Patient survival following cardiac or respiratory arrest in ICUs in our study was similar to patient survival reported in other studies of arrest in critical care units from the last two decades.8–13
In our study, about one in four patients (24.3%) survived to one year, and about one in six (15.9%) to five years. Survival was higher among our patients than among patients in previous studies whose arrest occurred in non-ICU hospital settings.4,14–20
About 60% of the patients in our study were initially resuscitated, and just over one-quarter survived to hospital discharge. In comparison, our previous study of survival outcomes following arrest in non-ICU hospital wards showed that about one-third regained a pulse, and 13% survived to hospital discharge.4
This difference suggests that cardiac or respiratory arrests in critical care units are distinct from those in non-ICU hospital wards. However, our ICU survival data are similar to those previously reported for witnessed arrests in non-ICU hospital wards.4
Collectively, the results of our two studies highlight the primacy of whether an arrest is witnessed over where the arrest occurs in hospital.
On average, survival to discharge from ICU for all patients has been reported to exceed 80%.21,22
In our study, only about 30% of the patients survived to ICU discharge after their arrest. Furthermore, at one-year follow-up, only 11% of patients whose arrest was due to pulseless electrical activity or asystole and 36% of those with other arrest rhythms were alive. The APACHE II score, a validated measure of the severity of acute illness in ICUs (but not coronary care units),23
was not an independent predictor of immediate or long-term death over its entire range. However, no patient survived to hospital discharge following an arrest due to pulseless electrical activity or asystole if their APACHE II score was 30 or higher. The independent predictors of death within 24 hours after arrest were male sex, arrest due to pulseless electrical activity or asystole, and longer duration of CPR. Predictors of longer term survival (eight months or more) were increasing age and longer duration of CPR.
Studies of cardiac arrests occurring out of hospital have shown an increased incidence of arrests in early morning. This was attributed to the cortisol- and catecholamine-surge upon awakening.24–26
However, it was unclear whether this pattern would apply to critically ill in-patients, where circadian influence is lessened.27,28
Results from our previous study of arrests occurring in non-ICU hospital settings suggested decreased survival with early morning cardiac arrest.4
In the current study, we found no early morning peak in total arrests, and no excess of early morning arrests due to pulseless electrical activity or asystole. This may be due in part to higher 24-hour nurse-to-patient ratios in critical care units. It may also be associated with the blunted endocrine response of prolonged critical illness.27,28
One of the highest survival rates yet reported following cardiac arrest (53%) was not in a hospital or an ICU setting; it was in a casino.29
Valenzuela and colleagues attributed this benefit to close observation, rapid response and a high percentage of arrests due to ventricular fibrillation. Similarily, a study involving laypeople using automated external defibrillators at an airport reported extremely high survival rates.30
Benefits were not attributed to specialized personnel or advanced equipment (beyond defibrillators). However, our ICU study results are still consistent with these findings, because they suggest the importance of rapid response and the influence of the type of arrest.
Our overall survival to hospital discharge of 26.9% was better than the 15.9% noted by Tian and coauthors, who reviewed the outcomes of 49 656 adults with a first arrest in the ICU over a similar period using the US National Registry of Cardiopulmonary Resuscitation.31
This difference may have occurred because we had more patients with ventricular tachycardia and ventricular fibrillation and included patients admitted to coronary care units. We did not find an increased risk of death on evenings and weekends, as was found by Tian and coauthors. ICUs in which one-to-one or two-to-one nurse-to-patient ratios, supported by fully trained intensivists within a Canadian health care system, may have accounted for the lack of an association between mortality and the time of arrest. Moreover, although Tian and coauthors reported an increased mortality among patients taking pressor medications before their arrest, they did not measure illness severity, duration of CPR or survival outcomes after hospital discharge.
Given the retrospective nature of our study, several limitations may introduce bias and limit generalizability. These include possible inaccuracies in charting, and possible failure to produce a record of cardiac or respiratory arrest for all appropriate patients. Ultimately our study was slightly underpowered, given an in-hospital mortality of 75%, which meant we would have required a sample of 563 patients. We were limited to the comorbidity data derived as part of the APACHE II score. In addition, we included arrests only up until 2005, because we wanted to describe survival over five years, a longer period than is typical of most studies. Regardless, the choice of study period excludes any putative benefit from recent clinical advances32–34
or updated guidelines on advanced cardiac life support.35
Our study showed no major improvement in survival following cardiac arrest with pulseless electrical activity or asystole as the presenting rhythm in the ICU despite many advances in critical care over the previous two decades. Although overall survival among ICU patients may have greatly improved, survival among those experiencing cardiac arrest in the ICU, particularly arrest due to pulseless electrical activity or asystole, remained comparatively poor. The independent predictors of death within 24 hours after arrest in an ICU were sex, the presenting rhythm and the duration of CPR. Predictors of later death (eight months or more after arrest) were age and duration of CPR. A key strategy to prevent or mitigate arrests needs to include earlier identification and response.