Noninvasive cardiac output monitors: a state-of the-art review.

1 o i C m m n a i w t i e d s DESPITE IMPROVEMENTS in resuscitation and supportive care, progressive organ dysfunction occurs in a large proportion of patients with acute, life-threatening illnesses and those undergoing major surgery.1-5 Recent data suggest that early aggressive resuscitation of critically ill patients may limit and/or reverse tissue hypoxia and progression to organ failure and improve outcome.6 In a landmark study, Rivers et al7 showed that a protocol of early goal-directed therapy reduces organ failure and improves survival in patients with severe sepsis and septic shock. Similarly, optimization of cardiac output (CO) in patients undergoing major surgery has been shown to reduce postoperative complications and the length of stay.8-13 By contrast, excessive fluid resuscitation has been associated with increased complications, increased lengths of intensive care unit and hospital stay, and increased mortality.14-17 These data suggest that fluid resuscitation should be titrated closely to minimize the risks of overor under-resuscitation.18 Over the last 2 decades, the understanding of the complexities of shock has improved, and conventional approaches to resuscitation have come under increasing scrutiny. The traditional measured variables of resuscitation have included blood pressure, pulse rate, central venous pressure, and arterial oxygen saturation. These variables change minimally in early shock and are poor indicators of the adequacy of resuscitation.19 Furthermore, the clinical assessment of CO and intravascular volume status are notoriously inaccurate.20 With the increased recognition of the limitations of traditional methods to guide resuscitation, newer techniques have emerged that dynamically assess patients’ physiologic response to a hemodynamic challenge. In patients with indices of inadequate tissue perfusion, fluid resuscitation generally is regarded as the first step in resuscitation. However, clinical studies consistently have shown that only about 50% of hemodynamically unstable patients are volume responsive.14 Therefore, the resuscitaion of hemodynamically unstable patients requires an accuate assessment of the patients’ intravascular volume status cardiac preload) and the ability to predict the hemodynamic esponse after a fluid challenge (volume responsiveness). undamentally, the only reason to give a patient a fluid hallenge is to increase the stroke volume (SV) (volume esponsiveness). If the fluid challenge does not increase the V, volume loading serves the patient no useful benefit and s likely to be harmful. Therefore, the measurements of SV nd CO are fundamental to the hemodynamic management f critically ill and injured patients and unstable patients in