The delta resistive index (delta RI or Δ RI) is a measurement that can be made when performing Doppler ultrasound.
In preterm babies who have hydrocephalus secondary to intraventricular haemorrhage, the delta RI can be used to determine whether decompression of the ventricular system with an external drain should be performed.
A delta RI is performed by measuring the RI of the anterior cerebral artery via the anterior fontanelle as normal and then repeating the processes following compression of the anterior fontanelle.
delta RI = 100 x (Compression RI - Baseline RI) / Baseline RI
If delta RI is greater than 45%, external drainage of ventricular system should be performed 1.