It is unknown whether the reported short-term reduction in cardiac arrests associated with the introduction of the medical emergency team (MET) system can be sustained.
We conducted a prospective, controlled before-and-after examination of the effect of a MET system on the long-term incidence of cardiac arrests. We included consecutive patients admitted during three study periods: before the introduction of the MET; during the education phase preceding the implementation of the MET; and a period of four years from the implementation of the MET system. Cardiac arrests were identified from a log book of cardiac arrest calls and cross-referenced with case report forms and the intensive care unit admissions database. We measured the number of hospital admissions and MET reviews during each period, performed multivariate logistic regression analysis to identify predictors of mortality following cardiac arrest and studied the correlation between the rate of MET calls with the rate of cardiac arrests.
Before the introduction of the MET system there were 66 cardiac arrests and 16,246 admissions (4.06 cardiac arrests per 1,000 admissions). During the education period, the incidence of cardiac arrests decreased to 2.45 per 1,000 admissions (odds ratio (OR) for cardiac arrest 0.60; 95% confidence interval (CI) 0.43–0.86; p = 0.004). After the implementation of the MET system, the incidence of cardiac arrests further decreased to 1.90 per 1,000 admissions (OR for cardiac arrest 0.47; 95% CI 0.35–0.62; p < 0.0001). There was an inverse correlation between the number of MET calls in each calendar year and the number of cardiac arrests for the same year (r2 = 0.84; p = 0.01), with 17 MET calls being associated with one less cardiac arrest. Male gender (OR 2.88; 95% CI 1.34–6.19) and an initial rhythm of either asystole (OR 7.58; 95% CI 3.15–18.25; p < 0.0001) or pulseless electrical activity (OR 4.09; 95% CI 1.59–10.51; p = 0.003) predicted an increased risk of death.
Introduction of a MET system into a teaching hospital was associated with a sustained and progressive reduction in cardiac arrests over a four year period. Our findings show sustainability and suggest that, for every 17 MET calls, one cardiac arrest might be prevented.
Despite advances in medical technology and the introduction of cardiac arrest teams, the mortality of in-hospital cardiac arrests remains high (approximately 85% ). Up to 80% of patients suffering cardiac arrests have signs of physiological instability (alterations in the commonly measured vital signs) in the 24 hour period before the event [2-4]. In response to this observation, hospitals are increasingly implementing specialized teams (variably named medical emergency teams (METs), rapid response teams, or outreach teams) to identify, review and treat unstable ward patients in the early phase of deterioration, with the goal of preventing cardiac arrests [5-8].
METs have been shown to reduce the incidence of cardiac arrests in hospitalized patients in short-term before-and-after studies [5-7]. DeVita and co-workers  have recently reported a 17% reduction in cardiac arrests in the 1.8 years after increased use of the MET service in a teaching hospital . The effectiveness of METs in achieving or sustaining this outcome for periods greater than this has not been shown to date.
Since the introduction of the MET service in our hospital, we have conducted an educational campaign to improve awareness in an attempt to increase use of the service. Sustained system change, however, requires a strong organizational commitment to safety  as well as continued education and awareness-raising activities. Institutionalization of system change may fail because of turnover of key employees  such as doctors and nurses. This may result in the introduction of new staff who are unfamiliar with the MET concept [8,11]. Thus, there is uncertainty that the MET system will continue to deliver any benefits that might have been demonstrated immediately after its introduction. In this study, we analyzed the incidence of cardiac arrests in the four years following the introduction of the MET service.
Materials and methods
The Austin Hospital is a 400 bed acute care hospital affiliated with the University of Melbourne. The hospital provides services such as cardiothoracic surgery and neurosurgery and is also the referral center for acute spinal injuries and liver transplantation for the state of Victoria. The intensive care unit (ICU) has 21 beds and receives approximately 2,000 admissions per year.
Approval was obtained from the Institution's Ethics Committee for implementation of the MET system and collection of the data related to it. The need for informed consent was waived by the committee.
Medical emergency responses
The acute care hospital has two levels of emergency response. The traditional 'Code Blue' call is intended for resuscitation of cardiac arrests and other sudden life-threatening medical emergencies. It consists of an anesthetic fellow, a coronary care fellow and nurse, an ICU fellow and nurse, as well as the Medical fellow of the receiving unit of the day. The MET is intended to review all medical emergencies other than cardiac arrests, and has been described in detail previously [7,12]. It consists of an ICU fellow and nurse, as well as the Medical fellow of the receiving unit of the day. It can be activated by any member of hospital staff according to pre-determined criteria that are based primarily on abnormalities of vital signs and clinical status. Specifically, the criteria include acute changes in heart rate (<40 or >130 beats/minute), systolic blood pressure (<90 mmHg), respiratory rate (<8 or >30 breaths/minute), oxygen saturation (<90% despite oxygen therapy) or conscious state. Any staff member can also initiate a MET review if they are worried about the patient for any other reason.
The study is a prospective before-and-after interventional trial. All patients admitted to the hospital for at least one night were considered as participants. The period 1 January 1999 to 31 August 1999 was the control or 'before' period. In the educational phase preceding implementation of the MET (1 September 1999 to 31 August 2000), detailed education and information sessions where held with all members of hospital staff. The period 'after' the implementation of the MET included the interval spanning from 1 September 2000 to 31 October 2004.
Data on admissions, cardiac arrests and MET calls
A log book of all emergency calls is maintained by the switchboard operators and contains details of the date and time of the call as well as the ward from which the call originated. Standardized case report forms on Code Blue calls are maintained independently by both the coronary care unit and ICU. Details from the switchboard log regarding time, date and ward calling the Code Blue calls were cross referenced with the case report forms and the ICU admission database. Calls were designated as 'documented cardiac arrest', 'not cardiac arrest' or 'insufficient data'. Information was confirmed by two investigators by analysis of the case report form and/or analysis of the patients file. A cardiac arrest was defined as the sudden onset of all of the following: no palpable pulse; no measurable blood pressure; no responsiveness; and the commencement of basic life support. Calls from the coronary care unit, operating room and emergency room (acute care areas) were not considered for analysis, as were calls in which the patient had a documented 'not for resuscitation' order prior to the call. To minimize bias in favor of the MET system, calls designated 'insufficient data' were still considered as being 'true cardiac arrests' in the educational phase and in the period after the introduction of the MET. Calls designated as 'not cardiac arrest' were then classified into one of nine subgroups (faint, seizure, haematemesis and melena, surgical bleeding, respiratory distress, altered conscious state, hypotension, arrhythmia, chest pain).
The number of cardiac arrests in each of the study periods ('before MET', 'educational phase preceding MET' and 'after MET implementation') was quantified and related to the number of hospital admissions lasting at least 24 hours for the same period. Information on the age, gender and initial documented rhythm were obtained from the case report forms. Data on patient hospital outcome and destination of hospital discharge were obtained from the hospital electronic database.
Data on the incidence of cardiac arrests during the three periods of the study were compared using the χ2 test and analyzed using MS Windows Stat-view (Abacus Concepts, Berkeley, CA, USA). Correlation between levels of MET service activation and the incidence of cardiac arrests was analyzed using the Spearman-rank test.
We performed multivariate logistic regression analysis using death as the dependent variable and patient gender, age, parent unit, primary rhythm and time of cardiac arrest as independent variables. Data were analyzed using SPSS (version 12, SPSS Inc, Chicago, IL, USA) and results are presented as odds ratio (OR) with 95% confidence intervals (CI). A p value of <0.05 was considered statistically significant.
The number of MET reviews associated with a decrease of one cardiac arrest was estimated by calculating the reciprocal of the line of regression of the association between the level of MET service activation and the incidence of cardiac arrests.
Characteristics of Code Blue calls
Compared to the period before the MET, there was an initial reduction in the number of Code Blue calls during the education phase (OR for Code Blue call 0.75; 95% CI 0.57–0.98; p = 0.033). After the implementation of the MET, however, there was a further significant reduction in Code Blue calls (OR for Code Blue call 0.51; 95% CI 0.41–0.64; p < 0.0001) (Table 1). At least 30% of Code Blue calls were made for indications other than cardiac arrest. Specifically, the major reasons for such Code Blue calls were respiratory distress, hypotension, altered Glasgow coma score, seizure and a simple collapse or faint (Table 1).
Table 1. Characteristics of Code Blue calls over the study period
In addition, there was no significant difference in the proportion of patients in whom a Code Blue call was made despite a prior documented 'not for resuscitation' order (OR 1.40; 95% CI 0.46–4.23; p = 0.57).
Impact of MET implementation on the incidence of cardiac arrests
When the Code Blue calls classified as 'insufficient data' were included as true cardiac arrests for the education and post-MET implementation period, the number of cardiac arrests before the MET, during the educational phase preceding the MET, and after the implementation of the MET was 66, 62 and 198, respectively (Table 1). The overall process of introduction of the MET was associated with a statistically significant reduction in cardiac arrests when compared with the period before the MET (multiple χ2 p < 0.0001). During the educational phase preceding the MET, the OR for risk of cardiac arrest was 0.60 (95% CI 0.43–0.86; p = 0.004) when compared with the period before the MET. After the introduction of the MET system, the OR of cardiac arrest was 0.47 (95% CI 0.35–0.62; p < 0.0001) when compared to the period before MET implementation and 0.77 (95% CI 0.58–1.03; p = 0.078) when compared to the educational phase. In the year 2004, there was a further reduction to a rate of 1.3 arrests per 1,000 admissions, such that the OR for cardiac arrest was 0.31 (95% CI 0.20–0.48; p < 0.0001) when compared with the period before the MET and 0.51 (95% CI 0.32–0.80; p = 0.003) compared with the educational phase preceding the MET.
Characteristics and outcome of documented cardiac arrests
There were 279 documented cardiac arrests during the study period (Table 2). The majority of these patients were male, and their average age was 71.3 years. Patients from five of the 20 units (general medicine, respiratory medicine, cardiology, renal medicine and haematology/oncology) comprised 62% of all calls. The majority (170/228, 74.6%) of patients who died following a cardiac arrest did so at the time of the cardiac arrest. The most common rhythms present on arrival of the cardiac arrest team were asystole (122/279, 43.7%) and pulseless electrical activity (70/279, 25.1%). The survival rate following a cardiac arrest was not affected by the introduction of the MET (OR for survival 0.60; 95% CI 0.30–1.21; p = 0.15) (Table 2).
Table 2. Characteristics of documented cardiac arrests
Several independent variables were shown to have an impact on outcome following cardiac arrest (Table 3). Male gender and an initial rhythm of asystole or pulseless electrical activity were associated with an increased risk of death following cardiac arrests. In addition, none of the 23 patients admitted under haematology/oncology survived a documented cardiac arrest in the study period.
Table 3. Predictors of death following cardiac arrest using multivariant logistic regression analysis
Predictors of a decreased risk of death following cardiac arrest included admission under cardiothoracic surgery, spinal cord injuries unit, cardiology unit, or an arrest between the hours of 08:00 and 10:00.
There was an inverse correlation (r2 = 0.84, p = 0.01) between the number of MET calls per 1,000 admissions in each calendar year and the number of cardiac arrests per 1,000 admissions over the corresponding period (Figure 1). The gradient of the line of regression for this correlation was -0.061, suggesting that for every 17 MET calls (1/0.061) there was an associated decrease of one cardiac arrest.
Figure 1. Correlation between the number of medical emergency team (MET) calls and the rate of cardiac arrests between 1999 and 2004.