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End‐tidal estimates of arterial PCO 2 for cardiac output measurement by CO 2 rebreathing: A study in patients with cystic fibrosis and healthy controls
Author(s) -
Pianosi P.,
Hochman J.
Publication year - 1996
Publication title -
pediatric pulmonology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.866
H-Index - 106
eISSN - 1099-0496
pISSN - 8755-6863
DOI - 10.1002/(sici)1099-0496(199609)22:3<154::aid-ppul3>3.0.co;2-p
Subject(s) - medicine , cystic fibrosis , cardiac output , cardiology , pco2 , anesthesia , hemodynamics
We set out to determine the effects of various estimates of arterial PCO 2 (PaCO 2 ) on calculation of cardiac output (Q) by the indirect Fick (CO 2 ) method in healthy children and children with cystic fibrosis (CF), and to develop a prediction equation for children for PaCO 2 , based on end‐tidal PCO 2 (PetCO 2 ). The study had 3 parts: 1) Twenty‐three healthy children exercised lightly and moderately while arterialized capillary blood gases and PetCO 2 were measured simultaneously so that a prediction equation for PaCO 2 could be derived from PetCO 2 . Cardiac output was measured by CO 2 rebreathing at each workload; different values for PaCO 2 (measured in arterialized capillary blood, end‐tidal, and PaCO 2 derived from the Bohr equation assuming normal dead space) were used to calculate Q; 2) our equation PaCO 2 = 0.647 PetCO 2 + 12.4 was tested prospectively to measure Q in 9 healthy children; and 3) cardiac output based on arterialized capillary PaCO 2 was compared with that based on Jones‐corrected PetCO 2 during light and moderate exercise in 16 CF patients whose forced expiratory volume in 1 second (FEV 1 ) range from normal to 37% predicted. Our results have shown that in health children end tidal based‐estimates of PaCO 2 tended to overestimate Q, whereas PaCO 2 values derived by the Bohr equation and assuming normal dead space tended to underestimate Q, compared with Q calculated from directly measured PaCO 2 . Our prediction equation resulted in good agreement compared with directly measured PaCO 2 when used to calculate Q (mean difference, +1.3%; range, +9% to −13%). CF patients with little or no airway obstruction had results similar to healthy controls, but those with severe airway obstruction had lower values for Q when PetCO 2 was used instead of directly measured PaCO 2 . We conclude that estimates of PaCO 2 from PetCO 2 are not reliable in patients with moderately severe pulmonary disease due to CF. In healthy children, the prediction equation for PaCO 2 from PetCO 2 derived in the present study gives results superior to other bloodless methods currently in use for computation of Q by the indirect Fick (CO 2 ) method. Pediatr Pulmonol. 1996; 22:154–160. © 1996 Wiley‐Liss, Inc.