Capnodynamic determination of end-expiratory lung volume in a porcine model of hypoxic pulmonary vasoconstriction

Aron Törnwall, Mats Wallin, Magnus Hallbäck, Per-Arne Lönnqvist, Jacob Karlsson
Karolinska University Hospital.
Sweden

Journal of Clinical Monitoring and Computing
J Clin Monit and Comput 2024;
DOI: 10.1007/s10877-024-01251-1

Abstract
Purpose: The capnodynamic method, End Expiratory Lung Volume CO₂ (EELV-CO₂), utilizes exhaled carbon dioxide analysis to estimate End-Expiratory Lung Volume (EELV) and has been validated in both normal lungs and lung injury models. Its performance under systemic hypoxia and variations in CO₂ elimination is not examined. This study aims to validate EELV-CO₂ against inert gas wash in/wash out (EELV- SF6, sulfur hexafluoride) in a porcine model of stable hemodynamic conditions followed by hypoxic pulmonary vasoconstriction and inhaled nitric oxide (iNO).
Methods: Ten mechanically ventilated piglets were exposed to a hypoxic gas mixture and selective pulmonary vasoconstriction. Inhalation of nitric oxide was used to reverse the pulmonary vasoconstriction. Paired recordings of EELV-CO₂ and EELV-SF6, were conducted to assess their agreement of absolute values.
Results: EELV-CO₂ showed a bias of + 5 ml kg^{– 1} compared to EELV-SF6, upper limit of agreement of 11 ml kg^{– 1} (95%CI: 9-13 ml kg^{– 1}), lower limit of agreement – 1 ml kg^{– 1} (95%CI: -3- 0 ml kg^{– 1}), mean percentage error 34%. Agreement between EELV-CO₂ and EELV-SF6 was largely constant but was affected by progressing hypoxia and reached maximum limit of agreement after iNO exposure. Re-introduction of normoxemia then stabilized bias and limits of agreement to baseline levels.
Conclusion: EELV-CO₂ generates absolute values in parallel with EELV -SF6. Stressing EELV-CO₂ with hypoxic pulmonary vasoconstriction and iNO, transiently impairs the agreement which stabilizes once normoxemia is reestablished.

Category
Class III. Pulmonary Hypertension Associated with Alveolar Hypoxia
Diagnostic Testing for Pulmonary Vascular Disease. Non-invasive Testing

Age Focus: Pediatric Pulmonary Vascular Disease

Fresh or Filed Publication: Fresh (PHresh). Less than 1-2 years since publication

Article Access
Free PDF File or Full Text Article Available Through PubMed or DOI: Yes