Is the New Zealand Early Warning Score useful following cardiac surgery?

Abstract

Aims: The rate of medical emergency team (MET) calling among post-cardiac surgery patients is unknown. We set out to determine what the call frequency would be if MET activation occurred in every instance that the early warning score (EWS) breached our local threshold, what the outcome was for these patients and what the calling rate might be if the proposed New Zealand EWS (NZEWS) system was implemented with 100% adherence.

Methods: The clinical records of 400 consecutive post-cardiac surgery patients were examined. The number of times a patient's EWS reached the threshold which mandated a call to the MET was determined, as was the actual rate of calling, the occurrence of inpatient death and re-admission to the intensive care unit (ICU). The rate of calling was then determined using the NZEWS, and with a routine modification to the heart rate score.

Results: There were 73 occasions (MET events) where the EWS reached the MET calling threshold. The MET was only called twice. There were no inpatient deaths and 12 ICU re-admissions in the study cohort. Nine ICU re-admissions were preceded by a MET event, two by cardiac arrest and one had neither. Re-scoring with NZEWS yielded 53 events. Eight of the 12 ICU admissions were preceded by a NZEWS event.

Conclusions: The rate of MET triggering EWS in patients post-cardiac surgery is high at 182/1,000 admissions. Using NZEWS could reduce the MET calling rate without significant risk to patient safety.