CA Treatment in a Pre-Hospital Setting

CA occurring in a pre-hospital setting is particularly dependent on quick, early response efforts, and bystander recognition and care of CA patients is quite important. The standard of care for CA patients is CPR, and a number of variations on the American Heart Association (AHA) guidelines for CPR (AHA 2000) have recently come under study, including active compression-decompression CPR (ACD-CPR), phased thoracic-abdominal active compression-decompression CPR (PTACD-CPR) and continuous chest compression CPR (CCC-CPR).

Standard CPR

Standard CPR (S-CPR) has been defined by the AHA to consist of chest compressions performed at a rate of 100/min, in accordance with studies showing optimal compression rates of >80/min and 120/min (AHA 2000; Sunde et al 1998). Rescue breathing is performed after every 15th chest compression, with each of two breaths lasting no more than two seconds each (AHA 2000). Although S-CPR has been taught to laypeople since 1974, evaluation of post-course performance of those trained in it has found layperson CPR to be ineffective. New guidelines have attempted to address some of these issues, including the fact that lay rescuers cannot be relied upon to effectively determine whether a patient has a pulse or not (AHA 2000), and the fact that many show what may be irrational or uninformed reluctance to perform rescue breathing due to a fear of infectious disease transmission (Berg et al 2001; Kern et al 2002; AHA 2000; Kern et al 2001).

CPR works by increasing perfusion to vital organs and enhancing the viability of myocardial cells (Truong and Rosen 1997). It can prevent VF from deteriorating into asystole and improves the chances of survival, but only if performed correctly, and at optimal rates of about 100 compressions/min (AHA 2000; Sunde et al 1998). This rate significantly increases cardiac output (CO), coronary perfusion pressure (CPP), and coronary blood flow velocity (Sunde et al 1998). Layperson CPR is often performed inadequately, and Xu et al (2002) determined this might be detrimental enough to cerebral blood flow that it should be bypassed if more effect resuscitation is en route. The benefit of waiting for better-trained personnel outweighs the risk of performing less-than-optimal CPR (Xu et al 2002).

ACD-CPR

ACD-CPR utilizes a hand-held device equipped with a suction cup to actively lift the chest during the decompression phase of CPR, thereby decreasing intrathoracic pressure (Figure 1). Studies have shown varying success with this type of CPR. A 1996 retrospective study conducted in Gšttingen, Germany (Panzer et al 1996) showed no overall difference in survivability between S-CPR and ACD-CPR, although it did show increased survival rates if the rhythm found at onset of CPR was asystole. Additionally, ACD-CPR was shown to increase survivability to the initial endpoint, return of spontaneous circulation (ROSC) (Panzer et al 1996). Other studies have shown superior mean arterial pressure (MAP) and organ perfusion (AHA 2000), and a 1998 study performed on pigs found cerebral blood flow, CPP, and mean aortic pressure all increased with an ACD-CPR rate of 90/min versus 60/min (Sunde et al 1998). The only overall improved survivability rates with ACD-CPR are from a study in France that showed one-year patient survivability increased from 2% to 5% (Plaisance et al 1999).

PTACD-CPR

PTACD-CPR merges the concepts behind ACD-CPR and interposed abdominal compression CPR (IAC-CPR) (AHA 2000). Two rescuers are needed to perform the compression components of IAC-CPR: one to perform chest compressions, and one to perform abdominal compressions (Figure 2). The aim of these compressions is to increase organ perfusion, and while two studies have shown increased ROSC and 24-hour survival rates with IAC-CPR, these results only apply to in-hospital treatment (AHA 2000). PTACD-CPR is performed with a handheld device on which two suction cups are attached, one of which is placed over the sternum and the other of which is placed over the epigastrium (Arntz et al 2001). The two cups are attached with a rigid handle so that when one is compressed, the other is actively decompressed, and vice versa (Figure 3). When Arntz et al (2001) tested one such device, the Lifestick, with the help of the Berlin EMS, they found implementation of PTACD-CPR resulted in a higher rate of ROSC versus S-CPR if the presenting rhythm was asystole (33% vs. none) (Arntz et al 2001). However, if the presenting rhythm was VF, S-CPR was superior in attaining ROSC (68% vs. 44%), and overall, S-CPR resulted in 50% ROSC versus 38% with PTACD-CPR. As for survival beyond ROSC, implementation of S-CPR resulted in a greater chance of survival to hospital admission (46% vs. 29%) and to hospital discharge (58% vs. none), with 86% of those surviving to hospital discharge attaining long-term survival greater than six months (Table 1). Despite these poor results with PTACD-CPR, the researchers found the overall practicability of use of the Lifestick device was better than that of ACD-CPR devices, which cause strain on rescuers due to the force needed to produce active chest decompressions. Additionally, PTACD-CPR resulted in fewer sternum or rib fractures compared to S-CPR (Arntz et al 2001). The Lifestick also eliminates the need for a second rescuer to perform abdominal compressions, making it better suited for pre-hospital care, in which multiple rescuers may not be present.

CCC-CPR

It has been well established that layperson CPR is not as effective as CPR performed by professional emergency care providers (Xu et al 2002; Kern et al 2002). Many lay rescuers, in addition to being unable to adequately find a pulse, take much longer than the recommended four seconds to deliver the two rescue breaths. Instead, some research has shown a more realistic time for layperson rescue breathing to be about 16 seconds (Kern et al 2002) - quadruple the recommended time - and this decreases the effectiveness of the ensuing chest compressions (AHA 2000). A factor compounding this problem is the fact that many laypeople trained in CPR show reluctance to performing mouth-to-mouth rescue breathing on people unrelated to them (Berg et al 2001; Kern et al 2002; AHA 2000; Kern et al 2001). CCC-CPR eliminates the rescue-breathing component of S-CPR, making it easy to administer with promising research results.

Two studies of the effects of CCC-CPR as compared to S-CPR found CCC-CPR resulted in better outcome after treatment (Berg et al 2001; Kern et al 2002). Berg et al determined the interruption of chest compressions for rescue breathing resulted in a lower number of chest compressions administered, lower CPP, and left ventricular myocardial blood flow throughout treatment on pigs (Berg et al 2001). While arterial oxygen saturation and pH were higher, and Pco2 lower, in the standard CPR trials, the left ventricular myocardial oxygen delivery and CO were not different from those of the CCC-CPR trials. Thus, the increased oxygenation benefits afforded by rescue breathing are negated by the poor hemodynamic effects of stopping compressions. This study found no significant difference in neurological outcome between the two trial groups (Berg et al 2001).

Kern et al, in their study, showed CCC-CPR provided a better outcome than S-CPR. A higher percentage of pigs in the CCC-CPR trials reached ROSC, all-endpoint survival, and neurological function retention/non-impairment than those in the standard CPR trials (Table 2) (Kern et al 2002). They, too, found the decreased number of chest compressions, along with the frequent, extended interruptions for rescue breathing, were detrimental to the effectiveness of standard CPR (Kern et al 2002).

CA Treatment in a Hospital Setting

Although all of the pre-hospital CA treatments are available for in-hospital use as well, the same is not true of all hospital treatments for pre-hospital rescuers. Surgical procedures and certain drug therapies must be administered by physicians, limiting their use to a hospital setting.

Minimally invasive direct cardiac massage

Closed-chest compressions, which are used in S-, ACD-, PTACD-, and CCC-CPR, are not as effective in creating coronary and cerebral perfusions as open-chest cardiac massage (OC-CM). OC-CM was the standard for cardiac resuscitation before the 1960s, when closed-chest compressions proved successful and current CPR techniques were developed (Bains 1998; Kouwenhoven 1960). It requires open-chest surgery, making it even more unfavorable in an emergent setting. However, because direct cardiac massage produces better coronary perfusion, recent studies have looked at methods to minimize the invasiveness of surgery. Minimally invasive direct cardiac massage (MID-CM) utilizes a small device inserted through a small incision in the chest to compress the heart internally. MID-CM was shown in 1995 to be technically feasible and equivalent to traditional OC-CM in maintaining aortic, pulmonary artery, and pulmonary pressures, and differences from baseline measurements in arterial pH and arterio-venous Pco2 were similar (Buckman et al 1995). A 2000 report found MID-CM to provide better resuscitation results than S-CPR, with ROSC occurring in 7/10 MID-CM animals versus 2/10 S-CPR animals. One-hour survival was also better for the MID-CPR trial animals (5/10 vs. 1/10) (Eynon 2000).

Paiva et al found that although ROSC rates were significantly higher for pigs treated with MID-CM as compared to those that received S-CPR (7/10 vs. 2/10), there was no significant difference in the increased rate of survival to one hour or 24 hours (Paiva et al 2000). The group found CPP levels to be similar in the two groups, and concluded the lack of significant difference between the MID-CM and S-CPR groups for the majority of comparisons to be due to the small study groups, suggesting further studies are in order (Paiva et al 2000).

Drug treatment for VF

Yet another variable in the equation for treating VF-induced CA is the availability of drugs. Epinephrine is used for its vasoconstriction properties (AHA 2000), but its effectiveness has been challenged. Two studies designed to test the efficacy of epinephrine versus vasopressin found conflicting results. Achleitner et al (2000) found vasopressin to be superior to epinephrine in maintaining myocardial function above a threshold necessary to achieve successful defibrillation, as well as one-hour survival (10/10 vs. 0/11), in pigs. CPP was also higher for the animals in the vasopressin group (Achleitner et al 2000). In contrast, Voelckel et al (2000) found that administration of epinephrine, either by itself or in combination with vasopressin, increased left ventricular myocardial blood flow, and that ROSC rates were significantly higher in epinephrine-treated pigs than in animals treated with vasopressin alone.

Other studies have focused on a variety of other drugs, or combinations of drugs, for use in cardiac resuscitation. Sun et al (2001) studied _-methylnorepinephrine (_MNE), a selective _2-adrenergic agonist, and its effects compared to epinephrine. Twenty rats were induced into VF, then treated with either _MNE or epinephrine. The two control groups consisted of a saline placebo group and a group treated with yohimbine, an _2-receptor blocker, before injection of _MNE. All the animals were successfully resuscitated after eight minutes of untreated VF, mechanical ventilation, precordial compression, and injection of the appropriate drug. However, those treated with _MNE showed better post-resuscitation myocardial function and survival, and these results were negated with pretreatment with yohimbine (Sun et al 2001). Seaberg et al have performed previous studies relating improved resuscitation rates with various drug combinations (Menegazzi et al 1993; Menegazzi et al 2000), and continued their research by testing the efficacy of magnesium. They found 100% ROSC and survival to one hour in pigs treated with a combination of epinephrine, lidocaine, bretylium, propranolol, magnesium, and U-74389G. ROSC and one-hour survival rates were no greater than 38% in control groups (Table 3) (Seaberg et al 2001).

Electrical Defibrillation

The first reported use of current-terminated VF was by the French physiologists Prevost and Battelli in 1899 (Sternbach et al 2000). Since then, the method has been refined and electrical defibrillation is now considered to be the most important link in the CA chain of survival (AHA 2000). The AHA states early defibrillation, defined as shock delivery within five minutes of EMS notification, to be a high-priority goal (AHA 2000; Kern et al 2001). In a hospital setting, this is often possible, but such quick EMS response to out-of-hospital CAs is not always possible. In instances when VF has continued untreated for longer periods of time, immediate defibrillation has been shown to be detrimental, oftentimes causing VF to deteriorate into asystole (Achletiner et al 2001; Cobb et al 1999; Leng et al 2001). Leng et al (2001) showed CPR and epinephrine provided better rates of survival after prolonged (>12 minute) VF. They postulate that the improved results are due to the better myocardial perfusion afforded by the CPR, making defibrillation more likely to succeed. The importance of improved perfusion is therefore of primary importance over the presence of a dysrhythmia (Leng et al 2001).

Niemann et al (2000) attempted to find the lower limit of VF duration at which point pre-defibrillation CPR was no longer beneficial. They compared two groups of pigs, one of which received immediate defibrillation after five minutes of VF, and one of which received 90 seconds of CPR before defibrillation. They found pre-shock CPR did not improve the response to first shock, decrease the incidence of post-shock deterioration to asystole, or increase the rate of ROSC. In fact, they found pre-shock CPR resulted in a significantly lower cardiac resuscitation rate (Niemann et al 2000). Two other studies have shown contrasting results (Achleitner et al 2001; Cobb et al 1999). In a review of 1117 patients in VF upon paramedic arrival, 639 of who received immediate defibrillation and 478 of who received 90 seconds of CPR prior to defibrillation, Cobb et al (1999) found higher rates of survival to all endpoints in the group treated with pre-shock CPR. Significantly higher differences in favor of pre-shock CPR were shown in all subsets of data for patients in VF for longer than four minutes before paramedic arrival (Cobb et al 1999). Achleitner et al (2001) evaluated the hemodynamics of patients treated with 90 seconds of pre-shock CPR and found this treatment provided increased CPP and MAP when VF endured for more than four minutes.

Automated external defibrillators (AEDs) have come into favor for their ease of use and increasingly lower cost (Xavier et al 2002; Yu et al 2001). Their availability also means AHA goals of providing quick defibrillation can be met (AHA 2000). However, in situations of prolonged untreated VF, AEDs have been shown to be less effective than immediate manual defibrillation with traditional defibrillators. Xavier et al (2002) examined the one-hour survival, 24-hour survival, and neurological outcome of patients treated with either immediate defibrillation following eight minutes of untreated VF or AED. AED use resulted in a 60-second delay of defibrillation, caused by the time the AED device requires to register and diagnose VF before delivering the shock. This 60-second delay caused decreased survival in all three categories when compared to the survival rates for immediate defibrillation (Table 4) (Xavier et al 2002).

Similarly, Yu et al (2001) found the rate of ROSC decreased as the delay before shock increased from three to 20 seconds, following seven minutes of untreated VF in pigs (Figure 4). They also found MAP decreased in a similar manner. These delay times are typical of the time it takes for AEDs to register and diagnose VF, and are indicative of the time periods in which CPR would have to be interrupted in order for the AED device to work (Yu et al 2001). They also mimic the delay times encountered when lay rescuers perform rescue breathing during CPR, which has been found detrimental in numerous studies mentioned earlier (Berg et al 2001; Kern et al 2002; AHA 2000).

Conclusion

Because there are many factors affecting the availability of various treatments for CA, a number of considerations must be taken into account when deciding which is most effective. Specialized devices are necessary to perform ACD- and PTACD-CPR, which are not always readily available to the lay rescuer who witnesses CA, and S-CPR performed by laypeople has been proven inefficient due to an inability to provide rescue breathing quickly enough when they are even willing to attempt rescue breathing in the first place. CCC-CPR is easier for the layperson to perform, especially in a single-rescuer scenario, while providing greater rates of multiple-endpoint survivability and good neurological outcome. Therefore, the AHA should consider revising its recommendations to instruct lay rescuers in a pre-hospital setting to perform CCC-CPR after notifying EMS of the need for more advanced care. Although some may question the practice of ignoring ventilation in favor of chest compressions only, enough evidence has shown lay rescuers, and especially lay rescuers acting alone, to be unable to provide adequate treatment to patients suffering from VF/CA if they must provide airway management in addition to chest compressions.

In a hospital setting, surgical techniques and drug therapies are more readily available. Because MID-CM has been shown to be technically feasible with minimal invasiveness, and because direct cardiac massage is more effective than closed-chest cardiac massage, clinicians should consider refining MID-CM techniques and making the use of MID-CM devices more widespread. Given that emergency physicians are already well trained in minor surgical procedures such as chest tube placement, MID-CM devices should prove easily adaptable to an emergency department setting. While various drug treatment therapies are being researched, none has been proven conclusively to be more effective than the rest. Therefore, drug treatments should continue to be evaluated in the hopes that the best treatment may be determined for in-hospital VF-induced CA. While some may find this recommendation to be premature given the lack of extensive data in this area, it is clear that the possibility for a more effective drug therapy than the current epinephrine guidelines exists.

Electrical defibrillation remains the most effective treatment of VF-induced CA, but more detailed recommendations for its usage must be made. Because the time to shock may be considerably longer than the five minutes recommended by the AHA, immediate defibrillation may be more harmful than beneficial, converting VF to asystole. Therefore, EMS rescuers should consider the application of 90 seconds of CPR prior to defibrillation, as this has shown in multiple studies to produce higher rates of survival. The existence of studies showing conflicting data must be taken into consideration, but more extensive research will provide conclusive findings. As for the application of AEDs, data showing a decrease in survival rates due to the extensive time required for the AED device to register and diagnose the correct dysrhythmia are significant, and suggest further research must be conducted before recommendations are made to provide AED access to lay people in numerous public settings. The goal of immediate or quick defibrillation is worthwhile, but even the simplest-to-use devices require precious time while a lay rescuer with infrequent practice in defibrillation struggles with a new device. Therefore, increased emphasis should be placed on maintaining perfusion through CCC-CPR until trained response personnel arrive on the scene.