When Ventilation Goes Wrong: Recognition and First Steps
CA-1 · draft
CA-1 Bootcamp day 11. Authored from cited abstracts; every claim carries a PMID.
Not reviewed. This deck cannot be opened, downloaded or sent
until you approve it. Read every point and its source first — they were drafted
from search results, not from clinical judgement.
Before induction
In volume-controlled ventilation a widening gap between peak and plateau pressure points at resistance somewhere between the ventilator and the alveolus, and the same obstruction under pressure control hides from you, because bench and modelling work showed delivered tidal volume did not fall until the tube was nearly completely occluded.
A capnograph that goes flat is a disconnection or a displaced tube until you have proved otherwise, and you should treat it that way: breathing-circuit disconnection was among the most frequently reported preventable critical incidents when anaesthetists were interviewed about their own near-misses, and international consensus guidance makes removal of the tube the default action when sustained exhaled carbon dioxide cannot be restored.
Trust the depth mark before you trust your stethoscope when you are new, because first-year residents in a randomised blinded trial missed endobronchial intubation on auscultation in 55 per cent of cases while insertion depth detected it with 88 per cent sensitivity, and that trial's own recommendation was to site tubes at 20 to 21 cm at the teeth in women and 22 to 23 cm in men.
Patient-ventilator dyssynchrony is not one thing but three - a problem with triggering the breath, with the flow delivered during it, or with cycling out of it - and each is identified by looking at the pressure, flow and volume waveforms rather than at the patient's chest.
Bronchospasm under anaesthesia usually shows itself as falling compliance and a falling saturation alongside the wheeze, and in the Australian incident reports the leading causes were airway irritation, a problem with the tracheal tube itself and aspiration of gastric contents - which is why you check the tube before you reach for the salbutamol.
Laryngospasm is treated first with your hands on the airway and only then with drugs, and if there is no intravenous line, suxamethonium can be given by the intramuscular, intraosseous or intralingual route - the delay you are racing is not hypoxaemia alone but the negative-pressure pulmonary oedema that intense inspiratory effort against a closed glottis produces.
Questions in the room
The capnograph trace has gone flat and the airway pressure has dropped to nothing - what is your first action, and what is your second?
Peak pressure has risen and plateau pressure has not. What does that tell you, and where is the problem?
How would you distinguish endobronchial intubation from a right-sided mucus plug at the head of this bed, without a chest X-ray?
The patient is biting the tube and the pressure trace is chaotic - is this dyssynchrony, laryngospasm or light anaesthesia, and how does your answer change what you give?
Oral boards stem
You are twenty minutes into a laparoscopic cholecystectomy in a 46-year-old smoker. The peak inspiratory pressure alarm sounds; the number has gone from 22 to 38 cmH2O, the delivered tidal volume has fallen from 500 to 340 mL, the capnograph still has a trace but its upstroke has become a slurred slope, and the saturation is 94 per cent and drifting. The surgeon says nothing has changed at his end. Walk me through what you look at, in what order, and what you do with your hands while you are looking.
Sources
Tung et al., Anesthesia and Analgesia 2002
PMID 12088967
Cooper et al., Anesthesiology 1984
PMID 6691595
Chrimes et al., Anaesthesia 2022
PMID 35977431
Sitzwohl et al., BMJ 2010
PMID 21062875
Doerschug and Peters, Clinics in Chest Medicine 2022
PMID 36116818
Westhorpe et al., Quality and Safety in Health Care 2005
PMID 15933304
Al-alami et al., Current Opinion in Anaesthesiology 2009
PMID 19434787
Bhattacharya et al., Chest 2016
PMID 27063348
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