 cm (158–188 cm), and 69 kg (50–90 kg), respectively. The male/female ratio was 7:3. Insertion was successful at the first attempt in the 10 remaining subjects. In seven subjects, the fiberoptic score was 4, and in three subjects it was 3. The start and end baseline values for GEBP and UESP were in the normal range for healthy, young subjects (12).

Topical anesthesia had no influence on GEBP or UESP (Table 1). There were no intradevice differences for the GEBP or UESP between conditions. There were no interdevice differences for the GEBP or the UESP at any condition. Compared with the baseline/start condition, deglutition frequency was increased after LMA or PLMA insertion (P < 0.02 for all), but it was unchanged after topical anesthesia and returned to baseline values after device removal. Deglutition frequency was similar for the LMA and PLMA at a 10-mL cuff volume, but it was more frequent for the LMA at a 30-mL cuff volume (P = 0.008). Deglutition frequency was not affected by the level of cuff inflation. All measurements were completed in each subject within 25 min after the application of topical anesthesia.


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  		Table 1. Gastroesophageal Barrier Pressure (GEBP), Upper Esophageal Sphincter Pressure (UESP), and Deglutition Frequency (DF) for the ProSeal (PLMA) and (LMA) Laryngeal Mask Airway Before Insertion, After Insertion, and After Removal
 

   Discussion
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
References
 
We found that oropharyngeal topical anesthesia does not interfere with resting esophageal sphincter function or deglutition frequency. This supports the findings of Nasrallah and Hendrix (9) for the lower esophageal sphincter and Ali et al. (10) for the upper esophageal sphincter. Physiologically, this suggests that oropharyngeal mucosal receptors do not play an important role in regulating esophageal sphincter pressure. Clinically, this suggests that oropharyngeal topical anesthesia will not interfere with esophageal manometry studies. It is interesting to note that Trifan et al. (14) showed that the injection of small amounts of water into the pharynx stimulates relaxation of the lower esophageal sphincter in a manner different from a normal swallow. We did not measure esophageal sphincter pressure as the topical anesthetic was being applied, and it is possible that a change in GEBP or UESP occurred at that time.

Our results indicate that LMA devices do not influence resting GEBP in awake subjects, but there is evidence that they may influence lower esophageal sphincter pressure in anesthetized subjects. Rabey et al. (7), by using a similar technique, showed that lower esophageal sphincter pressure is reduced during general anesthesia with the LMA. Sustained distension of the esophagus by balloon induces prolonged relaxation of the lower esophageal sphincter (3,15), and Rabey et al. (7) suggested that a similar reflex might be occurring during sustained pharyngeal distension with the LMA. It is interesting to note that Tournadre et al. (6) showed that cricoid pressure causes a reduction in lower esophageal sphincter pressure in awake subjects and suggested that this was related to a similar pharyngeal reflex. Our data suggest that this pharyngeal reflex does not occur in awake humans. We speculate that this reflex may occur only when higher brain function is impeded by general anesthesia. Although the study of Rabey et al. (7) has not been repeated, there is indirect support from lower esophageal pH studies that lower esophageal sphincter relaxation occurs during LMA anesthesia (16–19). However, several groups have shown that pharyngeal regurgitation is uncommon with the LMA (20–22). It seems that the LMA causes a reduction in lower esophageal sphincter tone and a reduction in lower esophageal pH, but the pharynx is spared from regurgitation. This may be related to the low volume of regurgitated fluid, the continued function of the UESP (23), or the effect of the LMA tip as a mechanical barrier in the hypopharynx (24).

The presence of LMA devices in the pharynx does not influence resting UESP in awake subjects. Vanner et al. (23) showed that insertion of the LMA had no effect on UESP in seven spontaneously breathing anesthetized patients. In a cross-over study comparing the PLMA and LMA (8), 2 of 60 paralyzed, anesthetized patients were seen fiberoptically to have an open upper esophageal sphincter. We found no differences in UESP between the LMA and PLMA. We speculate that any reduction in UESP found in anesthetized patients will be associated with both devices.

The presence of the LMA and PLMA increased deglutition frequency. This is probably triggered by mechanoreceptors in the pharynx, and our data suggest that these receptors are not blocked by topical anesthesia (3). Deglutition can be considered a protective reflex for the respiratory tract (25), and increased deglutition may reduce the risk of regurgitation and aspiration. It is possible that the reduction in GEBP detected by Rabey et al. (7) was related to an increase in deglutition frequency, rather than a reduction in lower esophageal sphincter pressure. It is interesting to note that deglutition frequency was more for the LMA than for the PLMA at a 30-mL cuff volume. This suggests that the fully inflated LMA cuff stimulates pharyngeal mechanoreceptors more than the fully inflated PLMA cuff. We speculate that it may be related to differences in cuff shape.

A limitation of our study was that we modified the LMA to provide access to the esophagus. Although it is possible to pull the manometer catheter behind the LMA, it is difficult to determine the upper border of the upper esophageal sphincter because the cuff prevents a sudden decrease in pressure. Our modified LMA cuff was identical to the LMA other than a slight blunting of the tip. We consider it unlikely that this would have influenced our results.

We conclude that resting GEBP and UESP are unaffected by oropharyngeal topical anesthesia and the LMA or PLMA in awake subjects, but deglutition frequency is increased by the LMA or PLMA. This may have implications for the incidence of regurgitation in these situations.


   References
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 

  1. Warner MA, Warner WE, Webber JG. Clinical significance of pulmonary aspiration during the perioperative period. Anesthesiology 1993; 78: 56–62.[Web of Science][Medline]
  2. Caplan RA, Posner KL, Ward RJ, Cheney FW. Adverse respiratory events in anesthesia: a closed claims analysis. Anesthesiology 1990; 72: 828–33.[Web of Science][Medline]
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  7. Rabey PG, Murphy PJ, Langton JA, et al. Effect of the laryngeal mask airway on lower oesophageal sphincter pressure in patients during general anaesthesia. Br J Anaesth 1992; 69: 346–8.[Abstract/Free Full Text]
  8. Brimacombe J, Keller C. The ProSeal laryngeal mask airway: a randomized, crossover study with the standard laryngeal mask airway in paralyzed, anesthetized patients. Anesthesiology 2000; 93: 104–9.[Web of Science][Medline]
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  13. Brimacombe J, Berry A. A proposed fiber-optic scoring system to standardize the assessment of laryngeal mask airway position [letter]. Anesth Analg 1993; 76: 457.
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Accepted for publication February 27, 2001.




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Lippincott, Williams & Wilkins Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999 HighWire Press