Selective positive end-expiratory pressure and intracardiac dimensions in dogs

Effects of differential ventilation with general vs. selective right (R) and left (L) positive end-expiratory pressure (PEEP) on left (LV) and right ventricular (RV) end-diastolic dimensions were compared in seven pentobarbital-anesthetized dogs. All three modes of PEEP reduced LV cross-sectional area: general PEEP more than RPEEP and RPEEP more than LPEEP. General PEEP and, to a lesser degree, RPEEP decreased both the LV anteroposterior diameter and LV septum-free wall diameter, whereas LPEEP reduced the LV septum-free wall diameter only. Cardiac output was unaffected by LPEEP, whereas general PEEP (20 cmH2O) reduced cardiac output by 48%, and RPEEP (20 cmH2O) reduced it by 23%. RV septum-free wall diameter was not changed by any mode of PEEP. In conclusion, cardiac output was better maintained with selective PEEP than with general PEEP because LV filling was less impeded with selective PEEP. During LPEEP LV assumed a different configuration than during RPEEP and general PEEP, probably reflecting a different pattern of heart-lung interaction.

A comparison of changes in esophageal pressure and regional juxtacardiac pressures

The relationship between esophageal pressure and juxtacardiac pressures was studied during positive end-expiratory pressure (PEEP) ventilation applied to both lungs or selectively to one lung. The experiments were performed in eight anesthetized dogs with balloon catheters in the esophagus and in the left and right pericardial and overlying pleural cavities and with an open-ended liquid-filled catheter in the pleural cavity. Bilateral PEEP (10, 20, and 30 cmH2O) caused progressive and similar increments in left and right pleural pressure. Selective PEEP, however, increased ipsilateral pleural balloon pressure more than contralateral pressure. The increase in ipsilateral pleural balloon pressure markedly exceeded the increase in esophageal pressure. There was a small increase in pleural open-ended catheter pressure that approximated the increase in esophageal pressure. During selective PEEP, pericardial balloon pressure remained uniform because of a decrease in ipsilateral pericardial transmural pressure. In conclusion, selective PEEP caused nonuniform increments in regional pleural balloon pressure. Left and right pericardial balloon pressure, however, increased uniformly with selective PEEP because of reduced ipsilateral pericardial transmural pressure. The esophageal balloon did not reflect the marked regional increments in pleural balloon pressure with selective PEEP and consistently underestimated the changes in pleural balloon pressure with general PEEP.