The venous-arterial difference in CO2should be interpreted with caution in case of respiratory alkalosis in healthy volunteers.
The venous-arterial difference in CO2(ΔCO2) has been proposed as an index of the adequacy of tissue perfusion in shock states. We hypothesized that the variation in PaCO2(hyper- or hypocapnia) could impact ΔCO2, partly through microcirculation adaptations. Fifteen healthy males volunteered to participate. For hypocapnia condition (hCO2), the subjects were asked to hyperventilate, while they were asked to breathe a gas mixture containing 8 % CO2for hypercapnia condition (HCO2). The 2 conditions were randomly assigned. Blood gases were measured at baseline before each condition, and after 5-7 min of either hCO2or HCO2condition. Microcirculation was assessed by the muscle reoxygenation slope measured with near infrared spectroscopy following a vascular occlusion test and by skin circulation with in vivo reflectance confocal microscopy. ΔCO2was significantly increased with hCO2while it tended to decrease with HCO2(non-significant). HCO2induced a moderate increase of the resaturation slope of NIRS oxygenation. Skin microcirculatory blood flow significantly dropped with hCO2, while it remained unchanged with hypercapnia. Our results warrant cautious interpretation of ΔCO2as an indicator of tissue perfusion during respiratory alkalosis.
Département d'anesthésie Réanimation, Centre Hospitalier Universitaire de Saint Etienne, 42055, Saint Etienne, France. jerome.morel@chu-st-etienne.fr.
Jerome
J
Morel
Département d'anesthésie Réanimation, Centre Hospitalier Universitaire de Saint Etienne, 42055, Saint Etienne, France.
Laurent
L
Gergelé
Département d'anesthésie Réanimation, Centre Hospitalier Universitaire de Saint Etienne, 42055, Saint Etienne, France.
Alexandre
A
Dominé
Département d'anesthésie Réanimation, Centre Hospitalier Universitaire de Saint Etienne, 42055, Saint Etienne, France.
Serge
S
Molliex
Service de Dermatologie Clinique, Centre Hospitalier Universitaire de Saint Etienne, 42055, Saint Etienne, France.
Jean-Luc
JL
Perrot
Service de Dermatologie Clinique, Centre Hospitalier Universitaire de Saint Etienne, 42055, Saint Etienne, France.
Bruno
B
Labeille
Service de Physiologie Clinique et de l'Exercice, Centre Hospitalier Universitaire de Saint Etienne, 42055, Saint Etienne, France.
Frederic
F
Costes
D000328:Adult; D000472:Alkalosis, Respiratory / Q000503:physiopathology*; D001158:Arteries / Q000503:physiopathology*; D001784:Blood Gas Analysis; D002245:Carbon Dioxide / Q000737:chemistry*; D064368:Healthy Volunteers; D006439:Hemodynamics; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006935:Hypercapnia / Q000503:physiopathology; D016857:Hypocapnia / Q000503:physiopathology; D008297:Male; D008833:Microcirculation; D018613:Microscopy, Confocal; D008875:Middle Aged; D010100:Oxygen / Q000737:chemistry; D010101:Oxygen Consumption; D010477:Perfusion; D015203:Reproducibility of Results; D019265:Spectroscopy, Near-Infrared; D014680:Veins / Q000503:physiopathology*; D055815:Young Adult
D002245:Carbon Dioxide; D010100:Oxygen
Healthy volunteers; Hypercapnia; Hypocapnia; Microcirculation; Venous–arterial difference in CO2