Left ventricular preload and function during graded haemorrhage and retranfusion in pigs: analysis of arterial pressure waveform and correlation with echocardiography.

BACKGROUND: Arterial pressure waveform analysis is a new method for assessment of cardiac preload. Despite the close correlation of parameters derived by its use with the degree of blood loss, their relationship with more precise estimates of cardiac preload remains controversial.
METHODS: Systolic pressure variation (SPV), delta up (dUp), and delta down (dDown), which are the changes in the arterial blood pressure (BP) during mechanical ventilation, were measured during graded haemorrhage and retransfusion in seven pigs under light halothane anaesthesia, and compared with changes in cardiac filling pressures and left ventricular end-diastolic volume (LVEDV), measured by echocardiography.
RESULTS: Significant changes in preload parameters and stroke volume (SV) but not in BP and heart rate occurred. SPV, dDown, and cardiac filling pressures correlated significantly with LVEDV. Following retransfusion, LVEDV returned to baseline values but the SV and left ventricular ejection fraction were significantly low. This deterioration in myocardial performance was associated with elevated dUp.
CONCLUSIONS: During mechanical ventilation, dDown and the SPV may serve as minimally invasive indicators of preload. The retransfusion stage that follows significant blood loss may be associated with deterioration in LV function.