Respiratory failure: type 1 and type 2

10 min read Last updated April 8, 2026

Surgical approach (if applicable)

  • Not an operation: respiratory failure is a physiological syndrome with medical/critical care management.
  • Procedural/critical care interventions that may be required
    • Airway: tracheal intubation, tracheostomy (selected prolonged ventilation).
    • Ventilation: NIV (CPAP/BiPAP), invasive ventilation, recruitment manoeuvres, prone positioning (ARDS).
    • Circulation/monitoring: arterial line, central venous access, echocardiography, pulmonary imaging; treat underlying cause (e.g., antibiotics, diuresis, bronchodilators, anticoagulation).

Anaesthetic management (if applicable)

  • Not a single anaesthetic procedure; principles apply when providing anaesthesia/sedation to a patient in respiratory failure (e.g., for CT, bronchoscopy, surgery).
  • Type of anaesthesia
    • Prefer local/regional techniques where feasible to avoid worsening ventilation/perfusion and CO2 retention.
    • If GA required: plan for controlled ventilation; avoid long apnoea; pre-oxygenate; consider RSI if aspiration risk; haemodynamic optimisation.
  • Airway device
    • ETT often preferred in significant respiratory failure (allows PEEP, controlled ventilation, suction, bronchoscopy).
    • SGA may be acceptable only in mild disease with preserved ventilation and low aspiration risk; beware hypercapnia with spontaneous ventilation under anaesthesia.
  • Duration
    • Procedure-dependent; minimise duration of sedation/GA; anticipate postoperative ventilatory support.
  • Pain
    • Pain increases ventilatory demand; use multimodal analgesia; avoid excessive opioids in type 2 failure; consider regional blocks/neuraxial where appropriate.
  • Perioperative priorities
    • Optimise oxygenation/ventilation pre-induction (NIV/CPAP, bronchodilators, diuresis, antibiotics).
    • Set ventilator to avoid VILI: low VT, appropriate PEEP, permissive hypercapnia if needed (unless contraindicated).
    • Plan extubation carefully; consider HDU/ICU; use NIV post-extubation in COPD/high-risk patients.

Definitions and classification

  • Respiratory failure = inability of the respiratory system to maintain adequate gas exchange.
  • Type 1 (hypoxaemic): PaO2 < 8.0 kPa on air (often with normal/low PaCO2).
    • Primary problem: oxygenation failure due to V/Q mismatch, shunt, diffusion limitation, or low inspired O2.
  • Type 2 (hypercapnic): PaCO2 > 6.0 kPa (often with hypoxaemia).
    • Primary problem: alveolar hypoventilation (reduced minute ventilation or increased dead space relative to ventilation).
  • Acute vs chronic type 2: chronic hypercapnia shows renal compensation (raised HCO3−, near-normal pH); acute has low pH.

Key physiology (high-yield)

  • Alveolar gas equation: PAO2 = FiO2 × (Patm − PH2O) − (PaCO2 / R).
    • At sea level on air: PAO2 ≈ 13–14 kPa (varies with PaCO2).
  • A–a gradient: PAO2 − PaO2; helps differentiate hypoxaemia due to hypoventilation/low FiO2 (normal A–a) vs V/Q mismatch/shunt/diffusion (raised A–a).
    • Normal increases with age; rough guide: (Age/4) + 4 (mmHg) or ~ (Age/4 + 1) kPa (approx).
  • V/Q mismatch: commonest cause of hypoxaemia; improves with supplemental O2 (unless large shunt).
  • Shunt (true shunt): perfusion without ventilation (e.g., consolidation, atelectasis, ARDS); hypoxaemia responds poorly to O2; improves with PEEP/recruitment and treating cause.
  • Hypoventilation: causes hypoxaemia with raised PaCO2 and typically normal A–a gradient; oxygen corrects PaO2 but not PaCO2 (may worsen CO2 in susceptible patients).
  • CO2 physiology: PaCO2 ∝ VCO2 / VA (alveolar ventilation). Small reductions in VA can cause large rises in PaCO2.

Causes

  • Type 1 causes (hypoxaemic)
    • V/Q mismatch: pneumonia, asthma/COPD exacerbation (early), pulmonary oedema, pulmonary embolism (often with hypocapnia initially), atelectasis.
    • Shunt: ARDS, lobar pneumonia, aspiration, severe atelectasis, intracardiac R→L shunt.
    • Diffusion limitation: interstitial lung disease, pulmonary fibrosis (often exertional hypoxaemia).
    • Low inspired O2: altitude; equipment/oxygen supply failure.
  • Type 2 causes (hypercapnic)
    • Airway/obstructive: COPD exacerbation, severe asthma (late), upper airway obstruction, OSA/OHS.
    • CNS depression: opioids, benzodiazepines, anaesthetics, brainstem stroke, head injury.
    • Neuromuscular: GBS, myasthenia, MND, spinal cord injury, phrenic nerve palsy.
    • Chest wall/ventilatory mechanics: kyphoscoliosis, obesity hypoventilation, flail chest, severe pain/splinting.
    • Increased dead space / ventilatory demand: severe COPD/emphysema, pulmonary embolism, sepsis/fever (increased CO2 production) with limited ventilatory reserve.

Clinical features

  • Type 1: dyspnoea, tachypnoea, cyanosis, agitation/confusion; may have signs of underlying cause (crackles, wheeze, fever, pleuritic pain).
  • Type 2: features of hypoventilation and CO2 retention: headache, drowsiness, confusion, asterixis, flushed skin, bounding pulse; may progress to coma.
  • Work of breathing: accessory muscle use, inability to speak, paradoxical breathing, exhaustion = impending ventilatory failure.

Investigations and interpretation

  • ABG: confirm PaO2/PaCO2, pH, HCO3−, lactate; compare with previous gases (chronicity).
  • Pulse oximetry: trend and response to oxygen; beware poor perfusion, dyshemoglobins, motion artefact.
  • CXR: pneumonia, oedema, pneumothorax, atelectasis; may be normal in PE/early asthma.
  • ECG/troponin/BNP where relevant; echocardiography for cardiac failure/right heart strain; CT pulmonary angiography if PE suspected.
  • Bedside: peak flow (asthma), spirometry if stable; NIF/VC in neuromuscular disease; ultrasound for effusion/pneumothorax; capnography if ventilated/sedated.

Immediate management (ABCDE)

  • A: airway patency; suction; consider adjuncts; early senior help; prepare for intubation if deteriorating.
  • B: oxygen strategy
    • Type 1: give high-concentration O2 initially (e.g., non-rebreathe) aiming SpO2 94–98% (unless at risk of hypercapnic failure).
    • At risk of type 2 (COPD/OHS/neuromuscular): controlled O2 aiming SpO2 88–92% pending ABG; reassess after 30–60 min.
  • B: ventilatory support escalation
    • CPAP: improves oxygenation in cardiogenic pulmonary oedema and some hypoxaemic failure (recruits alveoli, reduces shunt).
    • BiPAP/NIV: improves ventilation (reduces PaCO2) in COPD exacerbation with acute hypercapnic respiratory failure (AHRF).
    • Invasive ventilation: if NIV fails/contraindicated, severe hypoxaemia, inability to protect airway, exhaustion, haemodynamic instability, or reduced consciousness.
  • C: treat shock/arrhythmia; cautious fluids if pulmonary oedema; vasopressors if needed; consider sepsis bundle.
  • D: conscious level; consider CO2 narcosis, hypoxia, hypoglycaemia, stroke, toxins; reverse opioids carefully (naloxone titration).
  • E: temperature, infection source, PE risk, pneumothorax; analgesia; VTE prophylaxis; early ICU involvement.

Non-invasive ventilation (NIV): indications, contraindications, and targets

  • COPD AHRF: consider NIV when pH < 7.35 and PaCO2 > 6.0 kPa despite optimal medical therapy and controlled O2.
    • Also consider in OHS and some neuromuscular/chest wall disorders with hypercapnia.
  • Contraindications to NIV (practical exam list)
    • Inability to protect airway, vomiting/high aspiration risk, copious secretions, facial trauma/burns, recent upper GI surgery, uncooperative/agitated patient, severe haemodynamic instability, peri-arrest, untreated pneumothorax.
  • Monitoring and targets on NIV
    • Aim: improve pH, reduce PaCO2, reduce work of breathing, maintain SpO2 target range; repeat ABG after 1–2 hours and after changes.
    • Failure signs: worsening acidosis, persistent tachypnoea, rising PaCO2, deteriorating consciousness, intolerance, haemodynamic instability → intubate early.

Invasive ventilation principles (ICU/anaesthetic crossover)

  • Lung-protective ventilation: VT ~6 mL/kg predicted body weight; limit plateau pressure (commonly ≤30 cmH2O); appropriate PEEP; avoid high driving pressure.
  • Permissive hypercapnia may be acceptable to avoid barotrauma/volutrauma (contraindications include raised ICP, severe pulmonary hypertension/right heart failure in some cases, severe acidosis).
  • ARDS adjuncts: prone positioning, neuromuscular blockade (selected), conservative fluid strategy, recruitment manoeuvres (case-dependent).
  • COPD ventilation: avoid dynamic hyperinflation—lower RR, longer expiratory time, modest VT, accept higher PaCO2 if pH acceptable; monitor for auto-PEEP and hypotension.

Oxygen and CO2 retention in COPD (exam core)

  • Mechanisms of oxygen-induced hypercapnia
    • Reduced hypoxic pulmonary vasoconstriction → worsened V/Q mismatch → increased dead space and CO2 retention.
    • Haldane effect: oxygenation of Hb reduces CO2 carriage → increases PaCO2.
    • Reduced hypoxic ventilatory drive: usually smaller contribution than V/Q and Haldane, but relevant in some chronic retainers.
  • Practical implication: titrate O2 to 88–92% in patients at risk; check ABG; treat ventilation (NIV) rather than withholding oxygen in severe hypoxaemia.

Differentiating type 1 vs type 2 on ABG (pattern recognition)

  • Type 1: low PaO2 with normal/low PaCO2; often respiratory alkalosis early (tachypnoea).
  • Type 2 acute: raised PaCO2 with low pH; HCO3− normal/slightly raised.
  • Type 2 chronic: raised PaCO2 with near-normal pH and raised HCO3− (renal compensation).
  • Mixed disorders are common (e.g., COPD + sepsis → metabolic acidosis plus hypercapnia).
Define type 1 and type 2 respiratory failure and give typical ABG values.

Use kPa thresholds and describe the ABG pattern.

  • Type 1 (hypoxaemic): PaO2 < 8.0 kPa on air, with PaCO2 normal or low.
  • Type 2 (hypercapnic): PaCO2 > 6.0 kPa; PaO2 often low as well.
  • Acute type 2: low pH with little HCO3− rise; chronic type 2: raised HCO3− with near-normal pH.
A patient has PaO2 7.0 kPa, PaCO2 4.0 kPa on air. What mechanisms could explain this and how would you structure your differential?

This is type 1 respiratory failure (hypoxaemia with low/normal CO2).

  • Raised A–a gradient mechanisms: V/Q mismatch (commonest), shunt, diffusion limitation.
  • V/Q mismatch: pneumonia, pulmonary oedema, PE, asthma/COPD (early), atelectasis.
  • Shunt: ARDS, consolidation, aspiration, severe atelectasis; poor response to O2.
  • Diffusion: ILD/fibrosis (often exertional).
  • Low inspired O2: altitude/equipment failure (usually normal A–a gradient).
Explain the alveolar gas equation and how it helps interpret hypoxaemia in the viva.

State the equation, then apply it to A–a gradient reasoning.

  • PAO2 = FiO2 × (Patm − PH2O) − (PaCO2 / R).
  • If hypoxaemia with normal A–a gradient: think hypoventilation or low FiO2.
  • If hypoxaemia with raised A–a gradient: think V/Q mismatch, shunt, diffusion limitation.
A COPD patient on 15 L/min non-rebreathe becomes drowsy. Explain oxygen-induced hypercapnia.

Give the three mechanisms and indicate which is most important.

  • Worsened V/Q mismatch from reduced hypoxic pulmonary vasoconstriction → increased dead space and CO2 retention (major mechanism).
  • Haldane effect: oxygenation of Hb reduces CO2 binding → increases PaCO2.
  • Reduced hypoxic ventilatory drive: usually smaller contribution but can matter in chronic retainers.
  • Management: titrate O2 to SpO2 88–92%, repeat ABG, treat ventilation (NIV) rather than withholding oxygen if severely hypoxaemic.
Give indications and contraindications for NIV in acute hypercapnic respiratory failure.

Focus on COPD AHRF thresholds and practical contraindications.

  • Indication (COPD AHRF): pH < 7.35 with PaCO2 > 6.0 kPa despite optimal therapy and controlled oxygen.
  • Also: OHS, neuromuscular/chest wall disorders with hypercapnia (case-by-case).
  • Contraindications: inability to protect airway, vomiting/aspiration risk, copious secretions, facial trauma/burns, uncooperative patient, peri-arrest, severe instability, untreated pneumothorax.
How do you judge NIV success or failure, and when do you intubate?

Use clinical and ABG endpoints with early reassessment.

  • Reassess at 1–2 hours: improved pH, falling PaCO2, lower RR, reduced work of breathing, improved mental state, stable haemodynamics.
  • Failure: worsening acidosis, rising PaCO2, persistent tachypnoea/exhaustion, reduced consciousness, intolerance, haemodynamic instability, refractory hypoxaemia.
  • Intubate early if failing or contraindicated—avoid late crash intubation.
A patient has PaO2 6.5 kPa, PaCO2 8.5 kPa, pH 7.19. Classify and outline immediate management.

This is acute type 2 respiratory failure with severe acidaemia.

  • Controlled oxygen aiming SpO2 88–92% (unless peri-arrest—then treat hypoxaemia first).
  • Treat reversible causes: bronchodilators, steroids, antibiotics if infective, diuresis if oedema, naloxone if opioid-related, analgesia if splinting.
  • Start NIV urgently if appropriate and no contraindications; repeat ABG within 1 hour.
  • If reduced consciousness/exhaustion/instability or NIV failure: intubate and ventilate; anticipate hypotension (dynamic hyperinflation) in COPD.
Describe ventilator strategy in severe asthma or COPD to avoid complications.

Key is to avoid dynamic hyperinflation and barotrauma.

  • Use low RR, prolonged expiratory time (I:E 1:3–1:5), modest VT, allow permissive hypercapnia if pH acceptable.
  • Monitor for auto-PEEP, high peak pressures, hypotension; disconnect briefly if severe air-trapping causing cardiovascular collapse.
  • Treat bronchospasm: inhaled bronchodilators, IV magnesium, ketamine (selected), steroids; exclude pneumothorax.
A hypoxaemic patient does not improve with high-flow oxygen. What does this suggest and what are your next steps?

Poor response to oxygen suggests significant shunt.

  • Consider shunt physiology: consolidation, ARDS, atelectasis, intracardiac R→L shunt.
  • Escalate: apply PEEP (CPAP/NIV/IMV), recruit alveoli, treat cause (antibiotics, diuresis, physiotherapy/bronchoscopy for mucus plug), consider prone positioning in ARDS.
  • Urgently exclude pneumothorax and equipment failure; consider PE if appropriate (though PE often improves with O2 unless massive V/Q mismatch).
Explain how you would use the A–a gradient in an ABG viva to narrow the differential diagnosis of hypoxaemia.

Compute/estimate PAO2 and compare to PaO2; interpret normal vs raised.

  • Normal A–a: hypoventilation (CNS depression, neuromuscular weakness) or low FiO2 (altitude, oxygen supply issue).
  • Raised A–a: V/Q mismatch (common), shunt, diffusion limitation.
  • Response to oxygen: V/Q mismatch improves; shunt improves poorly; diffusion improves with O2 but may need higher FiO2.
List common perioperative triggers for type 2 respiratory failure and how you would prevent them.

Think drugs, mechanics, and pain.

  • Opioids/sedatives causing hypoventilation: use multimodal analgesia, titrate opioids, consider naloxone infusion if needed, monitor with capnography where possible.
  • Atelectasis and reduced FRC (supine, GA): recruitment/PEEP, early mobilisation, physiotherapy, CPAP/NIV post-op in high-risk patients.
  • Pain/splinting: regional techniques (epidural, blocks), adequate non-opioid analgesia.
  • Residual neuromuscular blockade: quantitative monitoring, appropriate reversal, extubate only when fully recovered.

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