Does this patient with a ventriculoperitoneal shunt have a complication? Shunt failure is common, with half of patients experiencing this within the first two years of shunt placement (Livingston 2011). Obstruction is a much more common complication than infection (Piatt 2008). Headache, nausea, vomiting, depressed mental status are common symptoms but have poor specificity. Some have suggested bradycardia as a more specific sign, but it is not sensitive (Livingston 2011). The sensitivity of CT scan is as low as 61% (Mater 2008).
If the history is concerning, but the radiologic tests are negative, further assessment is probably necessary, and the neurosurgeon who manages the patient should probably keep the privilege of directing this. Traditionally, shunt tap was used to assess for obstruction. With a 23 gauge butterfly needle, does fluid easily enter a 3 mL syringe? If significant backflow does not occur, or only with more than a mL of suction, there is a problem (Rocque 2008). An alternative method of testing, familiar to emergency physicians and well-away from surgical hardware, is lumbar puncture. Using cerebrospinal fluid opening pressure to screen for obstruction, some have claimed that this is an equally viable way to assess for shunt complications (Miller 2008). Of course, that only works if it is known to be a communicating hydrocephalus.
Finally, although this test has limited sensitivity, you can palpate the reservoir. If it is hard to compress, that suggests a distal obstruction. If it doesn’t refill within 3 seconds, that suggests a proximal obstruction.
-The history is not sensitive or specific for shunt obstruction
-CT scan of the head, though helpful, has limited sensitivity
-Reservoir hard to compress suggests distal obstruction
-Reservoir slow to refill suggests proximal obstruction