Accuracy and choice of procedures in 24-hour oesophageal pH monitoring with monocrystalline antimony electrodes

The incidence of gastroesophageal reflux with the laryngeal mask: a comparison with the face mask using esophageal lumen pH electrodes

To test the hypothesis that the laryngeal mask airway (LMA) predisposes patients to gastroesophageal reflux, we randomly assigned 55 patients having elective surgery to receive standardized anesthesia with the LMA or with conventional face mask (FM) plus airway. A pH-sensitive probe with two electrodes, 10 cm apart, was passed nasally into the esophagus 1 h before induction of anesthesia, and recordings were made continuously until 30 min after surgery. At the distal electrode, 30 cm from the anterior nares, there was a significant difference in the incidence of reflux: 53.6% with the LMA versus 22.2% with the FM (P < 0.05). At the level of the proximal electrode, 20 cm from the anterior nares, there was no difference between groups. Multiple reflux events, defined as two or more reflux events before, during, or after anesthesia, were significantly more frequent in the LMA group (P < 0.05). Reflux events continued in the postanesthesia care unit (PACU) in both groups with no significant difference between groups. There was no clinical evidence of aspiration of gastric contents in either group. Use of the LMA appears to result in increased reflux to the level of the mid to upper esophagus, and is associated with a more frequent incidence of multiple reflux events than use of the FM.

Variations in esophageal oxygen tension measured with intraluminal antimony electrodes

Monocrystalline antimony electrodes (crystallographically oriented monocrystalline antimony; COMA) are known to be sensitive to oxygen and to pH. Accordingly, it has been shown that COMA electrodes can be used for the measurement of tissue oxygen tension provided the pH remains constant or is accounted for by the simultaneous use of a glass electrode. In this study the combination of a COMA together with a glass electrode was evaluated for measurement of esophageal oxygen tension in 5 patients. The COMA electrodes showed a mean value of 2.1 pH units higher than the glass electrodes, corresponding to a pO2 level in the esophagus of 10 kPa. As the more protracted oxygen effect on the COMA electrodes was easily recognized, especially in levels of the pH above 7.8 units, they were used for indirect evaluation of intraluminal oxygen tension in the esophagus in a further 57 patients, monitored over 24 h for gastroesophageal reflux disease. The intraluminal pO2 decreased in the supine position and with increase in age. An increase in pO2 was seen after eating and during reflux periods. The changes in pO2 are interpreted as being secondary to blood flow alterations in the esophagus.

Role of hiatal hernia in delaying acid clearance

The aim of this study was to assess prospectively the relationship of a hiatal hernia to gastro-oesophageal reflux. Ninety five children with symptoms of gastro-oesophageal reflux in whom reflux was demonstrated radiologically were investigated. Oesophageal pH monitoring for 18 hours and endoscopy were performed in all patients. On the basis of radiology, patients were divided into those with hiatal hernia (n = 37) and those without (n = 58). Both groups had the same number of reflux episodes on pH monitoring. However, the median duration of the longest episode was significantly greater in the hiatal hernia group (30 min v 19 min), as was the number of reflux episodes longer than five minutes (5 v 4). The percentage with a pH < 4 just failed to be significantly different (13% v 8%). Hiatal hernia was also found to correlate with the presence of oesophagitis. The presence of a hiatal hernia delays the clearance of acid from the oesophagus and is associated with an increased incidence of oesophagitis.

Alkaline oesophageal reflux--an artefact due to oxygen corrosion of antimony pH electrodes

Antimony electrodes are widely used for gastro-oesophageal pH monitoring. They are also sensitive to oxygen, however, especially at low PO2 levels, which are known to shift recorded values in the alkaline direction. This study, which compares antimony and glass electrodes for oesophageal pH monitoring in six adults, shows that values recorded by antimony electrodes are 2.1 +/- 0.8 pH units (mean +/- SD) higher than by glass electrodes (p < 0.001; n = 7642). A further 52 patients with suspected gastro-oesophageal reflux were investigated by 24-h pH monitoring by means of antimony electrodes. In these patients the oesophageal pH was higher than 8.0 for 7% of the time (range, 0-60%). The alkaline periods recorded with antimony electrodes were all protracted in time, smoothly increasing from a neutral pH, and did not correspond to a sudden increase in pH, which would be expected if alkaline reflux had occurred. It is concluded that high pH values obtained by antimony electrodes are due to the oxygen sensitivity of the electrodes. The diagnosis of alkaline reflux seems to be valid only when pH monitoring is performed with glass electrodes or when values obtained with antimony electrodes are adjusted for the influence of the oxygen tension in the oesophagus.

Gastro-oesophageal reflux and regurgitation during general anaesthesia for termination of pregnancy

Gastro-oesophageal reflux (GOR) and regurgitation were investigated with an oesophageal pH electrode, inserted after the induction of general anaesthesia with methohexitone, in 100 patients undergoing termination of pregnancy, 50 in the first trimester and 50 in the second. GOR occurred in 17 patients, 8 in the first trimester and 9 in the second trimester. On withdrawal of the pH electrode into the pharynx it was found that only 2 of these patients had regurgitated, 1 from each trimester. Regurgitation was not clinically detectable and there was no pulmonary aspiration. Twenty three patients had hiccup of whom 10 refluxed, 9 of them immediately after starting to hiccup. Those patients with hiccup were more likely to reflux than the remainder (P<0.001). Patients with preoperative symptoms of GOR had no greater incidence of reflux during anaesthesia than those without symptoms. The function of the upper oesophageal sphincter appears to be preserved in the majority of these patients with the general anaesthetic technique used. This work therefore suggests that the need for rapid sequence induction is no greater in the second trimester than the first.

Variations in results of simultaneous ambulatory esophageal pH monitoring

Twenty-four-hour esophageal pH monitoring is regarded as the gold standard investigation for gastroesophageal reflux (GER) (1) and the possibility of an "incorrect" answer, false positive or false negative, is only rarely considered (2). However, when a group of infants in this hospital had such pH studies performed on two consecutive days, considerable differences in the results were found (3). This also had been reported from other centers (4-6). It seems likely that most of the differences were due to true "biological" variability in the amount of GER from day to day, but it remains possible that variation in the accuracy of the equipment in detecting acid reflux was also involved.

Antimony and glass pH electrodes can be used interchangeably in 24-hour studies of gastric acidity

Antimony and glass pH electrodes show almost identical experimental errors in continuously measuring buffer solutions at constant temperature over 24 hr. These errors are lower than the nominal quantization error of the instruments and are not properly described by the 24-hr drift determination. The addition of food particles to the solutions can induce severe reading artifacts. The longer response time reported in vitro of antimony electrodes when moving from pH 1 to pH 7 (3.4 sec vs 0.8 sec with glass electrodes) is irrelevant during in vivo pH-metry studies, because we found that the greatest absolute difference between raw fast acquired (4-6 sec) consecutive pH readings of two commonly used devices was 0.7 pH units in circadian profiles obtained from 413 subjects with various clinical conditions. In our in vivo studies, gastric acidity was monitored continuously with two side-by-side minielectrodes, which were variously combined (antimony-glass, A-G; antimony-antimony A1-A2; glass-glass, G1-G2) and applied on groups of 27 subjects matched for clinical condition. The 24-hr pH means and the 24-hr [H+] means calculated from the acidity profiles obtained with the three electrode combinations, lie on the identity line in each group. Using the Bland-Altman technique for assessing measurement agreement, the differences between the 24-hr pH means and the 24-hr [H+] means obtained with the three combined systems are similar (P = .903 and P = 0.824, respectively) and their 95% confidence limits are comprised within the range (+/-) of the reading error of the measuring systems (namely, +/- 0.3 pH units and +/- 12 mmol/liter in terms of [H+]).(ABSTRACT TRUNCATED AT 250 WORDS)

Gastro-oesophageal reflux in pregnancy at term and after delivery

Gastro-oesophageal reflux during a 40-minute reflux provocation test was assessed by lower oesophageal pH monitoring in 25 pregnant women at term, and again on about the second day after delivery. At term 17 women refluxed a total of 29 times; after delivery five women refluxed once each. There was a significant decrease in gastro-oesophageal reflux by the second day after delivery (p less than 0.05). Gastro-oesophageal reflux is, however, only one of the factors that predisposes to acid aspiration pneumonitis.

Gastric aspiration versus antimony and glass pH electrodes. A simultaneous comparative in vivo study

To carry out a simultaneous comparison of the 24-h in vivo performance of antimony and glass electrodes and the findings of intermittent gastric aspiration, a triple-probe system with closely adjacent tips was positioned in the gastric corpus of 10 subjects representing different clinical and pharmacologic conditions. We showed that pH values measured with the antimony and the glass units were well correlated to those assessed in gastric aspirates (rs = 0.87; b = 1.079; a = -0.33; and rs = 0.85; b = 1.121; a = -0.38, respectively). A proportional correlation (rs = 0.86; b = 0.97; a = 0.02) was also found between the two intraluminal pH measurements. With regard to the error frequency distributions obtained by comparing the three measuring systems two at a time, the pH pairs differed by no more than 1 pH unit in most cases (greater than 90%). It can be concluded that antimony and glass pH electrodes can be used interchangeably in 24-h intragastric acidity studies in man.