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

Accuracy of pH strip testing and pH liquid testing versus standard pH meter of gastric contents in critically ill patients: a diagnostic accuracy study

OBJECTIVE

The utilisation of pH level measurements from gastric contents may indicate the preferred tip position of a nasogastric tube or monitor the efficacy of stress ulcer prophylaxis in critically ill patients. We aimed to determine the accuracy of pH strip (pHS) tests and pH liquid (pHL) tests compared with the standard pH meter (pHM).

DESIGN

Diagnostic accuracy study.

SETTING

Gastric contents from medically critically ill patients.

PARTICIPANTS

In total, 113 gastric samples were collected from 27 critically ill patients.

OUTCOME MEASURE

The level of pH measured by pHM, pHS and pHL.

RESULTS

The pH values measured by pHM, pHS and pHL were 5.83 (IQR 5.12-6.61), 5.50 (IQR 5.00-6.00) and 5.75 (IQR 5.25-6.25), respectively. The pHS test showed greater accuracy, exhibiting a more positive correlation with the standard pHM measurement than the pHL test, with Y=0.95*X+0.56; rho=0.91, p<0.001, and Y=1.09*X - 0.72; rho=0.75, p<0.001, respectively. However, the pHS test demonstrated less agreement with the pHM than the pHL test, with biases of -0.27 versus 0.18, respectively. Noticeably, a slight variation in pHL from the standard pH values was found when we measured gastric contents with a pH lower than 5.

CONCLUSION

Both the pHS and pHL methods were good options for measuring gastric pH in critically ill patients. However, it was advisable to find alternative approaches to the pHL testing method when anticipated gastric acidity levels fall below 5.

TRIAL REGISTRATION NUMBER

TCTR20220530004.

Measuring Gastric pH in Tube-fed Children With Neurologic Impairments and Gastroesophageal Disease

OBJECTIVES

The aim of the study was to determine the extent of agreement between pH paper and handheld pH meter with a laboratory pH meter for gastric pH measurement in children with neurologic impairments and gastrostomy tubes who have gastroesophageal reflux disease (GERD).

METHODS

In this prospective observational study, gastric contents were aspirated from gastric or nasogastric tubes and the pH measured using 3 techniques: pH paper, handheld pH meter, and laboratory pH meter (the gold standard). Agreement between techniques was assessed with intraclass correlation coefficient (ICC), Bland-Altman analysis, and kappa statistic.

RESULTS

Among 43 patients contributing 67 gastric samples, the ICC was 0.75 (95% confidence interval [CI]: 0.69-0.97) between the handheld and laboratory meters, 0.69 (95% CI: 0.63--0.94) between the pH paper and laboratory meter and 0.69 (95% CI: 0.63-0.94) between the handheld meter and paper. The Bland-Altman analysis between the handheld and lab meters showed a mean difference of -0.03 pH units (limits of agreement: -0.52 to 0.47 pH units) and 0.17 pH units (limits of agreement: -0.99 to 1.33 pH units) between the paper and lab meter. The kappa coefficients for a pH ≥4 were 1.0 (95% CI: 1.0--1.0) between the handheld and lab meters and 0.9 (95% CI: 0.77--1.0) between the paper and lab meter.

CONCLUSIONS

The findings suggest that both point-of-care tests, the pH meter and pH paper, correlate well with the gold standard for testing pH with a laboratory pH meter, indicating usefulness in point-of-care testing for monitoring gastric pH in tube-fed children with neurologic impairments and GERD.

Effect of pH Test-Strip Characteristics on Accuracy of Readings

BACKGROUND

Little is known about characteristics of colorimetric pH test strips that are most likely to be associated with accurate interpretations in clinical situations.

OBJECTIVES

To compare the accuracy of 4 pH test strips with varying characteristics (ie, multiple vs single colorimetric squares per calibration, and differing calibration units [1.0 vs 0.5]).

METHODS

A convenience sample of 100 upper-level nursing students with normal color vision was recruited to evaluate the accuracy of the test strips. Six buffer solutions (pH range, 3.0 to 6.0) were used during the testing procedure. Each of the 100 participants performed 20 pH tests in random order, providing a total of 2000 readings. The sensitivity and specificity of each test strip was computed. In addition, the degree to which the test strips under- or overestimated the pH values was analyzed using descriptive statistics.

RESULTS

Our criterion for correct readings was an exact match with the pH buffer solution being evaluated. Although none of the test strips evaluated in our study was 100% accurate at all of the measured pH values, those with multiple squares per pH calibration were clearly superior overall to those with a single test square.

CONCLUSIONS

Test strips with multiple squares per calibration were associated with greater overall accuracy than test strips with a single square per calibration. However, because variable degrees of error were observed in all of the test strips, use of a pH meter is recommended when precise readings are crucial.

Combined application of nasogastric tubes and nasointestinal tubes in neurosurgical intensive care patients with stress ulceration: a novel solution to treatment and early enteral nutrition

Objective

Stress ulcers occur frequently in neurosurgical intensive care patients and can pose serious risks. We summarized the clinical experience of the combined application of nasointestinal tubes for early restoration of enteral nutrition and of nasogastric (NG) tubes for stress ulceration treatment in patients hospitalized in a neurosurgical intensive care unit.

Methods

From January 2011 to June 2011, a series of 67 patients with stress ulceration hospitalized in a neurosurgical intensive care unit were randomized to two groups. The control group (33 patients) received treatment with NG tube decompression and drainage according to international guidelines, and parenteral nutrition was changed to enteral feeding until there was no grossly visible blood in the NG tube. The nasointestinal tube group (34 patients) received treatment combining application of NG tubes and nasointestinal tubes. Drainage was performed with NG tubes as in the control group, with concurrent placement of nasointestinal tubes. Duration until resolution of stress ulceration and days until start of enteral nutrition were compared between the two groups.

Results

Duration until resolution of stress ulceration was 4.5 days in the control group and 4.3 days in the nasointestinal tube group. There was no difference between the two groups (P > 0.05). Duration until start of enteral nutrition was 4.5 days in the control group and 1 day in the nasointestinal tube group. There was an obvious difference between the two groups (P < 0.01).

Conclusions

The combined application of NG tubes and nasointestinal tubes in neurosurgical intensive care patients with stress ulceration is an effective means of treating stress ulceration and restoring early enteral nutrition.

Voltammetric pH sensing using carbon electrodes: glassy carbon behaves similarly to EPPG

Developing and building on recent work based on a simple sensor for pH determination using unmodified edge plane pyrolytic graphite (EPPG) electrodes, we present a voltammetric method for pH determination using a bare unmodified glassy carbon (GC) electrode. By exploiting the pH sensitive nature of quinones present on carbon edge-plane like sites within the GC, we show how GC electrodes can be used to measure pH. The electro-reduction of surface quinone groups on the glassy carbon electrode was characterised using cyclic voltammetry (CV) and optimised with square-wave voltammetry (SWV) at 298 K and 310 K. At both temperatures, a linear correlation was observed, corresponding to a 2 electron, 2 proton Nernstian response over the aqueous pH range 1.0 to 13.1. As such, unmodified glassy carbon electrodes are seen to be pH dependent, and the Nernstian response suggests its facile use for pH sensing. Given the widespread use of glassy carbon electrodes in electroanalysis, the approach offers a method for the near-simultaneous measurement and monitoring of pH during such analyses.

Voltammetric pH sensor based on an edge plane pyrolytic graphite electrode

A simple sensor for pH determination is reported using unmodified edge plane pyrolytic graphite (EPPG) electrodes. The analysis is based on the electro-reduction of surface quinone groups on the EPPG which was characterised using cyclic voltammetry (CV) and optimised with square-wave voltammetry (SWV). Under optimised conditions, a linear response is observed between the peak potential and pH with a gradient of ∼59 mV per pH (at 25 °C), which corresponds well with Nernstian behaviour based on a 2 proton, 2 electron system over the aqueous pH range 1.0 to 13.0. As such, an EPPG is suggested as a reagent free and robust pH sensing material.

Comparison of continuous pH-meter and intermittent pH paper monitoring of gastric pH in critically ill children

OBJECTIVE

A gastric pH below 4 increases the risk of gastrointestinal hemorrhage in critically ill patients. The pH can be monitored intermittently by testing the gastric aspirate using pH paper or continuously using a pH-meter (often in combination with multichannel intraluminal impedance). The objective of this study was to compare these two methods of pH measurement.

METHODS

An observational, prospective study was conducted in critically ill children between 1 month and 14 years with at least two risk factors for gastrointestinal hemorrhage. Gastric pH was measured continuously by a multichannel pH-meter tube and every 2 h using pH paper on aspirates of gastric juice.

RESULTS

A total of 471 gastric pH measurements were analyzed. The mean gastric pH measured by the pH-meter was 4.3±2.5 and that by pH paper was 3.9±2.2. The gastric pH was above 4 in 49.6% of the measurements taken on the basis of the gastric aspirate and in 49.8% of the pH-meter readings. The correlation between the two methods was moderate (0.59; P<0.001) but the concordance was low (0.54). The concordance with regard to determining a gastric pH above or below 4 was 77%.

CONCLUSION

pH paper is a simple and inexpensive method that can be useful for initial patient monitoring, but it should not be used as a substitute for monitoring by pH-meter in patients in whom strict control of the gastric pH is required.

Histamine 2 receptor antagonists vs intravenous proton pump inhibitors in a pediatric intensive care unit: a comparison of gastric pH

PURPOSE

The aim of this study was to assess gastric pH in critically ill pediatric patients receiving intravenous stress ulcer medication.

MATERIALS AND METHODS

A prospective study was done in 48 patients with a gastric tube in place who were receiving either ranitidine or a proton pump inhibitor and no enteral nutrition. Daily peak and trough gastric pHs were measured.

RESULTS

The median age was 7 years 5 months (range, 1 month to 19 years), the median weight was 31 kg (range, 3-130 kg), and the median pediatric risk of mortality 2 (PRISM2) score was 12.5 (range, 0-31). All patients were intubated and 8 received dialysis. The average trough pH was 4.4 +/- 1.6 in the ranitidine group, 4.9 +/- 1.8 in the once daily proton pump inhibitor group, and 5.0 +/- 1.2 in the twice daily proton pump inhibitor group (P = .16). The average peak pH was 5.3 +/- 1.8 in the ranitidine group, 5.9 +/- 1.6 in the once daily proton pump inhibitor group, and 6.0 +/- 1.0 in the twice daily proton pump inhibitor group (P = .06). Three (10%) of 28 trough pH measurements in the twice daily proton pump inhibitor group were more acidic than 4 vs 24 (40%) of 60 in the ranitidine group, and 22 (40%) of 56 in the once daily proton pump inhibitor group (P = .02). One (4%) of 27 peak pH measurements in the twice daily proton pump inhibitor group were more acidic than 4 vs 13 (20%) of 61 in the ranitidine group, and 9 (16%) of 56 in the once daily proton pump inhibitor group (P = .12). Three patients (6%; 95% confidence interval, 0.51%-16%) developed upper gastrointestinal bleeding, and 4 patients (8%; 95% confidence interval, 0%-13%) developed ventilator-acquired pneumonia.

CONCLUSIONS

Many critically ill pediatric patients receiving stress ulcer prophylaxis have a trough or peak gastric pH more acidic than 4.

Confirmation of nasogastric tube position by pH testing

INTRODUCTION

In 2004, the Medicines and Healthcare products Regulatory Agency (MHRA) advised that nasogastric (NG) tube position should be confirmed using pH strips or paper. However, gastric pH is raised by the use of H2-blockers and proton-pump inhibitors (PPIs) potentially producing false negative pH tests resulting in delayed feeding. In addition, colorimetric differentiation using pH strips may be more prone to bias and inaccuracy than direct pH measurements largely used to establish the threshold.

METHOD

To quantify this problem a 1 day survey of all the patients requiring NG and nasointestinal (NI) feeding was undertaken, to establish the numbers of patients receiving H2-Blockers or PPIs, with or without a safe swallow and the methods currently being used to confirm tube positioning. A second observational study was performed to establish the accuracy of six pH strips available to NHS trusts against four unlabelled pH solutions.

RESULTS

Forty-two per cent of patients receiving NG feeding were on H2-blockers or PPIs, including 13% who had a safe swallow for acidic drinks that could be subsequently aspirated to confirm position. In the second study 'testers' correctly identified pH's 3, 4, 5 and 6 with Mackery-Nagel 0-6, BDH 0-6 and 0-14 strips but overestimated pH 4 as pH 5 with Johnson 0-11 paper, underestimated pH 6 as pH 5 with Pehanon 0-12 paper and with Litmus classified pH 3-5 as acid (all), but half also classified pH 6 as acid.

CONCLUSION

Theoretically 29% of NG tube positions could not be confirmed by pH testing because of the usage of PPIs or H2-blockers and lack of swallow. Some pH strips are either inaccurate or their result misinterpreted by staff. Large surveys and trials of the actual efficacy and accuracy of pH testing are required.

Use of pericardial fluid pH to distinguish between idiopathic and neoplastic effusions

Pericardial effusion (PE) resulting from neoplasia usually is associated with a poor prognosis, whereas idiopathic PE frequently has a good prognosis. This study examined the utility of pH measurement to distinguish between these 2 etiologies. Dogs were classified as having idiopathic PE (n = 12) if pericarditis was diagnosed on histopathology (n = 4) or if no historical, physical, or echocardiographic evidence of recurrent PE was present for at least 6 months after pericardiocentesis (n = 8). Dogs were classified as having neoplastic PE (n = 25) if pericardial or myocardial neoplasia was detected on histopathology (n = 11) or a discrete mass associated with the right atrium, right ventricle, or the aorta was visualized on echocardiography (n = 14). Samples of PE were centrifuged and the supernatant pH was measured with a portable pH meter. The lowest pH (6.40) was found in a dog with idiopathic PE and the highest pH (7.85) was found in a dog with neoplastic PE. However, data from the 2 groups overlapped in 33 out of 37 (89%) instances, and median pH from the idiopathic and neoplastic groups was not significantly different (7.40 and 7.47, respectively; P = 0.28; difference in medians = -0.7; 95% CI, -0.26-0.06). Because of the degree of overlap, our data provide little justification for the use of pH measurement as a diagnostic test in cases of PE.

Pharmacologic prophylaxis and treatment of stress ulcers in critically ill patients

Most clinicians agree that critically ill patients are at significant risk of developing stress-related ulcers and may have already developed mucosal lesions even if they are asymptomatic. Many options, including new pharmacologic advances, are available for the treatment and prophylaxis of stress-related ulcers; therefore, all critically ill patients should receive prophylaxis, even if they do not require treatment. Nutrition may play a significant role in the future in preventing stress-related ulcers. By improving stores of critical elements such as antioxidants, vitamins, and minerals before surgery, patients may lower the risk of developing stress ulcers. Critical care clinicians are critical in preventing and treating stress-related ulcers and should be vigilant in their patient care.

Omeprozole therapy in pediatric patients after liver and intestinal transplantation

BACKGROUND

Proton pump inhibitors such as omeprazole are increasingly used to prevent stress-related gastric bleeding in critically ill patients. In this investigation, the acid-suppressive potency of omeprazole was assessed in one at-risk group, pediatric patients undergoing liver or intestinal transplantation, or both.

METHODS

Twenty-two patients ranging in age from 0.9 to 108 months (23.8 +/- 6.5) underwent isolated liver (n = 10) or intestinal (11 with composite liver allografts) transplantation. Omeprazole was delivered in bicarbonate suspension through a nasogastric tube. Therapy was started after surgery at 0.5 mg/kg every 12 hours. Gastric pH monitoring was performed approximately 2 days later.

RESULTS

For the entire group, mean gastric pH equaled 6.1 +/- 0.3, the same in recipients of isolated liver and intestinal allografts. Twelve of the 22 patients demonstrated a discontinuous omeprazole effect, that is, dissipation of acid reduction before the next dose. Five of the 12 patients with discontinuous omeprazole effect had mean gastric pH of less than 5 (3.9 +/- 0.4). In 4 of these 5, the omeprazole dosing interval was shortened to every 8 or every 6 hours, resulting in an increase in mean pH to 6.6 +/- 0.2 ( P < 0.01). In the remaining 10 of 22 patients, acid suppression was uninterrupted until the next dose. No patient experienced bleeding attributable to gastric erosion.

CONCLUSION

Omeprazole suspended in sodium bicarbonate is an effective acid-suppressing agent in pediatric recipients of liver or intestinal transplant, or both. A dosage of 0.5 mg/kg every 12 hours is sufficient for most patients, but dosing every 6 to 8 hours is required to assure maximal acid suppression in all.