Evaluation of a simplified therapeutic intervention scoring system (TISS-28) and the modified early warning score (MEWS) in predicting physiological deterioration during inter-facility transport

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There is an emerging demand for inter-facility transport (IFT) of patients in recent years following changes in the healthcare framework in Hong Kong but this carries certain risks. Anticipation of possible deterioration of patients is important for patient safety and therefore risk stratification of patients before transport is important. This study evaluated the simplified therapeutic intervention scoring system (TISS-28) and modified early warning score (MEWS) in predicting physiological deterioration en route. This is a prospective single centre study of all emergency IFT for adult patients, excluding patients with obstetric conditions, occurring between 1 January 2005 and 30 June 2006. The severity of illness was quantified in terms of TISS-28 and MEWS. Mann-Whitney test and receiver operator characteristic (ROC) curves were used to illustrate and compare their performance. Among 102 patients requiring IFT, 28 had physiological deterioration en route (27%). The TISS-28 scores upon dispatch ranged from 5 to 34 with a mean of 16.5+/-5.71 whereas MEWS ranged from 0 to 11 with a mean of 2.82+/-2.01. The incidence of physiological deterioration en route was significantly greater with a higher MEWS score (P=0.001) but this was not seen with the TISS-28 score. The area under the ROC curve for the predictive value of MEWS was 0.71 which performed better than TISS-28 (area under the curve=0.53). IFT represents a group of patients with vast heterogeneity. TISS-28 is not a useful tool for risk stratification prior to transport. MEWS was able to identify patients at risk but was not ideal.