Abstract
Objective—To evaluate the use of the oxygen content–based index, Fshunt, as an indicator of venous admixture (
s/t) at various fractions of inspired oxygen (Fio
2s) in anesthetized sheep undergoing Flung or 2-lung ventilation.
Animals—6 healthy adult female sheep.
Procedures—Sheep were anesthetized and administered 5 different Fio
2s (0.21, 0.40, 0.60, 0.80, and 1.00) in random order during 2-lung mechanical ventilation. Arterial and mixed venous blood samples were obtained at each Fio
2 after a 15-minute stabilization period. Vital capacity alveolar recruitment maneuvers were performed after blood collection. The previously used Fio
2 sequence was reversed for sample collection during Flung ventilation. Blood samples were analyzed for arterial, pulmonary end-capillary, and mixed venous oxygen content and partial pressure and for hemoglobin concentration. Oxygen hemoglobin saturation, s/t, Fshunt, and oxygen tension–based indices (OTIs; including Pao
2:Fio
2, alveolar-arterial difference in partial pressure of oxygen [Pao
2 – Pao
2], [Pao
2 – Pao
2]:Fio
2, [Pao
2 – Pao
2]:Pao
2, and Pao
2:Pao
2) were calculated at each Fio
2; associations were evaluated with linear regression analysis, concordance, and correlation tests. Intermethod agreement between s/t and Fshunt was tested via Bland-Altman analysis.
Results—Strong and significant associations and substantial agreement were detected between Fshunt and s/t. Relationships between OTIs and s/t varied, but overall correlations were weak.
Conclusions and Clinical Relevance—Whereas OTIs were generally poor indicators of s/t, Fshunt was a good indicator of s/t at various Fio
2s, regardless of the magnitude of s/t, and could be potentially used as a surrogate for s/t measurements in healthy sheep.
