Plateau and transpulmonary pressure with elevated intra-abdominal pressure or atelectasis.
BACKGROUND
ARDSnet standards limit plateau pressure (Pplat) to reduce ventilator induced lung injury (VILI). Transpulmonary pressure (Ptp) [Pplat-pleural pressure (Ppl)], not Pplat, is the distending pressure of the lung. Lung distention can be affected by increased intra-abdominal pressure (IAP) and atelectasis. We hypothesized that the changes in distention caused by increases in IAP and atelectasis would be reflected by Ptp but independent of Pplat.


METHODS
In Yorkshire pigs, esophageal pressure (Pes) was measured with a balloon catheter as a surrogate for Ppl under two experimental conditions: (1) high IAP group (n=5), where IAP was elevated by CO2 insufflation in 5 mm Hg steps from 0 to 30 mm Hg; and (2) Atelectasis group (n=5), where a double lumen endotracheal tube allowed clamping and degassing of either lung by O2 absorption. Lung collapse was estimated by increases in pulmonary shunt fraction.


RESULTS
High IAP: Sequential increments in IAP caused a linear increase in Pplat (r2=0.754, P<0.0001). Ptp did not increase (r2=0.014, P=0.404) with IAP due to the concomitant increase in Pes (r2=0.726, P<0.0001). Partial Lung Collapse: There was no significant difference in Pplat between the atelectatic (21.83+/-0.63 cm H2O) and inflated lung (22.06+/-0.61 cmH2O, P<0.05). Partial lung collapse caused a significant decrease in Pes (11.32+/-1.11 mm Hg) compared with inflation (15.89+/-0.72 mm Hg, P<0.05) resulting in a significant increase in Ptp (inflated=5.97+/-0.72 mm Hg; collapsed=10.55+/-1.53 mm Hg, P<0.05).


CONCLUSIONS
Use of Pplat to set ventilation may under-ventilate patients with intra-abdominal hypertension and over-distend the lungs of patients with atelectasis. Thus, Ptp must be used to accurately set mechanical ventilation in the critically ill.
Kubiak
Brian D
BD
Department of Surgery, Upstate Medical University, Syracuse, New York 13210, USA. kubiakb@upstate.edu
Gatto
Louis A
LA
Jimenez
Edgar J
EJ
Silva-Parra
Hugo
H
Snyder
Kathleen P
KP
Vieau
Christopher J
CJ
Barba
Jorge
J
Nasseri-Nik
Niloofar
N
Falk
Jay L
JL
Nieman
Gary F
GF
D000005:Abdomen / Q000503:physiopathology; D000818:Animals; D002404:Catheterization; D006973:Hypertension / Q000503:physiopathology; D008168:Lung / Q000502:physiology*; D008297:Male; D011312:Pressure; D001261:Pulmonary Atelectasis / Q000503:physiopathology*; D012121:Respiration, Artificial / Q000592:standards*; D013552:Swine; D055397:Ventilator-Induced Lung Injury / Q000517:prevention & control*