Yang-Tobin Study

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Yang KL, Tobin MJ. "A Prospective Study of Indexes Predicting the Outcome of Trials of Weaning from Mechanical Ventilation". The New England Journal of Medicine. 1991. 324(21):1445-1450.
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Clinical Question

In mechanically ventilated patients, what predictors determine success or failure of weaning patients from mechanical ventilation?

Bottom Line

The rapid shallow breathing index (RSBI) is the ratio of respiratory rate to tidal volume (f/VT). RSBI >105 accurately predicts weaning failure, while RSBI <105 is associated with weaning success.

Major Points

For years, clinical gestalt was the primary driver for decisions to wean patients from mechanical ventilation. Problems with its subjectivity and difficulties standardizing in clinical trials led to the development of objective measures for estimating the success of weaning from mechanical ventilation.

The Yang-Tobin Study was a prospective cohort study that described two new indices, the rapid shallow breathing index (RSBI) and the compliance, respiratory rate, oxygenation, and maximal inspiratory pressure (CROP) index. In an initial derivation cohort of 36 patients, investigators determined the threshold values predicting success of weaning for RSBI compared to other traditional indices. A validation phase evaluated each of these indices in 64 subsequent patients and calculated the sensitivity, specificity, positive predictive value, negative predictive value, and ROC curves. The RSBI outperformed the other indices, including CROP, at predicting success or failure. The study demonstrated that a RSBI >105 breaths/min/L predicted weaning failure, while a RSBI <105 breaths/min/L was associated with weaning success.

Guidelines

As of April 2015, no guidelines have been published that reflect the results of this trial.

Design

  • Single center, prospective, cohort study
  • N=100
    • Derivation cohort (n=36)
    • Validation cohort (n=64)
  • Physicians blinded to study design and derived threshold values

Population

Inclusion Criteria

  • Medical (ie, non-surgical) patients
  • Clinically stable mechanically ventilated patients in an ICU
  • Patients considered by their physicians to be ready to undergo a weaning trial

Exclusion Criteria

  • None specified

Baseline Characteristics

  • Mean age: 60 years
  • Female: 54%
  • 28% ARDS
  • 18% Pneumonia
  • 17% Obstructive airway disease
  • 13% CNS disorders
  • 14% Heart failure
  • 2% Pulmonary fibrosis
  • 8% Other

Interventions

  • Two new predictive indices: RSBI and CROP
    • RSBI: f/VT, where f=respiratory rate (breaths/min) and VT=tidal volume (liters)
    • CROP: integrates compliance, respiratory rate, oxygenation, and maximal inspiratory pressure
  • Two phases:
    • Derivation cohort determined threshold values for each index that best predicted success or failure of weaning mechanical ventilation
    • Validation cohort evaluated performance of these threshold values
  • Physicians decided when to wean mechanical ventilation. They were blinded to threshold values for each index, but had access to ABGs and other routine ventilatory measurements.
  • Criteria for weaning success was defined as the ability to sustain spontaneous breathing for ≥24 hours.
  • Criteria for weaning failure included:
    • PaCO2 ≥50 mmHg or increase in PaCO2 by ≥8 mmHg
    • Arterial pH ≤7.33 or decrease by ≥0.07
    • PaO2 ≤60 mmHg with FiO2 ≥50%
    • Diaphoresis, increased work of breathing
    • Tachycardia, arrhythmias
    • Hypotension

Outcomes

Derivation phase

Threshold values of indices that best predicted weaning success or failure
≤105 RSBI (breaths/min/liter)
≥13 CROP (ml/breaths/min)
≤15 Minute ventilation VT*f (liters/min)
≤-15 Maximal inspiratory pressure (cm H2O)
≥325 VT (ml)
≤38 Respiratory rate
≥0.35 PaO2/PAO2

Validation phase

Sensitivity
0.97 RSBI
0.81 CROP
0.78 Minute ventilation
1.00 Maximal inspiratory pressure
0.97 VT
0.92 Respiratory rate
0.81 PaO2/PAO2
Specificity
0.64 RSBI
0.57 CROP
0.18 Minute ventilation
0.11 Maximal inspiratory pressure
0.54 VT
0.36 Respiratory rate
0.29 PaO2/PAO2
Positive predictive value
0.78 RSBI
0.71 CROP
0.55 Minute ventilation
0.59 Maximal inspiratory pressure
0.73 VT
0.65 Respiratory rate
0.59 PaO2/PAO2
Negative predictive value
0.95 RSBI
0.70 CROP
0.38 Minute ventilation
1.00 Maximal inspiratory pressure
0.94 VT
0.77 Respiratory rate
0.53 PaO2/PAO2
ROC curves plotted the proportion of true positives against the proportion of false positives
0.89 RSBI
0.78 CROP
0.40 Minute ventilation
0.61 Maximal inspiratory pressure
0.87 VT
0.76 Respiratory rate
0.48 PaO2/PAO2

Criticisms

  • Positive and negative predictive values are not optimal measures for assessing the quality of a predictor, since they vary according to the prevalence or pretest probability of weaning success. However, likelihood ratios independent of pretest probability were calculated from the original data. The LR+ was 2.7 and the LR- was 0.05. This suggests that RSBI >105 was better at identifying weaning failure than an RSBI <105 is at identifying weaning success.
  • As a result, while RSBI can guide decisions about extubation, a RSBI <105 should not prompt extubation, especially in the face of clinical judgment suggesting extubation could be harmful.

Funding

Funding provided by grants from the American Lung Association and the Veterans Affairs Research Service.

Further Reading