Hypotension of ⩽110 mmHg is Associated with Increased Mortality in South African Patients After Trauma.

Introduction: This study used data from a prospectively maintained trauma database to assess the level of systolic blood pressure at which mortality rates for trauma begin to increase and to compare systolic blood pressure with base deficit as a predictor of outcome.

Methodology: The Pietermaritzburg Metropolitan Trauma Service maintains a prospective digital trauma registry. All trauma patients admitted to the service for the period January 2012-January 2015 were included. Analysis was performed on systolic blood pressure relative to a number of selected markers of outcome and a variety of physiological parameters.

Results: Out of an original data set of 2974 trauma patients, a total of 169 elective patients, 799 patients with isolated traumatic brain injury, and 27 patients with incomplete data were excluded to leave a sample size of 2148 patients. Of these, 1830 (85.2%) were males and 318 (14.8%) were females. The mean age (standard deviation) was 31.8 (12.0) years. The median age (interquartile range) was 29 (23-37) years. There were 89 deaths in this cohort (4.1%). The median systolic blood pressure (interquartile range) was 123 (112-136) mmHg. The median base deficit was -1.4 (interquartile range: -4.5 to 1). The inflection curves below with fitted non-linear curve clearly show the upward change in mortality frequency around a systolic blood pressure of ⩽110 mmHg as well for a base deficit below -5. A cutoff of <110 for systolic blood pressure yields a high sensitivity and very high positive predictive value of 82% (95% confidence interval: 81-84) and 98% (95% confidence interval: 97-98), but low specificity (56%) and negative predictive value (12%), respectively. Similar optimal cutoff analysis for base deficit versus mortality suggests base deficit >4.8 as a good predictor area under the curve (0.82; 95% confidence interval: 0.75-0.88). This cutoff yields a high sensitivity of 80% (95% confidence interval: 78-82), moderate specificity of 75% (95% confidence interval: 62-85), very high positive predictive value of 98% (95% confidence interval: 97-99) but low negative predictive value of 17% (15-28).

Conclusion: The data suggest that traumatic shock starts to become manifest at a systolic blood pressure of 110 mmHg and that a systolic blood pressure reading of 90 mmHg represents an advanced state of shock. Systolic blood pressure by itself is a poor predictor of mortality and outcome. Base deficit appears to be a far better predictor of mortality than systolic blood pressure. Future models to categorize shock will have to combine vital signs with biochemical markers of hypoperfusion.