title: Comparison of 3 different methods used to measure the rapid shallow breathing index.
abstract: OBJECTIVE
  Rapid shallow breathing index (RSBI) is conveniently measured through the ventilator. If continuous positive airway pressure (CPAP) is used, it may change the RSBI value. We measured the RSBI with a handheld spirometer and through the ventilator, with and without CPAP, to assess differences.
  
  
  METHODS
  Rapid shallow breathing index was measured in 3 ways: (1) CPAP 0 cm H(2)O and fraction of inspired oxygen (Fio(2)) 0.4, (2) CPAP 5 cm H(2)O and Fio(2) 0.4, and (3) ventilator disconnected and Fio(2) 0.21. Tidal volume and respiratory frequency were recorded from ventilator monitor values in methods 1 and 2, and from a handheld spirometer and observed respiratory frequency, in method 3.
  
  
  RESULTS
  A total of 170 measurements, each using all 3 methods, were obtained from 80 patients admitted to a medical intensive care unit. The mean RSBI values for methods 1, 2, and 3 were 98.1 ± 58.7, 87.6 ± 51.2, and 108.3 ± 65.3, respectively (P < .001). The RSBI decreased by 9.4% when using CPAP 0 cm H(2)O and by 19.1% when using CPAP 5 cm H(2)O.
  
  
  CONCLUSIONS
  The RSBI values measured through the ventilator with CPAP 5 cm H(2)O are much lower than the values measured with a handheld spirometer. Even the RSBI values measured with CPAP 0 cm H(2)O are significantly lower. This is attributable to the base flow delivered by some ventilators. The difference must be taken into account during weaning assessment.
authors.affiliation: Section of Pulmonary Diseases, Critical Care and Environmental Medicine, Tulane University Health Sciences Center, New Orleans, LA 70112, USA. ndesai1@tulane.edu
authors.forename: Neeraj R
authors.initials: NR
authors.lastname: Desai
authors.forename: Leann
authors.initials: L
authors.lastname: Myers
authors.forename: Francesco
authors.initials: F
authors.lastname: Simeone
mesh_terms: D000368:Aged; D045422:Continuous Positive Airway Pressure / Q000295:instrumentation / Q000379:methods*; D003625:Data Collection / Q000295:instrumentation*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D056152:Respiratory Rate; D013147:Spirometry; D013990:Tidal Volume; D015300:Ventilator Weaning / Q000379:methods*