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Use of the oxygen content–based index, Fshunt, as an indicator of pulmonary venous admixture at various inspired oxygen fractions in anesthetized sheep

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  • 1 Department of Clinical Studies-Philadelphia, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19147.
  • | 2 Department of Clinical Studies-Philadelphia, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19147.
  • | 3 New Bolton Center, Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA 19348.
  • | 4 Division of Veterinary Surgery, Department of Emergencies and Organ Transplantation, University of Bari, 70121 Bari, Italy.
  • | 5 Division of Veterinary Surgery, Department of Emergencies and Organ Transplantation, University of Bari, 70121 Bari, Italy.
  • | 6 Division of Anesthesia and Intensive Care, Department of Emergencies and Organ Transplantation, University of Bari, 70121 Bari, Italy.
  • | 7 Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616.
  • | 8 Division of Veterinary Surgery, Department of Emergencies and Organ Transplantation, University of Bari, 70121 Bari, Italy.
  • | 9 Division of Veterinary Surgery, Department of Emergencies and Organ Transplantation, University of Bari, 70121 Bari, Italy.

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 (Fio2s) in anesthetized sheep undergoing Flung or 2-lung ventilation.

Animals—6 healthy adult female sheep.

Procedures—Sheep were anesthetized and administered 5 different Fio2s (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 Fio2 after a 15-minute stabilization period. Vital capacity alveolar recruitment maneuvers were performed after blood collection. The previously used Fio2 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 Pao2:Fio2, alveolar-arterial difference in partial pressure of oxygen [Pao2 – Pao2], [Pao2 – Pao2]:Fio2, [Pao2 – Pao2]:Pao2, and Pao2:Pao2) were calculated at each Fio2; 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 Fio2s, regardless of the magnitude of s/t, and could be potentially used as a surrogate for s/t measurements in healthy sheep.

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 (Fio2s) in anesthetized sheep undergoing Flung or 2-lung ventilation.

Animals—6 healthy adult female sheep.

Procedures—Sheep were anesthetized and administered 5 different Fio2s (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 Fio2 after a 15-minute stabilization period. Vital capacity alveolar recruitment maneuvers were performed after blood collection. The previously used Fio2 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 Pao2:Fio2, alveolar-arterial difference in partial pressure of oxygen [Pao2 – Pao2], [Pao2 – Pao2]:Fio2, [Pao2 – Pao2]:Pao2, and Pao2:Pao2) were calculated at each Fio2; 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 Fio2s, regardless of the magnitude of s/t, and could be potentially used as a surrogate for s/t measurements in healthy sheep.

Contributor Notes

Funded by an internal grant of the University of Bari, Italy.

Presented in abstract form at the Association of Veterinary Anaesthesiologists' Spring Meeting, Bari, Italy, April 2011.

The authors thank Dr. Diana Bull for support in the mathematical aspects of the study.

Address correspondence to Dr. Larenza (larenza@vet.upenn.edu).