Singh I; Division of Pulmonary, Critical Care, New Haven, CT, USA
Waxman AB

European Respiratory Journal. 64(1), 2024 Jul.

BACKGROUND: 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 (Hba) and oxygen saturation (S aO2 ) with oxygen consumption
from exercise testing, while Fick COnon-arterial substitutes mixed venous
haemoglobin (Hbmv) and peripheral oxygen saturation (S pO2 ) 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.

METHODS: We performed a retrospective analysis of 296 consecutive
invasive cardiopulmonary exercise testing (iCPET) studies comparing oxygen
saturation from pulse oximetry (S pO2 ) and radial arterial (S aO2 ), Hba
and 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 inaccurate S pO2 .

RESULTS: When considering all stages from rest to peak exercise, Hba and
Hbmv demonstrated high correlation, while S pO2 and S aO2 as well as
COarterial and COnon-arterial demonstrated low correlation. Data loss was
significantly higher across all stages of exercise for S pO2 (n=346/1926
(18%)) compared to S aO2 (n=17/1923 (0.88%)). We found that pre- and
post-capillary ePH 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 S
pO2 data loss.

CONCLUSION: Reliance upon S pO2 during invasive exercise testing results
in the misclassification of pre- and post-capillary ePH, and unmeasurable
S pO2 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.