The CROP (Compliance, Rate, Oxygenation, Pressure) index incorporates several measures of respiratory function and was developed as a possible guide to weaning patients from mechanical ventilation.

Index Components:

(1) fraction of inspiratory effort reserve per breath: (dynamic compliance) * maximal negative inspiratory pressure)

(2) rate of energy expenditure per minute: (breaths per minute) / ((dynamic compliance) * maximal negative inspiratory pressure))

(3) 1 / (rate of energy expenditure per minute): high values indicate that respiratory demands are well matched by respiratory muscle strength

(4) measure of gas exchange: (PaO2) / (PAO2)


CROP index =

= (dynamic compliance in mL per cm H2O) * (maximal negative inspiratory pressure in cm H2O) * ((PaO2 in mm Hg) / (PAO2 in mm Hg)) / (respiratory rate of spontaneous breathing per minute)


PAO2 can be estimated as follows:


PAO2 in mm Hg =

= ((FIO2 as fraction from 0.21 to 1.00) * ((barometric pressure in mm Hg) - 47)) - (PaCO2 in mm Hg)



• A CROP index >= 13 indicates successful weaning from ventilation in adults with a sensitivity of 81%, specificity of 57%, positive predictive value of 71% and negative predictive value of 70%.



• According to Khan et al, the CROP index may not be useful in weaning infants or children.

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