Case 37: An Abnormal Capnogram

Abstract

A 7-year-old boy (41 lb) (American Society of Anesthesiologists physical status I [ASA 1]) is scheduled for an emergency appendectomy. The patient has had no previous anesthesia/surgery, and his family history is negative for anesthesia-related complications. General anesthesia is induced, and after the child is asleep, the trachea is intubated. Positive pressure ventilation is then instituted using the ventilator on the anesthesia machine. Both the initial end-tidal CO₂ value (40 mmHg) and the capnograph tracing are within normal limits, with an inspiratory CO₂ of zero. Anesthesia is maintained using meperidine and vecuronium with isoflurane and nitrous oxide in oxygen. Approximately 20 min into the case, the inspired end-tidal CO₂ increases and the capnogram is noted to be abnormal (Fig. 37.1). The CO₂ absorbent canister is visually inspected. The upper compartment has a slightly bluish cast, and no color change is seen in the bottom compartment to indicate exhaustion of the CO₂-absorbent granules. Other causes of the abnormal tracing are sought. The expiratory and inspiratory valves are examined and changed without improvement in the capnogram. Rebreathing continues to be apparent. The patient’s vital signs remain stable with a normal blood pressure (BP) and heart rate and 100 % oxygen saturation.