Given the difficulty of performing consistent CPR compressions, technology has turned to automation.
There are two types of automated compressors available. Pneumatically driven piston compressors were first introduced into clinical practice in the 90s. These devices drive a piston to compress the heart against the backbone in the same manner as manual CPR.
The earliest example is the Thumper from Michigan Instruments.
This device uses pneumatic power to drive a piston that is manually set by the rescuer to deliver a fixed depth of compression. The device can be set to comply with the Guidelines 2010, and there is an optional hands-free ventilation capability.
Similar in operation to the Thumper is the LUCAS device. Also pneumatically driven, the LUCAS differs from the Thumper in that is employs active decompression suction on the upstroke.
The third automated device is different from the previous two. The ZOLL AutoPulse is a load distributing band compressor that is mechanically actuated and battery driven. AutoPulse provides both direct compression and semi-circumferential thoracic compression. It automatically sizes the patient and
operates in both 30:2 and continuous compression mode.
None of the devices have been used in a completed randomized clinical trial to date. The AutoPulse was studied in a multi-center out of hospital study known as ASPIRE. The trial was stopped when data indicated that a secondary endpoint (survival to discharge) appeared to be trending toward better outcome with manual CPR. Subsequent analysis showed that all the data causing the variance was from a single study site and that site had made a change to the study protocol midway into the trial.
What has been learned is that the key to effective use of mechanical assist is that it be used in combination with high-quality manual CPR and deployed without delay. The average time to deployment in ASPIRE was 11 minutes and at one site no compressions were performed during the waiting period. A new randomized trial (CIRC) is currently underway and will take these very critical factors into consideration.
Despite the lack of results from a randomized trial, there is a significant amount of clinical data available, particularly with the AutoPulse. The following is a summary:
A Pilot Study in EMS with LUCAS
Axelsson et al. reported on a non-randomized controlled trial that evaluated the clinical consequences of the introduction of mechanical CPR in the EMS system for treatment of cardiac arrest. Patients included in the study all had experienced arrests. Exclusions from the trial included those under age 18, those undergoing trauma, pregnancy, hypothermia, intoxication, and hanging or drowning. Also excluded were those who experienced ROSC prior to the ALS unit arriving.
In the study, 105 patients were treated with LUCAS CPR and 169 patients with manual CPR. The median delay from onset of arrest to the arrival of the ALS unit was 12 minutes. When all patients were included in the analysis, there was no significant difference between the groups with regard to ROSC, survival to hospital admission or to hospital discharge.
The results for the LUCAS were then compared with a matched control population according to age, initial rhythm, witnessed status, etiology and delay to start of CPR. Again, no difference was found between the groups in any of the variables evaluated. (P values for this study were under 0.20 and not statistically significant.) Authors of the study noted that a critical issue within the study was the way in which patients were randomized and the delay in intervention. (Axelsson C et al., Resuscitation 2006;71;47-55)
Two studies compared patients treated with manual CPR to patients treated with AutoPulse to determine the impact of AutoPulse on the delivery of patients with sustained ROSC to the emergency department (ED).
Casner et al. at the San Francisco Fire Department conducted a retrospective, case-matched review of the impact of the AutoPulse on survival.
Specifically, the rate of delivery of 162 patients with ROSC to the ED was measured. The increased ROSC rate (35%) in the AutoPulse group was most pronounced when the initial presenting rhythm was asystole or pulseless electrical activity. (See Figure "ROSC to ED Rate.")
Casner M et al. Prehospital Emergency Care. 2005;9(1):61-67.
The graph on the left shows data from a study conducted in Volusia County, Fla. Swanson et al. compared the rate of delivery of patients in ROSC sustained to the ED, as well as EtCO2 readings, for 607 patients treated with manual CPR and 269 patients treated with the AutoPulse.
The major finding in this study was that the AutoPulse improved the rate of delivery of patients in ROSC sustained to the ED by 56%. Increased sustained ROSC rate was most pronounced when the initial presenting rhythm was asystole or PEA. Six survived greater than one year post arrest, five were neurologically normal. None of the subjects with manual CPR survived. AutoPulse produced pre-arrest levels of blood flow to the heart and brain (ACLS protocol – with epinephrine) and produced better EtCO2 results than manual CPR, and these results improved over time. (Swanson M et al., Circulation. 2006;114(18):II-554)
Ong, Ornato et al. at the Richmond Ambulance Authority in Virginia recently reviewed survival rates in 783 patients: 499 of whom had been treated with manual CPR and 284 who had been treated with the AutoPulse.
Using AutoPulse, there was a 235% improvement in survival to discharge, 88% improvement in survival to hospital admission and 71% improvement in field ROSC. All results were highly significant.
Virtually all the evidence supports the effectiveness of the AutoPulse device in increasing perfusion pressure, ROSC, and long-term survival rates. (Ong ME, Ornato J et al., JAMA. 2006;295(22):2629-2637)