The brain is encased in a closed box – the skull. Anything added to the box can raise the pressure inside of it and, the thought is, damage brain potentially secondary to that raised pressure. In situations where things have been added to the box secondary to trauma – blood or edema – it has long been thought that knowing just how high the pressure was inside the skull, and doing things to lower that pressure, would improve the outcomes in patients who have suffered traumatic brain injuries. It has become essentially standard of care. The Guidelines for the Management of Severe Traumatic Brain Injury give level II credence to,
Intracranial pressure (ICP) should be monitored in all salvageable patients with a severe traumatic brain injury (TBI; Glasgow Coma Scale [GCS] score of 3–8 after re- suscitation) and an abnormal computed tomography (CT) scan. An abnormal CT scan of the head is one that re- veals hematomas, contusions, swelling, herniation, or compressed basal cisterns.
And level III credence to,
ICP monitoring is indicated in patients with severe TBI with a normal CT scan if two or more of the following features are noted at admission: age over 40 years, uni- lateral or bilateral motor posturing, or systolic blood pres- sure (BP) 90 mm Hg.
I would say on their training and anecdotal experience plenty of neurosurgeons, those still involved in trauma and critical care, might give intracranial pressure monitoring even more weight.
Despite this, there is considerable equivocality to the role of intracranial pressure monitoring. While a majority of published retrospective studies have claimed that intracranial pressures above a certain level are associated with a worse outcome and have tried to assign causality to such by claims that controlling pressures below such levels leads to better outcomes, the data, even from these retrospective looks, is hardly homogenous.
There were no group differences in age, gender, or GCS. After adjusting for multiple potential confounding factors including, admission GCS, age, blood pressure, head AIS, and injury severity score (ISS), ICP monitoring was associated with a 45% reduction in survival (OR = 0.55; 95% CI, 0.39-0.76; p < 0.001).
There has never been a randomized trial of intracranial pressure monitoring for traumatic brain injury. At least there hadn’t. An ambitious project led by Dr. Randall Chestnut, based on U.S. money but out of centers in latin America with the ALAS and LABIC, just presented at the Congress of Neurological Surgeons. Patients with severe traumatic head injuries (Glasgow Coma Scale =<8) were randomized into those received intracranial pressure monitors and those note. Those not underwent standard therapies for suspected elevated intracranial pressures based on imaging characteristics and neurological exam; the same therapies directed at those patients who had monitors placed and had documented elevated intracranial pressures. There doesn’t appear to be a short term survival difference between the groups.
It isn’t a knock against the role of elevated intracranial pressure in outcomes following traumatic brain injury. It is, at least a slight knock it would appear, against invasive monitoring. Treating for presumed elevated intracranial pressure based solely off imaging findings and clinical exam appears to be just as efficacious, at least on some metrics, as treating a known intracranial pressure.
Monitoring intracranial pressure, while a common and relatively simple procedure, still requires an invasiveness that is not without risk and morbidities. It entails an incision on the scalp and creating a hole in the skull and then opening the cover around the brain to insert a foreign device into the brain itself. If it is true that the information provided by that device does nothing to improve the management and outcomes of brain injured patients then it is hard to justify such insertion on a routine basis as has become the standard of care. I’m interested to read when the results are finally published.