The influence of cardiac preload and positive end-expiratory pressure on the pre-ejection period.

The pre-ejection period (PEP) has recently been described as a potential parameter for monitoring cardiac preload. This study further investigated the influence of changes in intravascular volume status and the application of positive end-expiratory pressure (PEEP) on the pre-ejection period. In ten pigs, ECG, arterial pressure and stroke volume derived from an aortic flowprobe were registered. Global end-diastolic volume (GEDV) was measured by transcardiopulmonary thermodilution. Total blood volume (TBV) and intrathoracic blood volume (ITBV) were measured by the dye-dilution technique. Measurements were performed during normovolaemic conditions, after volume loading with haemodilution blood (20 ml kg(-1)) and following haemorrhage (30 ml kg(-1)) without PEEP and with PEEP (15 cm H(2)O) applied. Volume loading increased GEDV, ITBV, TBV and SV, whereas PEP remained constant. However, the changes were not significant (P > 0.05). Subsequent haemorrhage significantly decreased GEDV (from 436 to 308 ml), ITBV (from 729 to 452 ml), TBV (from 2,131 to 1,488 ml) (all P-values <0.05), and SV (from 20.7 ml to 14.3 ml, P < 0.001). However, PEP did not change significantly (from 73 to 82 ms, P > 0.05). No correlation between the changes in PEP and changes in any other variable was observed. It is concluded that PEP is not sensitive to the changes in intravascular volume status.