External Validation and Updating of the Cardiac Surgery Score for Prediction of Mortality in a Cardiac Surgery Intensive Care Unit.

OBJECTIVE: To externally validate the predictive performance of the logistic and additive Cardiac Surgery Score (CASUS), a postoperative severity of illness score designed specifically for prediction of mortality in the cardiac surgery intensive care unit. DESIGN: A retrospective analysis of prospectively collected data between July 1, 2012, and September 30, 2015. SETTING: Single university cardiac surgery intensive care unit in Canada. PARTICIPANTS: Consecutive adult patients (n = 4,519) admitted to the intensive care unit after cardiac surgery. INTERVENTION: None. MEASUREMENTS AND MAIN RESULTS: The mortality predicted by logistic CASUS was calculated for each patient on admission day 0 and postoperative days 2, 4, 7, and 10 using the original model equation. The mortality predicted by additive CASUS was determined on each day with separate logistic regression models, using the total score as a single variable. The observed mortality was 1.8%. Logistic CASUS overestimated mortality by 78%, 59%, 51%, 52%, and 29% on days 0, 2, 4, 7, and 10, respectively. After model updating with logistic calibration, logistic CASUS consistently provided estimates of death comparable with the observed mortality, as determined with the Hosmer-Lemeshow goodness-of-fit test. The stability of those estimates was confirmed by bootstrapping. Similar calibration results were obtained with additive CASUS. Logistic and additive CASUS had good discrimination with areas under the receiver operating characteristic curve greater than 0.7 on each study day. CONCLUSIONS: Recalibrated logistic CASUS reliably predicts mortality in the intensive care unit after cardiac surgery. Logistic regression models derived from additive CASUS perform as well as logistic CASUS.

Measurement of exercise ventilation by a portable respiratory inductive plethysmograph.

The purpose of this study was to evaluate the accuracy of a respiratory inductive plethysmograph (RIP) designed for ambulatory data collection during exercise by comparison to a pneumotachograph. Healthy young males (n=10) wore an elastic body garment embedded with inductance sensors encircling the rib cage and abdomen. Breathing frequency (f(R)), tidal volume (V(T)) and minute ventilation (V (I)) were monitored during 5min of rest, slow walking (3.7kmh(-1)), fast walking (6.1kmh(-1)) and slow running (8.9kmh(-1)) followed by an incremental treadmill test to exhaustion (14.4+/-2.7kmh(-1)). Mean f(R), V(T) and V (I) values were not statistically different between the two methods (P>0.05). Within each of the subjects at rest and different exercise intensities, the average coefficient of determination was high for f(R), V(T) and V (I) (R(2)=0.9233, 0.8743 and 0.9652, respectively) and the mean bias values were low (-0.102+/-2.91, 0.033+/-0.207 and -0.715+/-8.362, respectively). These data suggest that the ambulatory RIP provides reasonable estimates of ventilation during rest and exercise.