To the Editor:
In an interesting retrospective study including 2,524 perioperative cardiac arrest cases from Get With The Guidelines-Resuscitation (GWTG-R) registry, findings by Ramachandran et al.1 that one in three patients survives to hospital discharge and two of three survivors have neurologically intact survival are encouraging. The power of this study is its use of a large dataset that includes and adjusts for most of the known factors that can affect final outcomes after in-hospital cardiac arrest (IHCA), such as patients’ age, race, preexisting morbidities, time and location of cardiac arrest, initial pulseless rhythm, and many more. The authors have used appropriate methods for building predictors of survival from perioperative cardiac arrests and openly discussed the limitations of their work. However, this study is a retrospective analysis using observational designs that are inevitably subject to uncontrolled and unmeasured confounding.
First, this study cohort comprised 2,524 patients with perioperative cardiac arrests from 234 hospitals within GWTG-R registry between February 24, 2000 and August 3, 2008. American Heart Association GWTG-R registry is a large, hospital-based, clinical registry of IHCA that has been enrolling patients since January 2000.2 A retrospective analysis of 104,732 IHCA cases from 362 hospitals within GWTG-R registry between 2000 and 2009 shows that duration of hospital participation in GWTG-R registry is significantly associated with increased survival of the IHCA cases.3 Moreover, Merchant et al.4 find that the case-mix–adjusted IHCA event rate is highly variable across hospitals within GWTG-R registry, and hospital measures of volume and demographic features may explain the variation in case-mix–adjusted IHCA event rates. In the study by Girotra et al.5 including 84,625 patients with IHCA events from 374 hospitals within GWTG-R registry, survival improves significantly, and the rates of neurologic disability decrease significantly over time during the past decade. Thus, other than adjustments of potentially confounding patient-related and event-related factors, hospital characteristics and survival variability over time should also be considered when identifying independent predictors of survival and neurologically intact survival of patients with IHCA using multivariable logistic regression models. Otherwise, sensitivity and specificity of identified predictors would be decreased.
Second, this study showed that cardiac telemetry was significantly associated with improved survival to hospital discharge and neurological outcomes. We would like to know whether patients receiving cardiac telemetry have simultaneously used other monitoring measures (i.e., pulse oximetry and capnography) and whether there is any imbalance in other monitoring measures between patients with and without telemetry. Cardiac telemetry is the only continuous monitoring measure of a patient’s heart rate and rhythm. However, respiratory compromise is one of the leading causes of the IHCA events.6,7 The common sequences of the IHCA events after respiratory compromise probably are the following: hypoxia leading to fatigue/hypercarbia or hypercarbia leading to hypoxia–respiratory compromise–tachycardia–bradycardia and cardiac arrest. That is, cardiac monitoring detects only the terminal IHCA events caused by respiratory compromise. Thus, efforts to improve the outcomes of perioperative cardiac arrests may also need to focus on preventing respiratory compromise, which deteriorates into cardiac arrests, by increasing the respiratory monitoring. Brady et al.8 showed that monitored (i.e., electrocardiography, pulse oximetry, apnea, or bradycardia monitoring) and/or witnessed IHCA patients were more likely to be discharged with favorable neurologic outcome, but cardiac monitoring conferred no additional outcome benefit over direct observation of patients having IHCA.
Finally, overall survival-to-discharge rate in this study (31.7%) was double that in previous reports of IHCA on general hospital floors from GWTG-R database (15.3 to 17%). It is generally believed that survival and neurologic recovery of IHCA patients are closely associated with uninterrupted compressions, high-quality cardiopulmonary resuscitation, and basic life support interventions.9 In a retrospective analysis including 118,387 adult IHCA cases entered into GWTG-R database from January 1, 2000, to August 26, 2008,10 incidence of resuscitation system errors was shown as high as 26.8 to 40.4%. The most frequent errors were related to delay in medication administration, defibrillation, airway management, and chest compression performance errors. Resuscitation system errors occurred in the highest percentage of IHCA events in nonintensive care unit inpatient areas (40.4%) and were least frequently noted on IHCA events occurring in intensive care unit (25.8%), emergency department (27.2%), or operating room/postanesthesia care units (23.5%) (P = 0.0001). Furthermore, the presence of resuscitation system errors was associated with a decreased survival of IHCA. Other than the reasons deduced by authors in Discussion, therefore, we cannot exclude the possibility that decreased resuscitation system errors would have contributed to an improved overall survival of perioperative cardiac arrests in this study.
The authors declare no competing interests.