Conventional CPR typically generates around one-third to one-fourth of normal cardiac output, which is not sufficient to meet cerebral energy demands. In cryonics patients, cardiac output may be further compromised because many patients are atherosclerotic and/or have gone through a prolonged period of shock / multiple organ failure prior to pronouncement of legal death. However, conventional chest compression techniques can be improved and augmented to produce higher cardiac output and cerebral blood flow.
In cryonics, chest compression techniques range from manual chest compressions to mechanical high impulse active compression-decompression cardiopulmonary support (CPS). A recent technology that has been introduced to cryonics is the use of a mechanical load-distributing band CPS device, the Autopulse. Cerebral blood flow can be further augmented by using a respiratory impedance valve (such as the ResQPOD) and administration of vasoactive medications, such as epinephrine and vasopressin.
Although these interventions can improve cerebral blood flow during CPS, it is a well documented fact that many cryonics patients do not benefit from such improvements. Administration of vasoactive medications requires intravenous access which is often difficult to obtain in the typical cryonics patient. Similarly, the use of an impedance valve requires a patent airway which requires rapid and successful intubation of the patient. Clearly, it would be beneficial to have a technology that can be rapidly applied, is non-invasive, and does not require special technical knowledge or manual skills.
Abdominal compression appears to be such a technology. An air-inflatable cuff is positioned on top of the abdomen and secured in place. In some versions of the technology, a contoured cuff follows the lower border of the rib cage to minimize the chance of interference of the cuff with lung inflation during positive pressure ventilation. Constant abdominal compression is achieved by inflating the cuff during chest compressions. Abdominal compression increases coronary and cerebral blood flow by a) increasing intrathoracic pressure, b) increasing functional arterial resistance, and c) redistributing blood volume above the diaphragm out of the abdominal compartment (in: Biomedical Engineering Fundamentals, 2006).
In a recent study by Lottes et al. (2007), sustained abdominal compression was able to raise coronary perfusion pressure as much as vasopressor drugs. Progressively better results were obtained when abdominal pressure was increased from 100 mmHg to 500 mmHg. Optimal results were obtained when abdominal compression was used in combination with vasopressor drugs. This technology has also been evaluated in humans; Chandra et al. (1981) reported increased mean arterial, systolic, and diastolic blood pressure during CPR following cardiac arrest in humans.
Advantages of sustained abdominal compression in cryonics include: low fabrication costs, light in weight, indefinite shelf life, no refrigeration requirements, no electrical power requirements, easy to apply, immediate onset of action, constant effect over time (unlike medications), and immediately reversibility of the procedure.
The disadvantages of sustained abdominal compression are not evident but warrant careful consideration: (a) Abdominal compression may exacerbate ischemia-induced abdominal hemorrhage – this disadvantage is highly speculative since rupture of the inner lining of the gastric mucosa is a biochemical, not mechanical, event. It is clear, however, that abdominal compression is contra-indicated in patients with abdominal swelling and related gastrointestinal complications. The band and cuff may also interfere with placing a gastric tube to administer an antacid (I owe this point to Stephen Van Sickle). (b) Reversal of abdominal compression may rewarm the upper part of the body as a result of warmer blood having increased access to the upper torso and brain – this, again, is speculative and depends on the question of whether abdominal compression induces selective cooling of the torso. If such a scenario is possible, this effect might be limited by not reversing compression until internal cooling is started. The question remains, however, if better perfusion of the brain will offset slower cooling of the brain as a result of decreased surface cooling. (c) The inflatable cuff may interfere with the Autopulse technology – it is not likely that the two technologies will interfere because the lower part of the Autopulse band does not come into contact with the upper part of the abdominal compression cuff.
Another concern that has been raised about using this technology in cryonics concerns the possibility that abdominal binding has the effect of shunting blood to the upper torso and brain. The resulting lack of perfusion, and subsequent collapse of the vascular bed in the lower extremities, may make raising and cannulating the femoral vessels very difficult, if not impossible. An opposite view is that abdominal compression may actually facilitate femoral cannulation because it creates a bloodless field and enhances visibility of the vein by inflating and distending it (I owe this point to Brian Wowk). It should also be noted that not all cryonics stabilization cases are followed by blood washout through the femoral vessels. Examples include remote cases without blood washout, local cases, and cases in which the patient is cryoprotected in the field (in which surgical access may be obtained through median sternotomy or the cerebral vessels).
It remains to be seen if sustained abdominal compression becomes more popular in resuscitation medicine. Provided this technology is as effective as documented in the Lottes paper, contemporary cryonics stabilization procedures may benefit from such a simple technology to increase blood flow to the brain during CPS.
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Sustained abdominal compression during CPR raises coronary perfusion pressures as much as vasopressor drugs.
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