Dorothy A Perry1,2, Lindsay M Thomson1,2, Frank A Pigula3,4, Brian D Polizzotti1,2, James A DiNardo2,5, Arthur Nedder6, Kimberlee Gauvreau1,2, John N Kheir1,2. 1. Department of Cardiology, Boston Children's Hospital, Boston, Massachusetts. 2. Department of Pediatrics, Harvard Medical School, Boston, Massachusetts. 3. Department of Cardiovascular Surgery, Boston Children's Hospital, Boston, Massachusetts. 4. Department of Surgery, Harvard Medical School, Boston, Massachusetts. 5. Department of Anesthesia, Perioperative and Pain Medicine, Boston Children's Hospital, Boston, Massachusetts. 6. Department of Animal Resources at Children's Hospital, Boston Children's Hospital, Boston, Massachusetts.
Abstract
BACKGROUND: Hyperoxemia (arterial oxygen tension >100 mm Hg) may occur in critically ill patients and have effects on mixed venous saturation (SvO2 ) and on Fick-based estimates of cardiac output (CO). We investigated the effect of hyperoxemia on SvO2 and on assessments of CO using the Fick equation. METHODS: Yorkshire swine (n = 14) were anesthetized, intubated, and paralyzed for instrumentation. SvO2 (co-oximetry) and tissue oxygen tension (tPO2 , implantable electrodes) in brain and myocardium were measured during systematic manipulation of arterial oxygen tension (PaO2 ) using graded hyperoxia (fraction of inspired oxygen 0.21 → 0.8). Secondarily, oxygen- and carbon dioxide-based estimates of CO (FickO2 and FickCO 2 , respectively) were compared with measurements from a flow probe placed on the aortic root. RESULTS: Independent of changes in measured oxygen delivery, cerebral and myocardial tPO2 increased in proportion to PaO2 , as did SvO2 (P < 0.001 for all). Based on mixed model analysis, each 100 mm Hg increase in PaO2 resulted in a 4.8 ± 0.9% increase in SvO2 under the conditions tested. Because neither measured oxygen consumption, arterial oxyhemoglobin saturation or cardiac output varied significantly during hyperoxia, changes in SvO2 resulted in successively increasing errors in FickO2 during hyperoxia (34% during normoxia, 72% during FiO2 0.8). FickCO 2 lacked the progressively worsening errors present in FickO2 , but correlated poorly with CO. CONCLUSION: SvO2 acutely changes following changes in PaO2 even absent changes in measured DO2 . This may lead to errors in FickO2 estimates of CI. Further work is necessary to understand the impact of this phenomenon in disease states.
BACKGROUND: Hyperoxemia (arterial oxygen tension >100 mm Hg) may occur in critically illpatients and have effects on mixed venous saturation (SvO2 ) and on Fick-based estimates of cardiac output (CO). We investigated the effect of hyperoxemia on SvO2 and on assessments of CO using the Fick equation. METHODS: Yorkshire swine (n = 14) were anesthetized, intubated, and paralyzed for instrumentation. SvO2 (co-oximetry) and tissue oxygen tension (tPO2 , implantable electrodes) in brain and myocardium were measured during systematic manipulation of arterial oxygen tension (PaO2 ) using graded hyperoxia (fraction of inspired oxygen 0.21 → 0.8). Secondarily, oxygen- and carbon dioxide-based estimates of CO (FickO2 and FickCO 2 , respectively) were compared with measurements from a flow probe placed on the aortic root. RESULTS: Independent of changes in measured oxygen delivery, cerebral and myocardial tPO2 increased in proportion to PaO2 , as did SvO2 (P < 0.001 for all). Based on mixed model analysis, each 100 mm Hg increase in PaO2 resulted in a 4.8 ± 0.9% increase in SvO2 under the conditions tested. Because neither measured oxygen consumption, arterial oxyhemoglobin saturation or cardiac output varied significantly during hyperoxia, changes in SvO2 resulted in successively increasing errors in FickO2 during hyperoxia (34% during normoxia, 72% during FiO2 0.8). FickCO 2 lacked the progressively worsening errors present in FickO2 , but correlated poorly with CO. CONCLUSION: SvO2 acutely changes following changes in PaO2 even absent changes in measured DO2 . This may lead to errors in FickO2 estimates of CI. Further work is necessary to understand the impact of this phenomenon in disease states.