Title: Prognostic Value of Pulmonary Dead-Space Fraction and other Physiological Parameters in Patients with the Acute Respiratory Distress Syndrome

Authors: Osama M Momtaz, MD; Ali O Abdelaziz, MD; and Mohamed O Abdelaziz, MD

 DOI:  https://dx.doi.org/10.18535/jmscr/v4i11.05

Abstract

Background: Physiologic dead-space fraction (DSF) (ratio of dead space to tidal volume [VD/VT]) is the portion of tidal volume that does not participate in gas exchange. Newer evidence indicates that VD/VT is markedly elevated within 24 h of acute respiratory distress syndrome (ARDS) onset and is significantly elevated in non-survivors.  Moreover, sustained elevation of VD/VT in ARDS has been associated with higher mortality.

Objectives: to study the physiological dead space fraction and various physiological parameters in mortality prediction for patients with ARDS.

Methods: The study included 30 patients admitted to the ICU with ARDS. All patients were subjected to Full medical history, general examination, arterial blood gases, laboratory investigations, chest imaging, echocardiography and assessment by Acute physiology and chronic health evaluation (APACHE II)  and Lung injury scoring. Patients were followed up until ICU discharge or demise. Various physiological parameters including dead space fraction, airway resistance, static and dynamic pulmonary compliance, peak inspiratory pressure and positive end-expiratory pressure were measured.

Results: The overall mortality was 60%. The mean dead-space fraction was significantly higher in patients who died than in those who survived (0.67±0.08 vs. 0.57±0.09, P<0.001) (table 3). The risk of death increased as the dead-space fraction increased. The dead-space fraction was also independently associated with an increased risk of death in the multiple-regression analysis. For every increase of 0.05 in the dead-space fraction, the odds of death increased by 65 percent (odds ratio, 1.65; 95 percent confidence interval, 1.25 - 1.79; P=0.001) (table 4). Decreased both static and dynamic compliance as well as PaO2/FiO2 were independently associated with unfavorable outcome. The odds of death increased as the APACHE II and Lung injury scores increased and as compliance and  PaO2/FiO2 decreased. The positive end expiratory pressure was not associated with an increased mortality (odds ratio, 1.05; 95 percent confidence interval, 0.95 to 1.19; P=0.23). There was  significant negative  correlation between DSF on admission and static compliance (r= -0.43, P value 0.01), dynamic compliance (r= -0.47, P value 0.01)and PaO2/FiO2 (r=0.73, P value 0.001).

Conclusion: Measurement of the dead-space fraction at an early time of the diagnosis of the acute respiratory distress syndrome is a feasible , reliable in providing clinicians with more useful diagnostic and prognostic information early in the course of illness than the other physiological parameters. Measurement of the dead-space fraction could help clinical investigators to identify the patients who may benefit most from a particular tailoring of therapeutic intervention.

Keywords: ARDS,  dead space fraction , mortality predictors.

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Corresponding Author

Osama M Momtaz, MD

Email: usamamomtaz @yahoo.com, Mobile +2/ 01224274142, +2/ 01155560083