The choice of oxygen delivery interface — nasal cannula, simple mask, non-rebreather, or Venturi — is not interchangeable. Each delivers a different range of FiO₂ at different flow inputs, each has specific indications, and each fails in specific ways. A patient with a non-rebreather at 6 L/min is being under-delivered; a COPD patient in hypercapnic failure on a 50% Venturi is being correctly delivered a calibrated high FiO₂; a Type-II respiratory failure patient on a simple mask at 5 L/min is at risk of CO₂ rebreathing. This article covers what each interface actually delivers, where it is indicated, and how to pick correctly — including the fit issues that Indian facial morphology creates for masks sized for European or North American populations.
The audience is the respiratory therapist, nursing staff applying oxygen in emergency or ward settings, and home-care personnel equipping patients with the right interface for the prescribed flow.
The interfaces at a glance
| Interface | Flow range | Approx FiO₂ | Reservoir | Entrainment | Humidification |
|---|---|---|---|---|---|
| Nasal cannula (standard) | 1–6 L/min | 24–44% | None | Uncontrolled room air | Limited, needs add-on |
| Nasal cannula (high-flow) | 15–60 L/min | 30–100% | None | Controlled via blender | Heated, integrated |
| Simple mask | 5–10 L/min | 40–60% | None | Via side ports | Limited |
| Non-rebreather mask | 10–15 L/min | 60–90% | 600–1000 mL bag | Minimal (one-way valves) | Limited |
| Venturi mask | 4–15 L/min (device-specific) | Fixed 24, 28, 31, 35, 40, 50% | Fixed jet entrainment | Calibrated room-air mix | Can be heated |
| Partial rebreather mask | 6–10 L/min | 40–70% | 600–1000 mL bag | Partial expired gas re-entry | Limited |
The key concept distinguishing these devices is whether the delivered FiO₂ is fixed-performance (Venturi, HFNO) or variable-performance (cannula, simple mask, non-rebreather). Variable-performance interfaces deliver an FiO₂ that depends on the patient’s inspiratory flow rate, minute ventilation, and breathing pattern — a tachypnoeic patient with high peak inspiratory flow dilutes the delivered oxygen with room air, lowering effective FiO₂. Fixed-performance interfaces deliver a consistent FiO₂ regardless of patient breathing pattern.
Nasal cannula — 1 to 6 L/min
The nasal cannula is the default home and ward oxygen interface. Two prongs sit in the nostrils, the cannula loops over the ears, and oxygen flows from the concentrator output through the tubing into the naris.
Flow range. 1–6 L/min. Above 6 L/min, the gas is uncomfortably cold and dry, the nasal mucosa crusts, and the gain in FiO₂ is small. For > 6 L/min, switch to a mask or to high-flow nasal oxygen.
FiO₂ delivered. Rough rule: each 1 L/min adds ~4 percentage points to FiO₂ above room air (21%). So 1 LPM ≈ 24%, 2 LPM ≈ 28%, 3 LPM ≈ 32%, 4 LPM ≈ 36%, 5 LPM ≈ 40%, 6 LPM ≈ 44%. These are population averages. A tachypnoeic patient at 4 LPM may receive only 30% FiO₂ at the airway; a slow, quiet breather may receive 40%.
Indications.
- All LTOT at flows ≤ 6 LPM.
- Ward oxygen for stable patients without significant respiratory distress.
- Post-operative recovery at modest flows.
- Paediatric home oxygen (with appropriate paediatric cannula sizing).
Failure modes.
- Mouth-breathers receive reduced FiO₂ — the oxygen flows past closed nostrils and escapes.
- Nasal obstruction (polyps, deviated septum, upper respiratory infection) reduces delivery to the affected side.
- Cannula displacement overnight is common; check that the prongs remain in the nostrils at morning review.
- Skin breakdown behind the ears with prolonged use. Ear-loop cushions or tape across the cheeks reduce this.
- Dry mucosa, epistaxis, and crusting with extended use, particularly in dry Indian climates (Delhi winter, Rajasthan). Humidification via bubble humidifier helps; at flows ≥ 3 LPM in dry climates, humidification becomes important.
Indian facial-fit considerations. Paediatric cannulas are sized for small faces but adult Indian facial morphology tends toward smaller noses and smaller ear-loop-to-chin distances than the North American sizing base. Some ear-loop cannulas sit loose; the prong may be inadequately seated in the nostril. Pre-formed curved cannulas (Salter-style with nasal bend) fit better for many Indian adult patients than the straight prong types.
Simple mask — 5 to 10 L/min
A plastic mask covering the mouth and nose with side ports for exhalation and room-air entrainment. Oxygen flows into the mask at 5–10 L/min.
Flow range. Minimum 5 L/min to avoid CO₂ rebreathing. Maximum usable around 10 L/min — above this, the mask overfills and the patient is not getting benefit proportional to flow.
FiO₂ delivered. Variable. Approximately 40% at 5 LPM, 55–60% at 10 LPM. High patient minute ventilation or tachypnoea reduces delivered FiO₂ via side-port entrainment.
Indications.
- Ward or emergency oxygen at flows where cannula is inadequate.
- Short-term higher-FiO₂ delivery.
- Post-anaesthetic recovery.
Failure modes.
- CO₂ rebreathing if flow is too low. Never run a simple mask below 5 L/min. If the patient cannot tolerate 5 L/min, use a cannula instead.
- Claustrophobia, particularly in confused or anxious patients.
- Mask interferes with eating, drinking, and communication.
- Humidification is poor unless a heated humidifier is added upstream.
- The Indian patient with a smaller facial profile may have gaps at the mask edges; size the mask (paediatric, small-adult, medium-adult, large-adult) to the face.
Clinical position. Simple masks are widely used but rarely optimal. For stable oxygen delivery at equivalent FiO₂, Venturi is more predictable. For higher FiO₂, non-rebreather delivers more. Simple masks occupy a middle ground that is often filled by better choices in well-equipped settings.
Non-rebreather mask — 10 to 15 L/min
A simple mask fitted with a 600–1000 mL reservoir bag beneath the mask and a one-way valve between the bag and the mask. On inspiration, the one-way valve opens and the patient inhales from the bag (which has been filling with high-concentration oxygen). On expiration, expired gas is directed out side ports via additional one-way valves, preventing expired CO₂ from entering the reservoir.
Flow range. 10–15 L/min. The flow must be sufficient to keep the reservoir bag inflated throughout inspiration — a bag that deflates on each breath is running at insufficient flow.
FiO₂ delivered. Approximately 60–90%. The upper end requires a well-sealed mask and an intact one-way valve system. In practice, most bedside non-rebreathers deliver 70–80% FiO₂.
Indications.
- Severe acute hypoxaemia — pneumonia, pulmonary oedema, acute exacerbation of COPD (with caution in CO₂ retainers), acute respiratory failure bridge.
- Pre-intubation oxygenation.
- CO poisoning (delivers 100% FiO₂ to promote COHb off-loading; here specifically, non-rebreather is the intended therapy until hyperbaric therapy is available).
Failure modes.
- Inadequate flow → bag deflates → patient rebreathes exhaled gas and effective FiO₂ drops.
- Mask leaks → room-air entrainment → FiO₂ drops below advertised.
- Confused patients pull it off.
- Not appropriate for long-term use — typically a transitional device for hours, not days.
- Humidification is minimal.
Indian facial-fit considerations. Non-rebreathers are shipped in adult and paediatric sizes. For Indian adult patients with smaller faces, the small-adult size often fits better than the default medium-adult. Check mask seal at initial placement.
Price context. Non-rebreather masks in the Indian hospital disposables market: ₹80–250 per mask depending on brand, often used as single-patient single-use. The difference between a ₹80 and ₹250 non-rebreather is usually the quality of the one-way valves and the reservoir-bag material — the cheaper masks leak more and deliver lower FiO₂ than their advertised specification.
Venturi mask — calibrated FiO₂ via jet entrainment
A mask with a specific “Venturi adapter” at the inlet, sized for a particular FiO₂ (24, 28, 31, 35, 40, 50%). The adapter has a calibrated jet that creates a constant entrainment ratio — a known volume of room air is drawn in for every volume of oxygen passing the jet. Each adapter is typically colour-coded: blue for 24%, yellow for 28%, white for 31%, green for 35%, pink for 40%, orange for 50%.
Flow range. The specified flow varies by FiO₂ setting — lower FiO₂ uses lower driving flow (4–6 LPM for 24–28%) and higher FiO₂ uses higher driving flow (8–15 LPM for 40–50%). Each adapter has its recommended flow printed on it.
FiO₂ delivered. Fixed within narrow tolerance. A 28% Venturi delivers 28% FiO₂ at the airway regardless of whether the patient is quietly breathing or tachypnoeic. This is the defining property of a fixed-performance interface.
Indications.
- COPD with type-II respiratory failure or CO₂ retention risk — calibrated low FiO₂ (24–28%) avoids over-oxygenation and the hypercapnic-drive suppression that large-volume uncalibrated oxygen can cause (British Thoracic Society).
- Any clinical situation where a specific, reproducible FiO₂ is needed (titration studies, pulmonary-hypertension vasodilator trials).
- Patients whose FiO₂ requirement is known and whose tachypnoea would make variable-performance interfaces unpredictable.
Failure modes.
- Adapter mismatch — wrong adapter for the prescribed FiO₂ delivers the wrong concentration. Double-check the colour code and the printed FiO₂.
- Patient removes the mask or sleeps turned sideways — the entrainment jet requires unobstructed room-air flow.
- Low driving flow → the jet under-entrains and FiO₂ drifts off-target.
- Humidification is possible via heated inline humidifiers but reduces the predictability of delivered FiO₂ slightly.
Clinical position. Venturi is the correct interface for COPD patients in acute hypercapnic respiratory failure during emergency-department triage and early ward admission. It is also correct for any situation requiring calibrated FiO₂. It is not necessary for routine LTOT at home.
Price context. Venturi masks are sold as sets (one mask with multiple colour-coded adapters) at ₹150–500 per set. Adequate hospital inventory of all colour codes is a quality-of-care marker.
Partial rebreather mask
A less-common variant of the non-rebreather — a reservoir bag but without the one-way valve between the bag and the mask. The patient exhales the first portion of expired gas (dead-space, still high in oxygen, low in CO₂) back into the bag, then remaining expired gas vents out the side ports. FiO₂ delivered is typically 40–70% at 6–10 L/min. Used less frequently in modern Indian practice; non-rebreather has largely replaced it where available.
High-flow nasal oxygen (HFNO)
Not a disposable mask interface, but worth noting in context. HFNO (Optiflow, Airvo 2, Fisher & Paykel systems; Respironics V60 with compatible circuit; CPAP-adapted setups) delivers heated, humidified oxygen at 30–60 L/min via wide-bore nasal cannula, with FiO₂ titratable via blender from 21 to 100%. HFNO is hospital equipment; it is increasingly available in Indian tertiary ICUs post-COVID. At home, HFNO is not standard, though some post-transplant and selected chronic patients have been equipped with AIRVO units for long-term home use in developed markets.
Humidity across the interfaces
Oxygen from a concentrator is dry (2–5% relative humidity). Ambient room air is 30–70% RH. The airway normally receives gas at 100% RH at body temperature (37°C). Supplemental oxygen without added humidity thus desiccates the airway.
Bubble humidifier. Appropriate for cannula flows ≤ 4–5 L/min and for simple mask flows. Not appropriate as the sole humidifier for flows > 6 LPM.
Pass-over humidifier. Better than bubble at higher flows. Not heated.
Heated humidifier. Required for HFNO, and beneficial for any prolonged high-flow setup. Adds cost and complexity.
Integrated mask/circuit humidifier. HFNO systems (Airvo, Optiflow) integrate heated humidification. Standard masks do not.
Humidity mismatch clinical consequences — dry gas causes mucosal crusting, epistaxis, mucus plug formation, and (in paediatrics) airway obstruction. Indian dry climates (Delhi winter, Chandigarh winter, Rajasthan) amplify the problem. Coastal humidity is in a sense protective for cannula use; it also stresses the concentrator filter.
Indian disposables market and pricing
Approximate 2026 prices in the Indian hospital and home-care disposables market:
- Standard adult nasal cannula (3-metre tubing, single-use) — ₹20–60.
- Extended-tubing (7–10 metre) nasal cannula — ₹80–150.
- Pre-formed Salter-style cannula — ₹120–250.
- Paediatric cannula — ₹40–100.
- Simple mask with tubing — ₹60–150.
- Non-rebreather mask with reservoir bag — ₹80–250.
- Venturi mask set with adapters — ₹150–500.
- Bubble humidifier bottle (disposable, pre-filled) — ₹60–200.
- Bubble humidifier bottle (refillable) — ₹200–500.
- Heated humidifier (standalone) — ₹8,000–25,000.
Single-patient single-use is the hospital standard. Home patients in India commonly reuse cannulas for weeks or longer — the cost constraints make this understandable, but cannulas should be replaced at least monthly and immediately on visible soiling or kinking. Tubing that has developed a crack or a kink affects flow delivery.
Picking the interface in practice
For the prescriber facing a new oxygen prescription:
- Stable LTOT, flow 1–6 LPM → nasal cannula.
- Ward oxygen, moderate-flow, FiO₂ 40–60% needed short-term → simple mask at 5–10 LPM.
- Severe acute hypoxaemia, bridging to ICU or intubation, FiO₂ 60–90% needed → non-rebreather at 10–15 LPM.
- COPD with known or suspected CO₂ retention, acute setting → Venturi 24% or 28%.
- Any setting requiring calibrated reproducible FiO₂ → Venturi.
- Exertional-desaturation home patient needing intermittent high FiO₂ → cannula at home, simple mask for exertion if desaturation persists.
- Advanced ILD patient needing > 6 LPM at rest → consider non-rebreather bridging or dual concentrators with cannula, and reassess equipment adequacy.
Clinical takeaway
Interface selection matters at least as much as flow rate in determining what oxygen the patient actually receives. Nasal cannula for stable flows up to 6 L/min; simple mask for 5–10 L/min where cannula is inadequate; non-rebreather for severe acute hypoxaemia at 10–15 L/min; Venturi when a calibrated fixed FiO₂ is clinically important (especially in COPD with CO₂ retention). Humidification is not optional at higher flows and in dry Indian climates. Fit matters — Indian facial morphology warrants small-adult sizing in many patients, and pre-formed cannulas often fit better than ear-loop types.
Consult your physician before changing the oxygen interface; the correct cannula versus mask decision depends on diagnosis, flow, and failure-mode risk, not on family preference or ward stock availability.