ARTERIAL OXYGEN-TENSION OF PATIENTS WITH ABNORMAL LUNGS TREATED WITH HYPERBARIC-OXYGEN IS GREATER-THAN PREDICTED

The arterial oxygen (O-2) tension (PaO2) of patients with normal gas e xchange treated with hyperbaric oxygen (HBO2) can be predicted from th eir pre-HBO2 arterial to alveolar O-2 tension ratio (a/A) which remain s constant up to a PaO2 of 2,000 mm Hg. We observed that the a/A could not be used to predict the PaO2 of patients with impaired gas exchang e (reduced pre-NBO2 a/As) treated with HBO2. Our study provides inform ation about the PaO2 patients with abnormal lungs treated with HBO2. F or clinical reasons, we measured the PaO2 of 24 patients treated with HBO2. We obtained arterial blood gas values from patients with lung dy sfunction (a/A <0.75) prior to, during, and after HBO2. The pre-HBO2 a /A=0.45 +/- 0.17 (mean +/- SD). During HBO2 the a/A ranged from 0.7 to 0.8 depending on chamber pressure and returned to the pre-HBO2 baseli ne after HBO2. We conclude the following; (1) The hyperbaric PaO(2)s o f patients with a/A <0.75 is greater than expected. (2) However, the P aO2 is lower than in patients with normal lung function (a/A >0.75). P ossible explanations include improvement in ventilation/perfusion matc hing, reduction of venous admixture, and/or extra-alveolar uptake of O -2 (3) Exposures to HBO2 treatment pressures greater than recommended by existing protocols may be required in patients with impaired transf er of O-2 across the lung to achieve PaO(2)s similar to patients with normal lung function treated with HBO2.