A patient develops shock when cardiopulmonary function is compromised by a variety of conditions: cardiac failure, hypovolemia, trauma, sepsis, central nervous system damage and acute respiratory distress syndrome being the most common causes. Several well known complicated and simple scoring systems have been used to assess the potential danger to the patient. The APACHE III (Acute Physiology, Age, Chronic Health Evaluation) system assesses more than 20 factors and produces a score of 0 – 299 (normal range = 14 to 102). The Shock Index system assesses only two factors (SI = heart rate/systolic blood pressure) and produces a score of 0 – 1 (normal range = 0.5 to 0.7). These scoring systems attempt to quantify the risk of dying. However, they fail to consider the potential danger of reperfusion injury after successful resuscitation.
By traditional definition, shock is a medical emergency in which the body is not receiving an adequate flow of blood and oxygen, resulting in serious damage or death. There are three stages of shock. During Stage I (compensated) shock, the body draws on internal compensation mechanisms to maintain adequate perfusion. Medical intervention is most effective during this stage. In Stage II (decompensated) shock, internal compensation and medical intervention become less effective and the overt signs of under perfusion develop. In Stage III (irreversible) shock, internal compensation mechanisms and medical intervention completely fail. Organ failure and death is the final endpoint.
The blood pressure, arterial oxygen saturation and even cardiac output can often be normalized in the shock patient by medical, clinical and even mechanical means without really improving shock at the cellular level. Since the Viability Index (VI) quantifies the magnitude of the shock state separately from monitored hemodynamic or oxygenation values, it can be used to separate those patients who genuinely respond to treatment from those patients whose transiently improved vital signs provide false reassurance of the resolution of shock. Furthermore, the VI delineates a cut point beyond which the restoration of normal circulation (either by successful resuscitation or extracorporeal support) actually contributes to the patient’s demise by causing a lethal reperfusion injury to the tissues. A patient who exceeds the cut point may need a modified form of resuscitation that addresses the morbid ramifications of reperfusion injury.
Perfusion Theory is an educational platform for the Oxygen Pressure Field Theory (OPFT). August Krogh’s theoretical concept of the oxygen pressure field is explained and then applied to clinical applications in perfusion practice.