Question 30

College Answer

Principles of management include:

•    NIV better than intubation (if possible).

•    Do no harm – if IPPV consider I:E ratio / RR / TV or insp. pressure settings / flow pattern of breath to avoid dynamic hyperinflation and barotrauma.

•    Supported spontaneous ventilation preferred to fully ventilated IPPV if possible.

•    High enough mechanical ventilatory support to avoid respiratory muscle fatigue balanced out to avoid generating respiratory skeletal atrophy.

•    Extubate sooner rather than later if safe to do so and be prepared to support with NIV post- extubation.

•    Assess cough, airway protection and sputum load when considering extubation or use of NIV.

•    Supplemental oxygen and PEEP to appropriate levels for adequate oxygenation (eg. PO2 55mmHg in some patients).

•    Ventilation to get CO2 to appropriate levels (may not necessarily mean normalising CO2 to 40; ?allow permissive hypercapnoea).

•    Discontinue futile therapies if prognosis hopeless and deemed ethically appropriate with understanding & agreement of patient or appropriate surrogate.

Discussion

Mechanical ventilation of the COPD patient is briefly discussed elsewhere.

In summary,

• Avoid intubation; rely on NIV
• Use NIV to manage hypercapnea and to improve work of breathing in the acute setting
• If you have to intubate them, do so for the shortest possible period, and extubate them onto NIV as soon as is practical
• Avoid high plateau pressures, to avoid pneumothorax from emphysematous bullae
• Help sputum clearance by having regular breaks form NIV
• Aim for a PaO2 around 55-65; avoid hyperoxia
• use a short inspiratory rise time, match PEEP to auto-PEEP, increase the expiratory phase by increasing the expiratory flow trigger
• Use bronchodilators; anticholinergics are probably better than beta-agonists
• Use steroids
• Commence antibiotics if there is an infectious trigger
• Avoid futile treatment in severely exercise-limited patients

It has been pointed out that there are lots of different (reasonable-sounding) ways of answering a question which asks "how would you mechanically ventilate that". For example, it would be reasonable to discuss daily checks of ETT position, active circuit humidification, avoidance of ludicrously large tidal volumes or driving pressures, and so on. However, judging by the college answer, in a question like this these totally valid generic recommendations may not score marks.

One needs to read between the lines of the SAQ to score high marks (one of the qualities of a poorly written SAQ). Consider: the examiners gave you a woman with chronic airways disease, and asked you to discuss the management of her mechanical ventilation. The question really asks, "what are the principles of ventilating a COPD patient?" It is difficult to guess as to why the examiners designed this SAQ the way they did. Given how little additional information is available about the patient (she's female, 65 and her respiratory failure is acute), one can't exactly say that the rich detail of this complex clinical case vignette is necessary for the testing of candidates' higher analytic and synthesis skills. 

Siafakas, N. M., et al. "Optimal assessment and management of chronic obstructive pulmonary disease (COPD)." European Respiratory Journal 8.8 (1995): 1398-1420.