title: Transcutaneous Carbon Dioxide Monitoring in Subjects With Acute Respiratory Failure and Severe Hypercapnia.
abstract: BACKGROUND
  Transcutaneous carbon dioxide (P(tcCO2)) monitoring is being used increasingly to assess acute respiratory failure. However, there are conflicting findings concerning its reliability when evaluating patients with high levels of P(aCO2). Our study evaluates the accuracy of this method in subjects with respiratory failure according to the severity of hypercapnia.
  
  
  METHODS
  We included subjects with respiratory failure, admitted to a respiratory intermediate care unit, who required arterial blood gas analysis. Simultaneously, P(tcCO2) was measured using a digital monitor. Relations between P(aCO2) and P(tcCO2) were assessed by the Pearson correlation coefficient. Bland-Altman analysis was used to test data dispersion, and an analysis of variance test was used to compare the differences between P(aCO2) and the corresponding P(tcCO2) at different levels (level 1, <50 mm Hg; level 2, 50-60 mm Hg; level 3, >60 mm Hg).
  
  
  RESULTS
  Eighty-one subjects were analyzed. The main diagnosis was COPD exacerbation (45%). P(tcCO2) correlated well with P(aCO2) (r2 = 0.93, P < .001). Bland-Altman analysis showed a mean P(aCO2) - P(tcCO2) difference of 4.9 ± 4.4 with 95% limits of agreement ranging from -3.6 to 13.4. The difference between variables increased in line with P(aCO2) severity: level 1, 1.7 ± 3.2 mm Hg; level 2, 3.7 ± 2.8; level 3, 6.8 ± 4.7 (analysis of variance, P < .001).
  
  
  CONCLUSIONS
  Our study showed an acceptable agreement of P(tcCO2) monitoring with arterial blood gas analysis. However, we should consider that P(tcCO2) underestimates P(aCO2) levels, and its accuracy depends on the level of hypercapnia, so this method would not be suitable for acute patients with severe hypercapnia.
authors.affiliation: Respiratory Department, Hospital Universitario de Bellvitge, Hospitalet de Llobregat, Barcelona, Spain. yolanda.ruiz@bellvitgehospital.cat.
authors.forename: Yolanda
authors.initials: Y
authors.lastname: Ruiz
authors.affiliation: Respiratory Department, Hospital Universitario de Bellvitge, Hospitalet de Llobregat, Barcelona, Spain.
authors.forename: Eva
authors.initials: E
authors.lastname: Farrero
authors.affiliation: Respiratory Department, Hospital Universitario de Bellvitge, Hospitalet de Llobregat, Barcelona, Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: Córdoba
authors.affiliation: Respiratory Department, Hospital Universitario de Bellvitge, Hospitalet de Llobregat, Barcelona, Spain.
authors.forename: Nuria
authors.initials: N
authors.lastname: González
authors.affiliation: Respiratory Department, Hospital Universitario de Bellvitge, Hospitalet de Llobregat, Barcelona, Spain.
authors.forename: Jordi
authors.initials: J
authors.lastname: Dorca
authors.affiliation: Respiratory Department, Hospital Universitario de Bellvitge, Hospitalet de Llobregat, Barcelona, Spain.
authors.forename: Enric
authors.initials: E
authors.lastname: Prats
mesh_terms: D000368:Aged; D001785:Blood Gas Monitoring, Transcutaneous / Q000379:methods / Q000706:statistics & numerical data*; D002245:Carbon Dioxide / Q000097:blood*; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000097:blood* / Q000150:complications; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000379:methods; D029424:Pulmonary Disease, Chronic Obstructive / Q000097:blood / Q000150:complications; D015203:Reproducibility of Results; D012128:Respiratory Distress Syndrome / Q000097:blood* / Q000209:etiology; D012131:Respiratory Insufficiency / Q000097:blood* / Q000209:etiology
chemical_list: D002245:Carbon Dioxide
keywords: hypercapnia; noninvasive ventilation; respiratory care units; respiratory insufficiency; transcutaneous blood gas monitoring; transcutaneous capnometry; transcutaneous carbon dioxide partial pressure determination