Dead Space Fraction Changes During PEEP Titration Following Lung Recruitment in Patients With ARDS

Abstract

A significant change of V(D)/V(T), compliance and arterial oxygenation could be induced by PEEP titration in subjects with ARDS. Optimal PEEP in these subjects was 12 cm H₂O, because at this pressure level the highest compliance in conjunction with the lowest V(D)/V(T) indicated a maximum amount of effectively expanded alveoli. Monitoring of V(D)/V(T) was useful for detecting lung collapse and for establishing open-lung PEEP after a recruitment maneuver.

Recruitment Maneuvers and PEEP Titration

“…The appropriate level of PEEP should correspond to the lowest dead-space fraction (V D /V T ), as has been reported many years ago by Suter et al 66 and more recently by Fengnei et al 28 Because end-tidal P CO 2 (P ETCO 2 ) is determined, in part, by V D /V T , there has been interest in the use of capnography to assess best PEEP. In an experimental model of ARDS, Murray et al 67 reported that best PEEP was associated with the smallest difference between P aO 2 and P ETCO 2 .…”

“…PEEP is then decreased in 2-cm H 2 O decrements, and the compliance is measured at each step to determine best compliance. Others have used arterial oxygenation [25][26][27] or dead space 28 rather than compliance to identify best PEEP during the decremental PEEP titration. After using either compliance or oxygenation to identify the pressure at which recruitment is not maintained, the recruitment maneuver is then repeated, after which PEEP is set 2 cm H 2 O greater than the level identified as best compliance.…”

“…Multiple-organ dysfunction-free days (median 6 vs 20.5 d, respiratory failure-free days (median 7.5 vs 14.5 d), and hemodynamic failure-free days (median 16 vs 22 d) at 28 d were significantly lower in subjects with a compliance-guided setting of PEEP. In a physiologic study, Fengmei et al 28 reported that, using an open lung approach and decremental PEEP titration, best PEEP was similar for highest compliance and lowest V D /V T .…”

Decremental PEEP Titration: A Step Away From the Table

“…This is not a new approach to determining an optimal level of PEEP. [7][8][9][10][11][12] However, a quick look at the available evidence may leave clinicians questioning the usefulness of this method. In the provided Table of decremental PEEP studies there are noticeable differences in titration methods, monitored values, methods for prior recruitment, as well as what the "optimal" level of PEEP should be post procedure.…”

Capnography: A Feasible Tool in Clinical and Experimental Settings

“…Volumetric capnography is considered the best tool to measure dead-space volumes (physiological, alveolar, and anatomic), allowing a functional analysis and providing clinical clues about the efficiency of gas exchange. 3 The V D increases when the alveolar-capillary interface is compromised (eg, COPD, atelectasis, and ARDS), [15][16][17] during decreased pulmonary blood flow (eg, pulmonary embolism), 18 or when alveoli are overdistended (eg, high PEEP). Physiological dead space (V D ) involves the sum of anatomic V D , consisting of the portion of the airways that conducts gas without gas exchange, and alveolar V D , which consists of alveoli that are ventilated but not well perfused (V /Q mismatch).…”