Performance evaluation of APACHE II score for an Indian patient with respiratory problems

Realising the utility of scoring systems in mortality prediction of critically ill patients admitted to intensive care units (ICUs), studies worldwide have expressed a need to validate the Acute Physiology and Chronic Health Evaluation (APACHE) II score for databases of respective countries. Literature available in this area in the Indian context is scanty. The present study was undertaken to evaluate the performance of APACHE II score in prediction of mortality risk, as well as in determination of model validity in critically ill Indian patients with respiratory problems.

The study was prospectively carried out over 18 months at respiratory ICU of a tertiary Institute in New Delhi, which admitted consecutive medical (with lung ailments) and surgical (who had undergone any elective thoracic surgical procedure under general anaesthesia) patients. Based on chief indication of ICU admission, the medical patients were further divided into sub-groups I (respiratory) and II (non-respiratory). APACHE II points were assigned to all patients for calculating their individual predicted risks of mortality. Standard mortality ratio (SMR) was computed with 95 per cent confidence intervals (CI). Calibration of model was analysed by calculating Lemeshow and Hosmer goodness of fit X(2) statistic and by plotting calibration curve, whereas discrimination was evaluated by calculating area under a receiver operating characteristic (ROC) curve.

Of the 393 consecutive patients admitted to respiratory ICU during the study period, 63 were left out on account of exclusion criteria. Mean APACHE II score of the remaining 330 patients was 12.87+/-8.25 and range from 1 to 47. There were 287 (87%) survivors and 43 (13%) non-survivors, whose mean APACHE II scores, being respectively 11.34+/-6.75 (range 1-37) and 23.09+/-10.01 (range 5-47), were significantly different (P<0.01). The study had a predicted mortality of 7.9 per cent and an SMR value of 1.65 (95% CI from 0.4 to 3.0). Mean APACHE II score of those having medical ailments was significantly higher (P<0.01) than surgical patients. The non-respiratory sub-group had a significantly higher (P<0.01) mean APACHE II score than respiratory sub-group. 59 per cent of patients did not get APACHE II points owing to being <45 yr of age. In addition, against 10 immunocompromised patients, 77 others did not get APACHE II points despite having apparently compromised immunity due to co-existence of tuberculosis (TB), diabetes mellitus, dual pathologies or past history of anti-TB treatment. Observed and predicted mortality rose with 5-point APACHE II score, but did not correlate for patients of any comparable group. Average ICU stay of 16 days for those with medical disease was significantly longer (P<0.01) than 9.5 days for surgical patients. APACHE II scoring system showed a poor calibration and discrimination ability for Indian respiratory patients.

Despite the rise in observed and predicted mortality with 5-point APACHE II score, predicted mortality did not correlate with observed mortality for critically ill patients admitted to an Indian respiratory ICU. The scoring system also showed a poor calibration as well as discrimination. The model may be more useful for Indian patients by lowering down the cut-off value in allotment of age points and by awarding the weightage to factor like co-existing immunocompromised state.