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*Department of Gastroenterology, Department of Anaesthesia, Kantonsspital St. Gallen, Switzerland; Department of Anesthesiology and Critical Care Medicine, Innsbruck Medical University, Austria
Address correspondence and reprint requests to Jan Borovicka, MD, Department of Gastroenterology, Kantonsspital St. Gallen, CH-9000 St. Gallen, Switzerland. Address e-mail to jan.borovicka{at}kssg.ch.
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Introduction |
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Nonpharmacological measures for prevention of GER in the nonfasted awake individual (i.e., awaiting urgent surgery or urgent endoscopy) include specific body positioning, with the head-up as well as the head-down positions being described as suitable alternatives in the management of the patient at risk for regurgitation (3,4). The Report of the National Confidential Enquiry into Perioperative Deaths has also drawn attention to the use of postural changes for reducing the risk of aspiration (5).
The influence of postural changes on GER and reflux-inhibiting barrier pressure (BRP) has already been studied (6,7), but the results of those studies are not applicable to awake patients with full stomachs because the studies were conducted in fasted patients under the influence of general anesthesia. Moreover, those studies determined GER by means of pH-metry (pH-M), a method that does not detect nonacid reflux or gas reflux.
The aim of the present study was to use a combination of multichannel intraluminal impedance (MII) measurement, which permits determination of GER irrespective of pH value (8), pH-M, and intragastric-esophageal manometry (IEM) to evaluate the influence of a change in body position (20° head-up, supine, 20° head-down) on the frequency of GER and BRP in nonfasted awake individuals.
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Methods |
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The impedance catheter (Unisensor, Attikon, Switzerland) consisted of 3 impedance measuring segments, each consisting of 2 rings placed 2 cm apart. Measuring units were placed at 5, 9, and 13 cm above the lower esophageal sphincter (LES). Impedance measurement was used to distinguish between liquid and gas reflux. For liquid reflux, impedance decreases to 
50% from baseline. For gas reflux, impedance increases to 50% from baseline. The reflux has to be in retrograde (oral) flow and impedance changes have to be seen in at least two measuring units.
Esophageal pH was monitored with a separate unipolar electrode (SMT, Luzern, Switzerland) positioned 5 cm above the proximal margin of LES. The electrode was calibrated in buffers of pH 4 and pH 7 before and after study. pH-M was used to detect and evaluate reflux and to differentiate between acid, nonacid, and minor acid reflux and acid re-reflux as follows:
Acid reflux: Reflux starts at a pH more than pH 4.0 and nadir pH is less than pH 4.0.
Nonacid reflux: Reflux starts at a pH >4.0, nadir pH >4.0, and the pH decrease is less than one unit.
Minor acid reflux: Reflux starts at pH >4.0, nadir pH >4.0, and pH decrease is more than one unit.
Acid re-reflux: Reflux starts at a pH <pH 4.0.
Duration of reflux was measured in seconds until pH returned to a value above 4.0. In the case of re-reflux time was measured until pH returned to the primary level. Minimum reflux time was 5 s. All refluxes with a duration of <5 s were not evaluated.
IEM was performed with an eight-channel assembly incorporating a sleeve sensor (A-E27-LOSS-2, Dentsleeve Pty Ltd., Wayville, Australia) to record LES pressure. Intragastric pressure was recorded through a side hole located 1 cm beyond the distal margin of the sleeve. Side holes at the proximal margin of the sleeve and 5, 10, 15, 20, and 26 cm more proximal recorded motility in the esophageal body. The sleeve, gastric, and lower three esophageal side holes were perfused with degassed distilled water at a rate of 0.45 mL/min. The upper three esophageal side holes were perfused at a rate of 0.08 mL/min with a low compliance pneumohydraulic capillary infusion system. Each lumen was connected to external pressure transducers (SEDIA, Freiburg, Switzerland). Pressure was measured by determining the LES level and comparing it with the pull-through results. Basal LES pressure was measured at end-expiration and referenced to intragastric pressure. LES pressure was evaluated for each minute of the 10-min baseline and the 30-min main recording for each position. BRP was calculated as the difference between intragastric and LES pressure measured at end-expiration. Intragastric pressure and LES pressure was measured continuously and an average BRP was calculated for each minute. MII measurement, pH-M and IEM signals were processed and recorded by means of the same dedicated software program (SEDIA).
After topical nasal anesthesia, the IEM catheter was introduced. The LES was identified using a stationary pull-through technique, and the second most distal sensor was placed in the high-pressure zone of the LES. The MII catheter was placed 3 cm above the LES, and the pH-metry catheter was placed 5 cm above the LES. All three catheters were introduced nasally.
After placement of catheters the volunteers rested for 15 min and were then randomly placed in a flat supine position, a 20° head-down or a 20° head-up tilted body position. In each position, baseline recordings of LES pressure and gastric pressure were made during the first 10 min. Subsequently, the stomach was distended with 750 mL carbon dioxide and 300 mL orange juice, after which a recording was made for 30 min in each position. After completing the measurements in each body position (flat supine, 20° head-down, and 20° head-up), the volunteers sat for 30 min, after which gastric content was suctioned off through the IEM catheter. The same maneuver was repeated for the remaining two position measurements. After completing the survey a gastroscopic examination of esophagus, stomach, and duodenum was performed to evaluate gastric condition. pH-Metry, IEM, and MII were measured continuously and synchronously throughout the examination. Number of refluxes detected by MII measurement and pH-M were totaled up for each body position in each patient.
The distribution of data was determined by Kolmogorov-Smirnov analysis. Differences in median number and duration of refluxes among the three different positions were analyzed using the Kruskal-Wallis test for overall significance. For pairwise comparisons the Mann-Whitney U-test was used. Statistical significance was defined as P < 0.05. After Bonferroni correction for three comparisons P values of <0.017 indicated statistical significance. Data are expressed as median and 25th and 75th percentiles. SPSS for Windows 12.0 (SPSS, Chicago, IL) was used for all analyses.
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Discussion |
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Our study adds new information to previous studies that investigated anesthetized patients (6,7,9). Data obtained in those studies are not applicable to the awake patient at risk for GER because drugs commonly used during general anesthesia (i.e., muscle relaxants, atropine) influence LES pressure (10,11). Furthermore, in nonfasting individuals, the incidence of regurgitation is markedly increased after recent ingestion of food (12). To approximate as closely as possible the clinical scenario of a nonfasting patient (i.e., presenting for rapid sequence induction) we induced a nonfasting condition in our primarily fasted volunteers by administering 750 mL of carbon dioxide and 300 mL of orange juice.
When comparing the sitting position to the supine position in patients with GER disease, Freidin et al. (13) found no difference in the total reflux time or the acid clearance time. The prolonged acid clearance time in the head-down position observed in our volunteers was probably a result of the effect of gravity.
The previous study by el Mikatti et al. (9) involved tight methodical limits for determining GER because the pH-M used can show only GER with a pH <4. However, MII measurement makes it possible to demonstrate the smallest reflux quantities (>1 mL) independently of the degree of acidity. The combination of MII measurement and pH-M has proved to be superior for demonstration of GER in nonfasting individuals (8).
Because the LES is the natural barrier between the stomach and the esophagus, several studies have focused on LES measurements in the sitting and the supine positions and demonstrated a decrease in LES pressure in the sitting position (14,15). However, LES pressure is only one of two determinants used to calculate the reflux-inhibiting BRP (BRP = intragastric pressure – LES pressure). Accordingly, such an isolated measurement is of limited clinical value. Moreover, earlier measurements of LES pressure were taken with the perfused catheter method, which, in contrast to the intraluminal transducer method, cannot be referenced against atmospheric pressure (14) and thus does not permit a position-specific change in LES pressure to be measured.
The reflux-inhibiting protective value of an increase in hydrostatic pressure in the head-up position has been discussed by Salem et al. (16) in pediatric patients. Assuming an intragastric pressure of 18 cm H2O, a minimum 40° head-up posture would be necessary to overcome this pressure by increasing hydrostatic pressure by 19 cm H2O in a 28-cm-long adult esophagus. This is clearly more than the 20° head-up position in our study, which we consider to be a maximum possible tilt position in clinical practice.
In this connection, BRP also needs to be discussed. As early as 1961 Ruben et al. (17) indirectly referred to this BRP for the supine position when they determined the minimum airway pressure required to inflate the stomach during facemask ventilation. They reported the airway pressure needed to overcome the BRP and subsequent air insufflation of the stomach to be 19 cm H2O, which is similar to the BRP measured in our study in the head-up position (15.6 mm Hg). By contrast, in our volunteers the BRP in the supine and the head-down position was 19.4 mm Hg and 19.6 mm Hg, a range in which Ruben et al. found only a small number of air insufflations of the stomach (>25 cm H2O). This should be considered for facemask ventilation in the head-up position in patients during induction of anesthesia, although, in contrast to the supine or head-down position, insufflation of the stomach with air, and thus a further increase in intragastric pressure, can be provoked at low airway pressures.
One limitation of our study is that individuals with a BMI of >30 kg/m2 were not investigated, thereby excluding a subset of patients generally thought to be at special risk for GER and aspiration. However, the small number of volunteers enrolled in our study did not permit such an investigation. Harter et al. (18) showed that among otherwise healthy, fasted, obese surgical patients there is a less frequent incidence of combined large-volume, low-pH stomach content as compared with lean patients, and Hardy et al. (19) reported that GER on induction of anesthesia does not correlate with the volume of gastric content.
When studying GER and BRP for 3 body positions commonly used in regurgitation-endangered patients (+ 20°/0°/–20°), we found that specific positioning does not significantly influence frequency of GER or BRP. The optimal position for awake patients with a "full stomach" and at risk for GER should, therefore, be determined on the basis of other factors (i.e., type of patient‘s illness or technical expertise of the attending physician).
The authors thank Radu Tutuian, MD (Division of Gastroenterology/Hepatology, Medical University of South Carolina) for his thoughtful comments.
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Footnotes |
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Accepted for publication February 1, 2005.
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