Influence of an acute increase in systemic vascular resistance on transpulmonary thermodilution-derived parameters in critically ill patients.

OBJECTIVE: The transpulmonary thermodilution technique enables measurement of cardiac index (CI), intrathoracic blood volume (ITBV), global end-diastolic volume (GEDV), and extravascular lung water (EVLW). In this study, we analyzed the robustness of this technique during an acute increase in systemic vascular resistance (SVR).

DESIGN: Prospective, clinical study.

SETTING: Surgical intensive care unit in a university hospital.

PATIENTS AND METHODS: Twenty-four mechanically ventilated septic shock patients, who for clinical indications underwent extended hemodynamic monitoring by transpulmonary thermodilution and continuously received norepinephrine.

INTERVENTIONS AND MAIN RESULTS: After baseline measurements, mean arterial pressure was increased briefly by increasing norepinephrine dosage and hemodynamic measurements were repeated before a control measurement was obtained. At each time point, 15 cc of 0.9% saline (< 8 degrees C) was administered by central venous injection in triplicate. Fluid status and respirator adjustments were kept constant. ANOVA with an all-pairwise comparison method was used for statistical analysis. Heart rate, central venous pressure, and EVLW remained constant throughout, while SVR significantly changed from 551 +/- 106 to 746 +/- 91 dyn*s*cm(-5) and again to 566 +/- 138 dyn*s*cm(-5) (p < 0.05). However, CI and central blood volumes showed a reversible significant increase, i.e., ITBV went from 816 +/- 203 to 867 +/- 195 ml/m(2) and then to 821 +/- 205 ml/m(2) and GEDV from 703 +/- 178 to 747 +/- 175 ml/m(2) and finally to 704 +/- 170 ml/m(2), respectively. In eight patients, 2-D echocardiography was applied and revealed a reversible increase in left-ventricular end-diastolic area.

CONCLUSION: An acute increase in SVR by increasing norepinephrine dosage results in a reversible increase in central blood volumes (ITBV, GEDV) as measured by transpulmonary thermodilution and supported by echocardiography.