The respiratory rate to tidal volume ratio is a bedside measure of the extent of shallow breathing. Shallow breathing is a common finding in patients in whom weaning from a mechanical ventilator fails.
respiratory rate to tidal volume ratio =
= (respiratory rate in breaths per minute) / (tidal volume in liters)
where:
• Gluck and Corgian (1996) refer to this parameter as Rapid Shallow Breathing (RSB).
Interpretation:
• Yang et al found that a ratio of <= 105 indicates successful weaning from mechanical ventilation, while a ratio of > 105 predicts failure to wean from mechanical ventilation.
• Chatila et al found a ratio of <= 100 predicted successful weaning, with the ratio calculated 30-60 minutes after weaning more accurate in predicting outcome than that measured 1 minute after weaning.
Limitations:
• While useful in adults, Khan et al did not find this as useful in infants or children.
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