Am. J. Respir. Crit. Care Med., Vol 152, No. 2, Aug 1995, 504-510.
Effects of PEEP on liver arterial and venous blood flows
N Brienza, JP Revelly, T Ayuse and JL Robotham
Department of Anesthesia and Critical Care Medicine, Johns Hopkins Medical Institutions, Baltimore, MD 21287-4965, USA.
Total venous return decreases with positive end-expiratory pressure (PEEP).
It is likely that the liver plays an important role in this response,
either through the development of an increase in venous resistance or
through an increase in the venous backpressure at the outflow end of the
liver. In addition, hepatic arterial flow is reported to be selectively
decreased by the application of PEEP. Therefore, to clarify the effects of
PEEP on liver hemodynamics, we generated pressure-flow (P-Q) relationships
in both liver vascular beds of anesthetized, mechanically ventilated pigs
at PEEP of 0, 5, 10, and 15 cm H2O to obtain values of backpressure (Pback,
mm Hg) from linear extrapolation of the P-Q relationships and resistance
(mm Hg/ml/min/kg) from its slope. PEEP decreased portal vein flow (Qpv) and
caused an increase in the liver venous resistance (from 0.08 +/- 0.01 to
0.16 +/- 0.02 mm Hg/ml/min/kg; p < 0.05). Ppvback and right atrial
pressure (Pra) increased equally (from 5.1 +/- 0.3 to 9.9 +/- 0.4 mm Hg, p
< 0.05, and from 4.0 +/- 0.2 to 8.6 +/- 0.5 mm Hg, p < 0.05,
respectively, at PEEP 15). The reduction in portal venous flow was related
to an increase in the backpressure to flow (as a result of an increase in
Pra) and to an increase in liver venous resistances that may cause blood
pooling in the splanchnic compartment and decrease venous return through
the liver. PEEP increased Phaback (from 11.2 +/- 0.9 to 14.5 +/- 0.7 mm Hg
at PEEP 15, p < 0.05) but did not change hepatic arterial
resistance.(ABSTRACT TRUNCATED AT 250 WORDS)
