The construction of a coaxial circle breathing circuit encloses the inspiratory limb within the expiratory limb to preserve heat, humidity, anesthetic gas, and oxygen. However, the construction also makes kinks or breaks in the enclosed inspiratory limb difficult to detect. With kinking or disconnection of the central inspiratory limb, the patient may rebreathe expiratory gases, leading to a significant increase in dead space and concomitant respiratory acidosis. We describe a clinical case in which a disconnection in the inner inspiratory limb of a King (King Circuits, Noblesville, IN) coaxial breathing circuit resulted in severe respiratory acidosis 4 hours after induction during a craniotomy for tumor resection. Similar cases have been reported in the literature [1-3], but this one differs in the timing of the rebreathing and respiratory acidosis. Therefore, anesthetic providers who are aware that coaxial circuit failures associated with the inspiratory limb can occur at any time during surgery will be in a position to identify the problem early, thereby limiting the degree of respiratory acidosis that develops and reducing the risk of associated complications.