AVAPS vs iVAPS vs BiPAP ST - A Complete, Plain-Language Guide to Advanced BiPAP Modes
- Rajat Chauhan
- Jun 7, 2025
- 13 min read
Updated: 1 day ago
Who this is for: Patients, caregivers, and family members who have been prescribed—or are considering—an advanced BiPAP machine, and want to understand what these modes actually do before spending ₹1–3 lakh on
equipment.
Quick Answer
BiPAP ST adds a timed backup breath to standard BiPAP — used for central apnea and neuromuscular disease.
AVAPS (Philips) auto-adjusts pressure to deliver a consistent target tidal volume — used mainly for OHS and COPD with hypercapnia.
iVAPS (ResMed) does the same goal differently — it targets alveolar ventilation using a physiological algorithm, not just tidal volume.
All three require a doctor's prescription and a specialist setup. Do not adjust these settings yourself
What Are Advanced BiPAP Modes — And Who Needs Them?
Most people with obstructive sleep apnea (OSA) are treated with a CPAP or standard BiPAP. These work well for the majority. But a subset of patients have more complex conditions — their lungs or breathing muscles don't work properly, they retain CO2 at night, or they have both obstructive and central apneas. For these patients, standard BiPAP isn't enough.
Advanced BiPAP modes — BiPAP ST, AVAPS, and iVAPS — were developed to handle these harder cases. They go beyond simply splitting airway pressure into two levels (IPAP and EPAP). They actively adapt breath-by-breath to ensure the patient gets adequate ventilation, even when their own breathing effort is inconsistent.
Mode | What It Controls | Adapts Automatically? | Typical Use |
CPAP | Single fixed pressure | No | Simple OSA |
APAP | Single pressure (auto-range) | Yes — pressure only | OSA with variable needs |
BiPAP S | Fixed IPAP + fixed EPAP | No | OSA needs two-level pressure |
BiPAP ST | Fixed IPAP/EPAP + backup rate | No (rate is fixed) | Central apnea, NMD, COPD |
AVAPS | IPAP adjusts to hit the target volume; fixed EPAP | Yes — IPAP | OHS, COPD with hypercapnia |
AVAPS-AE | Both IPAP and EPAP auto-adjust | Yes — both | OHS + residual obstructions |
iVAPS | Targets alveolar ventilation; adjusts pressure support | Yes — pressure support | NMD, OHS, COPD, central apnea |
Who typically gets prescribed these modes?
Obesity Hypoventilation Syndrome (OHS) — excess weight makes breathing inefficient; CO2 builds up overnight
COPD with nocturnal hypoventilation — lungs can't expel CO2 properly
Neuromuscular diseases — ALS, Muscular Dystrophy, Post-Polio Syndrome
Central sleep apnea — the brain doesn't send consistent signals to breathe
Complex/mixed apnea — both obstructive and central events
Post-ICU step-down — weaning off invasive ventilation
What is BiPAP ST Mode?
BiPAP ST stands for Spontaneous/Timed. It is the simplest of the three advanced modes and is often the first step up from standard BiPAP S when a patient has inconsistent or inadequate breathing.
In standard BiPAP S (Spontaneous) mode, the machine only delivers a breath when it detects the patient has started to inhale. If the patient's respiratory drive is weak and they don't initiate a breath, the machine waits — and does nothing. For patients with neuromuscular disease, COPD, or central apnea, this can lead to long pauses in breathing during sleep.
BiPAP ST adds a Timed backup: if the patient does not take a breath within a set number of seconds, the machine delivers one automatically. This ensures a minimum breathing rate even if the patient's brain or muscles fail to trigger a breath.
BiPAP S vs BiPAP ST — Key Difference
Feature | BiPAP S | BiPAP ST |
Breath triggered by | Patient only | Patient or timer (whichever comes first) |
Backup rate | None | Yes — set in breaths/minute (BPM) |
Protection against apnea | None | Yes — guarantees minimum rate |
Settings needed | IPAP, EPAP | IPAP, EPAP, Backup Rate, I-Time |
Typical users | OSA, simple hypoventilation | Central apnea, NMD, COPD, overlap |
BiPAP ST Settings Explained
IPAP (Inspiratory Positive Airway Pressure) — The higher pressure delivered when the patient inhales. Typically 10–25 cmH2O. Higher IPAP = larger breath volume.
EPAP (Expiratory Positive Airway Pressure) — The lower pressure during exhalation. Typically 4–8 cmH2O. Keeps the airway open and prevents collapse.
Backup Rate (BPM) — Breaths per minute guaranteed by the machine. If the patient takes 14 breaths on their own, the machine doesn't intervene. If they slow to 10, the machine triggers the remaining 4.
I-Time (Inspiratory Time) — How long the IPAP pressure lasts per breath. Usually 0.8–1.5 seconds. Longer I-Time = more air delivered per breath.
Rise Time — How quickly pressure ramps up from EPAP to IPAP at the start of each breath. Faster rise = more abrupt; slower rise = softer, more natural feel.
When does a doctor prescribe BiPAP ST instead of BiPAP S?
Your overnight sleep study (polysomnography) or nocturnal oximetry shows persistent central apneas (breathing pauses without airway obstruction). OR your neuromuscular disease means you cannot reliably trigger every breath. OR your COPD is causing CO2 retention that BiPAP S alone can't correct because you have too many missed breaths.
What Is AVAPS? (Average Volume Assured Pressure Support)
AVAPS is a pressure mode developed by Philips Respironics, available on their DreamStation, A30, and A40 BiPAP machines. The name describes exactly what it does: it assures that the average tidal volume (the size of each breath) stays close to a target set by your doctor.
With standard BiPAP ST, the IPAP pressure is fixed. If your breathing muscles get tired at 2 am and your tidal volume drops from 500 mL to 350 mL, the machine doesn't notice — it just keeps delivering the same IPAP. You could be under-ventilated for hours.
AVAPS notices this. It continuously measures the tidal volume it's delivering and adjusts the IPAP up or down — slowly, over multiple breaths — to bring it back toward your target. If your muscles are working well, IPAP stays low. If they weaken, IPAP increases. The result is more consistent CO2 removal throughout the night.
How AVAPS Works — Step by Step
Step | What Happens |
1. Doctor sets the target | A tidal volume target is set — typically 8–10 mL per kg of ideal body weight (e.g., 500 mL for a 60 kg patient) |
2. Machine measures | Every few breaths, AVAPS measures the actual exhaled tidal volume |
3. IPAP adjusts | If actual volume < target, IPAP increases slightly. If actual > target, IPAP decreases slightly |
4. IPAP stays in range | IPAP cannot go below IPAP_min or above IPAP_max — set by your doctor to keep therapy safe and comfortable |
5. EPAP stays fixed | Unlike AVAPS-AE, standard AVAPS does not adjust EPAP — it remains constant |
AVAPS Settings Explained
IPAP Min — The lowest pressure AVAPS will use. Set to the minimum needed to prevent hypoventilation on a good night. If set too low, CO2 may rise.
IPAP Max — The ceiling. AVAPS will never exceed this. Protects against discomfort from excessively high pressures. Typically 5–8 cmH2O above IPAP Min.
EPAP — Fixed. Set to keep the airway open. If the patient still has obstructive events, the doctor may increase EPAP or switch to AVAPS-AE.
Target Tidal Volume — The goal breath size in mL. Calculated by a doctor based on ideal body weight. Most adults: 400–600 mL.
Backup Rate — Available in AVAPS mode (it operates like a BiPAP ST underneath). Set to ensure a minimum breathing rate.
What Is AVAPS-AE? (Auto-EPAP)
AVAPS-AE is an enhanced version of AVAPS available on Philips DreamStation machines. The 'AE' stands for Auto EPAP — meaning the machine automatically adjusts EPAP as well as IPAP.
Standard AVAPS fixes the EPAP. If a patient with OHS also has residual obstructive apneas that only appear at certain sleep positions or REM stages, a fixed EPAP may not always be enough to keep the airway open. AVAPS-AE detects these obstructions and raises EPAP dynamically to resolve them — essentially combining AVAPS volume targeting with APAP-like obstruction response.
Feature | AVAPS | AVAPS-AE |
EPAP | Fixed | Auto (adjusts to resolve obstructions) |
IPAP | Auto (targets tidal volume) | Auto (targets tidal volume) |
Best for | Hypoventilation without residual OSA | Hypoventilation WITH residual obstructive events |
Available on | Philips A30, A40, DreamStation BiPAP | Philips DreamStation BiPAP AVAPS-AE |
What is iVAPS? (Intelligent Volume Assured Pressure Support)
iVAPS is ResMed's equivalent to AVAPS, available on their AirCurve 10 VAuto, Lumis 100, and Lumis 150 machines. Like AVAPS, it automatically adjusts pressure to ensure adequate ventilation. But the underlying algorithm is meaningfully different.
Where AVAPS targets tidal volume (the total volume of air per breath), iVAPS targets alveolar ventilation — the amount of air that actually reaches the alveoli (the gas-exchange sacs in the lungs) and does useful work. This is a more physiologically precise target because not all the air you inhale reaches the alveoli — some stays in the airways (dead space) and does not exchange gas.
iVAPS estimates the patient's dead space and subtracts it to target only the ventilatory work that matters for CO2 removal. The result is that iVAPS can work at lower, more comfortable pressures for some patients, because it isn't chasing overall tidal volume — it's chasing effective ventilation.
How iVAPS Differs from AVAPS
Aspect | AVAPS (Philips) | iVAPS (ResMed) |
What it targets | Tidal volume (total breath size) | Alveolar ventilation (effective gas exchange) |
Algorithm basis | Volume averaging over several breaths | Physiological model: estimates dead space, breathing frequency |
Pressure adjusted | IPAP only (EPAP fixed in standard) | Pressure Support (difference between IPAP and EPAP) |
Backup rate handling | Fixed backup rate (ST-like) | Targets minute ventilation; adjusts rate dynamically |
Response speed | Slow, averaging — less reactive | Can respond faster to sudden changes |
Pressure range needed | May need higher IPAP Max | Often comfortable at lower PS due to dead-space correction |
Machine brand | Philips Respironics | ResMed |
Available machines | A30, A40, DreamStation AVAPS | AirCurve 10 VAuto, Lumis 100/150 VPAP ST-A |
iVAPS Settings Explained
Target Alveolar Ventilation (VA) — Set by the doctor based on body weight and CO2 target. The machine works backwards from this to determine how much pressure support is needed.
Dead Space — The machine can be programmed with an estimated dead space value (default ~150 mL for most adults). This refines the algorithm.
Pressure Support Min/Max — The range within which PS can vary. Like AVAPS's IPAP Min/Max, this keeps therapy safe and bounded.
EPAP — Can be fixed or set to auto in ResMed's implementation.
Backup Rate — A minimum rate is set; iVAPS adjusts above it as needed to meet the ventilation target.
Practical difference for patients:
You won't feel a meaningful difference between AVAPS and iVAPS night-to-night — both feel like a BiPAP that gently adjusts itself. The difference is in how well they handle your specific condition. Your pulmonologist will choose based on: your diagnosis, your CO2 targets from blood gas results, and which machine is available in your city. In Chandigarh, Delhi, Jaipur, and Lucknow, Healthy Jeena Sikho stocks Philips AVAPS machines for both rent and sale.
AVAPS vs iVAPS vs BiPAP ST: Full Side-by-Side Comparison
Feature | BiPAP ST | AVAPS (Philips) | iVAPS (ResMed) |
Volume targeting | No — fixed IPAP | Yes — tidal volume | Yes — alveolar ventilation |
IPAP auto-adjusts | No | Yes | Yes (via PS adjustment) |
EPAP auto-adjusts | No | No (AVAPS-AE: Yes) | Optional |
Backup rate | Fixed BPM | Fixed BPM | Dynamic (adjusts to meet VA target) |
Algorithm type | Timed trigger | Volume averaging | Physiological model |
Complexity | Lowest | Medium | Highest |
Setup requires | IPAP, EPAP, Rate, I-Time | IPAP Min/Max, EPAP, Target Vol, Rate | Target VA, Dead Space, PS Min/Max, EPAP, Rate |
Machines (India) | Multiple brands | Philips A30, A40, DreamStation | ResMed AirCurve, Lumis |
Rent/Buy in India | Yes — widely available | Yes — Healthy Jeena Sikho | Less common — check availability |
Which Mode Does Your Doctor Prescribe and When?
The mode choice is always based on your diagnosis, overnight blood gas or oximetry results, and how well simpler therapy has worked. Here is how doctors typically progress:
Condition | First Line | If First Line Fails / More Severe | Notes |
Obesity Hypoventilation Syndrome (OHS) | CPAP or BiPAP S | AVAPS or AVAPS-AE | If CO₂ is still elevated after 3 months on CPAP |
COPD with nocturnal hypercapnia | BiPAP ST | AVAPS or iVAPS | Target pCO₂ < 45–50 mmHg |
Neuromuscular disease (ALS, MD, SMA) | BiPAP ST | iVAPS or AVAPS | iVAPS preferred by some clinicians — lower pressures |
Central sleep apnea | CPAP or ASV | ASV contraindicated if EF < 45% (heart failure) | |
Complex/mixed apnea | APAP or AVAPS-AE | iVAPS | Both obstructive and central components are present |
Post-polio syndrome | BiPAP ST | iVAPS or AVAPS | Nocturnal hypoventilation often progresses |
Post-ICU weaning | BiPAP ST | iVAPS | Hospital step-down; ResMed Lumis used in wards |
Which Machines Offer These Modes in India?
Not every BiPAP machine in India supports AVAPS or iVAPS. These are specialist modes found only on higher-end devices. Below are the main machines available:
Mode | Machine Model | Brand | Rent / Buy |
BiPAP ST | DreamStation BiPAP ST, AirCurve 10 S, BMC RESmart | Philips/ResMed/BMC | Rent & Sale — widely available |
AVAPS | DreamStation BiPAP AVAPS, A30, A40 | Philips Respironics | Available at Healthy Jeena Sikho |
AVAPS-AE | DreamStation BiPAP AVAPS-AE | Philips Respironics | Available at Healthy Jeena Sikho |
iVAPS | AirCurve 10 VAUTO, Lumis 100 VPAP ST-A, Lumis 150 VPAP ST-A | ResMed | Check availability |
Renting vs Buying an AVAPS/iVAPS Machine
These machines cost ₹1–3 lakh to purchase outright. Renting is the smart first step — it lets you confirm the therapy works and your settings are right before committing to a purchase.
Healthy Jeena Sikho offers monthly rental of Philips AVAPS machines with door delivery across Chandigarh, Delhi, Jaipur, and Lucknow. A doctor's prescription for the mode and settings is required.
Understanding Your Machine's Settings (For Patients and Caregivers)
If you or a family member has just been set up on an AVAPS, AVAPS-AE, or iVAPS machine, the settings screen may look intimidating. Here is a plain-language guide to what each number means — not so you change them, but so you understand what the machine is doing.
Settings Common to All Three Modes
EPAP (4–12 cmH2O typically) — Think of this as the 'floor pressure' that keeps your airway from collapsing while you breathe out. Too low and the airway collapses. Too high and it's hard to exhale.
Backup Rate (8–14 BPM typically) — The machine's safety net. If you stop breathing for more than a few seconds, it delivers a breath. You won't notice this unless your breathing actually stops.
I-Time (0.8–1.5 sec) — How long each machine-triggered breath lasts. Shorter = faster, more natural. Longer = more air per breath.
Rise Time (1–6 on most machines) — How quickly pressure goes from EPAP to IPAP at the start of a breath.
Lower number = faster, more abrupt.
Higher = softer ramp. Most people prefer 2–3.
Settings Specific to AVAPS
IPAP Min and IPAP Max — The range within which AVAPS adjusts. If your doctor sets IPAP Min = 12 and IPAP Max = 20, the machine will never go below 12 or above 20 cmH2O — it will find the right level within this band.
Target Tidal Volume (e.g., 500 mL) — The breath volume the machine is trying to achieve. Roughly: ideal body weight in kg × 8–10 mL.
Settings Specific to iVAPS
Target Alveolar Ventilation (e.g., 4.5 L/min) — How much useful breathing the machine targets per minute. Your pulmonologist calculates this from your ideal body weight and CO2 targets.
Estimated Dead Space (default ~150 mL) — The amount of each breath that doesn't reach the alveoli. iVAPS uses this to be more precise. Usually left at the default unless your doctor changes it.
Important: Never Change These Settings Yourself
AVAPS and iVAPS settings are calculated from blood gas results, lung function tests, and overnight oximetry data. Changing IPAP Max, target volume, or backup rate without medical guidance can result in under-ventilation (CO2 builds up) or pressure discomfort. If your machine feels wrong — contact your prescribing doctor or call Healthy Jeena Sikho's support line for guidance
Frequently Asked Questions
Q1. Is AVAPS the same as BiPAP?
No. AVAPS is an advanced mode that runs on a BiPAP-type machine. A standard BiPAP delivers fixed IPAP and EPAP — what you set is what you get, all night. AVAPS adds volume targeting: it adjusts IPAP automatically to ensure each breath delivers a consistent volume. All AVAPS machines are BiPAPs, but not all BiPAPs are AVAPS.
Q2. Which is better — ResMed iVAPS or Philips AVAPS?
Neither is universally better. Both are clinically validated for OHS, COPD, and neuromuscular disease. iVAPS uses a more physiologically sophisticated algorithm that can work at lower pressures for some patients. AVAPS is simpler to set up and very well-studied. The choice depends on your diagnosis, your pulmonologist's preference, and which machines are available in your city. In North India, Philips AVAPS machines are more widely stocked.
Q3. Can I switch from CPAP to AVAPS or iVAPS myself?
No — and this is important. CPAP, AVAPS, and iVAPS are fundamentally different therapy modes. AVAPS and iVAPS require a different prescription, specific settings calculated from your blood gas results and body weight, and ideally an initial titration study. Using an AVAPS machine on CPAP settings will not work correctly.
Q4. What diseases require iVAPS or AVAPS therapy?
The main conditions are: Obesity Hypoventilation Syndrome (OHS), COPD with nocturnal CO2 retention (hypercapnia), neuromuscular diseases (ALS, Muscular Dystrophy, Post-Polio Syndrome, Spinal Muscular Atrophy), central sleep apnea (where ASV is not appropriate), and complex/mixed apnea not controlled by CPAP.
Q5. Does AVAPS help with CO2 levels?
Yes — that is its primary purpose. By ensuring a consistent tidal volume breath after breath, AVAPS ensures adequate ventilation. Adequate ventilation means CO2 is being expelled normally. Studies show AVAPS can bring elevated CO2 levels back to the normal range in OHS and COPD patients within weeks of starting therapy.
Q6. What is the difference between AVAPS and AVAPS-AE?
Standard AVAPS only auto-adjusts IPAP while keeping EPAP fixed. AVAPS-AE also auto-adjusts EPAP — like an APAP function — to handle residual obstructive events. AVAPS-AE is used when a patient has both hypoventilation AND ongoing obstructive apneas that a fixed EPAP can't fully control.
Q7. Can I rent a Philips AVAPS machine in Chandigarh or Delhi?
Yes. Healthy Jeena Sikho offers monthly rental of Philips DreamStation AVAPS and AVAPS-AE across Chandigarh, Delhi, Jaipur, and Lucknow. Door delivery is available. A doctor's prescription specifying the mode and settings is required before rental or purchase.
Q8. How long does it take to adjust to AVAPS or iVAPS?
Most patients feel the difference in the first 2–4 weeks — better morning energy, reduced headaches (caused by overnight CO2 build-up), and improved daytime alertness. Full adaptation — where the body adjusts to consistent overnight ventilation — typically takes 4–8 weeks. Mask comfort and compliance are the biggest factors in whether therapy succeeds.
Q9. Is BiPAP ST covered by insurance in India?
Some corporate health insurance plans and TPA schemes cover BiPAP ST and AVAPS machines under Durable Medical Equipment (DME) benefits, but this varies by insurer and policy. Most policies require a specialist prescription (pulmonologist or sleep physician) and a diagnostic report. Contact your insurer with your prescription for coverage verification.
Summary: How to Think About These Three Modes
If you're thinking... | The answer is... |
"My doctor said I need a backup rate because I stop breathing" | BiPAP ST — it guarantees a minimum breathing rate |
"I have OHS and my CO₂ is high even on CPAP" | AVAPS or AVAPS-AE (Philips) — auto-adjusts pressure to control CO₂ |
"I have ALS/MND and need non-invasive ventilation" | iVAPS or AVAPS — both validated for NMD; iVAPS may need lower pressures |
"I have both sleep apnea and high CO₂" | AVAPS-AE — targets volume AND handles obstructions |
"I can't afford to buy, I want to try first" | Rent a Philips AVAPS from Healthy Jeena Sikho — monthly rental, door delivery |
Medical Disclaimer: This article is for educational purposes only. AVAPS, iVAPS, and BiPAP ST are prescription medical therapies. All settings must be determined by a qualified pulmonologist or sleep specialist based on individual diagnostic results. Do not adjust your machine settings without medical guidance.
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