Which Mapleson circuit is considered the worst for spontaneous ventilation?

The Mapleson C circuit is considered the worst for spontaneous ventilation primarily due to its design and efficiency characteristics. In spontaneous ventilation, the patient relies on their own ability to breathe, and the design of the Mapleson C circuit contributes to inferior performance in terms of delivering oxygen and removing carbon dioxide during such breathing patterns.

In Mapleson C, the arrangement of the components means that it has a higher resistance and a longer time constant compared to other circuits when it comes to the delivery of fresh gas to the patient's lungs and the evacuation of expired gases. During spontaneous ventilation, this can lead to an inadequate fresh gas flow reaching the patient, resulting in less effective ventilation. The circuit does not allow for rapid changes in gas concentration, which is imperative for effective spontaneous ventilation.

The performance of the Mapleson circuits is ranked primarily based on their efficiency in supplying fresh gas and facilitating patient ventilation. In this context, while other circuits like A, D, and B are designed to provide better performance during spontaneous breathing efforts, Mapleson C is recognized as falling short in this regard, leading to its classification as the least favorable option for spontaneous ventilation scenarios.