RSBI

Q: If Rapid Shallow Breathing Index (RSBI) is measured while a patient is attached to the ventilator, respiratory rate should be counted? (select one)

A) manually

B) sensed by ventilator

Answer: A

One of the common mistakes clinicians make while measuring RSBI is to read the respiratory rate from the ventilator. The RSBI formula is simple: Respiratory Rate (f) divided by Tidal Volume in Litres. 

RSBI = f/TV(L)

Ideally, RSBI should be measured via a hand-held spirometer attached to the endotracheal tube (ETT) while the patient breathes room air for one minute - which means no ventilator assistance. 

In the real world, RSBI is usually obtained while a patient is attached to a ventilator. In such cases, the ventilator should be switched to a pressure support (PS) of 0 cm H2O and a positive end-expiratory pressure (PEEP) of 0 cm H2O, without flow or pressure trigger for one minute. 

Although tidal volume can be measured from the ventilator, the respiratory rate should be manually counted as the ventilator underestimate the respiratory rate. If a patient's inspiratory effort is not sensed by the ventilator, it will not be registered by the machine, but a clinician will sense it. This is a common scenario in patients with COPD. This will give falsely 'passed' RSBI and potentially may require re-intubation.

#ventilators

References:

1. Yang KL, Tobin MJ. A prospective study of indexes predicting the outcome of trials of weaning from mechanical ventilation. N Engl J Med 1991; 324:1445.

2. El-Khatib MF, Zeineldine SM, Jamaleddine GW. Effect of pressure support ventilation and positive end expiratory pressure on the rapid shallow breathing index in intensive care unit patients. Intensive Care Med 2008; 34:505.

3. Patel KN, Ganatra KD, Bates JH, Young MP. Variation in the rapid shallow breathing index associated with common measurement techniques and conditions. Respir Care 2009; 54:1462.

4. Desai NR, Myers L, Simeone F. Comparison of 3 different methods used to measure the rapid shallow breathing index. J Crit Care 2012; 27:418.e1.