What Should Actually Happen During a PM?

What preventive maintenance is supposed to accomplish, what a biomed should actually be looking for, and why a PM should be more than clicking through a checklist and putting on a new sticker

Preventive maintenance can become dangerously routine.

Back to Biomed Basics

What This Page Explains

This page covers:

The Simple Version

A good PM usually answers several questions:

Is the equipment physically intact?

Does it perform the functions someone depends on?

Are important measurements or outputs within specification?

Do required alarms and safety systems operate correctly?

Are wear items, batteries, filters, or scheduled components still acceptable?

Did anything show up that should be repaired before the device goes back into service?

The PM is not complete because every box has a check mark.

It is complete when the required inspection and testing have actually established the condition of the equipment.

PM Is Not the Same Thing as Corrective Maintenance

Corrective maintenance begins because something is wrong.

Preventive maintenance usually begins because the device reached a scheduled maintenance point.

That difference matters.

During corrective maintenance, you often start with:

What failed?

During PM, you often start with:

What could be degrading without anyone noticing yet?

PM Looks for Hidden Problems

Some failures are obvious.

A broken display gets reported.

A device that will not power on gets reported.

Other problems can remain hidden.

Examples include:

The device may still appear normal to the user.

That is where PM can add value.

Start With the Correct Procedure

Before doing anything else, know what procedure applies.

Possible sources include:

Do not create the PM from memory if an approved procedure exists.

Why the Manufacturer Procedure Matters

The manufacturer knows:

That does not mean every organization must always use the OEM schedule forever.

But changes to the maintenance strategy should be deliberate and supported by the organization's maintenance program.

Read the Procedure Before the First PM

Do not discover halfway through the job that you need:

Planning matters.

Physical Inspection

A physical inspection is often the first meaningful step.

Look at the whole device.

Ask:

Does anything about this equipment suggest deterioration, damage, contamination, or unsafe use?

Power Cord and Plug

For mains-powered equipment, inspect:

A device can pass functional testing with a damaged cord.

Enclosure

Look for:

The significance depends on where the damage is.

A cracked decorative cover and a cracked patient-support structure are not equivalent.

Connectors

Inspect frequently used connectors.

Look for:

These are common sources of intermittent failure.

Wheels, Brakes, and Mechanical Hardware

For mobile equipment, check:

A perfectly calibrated device can still be unsafe if the cart rolls when the brake should hold.

Cleaning and Contamination

Look for:

If the device cannot be properly cleaned because of physical damage, that may matter even when electronics work.

Visual Inspection Should Not Become a Five-Second Glance

The point is to identify deterioration before it becomes failure.

Functional Testing

Functional testing asks:

Does the device actually perform the function it is designed to perform?

Example: Patient Monitor

You may verify functions such as:

depending on configuration and procedure.

Example: Infusion Pump

You may verify:

Function vs Accuracy

This distinction is important.

A pump can:

Move fluid

without delivering:

The correct amount of fluid.

A monitor can:

Display NIBP

without measuring pressure accurately.

Functional operation and performance accuracy are related but not identical.

Performance Verification

Performance verification compares actual device behavior with a known reference or manufacturer specification.

Examples include:

Use the Correct Test Equipment

The analyzer should be:

Do Not Let the Device Verify Itself

Internal diagnostics are useful.

But if the parameter matters enough to require independent verification, use an external reference.

Example

Ventilator says:

500 mL.

External analyzer says:

435 mL.

The ventilator display alone does not prove output accuracy.

Calibration

Calibration does not always mean adjusting the device.

In many PMs, you are verifying whether calibration remains within specification.

If It Passes

No adjustment is needed.

If It Fails

Now you may need:

depending on the device.

Do Not Calibrate Around a Mechanical Failure

Suppose a pressure channel reads low because of a leak.

Do not simply adjust calibration until it matches.

Fix the leak.

As-Found Condition Matters

If the device fails before adjustment, record the as-found condition when required.

That history can reveal drift.

Batteries

Battery evaluation is an important part of many PM programs.

A battery may:

while having poor actual capacity.

What Should You Check?

Depending on equipment:

Transport Equipment Deserves Particular Attention

A monitor used during patient transport depends much more heavily on reliable battery operation than equipment that normally remains plugged in.

Battery Safety

Inspect for:

A physically damaged lithium-ion battery is not merely a failed runtime test.

Alarms

Alarm verification deserves real attention.

A device may perform its primary function correctly while a critical alarm fails.

Check What the Procedure Requires

This may include:

Weak Alarm Audio

If the speaker is barely audible, do not ignore it because:

Technically there is sound.

The alarm must serve its intended function.

Safety Systems

Depending on equipment, PM may include:

These systems may rarely activate clinically.

That makes scheduled verification more important, not less.

Filters

Filters are classic PM items because they deteriorate slowly.

A dirty filter can cause:

Do Not Just Look at the Fan

A fan can spin while a clogged filter prevents meaningful airflow.

Cooling Path

Inspect the full path:

Scheduled Replacement Items

Some manufacturers specify replacement of parts based on:

Examples might include:

Follow the applicable procedure.

Do Not Replace Parts Merely Because “We Always Do”

Know why the interval exists.

Do Not Skip Scheduled Items Without Authorization

Conversely, do not ignore a manufacturer requirement because:

It still looks fine.

Usage-Based Maintenance

Some components wear based more on:

than calendar time.

Example

A high-use pump and low-use backup pump may age differently even if purchased on the same date.

Software and Firmware

PM can also be an opportunity to document:

when relevant.

Do You Update Software During Every PM?

Not automatically.

Software updates can introduce:

Follow the organization's update process.

Configuration

Some PM procedures include checking:

Do Not Reset Clinical Configuration Accidentally

Document settings before major changes.

Electrical Safety Testing

Electrical safety testing may be part of PM depending on:

It should not become:

Plug everything into the analyzer because that is what PM means.

Use the appropriate procedure.

What Electrical Safety Testing Proves

It can provide evidence about:

It does not prove:

PM Should Follow the Device Architecture

Think about how the device can fail.

For a ventilator:

matter greatly.

For a surgical table:

matter greatly.

The PM should make sense for the equipment.

PM Should Not Be Checklist Theater

A checklist is useful because it promotes consistency.

But it can become meaningless if technicians only focus on:

Getting to the bottom of the page.

Ask Why Each Test Exists

If you understand the failure mode behind a test, you are more likely to notice abnormal behavior that falls between the boxes.

Example

Procedure says:

Inspect power inlet.

A technician who understands why may notice:

rather than simply checking:

PASS.

What If Something Fails During PM?

The device has now become a corrective-maintenance problem too.

Do not simply mark the PM complete and create another work order without addressing the failed condition according to facility workflow.

Example

PM finds:

Battery capacity below requirement.

The equipment should not return to service with:

A known failed battery

just because the rest of PM passed.

Failed PM Is Useful

It means the maintenance process detected a problem before clinical use did.

That is exactly what PM is supposed to do.

Borderline Results

Be careful with values right near specification limits.

Review:

Do Not Test Until It Passes

If a measurement fails twice and passes once, do not automatically choose the passing result.

Investigate the variability.

Repeatability Matters

Unstable performance can itself be a problem.

PM and Equipment History

Review previous PM results when useful.

Look for trends.

Example:

Battery capacity:

90%

then:

75%

then:

58%.

That tells you more than the current result alone.

Same Parameter Adjusted Every PM

Repeated adjustment may suggest:

PM Duration

A good PM does not have one universal duration.

A simple device may take minutes.

A complex system may take much longer.

Faster Is Not Automatically Better

Efficiency comes from:

not skipping meaningful testing.

Organize Your Bench

Having the correct:

ready improves speed without reducing quality.

PM Labels

The sticker is the end of the process.

It is not the process.

What a Sticker Does Not Tell You

It does not tell you:

That information belongs in the service record.

Real-World Example: Monitor PM

Visual inspection:

Good.

ECG:

Pass.

SpO2:

Pass.

NIBP:

Reads 18 mmHg high against calibrated reference.

The monitor powers on and looks perfect.

The PM found a hidden performance issue.

Real-World Example: Infusion Pump PM

Pump runs normally.

Flow passes.

Occlusion pressure inconsistent.

That may require further investigation before return to service.

Real-World Example: Ventilator PM

Volume and pressure pass.

Audible alarm intermittently cuts out.

The device is not ready merely because ventilation performance passed.

Real-World Example: Bed PM

Electronics operate.

One caster brake does not hold.

That mechanical issue may be the most important finding of the entire PM.

Common Mistakes

Treating PM as a Sticker Replacement

The sticker documents completion.

It does not create equipment reliability.

Performing Every Device's PM the Same Way

Follow equipment-specific requirements.

Testing Only What Is Easy

The important function may be inconvenient to test.

Trusting Internal Self-Tests for Everything

Use independent references where required.

Ignoring Physical Damage Because Electronics Pass

Safety is broader than electronics.

Adjusting Calibration Before Investigating the Cause

Do not calibrate around failure.

Returning Equipment With a Known Failed PM Item

Resolve or appropriately manage the failure first.

A Useful PM Framework

Think:

Physical Condition

↓

Basic Function

↓

Measured Performance

↓

Safety Systems

↓

Wear Items

↓

Required Documentation

That gives the PM structure.

Another Useful Question

Ask:

If this device fails clinically tomorrow, what part of today's PM would I point to as evidence that I meaningfully checked the function involved?

That question helps separate meaningful verification from checkbox completion.

What Did You Actually Prove?

If a monitor passes electrical safety:

You proved:

The tested electrical safety parameters met the applicable limits.

You did not prove:

If the device passes the complete approved PM procedure:

You have much broader evidence about its condition.

But even then:

PM is a snapshot.

It does not guarantee the device cannot fail tomorrow.

Final Thoughts for Biomeds

A good PM is not about trying to predict every future failure.

You cannot.

It is about deliberately looking for the kinds of deterioration and hidden faults that can reasonably be detected before they cause trouble.

Inspect the equipment.

Exercise the functions.

Measure what matters.

Test the protections.

Look at the wear items.

Document the evidence.

Then put on the sticker.

Not the other way around.

The goal is not:

Complete PM.

The goal is:

Establish reasonable confidence that this equipment is ready to continue doing the job people expect it to do.

And before you close the work order, ask:

What did I actually prove during this PM?

— Jake

Important Note

Preventive-maintenance scope, intervals, inspection items, test limits, scheduled replacements, calibration requirements, electrical-safety testing, and return-to-service criteria vary by medical-device manufacturer, facility maintenance program, equipment risk, and applicable requirements. Follow current manufacturer documentation and your organization's approved maintenance procedures.

Related Biomed Basics

Back to Biomed Basics