Distinguishing cerebrospinal fluid from saline used to identify the extradural space

Because of the potential seriousness of unrecognized dural puncture-during the performance of extradural analgesia and the widespread use of normal saline for the ''loss of resistance'' technique, it is important to differentiate between cerebrospinal fluid (CSF) and saline dripping from the extradural needle. During insertion of lumbar drains in 10 neurosurgical patients, we first identified the extradural space using saline for loss of resistance. Temperature (using the back of the gloved hand), pH, glucose and protein (using urine testing sticks) were tested by a blinded observer for ability to distinguish saline aspirated from the extradural space from CSF aspirated on establishing the dural puncture. Temperature, glucose and protein were independently 100% accurate in distinguishing saline from CSF. One saline sample had a pH value greater than 7 compared with nine CSF samples. We conclude that simple bedside testing for temperature, glucose, protein and pH accurately distinguished between CSF and saline used to identify the extradural space.