Ventilator Management Basics: Modes, Settings, and Airway Pressures

CA-1 · draft

CA-1 Bootcamp day 7. 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

An international expert consensus recommends starting intraoperative ventilation at a tidal volume of 6 to 8 mL per kilogram of predicted body weight with PEEP of 5 cm H2O, individualising PEEP thereafter and using the lowest effective pressure and fewest breaths when recruiting — which means the tidal volume is calculated from the patient's height, not from what the scale said.
Set the respiratory rate to the end-tidal CO2 and then resist the urge to keep dialling it up, because in a pooled analysis of two large intraoperative ventilation trials the patients whose end-tidal CO2 ran below 4.7 kPa received higher weight-adjusted minute ventilation and developed more postoperative pulmonary complications (34% versus 23%), with an inverse linear relationship between mean end-tidal CO2 and complications.
Low tidal volume is not a charm you cast on its own — a randomised trial of 6 versus 10 mL/kg predicted body weight with PEEP of 5 in both arms found no difference in postoperative pulmonary complications (38% versus 39%), while a Bayesian network meta-analysis found the benefit came from low tidal volume combined with moderate PEEP of 5 to 8 cm H2O rather than from the small tidal volume alone.
Plateau pressure minus PEEP is the driving pressure, and in an individual-patient meta-analysis of 17 randomised trials driving pressure was associated with postoperative pulmonary complications (odds ratio 1.16 per 1 cm H2O) while tidal volume on its own was not; the gap between peak and plateau is a different quantity altogether — it is resistive, and it grows with airway resistance, smaller endotracheal tubes and shorter inspiratory times.
Volume control promises a tidal volume, pressure control promises a pressure and assures neither the other, and pressure support only assists breaths the patient starts — and each has a catch worth knowing: the volume a traditional anaesthesia ventilator actually delivers in volume control is degraded by breathing-circuit compliance and fresh gas flow until the machine compensates for both, while adding pressure support to a spontaneously breathing patient with a laryngeal mask cut the postoperative fall in end-expiratory lung volume from about 17% to about 8%.
In a meta-analysis of 51 randomised trials in adults having abdominopelvic surgery, second-generation supraglottic airways reduced major perioperative airway complications compared with tracheal tubes (risk ratio 0.41) with no clear difference in regurgitation or aspiration and much less sore throat, hoarseness and coughing, but they more than tripled the risk of inadequate ventilation (risk ratio 3.36) — so the supraglottic airway buys a quieter throat and the tube buys a ventilation you can count on.

Questions in the room

What is this patient's predicted body weight, and how far is it from what the scale said?
Peak went up and plateau barely moved — is that a lung problem or a tube problem, and how would you tell?
You are hyperventilating him to an end-tidal CO2 of 28. What is that buying you, and what is it costing?
If this were a 40-minute knee arthroscopy instead, would you still put a tube in — and what would you give up if you did not?

Oral boards stem

A 58-year-old man, 170 cm and 92 kg, is having a laparoscopic sigmoid colectomy. You have induced, given rocuronium, intubated with an 8.0 tube and confirmed the position. The examiner points at a blank ventilator screen and asks you to set it — mode, rate, tidal volume, PEEP — and to say where on that screen you would look to know whether your settings are being delivered. Then the surgeon insufflates, the peak pressure rises from 19 to 32, and the plateau moves from 15 to 19; the examiner asks what has just happened and what you would change.

Sources

Young et al., Br J Anaesth 2019 PMID 31587835
Nasa et al., Br J Anaesth 2025 PMID 40930872
Karalapillai et al., JAMA 2020 PMID 32870298
Deng et al., Br J Anaesth 2020 PMID 32007240
Neto et al., Lancet Respir Med 2016 PMID 26947624
Ilia et al., Pediatr Crit Care Med 2020 PMID 31688716
Bachiller et al., Anesth Analg 2008 PMID 18420850
Sudy et al., Acta Anaesthesiol Scand 2024 PMID 37923301
de Carvalho et al., Anesth Analg 2025 PMID 39466638
Bernardini et al., Anaesthesia 2009 PMID 19860753
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