Prove it: Ventilation improves survival from cardiac arrest

Highlights:
Introduction
The Review
What It Means for You

Introduction
Medic 12 responds to a nursing home on a report of an unconscious person. The medics arrive to find nursing home personnel performing chest compressions, but no one is ventilating. No bag-mask device is even present on their emergency cart.

Firefighters take over cardiopulmonary resuscitation (CPR) while the medics place the patient on a cardiac monitor. The patient’s rhythm is ventricular fibrillation (VF) and the medics promptly deliver a countershock at 200 joules. Following the shock firefighters immediately resume CPR, while the medics establish intravenous (IV) access and secure the airway with a supraglottic tube. After several rounds of vasopressors, a single dose of an antiarrhythmic, and one additional countershock, the patient achieves return of spontaneous circulation (ROSC).

The patient maintains a pulse and adequate blood pressure during the short transport to the hospital. After giving a verbal report to the waiting emergency department (ED) team, one medic begins the written report. Before completion however, the patient re-arrests and does not ultimately survive.

On the way back to the station, the two medics discuss the case. One medic expresses frustration that the nursing home staff did not ventilate the patient before the ambulance arrived. If they simply provided ventilation, the medic complains, the patient may have survived the cardiac arrest.

The review
Paper Reviewed: Mosier, J., Itty, A., Sanders, A., Mohler, J., Wendel, C., Poulsen, J., Shellenberger, J., Clark, L., & Bobrow, B. (2010). Cardiocerebral resuscitation is associated with improved survival and neurologic outcome from out-of-hospital cardiac arrest in elders. Academic Emergency Medicine, 17, 269-275. doi: 10.1111/j.1553-2712.2010.00689.x

In 2004, the Arizona Department of State Health Services initiated a registry of out-of-hospital cardiac arrest data as part of statewide quality improvement program. At the time of the study, 62 emergency medical service (EMS) agencies representing approximately 80% of Arizona’s population submitted data to the registry. Thirty-two of those agencies followed standard basic life support (BLS) and advanced cardiovascular life support (ACLS) as advocated by the American Heart Association (AHA).

The other 30 EMS agencies followed a different approach to the management of cardiac arrest known as cardiocerebral resuscitation (CCR). Responders using this approach immediately delivered 200 non-interrupted chest compressions at a rate of 100 compressions per minute without delivering bag-mask assisted ventilation when they arrived at the scene of a patient in cardiac arrest. At the end of the 200 compressions, rescuers analyzed the rhythm and delivered a single countershock, if indicated. Following the countershock, the rescuers immediately delivered 200 additional uninterrupted chest compressions without checking for a pulse or rhythm conversion. At the end of the compression period, rescuers delivered a second countershock if necessary and immediately began a third period of 200 uninterrupted chest compressions. Following the third compression cycle and the third countershock, medics performed endotracheal intubation and began ventilating the patient. As soon as they could obtain IV or IO access, medics administered 1 mg of epinephrine and delivered additional doses during each of the three remaining compression cycles. If the patient did not achieve ROSC by then, medics followed standard ACLS guidelines.

Researchers identified all pulseless and apneic patients entered into the registry during a 45-month period from 01 January 2005 and 30 September 2008. The study sample only included patients who received a field resuscitation attempt for a cardiac arrest of presumed cardiac etiology. Researchers excluded patients with obvious signs of death, a documented Do Not Attempt Resuscitation (DNAR) order, children under the age of 18 years, cardiac arrest witnessed by EMS personnel, and cardiac arrest presumed to have a non-cardiac etiology.

Researchers compared outcomes stratified by age group for patients receiving standard ACLS resuscitation interventions to those receiving CCR interventions. The primary outcome measures were survival to hospital discharge and neurological function of the survivors. The research team measured neurological outcome using the cerebral performance category (CPC), which assigns a score between 1 and 4 based on neurological function. A CPC score of 1 represents a conscious and alert patient who is able to return to work with only mild neurologic or psychological deficit. A CPC of 4 on the other hand, represents patients in a coma or persistently vegetative state. Researchers in this study considered a CPC score of 1 or 2 to represent good neurologic outcome.

In addition to the primary outcome measures, the researchers performed a regression analysis to identify independent factors that could predict survival. This mathematical formula examines the effect that individual interventions have on survival, when healthcare providers perform multiple interventions during the course of care.

EMS agencies entered 5000 patients into the registry during the study period. Researchers removed 1485 patients who met exclusion criteria leaving 3515 patients in the study cohort. The demographic and cardiac arrest variables were not significantly different between the two groups. Two hundred and four patients survived for an overall survival rate in both groups of 5.8%.

The researchers reported the results as an odds ratio (OR), which is a way to express the odds of an event occurring in two different groups (Goldin, 2007). In this study, the researchers wanted to determine the odds of survival in the group receiving CCR compared to the odds of survival in the group receiving standard ACLS. If the odds ratio is greater than 1, survival in the CCR is more likely to occur. If the odds ratio is less than 1, survival in the CCR group is less likely to occur.

For the total study sample, the odds of survival increased for all patient age groups if the rescuers performed CCR instead of traditional ACLS procedures (Table 1). The greatest benefit appeared in the group of cardiac arrest patients under the age of 40 years with the odds of survival in the CCR group being almost 6 times higher than survival in the Standard ACLS group.

In the secondary analysis of patients who experienced ventricular fibrillation or pulseless ventricular tachycardia (VF/pVT), the same increased odds of survival remained for each age group (Table 2).

The researchers performed a regression analysis in the CCR group to identify any independent factors that affect survival. This analysis resulted in five interesting observations:

• If a bystander witnessed the arrest, patients were three times more likely to survive (OR = 3.3; 95% CI = 1.8 to 6.1) than if the arrest was unwitnessed.
• Patients with a presenting rhythm of VF/pVT were seven times more likely to survive (OR = 7.0; 95% CI = 3.9 to 12.5) than those who presented in asystole or pulseless electrical activity.
• Patients presenting with agonal respirations were over four and a half times more likely to survive (OR = 4.6; 95% CI = 2.6 to 8.2) than patients without agonal respirations.
• The odds of survival decreased for every minute of EMS delay before arriving on the scene (OR = 0.87, 95% CI = 0.76 to 0.99).
• For every 10-year increase in patient age, the odds of survival decreased (OR = 0.79, 95% CI = 0.67 to 0.93).

The researchers also examined neurologic outcome for all the patients that survived long enough for physicians to discharge them from the hospital. Of the 204 survivors in both groups, the researchers were able to collect outcome data for only 147 of them. More patients had favorable neurologic outcome (CPC of 1 or 2) if they received CCR compared to standard ACLS (96.6% vs. 85%). After adjusting for witnessed arrest and the presence of VF/pVT as the initial rhythm, the odds were six times greater that patients who received CCR would have a favorable neurologic outcome (OR = 6.54, 95% CI = 1.31 to 32.8).

What it means for you
Rescue breaths are not as important as chest compressions during the early stages of cardiac arrest because oxygen levels remain high for some time after the heart stops beating (Berg, Hemphill, Abella, Aufderheide, Cave, Hazinski, Lerner, Rea, Sayre, & Swor, 2010). When the arrest occurs, the arterial side of the patient’s circulatory system is filled with oxygenated blood that suddenly stops moving. Rescuers who perform no intervention other than chest compressions will move oxygenated blood through the capillary beds of the patient’s organs thus facilitating gas exchange at the tissue level.

In the absence of airway obstruction, compression of the chest forces air out of the lungs allowing carbon dioxide elimination while chest recoil draws fresh oxygen into the airway (Bang, Herlitz, & Martinell, 2003; Berg, Kern, Hilwig, Berg, Sanders, Otto, & Ewy, 1997; Berg, Kern, Hilwig, & Ewy, 1997; Bobrow, Zuercher, Ewy, Clark, Chikani, Donahue, Sanders, Hilwig, Berg, & Kern, 2008; Clark, Larsen, Culley, Graves, & Eisenberg, 1992; Tang, Weil, Sun, Kette, Gazmuri, O’Connell, & Bisera, 1994). Additionally, the agonal breaths that are often present early in the cardiac arrest produces some air movement through the respiratory tract thus permitting some degree of gas exchange (Berg, Kern, Hilwig, Berg, Sanders, Otto, & Ewy, 1997; Berg, Kern, Hilwig, & Ewy, 1997; Tang, Weil, Sun, Kette, Gazmuri, O’Connell, & Bisera, 1994).

CPR produces only about one-third of normal cardiac output, thereby resulting in diminished blood flow to the lungs (Woorhees, Babbs, & Tacker, 1980; Weil, Bisera, Trevina, & Rackow, 1985; Rubertsson, Grenvik, Zemgulis, & Wiklund, 1995). Reduced perfusion of the pulmonary capillary beds requires lowered ventilation volumes in order to achieve the same degree of oxygen saturation and carbon dioxide elimination. One animal model seems to suggest that the volume produced by this type of passive ventilation may be sufficient for several minutes after the onset of cardiac arrest (Chandra, Gruben, Tsitlik, Brower, Guerci, Halperin, Weisfeldt, & Permutt, 1994).

However, at some point, ventilation becomes necessary in order to replenish depleted blood oxygen levels. Researchers have still not identified the precise interval that a patient can go without assisted ventilation (Becker, Berg, Pepe, Idris, Aufderheide, Barnes, Stratton, & Chandra, 1997; Berg, Kern, Hilwig, Berg, Sanders, Otto, & Ewy, 1997; Berg, Kern, Hilwig, & Ewy, 1997; Sanders, Otto, Kern, Rogers, Perrault, & Ewy, 1988; Steen-Hansen, 2010; Tang, Weil, Sun, Kette, Gazmuri, O’Connell, & Bisera, 1994; Weil, Rackow, Trevino, Grundler, Falk, & Griffel, 1986). This study seems to suggest, but does not prove that the time interval may be at least six minutes.

Although this study illuminates a very important concept in resuscitation, there are several limitations. First, the study is retrospective in nature, meaning that the researchers used data that already existed in a database. Retrospective studies are useful for establishing a relationship between two characteristics, such as CCR and survival. However, retrospective studies do not allow the researcher to blind the caregivers from knowing which patient received CCR nor does it allow control of any variables. Without that control, one can never be sure that one thing causes the other.

The study also assumes that the medics followed their medical protocols, regardless of whether their agencies practice standard ACLS or CCR resuscitation principles. The researchers have no way of verifying that any of the medics actually followed their medical director’s guidelines. Other researchers have observed that medics may not follow ACLS medication administration recommendations in 86% of out-of-hospital cardiac arrests (Scliopou, Mader, Durkin, & Stevens, 2006).

The association of CCR and improved neurologic outcome is also hampered by the fact that the researchers could only collect outcome data on less than three-fourths of the survivors. One can only speculate as to the impact on group neurologic outcome if information was available on every survivor.

By the publication deadline for the Guidelines 2010, the consensus opinion of the writing group for the Advanced Cardiovascular Life Support Guidelines was that insufficient evidence existed to recommend removal of ventilation from standard resuscitation guidelines for advanced providers (Neumar, Otto, Link, Kronick, Shuster, Callaway, Kudenchuk, Ornato, McNally, Silvers, Passman, White, Hess, Tang, Davis, Sinz, & Morrison, 2010).

It will be interesting to see what 2015 brings.