Circadian pattern of activation of the medical emergency team in a teaching hospital

Jones D, et al. Critical Care 2005;9:R303-R306

Introduction

Hospital medical emergency teams (METs) have been implemented to reduce the incidence of cardiac arrests on general wards. Essential components are the early recognition of potentially dangerous changes in vital signs followed by the immediate consultation of an experienced ICU team. The success of the MET system relies on the assumption that early intervention in the course of clinical deterioration improves patient outcome. Recently it has been reported that the implementation in an Australian teaching hospital resulted in a 65% relative risk reduction for in-hospital cardiac arrest over a 4-month period. The aim of this study was to determine the circadian pattern of MET activation and to relate it to nursing and medical activities in the same hospital.

Study

This is a retrospective observational study of the time of activation for 2568 incidents in a four year period of MET attendance. Each attendance was allocated to one of 48 half-hour intervals over the 24-hour daily cycle. The calling criteria were based on acute changes in heart rate (<40 or >130 beats/min), systolic blood pressure (<90 mmHg), respiratory rate (<8 or >30 breaths/min), conscious state, urine output (<50 ml/4 hours), and oxygen saturation derived from pulse oximetry (<90%, despite oxygen administration). In addition, the calling criteria contained a 'staff member is worried' category to allow staff to summon senior assistance to manage any possible emergency situation. Results showed a 53% occurrence of MET calls between 18.00 and 08.00. There was a tendency for an increasing proportion of calls to occur after hours. Increased activity of the MET service was seen in the half-hour following routine observations, and in the half-hour before routine nursing handover.

Discussion

The most important message from this study is the fact that most MET calls occur after hours and are related to routine nursing care. This has important consequences for the organization of the MET as a 24-hour coverage appears to be essential. As suggested by the authors more frequent rounding by the nurses or continuous monitoring may even lead to earlier recognition but unfortunately the authors do not provide the number of appropriate and inappropriate calls and more importantly there is no evaluation of patients that did not receive MET assistance although calling criteria were present. Many in-hospital calamities have a typical circadian pattern. For example, acute cardiac ischemia, myocardial infarction and cardiac arrest occur more frequently between 08.00 and 12.00 hours. It would be interesting to see if increased observation during this "critical period" would be a further improvement. It is important to recognize that this study was performed in a single centre with predefined calling criteria. Although other calling criteria may result in another diurnal pattern this study provides us with important clues how to organize an "outreach" service.

A.Draisma, AGIKO Intensive Care
J.G. van der Hoeven, Internist-intensivist