The practice of critical care medicine revolves around the monitoring of patients to identify acute physiologic deterioration and the titration of therapies aimed at supporting internal homeostasis. Central to this practice is the evaluation of therapies or stresses designed to assess homeostatic reserve and to uncover pathologic processes. Both the cardiovascular and respiratory systems have received particular attention because of the ease with which specific haemodynamic and respiratory parameters can be measured, the ability to modulate their status with therapies, and the intimacy of both cardiovascular and respiratory status to overall homeostasis. These forms of assessment are referred to as clinical trials, and if performed in a rigorous fashion are referred to as controlled clinical trials. Clinical trials form much of the basis for titration of therapy, wherein a specific therapy is adjusted so as to optimise its effectiveness in an individual. Titration is typically done once a diagnosis has already been made or a treatment identified, such as with the titration of antihypertensive therapy in either hospital or outpatient setting. This review will focus on the exploratory aspect of clinical trials wherein a specific manoeuvre is performed to determine either the aetiology or severity of a pathophysiologic problem.
Central to the combined diagnostic and therapeutic approach to the critically ill subject is the evaluation of both the basal physiologic status and its subsequent change over time consequent to a therapeutic intervention.
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