title: Mild hypercapnia after uncomplicated heart surgery is not associated with hemodynamic compromise.
abstract: OBJECTIVE
  The aim of this study was to examine the effects of small changes in PaCO(2) on hemodynamic parameters after uncomplicated heart surgery with cardiopulmonary bypass.
  
  
  METHODS
  This was a prospective, randomized crossover study.
  
  
  METHODS
  A large academic medical center.
  
  
  METHODS
  Twenty-four subjects who were scheduled for elective cardiac surgery were enrolled in this study.
  
  
  METHODS
  Each subject underwent the normal procedures that are associated with cardiac surgery. General anesthesia, including muscle relaxation, were continued in the immediate postoperative period. Measured tidal volumes and minute ventilation were kept constant for the duration of the study. Target PaCO(2) concentrations of 30, 40, and 50 mmHg were achieved by adding varying amounts of exogenous CO(2) gas to the inhaled oxygen. Various measurements were made at each target PaCO(2), including cardiac index, mixed venous oxygen saturation, blood pressure, heart rate, and pulmonary artery pressure.
  
  
  RESULTS
  Twenty-four patients were enrolled. Seven were withdrawn before commencement of the study. The cardiac index increased when the PaCO(2) was increased from 30 to 40 mmHg (p < 0.001) and remained unchanged between 40 and 50 mmHg. Mixed venous oxygen saturation increased (p < 0.001) with elevations in PaCO(2) up to 50 mmHg and decreased again when the PaCO(2) was returned to 30 mmHg. The blood pressure decreased (p < 0.001) with increasing PaCO(2). The pulmonary pressure increased (p < 0.001) with elevations in PaCO(2). No patient became hemodynamically unstable or had any arrhythmias.
  
  
  CONCLUSIONS
  The findings of this study suggest that unless there is a specific contraindication to mild hypercapnia, such as pulmonary hypertension or hemodynamic instability, concerns about mild respiratory acidosis should not prevent weaning of sedation and mechanical ventilation after uncomplicated heart surgery.
authors.affiliation: Department of Anesthesiology, Washington University School of Medicine, St Louis, MO 63110, USA.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Avidan
authors.forename: Syed Z
authors.initials: SZ
authors.lastname: Ali
authors.forename: Heidi
authors.initials: H
authors.lastname: Tymkew
authors.forename: Eric
authors.initials: E
authors.lastname: Jacobsohn
authors.forename: Charl J
authors.initials: CJ
authors.lastname: De Wet
authors.forename: Laureen L
authors.initials: LL
authors.lastname: Hill
authors.forename: Michael
authors.initials: M
authors.lastname: Pasque
mesh_terms: D001794:Blood Pressure; D006348:Cardiac Surgical Procedures; D002315:Cardiopulmonary Bypass; D018592:Cross-Over Studies; D005260:Female; D006339:Heart Rate; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology*; D008297:Male; D010101:Oxygen Consumption; D011446:Prospective Studies; D011651:Pulmonary Artery / Q000503:physiopathology