Comparison of clinical information gained from routine blood-gas analysis and from gastric tonometry for intramural pH

Abstract

The measurement of gastric intramucosal pH (pH i) has been advocated to assist in decision-making for critically ill patients. To assess whether the information obtained from the measurement of pH i can be obtained from other measurements of metabolic acidosis, we studied 20 consecutive patients admitted to the intensive care unit. A mean of eight (range two to fourteen) data sets per patient were obtained, comprising measurement of arterial pH, pO 2, pCO 2, and oxygen saturation, tonometer balloon fluid pCO 2, arterial pressures, and cardiac output. Bicarbonate concentration, base deficit or excess in blood and extracellular fluid, and pH i were calculated from these measurements. Relations between the variables and pH i were assessed by within-subject correlation comparisons. There were significant correlations ( r>0·6, p<0·001) between markers of metabolic acidosis (base deficit in blood and extracellular fluid and bicarbonate concentration) and pH i. A blood base deficit of -4·65 or less and an extracellular-fluid base deficit of -6·13 or less could estimate pH i below 7·32 (lower limit of normal range) with sensitivity of at least 77% and specificity of at least 96%. There was no patient in whom either pH i or blood base deficit consistently reflected acidosis when the other variable did not. We conclude that the information that is obtained by gastric tonometry for pH i can be obtained more simply from measurements of metabolic acidosis; these variables can be calculated from routinely available blood-gas measurements.