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J Res Med Sci. 2019 Feb 25;24:16. doi: 10.4103/jrms.JRMS_349_18. eCollection 2019.

The prognostic value of rapid shallow breathing index and physiologic dead space for weaning success in intensive care unit patients under mechanical ventilation.

Author information

Alzahra Hospital Pulmonary Department, Isfahan University of Medical Sciences, Isfahan, Iran.
Shariati Hospital Pulmonary Department, Tehran University of Medical Sciences, Tehran, Iran.
Anesthesiology and Critical Care Research Center, Isfahan University of Medical Sciences, Isfahan, Iran.
Department of Community and Preventive Medicine, Faculty of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran.



Mechanical ventilation (MV) is a life-saving intervention that should be considered for patients with respiratory failure. This study was conducted to evaluate the predictive value of physiologic dead space for weaning success and compare it with rapid shallow breathing index (RSBI).

Materials and Methods:

This cross-sectional study was conducted on 80 intensive care unit (ICU) patients who were under MV and candidate for weaning; among them, 68 patients experienced weaning success. RSBI was measured by dividing the respiratory rate by tidal volume. End-tidal CO2 (PETCO2) was obtained using caponometry, then dead-space was calculated as (VD/VT = (PaCO2 - PETCO2)/PaCO2). PaCO2 was also obtained from arterial blood gas recorded chart.


Age, PaCO2, PETCO2, and RSBI were significantly different between those patients with and without weaning success (P < 0.05). RSBI ≤ 98 could predict the success of weaning with sensitivity 91.7%; specificity 76.5% and (AUC) area under the ROC curve (AUC = 0.87; 95% confidence interval [CI]: 0.78-0.94; P < 0.001). Dead space was not statistically significant prognostic index (AUC = 0.50; 95% CI: 0.31-0.69; P = 0.09).


In our study, RSBI was an effective predictive index for weaning success in ICU patients under MV, but dead space did not show significant predictive value. Further studies with larger sample sizes for providing more evidence are recommended.


Intensive care unit; mechanical ventilation; physiologic dead-space; rapid shallow breathing index; weaning

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