Alternative Methods Of Closedchest

The rationale for most of the alternative methods of closed-chest CPR that have been decribed are based on one of two proposed mechanisms of blood flow during CPR chest compression. The cardiac pump theory proposes that compression of the heart between the sternum and the spine squeezes blood out of the ventricles in a forward flow direction in a manner generally similar to normal myocardial contraction. The thoracic pump theory proposes that pressurization of the entire thorax, not just the heart, is responsible for blood flow and that the heart serves only as a passive or partially compressed conduit for blood flow. Net forward blood flow occurs due to competent closure of venous valves during diastole at the thoracic inlet during chest compression. The evidence for and against each theory is beyond the scope of this chapter, but it is accurate to state that the precise mechanism of blood flow during closed-chest CPR remains controversial and may vary based on individual anatomic features. Alternative methods of performing closed-chest CPR have largely been based on efforts to exploit one or both of the two proposed mechanisms.

High-Impulse CPR

In 1984, Maier et al reported a laboratory study comparing compression rates of 100 per minute and 150 per minute with the conventional rate of 60 per minute advocated prior to 1986.1 They observed increases in cardiac output that were roughly linear to the increase in compression rate, while stroke volume remained relatively constant. The compression force and velocity of impact used with these rapid CPR compression rates led to the term "high-impulse" CPR. This work was partially responsible for the increase in the recommended CPR compression rate from 60 min -1 to 80 to 100 per minute.

Interposed Abdominal Compression CPR (IAC CPR)

Compression of the abdomen during cardiac arrest generates aortic pressures similar to chest compressions. The hypothesis that CPR diastolic aortic pressure and venous return from the abdomen might be augmented by abdominal compressions led to the idea of IAC CPR. One person performs the chest compressions of standard CPR while another person applies a similar compression over the central abdomen during the relaxation phase of chest compression. The hemodynamic effects of IAC CPR in laboratory investigations have not been consistent, but most have shown increases in CPR diastolic aortic pressure, coronary perfusion pressure, and cardiac output. Results of clinical studies of IAC CPR have been highly variable. Some studies have shown no evidence of improved resuscitation outcome, whereas others have demonstrated significant improvements in ROSC and survival to hospital discharge.2 Differences in study populations and the technical performance of IAC CPR may be the reasons for the variable results obtained. At present, the data supporting the use of IAC CPR are not sufficient to recommend its routine application. It could also be argued that IAC CPR is physiologically very similar to high-impulse CPR with the compressions performed by two persons rather than one. However, if perfusion with standard CPR is judged to be inadequate, attempting iAc CPR is a reasonable alternative intervention.

Active Compression-Decompression CPR (ACD CPR)

Standard CPR involves a forceful or "active" chest compression phase with elastic recoil of the chest wall during the relaxation phase ("passive" decompression). The ACD CPR device consists of a circular suction cup connected to a handle with a force gauge ( Fig. 20-1). With the suction cup securely attached at the midsternal chest, CPR is performed with force applied both downward (active compression) and upward (active decompression) during CPR.3 One advantage of the ACD CPR device is that it tends to decrease the venous system pressure to a greater extent than the arterial pressures during the active decompression phase. This may increase venous return and increase the coronary perfusion pressure gradient during CPR diastole. Although initial clinical reports have indicated some improvement in ROSC and survival, a large randomized clinical trial in in-hospital cardiac arrest (773 patients) and out-of-hospital cardiac arrest (1011 patients) showed no improvement in survival for the ACD CPR device as compared with standard CPR.3 There is presently insufficient evidence to support the routine use of ACD CPR. However, as noted for other alternative CPR techniques, if standard CPR is judged to be ineffective, ACD CPR is another option. Unlike some of the other alternative techniques, ACD CPR requires a special device, and this limits its applicability.

FIG. 20-1. The Ambu CardioPump (Ambu International Inc., Copenhagen, Denmark) is used for active compression-decompression cardiopulmonary resuscitation (ACD-CPR). The silicone rubber suction cup is positioned mid-chest at the level of the nipples. Using the circular plastic handle, the device is pushed downward during the compression phase followed by active withdrawal during the decompression phase. Force of compression and decompression is measured by the gauge located within the handle and is easily viewed by the operator during CPR. (From Lurie KG, Shultz JJ, Callaham ML, et al: Evaluation of active compression-decompression CPR in victims of out-of-hospital cardiac arrest. JAMA 271:1405, 1994, with permission.)

Phased Chest and Abdominal Compression-Decompression

Tang et al have described the use of a device that combines the concepts of IAC CPR and active compression-decompression. 4 This technique involves the use of a device called the Lifestick resuscitator. This device has chest and abdominal pads connected to an adjustable rigid frame with a handle at each end ( Fig 2.0.-2). The pads are attached to the sternum and the upper abdomen by an adhesive. Using a seesaw motion, the chest and abdomen are compressed in an alternating pattern. The preliminary report of this technique by Tang et al in a survival model of swine cardiac arrest showed improved CPP, ROSC, and 48-h survival. At present, there have been no reports of the use of this device in human cardiac arrests.

FIG. 20-2. Sequencing compression-decompression with the Lifestick resuscitator. The subject's head is on the right. Chest compression ( A) is coincident with abdominal decompression (B). This is followed by chest decompression (C) and abdominal compression (D). (From Tang et al,4 with permission.)

Circumferential Thoracic Vest CPR

As noted above, the thoracic pump theory proposes that cyclic fluctuations in intrathoracic pressure created by CPR chest compressions are responsible for blood flow. Thus, efforts to maximize the intrathoracic pressure generated while limiting trauma to the chest would be advantageous. This led to the conception of the circumferential thoracic vest CPR device. This involves the placement of a vest around the thorax and pressurizing the thorax from all directions as opposed to localized pressure over the lower sternum (Fig 2.0.-3). Halperin et al have reported their preliminary experience in humans with a refined circumferential vest CPR

device and found significant improvements in coronary perfusion pressure and initial ROSC. 5 In patients failing prolonged resuscitative efforts, peak CPR-systolic aortic pressure increased from an average of 78 mmHg with manual CPR to an average of 138 mmHg with vest CPR. In 34 patients randomized to receive manual CPR versus vest CPR after an average of 11 min of unsuccessful manual CPR, 8 of 17 vest CPR patients had ROSC compared with only 3 of 17 manual CPR patients. Although this appears to be a promising alternative method of CPR, a substantial amount of clinical investigation is still needed to clarify its potential benefit. Such clinical investigations have been hampered by issues of informed consent.

FIG. 20-3. A comparison of the thoracic vest system for cardiopulmonary resuscitation (vest CPR) with the standard manual CPR. The vest contains a bladder that is inflated and deflated by the pneumatic system. Defibrillation can be accomplished during chest compression through the flat defibrillator electrodes ( dashed circles) under the vest. The ECG can be recorded through the same electrodes. The lower panels show schematic representations of transverse sections of the midthorax during vest CPR and manual CPR. The thoracic size during chest relaxation is shown by the solid lines. The arrows indicate force applied to the thorax during chest compression. With vest inflation, there is a relatively uniform decrease in the dimensions of the thorax. With manual CPR, the sternum is displaced during compression (arrow) and the lateral thorax can bulge, thereby increasing thoracic volume and reducing the intrathoracic pressure generated during compression. (From Halperin et al,5 with permission.)

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