2000 OPEN FORUM Abstracts
THE ABDOMINAL COMPARTMENT SYNDROME (ACS) INFLUENCES INTRINSIC POSITIVE END-EXPIRATORY PRESSURE (PEEPI) IN THE ACUTE RESPIRATORY DISTRESS SYNDROME (ARDS)
RH Kallet RRT, M Siobal RRT, K Brady MD, JD Marks PhD MD. Department of Anesthesia, San Francisco General Hospital. San Francisco, CA
Background: Dynamic hyperinflation causes PEEPI and is directly proportional to minute ventilation ([Vdot]E) and airways resistance, and is inversely proportional to expiratory time (TE). PEEPI occurs in ARDS partly because tissue resistance is rate-dependent (1). ACS causes high intra-abdominal pressure that may be transmitted to the pleural surface (2) thus, affecting measured PEEPI. We report the effects of increasing TE and decreasing [vdot]E on measured PEEPI in a 43 year-old man with ARDS complicated by ACS and bronchospasm.
Case Summary: The patient was paralyzed and ventilated in a volume mode at 7 mL/kg with an inspiratory plateau pressure = 45 cm H2O on 15 cm H2O set PEEP. A rate of 32 produced a pH = 7.29 and an arterial carbon dioxide tension = 63 mm Hg. Static (stat) and dynamic (dyn) PEEPI were measured at a fixed inspiratory time of 0.75s as the rate was decreased to 22 (TE: 1.13 to 1.98s; [Vdot]E: 14 to 9.3L/m). Compliance decreased from 17 to 14 mL/cm H2O; peak expiratory flow rate (which reflects elastic recoil) increased from 65 to 71 L/m. The difference between PEEPI-dyn and PEEPI-stat (which reflects ventilation inhomogeneity) narrowed from 5.3 to 1 cm H2O as TE increased. Yet, PEEPI-stat did not change despite the fact that the end-expiratory flow rate decreased from 10 to 0 L/m and the trapped volume (Vtrap) detected during the PEEPI-stat measurement also decreased.
Discussion: Our data suggests that in ARDS complicated by ACS, PEEPI may primarily reflect transmitted intra-abdominal pressure rather than dynamic hyperinflation. Prolonging TE may lessen ventilation in homogeneity, but paradoxically may potentiate collapse of unstable alveoli and worsen chest compliance (3).
1. Broseghini C, Brandolese R, et al. Respiratory resistance and intrinsic PEEP in patients with ARDS. Eur Respir J 1988; 1: 726-731.
2. Barnes GE, Laine GA, et al. Cardiovascular response to elevation of intra-abdominal hydrostatic pressure. Am J Physiol. 1985; 248(17): R208-R213.
3. Gurevitch MJ. Selection of I:E Ratio. Kacmarek RM. Current Respiratory Care Techniques. Chap. 28. BC Decker. 1988. (See Original for Figure)