When interpreting invasive hemodynamic pressures, consideration should be given to technical aspects including the zero reference level, dynamic response of the monitoring system, and effects of changes in intrathoracic pressures.
Much diagnostic information can be gleaned from the analog waveform of directly measured pressures, both arterial blood pressure and cardiac filling pressures.
Interpretation of filling pressures like central venous pressure (CVP) and pulmonary artery occlusion pressure (PAOP) is confounded by many variables, notably changes in ventricular compliance, valvular abnormalities, and positive pressure ventilation.
Pulmonary artery catheter monitoring without a structured therapeutic intervention protocol has generally not been found to be beneficial in most perioperative and critical care settings. It might still be justified in very high-risk patients or in critically ill patients who do not respond to empiric therapy.
There are no accepted gold standards for cardiac output measurement. It is more clinically useful to follow trends in cardiac output rather than considering absolute values.
Functional indices based on respiratory variation in hemodynamic parameters are better predictors of fluid responsiveness compared with static filling pressures or volumetric indices.
Metabolic indices like lactate, base excess, and venous oxygen saturation should be included in the hemodynamic assessment of the critically ill patient.
Preemptive goal directed therapy, aimed at optimization of hemodynamic goals before and during surgery, has been found to decrease mortality in high-risk surgical patients and decrease morbidity in moderate-risk patients.
One can ascribe the birth of hemodynamic monitoring to the British anesthesiologist Joseph T. Clover (1825-1882), who emphasized the need to have one's finger on the pulse while giving chloroform anesthesia (Fig. 30-1).1 The word "monitor" originated in the Latin word monere, meaning "to warn." Indeed, one of the more commonly associated roles of monitoring devices is to alert the anesthetist of changes in patient condition. However, an additional goal of "monitoring" relates to regulation and control: The anesthetist uses information gleaned from the monitors to modify therapeutic interventions and then uses the monitors again to gauge the effect of these interventions, and so on, in a continual feedback-control loop.2 For the patient to gain benefit from the monitor used, several conditions must be fulfilled. First, monitoring data need to be correctly interpreted; both the technical and physiologic aspects of the monitor need to be perfectly understood by the physician-user. Second, effective clinical interventions should exist to treat the underlying problem. Third, risks associated with the monitor itself should be recognized and minimized. Monitor information not followed by effective interventions will not benefit the patient, and information that is mistakenly interpreted can even lead to patient harm by prompting wrong interventions.3
Figure 30-1.Graphic Jump Location
Joseph T. Clover (1825-1882), a pioneer of monitoring during anesthesia. [Reproduced with permission from the Wellcome Library, London.]
This chapter describes the technical and physiologic principles behind the more commonly used perioperative hemodynamic monitors, present existing data regarding their ...