Review

Evolution and new perspective of chest compression mechanical devices

Alejandra Gaxiola MS^a, Joseph Varon MD^b,?

^aUniversidad Autonoma de Baja California, Tijuana, Baja California, Mexico

^bThe University of Texas Health Science Center of Houston, The University of Texas Medical Branch at Galveston, St Luke’s Episcopal Hospital, Houston, TX, USA

Received 30 August 2007; revised 5 November 2007; accepted 11 November 2007

Abstract Cardiac arrest is a major concern in health care, owing to its high incidence and mortality rates. Since the development of external cardiopulmonary resuscitation (CPR), there has been little advancement in nonpharmacologic therapies that have increased survival rates associated with cardiac arrest. Consequently, there has been much interest in the development of new techniques to improve the efficacy of CPR, particularly in the development of devices. Initially, many of the devices developed were not considered functional and failed to gain acceptance in the clinical setting. Recently, however, several devices have been developed which have progressed the administration of CPR and garnered acceptance in the clinical setting. In this article we will briefly review some of the more common mechanical devices developed to increase the safety and efficacy of CPR administration.

(C) 2008

Introduction

Cardiac arrest is an important topic for investigation and innovation from a therapeutic standpoint as it has a high incidence of morbidity and mortality. More common in the adults, as opposed to the pediatric population, cardiac arrest is responsible for more than half of all deaths caused by cardiovascular disease [1,2]. In United States, estimates of 225000 to 750000 people annually require cardiopulmonary resuscitation (CPR), and there are approximately 1000 sudden cardiac deaths daily [2,3]. Since 1969, when closed chest compressions were developed, there have been few improvements in therapeutic measures that could increase survival rates related to cardiac arrest. Consequently, there

* Corresponding author. Dorrington Medical Associates PA, 2219 Dorrington St, Houston, TX 77030-3209, USA. Tel.: +1 713 669 1670;

fax: +1 713 669 1671.

E-mail address: [email protected] (J. Varon).

have been much study and innovation in development of Alternative techniques, particularly with regard to mechanical devices to enhance the quality and efficacy of CPR.

Despite technological advances, the survival rates for cardiac arrest are dismal [2,4-6]. Reports on the incidence of survival from a cardiac arrest in adults range from 0% to 29% [1,3,6-9]. Cardiac arrests are uncommon in the pediatric population and have a better prognosis in the inpatient setting, with survival rates between 15% and 65%. Conversely, cardiac arrest occurring as an outpatient, in the pediatric population, has lower survival rates from 9% to 25% [10]. Although modern CPR was developed more than 40 years ago, cardiac arrest maintains a high mortality rate [10]. In response to this ongoing challenge, with the introduction of new mechanical devices for chest compres- sions and the development of special techniques to improve the Quality of CPR, we have recently begun to see improvements in this area of medicine that are expected to improve Post-Cardiac arrest survival rates.

0735-6757/$ - see front matter (C) 2008 doi:10.1016/j.ajem.2007.11.016

Cardiopulmonary resuscitation

The goal of CPR is to artificially provide sufficient blood flow to the brain and heart extending the patients viability, so the patient may reestablish spontaneous circulation without the need for further intervention [11]. This can be achieved through manual heart (ie, chest) compressions and the resultant changes that occur in intrathoracic pressure during chest compression. Chest compressions in CPR are divided into 2 phases, the compression phase and the decompression phase. The purpose of the compression phase is to eject blood from the heart to the vital organs, whereas the decompression phase is intended to increase the flow of blood back to the heart [12]. During active compression, there is increase in the intrathoracic pressure, which is conveyed to the cardiac chambers and vascular compartments as well as to the arterial system. In opposition, during decompression the chest recoils back, affecting a decrease in intrathoracic pressure to levels less than the extrathoracic venous pressure, which then causes a return of the blood flow to the thorax [12,13].

The use of external CPR techniques contributes approxi- mately 20% to 40% blood flow to the central nervous system, and 10% to 20% blood flow to the heart, as compared to normal adults [14]. infants and children have a greater deformation capacity of the chest resulting in improved compression of the heart; thus, outcomes for infants and children are more favorable than those of adults. The increased survival rates noted when CPR is performed in infants and children are likely due to the ability to achieve greater intrathoracic pressures and, consequently, better flow to their vital organs [13]. Therefore, it is reasonable to expect that improved CPR techniques, and increased blood flow during resuscitation, could likewise contribute to increased survivability rates in adults.

There are many advantages with using mechanical devices as compared to human effort in the performance of CPR. One

Fig. 1 ACDC Thumper. Inside a portable ice bath. This device is driven by the pressure of an oxygen tank. The US Food and Drug Administration has not approved this device, so it is not for clinical use, only laboratory use. Reproduced with permission from Cryonics Institute (http://www.cryonics.org).

Fig. 2 AutoPulse device. One of the mechanical chest compres- sion devices that is approved for clinical use, since year 2000.

advantage of mechanical devices is the consistency of delivering the same frequency and depth of compressions, as opposed to the inter-rescuer variations that affect the quality of chest compression. Another advantage of using a device is that at the same time you ventilate, the patient can be defibrillated without the need of interruption in CPR. Fewer interruptions of compressions have been attributed to better patient outcomes [8,15,16]. In addition, the fatigue a rescuer experiences with continuous CPR is also a concern. This article will review and examine some of the advantages and disadvantages, and make comparisons of the outcomes associated with delivering manual chest compressions vs Mechanical chest compressions.

History of mechanical devices

The modern use of closed-chest compressions was introduced in 1969 by Kouwenhoven et al [17]. Shortly thereafter, there was much interest in the use of mechanical devices to decrease the exhausting work demands of manual chest compression, with the additional benefit of consistency of depth and force of compressions [18]. The first reported chest compression device was an electropneumatic machine designed by Bramson, which required compressed gas to drive a spring-loaded piston with a force of 60 to 75 lb onto the patient’s sternum [18]. Subsequently, other devices for automated chest compression included the Rodriquez Tocker Automatic external cardiac massage machine (an automatic machine synchronized to an electrocardiographic monitor with an alarm system to alert of tachycardia or bradycardia); the Butterworth-LSI external cardiac compressor; the Beck- Rand external cardiac compression machine (a battery powered machine); the Cardio-Massager and Cardio Pulser, which are both operated manually; the Iron Heart and Baxter H-L-R, each powered by oxygen [18,19]; and the Thumper

Table 1 Facts on mentional mechanical devices Device Studies Efficacy

Table 1 (continued)

Device Studies Efficacy

ACDC- CPR

Plaisance et al, 1999 [43]

Mauer et al, 1999 [47]

Orliaguet et al, 1995 [48]

Skogvoll and Wik, 1999 [51]

Panzer et al, 1996 [50]

Reported survival at 1 year was significantly greater among patients who underwent ACDC- CPR as compared to patients who received S-CPR (5% vs 2%, P =

.03). Likewise, the rate of patients lacking neurologic impairment at the time of hospital discharge was significantly greater in the ACDC- CPR patients as opposed to the S- CPR patients (6% vs 2%, P = .01). The survival rates for the ACDC- CPR group were significantly better than those for the S-CPR group (23.8% vs 20.6%, respectively; P b .05). However, the improvements demonstrated in the ACDC-CPR group were likely skewed owing to the influence of results from 1 study site.

Moreover, the discharge survival rate was not statistically significant 7% for ACDC-CPR vs 5.8% for S-CPR (P = .23).

Found a significantly greater value of peak ETCO₂ in the ACDC-CPR group (27.6 +- 3.0 vs 15.6 +- 2.2

mm Hg) (P b .05).

The authors found no significant difference in the survival rates between the 2 groups: S-CPR (12%) vs ACDC-CPR (13%).

They examined the rates of ROSC, admission to hospital, survival at 24 h, hospital discharge, and neurologic outcome in ACDC-CPR- (54%) and S-CPR-treated patients (46%). The authors found no significant benefit in the outcome parameters for the ACDC-CPR- treated group; however, patients regaining ROSC showed a significant difference in favor of S-CPR for the end points of

Steen et al, 2002 [54]

Rubertsson and Karlsten, 2005 [55]

LifeBelt Niemann et al,

2006 [58]

neurologic outcome. Conversely, if the interval of receiving LUCAS- CPR was N15 min or it was a nonwitnessed cardiac arrest, there were no 30-day survivors.

In an animal study with 4 different pig models with induced ventricular fibrillation and in an artificial thorax model. In the artificial thorax model, superior pressure and flow were obtained with LUCAS as compared to S- CPR. In the pig models, significantly higher cardiac output, carotid artery blood flow, ETCO₂, intrathoracic decompression- phase aortic- and CPPs (10 mm Hg with S-CPR vs 15 mm Hg with LUCAS) were obtained, also with LUCAS-CPR (83% ROSC)

compared to S-CPR (0% ROSC). Reported significantly higher levels of the “mean cortical cerebral blood flow during CPR” when using the LUCAS-CPR device (65% of baseline blood flow compared with 40% in the S- CPR group, P = .041). They also reported significantly higher levels of ETCO₂ in the LUCAS-CPR group. Mean arterial pressure, ROSC, and jugular bulb oxygen saturation showed no significant difference between the 2 groups. With the use of the LifeBelt, there were significantly greater levels of CPP compared to S-CPR at 1 min (15 +- 8 vs 10 +- 6 mm Hg, P b .05)

and 5 min (17 +- 4 vs 13 +- 7 mm Hg, P b .02) of chest compression. Similarly, there were significantly greater levels of ETCO₂, LifeBelt compared to S-CPR (20 +- 7 vs 15 +- 5 mm Hg, respectively; P b .05) at 1 min.

LUCAS Steen et al,

2005 [53]

hospital admission (46% vs 41%,

P = .59), 24-h survival (40% vs 31%, P = .28), and hospital

discharge (29% vs 17%, P = .09). Of 100 patients studied, 31% had a stable ROSC and were subsequently admitted to the intensive care unit. Of the patients with witnessed cardiac arrest who received LUCAS-CPR within 15 min from the ambulance call (n = 43), 16% survived for 30 days with good

AutoPulse

vest CPR

Ong et al,

2006 [52]

Krep et al, 2007 [20]

AutoPulse produces a CPP of ~21 mm Hg compared to ~14 mm Hg

produced by S-CPR and generates

~36% of normal Coronary blood flow compared to ~13% generated in the S-CPR device.

The rate of successful resuscitation was 54.3% and ETCO₂ ranged from 15 to 45 mm Hg. No complications or adverse effects were associated with the use of the device.

(Michigan Instruments Inc, Grand Rapids, MI) (Fig. 1), which has been continuously redesigned and is currently used in many research laboratories [19-21].

In 1989, another device, the vest CPR was introduced, and consisted of a vest that could be placed around the chest to be quickly inflated and deflated [18]. This device has undergone several evolutions and is currently called the AutoPulse CPR load-distributing band (Fig. 2). It is currently approved for use and available in several hospitals throughout the USA [22].

In 1992, the active compression decompression (ACDC- CPR) technique [23] was introduced by a commercial device called the Cardio-Pump. This machine was developed as a result of an unexpected resuscitation, successfully performed by a lay person using a toilet plunger [24]. The use of the toilet plunger spurred interest in using active decompression to enhance CPR. The discovery of the technique of active compression alternating with active decompression, which had no previous record of use, has been recognized as an effective way to increase blood flow, as it helps to increase the blood return in the recoil phase.

The Michigan Instruments Heart-Lung Machine (Thum- per) is an instrument used in the delivery of ACDC-CPR. The ACDC Thumper unit can induce heart pumping action by compression, as well as active decompression to lift the chest with a rubber suction cup (like a toilet plunger, ie, “plumber’s helper”). The ACDC Thumper is driven by the pressure of an oxygen tank and is quite portable. The Thumper can deliver steady compressions and decompres- sions, or can deliver 5 cycles of ACDC action simulta- neously with a cycle of oxygen ventilation through an air mask. Knobs on the ACDC Thumper allow for adjustment of the force of compression, the force of decompression, and the volume of oxygen delivered during a ventilation. Another device using this ACDC-CPR mechanism called the ResQPump (Advanced Circulatory Systems, Inc, Eden Prairie, Minn) is currently being evaluated for its effective- ness [25].

Since their initial development, the use of automated chest compression devices has demonstrated efficacy and continued to gain acceptance (Table 1). In 2000, the American Heart Association and European Resuscitation Council published recommendations for “alternative tech- niques to standard Manual CPR” in the Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovas- cular Care of 2000 [26]. These techniques included interposed abdominal compression CPR, high-frequency CPR, phased thoracic-abdominal compression-decompres- sion CPR, simultaneous ventilation-compression CPR, ACDC-CPR, and the use of mechanical devices such as the vest CPR and mechanical (piston) CPR devices as an adjunct, to enhance compression and diminish exhaustion of the person delivering CPR. In addition, other adjunctive techniques were recommended such as the impedance threshold valve and Open Chest CPR [26].

Throughout the development of the various automated chest compression devices, there have been complications

associated with the use of these devices, such as fractures associated with the high forces delivered. These fractures are similar to those seen with conventional CPR, although the incidence may be more frequent with the use of a mechanical device. The additional time associated with obtaining, applying, and adjusting the machines, and the inconvenience of devices that are operated by battery, electricity, or that were not portable are also considered disadvantages [18]. Although advances in automated chest compression devices have been made, and the safety of these devices has likewise improved, caution should still be exercised when considering the use of mechanical compression devices.

Mechanical devices

There have been many studies that have proposed possible causes of the failure to achieve an optimal outcome with CPR and accomplish resuscitation [3,15,27-33]. These studies have evaluated the quality of CPR performance, as this may be a factor associated with poor outcomes. Some studies have shown that the Quality of chest compressions provided by the medical staff deteriorates remarkably after a relatively short time [3,15,27,31]. In addition, there are other deficiencies observed during the performance of conven- tional/standard CPR (S-CPR) chest compression, such as failure to maintain the relationship of compressions to ventilations. It has been determined that a compression-to-

Fig. 3 LUCAS device. Using LUCAS device inside an ambulance. One of the benefits of this device is the opportunity to use it in an ambulating car with no change in movement as compared to other devices. Reproduced with permission from JOLIFE 2007.

Fig. 4 LifeBelt device. Light, handheld, manual chest compres- sion device that can adapt to thorax sizes.

ventilation ratio of 30:2 is more efficient than a 15:2 ratio, as it improves the blood flow to the vital organs [15,22,28,34,35]; however, the 30:2 ratio can be very demanding for the rescuer. Additional disadvantages to S- CPR chest compression may include deficient ventilations, hyperinflation or hyperventilation [29], slow compression rate, inappropriate compression depth (either too superficial or too profound) [28,30,33], and interruptions between compressions [16,32]. Furthermore, in S-CPR, the blood return to the heart depends only on the passive recoil of the chest wall. In contrast, CPR performed with the use of mechanical devices exerts an external force enhancing the recoil of the wall resulting in increased venous return in addition to the normal recoil of the chest wall.

coronary perfusion pressure experimentally is one of the best indicators of successful return of spontaneous circulation (ROSC) [14,36]. In 2000, Kern [14], at the University of Arizona, using an animal model, concluded that a CPP of 30 mm Hg was ideal for long-term survival. Coronary perfusion pressure levels of less than 10 mm Hg were related with no success in resuscitation, and CPP levels greater than 40 mm Hg were correlated with diminished long- term outcome that is related to an increase in complications, likely due to the introduction of elevated forces.

It has been demonstrated that with S-CPR the CPP reaches only approximately 20% to 30% of normal [33]. To measuring CPP during CPR (to maintain optimal CPP pressure) requires the use of invasive techniques that are not practical. An alternate method to assess cardiac output during CPR is to measure the end-tidal carbon dioxide (ETCO₂) pressure [37,38]. End-tidal CO₂ has been correlated with cardiac output and may serve as a prognostic value for survival [36].

Considering the aforementioned limitations of S-CPR chest compression, there have been advances in techniques to improve the quality of CPR and, as a result, improve long-term outcome and survival rates. One of the main goals of advancements in these techniques has been to

increase the CPP of the patient, and thus the ROSC. These techniques are categorized as invasive techniques that include open-chest massage and minimally invasive direct cardiac massage [14]. In addition, there is a second category of closed-chest techniques that include the ACDC-CPR device, the impedance threshold device, the intrathoracic pressure regulator, the AutoPulse device (Fig. 2), the Lund University Cardiac Assist System (LUCAS) (Fig. 3), and the LifeBelt (Fig. 4) [25].

Active compression-decompression

The purpose of the ACDC-CPR technique is to increase the negative intrathoracic pressure during the decompression phase. This increases the venous return to the heart and thus increases cardiac output, coronary and cerebral blood flow, arterial blood pressure, and ETCO₂. In the compression phase, blood is pumped out of the thorax with positive pressure [9,23,25,39,40].

There are several devices that perform the ACDC-CPR method. One such device that is being evaluated is the ResQPump [25]. It consists of a round handle for stability, a calibrated pressure measuring device, and a suction cup [41]. Its mechanism of action consists of compression on the mid- sternum, as in S-CPR, followed by suction of the thorax in the decompression phase to increase the recoil. If necessary, the pressure measuring device can be used to measure the force delivered and adjustments can be made as needed [39,40,42]. A similar device, using the same technique, previously mentioned, is the CardioPump.

The disadvantage associated with the ACDC-CPR method, and the devices mentioned above, is that perform- ing CPR with either of these devices is physically very demanding for rescuers, and they may fatigue much faster than if performing S-CPR [43]. It has been shown that the amount of effort required to operate the ACDC-CPR is approximately 25% more than when performing S-CPR [44]. These findings were confirmed by Elvira et al [41], when they measured the lactate concentrations in blood after performing S-CPR and ACDC-CPR, which revealed higher Blood lactate levels in the rescuers who used the ACDC-CPR. In addition, there is a greater incidence of local trauma to the thorax [45,46]. Moreover, the use of this method and these devices in the pediatric population requires several sizes of the device based on the size of the patient [46].

There have been several studies evaluating the efficacy of ACDC-CPR compared to S-CPR. Some of these studies have shown benefit [43,47,48], whereas others have found no difference between the 2 methods [49-51]. In a study of 750 patients by Plaisance et al [43], 377 patients underwent S-CPR and 373 patients underwent ACDC-CPR. The authors reported that survival at 1 year was significantly greater among patients who underwent ACDC-CPR

as compared to patients who received S-CPR (5% vs 2%, P =

.03). Likewise, the rate of patients lacking neurologic impairment at the time of hospital discharge was signifi- cantly greater in the ACDC-CPR patients as opposed to the S-CPR patients (6% vs 2%, P = .01).

In a prospective randomized trial by Mauer et al [47], 1410 patients received ACDC-CPR and 1456 received S- CPR. The survival rates for the ACDC-CPR group were significantly better than those for the S-CPR group (23.8% vs 20.6%, respectively; Pb 0.05). However, the improvements demonstrated in the ACDC-CPR group were likely skewed owing to the influence of results from 1 study site. Moreover, the discharge survival rate was not statistically significant: 7% for ACDC-CPR vs 5.8% for S-CPR (P = .23). Lastly, the complication rates associated with the aforementioned therapies were assessed and revealed a significantly high number of patients with sternal ecchymosis in the ACDC- CPR group (P b .01).

Orliaguet et al [48], in a prospective study including 16 patients, compared S-CPR and ACDC-CPR and found a significantly greater value of peak ETCO₂ in the ACDC- CPR group (27.6 +- 3.0 vs 15.6 +- 2.2 mm Hg) (P b .05),

suggesting that ACDC-CPR could improve cardiac output compared with S-CPR.

In a single-center, randomized population-based study spanning 4 consecutive years, Skogvoll and Wik [51] compared the survival rates of 302 patients who received either S-CPR (n = 145) or ACDC-CPR (n = 157). The authors found no significant difference in the survival rates between the 2 groups: S-CPR (12%) vs ACDC-CPR (13%). Furthermore, the authors noted difficulties associated with the use of the ACDC-CPR device that included a lack of adherence of the CardioPump to the thorax during the decompression phase, due to large breasts, hairy thorax, and/ or abnormal anatomy of the thorax.

In a retrospective, nonrandomized study of 152 adult patients with prehospital cardiac arrest not caused by trauma or hypothermia, Panzer et al [50] examined the rates of ROSC, admission to hospital, survival at 24 hours, hospital discharge, and neurologic outcome in ACDC-CPR- (54%) and S-CPR-treated patients (46%). The authors found no significant benefit in the outcome parameters for the ACDC- CPR-treated group; however, patients regaining ROSC showed a significant difference in favor of S-CPR for the end points of hospital admission (46% vs 41%, P = .59), 24- hour survival (40% vs 31%, P = .28), and hospital discharge (29% vs 17%, P = .09).

Load-distributing band CPR or vest CPR

The CPR vest, now called the AutoPulse, has been approved for use since 2000 [22]. This device has a light, portable, constricting band (either pneumatic or electrical) that is similar to a large blood pressure cuff attached to a

backboard. This vest produces rapid positive and negative changes in intrathoracic pressure as it inflates and deflates, compressing the anterior and anterior-lateral chest walls [25]. Advantages of this device are that it reduces the chest compression interruptions when the patient is being transferred, produces a consistent compression depth on a larger area of the thorax, and reportedly does not interfere with defibrillation. One potential problem associated with the use of this device is that there may be a delay in initiating

CPR while applying the device.

The AutoPulse (Fig. 2) has been shown to be efficacious, as it produces better blood flows and pressures than with S- CPR. It produces a CPP of ~21 mm Hg compared to ~14

mm Hg produced by S-CPR [52] and generates ~36% of

normal coronary blood flow compared to ~13% generated in S-CPR [52].

Krep et al [20], in a prospective observational preclinical study, found the AutoPulse system to be an effective and safe mechanical apparatus. The rate of successful resuscitation was 54.3% and ETCO₂ ranged from 15 to 45 mm Hg. No complications or adverse effects were associated with the use of the device.

Lund University Cardiopulmonary Assist System

LUCAS (Fig. 3) is a gas-driven CPR pneumatic device that uses either oxygen or air, and delivers both automatic chest compressions and active decompressions. It is composed of a plunger homologous to that of the ACDC- CPR device, previously described, that is attached to a backboard. In 1 minute, it provides 100 compressions/ decompressions [25], with a peak of maximum depth for each compression of 5 cm, and a maximum force of 500 N for compressions and 410 N for decompressions. LUCAS can operate for 30 minutes with 1 bottle of gas [53]. However, LUCAS is a noisy device, sometimes requiring the use of ear plugs.

In 2002, LUCAS-CPR was tested in the prehospital care [53]. Three ambulances were equipped with LUCAS in 2 cities in Southern Sweden (Lund and Malmo) [53]. LUCAS was applied on patients with any etiology of cardiac arrest. Of 100 patients studied, 31% had a stable ROSC and were subsequently admitted to the intensive care unit. Of the patients with witnessed cardiac arrest that received LUCAS- CPR within 15 minutes from the ambulance call (n = 43), 16% survived for 30 days with Good neurologic outcome. Conversely, if the interval of receiving LUCAS-CPR was more than 15 minutes or was a nonwitnessed cardiac arrest, there were no 30-day survivors. As a result of these findings, in 2005 all ambulances in Skane (Southern Sweden) were supplied with a LUCAS device for opportune treatment in all emergencies [53]. LUCAS is now available in the United States for clinical use [25].

Steen et al [54] compared LUCAS-CPR to S-CPR in an animal study with 4 different pig models with induced ventricular fibrillation and in an artificial thorax model. In the artificial thorax model, superior pressure and flow were obtained with LUCAS as compared to S-CPR. In the pig models, significantly higher cardiac output, carotid artery blood flow, ETCO₂, intrathoracic decompression-phase aortic- and CPPs (10 mm Hg with S-CPR vs 15 mm Hg with LUCAS) were obtained, also with LUCAS-CPR (83% ROSC) compared to S-CPR (0% ROSC) [54].

The authors also conducted a pilot study with 20 patients in whom CPR failed and concluded that LUCAS was a light device, easy to apply and use in a correct position, and that it worked optimally during transport on stretchers and in ambulances [54].

Rubertsson and Karlsten [55], in an animal study comparing S-CPR and LUCAS-CPR, reported significantly higher levels of the “mean cortical cerebral blood flow during CPR” when using the LUCAS-CPR device (65% of baseline blood flow compared with 40% in the S-CPR group; P = .041). They also reported significantly higher levels of ETCO₂ in the LUCAS-CPR group. Mean arterial pressure, ROSC, and jugular bulb oxygen saturation showed no significant difference between the 2 groups.

The results of the studies by Steen et al [54] and Rubertsson and Karlsten [55] are also supported by case report studies which assessed the LUCAS-CPR device and demonstrated its efficacy during unique cardiac arrest situations [56,57].

Lifebelt

The LifeBelt (Fig. 4) consists of a light (5 lb), handheld, manual chest compression device that can adapt to thorax sizes up to 55 in. Its mechanism of action is similar to the vest CPR in that it compresses the sternum and lateral walls of the chest to provoke increased blood flow. Moreover, it was designed to lessen user fatigue [25,58].

Niemann et al [58], in an angiographic study of pigs (15 used LifeBelt and 14 S-CPR), reported that, with the use of the LifeBelt, there were significantly greater levels of CPP compared to S-CPR at 1 minute (15 +- 8 vs 10 +- 6 mm Hg,

P b .05) and 5 minutes (17 +- 4 vs 13 +- 7 mm Hg, P b .02) of chest compression. Similarly, there were significantly greater levels of ETCO₂ with LifeBelt compared to S-CPR (20 +- 7 vs 15 +- 75 mm Hg, respectively; P b .05) at 1 minute.

Conclusion

Despite the evolution of CPR, there have been few improvements in the outcomes of patients with cardiac arrest who receive conventional CPR, which has become a major

concern to health providers and investigators alike. Shortly after the development of CPR, investigation of mechanical devices to improve CPR administration had begun. Unfortu- nately, many of the early devices were not considered functional in the clinical and emergency setting; however, these devices have evolved and become not only functional but safe and efficacious. In 2000, automatic CPR devices began to receive approval for clinical use. Presently, focus is on improving the already existing devices or on implement- ing more functional, simple, and qualitative devices for future use. There are currently several devices undergoing evaluation for approval for clinical use. In addition, there are other approaches such as the inspiratory impedance thresh- old method that increases the blood flow back to the chest by stopping the inspiratory gas interchange during decompres- sion, thus generating increased negative pressure in the thorax and augmenting venous return.

Chest compression devices such as the AutoPulse, ACDC-CPR with ResQPump, LUCAS, and LifeBelt are very promising. They have demonstrated in studies and practical use that they are efficacious and have advantages as compared with S-CPR. It is anticipated that over the next

5 years, with increased use, acceptance, and refinement, these devices will lead to greater efficacy, safety, and improved patient outcomes. Although more studies need to be done, we encourage and eagerly anticipate these advancements and the use of these devices, so that in the near future we may improve the efficacy of CPR and reduce the incidence of mortality associated with cardiac arrest.

Acknowledgments

The authors would like to thank Richard Pistolese for his assistance in the preparation and review of this manuscript.

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