Information about venous gas emboli improves prediction of hypobaric decompression sickness

Hypothesis : Information about venous gas emboli (VGE) detected in the pulmonary artery such as the occurrence of VGE, Grade of VGE, the time when VGE first appear, and the time course of the Grade or occurrence of VGE, could be used to better assess the probability of decompression sickness [P (DCS) ] in any hypobaric decompression. We hypothesized that these data would improve the estimate of P (DCS) since objective measurements of the decompression stress are available for the individual. Methods: A binary correlation and survival analysis approach were used on information from 1,322 hypobaric chamber exposures to establish the relationships between VGE and DCS. Results: Based on the correlation analysis, the absence of VGE is highly correlated with the absence of a DCS symptom, as evident from a negative predictive value of 0.98. However, the presence of VGE in the pulmonary artery is not highly correlated with a subsequent DCS symptom, as evident from a positive predictive value of 0.39 for Grades III and IV VGE. The correlation results suggest the presence of VGE in the pulmonary artery is a necessary, but not sufficient, condition for DCS. Based on the survival analysis, the log logistic survival model, a one-variable model with two parameters gave a log likelihood (LL) of -757. This model was expanded to include seven additional variables, including four about VGE, and the nine-parameter model gave a better LL of -481. Conclusion: Information about VGE plus other variables known to influence DCS is useful to better assess the P (DCS) for hypobaric decompressions.