Decreases in Mixed Venous Blood O2 Saturation in Cardiac Surgery Patients Following Extubation. (March 2020)

• Record Type: Journal Article
• Authors: Williams, Jeffrey; McLean, Anna; Ahari, Jalil; Jose, Arun; Al-Helou, Georges; Ibi, Italo; Najam, MD, Farzad; Gutierrez, Guillermo
• Is Part Of: Journal of intensive care medicine. Volume 35:Number 3(2020)
• Page Start: 264
• Page End: 269
• Publication Date: 2020-03
• Subjects: O2 delivery -- O2 consumption -- mixed venous -- mechanical ventilation -- cardiac surgery; Critical care medicine -- Periodicals; Critical Care -- Periodicals; Soins intensifs -- Périodiques; Soins intensifs; Périodique électronique (Descripteur de forme); Ressource Internet (Descripteur de forme); 616.02805
• DOI: 10.1177/0885066617741435
• Languages: English
• ISSNs: 0885-0666

Abstract

Background: Decreases in mixed venous O2 saturation (Sv O2 ) have been reported to occur in postcardiac surgery patients during weaning from mechanical ventilation. Our aim was to establish whether the physiological mechanism responsible for this phenomenon was a decrease in systemic O2 delivery (DO2 ) or an increase in global O2 consumption (V ˙ O 2 ). Methods: We studied 21 mechanically ventilated, postoperative cardiac patients for 30 minutes before and 60 minutes after extubation. We monitored continuously arterial O2 saturation by pulse oximetry (Sa O2 ) and central venous O2 saturation (Scv O2 ) with an oximetry catheter. Mixed venous O2 saturation (Sv O2 ) and cardiac output were also measured continuously with an oximetry pulmonary artery catheter. Systemic O2 delivery andV ˙ O 2 were calculated according to accepted formulae. Results: Immediately following extubation, Scv O2 and Sv O2 decreased rapidly ( P < .01). Systemic O2 consumption increased from 65 (57) mL·min −1 to 194 (66) mL·min −1 ( P < .05) with no changes in DO2 . Consequently, systemic O2 extraction rose from 38% (8%) to 45% (9%; P < .01). Preoperative left ventricular ejection fraction correlated with the decline in Sv O2 postextubation. All patients weaned successfully. Conclusions: Decreases in Sv O2 after discontinuation of ventilatory support in postcardiac surgery patients occur asV ˙ O 2 increases in response to greater energy requirements by muscles of ventilation that are not initially matched by increases in DO2 .