morbidity (Jacobson, 1994) [20]. Some investigators believe that aggressive treatment of general tissue hypoxemia can prevent stress ulcer bleeding (Tryba, 1994)[31]. While intraluminal gastric pH (pH L ) is readily measured by aspirates tested with litmus paper or a nasogastric tube with an antimony or glass electrode tip that can monitor pH continuously, intramucosal gastric pH (pH I ) requires a more complicated assessment technique with a balloon tonometer. This updated review is limited to the measurement of pH L .