THE INDUCTION AND INTUBATION of critically ill patients are high-risk interventions,
with nearly half of patients experiencing a major adverse event, such as cardiovascular
instability, severe hypoxia, or cardiac arrest.
1
Preexisting physiologic derangements are a major contributor to decompensation, and
the term “physiologically difficult airway” is used to describe patients with significant
physiologic alterations prior to airway management.
2
Although many factors may contribute to a patient with a physiologically difficult
airway, the derangements of most concern are hypotension, hypoxia, severe metabolic
acidosis, and right ventricular dysfunction.
2
Inducing a patient who is already hypotensive can be dangerous, as both the induction
agents, as well as positive-pressure ventilation, can worsen hypotension. Risk factors
for periintubation hypotension have been explored recently, and one study derived
and validated a scoring system for periintubation hypotension in critically ill patients
(C-statistic 0.75 [95% CI 0.72-0.78]).
3
Given the literature surrounding the negative downstream effects of hypotension on
the critically ill, one could argue that preventing further decreases in blood pressure
is the most important consideration when faced with intubation in a patient with preexisting
hypotension. For example, a multicenter cohort study demonstrated that mean arterial
pressures ≤65 mmHg in critically ill patients were associated with an increased risk
of 30-day major adverse cardiac or cerebrovascular events and increased 30-day mortality.
This held true even for hypotension of limited duration.
4
Preexisting hypoxia is also a significant risk factor for decompensation because
any apnea time is tolerated poorly by patients with limited arterial oxygen content
reserve. Additionally, induction agents typically worsen the ventilation-perfusion
mismatch that is already present to some degree in hypoxic patients. Hypoxia, in general,
also places patients at greater risk for hemodynamic instability, arrhythmia, and
cardiopulmonary arrest.
3
Severe metabolic acidosis contributes to a physiologically difficult airway, as any
apnea time will result in an increased PaCO2 and a worsening acidosis. Preexisting right ventricular dysfunction presents many
challenges to intubation, as the rise in PaCO2 with induction will result in increases in pulmonary arterial pressures and right
ventricular strain. Additionally, positive-pressure ventilation tends to overall reduce
preload and may precipitate cardiovascular collapse due to insufficient preload to
a poorly functioning right ventricle. Patients with a physiologically difficult airway
may possess one or a combination of these physiologic derangements. Once a physiologically
difficult airway is identified, the next challenge for the clinician is to design
an induction regimen that would be best tolerated by a patient with preexisting physiologic
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Publication history
Published online: January 06, 2023
Publication stage
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