With experience, the feel of manual ventilation tells you a great deal about the patency of the airway.
With experience using this technique, the quality of the airway can be determined within 2-3 breaths.
During inspiration: Gentle manual ventilation, with slow inspiration, and keeping the airway pressure below 20 cm H2O, should lead to easily visible chest rise. There should be no noise of leak or stridor.
During expiration: Once inspiration is complete, the
chest should fall passively in 1-2 s. The anaesthetic bag should refill
rapidly. Many erroneously believe that the anaesthetic bag refills from
the fresh gas flow. In fact, it refills mostly from patient expiration,
which has approximately 5-10 times the flow rate of the fresh gas flow
(20-30 L/min vs. 2-8 L/min).
Minor degrees of airway obstruction lead to delayed expiration, and slow refilling of the anaesthetic bag. Significant airway leakage will also prevent the anaesthetic bag from refilling.