4.2 Respiratory Failure & Oxygenation Support

Type I vs. Type II Respiratory Failure

Distinguishing the two types of acute respiratory failure drives completely different management, so the PCCN tests this distinction repeatedly.

Some patients—especially those with COPD or severe ARDS—develop combined failure: chronic hypoxemia plus acute-on-chronic hypercapnia. Always compare the current ABG to the patient's known baseline before labeling an exacerbation.

Failure to Wean

"Failure to wean" describes a patient who cannot tolerate reduced ventilator support despite resolution of the acute process. Before a spontaneous breathing trial (SBT), assess weaning readiness: adequate oxygenation (PaO2/FiO2 >150–200, PEEP ≤5–8 cmH2O), hemodynamic stability, adequate mental status, and intact cough/airway protection. Two bedside predictors:

• Rapid shallow breathing index (RSBI) = respiratory rate ÷ tidal volume (in liters). A value <105 predicts weaning success; higher values predict failure.
• Negative inspiratory force (NIF) more negative than −20 to −25 cmH2O suggests adequate respiratory muscle strength.

Failure to wean has many causes: unresolved lung pathology, respiratory muscle weakness/deconditioning, cardiac dysfunction unmasked by the negative intrathoracic pressure of spontaneous breathing, delirium, malnutrition, or persistent sedation.

Oxygen Delivery Devices

Match the device to how much FiO2 and flow the patient needs:

• Nasal cannula — 1–6 L/min, delivers roughly 24–44% FiO2 (variable, depends on the patient's own inspiratory flow)
• Simple face mask — 5–10 L/min, roughly 35–50% FiO2; needs at least 5 L/min to flush exhaled CO2
• Venturi (air-entrainment) mask — delivers a precise, fixed FiO2 (24–50%) regardless of the patient's breathing pattern; preferred in COPD when titrated oxygenation is essential
• Non-rebreather mask — 10–15 L/min with a reservoir bag that must stay inflated, delivers up to roughly 80–95% FiO2; the highest FiO2 available without positive pressure
• High-flow nasal cannula (HFNC) — heated, humidified flows up to 60 L/min with FiO2 up to 100%; reduces anatomic dead space, provides a modest PEEP effect, and is often better tolerated than a mask

Noninvasive Positive Pressure Ventilation (NIV)

CPAP (continuous positive airway pressure) delivers one constant pressure throughout the respiratory cycle. It splints open the upper airway and recruits collapsed alveoli, primarily improving oxygenation. Classic indications: obstructive sleep apnea and cardiogenic pulmonary edema.

BiPAP (bilevel positive airway pressure) delivers two pressures: a higher inspiratory positive airway pressure (IPAP) that augments tidal volume and offloads the work of breathing, and a lower expiratory positive airway pressure (EPAP) that keeps alveoli open, similar to PEEP. Because IPAP actively assists each breath, BiPAP improves ventilation (CO2 clearance) as well as oxygenation, making it first-line for acute hypercapnic respiratory failure from a COPD exacerbation when the patient is alert, hemodynamically stable, and able to protect the airway.

Contraindications to NIV include decreased level of consciousness/inability to protect the airway, hemodynamic instability, facial trauma or recent facial surgery, uncontrolled vomiting, and copious secretions the patient cannot clear.

Prone Positioning and Tracheostomy

Prone positioning for 12–16+ hours a day improves oxygenation in moderate-to-severe ARDS by recruiting dorsal lung units and improving V/Q matching; it requires a coordinated team and careful attention to lines, the endotracheal tube, and pressure points (face, eyes, chest). Tracheostomy is considered when mechanical ventilation is expected to extend beyond roughly 1–2 weeks or the patient cannot wean; it reduces dead space and sedation needs, improves comfort and secretion clearance, and allows earlier mobility and speech (with a speaking valve) compared with prolonged translaryngeal intubation.

Recognizing Deterioration Early

Regardless of which failure type is present, escalating respiratory distress shares common warning signs that warrant immediate provider notification: rising respiratory rate with shallow tidal volumes, increasing accessory muscle use, paradoxical or see-saw chest/abdominal movement, diaphoresis, inability to speak in full sentences, a falling SpO2 despite an increasing FiO2, and any new confusion or lethargy — hypercapnia and hypoxemia both alter mental status before they cause cardiac arrest. A patient who looks "too calm" after a period of severe distress may be tiring rather than improving, echoing the same fatigue pattern seen in status asthmaticus.

Tracheostomy Timing and Care Considerations

Early tracheostomy (roughly within the first 1–2 weeks of anticipated prolonged ventilation) is generally associated with less sedation exposure, earlier mobility, and improved patient comfort compared with waiting through repeated failed extubation attempts, though the ideal timing is individualized. After placement, priorities include maintaining a secured, patent airway; humidifying delivered gas since the upper airway's natural warming/humidifying function is bypassed; suctioning only as needed (not on a fixed schedule) to avoid mucosal trauma; and assessing for stoma bleeding, subcutaneous emphysema, or tube displacement, which can rapidly compromise the airway in the first postoperative days before a stable tract has formed.