BiPAP Modes Explained: S, ST, AVAPS,iVAPS and PC

What Each Mode Does, When Doctors Prescribe It, and How Pressure Settings Work   If your doctor has prescribed a BiPAP machine, you may have noticed that it has a mode setting — S, ST, T, AVAPS, iVAPS, or PC. These modes are not interchangeable. Each one is designed for a specific condition, breathing pattern, and level of respiratory support. Understanding your mode helps you use the machine correctly, recognise when something feels wrong, and have more informed conversations with your doctor.

This guide explains all six BiPAP modes in plain language — what they do, who they are for, and what the IPAP and EPAP pressure settings mean.

What Is BiPAP and How Is It Different from CPAP?

BiPAP (Bilevel Positive Airway Pressure) delivers two different pressure levels: a higher pressure when you inhale (IPAP — Inspiratory Positive Airway Pressure) and a lower pressure when you exhale (EPAP — Expiratory Positive Airway Pressure). This two-level approach makes breathing out much easier than on a CPAP machine, which holds one fixed pressure throughout.

BiPAP is typically prescribed for patients who cannot tolerate CPAP, or whose condition requires ventilatory support beyond what CPAP provides — such as COPD, obesity hypoventilation syndrome (OHS), neuromuscular disease (NMD), or central sleep apnoea.

Term	Full Name	What It Does	Typical Range
IPAP	Inspiratory Positive Airway Pressure	Pressure during inhalation — keeps airway open and supports breathing in	10–25 cm H₂O
EPAP	Expiratory Positive Airway Pressure	Pressure during exhalation — prevents airway collapse and CO₂ rebreathing	4–12 cm H₂O
PS	Pressure Support	Difference between IPAP and EPAP (IPAP − EPAP)	4–10 cm H₂O

The 6 BiPAP Modes Explained

Not all BiPAP machines offer all modes. Entry-level machines typically offer S and ST. Advanced machines (Philips A40, ResMed AirCurve 10 VAuto/ST/ASV, BMC RESmart) add AVAPS, iVAPS, and PC modes. Your machine will only display the modes it supports

• BiPAP S (Spontaneous Mode)

In S mode, the machine responds entirely to your own breathing effort. It switches to IPAP when it detects you are inhaling, and drops to EPAP when you exhale. There is no backup rate — the machine does not breathe for you if you stop breathing.

Used for: Obstructive Sleep Apnoea (OSA) patients who could not tolerate CPAP. Patients who have adequate respiratory drive and do not need a backup rate.

Typical settings: IPAP: 10–20 cm H₂O | EPAP: 4–10 cm H₂O | PS: 4–8 cm H₂O

• BiPAP ST (Spontaneous/Timed Mode)

ST mode is S mode with a safety net. It still responds to your breathing (Spontaneous), but if you do not take a breath within the set time window, the machine delivers one automatically (Timed). This backup rate is measured in breaths per minute (BPM). ST is the most commonly prescribed BiPAP mode for serious respiratory conditions.

Used for: COPD with hypercapnia (raised CO₂), Obesity Hypoventilation Syndrome (OHS), Central Sleep Apnoea, Neuromuscular Disease (NMD) such as ALS/MND or muscular dystrophy, post-ICU patients transitioning to home ventilation.

Typical settings: IPAP: 12–25 cm H₂O | EPAP: 4–10 cm H₂O | Backup Rate: 10–14 BPM | Rise Time: 1–3

• BiPAP T (Timed Mode)

In T mode, the machine controls the full breathing cycle — both the rate and the timing of each breath. Your own breathing effort is ignored. The machine delivers breaths at a fixed rate regardless of whether you are trying to breathe or not. T mode is rarely used for home therapy and is mainly seen in hospital or ICU settings.

Used for: Patients with severely impaired respiratory drive who cannot trigger the machine reliably. Rarely prescribed for home use.

Typical settings: IPAP: set by physician | EPAP: set by physician | Rate: fixed BPM set by physician

• BiPAP AVAPS (Average Volume Assured Pressure Support)

AVAPS automatically adjusts the IPAP pressure breath-by-breath to ensure you receive a consistent tidal volume (the amount of air per breath). You set a target tidal volume, and the machine varies IPAP within a set range to hit that target — even as your breathing needs change through the night. This is particularly useful for patients whose respiratory muscle strength varies (e.g., NMD patients who breathe harder when awake than during REM sleep).

Used for: Neuromuscular Disease (ALS, muscular dystrophy, spinal muscular atrophy), Obesity Hypoventilation Syndrome where pressure needs change during REM sleep, COPD with significant nocturnal hypoventilation.

Typical settings: Target tidal volume: 6–8 ml/kg ideal body weight | IPAP min: 10 | IPAP max: 20–25 | EPAP: 4–8

• BiPAP iVAPS Intelligent Volume Assured Pressure Support

iVAPS is Philips ResMed's more advanced take on volume-assured therapy. Unlike AVAPS which targets tidal volume, iVAPS targets alveolar ventilation (the actual gas exchange at lung level). It also adjusts the backup respiratory rate automatically based on your natural breathing pattern — making it more adaptive than AVAPS. Available on the ResMed AirCurve 10 ST-A and Lumis series.

Used for: Advanced neuromuscular disease, OHS with complex ventilatory needs, patients who need intelligent backup rate adjustment, COPD-OHS overlap syndrome.

Typical settings: Target alveolar ventilation: set by physician | IPAP range: 10–25 | EPAP: 4–8 | Auto backup rate: yes

• BiPAP PC / PC-SIMV Pressure Controlled / Pressure Controlled-SIMV

PC mode delivers breaths at a set pressure and a set rate — similar to a pressure-controlled ventilator. SIMV (Synchronised Intermittent Mandatory Ventilation) allows spontaneous breaths between the mandatory machine breaths. These modes are typically used in hospital-grade home ventilators rather than standard BiPAP machines.

Used for: Patients with high ventilatory dependency — advanced NMD, spinal cord injury, post-tracheostomy patients transitioning from hospital to home.

Typical settings: Requires full clinical setup and physician programming. Not adjusted by the patient.

BiPAP Modes Comparison Table

Use this table to understand at a glance how each mode differs from the others.

Mode	Responds to Breath?	Backup Rate	Auto Pressure	Condition
S	Yes	No	No	OSA
ST	Yes	Yes	No	COPD, OHS
T	No	Fixed	No	Severe failure
AVAPS	Yes	Yes	Yes	NMD, OHS
iVAPS	Yes	Auto	Yes	Advanced cases
PC/SIMV	Optional	Yes	No	Ventilator patients

Which BiPAP Mode Does Your Doctor Set — and Why?

The mode your doctor prescribes depends entirely on your diagnosis and the nature of your breathing problem. Here is a quick reference by condition:

Condition	Recommended Mode	Why This Mode
Obstructive Sleep Apnoea (OSA) — CPAP intolerant	BiPAP S	Lower expiratory pressure makes it easier to breathe out. No backup needed as respiratory drive is normal.
COPD with hypercapnia (raised CO₂)	BiPAP ST	Backup rate ensures adequate ventilation even during sleep when breathing effort drops. Helps flush CO₂.
Obesity Hypoventilation Syndrome (OHS)	BiPAP ST or AVAPS	ST for milder cases. AVAPS preferred when pressure needs fluctuate significantly during REM sleep.
Neuromuscular Disease (ALS, muscular dystrophy, SMA)	AVAPS or iVAPS	Muscle weakness progresses over time. Volume-assured modes adapt automatically as strength declines.
Central Sleep Apnoea	BiPAP ST or ASV	ST provides backup breathing. ASV (Adaptive Servo-Ventilation) is used for complex/mixed apnoea patterns.
Post-ICU / hospital discharge with ventilator dependency	BiPAP ST, AVAPS or PC/SIMV	Mode chosen based on residual respiratory drive and degree of ventilator dependency at discharge.

Understanding Your IPAP and EPAP Pressure Settings

Your BiPAP prescription will include specific IPAP and EPAP values set by your doctor or sleep specialist, usually after a titration study (a sleep study where pressures are tested and adjusted). These numbers are measured in centimetres of water pressure (cm H₂O). What the Pressure Support (PS) Number Means Pressure Support = IPAP − EPAP. This gap determines how much help you get with each breath. A PS of 4 provides mild support; a PS of 10 or more provides significant ventilatory support. Most patients start with PS 4–6 and titrate upward based on AHI and CO₂ levels.

Typical Pressure Ranges by Condition

Condition	IPAP Range	EPAP Range	Pressure Support	Backup Rate
OSA (CPAP intolerant)	10–16	4–8	4–6	Not required
COPD with hypercapnia	14–22	4–8	6–10	10–14 BPM
OHS	14–22	6–10	6–10	10–14 BPM
Neuromuscular Disease	14–25	4–8	8–14	12–16 BPM
Central Apnoea	10–18	4–8	4–8	10–14 BPM

 Do Not Change Your Pressure Settings Without Medical Guidance BiPAP pressure settings are prescribed for your specific condition. Setting IPAP too high can cause aerophagia (air swallowing), central apnoea events, or discomfort. Setting EPAP too low may not adequately prevent airway collapse. If your therapy feels uncomfortable or your AHI is rising, speak to your doctor or sleep specialist before adjusting any settings.

Signs Your BiPAP Settings or Mode May Need Review

Contact your doctor or sleep specialist if you experience any of the following:

Symptom	What It Suggests
Bloating, burping, or stomach discomfort	Suggests IPAP is too high or EPAP too low — air is entering the stomach (aerophagia)
Waking up gasping or feeling breathless	Backup rate may be too low, or mode may need upgrading from S to ST
Machine is ‘fighting’ your breathing rhythm	Rise time may be too fast/slow, or mode may not be responding to your breathing pattern
Morning headaches or persistent fatigue	Possible CO₂ retention — pressure support may be insufficient
AHI above 5 despite using the machine	EPAP too low (allowing obstructions) or IPAP insufficient to splint the airway
Difficulty tolerating therapy — too much pressure	EPR or pressure relief settings may help; or mode change to S from ST

BiPAP S vs ST: The Most Common Question Most patients are prescribed either S or ST mode, and the difference matters more than people realise.

Feature	BiPAP S	BiPAP ST
Backup breathing	No	Yes — delivers a breath if you pause too long
Who controls breathing rate	You — entirely	You mostly, machine as backup
Best for	OSA, UARS, CPAP intolerance	COPD, OHS, NMD, Central Apnoea
Risk if breathing stops	Machine does not respond	Machine delivers a breath automatically
Typical cost (rental)	Lower — standard BiPAP	Higher — requires ST-capable machine

Frequently Asked Questions

Q: What is the difference between IPAP and EPAP?

IPAP (Inspiratory Positive Airway Pressure) is the higher pressure the machine delivers when you breathe in. EPAP (Expiratory Positive Airway Pressure) is the lower pressure during exhalation. The difference between the two is called Pressure Support. A higher pressure support means you get more help with each breath

Q: What is the difference between BiPAP S and BiPAP ST? BiPAP S (Spontaneous) only responds to your own breathing effort — it does not deliver breaths independently. BiPAP ST (Spontaneous/Timed) adds a backup rate: if you stop breathing for a set period, the machine delivers a breath. ST is prescribed when there is a risk of central apnoea or inadequate ventilation during sleep. Q: Can I change the mode on my BiPAP machine myself? No. BiPAP modes and pressure settings are set by your prescribing doctor or sleep specialist, usually under clinical menu access which is password-protected on most machines. Changing the mode without guidance can be unsafe — especially if you need a backup rate for your condition. Always consult your doctor before making any changes.

Q: Why does my BiPAP make me feel bloated? Bloating or burping during or after BiPAP therapy (called aerophagia) is usually caused by IPAP pressure set too high, causing air to enter the oesophagus and stomach rather than the lungs. It can also happen if EPAP is too low. Speak to your doctor — adjusting the pressure support or switching to AVAPS mode can often resolve this.

Q: What is AVAPS and is it better than BiPAP ST? AVAPS (Average Volume Assured Pressure Support) is not necessarily 'better' than ST — it is designed for different patients. AVAPS automatically adjusts the IPAP to maintain a consistent tidal volume, making it more adaptive than ST which uses fixed pressures. AVAPS is typically prescribed for neuromuscular disease and OHS where breathing needs change significantly during different sleep stages. Q: How do I know if my BiPAP mode is working? Signs of effective BiPAP therapy: waking feeling refreshed, AHI below 5 (visible on machine display or app), no morning headaches, no excessive daytime sleepiness, SpO above 94% overnight (if monitored). If you are experiencing persistent fatigue, headaches, or high AHI despite using the machine, your mode or settings may need adjustment. Q: Which BiPAP machines support AVAPS and iVAPS in India? AVAPS is available on the Philips Dream Station BiPAP ST-A and Philips A40ventilator. iVAPS is available on the ResMed AirCurve 10 ST-A and ResMed Lumis series. These are prescription-grade machines available for rent through Healthy Jeena Sikho for patients with COPD, OHS, or neuromuscular disease. Q: Can BiPAP be used without a humidifier? Yes, but heated humidification is strongly recommended for most BiPAP patients — especially at higher pressures. Without humidification, the dry pressurised air can cause nasal dryness, congestion, nosebleeds, and sore throat, which reduces compliance. Most modern BiPAP machines have an integrated heated humidifier. Need a BiPAP Machine on Rent in India? Healthy Jeena Sikho supplies BiPAP S, ST, and AVAPS machines from Philips, ResMed, and BMC on rental across Delhi NCR, Mumbai, Bangalore, Hyderabad, Chandigarh, and 15+ cities. All machines are clinically sanitised, set up at your home by our trained team, and backed by 24/7 support. We work with your doctor to ensure you receive the correct mode and pressure settings. Call / WhatsApp: +91 98769 78488 | www.healthyjeenasikho.com