title: Comparison of end-tidal and transcutaneous measures of carbon dioxide during general anaesthesia in severely obese adults.
abstract: BACKGROUND
  Patients with severe obesity (body mass index (BMI) greater than 35 kg x m(-2)) present difficulties for end-tidal carbon dioxide (FE'(CO(2))) monitoring. Previous studies suggest that transcutaneous (TC) carbon dioxide measurements could be valuable, so we compared FE' and TC measures with Pa(CO(2)) in severely obese patients during anaesthesia.
  
  
  METHODS
  We studied patients with severe obesity (BMI >or=40 kg x m(-2)) undergoing gastric bypass surgery. Carbon dioxide was measured with both FE' and TC devices. The difference between each measure (FE'(CO(2)) and TC-CO(2)) and the Pa(CO(2)) was averaged for each patient to provide one value, and data compared with a non-paired, two-way t-test, Fisher's exact test.
  
  
  RESULTS
  We studied 30 adults (aged 18-54 yr, mean 41, SD 8.0 yr; weight: 115-267 kg, mean 162, SD 35 kg). The absolute difference between the TC-CO(2) and Pa(CO(2)) was 0.2 (0.2) (mean, SD) kPa while the absolute difference between the FE'(CO(2)) and Pa(CO(2)) was 0.7 (0.4) kPa (P<0.0001). The bias and precision were +0.1 (0.3) kPa for TC vs arterial carbon dioxide and -0.7 (0.4) kPa for FE' vs arterial carbon dioxide.
  
  
  CONCLUSIONS
  Transcutaneous carbon dioxide monitoring provides a better estimate of Pa(CO(2)) than FE'(CO(2)) in patients with severe obesity.
mesh_terms: D000293:Adolescent; D000328:Adult; D000768:Anesthesia, General; D001785:Blood Gas Monitoring, Transcutaneous / Q000379:methods; D001794:Blood Pressure / Q000502:physiology; D015992:Body Mass Index; D002245:Carbon Dioxide / Q000097:blood*; D005260:Female; D015390:Gastric Bypass / Q000379:methods; D006801:Humans; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods; D009767:Obesity, Morbid / Q000097:blood* / Q000601:surgery
chemical_list: D002245:Carbon Dioxide