RESUMO
OBJECTIVE: To compare the influence of pulse indicator continuous cardiac output (PiCCO) in monitoring tidal volume (V(T)) under pressure control ventilation mode and volume-controlled ventilation mode in sheep. METHODS: After anesthesia and tracheotomy, 5 sheep, which were apneic and receiving mechanical ventilation. Twenty minutes later, central venous pressure (CVP) and cardiac function were monitored with different selected V(T) levels of 6, 10, 15, 20 ml/kg under bi-level positive airway pressure (BiPAP) mode by changing the pressure of inspiration, or under the synchronized intermittent mandatory ventilation (SIMV) mode with the same ventilation conditions. RESULTS: In both modes, the increase in V(T) led to an decrease of cardiac index (CI) and intrathoracic blood volume index (ITBVI), reaching a statistically significant difference at 15 ml/kg [SIMV mode: CI (3.94 + or - 1.03) L x min(-1) x m(-2), ITBVI (707 + or - 105) ml/m(2); BiPAP mode: CI (4.11 + or - 1.11) L x mi(-1) x m(-2), ITBVI (715 + or - 122) ml/m(2)] and 20 ml/kg [SIMV mode: CI (3.87 + or - 1.04) L x min(-1) x m(-2), ITBVI (705 + or - 116) ml/m(2); BiPAP mode: CI (3.64 + or - 0.96) L x min(-1) x m(-2), ITBVI (694 + or - 114) ml/m(2)] compared with 6 ml/kg [SIMV mode: CI (4.96 + or - 1.58) L x min(-1) x m(-2),ITBVI(811 + or - 169) ml/m(2); BiPAP mode:CI(5.67 + or - 1.96) L x min(-1) x m(-2), ITBVI (823 + or - 182) ml/m(2), all P<0.05]; an increase in systemic vascular resistance index (SVRI) and mean airway pressure (Pmean) at 15 ml/kg [SIMV mode: SVRI (237.6 + or - 56.2) kPaxs(-1) x L(-1), Pmean (14.0 + or - 3.2) cm H(2)O (1 cm H(2)O=0.098 kPa); BiPAP mode: SVRI (230.8 + or - 32.9) kPaxs(-1) x L(-1), Pmean (13.0 + or - 2.2) cm H(2)O] and 20 ml/kg [SIMV mode: SVRI (253.1 + or - 76.7) kPaxs(-1) x L(-1), Pmean (18.2 + or - 4.8) cm H(2)O ; BiPAP mode: SVRI (246.7 + or - 48.8) kPaxs(-1) x L(-1), Pmean (16.8 + or - 3.3) cm H(2)O] compared with 6 ml/kg [SIMV mode: SVRI (184.8 + or - 47.5) kPaxs(-1) x L(-1); Pmean (8.8 + or - 1.6) cm H(2)O; BiPAP mode: SVRI (184.5 + or - 51.5) kPaxs(-1) x L(-1), Pmean (8.6 + or - 0.5) cm H(2)O, all P<0.05]; but there was no significant effects on CVP, heart rate (HR), mean blood pressure (MBP). There was no significant difference of CI, ITBVI, SVRI and Pmean between the two ventilation modes with various V(T) levels. CONCLUSION: When the cardiac function was normal, the increase in V(T) led to a decrease of CI and ITBVI, but it had no significant effects on CVP. There was no significant difference of CI and ITBVI in the two ventilation modes, both were decreased. So a relatively constant V(T) should be maintained in determining ITBVI.