REDEFINING CARDIOVASCULAR PERFORMANCE DURING RESUSCITATION - VENTRICULAR STROKE WORK, POWER, AND THE PRESSURE-VOLUME DIAGRAM

Objectives: (1) To compare left ventricular stroke work index (SW) and left ventricular power output (LVP), hemodynamic variables that encom pass blood pressure as well as blood flow, with the purely flow-derive d hemodynamic and oxygen transport variables as markers of perfusion a nd outcome in critically injured patients during resuscitation, (2) To use the ventricular pressure-volume diagram to define characteristic hemodynamic patterns in the determinants of SW and LVP that are associ ated with survival. Methods: This was a cohort study at a university L evel I trauma center during the course of 1 year. A consecutive series of patients was monitored with a volumetric pulmonary artery catheter during the initial 48 hours of resuscitation, Heart rate, SW, LVP, ca rdiac index, and oxygen delivery and consumption during resuscitation were compared using multivariate logistic regression analysis with reg ard to the ability to clear lactate in less than 2 1 hours and surviva l. Receiver operating characteristic curves were constructed to determ ine threshold values for SW and LVP, Ventricular pressure-volume diagr ams were used to describe characteristic patterns in the determinants of SW and LVP in survivors and nonsurvivors, Preload was expressed as left ventricular end-diastolic volume index, afterload as aortic input impedance (E-n), and contractility as ventricular end-systolic elasta nce (E-es). The ratio of E-a/E-es (RATIO) was used as a measure of ven tricular-arterial coupling, which describes the efficacy of energy tra nsfer from the heart to the vascular system. Results: One hundred elev en patients (87 survivors, 24 nonsurvivors) met study criteria. Surviv ors had a significantly higher SW (4,510 +/- 1,070 vs. 3,440 +/- 980 m m Hg.mL.m(-2); p < 0.0001) and LVP (370 +/- 94 vs. 270 +/- 81 mm Hg.L. min(-1).m(-2); p < 0.0001) than nonsurvivors. Heart rate, SW, and LVP were the only studied variables that were significantly related to lac tate clearance and survival by logistic regression. Threshold values d etermined by the receiver operating characteristic curves were 4,000 m m Hg.mL.m(-2) for SW and 320 mm Hg.L.min(-1).m(-2) for LVP. Survivors had better ventricular-arterial coupling than nonsurvivors, indicated by a lower RATIO (0.32 +/- 0.22 vs. 0.53 +/- 0.38; p = 0.003), This lo wer RATIO was attributable to lower levels of E-H (2.7 +/- 0.7 vs. 3.4 +/- 0.8 mm Hg.mL(-1).m(-2); p = 0.0003) and a trend toward higher lev els of E-es (13 +/- 11 vs. 9.9 +/- 7.3 mm Hg.mL(-1).m(-2); p = 0.12). Conclusion: Thermodynamic perfusion variables that encompass both pres sure and flow, such as SW and LVP, are more closely related to perfusi on and outcome than the purely flow-derived variables. The higher SW a nd LVP in survivors is related to better ventricular-arterial coupling , and therefore more efficient cardiac function. Cutoff values for LVP of 320 mm Hg.L.min(-1).m(-2) and for SW of 4,000 mm Hg.mL.m(-2) may b e useful thresholds for evaluating hemodynamic performance during resu scitation.