This technique is designed to augment the thoracic pump mechanism of blood flow. In animal models, superior vena cava (SVC) CPR increased systolic pressure and carotid blood flow. However, clinical trials of SVC-CPR have shown that survival was better with standard techniques. [184 ] , [185 ] According to the 1992 AHA guidelines, SVC-CPR is not recommended. [43 ]
The technique of IAC-CPR involves standard chest compressions with a second person applying compressions to the abdomen during the relaxation phase of the chest compressions. [186 ] The theoretical advantage of this technique is that the abdominal aorta is compressed during “diastole,” augmenting aortic diastolic pressure, and released during “systole,” improving forward flow (analogous to an intraaortic balloon pump). In contrast to abdominal binding, in which the liver is forced upward beneath the sternum, with IAC-CPR the liver can move downward during chest compressions, decreasing the likelihood of serious hepatic injury. IAC-CPR is not associated with increased rates of intraabdominal injuries or aspiration. [186 ] Human studies of IAC-CPR have yielded mixed results. [187 ] , [188 ] However, in two recent trials, IAC-CPR was found to increase resuscitation rates and survival to discharge for inpatient cardiac arrests. [189 ] , [190 ] Presently, this technique is still classified as experimental by the AHA.
High-impulse CPR is a technique in which compressions are delivered with high force at high rates. Animal studies have shown dramatic increases in coronary blood flow and cardiac output using high-impulse CPR. [64 ] , [171 ] In addition, early and late survivals are significantly better than with standard CPR. [162 ] The AHA still classifies high-impulse CPR as an experimental technique. [43 ] However, the current recommendation of a rate of 100 compressions per minute with a 50 percent compression cycle is, in essence, a high-impulse technique. Further study is needed to determine if high-impulse CPR improves survival clinically.
These devices also are designed to augment the thoracic pump. They increase intrathoracic pressure by limiting downward movement of the diaphragm during compression. [191 ] Although animal studies have shown increased aortic pressures and carotid blood flow with these devices, [195 ] their use may increase right atrial and intracranial pressures, limiting blood flow to the heart and brain. [193 ] In addition, some investigators have noted an increased incidence of serious intraabdominal complications, particularly liver lacerations, with abdominal binding and a pneumatic antishock garment. [194 ]
The pneumatic vest is designed to augment the thoracic pump mechanism. The device consists of a vest containing a bladder. Air is forced into and out of the vest by a pneumatic drive system. Preliminary human trials of vest CPR were reported in 1993. [195 ] Vest CPR was shown to increase aortic diastolic and coronary perfusion pressures and the rate of return of spontaneous circulation. However, no patients survived to discharge. Vest CPR may lower the risk of traumatic complications, however.
The concept of the ACD device originated from the observation that a man was resuscitated successfully from cardiac arrest on two separate occasions by family members using a plunger. [196 ] The device consists of a hand-held suction cup with a central piston and handle. ACD CPR has been shown to improve aortic and coronary perfusion pressures, as well as cerebral, coronary, and renal blood flow. [197 ] – [200 ] ACD is thought to improve ventricular filling and coronary flow by creating a negative intrathoracic pressure during the release phase. [201 ] Two clinical studies have reported significant increases in the rates of return of spontaneous circulation and 24-hour survival with the ACD device. Survival to discharge was higher with ACD in both studies but did not reach statistical significance. [202 ] , [203 ] The ACD device is portable, easy to use, and inexpensive, making it an attractive adjunct to standard CPR.
Cardiopulmonary bypass (CPB) has been used successfully in cardiac arrest patients. [204 ] – [206 ] Hemodynamics, survival, and neurologic function are improved in animals treated with early CPB versus those treated with standard CCM. [207 ] – [209 ] However, this technique is limited to tertiary care centers.
The IABP has been shown to be effective in improving hemodynamic parameters during closed chest resuscitation in animal models. [210 ] , [211 ] At present, no randomized studies of the IABP in the setting of cardiac arrest have been performed.
The technique of DMVA was devised in the 1960s for the treatment of victims of cardiac arrest. The device consists of a cup that is placed directly on the heart via a left anterior thoracotomy. The cup has a semirigid outer shell and a pliable inner diaphragm. Air is alternately insufflated and withdrawn from the space between the inner diaphragm and the outer shell. As the diaphragm expands, the heart is compressed, forcing blood out of the ventricles. Forward flow is directed by the cardiac valves. During “diastole,” the diaphragm remains in contact with the epicardial surface and enhances diastolic filling. DMVA provides similar hemodynamics and superior ischemic tolerance and neurologic outcome compared with CPB. [212 ] – [214 ] The utility of the device for cardiac arrest is limited by the time required to place it, which, although short, necessitates a thoracotomy and interruption of chest compressions. More likely the future role for DMVA is bridging transplantation candidates, which has been done successfully, or bridging to a long-term implantable LV assist device. [215 ]