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Clinical Investigations

International Multicenter Survey of Perioperative Management of External Ventricular Drains: Results of the EVD Aware Study

Lele, Abhijit V. MBBS, MD, MS, FNCS*; Mills, Brianna PhD; Qiu, Qian MBA; Schloemerkemper, Nina MD, Dr.Med., FRCA; Naik, Bhiken Ishwarlal MBBCh§; Williams, James MD, PhD; Venkat-Raghavan, Lakshmikumar MBBS, MD, FRCA, FRCPC; Vavilala, Monica S. MD*; EVD Aware Study Collaborators

Author Information
Journal of Neurosurgical Anesthesiology: April 2020 - Volume 32 - Issue 2 - p 132-139
doi: 10.1097/ANA.0000000000000580


External ventricular drains (EVDs) are placed for the relief of symptomatic hydrocephalus associated with nontraumatic subarachnoid hemorrhage,1 intracerebral hemorrhage,2 and traumatic brain injury.3 They are a means to monitor intracranial pressure (ICP) and to decompress the cerebrospinal fluid (CSF) compartment to reduce ICP. Anesthesiologists are involved in the preoperative assessment, transport and intraoperative management of patients with EVDs undergoing neurosurgical procedures for intracerebral hematoma evacuation, cerebral aneurysm clipping, or decompressive craniectomy, neurointerventional procedures for cerebral aneurysm coiling, and non-neurosurgical procedures.

The majority of the EVDs placed in the United States are inpatients admitted to academic medical institutions,4 many of whom are cared for in an intensive care unit (ICU), but this practice may vary worldwide. Transporting neurocritically ill patients with EVDs may be associated with elevations in ICP, especially in those with high baseline CSF output, high baseline ICP, and those in whom the EVDs are being used for active CSF drainage.5,6 The perioperative practices of anesthesiologists in areas such as preoperative assessment, intraoperative management, and transport of patients with indwelling EVDs are not well defined. Moreover, adherence to guidelines on EVD management published by the Society for Neuroscience in Anesthesiology and Critical Care (SNACC)7 is unknown, and may vary across the world.

In this study, we examined: (1) the variability in the perioperative management of patients with EVDs among anesthesiologists; (2) adherence to published guidelines by location of practice (United States vs. non-United States), neuroanesthesiologists versus non-neuroanesthesiologists, number of EVDs managed annually, self-reported comfort in managing EVDs; and (3) awareness of SNACC guidelines and institutional EVD policies.

The aim of the EVD Aware study is to provide information with regard to the management of patients with EVD among anesthesiologists, and identify areas for improvement in the perioperative management of EVDs.


The University of Washington IRB approved the study, and all participating sites received local IRB approval. Participation in the survey was voluntary, and respondents were not provided with any incentive to participate. Participation in the survey implied informed consent.

Population, Inclusion, and Exclusion Criteria

We conducted an online survey of anesthesiologists between November 2017 and April 2018. Study sites were identified via invitation to neuroanesthesia Fellowship directors and chiefs of neuroanesthesia divisions listed on the SNACC website,8 as well as to organizers of the 2018 Annual Meeting of the Indian Society of Neuroanesthesiology and Critical Care (an affiliate society of SNACC) by electronic mail.

A 31-question English language survey (Supplementary Table 1, Supplemental Digital Content 1, was designed based upon recommendations in the SNACC guidelines for the perioperative management of external ventricular and lumbar drains,7 and placed on the Research Electronic Data Capture (REDCap) Institute of Translational Health Sciences University of Washington website.9 Study data were collected and managed using REDCap electronic data capture tools10 hosted at the Institute of Translational Health Sciences. REDCap is a secure, web-based application designed to support data capture for research studies, providing: (1) an intuitive interface for validated data entry; (2) audit trails for tracking data manipulation and export procedures; (3) automated export procedures for seamless data downloads to common statistical packages; and (4) procedures for importing data from external sources.

The survey underwent an internal and external peer review process for content verification and validity. A link to the survey was e-mailed to each site’s principal investigator who then distributed the survey electronically to anesthesiologists at their respective institutions, inviting them to participate in the study. The survey participants received at least 3 reminders. A paper copy of the survey was distributed, and responses collected, at the annual meeting of the Indian Society for Neuroanesthesiology and Critical Care on January 21, 2018, and a paper copy translated into the Mandarin language was distributed to anesthesiologists from Taiwan.

We examined factors associated with adherence to SNACC EVD guidelines: (1) location of practice—United States versus non-United States (Canada, Finland, India, Taiwan, and the United Kingdom) sites; (2) neuroanesthesiologists versus non-neuroanesthesiologists; (3) numbers of EVDs managed annually; (4) self-reported comfort in the management of EVDs; (5) awareness of SNACC guidelines; and (6) awareness of institutional protocols. For the purpose of this study, a neuroanesthesiologist is defined as a practicing anesthesiologist with subspecialty Fellowship training in neuroanesthesiology and/or neurocritical care.

We developed the EVD Guideline Adherence Score (EVD-GAS) (Supplementary Table2, Supplemental Digital Content 2, EVD-GAS is a composite of scores in 3 areas: (1) preoperative: 1 point for each of 8 elements included in the SNACC EVD guidelines—CSF color, CSF output, ICP values, ICP trends, EVD setting, EVD clamp trial, Glasgow Coma Score, and baseline neurological examination; (2) intraoperative: 1 point each for 4 elements included in SNACC EVD guidelines (CSF color, CSF output, EVD setting, clamp status), and 1 point if CSF values were documented regardless of frequency (either every 15, 30 minor every 1 h) and 1 point if ICP value was documented regardless of frequency (either every 15, 30 minor every 1 h); (3) transport: 1 point if anesthesiologists always mounted the EVD on a pole, 1 point if anesthesiologists always monitored ICP during transport, and 1 point if anesthesiologists considered either keeping the EVD open or closed to CSF drainage depending upon clinical status. The maximum EVD-GAS was 17, with 8, 6, and 3 points for the preoperative, intraoperative, and transport domains, respectively.

Data Handling

The survey was protected on 18 HIPAA identifiers including name, address, date of birth, sex. All survey data were anonymously collected on the University of Washington Institute of Translational Health Sciences hosted the REDCap system. Data presented are deidentified at institutional and provider level.

Data Analysis

The outcomes tested were: (1) preoperative preparation of patient with an EVD; (2) in-hospital transportation of patients with an EVD; (3) type and frequency of documentation of EVD-related information in the intraoperative anesthesia record; (4) knowledge of awareness of EVD-related adverse events; and (5) preferred method for obtaining formal EVD training.

Anesthesiologists’ management of EVDs was compared by their neurosubspecialty training status with regard to the 3 domains of preoperative assessment, patient transportation, and intraoperative evaluation. For each item in the subdomains, 1 was assigned as adherence to guidelines and 0 as nonadherence. A missing response was assumed to be nonadherence. An overall EVD-GAS was created by summing up subdomain scores. All subdomain and overall adherence scores were further compared by important demographic and clinical factors.

Demographic and clinical data for the whole cohort of respondents were reported as counts with percentages for categorical data, including missing data as a separate category. χ2 tests or the Fisher exact tests were used for categorical data, and Student’s t tests or analysis of variance tests for continuous variables. Bivariate linear regressions were performed to examine the relationships between demographic and clinical factors and overall EVD-GAS (outcome) by calculation of coefficients. The significance level was defined with a P-value <0.05. Stata MP 13.1 (Stata Corporation, College Station, TX)11 was used for all analyses.


A total of 599 of 1830 anesthesiologists responded to the survey (32.7% response rate). Highlights of the survey respondents’ characteristics are presented in Table 1. The majority (68.1%) reported managing <25 patients with an EVD annually, 54% reported being comfortable or very comfortable managing EVDs, 21% reported receiving formal training in EVD management, 25.9% were aware of the SNACC EVD guidelines, and 39.7% were aware of local institutional EVD policies. Most (96% of respondents) reported that they do not currently participate in any clinical competency or continued medical education course dedicated to EVD management. Neuroanesthesiologists comprised 23.9% of the study sample, and non-US-based anesthesiologists 20.5%.

Demographic Information From the EVD Aware Survey Sent to Anesthesiologists (N=599)

Preoperative Assessment of Patients With EVDs

Overall, in their routine preoperative assessment of patients with EVDs, 86.8% of participants reported inclusion of ICP values, 76.1% baseline neurological examination, 67.9% the setting of the EVD, 65.3% hourly CSF output, 66.4% ICP trends, 57.6% CSF color, 51.8% Glasgow Coma Score, and 26.5% EVD clamp trial data. Compared with non-neuroanesthesiologists, neuroanesthesiologists reported that they were more likely to include baseline neurological examination (83.2% vs. 73.9%, P=0.023), hourly CSF output (74.8% vs. 62.3%, P=0.006), ICP trends (79% vs. 62.5%, P<0.001), CSF color (70.6% vs. 53.5%, P<0.001), and EVD clamp trial (37.1% vs. 23.2%, P<0.001) in their routine preanesthetic assessment (Table 2).

External Ventricular Drain (EVD) Aware Survey Responses (N=599) by Neuroanesthesiologists and Non-neuroanesthesiologists

Intrahospital Transport of Patients With EVDs

Overall, only 14.2% of all anesthesiologists reported routinely transporting patients with the EVD mounted on a dedicated pole. The majority (51.1%) reported that they always left EVDs closed to CSF drainage during transport, and only 13.4% reported routinely monitoring ICP during transport (Table 2), with no differences between neuroanesthesiologists and non-neuroanesthesiologists.

Intraoperative Management of Patients With EVDs

Overall, 84% of anesthesiologists reported that they document CSF data in the intraoperative anesthesia record. The most commonly recorded CSF variables CSF output (66.6%). In total, 24.9% of respondents document CSF color and 57% ICP (Table 2). ICP data were documented most frequently, that is, every 15 minutes (39.1%),while CSF data were documented every hour (41.4%).

Setting Up the EVD and Obtaining Expert Help in Troubleshooting in the Operating Room

Operating room nurses (42%), anesthesia technicians (24%), and neurocritical care nurses (15%) were reported to typically assist in setting up EVDs in the operating room. To troubleshoot EVD-related issues, anesthesiologists reported seeking help from neurosurgeons (79.7%), anesthesiology colleagues (34.8%) and neurocritical care nurses (19.3%). Compared with non-neuroanesthesiologists, neuroanesthesiologists were more likely to seek assistance from neurosurgeons (90.5% vs. 76% P<0.001).

Adverse Events Related to EVDs

Overall, 40% of participants reported that they were aware of an EVD-related adverse event that had occurred at their institution, 28% that there had been no EVD-related adverse events at their institution and 32% that they did not know if an adverse event had occurred at their institution. The commonly reported adverse events included CSF overdrainage-related complications (56%), spillage of CSF, and contamination of the EVD system (26%), flushing of the catheter to clear debris (15%), and accidental injection of medications into the EVD (11%).

Factors Affecting EVD Guideline Adherence Scores

EVD-GAS scores (Table 3) were higher among anesthesiologists who reported being very comfortable managing patients with EVDs (9.93±3.33) compared with those who reported being comfortable (9.71±2.68), neutral (8.49±2.94), slightly uncomfortable (8. 41±3.07), or uncomfortable (6.93±2.9) (P<0.001). The scores were also higher among anesthesiologists from the United States compared with non-US respondents (9.22±2.91 vs. 8.54±3.48, P=0.025), among neuroanesthesiologists compared with non-neuroanesthesiologists (10.03±3.12 vs. 8.79±2.97, P<0.001), and in those who were aware of SNACC EVD guidelines compared with those who were not (9.95±2.9 vs. 8.83±2.99, P<0.001).

Factors Affecting EVD Guideline Adherence Score (EVD-GAS)

Overall, 83% of anesthesiologists reported that they would be interested in receiving formal training about EVD management, either in an online educational format (56%), YouTube video (50%), written educational document (21%), or smartphone application (18%).


We conducted an international multicenter survey to examine perioperative EVD management practices among anesthesiologists. Our results are based on these reported practices rather than observed clinical practice. The main findings of this study are: (1) compared with non-neuroanesthesiologists, more neuroanesthesiologists consider CSF color, EVD clamp trial, Glasgow Coma Score, and baseline neurological examination important during preoperative assessment; (2) despite that most patients are reported to be transported with the EVD closed to CSF drainage, EVDs may not be routinely mounted on a pole and ICP is not routinely monitored; (3) reported adherence to SNACC guidelines on the perioperative management of EVD is highest among those who self-reported comfort in managing EVDs; and (4) awareness of the SNACC EVD guideline is low. This is the largest study investigating perioperative EVD management practices, and it identifies opportunities for education and practice improvement in relation to the anesthesia care of critically ill neurological patients with EVDs.

Perioperative Management of EVDs by Anesthesiologists

In the United States, the majority of the patients (>70%) with EVDs are admitted to not-for-profit academic institutions.4 After EVD placement by a neurosurgeon, maintenance, monitoring, and troubleshooting of the EVD is essentially a neurocritical care nursing responsibility.12 The American Society of Anesthesiology (ASA) practice guidance document entitled “The Principles of Critical Care Medicine” recognizes the importance of neurological evaluation and measures to optimize cerebral and spinal cord perfusion to minimize adverse neurological outcomes associated with hypoperfusion or increased ICP.13 In the content outline for the American Board of Anesthesiology’s basic and advanced written examination, candidates may be tested on ICP-related issues in the sections on monitoring methods, physiology of organ-based advanced clinical sciences, and special problems of anesthesia for neurosurgery. However, EVD specific testing is not currently a part of this process,14,15 ICP monitoring is also not included in the ASA basic monitoring requirements for patients undergoing anesthesia.16

It is evident from the current study that, presently, most anesthesiologists will likely have no formal training in EVD management, and thus the results of the study can likely be generalized to the anesthesiology community at large. There is therefore an opportunity to increase global awareness as well as education on this issue, provide EVD specific training to anesthesiologists, and design a curriculum for EVD management and make this a training requirement during rotations to neurosurgery and neurocritical care.

Transporting Neurocritically Ill Patients

It is also evident from our study that ICP may not be routinely monitored during transport of patients with EVDs. Transport of neurocritically ill patients can contribute to secondary brain injury due to the occurrence of cerebral hypoperfusion,5,17,18 elevated ICP,5,6,17,19 and reduction in cerebral oxygenation,17 and this remains an area of concern.20

Although it is accepted practice to keep EVDs closed to drainage during transport due to concerns of CSF overdrainage, ICP may not be routinely monitored during intrahospital transports.18 A previous study by Chaikittisilpa et al5 showed that patients with EVDs that had never been clamped in the ICU are at highest risk for elevation in ICP during intrahospital transport. In fact, it is important to note that a proportion of anesthesiologists report transporting patients with EVDs open to CSF drainage. This could be due to the fact that pretransport clinical parameters such as ICP values and trends, hourly CSF output and tolerance to EVD clamp (EVD clamp trial data) may indicate that a patient is unlikely to tolerate EVD clamping during transport. Interestingly, fewer than 20% of anesthesiologists in our survey obtain EVD clamp trial data during their preoperative screening, and it is largely unknown how many patients undergo EVD clamp trial in the ICU before initiation of intrahospital transport. This deserves further examination.

In order to ensure a safe intrahospital transport focused on patient-centric decision-making, clinicians should obtain information with regard to hourly CSF output, baseline ICP, and the ability to tolerate clamping of EVD as a part of their routine pretransport checks. In patients who have high CSF output, high baseline ICP, and those who are unable to tolerate EVD clamping, transport may be undertaken with the EVD open to CSF drainage and intermittent monitoring of ICP. If patients tolerate clamping by virtue of low baseline CSF drainage and low baseline ICP, transport may be undertaken with EVD closed to CSF drainage with continuous ICP monitoring. The emphases here is to ascertain the tolerance of an individual to EVD clamping before transport, rather than exposing any patient to an inadvertent “clamp trial” during an intrahospital transport.

Transport of neurocritically ill patients with EVDs may be undertaken by providers who have formal training,21 and ready access to the SNACC perioperative EVD management checklist and educational document22 to risk stratify which patients will tolerate clamping of EVDs during transport. Intrahospital transport of the neurocritically ill may include routine monitoring of ICP during all transports with added vigilance that all necessary medical supplies be readily available during transport. Transport equipment should include: (1) oxygen supply; (2) vital sign monitoring including electrocardiogram, pulse oximetry, noninvasive blood pressure; (3) specialized monitoring such as ICP; (4) emergency drugs not limited to atropine, epinephrine, calcium chloride, and; (5) a master key to patient transport elevators.

EVD Guideline Adherence Score

In this study we calculated EVD guidelines adherence rates based on reported rather than actual clinical practices. The possibility that self-reported adherence to guidelines, assessed by overall EVD-GAS scores in this study, may overestimate true adherence23 is concerning. The fact that self-reported comfort in managing EVDs had the strongest value in adherence rates to EVD guidelines is interesting because it may provide validity for the calculation of the score. This deserves examination in future studies. Self-reported comfort with EVD management may be enhanced by formal training of anesthesiologists in the management of EVDs. The EVD-GAS score could be used to conduct preneuroanesthesia and postneuroanesthesia or neurocritical care rotations to evaluate a candidate’s baseline and postrotation knowledge in managing EVDs. It might also be the basis for an annual assessment of EVD competency for attending anesthesiologists. We believe that the EVD-GAS score should be used as process measure rather than an outcome measure as its association with a reduction in adverse perioperative outcomes remains unknown. However, this deserves formal examination through a validation study.

EVD Guideline Awareness and Educational Opportunities to Improve Patient Care

This study found a low-reported awareness of EVD guidelines among practicing anesthesiologists. Although there are no studies that have examined guideline awareness in neuroanesthesia, the general medical literature suggest that such awareness may vary from 33%24 to 99%.25 The reasons for the low awareness of EVD guidelines could be related to limited exposure to a particular area of interest at a provider level, or to more widespread lack of dissemination of guidelines at local, institutional, or organizational levels. Ways to improve guideline awareness at an organizational level include electronic (e-blast) to society members, online publication of guidelines, endorsement and dissemination of guidelines by affiliated organizations to attract a larger target audience, and, at an institutional level, by periodic departmental and divisional educational updates. By hosting the EVD guidelines and publishing an online educational perioperative EVD management document to accompany its guidelines, SNACC has made valuable efforts in this regard. However, more work is required to ensure dissemination of this guideline to all anesthesiologists.

Formal training in EVD management is currently lacking but, as evident from the results of this survey, is highly desired. Consideration should be given to the inclusion of formal EVD training in anesthesiology residency curriculums, as well incorporation as an important milestone that all graduating anesthesia residents as well as neuroanesthesia and neurocritical care Fellows must achieve. Formal training may be accomplished by completion of a continued medical education course, either online or in a simulated session. EVD management content in an online educational toolkit and “how-to” videos may be maintained on an institutional intranet, as well as on SNACC and affiliated Societies’ websites. The use of social media in the maintenance and dissemination of this essential educational information should also be harnessed. Harmonization between local, regional, national, and international guidelines may further enhance global appeal to promote EVD safety.


There are some limitations to our study. Non-neuroanesthesiologists and anesthesiologists who do not routinely manage patients with EVDs may have opted out of the survey. This many have contributed to the low survey response rate, and affected the significance of the responses. The sampling method in this study relied on acceptance of potential sites in participation in the survey, as well as the make-up of the anesthesia departments with respect to the proportion of neuroanesthesiologists and non-neuroanesthesiologists, a factor we did not control for. The proportion of neuroanesthesiologists versus non-neuroanesthesiologists likely reflects sampling bias due to lack of formal training opportunities/Fellowship programs in neuroanesthesia and/or neurocritical care. In order to examine this we reviewed the survey responses to better understand the differences in such representation. Among non-US sites, neuroanesthesiologists comprised 60% of the participants from India, 31.8% from Finland, 90% from the UK, 50% from Taiwan, and 38.5% from Canada. Among US sites, neuroanesthesiologists comprise 17% of the total survey participants, and the proportion of neuroanesthesiologists varied between 9% and 35% among individual institutions. Therefore, we believe that there is a comparable representation of neuroanesthesiologists between US and non-US sites; in fact, a larger proportion of survey participants among non-US sites were neuroanesthesiologists. However, our results may not necessarily reflect the true situation in countries without formal Fellowship training programs. The survey was sent to selected institutions based on the presence of neuroanesthesia Fellowship programs or neuroanesthesia subspecialty divisions, so there is a risk of selection bias which may limit the generalizability of our findings; however, the results may be translatable across institutions worldwide. The potential for recall bias also exists because some respondents may not have taken care of patients with EVDs for a while, or not at all. In summary, this was a convenience sample of anesthesiologists and we did not control for equal distribution of neuroanesthesiologists and non-neuroanesthesiologists amongst US and non-US sites.

The majority of participants in this voluntary survey were non-neuroanesthesiologists so its results may be of interest to the non-neurotrained anesthesia community as well as to specialized neuroanesthesiologists, and this may confirm external validity of the results.


EVD management practices by anesthesiologists in the perioperative period are heterogeneous, and this creates opportunities for formal EVD management training. In order to promote a culture of EVD safety, there is a need for global awareness of the problem, and formal training and continued medical education of anesthesiologists managing patients with EVDs. The potential impact of EVD management guidelines on patient outcomes warrants further examination.


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intracranial pressure monitoring; external ventricular drain; perioperative; transport

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