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

Does gastric tonometry-guided therapy reduce total mortality in critically ill patients?

Zhang and colleagues have recently published a systematic review and meta-analysis of six studies and conclude that ‘gastric tonometry guided therapy can reduce total mortality in critically ill patients’. So why did gastric tonometry come and go, and what can we learn from this piece of modern history?

Gastric Tonometry as a Prognostic Index of Mortality in Sepsis

BACKGROUND

Splanchnic hypoperfusion in sepsis leads to translocation of bacteria from gut and development of multi-organ dysfunction syndrome (MODS), with increased mortality in critically ill patients. Gastric tonometry can detect this hypoperfusion by measuring carbon dioxide tension (PgCO2) and intramucosal pH (pHi) from gastric mucosa. Therapeutic intervention aimed at improving gut perfusion can improve the outcome and prognosticate the mortality in sepsis patients.

METHODS

100 patients with clinical diagnosis of sepsis were included and divided into two groups of 50 each. Group A patients were managed traditionally without gastric tonometry and in Group B gastric tonometry was used for therapeutic intervention. The intramucosal PCO2, pHi, end tidal carbon dioxide tension (EtCO2) and (PgCO2-EtCO2) differences were monitored at 0, 12 and 24 hours interval.

RESULT

Overall mortality in Group A was 64 % and 54 % in Group B. In Group B 45% patients developed MODS and 54 % died with low pHi. As an index of mortality low pHi had a sensitivity of 70% and specificity of 65%.

CONCLUSION

There is a good correlation between mortality prediction on the basis of pHi and PgCO2-EtCO2 difference and actual mortality in critically ill patients. The gastric tonometer should be used to predict mortality and guide resuscitation in septicemia.

Effect of proton pump inhibitors on gastric juice volume, gastric pH and gastric intramucosal pH in critically ill patients : a randomized, double-blind, placebo-controlled study

OBJECTIVE

This study aimed to determine the effect of administration of a single-dose proton pump inhibitor (PPI) on gastric intramucosal pH (pHi), gastric juice volume and gastric pH in critically ill patients.

METHODS

This prospective, randomized, double-blind, placebo-controlled study included 75 patients who were divided into five groups that received the following treatment: group C (n = 15), saline 100 mL; group O (n = 15), omeprazole 20 mg; group P (n = 15), pantoprazole 40 mg; group E (n = 15), esomeprazole 20 mg; and group R (n = 15), rabeprazole 20 mg. All treatments were administered nasogastrically in 100 mL of physiological saline. Measurements of gastric pHi, gastric juice volume and gastric pH were obtained immediately before and 2, 4 and 6 hours after administration of treatments. In addition, gastric content was aspirated and its volume was recorded.

RESULTS

Initial gastric pHi, gastric juice volume and gastric pH values were not statistically significantly different among the groups (p > 0.05). No statistically significant difference in gastric pHi was seen among the groups before or 2, 4 or 6 hours after saline or PPI administration. At hours 2, 4 and 6, gastric pH in the pantoprazole, esomeprazole and rabeprazole groups increased significantly, whereas gastric juice volume decreased significantly, compared with the omeprazole and placebo groups (p < 0.001). No statistically significant differences were seen between the pantoprazole, esomeprazole and rabeprazole groups.

CONCLUSION

This is the first study to show that single-dose pantoprazole, esomeprazole and rabeprazole are associated with greater gastric pH increase and greater gastric juice volume decrease than omeprazole in critically ill patients. Our study also suggests that PPIs do not affect gastric pHi measurements in critically ill patients and can be administered during pH monitoring.

The Relationship Between a Pentagastrin-Stimulated Gastric Luminal Acid Production Test (Gastrotest) and Enteral Feeding-Related Gastrointestinal Complications in Critically Ill Patients

Gastrointestinal feeding-related complications (GICs) are common in critically ill patients. Unfortunately, patients at risk for GICs cannot be easily identified. Therefore, we performed a prospective study of 20 critically ill patients to determine the association between a pentagastrin-stimulated gastric acid production test and GICs. Before feeding, the change in the pH of gastric juice was measured in response to a subcutaneous injection of pentagastrin (Gastrotest). We recorded GICs and the feeding volume ratio during each patient's intensive care unit (ICU) stay. Nineteen patients' data were analyzed and 9 patients (47%) developed > or =1 GIC, including large gastric residuals, 26%; abdominal distension, 26%; and vomiting, 21%. Patients with GICs had a longer length of ICU stay (mean 21.3, range 5-45 versus 10.1, range 3-32; P < 0.05). The 9 patients (47%) who were Gastrotest responders before starting enteral feeding exhibited a significantly larger volume ratio (P = 0.01) and fewer GICs (1 [11%] versus 8 [80%]; P < 0.05). Abdominal distension was seen in only nonresponders. The positive and negative predictive values for this test's ability to predict GICs were 80% and 88.9%, respectively. Responding to a pentagastrin-stimulated gastric luminal acid production test is associated with the administration of larger volumes of enteral feed and fewer GICs.

Lack of effect of ranitidine on gastric luminal pH and mucosal PCO2 during the first day in the ICU

BACKGROUND

Histamine(2) (H(2))-blocking agents can attenuate intragastric CO(2)-production by reducing gastric acid secretion and preventing the interaction between H(+) and bicarbonate. However, gastric acid production may be impaired in acute circulatory failure due to poor mucosal perfusion, and H(2)-blockade could further impair mucosal perfusion.

METHODS

Forty patients with acute circulatory and/or respiratory failure, age 61 +/- 16 years (mean +/- SD), APACHE II score 21 +/- 7, and SOFA score 8 +/- 3, received randomly either ranitidine, 50 mg (R) or placebo (P) every 8 h. Gastric intraluminal pH (gpH; antimony probe with external reference electrode) and mucosal pCO(2) (prCO(2), semicontinuous air-tonometry) were measured during 24 h, and blood gases were taken at 6-h intervals.

RESULTS

Gastric intraluminal pH was 4.3 +/- 2.4 in P and 5.1 +/- 1.6 in R (NS). Mean prCO(2) was 6.8 +/- 2.7 kPa in P and 7.4 +/- 2.1 kPa in R, and mucosal-arterial pCO(2) gradient (Delta pCO(2)) was 2.2 +/- 2.9 kPa and 2.4 +/- 2.4 kPa, respectively (NS). Within-patient variabilities of gpH and prCO(2) were not influenced by ranitidine. A posthoc analysis revealed that non-survival in R was associated with a low mucosal pHi after 24 h (P = 0.002). This was explained by a low arterial pH but not by differences in gpH or prCO(2).

CONCLUSION

In acute respiratory and circulatory failure, H(2) blockade has an inconsistent impact on gpH and does not reduce variabilities of gpH or prCO(2).

Intermittent enteral nutrition--a comparative study examining the effect on gastric pH and microbial colonization rates

In a prospective randomized study we aimed to examine the effect on gastric pH and microbial colonization of enteral nutrition (EN) delivered both by intermittent and continual infusion. Forty-three mechanically ventilated patients were randomized to receive EN by one of three methods, intermittent or continual gastric or continual jejunal. We sampled gastric aspirate for pH and culture in all patients at 0600 hours and pH in gastric intermittent feeders at 2200 hours daily. Patients were studied for 12 days or until extubated. Data was obtained on 41 patients, of whom 73% had a diagnosis of trauma. Median APACHE II score was 17 and ventilation time 11 days. Twelve patients received gastric continuous, 15 gastric intermittent and 14 jejunal nutrition. No significant difference was observed between the three groups with regard to median 0600 pH (P = 0.16). This was lowest in the jejunal group (3.2) followed by the gastric intermittent group (4.0) and then gastric continuous group (5.0). With overnight cessation of EN in the gastric intermittent group, the median pH fell from 5.2 at 2200 to 4.0 at 0600 (P = 0.01) with no effect on gastric colonization. The probability of gastric colonization over time however was significantly lower in the jejunal group compared with the two gastric groups (Log rank test, P = 0.02). These results demonstrate that in a patient population consisting predominantly of trauma, overnight cessation of EN made no overall difference to 0600 gastric pH or colonization rates. The preservation of pH and lowered colonization in those given jejunal feeding may have implications in the pathogenesis of ventilator-associated infection and may warrant further study using larger patient numbers.

Comparison of oesophageal and gastric air tonometry in patients with circulatory failure

BACKGROUND

Gastric PCO2 measured by balloon tonometry can estimate the adequacy of splanchnic perfusion. However, enteral feeding and gastric content can interfere with gastric PCO2 assessment. Tonometry in other sites of the body could avoid these problems. We therefore tested the hypothesis that oesophageal air tonometry would give results similar to gastric tonometry.

METHODS

We studied 20 consecutive patients (mean age 68 (SD 9) [range 49-81] yr, 18 males, SAPS II score 55 (SD 18), ICU mortality 55%) with circulatory disorders during mechanical ventilation in the intensive care unit. Tonometer probes were placed via the nose, one into the stomach and the other in the oesophagus. PCO2 was measured with two automated gas analysers, at admission and 30 min, 1, 2, 3, 32, 40, and 48 h thereafter.

RESULTS

One hundred and forty-eight paired measurements were obtained. Gastric PCO2 was greater than oesophageal PCO2 on admission (7.19 (1.43) vs 5.89 (0.73) kPa, P < 0.01) and subsequently. Differences between the measures correlated (r = 0.67) with the mean absolute value, indicating that overestimation increased as gastric PCO2 increased.

CONCLUSIONS

Oesophageal PCO2 is less than gastric PCO2, and the difference is greater when gastric PCO2 levels are greater. Air tonometry may not measure regional PCO2 levels in the oesophagus satisfactorily. Other methods and sites for carbon dioxide tonometry should be examined.

Does gastric juice pH influence tonometric PCO2 measured by automated air tonometry?

To determine the influence of changes in gastric juice pH due to intravenous administration of pentagastrin and omeprazole on intramucosal regional PCO2 (Pr(CO2)), we investigated 17 healthy human volunteers. Gastric juice pH was obtained from a glass pH electrode for continuous gastric juice pH measurement and Pr(CO2))was measured by using automated air tonometry. After baseline (8:00 A.M.-9:00 A.M.) the subjects received 0.6 microg/kg/h pentagastrin intravenously for 1 h (9:00 A.M.-10:00 A.M., after stimulation 10:00 A.M.-11:00 A.M.) and 40 mg omeprazole intravenously (after omeprazole 11:00 A.M.-3:00 P.M.). Following pentagastrin administration gastric juice pH significantly decreased from 1.2 +/- 0.4 to 0.6 +/- 0.4 (mean +/- SD, p < 0.007, versus baseline), whereas omeprazole transiently increased luminal pH up to 4.4 +/- 1.7 (p < 0.007 versus baseline). These subsequent changes in gastric juice pH were accompanied by a significant increase in Pr(CO2) from 48 +/- 12 to 61 +/- 17 mm Hg (p < 0.007 versus baseline) and a decrease to 44 +/- 5 mm Hg (p < 0.002 versus pentagastrin), respectively. A gastric juice pH > 4 considerably reduces mean gastric Pr(CO2) and interindividual variability. Thus omeprazole may improve the validity of gastric tonometry data.

Reduced gastric acid production in burn shock period and its significance in the prevention and treatment of acute gastric mucosal lesions

AIM: To investigate the changes of gastric acid production and its mechanism in shock period of severe burn in rats.

METHODS: A rat model with 30% TBSA full-thickness burn injury w as employed and the gastric acid production, together with gastric mucosal blood flow (GMBF) and energy charge (EC) were measured serially within 48 h postburn.

RESULTS: The gastric acid production in the acute shock period was markedly inhibited after severe burn injury. At the 3rd h postburn, the gas tricjuice volume, total acidity and acid output were already significantly decreased (P < 0.01), and reached the lowest point, 0.63 mL/L ± 0.20 mL/L, 10.81 mmol/L ± 2.58 mmol/L and 2.23 mmol/h ± 0.73 mmol/h respectively, at the 12th h postburn. Although restored to some degree 24 h after thermal injury, the variables above were still statistically lower, compared with those of control animals at the 48th h postburn. The GMBF and EC were also significantly reduced after severe burns, co nsistent with the trend of gastric acid production changes.

CONCLUSION: Gastric acid production, as well as GMBF and EC was predominantly decreased in the early postburn stage, suggesting that gastric mucosal ischemia and hypoxia with resultant disturbance in energy metabolism, but not gastric acid proper, might be the decisive factor in the pathogenesis of AGML after thermal injury, and that the preventive use of anti-acid drugs during burn shock period was unreasonable in some respects. Therefore, taking effective measures to improve gastric mucosal blood perfusion as early as possible postburn might be more preferable for the AGML prevention and treatment.

Does splanchnic ischemia occur in isolated neurotrauma? A prospective observational study

OBJECTIVE

To characterize the incidence and severity of splanchnic ischemia, as defined by gastric tonometry, in patients with isolated severe head injury and to examine the relationship between cerebral hemodynamics and splanchnic ischemia.

DESIGN

Prospective observational study.

SETTING

Neurosurgical intensive care unit in a tertiary referral center.

PATIENTS

Ten patients with severe neurotrauma.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The mean arterial pressure, intracranial pressure, and gastric mucosal P(CO2) measurements were recorded at 15-min intervals. Intramucosal pH was calculated every 3 hrs. All patients received stress ulcer prophylaxis. Nine patients received noradrenaline infusions to maintain a target cerebral perfusion pressure of 70 mm Hg. The mean baseline gastric mucosal P(CO2) and intramucosal pH were 38+/-10 torr and 7.38+/-0.1 pH units, respectively. Nine patients manifested low intramucosal pH during the study period. Gastric mucosal P(CO2) values ranged from 36 to 132 torr. Intramucosal pH measurements ranged from 6.9 to 7.47. The mucosal gap ranged from -12 to +93 torr (mean +/- SD, 17+/-17 torr). The pH gap ranged from -0.1 to +0.54 pH units (mean +/- SD, 0.14+/-0.11 pH units). There was no statistically significant relationship between cerebral hemodynamics, the use of inotropes, and gastric mucosal P(CO2), or intramucosal pH.

CONCLUSIONS

Splanchnic ischemia (intramucosal pH, <7.3) occurs commonly in isolated neurotrauma, with a statistically nonsignificant trend toward development of mucosal ischemia with decreased cerebral perfusion.

Validation of air as an equilibration medium in gastric tonometry: an in vitro evaluation of two techniques for measuring air PCO2

This laboratory-based bench study was undertaken to evaluate the accuracy and equilibration characteristics of air and saline respectively as CO2 equilibrating media in the silicone balloon of a gastric tonometer and to compare two methods of measuring air PCO2. Two gastric tonometers were suspended in a bath containing 0.9% saline maintained at 37 degrees C. Certified calibration gases at three different CO2 concentrations were bubbled into the bath. When the bath PCO2 measurement was stable the tonometers were primed with 5 ml of air and 2.5 ml normal saline respectively and allowed to equilibrate for 30 and 90 minutes. Following equilibration, samples were aspirated and analysed in duplicate in a blood gas analyser. Bias and precision were calculated from the measured and expected PCO2 values. A consistent negative bias (21-23%) was seen with air at all three CO2 concentrations at 30 and 90 minutes with a coefficient of variation between 2.7 and 3.3%. Imprecise data were obtained with saline at different levels of CO2. A similar experimental set-up was used to compare air PCO2 measurement by a blood gas analyser and an infra-red analyser (Tonocap). Similar bias was obtained with the blood gas analyser with respect to air PCO2 measurement as in experiment 1. The infra-red analyser measurement was highly precise with negligible bias. Air appears to be a better CO2 equilibration medium during bench testing of tonometry producing a systematic negative offset and requiring a uniform correction factor of 1.25. This correction factor is independent of equilibration time and equilibrating CO2 concentration. The use of the infra-red analyser eliminates any bias in the measurement of air PCO2 and obviates the need for a correction factor.

Does gastric tonometry work? Yes

Gastric tonometry is gaining acceptance rapidly as a noninvasive method of monitoring tissue dysoxia in a key organ system that previously could not be assessed easily. In addition to being noninvasive, gastric tonometry also identifies dysoxia in shock sooner than currently available monitors. This allows for more timely intervention with a subsequent improvement in prognosis in defined groups of patients. Tonometry data that suggest continued dysoxia despite intervention should signal clinicians to seek alternative diagnoses or to question the efficacy of current therapies, including antibiotics.

Effect of nasogastric suction and ranitidine on the calculated gastric intramucosal pH

OBJECTIVE

To study the effect of nasogastric suction and ranitidine on the determination of gastric intramucosal pH (pHi).

DESIGN

Prospective study.

SETTING

Clinical research unit at a university hospital intensive care department.

SUBJECTS

12 healthy volunteers.

INTERVENTIONS

After a 2-h measurement control period a tonometer was connected to nasogastric suction for 2 h, and thereafter ranitidine was given intravenously and gastric pHi measured.

MEASUREMENTS AND RESULTS

During each 2-h measurement period gastric PCO2, gastric pHi, and pH gap were determined every 30 min. Luminal pH was measured after insertion of tonometer and at the end of each study period. Neither nasogastric suction nor ranitidine had an effect on the coefficient of variation for either gastric PCO2 or pHi. Compared to control and nasogastric suction periods, after ranitidine mean gastric pHi was higher (control 7.22 +/- 0.08; nasogastric suction 7.23 +/- 0.07; after ranitidine 7.31 +/- 0.06, p < 0.001) mean gastric PCO2 lower (control 6.4 +/- 1.3; nasogastric suction 6.5 +/- 1.3; after ranitidine 5.3 +/- 0.9, p < 0.001) and pH gap lower (control 0.18 +/- 0.08; nasogastric suction 0.17 +/- 0.05; after ranitidine 0.09 +/- 0.06, p < 0.01). Luminal pH increased after ranitidine in each subject.

CONCLUSIONS

H2 blockers have no effect on the reproducibility of gastric pHi measurements, but the use of H2 blockers modifies the normal values for gastric pHi in healthy subjects.

Bladder epithelial oxygen tension--a new means of monitoring regional perfusion? Preliminary study in a model of exsanguination/fluid repletion

OBJECTIVE

To assess whether monitoring of bladder epithelial oxygen tension (BEOT) would provide an indication of regional (renal) organ perfusion in an exsanguination/fluid repletion animal model.

DESIGN

Prospective non-randomized laboratory study.

SETTING

Research laboratory.

INTERVENTIONS

Eight anaesthetised, spontaneously breathing Sprague-Dawley male rats weighing approximately 200 g were instrumented. They received 1-ml aliquots of fluid until no further haemodynamic improvement was seen, followed by removal of 1-ml aliquots of blood until renal blood flow fell by 50%. The animal was then resuscitated with repeated 1 to 2-ml aliquots of fluid until no further improvement was achieved and, finally, progressively exsanguinated to cardiovascular collapse.

MEASUREMENTS AND RESULTS

A continuous Clark-type oxygen electrode lying in contact with the inside wall of the bladder measured changes in BEOT during these exsanguination and fluid repletion manoeuvres. Changes in BEOT closely mirrored both systemic (blood pressure and aortic blood flow) and regional (renal blood flow) haemodynamic changes. A direct correlation existed between percentage change in BEOT and base deficit, and an indirect correlation was seen with arterial oxygen tension.

CONCLUSIONS

Measurement of BEOT may be a useful and relatively non-invasive means of monitoring regional organ perfusion. Further studies are warranted.

Splanchnic tonometry: a review of physiology, methodology, and clinical applications

The objective of this article is to review splanchnic tonometry. The English literature, involving both animal and human studies, was used for review, with emphasis on papers on physiological and methodological principles and clinical applications. Tonometry involves the measurement of intraluminal PCO2 as a measure of mucosal PCO2 in the gastrointestinal tract via a catheter in, for instance, stomach or sigmoid colon, and the calculation, with help of the blood bicarbonate content and the Henderson-Hasselbalch equation, of the mucosal pH (pHi). The latter is considered as a relatively simple index of the adequacy of mucosal blood flow. Concerning methodology, it is still unclear whether acid secretion should be inhibited for proper assessment of PCO2 in the stomach. Buffering of bicarbonate by gastric acid may elevate the intraluminal PCO2 independently from mucosal PCO2, thereby confounding pHi as a measure of perfusion adequacy. This can be prevented by inhibition of acid secretion. Authors have raised doubts whether the composite variable pHi is of additive value to the acid-base status of arterial blood, so that it is unclear whether a subnormal pHi is a specific and sensitive indicator of mucosal ischemia, as suggested by others on the basis of a decline in the pHi along the gastrointestinal tract in animals subjected to vascular occlusion or circulatory shock. Moreover, tissue PCO2 depends on the PCO2 of supplying blood. Conversely, the bicarbonate concentration in ischemic mucosa may not equal that in arterial blood. Taken together, an elevated tonometer fluid arterial blood PCO2-gradient might be a more sensitive and specific indicator of mucosal ischemia than a decrease in the pHi, analogous to an increase in tissue PCO2 and widening of the venoarterial PCO2 gradient during various types of hypoperfusion, in animals and humans. Although splanchnic ischemia is an early event in shock, the sensitivity and specificity of this index for mucosal ischemia and its clinical value, relative to that of the pHi, have not been formally evaluated yet. Nevertheless, the pHi has been suggested to be of predictive value for gastrointestinal complications, multiple organ failure, success or failure of weaning from mechanical ventilation, and outcome in critically ill patients. Tonometry may be a useful monitoring technique to guide treatment and to improve survival. Splanchnic tonometry is a relatively simple, noninvasive, and thereby promising technique to monitor the critically ill. However, some aspects need further evaluation before the technique can be advocated for routine use.