[Study on the effect of control mode of pressure and volume on cardiac index and intrathoracic blood volume index in critically ill patients].

OBJECTIVE: To compare the effect of control mode of pressure and volume of mechanical ventilation on cardiac index (CI), intrathoracic blood volume index (ITBVI) in patients.

METHODS: Twenty-four patients in whom mechanical ventilation and pulse indicator continuous cardiac output (PiCCO) monitoring were necessary were involved, and they were divided into normal heart function group (9 cases) and heart dysfunction group (15 cases) on the base of CI. Mechanical ventilation was used with the mode of bi-level positive airway passage (BIPAP), and the inspiratory pressure was maintained at the tidal volume (V(T)) of 6, 10, 15 ml/kg. After the mechanical ventilation mode was changed to synchronized intermittent mandatory ventilation (SIMV) and maintained for 20 minutes, breathing mechanics and central venous pressure (CVP), CI, ITBVI were measured.

RESULTS: In the normal heart function group, there were decrease in mean arterial pressure (MAP), CI and ITBVI, increase in heart rate (HR), mean airway pressure (Pmean) and intrinsic positive end expiratory pressure (PEEPi) in both modes of mechanical ventilation without significant difference (P values were 0.067, 0.124, 0.348, 0.328, 0.110, 0.187, respectively). Systemic vascular resistance index (SVRI) was higher in the BIPAP group compared with SIMV group (P=0.030). In the heart dysfunction group, the CI and ITBVI were decreased in the SIMV mode, and CI was decreased significantly in the 10 ml/kg group (P<0.05). Pmean in BIPAP group was increased than that in SIMV group in all V(T) levels (P values were 0.003, 0.000, 0.004, respectively). There was no significant difference in SVRI, HR, MAP and PEEPi in all groups.

CONCLUSION: In the two mechanical ventilation modes, with an increase in V(T), CI and ITBVI may decrease. The Pmean is lower when BIPAP mode in used compared with SIMV, when V(T) is same. So mechanical ventilation and V(T) can influence the readings of CI and ITBVI when PiCCO monitoring is employed.