CROP Index

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)

Interpretation:

• 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%.

Limitations:

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