title: Breathing pattern in weaning patients: comparison of two inspired oxygen fractions.
abstract: OBJECTIVE
  An inspired oxygen fraction (FiO2) of 40% is often used for weaning patients, but lower FiO2 values are also recommended, if arterial oxygen pressure (PaO2)/ FiO2 >150-200 mmHg. This study aimed to compare respiratory variables and vital data values recorded during use of sufficient FiO2 (ideal) to maintain peripheral oxygen saturation at 92% with values recorded during use of FiO2 established at 40% (baseline) in weaning patients.
  
  
  METHODS
  Prospective cross-over study. Respiratory variables (respiratory frequency, tidal volume, occlusion pressure, inspiratory time/total time ratio) and vital data (blood pressure and heart rate) were collected sequentially at 30 and 60 minutes with baseline FiO2, followed by ideal FiO2. These were compared to a generalized linear model for repeated measurements. Comparisons between baseline and ideal FiO2 values, and arterial blood gases were evaluated by the Student's t or Wilcoxon tests.
  
  
  RESULTS
  In 30 adult patients the median of ideal FiO2 was 25% (IQ25%-75% 23-28). This was significantly lower than baseline FiO2 (40%) (p< 0.001). No significant difference was found in the PaO2/ FiO2 ratio between baseline FiO2 (269±53) and ideal FiO2 (268±47). Tidal volume was significantly lower during use of ideal FiO2 (p=0.003) and blood pressure was significantly higher during use of baseline FiO2 (p=0.041), but there was no clinical significance. The remaining variables were not affected by reduction in FiO2. The ideal FiO2 did not influence remaining variables.
  
  
  CONCLUSIONS
  These results suggest that FiO2 levels sufficient to ensure a SpO2>92% did not alter breathing patterns or trigger clinical changes in weaning patients.
authors.affiliation: Departamento de Fisioterapia, Pontifícia Universidade Católica de Minas Gerais, Betim, MG, Brasil.
authors.forename: Gisele do Carmo Leite Machado
authors.initials: Gdo C
authors.lastname: Diniz
authors.affiliation: Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brasil.
authors.forename: Walter Araújo
authors.initials: WA
authors.lastname: Zin
authors.affiliation: Departamento de Clínica Médica, Faculdade de Medicina, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brasil.
authors.forename: Fernando Antônio
authors.initials: FA
authors.lastname: Botoni
authors.affiliation: Hospital Governador Israel Pinheiro, Belo Horizonte, MG, Brasil.
authors.forename: Aldemar Vilela de
authors.initials: AV
authors.lastname: Castro
authors.affiliation: Faculdade de Ciências Médicas de Minas Gerais, Belo Horizonte, MG, Brasil.
authors.forename: Maria da Glória
authors.initials: Mda G
authors.lastname: Rodrigues-Machado