AJP - Heart and Circulatory Physiology, Vol 249, Issue 4 770-H776, Copyright © 1985 by American Physiological Society
LV filling pressure during PEEP measured by nadir wedge pressure after airway disconnection
R. S. Carter, J. V. Snyder and M. R. Pinsky
Pulmonary arterial occlusion pressure (Ppao) may not accurately reflect
left ventricular filling pressure (LVFP) during ventilation with positive
end-expiratory pressure (PEEP) because increases in pleural pressure (Ppl)
increase measured intrathoracic vascular and cardiac chamber pressures
relative to atmospheric while decreasing LVFP by decreasing venous return.
Steady-state values of Ppao off PEEP are not useful in understanding the
hemodynamics on PEEP because of changes in blood volume distribution and
ventricular afterload associated with the removal of PEEP. We hypothesized
that changes in Ppao immediately after abrupt airway disconnection from
PEEP selectively reflect removal of PEEP-associated Ppl changes prior to
other physiological changes. In pentobarbital-anesthetized closed-chest
dogs, we compared absolute left atrial pressure and left atrial pressure
relative to Ppl (Platm) prior to abrupt disconnection from 15 cmH2O PEEP
(on-PEEP), with Ppao at its nadir (nadir Ppao) following airway
disconnection in three sequential conditions: control (normal), after
propranolol-induced acute ventricular failure, and after oleic acid-induced
lung injury. For all conditions at low LVFP (less than 9 Torr), nadir Ppao
reflects Platm better than on-PEEP Ppao, while at higher LVFP (greater than
9 Torr), on-PEEP Ppao better reflects Platm than nadir Ppao (P less than
0.05). Accurate predictions of on-PEEP Platm can be made using both on-PEEP
and nadir Ppao values in a multiple regression equation.
