The Effect of Low Opening Pressure on the Ability to Wean Emergent External Ventricular Drains

Introduction: Intracranial pressure (ICP) monitoring is an established neuro-critical care modality that is integral in assessing the physiologic effect of various brain insult pathologies causing hydrocephalus. External Ventricular Drains (EVDs) have the ability to mitigate intracranial pressure and prevent secondary brain injury by draining CSF, facilitating blood clearance, and monitoring ICP. While intracranial monitoring of low and high pressures throughout patient care is indicative of patient status, the ramifications of opening pressure (OP) measurements as a prognostic measure are largely uninvestigated.

Methods: A retrospective chart review was performed on all patients above the age of 18 with an EVD placement from January 2016 to December 2022 at Allegheny General Hospital in Pittsburgh, PA. Exclusion criteria included intra-operative EVD placements and patients with any prior neurosurgical history. EVD wean was defined as the ability to wean without additional neurosurgical procedures (shunt, ETV).

Results: We analyzed 220 patient charts and distributed opening pressure measurements into four categories: Low: 0-7 cm H2O, Normal: 8-20 cm H2O, Slightly Elevated: 21-28 cm H2O, and High: 29+ cm H2O. Using a multivariable logistic regression model, we found the interaction between opening pressure, age, and BMI to be significant when analyzing patients’ ability to wean following primary EVD insertion. Specifically, in the low OP group, a one standard deviation increase in age reduces the predicted odds of an EVD wean by a multiplicative factor of 0.38 (95% CI = [0.14,0.9]). Also, in the low OP group, a one standard deviation increase in BMI reduces the predicted odds of an EVD wean by a multiplicative factor of 0.34 (95% CI = [0.13, 0.82]).

Conclusion : Reduced total patient procedures decrease the risk of infection, brain injury, and hemorrhage. Patients in the low opening pressure group have decreased chances of EVD weaning which are exacerbated by increased BMI and age. Further investigation into opening pressures is needed.