Discuss the tailoring of oxygen requirements and delivery systems for a COPD patient with severe hypoxaemia and an infective exacerbation

Oxygen is a drug: it must be prescribed with a target saturation range, a device and a flow rate, and signed for on the drug chart like any other medicine.

The therapeutic target is a saturation range, not a flow rate. In COPD with an infective exacerbation the aim is SpO 88–92% pending arterial blood gases — adjust upward to 94–98% only if the ABG shows a normal PaCO and 2 2 there is no history of previous hypercapnic failure requiring ventilation.

Why the ceiling matters: excess oxygen in the chronic CO retainer produces hypercapnia by reversal of hypoxic 2 pulmonary vasoconstriction with worsened V/Q mismatch (the dominant mechanism), the Haldane effect, and to a lesser extent depression of hypoxic respiratory drive — leading to respiratory acidosis, narcosis and death. Pathy's warns of depressed hypoxic drive, increased coronary and cerebral arterial resistance and worsened acidosis, and advises target saturations in this range.

The opposite error is equally lethal: oxygen must never be withheld from a severely hypoxaemic patient for fear of retention. Hypoxaemia kills faster than hypercapnia; treat the hypoxaemia and manage the CO with ventilatory 2 support.

Baseline saturations are lower in the very old — clinically stable people over 70 may sit at 92–94% and require no oxygen; know the patient's stable baseline before treating a number.

Immediate assessment: respiratory rate, level of consciousness, ability to speak, accessory muscle use, SpO , and 2 an arterial blood gas within 30–60 minutes of starting oxygen — and repeated 30–60 minutes after every significant change in FiO .

Classify the failure from the ABG: Type 1 (PaO < 8 kPa / 60 mmHg with normal or low PaCO ) versus Type 2 2 2 (PaO < 8 kPa with PaCO > 6.5 kPa / 50 mmHg). Then distinguish acute hypercapnic failure (low pH, normal 2 2 bicarbonate) from acute-on-chronic (low pH with raised bicarbonate and base excess) — the bicarbonate tells you how chronic the retention is.

Look for the treatable precipitant simultaneously: purulent sputum and consolidation, pneumonia (which in older adults is frequently afebrile and non-productive), pneumothorax, pulmonary embolism, heart failure, arrhythmia, sedative drugs and aspiration.

Venturi (high-flow, fixed-performance) masks are the device of choice in COPD because they deliver a predictable, constant FiO independent of the patient's inspiratory flow — start at 24% at 2–3 L/min or 28% at 4 2 L/min. If the respiratory rate exceeds 30/min, increase the flow through the Venturi barrel by up to 50% to maintain the entrained FiO (the barrel colour, not the flow, sets the concentration).

Nasal cannulae (1–2 L/min) are an acceptable alternative once the patient is stable and the target range is reliably held: better tolerated, allow eating, talking and expectoration, and reduce delirium and claustrophobia in the older patient — but they are variable-performance, with FiO depending on minute ventilation and mouth-breathing.

Simple face mask (5–10 L/min) delivers roughly 40–60% and is generally unsuitable in COPD; below 5 L/min there is a risk of CO rebreathing within the mask.

Reservoir (non-rebreathing) mask at 15 L/min gives 60–90% and is reserved for critical illness or life-threatening hypoxaemia (SpO < 85%) as an emergency bridge — step down to a Venturi mask as soon as the 2 gas is available.

Humidification should be added for flows above 4 L/min, for prolonged therapy and where secretions are tenacious, to preserve mucociliary clearance — important where the cough reflex is already blunted by ageing.

High-flow nasal cannula (HFNC) delivers heated, humidified gas at 30–60 L/min with a precisely titrated FiO , 2 washes out anatomical dead space, generates a small PEEP effect and improves secretion clearance. It has proved safe and effective in exacerbated COPD in both normocapnic and hypercapnic respiratory failure, and is particularly valuable where there is a do-not-intubate order or where intermediate care is needed outside the ICU.

Non-invasive ventilation (NIV/BiPAP) is the key intervention in acute hypercapnic failure: indicated when pH < 7.35 with PaCO > 6.5 kPa despite maximal medical therapy and controlled oxygen. NIV reduces mortality, need 2 for intubation and length of hospital stay. Start at IPAP 10–12 and EPAP 4–5 cmH O, titrating IPAP upward to 2 20–25 by response, with oxygen entrained to keep SpO 88–92%; repeat the gas at 1 and 4 hours.

Invasive ventilation is considered for pH < 7.25 with deteriorating consciousness, NIV failure or intolerance, cardiovascular instability or inability to protect the airway — but the decision must be made on premorbid function, frailty and previously stated wishes, not chronological age, and a ceiling of care should ideally be documented before deterioration. Concurrent Treatment of the Exacerbation and Discharge

Treat the exacerbation in parallel: nebulised salbutamol and ipratropium driven by air, not oxygen, in the CO 2 retainer (with nasal oxygen alongside at 1–2 L/min); systemic corticosteroids; and antibiotics where sputum is purulent — beta-lactam ± inhibitor, doxycycline or a fluoroquinolone, with anti-pseudomonal cover (ciprofloxacin, anti-pseudomonal cephalosporin or aminoglycoside) if bronchiectasis coexists.

Additional supportive measures: chest physiotherapy and secretion clearance, VTE prophylaxis, correction of dehydration and hypokalaemia, delirium prevention, review of sedatives and opioids, and nutritional support — hypercatabolism and muscle loss are hallmarks of severe exacerbation in the elderly.

Wean the oxygen deliberately: step down device and FiO as the patient improves, reassess on air before 2 discharge, and do not assess for LTOT during the acute episode — LTOT must be prescribed during a period of clinical stability, generally at least 6–8 weeks after the exacerbation, in a non-smoker.

Practical geriatric issues with home oxygen: long tubing and concentrators are a falls hazard; there are safety concerns where there is cognitive impairment or poor manual dexterity; fire risk mandates that the patient and household are non-smokers; care-home residents using overnight concentrators may need portable cylinders for daytime rooms; and staff and carers require training. Issue oxygen alert cards recording previous blood-gas results to guide future emergency treatment.