title: Hypercapnia test as a predictor of success in spontaneous breathing trials and extubation.
abstract: BACKGROUND
  The ventilatory capacity of the respiratory neuromuscular system can be studied with the hypercapnia test.
  
  
  OBJECTIVE
  To determine whether decreased response to the hypercapnia test is associated with failure to pass a spontaneous breathing trial (SBT) or extubation failure.
  
  
  METHODS
  We studied 103 intubated patients ready for SBT. We used a hypercapnia test in which we approximately doubled the dead space and thus caused re-inhalation of expired air. We calculated 3 ratios: the ratio of P(0.1) (airway occlusion pressure 0.1 s after the onset of inspiratory effort) during hypercapnia test to baseline P(0.1); the ratio of the change in minute volume [DeltaV(E)] to the change in P(aCO(2)) (we call this ratio the hypercapnic ventilatory response); and the ratio of the change in P(0.1) [DeltaP(0.1)] to the change P(aCO(2)) (we call this ratio the hypercapnic-respiratory-drive response).
  
  
  RESULTS
  Thirty-six patients failed the SBT, and 11 patients failed extubation. The mean values for the SBT/extubation-success group, the extubation-failure group, and the SBT-failure group, respectively, were: ratio of hypercapnia-test P(0.1) to baseline P(0.1): 4.3 +/- 2.7, 3.7 +/- 1.3, and 3.0 +/- 1.8 (P = .03); hypercapnic ventilatory response: 0.60 +/- 0.35 L/min/mm Hg, 0.50 +/- 0.26 L/min/mm Hg, and 0.31 +/- 0.21 L/min/mm Hg (P < .001); hypercapnic respiratory-drive response: 0.48 +/- 0.24 cm H(2)O/mm Hg, 0.42 +/- 0.19 cm H(2)O/mm Hg, and 0.27 +/- 0.15 cm H(2)O/mm Hg (P < .001). For predicting SBT/extubation success, the sensitivities and specificities, respectively, were: ratio of hypercapnia-test P(0.1) to baseline P(0.1) 0.80 and 0.47; hypercapnic ventilatory response 0.86 and 0.53; hypercapnic respiratory-drive response 0.82 and 0.55.
  
  
  CONCLUSIONS
  The SBT/extubation-failure patients had less response to the hypercapnia test than did the SBT/extubation-success patients, and the hypercapnia test was not useful in predicting SBT or extubation success.
authors.affiliation: Intensive Care Unit, Hospital Universitario Son Dureta, C/ Andrea Doria 55, 07014 Palma de Mallorca, Spain. jmraurich@hsd.es
authors.forename: Joan M
authors.initials: JM
authors.lastname: Raurich
authors.forename: Gemma
authors.initials: G
authors.lastname: Rialp
authors.forename: Jordi
authors.initials: J
authors.lastname: Ibáñez
authors.forename: Carlos
authors.initials: C
authors.lastname: Campillo
authors.forename: Ignacio
authors.initials: I
authors.lastname: Ayestarán
authors.forename: Carmen
authors.initials: C
authors.lastname: Blanco
mesh_terms: D000368:Aged; D005260:Female; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology*; D001239:Inhalation / Q000502:physiology; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D020127:Recovery of Function / Q000502:physiology; D012129:Respiratory Function Tests; D012131:Respiratory Insufficiency / Q000209:etiology / Q000503:physiopathology* / Q000628:therapy*; D016896:Treatment Outcome; D015300:Ventilator Weaning / Q000379:methods*