title: Respiratory CO2 response depends on plasma bicarbonate concentration in mechanically ventilated patients.
abstract: OBJECTIVE
  There is controversy about the effects of high plasma bicarbonate concentration ([HCO3(-)]) and the CO2 response test. We analyzed the relationship between [HCO3(-)] and the variation in hydrogen ion concentration (pH) for a given change in PaCO2, and its effects upon CO2 response.
  
  
  METHODS
  A retrospective study was carried out.
  
  
  METHODS
  Two intensive care units.
  
  
  METHODS
  Subjects with and without chronic obstructive pulmonary disease (COPD), at the beginning of weaning from mechanical ventilation.
  
  
  METHODS
  The CO2 response was evaluated by the re-inhalation of expired air method, measuring the hypercapnic ventilatory response (ΔVE/ΔPaCO2) and hypercapnic drive response (ΔP01/ΔPaCO2), where VE is minute volume and P0.1 is airway occlusion pressure 0.1s after the initiation of inspiration.
  
  
  METHODS
  [HCO3(-)] and CO2 response.
  
  
  RESULTS
  A total of 120 patients in the non-COPD group and 48 in the COPD group were studied. COPD patients had higher mean [HCO3(-)] than non-COPD patients (33.2 ± 5.4 vs. 25.7 ± 3.7 mmol/l, p<0.001). In both non-COPD and COPD patients we observed a significant inverse linear relationship between [HCO3(-)] and pH change per mmHg of PaCO2 (p<0.001), ΔVE/ΔPaCO2 (p<0.001) and ΔP0.1/ΔPaCO2 (p<0.001).
  
  
  CONCLUSIONS
  There is an inverse linear relationship between [HCO3(-)] and the variation of pH for a given change in PaCO2 and the CO2 response.
authors.affiliation: Servei de Medicina Intensiva, Hospital Son Llàtzer, Palma de Mallorca, Illes Balears, Spain.
authors.forename: G
authors.initials: G
authors.lastname: Rialp
authors.affiliation: Servei de Medicina Intensiva, Hospital Universitari Son Espases, Palma de Mallorca, Illes Balears, Spain. Electronic address: joan.raurich@ssib.es.
authors.forename: J M
authors.initials: JM
authors.lastname: Raurich
authors.affiliation: Servei de Medicina Intensiva, Hospital Universitari Son Espases, Palma de Mallorca, Illes Balears, Spain.
authors.forename: J A
authors.initials: JA
authors.lastname: Llompart-Pou
authors.affiliation: Servei de Medicina Intensiva, Hospital Universitari Son Espases, Palma de Mallorca, Illes Balears, Spain.
authors.forename: I
authors.initials: I
authors.lastname: Ayestarán
authors.affiliation: Servei de Medicina Intensiva, Hospital Universitari Son Espases, Palma de Mallorca, Illes Balears, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Ibáñez
mesh_terms: D000368:Aged; D001639:Bicarbonates / Q000097:blood*; D002245:Carbon Dioxide / Q000502:physiology*; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008297:Male; D008875:Middle Aged; D010092:Oximetry; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology* / Q000628:therapy; D012121:Respiration, Artificial; D012189:Retrospective Studies
chemical_list: D001639:Bicarbonates; D002245:Carbon Dioxide
keywords: Bicarbonate; Bicarbonato; Centro respiratorio; Chronic obstructive pulmonary disease; Enfermedad pulmonar obstructiva crónica; Hipercapnia; Hypercapnia; Mechanical ventilation; Respiratory center; Ventilación mecánica