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

The direct Fick principle is the standard for calculating cardiac output (CO) to detect CO-dependent conditions like exercise pulmonary hypertension (ePH). Fick COarterial incorporates arterial haemoglobin and oxygen saturation (SaO2) with oxygen consumption from exercise testing, while Fick COnon-arterial substitutes mixed venous haemoglobin 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. We performed a retrospective analysis of 296 consecutive invasive CPET (iCPET) studies comparing oxygen saturation from pulse oximetry and radial arterial, arterial haemoglobin and mixed venous haemoglobin, and CO calculated with arterial and non-arterial values. We assessed the risk of misclassification of pre- and post-capillary ePH, and data loss due to inaccurate SpO2. When considering all stages from rest to peak exercise arterial and mixed venous haemoglobin demonstrated high correlation, while SpO2 and SaO2, as well as COarterial and COnon-arterial demonstrated a low correlation. Data loss was significantly higher across all stages of exercise for SpO2 (n=346/1926,18%) compared to SaO2 (n=17/1923, 0.88%). We found that pre- and post-capillary exercise pulmonary hypertension were misclassified as COnon-arterial data (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 more SpO2 data loss. Reliance upon SpO2 during invasive exercise testing results in the misclassification of pre- and post-capillary ePH, and unmeasurable SpO2 for 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.