Airway resistance measures how much the airways themselves resist airflow, and rises with bronchospasm, secretions, or a kinked or too-narrow breathing tube.
Normal (allowing for the tube's own resistance).
Mildly elevated.
Elevated — look for bronchospasm or secretions.
Markedly elevated — kinked tube, plugging, or severe bronchospasm.
Given: peak 30, plateau 20 cmH₂O, flow 1 L/sec.
Narrowed airways make air harder to push through, raising peak pressure.
Classic causes are bronchospasm, mucus plugging, a kinked circuit or tube, or the patient biting the tube. All raise peak pressure while plateau pressure stays the same.
Roughly less than 5–10 cmH₂O/L/sec, though it varies with the size of the endotracheal tube — a narrow tube adds resistance on its own.
Peak pressure includes both airway resistance and lung stiffness; plateau pressure (measured with no flow) reflects stiffness alone. The gap between them, divided by flow, isolates resistance.
By addressing the cause — bronchodilators for bronchospasm, suctioning for secretions, un-kinking or replacing the tube — rather than simply raising ventilator pressures.