A pneumatic tourniquet may continue to inflate, display numbers, and sound alarms even when its pressure measurement is no longer as accurate as it was when the device was new.

This gradual change is commonly described as calibration drift.

For hospitals, it is a particularly important maintenance issue because an inaccurate tourniquet may not look obviously broken. The display may remain stable while the pressure delivered to the cuff differs from the value staff believe they have selected.

What Is Calibration Drift?

Automatic tourniquet systems use pressure sensors and control electronics to measure and regulate cuff pressure.

The device compares actual pressure with the selected value and operates pumps or valves to correct any difference.

Over time, measurement accuracy can change because of:

• Sensor aging
• Electronic drift
• Repeated mechanical cycling
• Environmental exposure
• Component wear
• Previous repairs
• Physical impact

If the pressure sensor's reference changes, displayed pressure can gradually move away from actual pressure.

Why It Is Different From an Air Leak

An air leak often creates obvious symptoms.

Pressure may fall repeatedly, the pump may run frequently, or a low-pressure alarm may activate.

Calibration drift can be less visible.

For example, the display might remain steadily at 250 mmHg even though an independent calibrated reference measures another value.

That creates two possible risks.

Actual pressure lower than displayed: the surgical field may be inadequate.

Actual pressure higher than displayed: the limb may receive more compression than intended.

This is why stable pressure and accurate pressure are not the same thing.

Excess Pressure Matters Because Pressure Is Patient-Specific

AORN's current pneumatic-tourniquet guideline recommends setting inflation pressure according to the individual patient instead of applying one standard pressure to everyone.

That approach only works as intended when the device can deliver the selected pressure within its specified performance range.

If a clinician has deliberately selected a lower patient-specific pressure but the machine materially over-delivers because of calibration error, some of the benefit of individualized pressure selection is lost.

Low Actual Pressure Can Also Create Problems

Under-delivery can produce an incomplete bloodless field.

The response may then be to increase the displayed setting.

If the underlying problem is calibration rather than patient physiology, this can create inconsistent operation and make troubleshooting more difficult.

Before assuming a patient “needs more pressure,” staff should consider whether the system, cuff, tubing, and measurement accuracy are functioning correctly.

Pressure Accuracy Is Not the Same as Display Resolution

This distinction is important in tenders.

A system that shows values in 1 mmHg increments does not necessarily have ±1 mmHg accuracy.

Three separate specifications may exist:

Display resolution: smallest value visible on the screen.

Adjustment increment: smallest change the operator can select.

Control accuracy: difference allowed between controlled pressure and the specified/reference value.

Rayland Medical's current touchscreen system lists pneumatic control accuracy of 1 kPa, approximately 8 mmHg. Its physical-button system lists pressure adjustment precision of ±25 mmHg.

These published parameters should be clarified when writing tender requirements because manufacturers may use different terminology.

How Can Calibration Drift Be Detected?

Hospitals should follow the manufacturer's maintenance instructions, but pressure verification generally requires comparison against a suitable calibrated reference.

A check can reveal whether the displayed and actual values remain within the manufacturer's permitted tolerance.

Verification should cover the operating range relevant to clinical use rather than checking only whether the unit can inflate.

Useful maintenance questions include:

• What reference equipment is required?
• Which pressure points should be checked?
• What tolerance is acceptable?
• Who is authorized to adjust calibration?
• What happens if the device fails verification?

Do not invent a maintenance interval simply because another tourniquet brand uses one. Follow the instructions for the actual model and local hospital policy.

Historical Evidence Shows Why Verification Matters

Pressure accuracy problems are not theoretical.

A published hospital survey found substantial inaccuracies in a sample of pneumatic tourniquet pressure gauges and also identified defective valves, leading the authors to recommend more frequent testing and maintenance.

The study is old and should not be used to estimate the performance of modern electronic systems. Its useful lesson is that a pressure device can remain in clinical circulation while its accuracy has deteriorated.

Modern digital displays do not remove the need for verification.

Cuffs and Tubing Can Mimic Calibration Problems

If independent pressure testing shows that the console itself is accurate, investigate the rest of the pneumatic circuit.

Potential causes of unstable or unexpected pressure include:

• Leaking cuff
• Damaged tubing
• Loose connector
• Worn O-ring
• Restricted hose
• Pump or valve problem

A 2026 FDA recall involving sterile tourniquet hoses provides a current reminder that accessories in the pressure path are safety-relevant components, not simply replaceable convenience items.

Alarm Accuracy Depends on Measurement Accuracy

Tourniquet alarms depend on sensor information.

If the pressure measurement itself is incorrect, an alarm threshold based on that measurement may not represent the true cuff condition accurately.

This is why maintenance should not be limited to checking whether the alarm produces a sound.

The complete control loop needs to be considered:

Sensor → Measurement → Display → Regulation → Alarm

Calibration History Matters for Fleet Management

Hospitals operating several tourniquets should identify equipment by serial number and maintain service records.

Useful information includes:

• Device ID
• Calibration/verification date
• Test result
• Repairs performed
• Pressure sensor replacement
• Pump or valve work
• Battery service
• Next action required under hospital policy

This makes it easier to identify one unit that behaves differently from the rest of the fleet.

Procurement Should Ask About Service Before Purchase

A tourniquet specification should not end with maximum pressure.

For new equipment, ask the supplier about:

• Pressure-control specification
• Verification method
• Service documentation
• Calibration support
• Spare parts
• Pressure-sensor servicing
• Technical support

Rayland Medical supplies both touchscreen and physical-button pneumatic tourniquet systems with published pressure-control specifications, allowing these requirements to be reviewed before a hospital or distributor confirms the model.

Calibration drift is a maintenance problem that can remain invisible during normal startup. The safest approach is therefore not to wait until staff notice an obviously unstable pressure reading. Regular verification according to the device manufacturer's instructions helps confirm that the number on the display still represents the pressure the system is expected to deliver.