Non-arterial line cardiac output calculation misclassifies exercise pulmonary hypertension and increases risk of data loss particularly in black, scleroderma and Raynaud's patients during invasive exercise testing

Abstract

BackgroundThe direct Fick principle is the standard for calculating cardiac output (CO) to detect CO-dependent conditions like exercise pulmonary hypertension (ePH). Fick COarterialincorporates arterial haemoglobin (Hba) and oxygen saturation (SaO2) with oxygen consumption from exercise testing, while Fick COnon-arterialsubstitutes mixed venous haemoglobin (Hbmv) and peripheral oxygen saturation (SpO2) in the absence of an arterial line. The decision to employ an arterial catheter for exercise testing varies, and discrepancies in oxygen saturation and haemoglobin between arterial and non-arterial methods may lead to differences in Fick CO, potentially affecting ePH classification.MethodsWe performed a retrospective analysis of 296 consecutive invasive cardiopulmonary exercise testing (iCPET) studies comparing oxygen saturation from pulse oximetry (SpO2) and radial arterial (SaO2), Hbaand Hbmv, and CO calculated with arterial (COarterial) and non-arterial (COnon-arterial) values. We assessed the risk of misclassification of pre- and post-capillary ePH and data loss due to inaccurateSpO2.ResultsWhen considering all stages from rest to peak exercise, Hbaand Hbmvdemonstrated high correlation, whileSpO2andSaO2as well as COarterialand COnon-arterialdemonstrated low correlation. Data loss was significantly higher across all stages of exercise forSpO2(n=346/1926 (18%)) compared toSaO2(n=17/1923 (0.88%)). We found that pre- and post-capillary ePH were misclassified as COnon-arterialdata (n=7/41 (17.1%) and n=2/23 (8.7%), respectively). Patients with scleroderma and/or Raynaud's (n=11/33 (33.3%)) and black patients (n=6/19 (31.6%)) had moreSpO2data loss.ConclusionReliance uponSpO2during invasive exercise testing results in the misclassification of pre- and post-capillary ePH, and unmeasurableSpO2for black, scleroderma and Raynaud's patients can preclude accurate exercise calculations, thus limiting the diagnostic and prognostic value of invasive exercise testing without an arterial line.