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Kể từ khi các biện pháp áp lực điền có thể không phản ánh chính xác khối lượng thất, tăng lãi suất phát sinh trong các biện pháp RVEDVI, LVEDA, cuối tâm trương toàn cầu khối lượng (GEDV), và khối lượng máu tổng intrathoracic (TIBV). | Protocolized Cardiovascular Management Based on Ventricular-arterial Coupling 383 predictive values for both right atrial pressure and PAOP were seen in a study of septic ventilator-dependent patients reported by Michard et al. 10 11 . Since measures of filling pressures may not accurately reflect ventricular volumes increased interest has arisen in the measure of RVEDVI LVEDA global end-diastolic volume GEDV and total intrathoracic blood volume TIBV . Although patients with RVEDI values 120 ml m2 are less likely to increase their cardiac output in response to fluid loading the predictive value of this measure is poor 12 . LVEDA perhaps the closest measure of left ventricular preload does not predict increased cardiac output in response to volume expansion 13 . Total thoracic blood volume is slightly better than both right atrial pressure and PAOP in predicting an increase in cardiac output in response to volume expansion 6 but again as many as one-third of patients with a low total thoracic blood volume did not increase their cardiac output by 15 . Finally GEDV values negatively correlated with the subsequent change in cardiac output in response to volume expansion however no specific values could be used to predict response 14 . Thus in all cases measures of preload do not reliable predict preload-responsiveness. One is left with the undeniable fact that preload does not equate to preloadresponsiveness. Although the majority of subjects who are hypovolemic and responsive to volume expansion with an increase in cardiac output will have reduced cardiac filling pressures and volumes many patients with low filling pressures or absolute cardiac volumes may not be preload-responsive whereas many other patients with high filling pressure and expanded cardiac volumes maybe preload-responsive. Thus the reasons why measures of cardiac filling pressures are such poor predictors of preload responsiveness are that they are inaccurate measures of left ventricular preload which
