The association between arterial oxygen tension, hemoglobin concentration, and mortality in mechanically ventilated critically ill patients

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Date: July 2018
Publisher: Medknow Publications and Media Pvt. Ltd.
Document Type: Report
Length: 4,475 words
Lexile Measure: 1620L

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Byline: Mahesh. Ramanan, Nick. Fisher

Background: Hypoxemia and anemia are common findings in critically ill patients admitted to Intensive Care Units. Both are independently associated with significant morbidity and mortality. However, the interaction between oxygenation and anemia and their impact on mortality in critically ill patients has not been clearly defined. We undertook this study to determine whether hemoglobin (Hb) level would modify the association between hypoxemia and mortality in mechanically ventilated critically ill patients. Methods: We performed a retrospective cohort study of all mechanically ventilated adult patients (aged >16 years) in the Australian and New Zealand Intensive Care Society Adult Patient Database (APD) admitted over a 10-year period. Multivariate hierarchical logistic regression was used to assess the relationship between hypoxemia and hospital mortality stratified by Hb. Results: Of 1,196,089 patients in the APD, 219,723 satisfied our inclusion and exclusion criteria. There was a linear negative relationship between hypoxemia and hospital mortality which was significantly modified when stratified by Hb. Hb independently increased the risk of mortality in patients with arterial oxygen tension <102. Conclusions: Hb is an effect modifier on the association between oxygenation and mortality.

Introduction and Objectives

Delivery of oxygen to the tissues (DO2) is a necessary condition for cellular respiration. DO2 is determined by the product of cardiac output and arterial oxygen content (CaO2). CaO2 is determined by hemoglobin concentration (Hb, g/L), arterial oxygen tension (PaO2, mmHg), and arterial oxygen saturation (SaO2) as per the equation: CaO2 (ml/L) = (SaO2 x Hb [g/L] x 1.37) + (PaO2 [mmHg] x 0.003). Hypoxemia [1],[2] and anemia [3],[4] are common among critically ill patients admitted to Intensive Care Units (ICUs). They are both associated with increased mortality.[5],[6] Hypoxemia is frequently treated with supplemental oxygen delivery and mechanical ventilation in ICUs.[7] However, high fractional inspired oxygen [8],[9],[10] (FiO2) and possibly hyperoxemia [1],[2],[11] have also been associated with increased mortality and morbidity. Anemia can be treated with red cell transfusion, but liberal transfusion strategies have also been associated with higher mortality and morbidity in ICU and non-ICU patients.[12],[13],[14],[15] Nonetheless, both supplemental oxygen and red cell transfusion are frequently administered therapies for critically ill patients. A better understanding of the association between CaO2 and mortality may help us better elucidate triggers and targets for these therapies and guide future trials of these therapies in critically ill patients. We undertook this study to investigate the interaction between hypoxemia, as characterized by PaO2 and PaO2/FiO2 ratio (PFR), and Hb levels, and their association with hospital mortality in mechanically ventilated critically ill patients. Our hypothesis was that patients' Hb level would modify the relationship between oxygenation and mortality, specifically that the presence of lower Hb levels would increase the independent risk of death with increasing hypoxemia.

Methods

Study design

We performed a retrospective cohort study of all mechanically ventilated adult patients (aged >16 years) in the Australian and New Zealand Intensive Care Society (ANZICS) Adult Patient Database (APD) admitted between January 1, 2006 and December 31, 2015. The APD is one of four clinical quality...

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Source Citation   

Gale Document Number: GALE|A547348106