How it works

Intensive care mechanical ventilator

A closed-loop gas delivery system that mixes air and oxygen, delivers controlled breaths through valves and sensors, and protects the patient with alarms and a safety valve.

Course: Ventilator Service — Level 1

Principle

An ICU ventilator takes high-pressure medical air and oxygen from the hospital pipeline or cylinders (or uses an internal turbine/blower for air), reduces and regulates them, mixes them to the set oxygen concentration, and delivers each breath through a proportional inspiratory valve. A controller closes the loop on flow and pressure sensors to deliver either a target volume or a target pressure, according to the mode, and synchronises with the patient's own effort using pressure or flow triggers. During expiration an actively controlled expiratory valve holds the set PEEP. The delivered gas is monitored independently (pressure, flow/volume, FiO2), and alarms warn of disconnection, obstruction, high pressure, low minute volume, apnoea, gas supply failure and technical faults. A mechanical safety valve opens if pressure becomes excessive, and an ambient (anti-asphyxia) valve lets the patient breathe room air if the ventilator fails. Gas is humidified by a heated humidifier or an HME filter. The ventilator is life-support equipment: every repair must end with a full performance verification.

The chain, block by block

Block	What it does	How it fails
Gas inlets: O2 and air (pipeline, cylinder, or turbine)	Inlet connectors with filters, check valves and water traps receive gas; turbine-based units generate their own air from room air.	Low gas supply alarms, water in the air inlet from a wet pipeline, clogged inlet filters, leaking check valves causing cross-flow between gases; turbine wear or overheating on blower units.
Pressure regulators and gas mixing	Reduce supply pressure to a stable working pressure and mix air and O2 (proportional valves or blender) to the set FiO2.	FiO2 deviations, oscillating or unstable delivery, regulator drift.
Inspiratory valve and flow sensor	Proportional valve meters gas flow; flow sensor provides closed-loop feedback.	Volume or flow inaccuracy, high-flow limitation, calibration failures, valve sticking.
Oxygen sensor	Measures delivered O2 concentration; galvanic cells are consumables, paramagnetic sensors are not.	Galvanic cells drift and expire, giving FiO2 alarms or failed calibration; requires periodic replacement.
Patient circuit, filters and humidification	Carries gas to and from the patient; bacterial/viral filters protect the machine; humidifier or HME conditions the gas.	Leaks, condensate in tubing, blocked filters increasing resistance, humidifier temperature alarms. Most 'ventilator' alarms in practice originate here.
Expiratory valve and expiratory flow sensor	Controls PEEP and exhalation; measures exhaled volume.	PEEP instability, auto-PEEP misreading, exhaled volume errors from a contaminated or wet sensor, diaphragm wear; parts may require reprocessing.
Pressure sensors and safety/ambient valves	Independent pressure transducers monitor airway pressure; safety valve limits maximum pressure; ambient valve allows spontaneous breathing on failure.	Pressure reading offset, failed self-test, safety valve not opening or leaking.
Controller, monitoring and alarms	Runs modes and triggers, displays waveforms and parameters, generates alarms; often includes a separate monitoring processor.	Touch screen and encoder failures, alarm speaker failure, software errors, internal battery not holding charge.
Power supply and internal battery	Mains supply with internal and sometimes hot-swap batteries for transport and outages.	Battery capacity loss leads to short run times on mains failure; batteries need periodic capacity testing and replacement.

Block

What it does

How it fails

Gas inlets: O2 and air (pipeline, cylinder, or turbine)

Inlet connectors with filters, check valves and water traps receive gas; turbine-based units generate their own air from room air.

Low gas supply alarms, water in the air inlet from a wet pipeline, clogged inlet filters, leaking check valves causing cross-flow between gases; turbine wear or overheating on blower units.

Pressure regulators and gas mixing

Reduce supply pressure to a stable working pressure and mix air and O2 (proportional valves or blender) to the set FiO2.

FiO2 deviations, oscillating or unstable delivery, regulator drift.

Inspiratory valve and flow sensor

Proportional valve meters gas flow; flow sensor provides closed-loop feedback.

Volume or flow inaccuracy, high-flow limitation, calibration failures, valve sticking.

Oxygen sensor

Measures delivered O2 concentration; galvanic cells are consumables, paramagnetic sensors are not.

Galvanic cells drift and expire, giving FiO2 alarms or failed calibration; requires periodic replacement.

Patient circuit, filters and humidification

Carries gas to and from the patient; bacterial/viral filters protect the machine; humidifier or HME conditions the gas.

Leaks, condensate in tubing, blocked filters increasing resistance, humidifier temperature alarms. Most 'ventilator' alarms in practice originate here.

Expiratory valve and expiratory flow sensor

Controls PEEP and exhalation; measures exhaled volume.

PEEP instability, auto-PEEP misreading, exhaled volume errors from a contaminated or wet sensor, diaphragm wear; parts may require reprocessing.

Pressure sensors and safety/ambient valves

Independent pressure transducers monitor airway pressure; safety valve limits maximum pressure; ambient valve allows spontaneous breathing on failure.

Pressure reading offset, failed self-test, safety valve not opening or leaking.

Controller, monitoring and alarms

Runs modes and triggers, displays waveforms and parameters, generates alarms; often includes a separate monitoring processor.

Touch screen and encoder failures, alarm speaker failure, software errors, internal battery not holding charge.

Power supply and internal battery

Mains supply with internal and sometimes hot-swap batteries for transport and outages.

Battery capacity loss leads to short run times on mains failure; batteries need periodic capacity testing and replacement.

Symptom → where to look first

Symptom	Suspect first
Frequent leak or low volume alarms	Patient circuit and connections first, then expiratory valve seal, then flow sensor calibration.
FiO2 deviation alarms	O2 sensor (galvanic cell expiry) first, then gas supply pressures and mixing valves.
Exhaled volume reads wrong or fluctuates	Expiratory flow sensor: contamination, moisture from humidification, calibration.
PEEP unstable or cannot reach set PEEP	Expiratory valve diaphragm/seal, leaks in circuit, exhalation valve control.
Gas supply alarm while pipeline seems fine	Inlet filters, water traps, check valves and supply hose; verify pipeline pressure at the outlet.
Self-test fails on leak test	Circuit and seals, then internal pneumatic leaks, with the test performed exactly per manufacturer setup.
Short battery run time / switches off on mains loss	Internal batteries: capacity test and replacement.
Pressure readings offset or occlusion alarms without obstruction	Pressure transducers, their sensing lines, moisture in the lines.

Symptom

Suspect first

Frequent leak or low volume alarms

Patient circuit and connections first, then expiratory valve seal, then flow sensor calibration.

FiO2 deviation alarms

O2 sensor (galvanic cell expiry) first, then gas supply pressures and mixing valves.

Exhaled volume reads wrong or fluctuates

Expiratory flow sensor: contamination, moisture from humidification, calibration.

PEEP unstable or cannot reach set PEEP

Expiratory valve diaphragm/seal, leaks in circuit, exhalation valve control.

Gas supply alarm while pipeline seems fine

Inlet filters, water traps, check valves and supply hose; verify pipeline pressure at the outlet.

Self-test fails on leak test

Circuit and seals, then internal pneumatic leaks, with the test performed exactly per manufacturer setup.

Short battery run time / switches off on mains loss

Internal batteries: capacity test and replacement.

Pressure readings offset or occlusion alarms without obstruction

Pressure transducers, their sensing lines, moisture in the lines.

Safety

Site and infrastructure

Medical gas pipeline outlets for O2 and medical air at the pressure range specified by the ventilator manufacturer, with correct non-interchangeable connectors; check for water and oil in medical air.
Backup gas: cylinders with regulators available for transport and pipeline failure.
Grounded mains outlets on essential (emergency-generator-backed) circuits; ventilator internal battery charged.
Exhaust and room ventilation adequate, especially where oxygen concentrations may build up near bedspaces.
Room temperature and humidity within operating range; no use near MRI unless the device is labelled MR-conditional for that environment.

Preventive maintenance basics

Follow the manufacturer's preventive maintenance kit schedule (seals, diaphragms, filters, O2 cell, batteries) based on operating hours or time.
Calibrate flow, pressure and O2 sensors; run the full self-test with a test lung.
Verify performance with a calibrated gas flow analyser: tidal volume, pressure, PEEP, FiO2, flow, in several modes, against tolerance.
Test all alarms: disconnection, high pressure, low minute volume, apnoea, gas supply loss, power failure, O2 limits.
Check safety valve and ambient (anti-asphyxia) valve function.
Test battery run time and switch-over from mains to battery.
Perform electrical safety testing (IEC 62353 or locally required standard).
Inspect and clean inlet filters, water traps, fan filters; inspect gas connectors and hoses for wear and leaks.

Safety

Never service a ventilator connected to a patient; arrange a replacement and transfer before any work.
Oxygen enriches combustion: no oil or grease on oxygen fittings, no open flames or sparks, and use only oxygen-compatible lubricants where the manufacturer specifies them.
Compressed gases: depressurise and disconnect supplies before opening the pneumatic system; cylinders must be secured and handled with care.
Treat expiratory components, filters and sensors as contaminated; use PPE and follow reprocessing instructions.
After any repair, the device must pass full performance verification and alarm checks before return to clinical use; document the result.

Model pages

GE HealthCareCarescape R860Pneumatically driven ICU ventilator for adult, paediatric and neonatal patients that runs from wall (or compressor) air and oxygen and is used in intensive care units and step-down wards.MindraySV600 / SV650Mindray's mid-to-high-end ICU ventilator for adult, paediatric and (with the neonatal module) neonatal patients, running on wall air and O2 or on an optional internal blower, used in ICUs, emergency departments and for in-hospital transport.

Manufacturers

Dräger · Hamilton Medical · Getinge (Maquet) · GE HealthCare · Medtronic (Puritan Bennett) · Philips Respironics · Vyaire / ZOLL · Mindray · Löwenstein Medical · Nihon Kohden · Comen · Aeonmed