Clinical paperThe objective medical emergency team activation criteria: A case–control study☆
Introduction
Studies from around the world have consistently shown that hospital patients suffer serious and preventable adverse events that may result in prolonged hospitalisation, permanent injury and death.1, 2, 3, 4 Of these events, cardiac arrests, unplanned intensive care unit (ICU) admissions and unexpected deaths are three of the most serious.1, 2, 5, 6, 7 Survival from in-hospital cardiac arrest remains poor despite decades of attention and research,8, 9 and patients suffering in-hospital cardiac arrest in a non-critical care area are even more likely to die.7 Patients admitted to the ICU from the wards have a higher severity of illness and mortality than similar patients admitted from the emergency department or operating theatres.10, 11, 12 Although the circumstances leading up to these events are complex, the realisation that routinely documented clinical observations may serve as predictors for up to 24 h prior to the actual event,13 has lead to the development of “early warning systems” in various countries.14, 15, 16, 17 The first of these, and the most rigorously evaluated to date, is the Medical Emergency Team (MET) system.14, 18
The MET activation criteria, used to detect patients at risk of serious adverse events and to trigger activation of the MET, have been used without formal evaluation since 1990.14 Although clinical observations such as tachypnoea, decreased level of consciousness and systolic hypotension have been shown to be associated with in-hospital cardiac arrest and death,19, 20, 21, 22, 23 different combinations of criteria are in use, and there is no consensus on the ideal set of criteria or their optimal cut-off values.24, 25, 26, 27, 28
Many health-care systems are devoting significant resources to implement early warning and MET-like systems. Given the central role of the activation criteria within these systems, it is imperative that the activation criteria are as accurate as possible.
We conducted a nested, matched case–control study in order to evaluate the ability of published objective clinical MET activation criteria (Table 1) to identify patients at risk of cardiac arrest, unplanned ICU admission or unexpected death, and to determine whether modifying their cut-off values would improve their sensitivity, specificity and predictive value.
Section snippets
Materials and methods
The eleven hospitals from the MERIT study that were not allocated a MET system were invited to take part in this study.18 Of these, seven hospitals (four university affiliated, three community) participated. Approval was obtained from the human research ethics committee of each hospital.
The adverse events examined by this study were unexpected cardiac arrests, unplanned ICU admissions and unexpected deaths. A cardiac arrest was defined as occurring when a patient lacked a palpable pulse. An
Statistics
Where observations were missing, it was assumed that these observations would not have resulted in activation of the MET system. Univariate odds ratios for the occurrence of an adverse event were obtained for each of the activation criteria using conditional logistic regression adjusted for clustering by hospital, using the Huber/White/sandwich method of adjustment of variance estimates.29
We then assessed the diagnostic accuracy of each established objective MET activation criterion
Results
A total of 503 eligible index cases were identified. Of these, 53 could not be matched and were excluded. The remaining 450 cases (89.5% of the eligible case population) and their 520 matched controls were included. The case and control numbers by hospital are presented in Table 2. After exclusion of admissions of less than 24 h, the incidence of all three serious adverse events was calculated as 13.9 per 1000 admissions per year (95% CI 13.5–14.3/1000 admissions per year). The incidence of
Discussion
We conducted a case–control study to examine the ability of a pre-defined set of objective clinical observations to identify patients at risk of cardiac arrests, unexpected deaths and unplanned ICU admissions. We found that when a respiratory rate greater than 36 breaths/min, heart rate greater than 140 beats/min, systolic blood pressure less than 90 mmHg and decrease in the GCS score of more than two points were combined, they predicted a serious event within 24 h with a high specificity (93.7%,
Conclusion
This study confirms that in combination, a high heart rate and respiratory rate, low systolic blood pressure and a decrease in the GCS score are specific predictors of cardiac arrest, unplanned ICU admission and unexpected death. The set of objective criteria used during the MERIT study had relatively low sensitivity and positive predictive values for the adverse events studied. Even after modification, the best achievable positive predictive value was 15.7%, with a corresponding sensitivity of
Conflict of Interest Statement
All authors declare that they have no personal or financial relationships that could inappropriately influence their work.
Acknowledgements
The MERIT study is a collaboration of the Simpson Centre for Health Services Research and the ANZICS Clinical Trials Group. We thank Dr. Michael Parr for reviewing the manuscript.
The study was funded by grants from the National Health and Medical Research Council of Australia, the Australian Council for Safety and Quality in Health Care and the Australian and New Zealand Intensive Care Foundation as part of the MERIT study.
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A Spanish translated version of the summary of this article appears as Appendix in the final online version at 10.1016/j.resuscitation.2006.08.020.
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See Appendix A.