CHAPTER 23 ENDPOINTS OF RESUSCITATION
The optimal endpoint of resuscitation has been debated since the early 20th century when Cannon espoused his controversial viewpoints concerning limited volume resuscitation, and it continues to be a topic of tremendous discussion and study. The ideal endpoint should be readily obtainable and easily interpretable. The goal is to provide adequate oxygen delivery (DO2) and therefore tissue perfusion without producing the complications of over-resuscitation. This is accomplished primarily by increasing cardiac output via increases in preload (volume loading) or vasoactive drugs. Multiple diagnostic measurements have been used to determine both optimal cardiac performance and adequate tissue perfusion. While no single value can be used exclusively, various measurements do allow uniformity in comparing adequacy of resuscitation. The values provide the ability over time to determine whether a patient is being properly resuscitated. These can be categorized into hemodynamic parameters, metabolic parameters, and regional perfusion endpoints.
HEMODYNAMIC PARAMETERS
Vital Signs and Clinical Endpoints
Shock has been defined in a multitude of ways, but can best be described as a lack of adequate tissue perfusion, and thereby an impairment of oxygen delivery and removal of waste products. The six basic advanced trauma life support (ATLS) physiologic parameters that have been used to identify shock are heart rate, respiratory rate, blood pressure, urine output, level of consciousness, and pulse pressure. Urine output and level of consciousness are direct measurements of tissue perfusion, and are defined by the classes of shock. Renal blood flow correlates with arterial pressure, but can be subject to significant autoregulation during periods of hypoperfusion. Level of consciousness is less reliable when influenced by intoxication, central nervous system injury, and medication. Heart rate and respiratory rate can be notoriously misleading (Table 1). Anxiety, pain, and stress secondary to the emotional impact of trauma can falsely elevate these physiologic parameters. This can confuse the picture and mask the underlying severity of shock. The diagnosis of shock is best made by observing the body’s main compensatory mechanism: redistribution of blood flow.