How to troubleshoot a negative Intracranial Pressure (ICP) reading?

Troubleshooting Negative ICP Readings

Negative ICP readings are almost always technical artifacts caused by system malfunction, air in the monitoring system, improper zeroing, or catheter obstruction—not true physiological values—and require immediate systematic troubleshooting to restore accurate monitoring.

Understanding the Problem

Negative ICP values are physiologically implausible and indicate a technical problem with your monitoring system rather than actual intracranial dynamics 1, 2. Normal ICP ranges from 5-15 mmHg in adults, and even in cases of over-drainage, ICP should not read negative 2.

Systematic Troubleshooting Approach

Step 1: Check System Zeroing and Calibration

• Re-zero the transducer at the level of the foramen of Monro (external auditory meatus) with the patient's head in the current position 3, 4
• Ensure the arterial pressure transducer position is correctly adjusted, as improper positioning causes false readings 3
• Verify the transducer is at the correct anatomical reference point—moving the transducer below this level will artificially lower readings 1

Step 2: Inspect for Air Bubbles and Leaks

• Examine the entire fluid column for air bubbles in the tubing, which create compressible spaces and dampen pressure transmission 1
• Elevate pressure in external tubing and connections to detect microleaks that may not be immediately visible 1
• Check all connection points between the catheter, tubing, transducer, and monitor for loose fittings 1

Step 3: Assess Catheter Patency

• If using a ventricular catheter with drainage capability, temporarily close the drain and observe if pressure readings normalize—this distinguishes between true ICP and flow-related artifacts 5
• When drainage ports become blocked, a pressure gradient develops between inside and outside the catheter, causing falsely low readings that only equalize when flow stops 5
• Inject a small volume of sterile saline (0.5-1 mL) through the system to verify patency and observe for appropriate pressure response 1
• Never flush aggressively, as this can cause intracranial hemorrhage or tissue damage 1

Step 4: Evaluate for CSF Over-Drainage

• Check if excessive CSF drainage has occurred, particularly in patients with skull fractures, craniotomy defects, or external ventricular drains set at inappropriate heights 1
• Adjust EVD height if set too low relative to the patient's head position 1
• In patients with cerebral death or significant CSF leaks, ICP monitoring may be unreliable and require special attention to technique 1

Step 5: Verify Monitor Function

• Test the monitoring system with a known pressure source to confirm the electronic components are functioning properly 1
• Check that cables are properly connected and not damaged 2
• Ensure the monitor is set to the correct pressure scale and units 2

Critical Pitfalls to Avoid

• Do not assume negative readings are accurate and adjust therapy based on them—this can lead to dangerous under-treatment of elevated ICP 1, 2
• Do not continue monitoring with a malfunctioning system—inaccurate ICP data is worse than no data, as it may result in inappropriate therapy 1
• Avoid excessive manipulation of intraventricular catheters, which increases infection risk (6-22% bacterial meningitis rate) 3
• Never perform aggressive flushing of ICP monitoring systems, as this can cause intracranial hemorrhage 1

When to Replace the System

If troubleshooting fails to resolve negative readings, replace the entire monitoring system including catheter if necessary, as continued use of a malfunctioning system provides misleading data that can harm the patient 1, 2. The risks of catheter replacement (hemorrhage 1-3.8%, infection 6-22%) must be weighed against the critical need for accurate ICP monitoring in managing cerebral perfusion pressure and preventing herniation 3.

Documentation

Record all troubleshooting steps, time of malfunction detection, interventions performed, and when accurate readings were restored 2. This information is essential for quality assurance and may reveal patterns suggesting equipment or technique issues 2.