ABSTRACT
OBJECTIVE: (1) To assess the impact of high intrathoracic pressure on left ventricular volume and function. (2) To test the hypothesis that right ventricular end-diastolic volume (RVEDV) and intrathoracic blood volume (ITBV) represent cardiac preload and are superior to central venous pressure (CVP) or pulmonary capillary wedge pressure (PCWP). The validity of these parameters was tested by means of correlation with left ventricular end-diastolic volume (LVEDV), the true cardiac preload. DESIGN: Prospective animal study. SUBJECTS: Fifteen adult sheep. INTERVENTIONS: All animals were studied before and after saline washout-induced lung injury, undergoing volume-controlled ventilation with increasing levels of PEEP (0, 7, 14 and 21 cmH2O, respectively). MEASUREMENTS AND MAIN RESULTS: Left ventricular ejection fraction (LVEF), stroke volume (LVSV) and LVEDV were measured using computed tomography. ITBV and RVEDV were obtained by the thermal dye dilution technique. At PEEP 21 cmH2O, LVSV significantly decreased compared to baseline, PEEP 0 and PEEP 7 cmH2O. LVEDV was maintained except for the highest level of PEEP, while LVEF remained unchanged. RVEDV and RVEF also remained unchanged. The overall correlation of RVEDV and ITBV with LVEDV was satisfactory ( r=0.56 and r=0.62, respectively) and clearly superior to cardiac filling pressures. CONCLUSION: In the present study, (1) ventilation with increasing levels of PEEP did not alter RV function, while LV function was impaired at the highest level of PEEP; (2) unlike cardiac filling pressures, ITBV and RVEDV both provide valid estimates of cardiac preload even at high intrathoracic pressures.
Subject(s)
Blood Volume , Disease Models, Animal , Positive-Pressure Respiration , Respiratory Distress Syndrome/physiopathology , Respiratory Distress Syndrome/therapy , Ventricular Function, Left , Ventricular Function, Right , Animals , Cardiac Volume , Central Venous Pressure , Monitoring, Physiologic/methods , Monitoring, Physiologic/standards , Positive-Pressure Respiration/adverse effects , Positive-Pressure Respiration/methods , Prospective Studies , Pulmonary Wedge Pressure , Respiratory Distress Syndrome/chemically induced , Sheep , Sodium Chloride , Stroke Volume , Thermodilution , Tomography, X-Ray Computed , Treatment OutcomeABSTRACT
OBJECTIVE: To examine the effects of positive end-expiratory pressure (PEEP) on extravascular lung water (EVLW), lung tissue, and lung volume. DESIGN AND SETTING: Experimental animal study at a university research facility. SUBJECTS: Fifteen adult sheep. INTERVENTIONS: All animals were studied before and after saline washout-induced lung injury while ventilated with sequentially increasing PEEP (0, 7, 14, or 21 cmH(2)O). MEASUREMENTS AND RESULTS: Lung volume was determined by computed tomography and EVLW by the thermal dye dilution technique. Saline washout significantly increased lung tissue volume (21+/-3 to 37+/-5 ml/kg) and EVLW (9+/-2 to 36+/-9 ml/kg). While increasing levels of PEEP reduced EVLW (30+/-7, 24+/-8, and 18+/-4 ml/kg), lung tissue volume remained constant. Total lung volume significantly increased (50+/-8 ml/kg at PEEP 0 to 77+/-12 ml/kg at PEEP 21). Nonaerated lung volume significantly decreased and was closely correlated with the changes in EVLW ( r=0.67). In addition, a highly significant correlation was found between PEEP-induced decrease in nonaerated lung volume and decrease in transpulmonary shunt ( r=0.83). CONCLUSIONS: The main findings are as follows: (a) PEEP effectively decreases EVLW. (b) The decrease in EVLW is closely correlated with the PEEP-induced decrease in nonaerated lung volume, making EVLW a valuable bedside parameter indicating alveolar recruitment, similar to measurements of transpulmonary shunt. (c) As excess tissue volume remained constant, however, EVLW may not be suitable to reflect overall severity of lung disease