Which Mapleson circuit is regarded as the worst for spontaneous ventilation?

Mapleson D is considered the least effective circuit for spontaneous ventilation due to its characteristics that hinder efficient gas exchange. This circuit has a high fresh gas flow requirement and a longer time to achieve optimal anesthetic concentration, which can negatively impact spontaneous breathing efforts.

In this system, the design results in an increased reservoir bag size and a configuration that contributes to less effective ventilation compared to other circuits, especially during spontaneous breathing. The disadvantage is particularly notable when quick response to changing ventilatory demands is needed, as the circuit's design does not facilitate rapid delivery of fresh gases to the patient. This often leads to inadequate ventilation and compromised oxygenation for patients relying on spontaneous breathing.

Other Mapleson circuits, such as A, B, and C, offer better support and quicker responsiveness for spontaneous ventilation, making them preferable when spontaneous ventilation is anticipated.