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External ventricular catheters: is it appropriate to use an open/monitor position to adequately trend intracranial pressure in a neuroscience critical care environment?


Intracranial pressure (ICP) monitoring can be an important assessment tool in critically and acutely ill patients. An external ventricular drain offers a comprehensive way to monitor ICP and drain cerebrospinal fluid. The Monro-Kellie hypothesis, Pascal's principle, and fluid dynamics were used to formulate an assumption that an open/monitor position on the stopcock is an adequate trending measure for ICP monitoring while concurrently draining cerebrospinal fluid. Data were collected from 50 patients and totaled 1053 separate number sets. The open/monitor position was compared with the clamped position every hour. An order for "open to drain" was needed for appropriate measurement and nursing care. Results showed the absolute average differences between open/monitor and clamped positions at 1.6268 mm Hg. This finding suggests that it is appropriate to use an open/monitor position via an external ventricular drain for adequate trending of patients' ICP.

Keywords: external ventricular drain, intracranial pressure, neuroscience, nursing


An external ventricular drainage (EVD) system is the most commonly used technology to monitor intracranial pressure (ICP) and drain cerebrospinal fluid (CSF) to manage rising ICP in patients with traumatic brain injury, subarachnoid hemorrhage, hydrocephalus, brain tumor, or neurological disease (Wong, 2011). Nurses monitor ICP with an EVD hourly to assess changes in cerebral hemodynamics.

Along with monitoring ICP, the nurse is responsible for frequent neurological assessments. On the basis of provider orders, the nurse may also need to drain CSF via the EVD to decrease an elevated ICP. Intracranial hypertension is noted when there is an alteration in the pressure-volume relationship within the cranial vault. Restoring a normal balance can improve neurologic recovery.

The aim of this study was to show whether using the null position on the EVD provides adequate inter-hour trending of a patient's ICP. The hypothesis was based on the Monro-Kellie hypothesis, fluid dynamics, closed system, and pressure physics. This proposition includes vertical pressure variation and Pascal's principle. In a closed pressure system, according to Pascal's principle, "pressure exerted anywhere in a confined incompressible fluid is transmitted equally in all directions throughout the fluid such that the pressure ratio remains the same" (Georgia State University, 2012).
Pascal's Principle

[DELTA]P = [rho]g([DELTA]h)


P = hydrostatic pressure

p = fluid density

g = acceleration due to gravity

h = height of fluid higher than the measurement point

In nursing practice, understanding the relationship of fluid pressure to an EVD increases user knowledge and leads to safe clinical practice. To illustrate, if CSF flow within the EVD tubing is blocked, fluid dynamics present that the pressure within the tubing is now increased. This situation places the patient at risk for alteration in pressure volume, which may lead to brain herniation. It is imperative that the nurse act on the knowledge of the pressure variation to prevent a catastrophic event for the patient.

Review of the Literature

A review of the literature was conducted to determine whether there was an existing research and, if so, did the evidence suggest the use or contraindication of an open/monitor method. Resources investigated included the American Association of Neuroscience Nurses (2012) clinical practice guideline series, American Association of Neuroscience Nurses (2014) Web site portal listserv, the Clinical Practice of Neuroscience Nursing (Hickey, 2011), and the American Association of Critical Care Nurses (2014) Web site education search engine. No conclusive evidence was found regarding the use of the null position in relation to trending patients' ICPs.


The study was submitted and approved by the investigator's institutional review board. Fifty patients were assessed during a period of 3 months. Patients were enrolled in the study upon placement of an EVD. The patients had a current order from the physician to keep the EVD at continuous drainage. Nurses placed the stopcock in the null position and assessed the patients' ICP hourly. Hourly documentations of the open/monitor reading and the clamped reading were documented on the form created for this study.

The open/monitor method describes the positioning of the stopcock below the burette on the EVD to allow CSF to drain from the catheter and to obtain an ICP value on the bedside monitor. The clamped method is used to describe the stopcock positioned so that CSF will not drain; however, an ICP waveform and value will appear on the monitor.

Staff nurses in the neuroscience critical care unit assisted with data collection. The following protocol and standardized process was reviewed with the nursing staff:

1. A provider order was reviewed stating that the drain is to be open to monitor (open/monitor method).

2. A printout of the clamped EVD strip and the open EVD strip was placed in the chart daily.

3. The EVD was placed in the null position while the study took place.

4. During the period of ICP measurement, the nurse noted the number on the monitor for the ICP. This number was deemed as the open/null number.

5. The nurse recorded this number in the appropriate hourly space on the study data collection form.

6. The nurse then clamped the EVD.

7. A period of 1 minute elapsed to afford a true closed number reading. This number was deemed as the clamped number.

8. The nurse recorded this number in the appropriate hourly space on the study data collection form.

This process continued until the patient tolerated either continuous clamping, removal of the EVD, or drainage of CSF without monitoring. Data collection forms were kept on the front of the patient chart and collected at the end of a 24-hour period. At 7:00 AM, a new form was placed on the front of the patient's chart. Documented strips visualizing the ICP wave form at both the open/monitor and clamped positions were retrieved to assess waveform accuracy.

Additional data collection questions included the following:

1. Is the patient a trauma patient?

2. In what location was the EVD placed?

3. Was there any intrathecal medications given?

4. Did the patient receive hypertonic solutions?

Data points from these forms were collected and assessed to test the hypothesis.


Statistical analysis was performed using IBM SPSS data analysis and statistical software version 21. Upon completion of data entry into an Excel spreadsheet, all data were imported into the SPSS. A k agreement was performed to determine whether the 2 methods of clamping versus open/monitor agreed more than by chance. For the absolute mean difference, the clamped measurement was subtracted by the open measurement. The absolute value was analyzed, and, finally, the mean of all data points was determined for the difference between measuring the clamped and measuring open/monitor across all data points.


One thousand fifty-three sets of data from the 50 patients were analyzed. An example of the data set can be visualized in Supplemental Digital Content 1 (available at All data were given the set value for an appropriate ICP from 0 to 20 mm Hg. Normal pressure was defined as an ICP of 0 to 20 mm Hg, and abnormal pressure is defined as an ICP of 21 mm Hg and higher.

Using the High Open * High Clamp cross-tabulation (Table 1), data were first differentiated between normal pressure (which is any number in between 0 and 20 mm Hg) (agreement [0]) and abnormal pressure (which is any number higher than 20 mm Hg) (disagreement [1]). Normal ICP was given the number 0 and the label agreement, and abnormal ICP was given the number 1 and the label disagreement.

Results of the High Open * High Clamp cross-tabulation where the open and clamped positions both indicated normal pressure in the patients totaled 1022. Measurements in the open and clamped positions where pressure was outside the normal pressure range totaled 6 data points. Both methods of measuring agreed that the patients had pressure in high ranges greater than 20 mm Hg.

Finally, 25 measurements where the open and clamped positions indicated different pressures included 23 sets where the clamped position indicated high pressure and the open position indicated normal pressure and 2 sets where the clamped position indicated normal pressure and the open position indicated high pressure.

Clamped and Open/Monitor Methods

When comparing the open/monitor method with the clamped method of measuring pressure, the results showed agreement that ICP was within 3 mm Hg, 1028 of 1053 or 97.6% of the time. The comparisons were not in agreement, 25 of 1053 or 2.4% of the time. Of the 2.4% that disagreed, most came from the clamped method indicating high pressure, whereas the open method indicated pressure within normal ranges but within 3 mm Hg, or 23 of 25 or 92% of the time. The 2 disagreements where the open measurement was higher than the clamped measurement were from the same patient (ID 24). Sixteen disagreements came from the same 2 patients (IDs 14 and 15) and were substantially different (all but one had a difference > 20), 16 of 25 data points or 64%.

The mean absolute difference, or final distinct difference between the 2 measuring methods, was approximately 1.63 mm Hg (Table 2). There were 95 instances where the 2 methods produced a difference in the measurement of greater than 3 mm Hg. That is, 9% of the time (95/1053), the difference in measurements was greater than agreed upon acceptable ranges. Furthermore, 38% of the time (400/1053), there was no difference, and 53% of the time (558/1053), the difference between measurements was 3 mm Hg or less (Table 3).

Of the 50 data sets collected, 6 patients had traumatic injuries, and 44 were nontraumatic; 28 had the EVD placed on the left side, and 23 had the EVD placed on the right side; 50 patients did not receive intrathecal medication, 6 patients received hypertonic solutions, and 44 did not receive hypertonic solutions (Table 4).


The hypothesis for this research was to determine the appropriateness for the trending of ICP waveform and number determination using the open/monitor method. The findings suggest that trending is appropriate for patients who are neurologically critically injured and need constant pressure monitoring. Knowing when a patient's ICP is trending upward during the interhour can provide time for lifesaving measures.

The observations that did not return results as favorable included IDs 14, 15, and 24.

IDs 14 and 15 were both from the same patient. This patient was a 51-year-old who was found unconscious by the emergency medical service with vomiting and intermittent tensing of extremities for two 10-second periods. Initial systolic blood pressure readings reached 250 to 260 mm Hg, with a heart rate in the low 60s. Admission Glasgow Coma Scale was 3. Initial computed tomographic scan of the patient revealed a large focal parenchymal hematoma in the left caudate nucleus with ventricular extension, layering in the occipital horns bilaterally, and obstruction of the CSF. Hemorrhage extended into the fourth ventricle tracking through the foramina of Luschka into the cistema magna and subarachnoid spaces. There was subarachnoid hemorrhage in the frontal and parietal convexity sulci. There was a significant left to right midline shift measuring 1.3 cm with effacement of the suprasellar cistern and mass effect on the brainstem that was consistent with uncal herniation.

Upon arrival, contralateral EVDs were placed to help facilitate CSF drainage and blood flow. Both EVDs were set at 0 mm Hg, midline to the tragus. This patient received 3 doses of 23.4% hypertonic saline to help reduce swelling. In addition, a hypertonic infusion of 3% sodium chloride was administered at 60 rnL/h.

ID 24 was not favorable because of the ICP numbers on both open/monitor and clamped positions being out of the normal range for ICP.

Conclusions and Recommendations

The absolute mean between the clamped drain reading and the open/monitor placement was 1.6268. A difference of no greater than 3 was adequate for monitoring and treating patients for increased ICP. On the basis of the findings from this study, it is recommended to clamp the EVD each hour to obtain a hue ICP reading and waveform assessment. However, this research shows potential patient benefit to watching interhour ICP trends while maintaining the ability to drain CSF. Further research is currently needed.

Current nursing methods include clamping the EVD each hour, recording the ICP result, and then opening the EVD to resume drainage of CSF. This practice of keeping the EVD at an open/monitor position does not allow the nurse or provider to monitor ICP readings intrahourly. Using the open/monitor position on an EVD allows for a close trending of ICP, including intrahourly pressure readings to perform a quicker treatment of increased ICP.

Waveform analysis concluded similar wave forms with the open/monitor and clamped methods. The clamped methods were more accurate for the interpretation of intracranial compliance. Recommendations for nurses include continuing to clamp the EVD each hour for an accurate waveform analysis.

Study limitations were a limited sample size and lack of previous research studies on this subject. Recommendations include replication of this study to determine whether the findings are consistent. This information will provide additional evidence to support the practice of monitoring ICP in the open/monitor position. In addition, replicating this study with a different patient population (eg, subarachnoid hemorrhage) would provide additional information to guide nursing practice.


The authors thank Victoria Schirm, PhD, RN, Director of Nursing Research at Penn State Hershey, for her helpful guidance on the development of this manuscript.


American Association of Critical Care Nurses. (2014). Listserv website portal. Retrieved from

American Association of Neuroscience Nurses. (2012). Clinical practice guideline series: Care of the patient undergoing intracranial pressure monitoring/external ventricular drainage or lumbar drain. Retrieved from apps/ws_downloads/download.php?file=58

American Association of Neuroscience Nurses. (2014). Listserv website portal. Retrieved from

Georgia State University. (2012). Hyperphysics. Retrieved from

Hickey, J. (2011). The clinical practice of neurological and neurosurgical nursing (6th ed.). Philadelphia, PA: Lippincott Williams & Wilkins.

Wong, F. W. (2011). Cerebrospinal fluid collection: A comparison of different collection sites on the external ventricular drain. Dynamics, 22(3), 19-24.

Questions or comments about this article may be directed to Nicole E. Sunderland, MSN RN SCRN CCRN, at NSunderland@ She is a Clinical Nurse, Neuroscience Critical Care Unit, Department of Nursing, Penn State Milton S. Hershey Medical Center, Hershey, PA.

Nancy E. Villanueva, PhD CRNP BC CNRN, is Neurosurgery Nurse Practitioner, Department of Neurosurgery, Temple University Health System, Philadelphia, PA.

Susan J. Pazuchanics, MSN RN CCRN NE-BC, is Clinical Nurse Educator, Department of Nursing, Penn State Milton S. Hershey Medical Center, Hershey, PA.

The authors declare no conflicts of interest.

DOT: 10.1097/JNN.0000000000000255
TABLE 1. High Open * High Clamp Cross-Tabulation

                 High Clamp

Count      0        1      Total

High 0    1022       23     1045
Open 1       2        6        8
Total     1024       29     1053

TABLE 2. Agreement of Methods and
Mean Absolute Difference

Methods agree              1028    0.9763
Methods did not agree        25    0.0237
Mean absolute difference           1.6268

TABLE 3. The Count and Proportion
Between Pressure Differences

                             Count    Proportion

No difference                  400        0.3799
Difference between 1 and 3     558        0.5299
mm Hg
Differences > 3 mm Hg           95        0.0902

TABLE 4. Characteristics of Patients With an
External Ventricular Drain (EVD) (N = 50)

Characteristic                  %

  Yes                           6
  No                           44
Location of EVD
  Right                        23
  Left                         28
Intrathecal medication given
  Yes                           0
  No                           50
Hypertonic solution given
  Yes                           6
  No                           44
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Article Details
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Author:Sunderland, Nicole E.; Villanueva, Nancy E.; Pazuchanics, Susan J.
Publication:Journal of Neuroscience Nursing
Article Type:Report
Date:Oct 1, 2016
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