"Apnea-volume" warning during normal ventilation of the lungs: an unusual leak in the Narkomed 4 Anesthesia System.

We report a case of an unusual breathing circuit leak in the Narkomed 4 Anesthesia System due to a loose retaining ring at the junction of the expiratory valve assembly and the Spiromed Respiratory Volume Monitor. In the presence of the leak, the monitor panel displayed the messages "apnea volume" and "minute volume low," yet the low airway pressure alarm was not triggered and other parameters and clinical signs pointed to normal ventilation of the lungs. These conflicting data led to some delay in localizing the leak. After conclusion of the case, we found that occult loosening of this ring without causing leaks large enough to fail the FDA generic or manufacturer-recommended leak checks can occur. We recommend checking the tightness of this ring during routine leak checks and after rotating the expiratory valve assembly during re-positioning of the anesthetic system.