Prospective trial comparing a combination pH probe-nasogastric tube with aspirated gastric pH in intensive care unit patients

A controlled comparison of traditional feeding tube verification methods to a bedside, electromagnetic technique

BACKGROUND

Benefits of enteral feeding are diminished by aspiration pneumonia and mechanical complications of misplaced feeding tubes. To avoid complications, clinicians determine the location of the tip before feeding. This study compares diagnostic test characteristics of 4 techniques for tip localization.

METHODS

A prospective, blinded trial was conducted on the wards and critical care units of four acute-care hospitals. Patients requiring at least 3 days of enteral feeding were studied. Four observers at each institution used a randomly assigned technique to determine a tube's tip location. Methods included auscultation, aspiration with inspection or pH determination of aspirated material, and a recently developed electromagnetic technique. Results were compared with radiographic determination. Success rates were compared using sensitivity, specificity, and likelihood ratios.

RESULTS

The 4 methods agreed with the radiograph in (mean, 95% confidence interval): 84 (80 to 88)%, 50 (45 to 55)%, 56 (51 to 61)%, and 76 (72 to 81)% of observations, respectively. Only the electromagnetic method and aspiration identified all tubes located above the diaphragm (negative likelihood ratio 0 and sensitivity 100%). Aspiration was unsuccessful in making a determination in 53% of the observations, whereas the electromagnetic method was successful 90% of the time.

Clinical utility of pH paper versus pH meter in the measurement of critical gastric pH in stress ulcer prophylaxis

OBJECTIVE

To evaluate the clinical utility of measuring gastric pH with a pH meter vs. pH paper in critical care patients.

DESIGN

Prospective comparison of gastric pH measurements, using both pH meter and pH paper.

SETTING

Surgical intensive care unit (ICU) at a rural Midwestern university medical center.

PATIENTS

Fifty-one patients who received therapy for prophylaxis of stress ulcers in the surgical ICU.

INTERVENTIONS

Therapy for stress ulcer prophylaxis was monitored.

MEASUREMENTS AND MAIN RESULTS

The pH of 985 gastric samples, taken from 51 patients, was measured with both pH meter and pH paper. The pH meter and pH paper measures demonstrated a concordance correlation coefficient of .896. The mean difference between the two measures (pH paper - pH meter) was estimated to be between -0.4 and 1.4, suggesting a positive bias for the paper. The prevalence of events representing clinically relevant differences between the pH meter and pH paper in the measurement of the same gastric sample was calculated. The frequency with which each of the events occurred consecutively (or, in one case, two nearly consecutive events on the same day) was also calculated. Bias in a clinically relevant range was estimated. A set of "probability profiles" was constructed.

CONCLUSIONS

A hand-held pH meter and pH paper are not interchangeable measures of gastric pH. The pH paper exhibits an appreciable positive bias compared with a hand-held pH meter in the clinically relevant range of 2 to 6. More research is needed to determine if that bias affects treatment outcomes. We recommend the use of a pH meter for patients who demonstrate pH readings of < or = 4, consecutive with readings of < or = 5.

A prospective study of simplified omeprazole suspension for the prophylaxis of stress-related mucosal damage

OBJECTIVES

To determine the efficacy, safety, and cost of simplified omeprazole suspension in mechanically ventilated critically ill patients who have at least one additional risk factor for stress-related mucosal damage.

DESIGN

Prospective, open-label study.

SETTING

Surgical intensive care and burn unit at a university tertiary care center.

PATIENTS

Seventy-five adult, mechanically ventilated patients with at least one additional risk factor for stress-related mucosal damage.

INTERVENTIONS

Patients received 20 mL of simplified omeprazole suspension (containing 40 mg of omeprazole) initially, followed by a second 20-mL dose 6 to 8 hrs later, then 10 mL (20 mg) daily. Simplified omeprazole suspension was administered through a nasogastric tube, followed by 5 to 10 mL of tap water. The nasogastric tube was clamped for 1 to 2 hrs after each administration.

MEASUREMENTS AND MAIN RESULTS

The primary outcome measure was clinically significant gastrointestinal bleeding determined by endoscopic evaluation, nasogastric aspirate examination, or heme-positive coffee ground material that did not clear with lavage, which was associated with at least a 5% decrease in hematocrit. Secondary efficacy measures were gastric pH measured 4 hrs after omeprazole was first administered, mean gastric pH after omeprazole was started, and the lowest gastric pH during omeprazole therapy. Safety-related outcomes included the occurrence rate of adverse events and pneumonia. No patient experienced clinically significant upper gastrointestinal bleeding after receiving omeprazole suspension. The 4-hr postomeprazole mean gastric pH was 7.1, the mean gastric pH after starting omeprazole was 6.8, and the mean lowest pH after starting omeprazole was 5.6. The occurrence rate of pneumonia was 12%. No patient in this high-risk population experienced an adverse event or a drug interaction that was attributable to omeprazole.

CONCLUSIONS

Simplified omeprazole suspension prevented clinically significant upper gastrointestinal bleeding and maintained gastric pH of > 5.5 in mechanically ventilated critical care patients without producing toxicity.

Assessment of 24-hour gastric pH measurements in trauma patients receiving intravenous famotidine by intermittent bolus versus continuous infusion administration

OBJECTIVE

To compare the effects of intermittent bolus versus continuous infusion intravenous famotidine on gastric pH in critically ill trauma patients.

DESIGN

Twenty patients were randomized to receive famotidine by intermittent bolus or continuous infusion for 24 hours. Patients fasted during the study period. Hourly gastric pH measurements were made using an indwelling sensor/sump tube.

SETTING

The study was conducted in a university teaching hospital.

PARTICIPANTS

Adult patients admitted to the neurosurgical or surgical/trauma intensive care unit within 72 hours of traumatic injury were enrolled in the study if they had two consecutive hourly gastric pH readings of < 4 without receiving antacids, sucralfate, or histamine2-antagonists.

MAIN OUTCOME MEASURES

Groups were compared with regard to (1) total dose of famotidine received/24 hours, and (2) number of dosage changes required to maintain a gastric pH value of > or = 4.

RESULTS

The median dose of famotidine required to maintain a gastric pH > or = 4 was 50 mg/24 h (25th-75th percentiles = 40-55 mg) in the intermittent bolus group compared with 42 mg/24 h (25th-75th percentiles = 42-52 mg) in the continuous infusion group (p = 0.9577). A dosage increase was required by 5 of 8 patients (62 percent) receiving intermittent bolus therapy, whereas only 2 of 8 patients (25 percent) in the continuous infusion group required a dosage adjustment (p = 0.315, power = 0.318).

CONCLUSIONS

Intravenous famotidine (40-50 mg/d) effectively controlled gastric pH in critically ill trauma patients. Patients treated with intermittent bolus therapy required slightly more drug and more frequent dosage adjustments to achieve a gastric pH > or = 4. These differences did not reach statistical significance.

Low intramucosal pH is associated with failure to acidify the gastric lumen in response to pentagastrin

OBJECTIVE

To determine if low gastric intramucosal pH is associated with impaired secretion of gastric acid after pentagastrin stimulation.

DESIGN

Prospective study.

SETTING

Intensive care unit of a university teaching hospital.

PATIENTS

20 patients requiring mechanical ventilation.

INTERVENTIONS

All patients with a gastric luminal pH > 4 were given pentagastrin 6 micrograms/kg s.c. to stimulate gastric acid secretion and the response assessed by further measurements of gastric luminal pH.

MEASUREMENTS AND RESULTS

Gastric intramucosal pH (pHi) and luminal pH (pHL) were measured. Patients were divided into two groups on the basis of a low or normal pHi (A value of 7.35 was taken as the lower limit of normal). Patients (n = 6) with normal pHi (7.40 +/- 0.05 [mean +/- SD]) and a luminal pH > 4 (5.65 +/- 1.25) all had a decrease in pHL in response to pentagastrin (decrease in pHL 4.02 +/- 1.52). Of the patients (n = 7) with low pHi (7.2 +/- 0.13) and a pHL > 4 (6.51 +/- 0.48) only one responded to pentagastrin (decrease in pHL for this group 0.93 +/- 1.86). Patients with a pHL < 4 (2.4 +/- 0.71) were not given pentagastrin (n = 7).

CONCLUSION

Some critically ill patients with low gastric intramucosal pH appear to have an impaired ability to acidify the gastric lumen in response to pentagastrin.

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.