Predicting cardiac arrest on the wards: a nested case-control study

Abstract

Background: Current rapid response team activation criteria were not statistically derived using ward vital signs, and the best vital sign predictors of cardiac arrest (CA) have not been determined. In addition, it is unknown when vital signs begin to accurately detect this event prior to CA.

Methods: We conducted a nested case-control study of 88 patients experiencing CA on the wards of a university hospital between November 2008 and January 2011, matched 1:4 to 352 control subjects residing on the same ward at the same time as the case CA. Vital signs and Modified Early Warning Scores (MEWS) were compared on admission and during the 48 h preceding CA.

Results: Case patients were older (64 ± 16 years vs 58 ± 18 years; P = .002) and more likely to have had a prior ICU admission than control subjects (41% vs 24%; P = .001), but had similar admission MEWS (2.2 ± 1.3 vs 2.0 ± 1.3; P = .28). In the 48 h preceding CA, maximum MEWS was the best predictor (area under the receiver operating characteristic curve [AUC] 0.77; 95% CI, 0.71-0.82), followed by maximum respiratory rate (AUC 0.72; 95% CI, 0.65-0.78), maximum heart rate (AUC 0.68; 95% CI, 0.61-0.74), maximum pulse pressure index (AUC 0.61; 95% CI, 0.54-0.68), and minimum diastolic BP (AUC 0.60; 95% CI, 0.53-0.67). By 48 h prior to CA, the MEWS was higher in cases (P = .005), with increasing disparity leading up to the event.

Conclusions: The MEWS was significantly different between patients experiencing CA and control patients by 48 h prior to the event, but includes poor predictors of CA such as temperature and omits significant predictors such as diastolic BP and pulse pressure index.

Figures

Figure 1.

Modified Early Warning Score (MEWS). Unresp = Unresponsive.

Figure 2.

Change in individual vital signs from admission. For each vital sign, change from admission was calculated by subtracting each patient’s closest value prior to time of case patient cardiac arrest (T0) by the admission value. P values refer to case patient vs control subject change from baseline comparisons. An asterisk signifies that the change from baseline for the individual vital sign is statistically significant.

Figure 3.

Change in MEWS over time. Vital signs on admission and in the 48 h prior to T0 were used to calculate MEWS scores, and comparisons were made between case and control mean scores at 8-h time points in the 48 h prior to T0. See Figure 1 and 2 legends for expansion of abbreviations.