An Audible Indication of Exhalation Increases Delivered Tidal Volume During Bag Valve Mask Ventilation of a Patient Simulator Samsun Lampotang, PhD, D. E. Lizdas, BSME, N. Gravenstein, MD, and S. Robicsek, MD Departments of Anesthesiology and Neurosurgery, University of Florida College of Medicine and the Departments of Mechanical and Aerospace Engineering and Electrical and Computer Engineering, University of Florida College of Engineering, Gainesville, Florida Self-inflating manual resuscitators (SIMRs) can mis- lead caregivers because the bag, unlike a Mapleson- type device, reinflates even without patient exhala- tion. We added a whistle as an audible indicator to the exhalation port of a SIMR. In randomized order, each participant provided two sets of breaths via mask ventilation with a SIMR, one with and one with- out audible feedback, to a Human Patient Simulator modified to log lung volume changes. The last three breaths in each set were used to compare average tidal volume (Vt) under both conditions. Eighty- seven advanced cardiac life support trainees (54 males, 33 females) with clinical experience averaging 6.4  9.4 yr were recruited. Average Vt delivered with the standard SIMR was 486  166 mL and 624  96 mL with the modified SIMR. Average Vt delivered by a modified SIMR was significantly larger by 40% when it followed standard SIMR use and 19% when using the modified SIMR first. Use of a SIMR with an audible indicator of exhalation significantly (P  0.001) increased mask ventilation of a patient simula- tor, suggesting that mask ventilation of a patient with a SIMR may also be increased by objective, real-time feedback of exhaled Vt. (Anesth Analg 2006;102:168 –71) T he design and user interface of self-inflating manual resuscitators (SIMR), also known as self- inflating resuscitation bags and commonly known as “Ambu bags,” can mislead caregivers be- cause the bag reinflates after compression regardless of whether the patient is exhaling or is being properly ventilated. The refilling of the bag may be mistakenly interpreted as an indication that the lungs are being effectively ventilated and that the patient is exhaling based on the function of Mapleson-type ventilating systems and an anesthesia machine breathing bag where, at low or typical fresh gas flows, bag reinfla- tion is in large part both a result and an indication of adequate patient exhalation. Furthermore, novices, or those who do not use SIMRs regularly, may not achieve an effective seal when using an SIMR with a facemask, potentially diminishing the effectiveness of resuscitation efforts. We conducted a simulator-based study to deter- mine if an audible indicator of exhalation would assist caregivers across a broad range of clinical experience in delivering tidal volume (Vt) that reflects the vol- ume squeezed out of the SIMR and facemask seal. Methods In consultation with our IRB, it was determined that IRB approval and informed consent were not required because a device (not the participants) was being eval- uated on a patient simulator (not a patient). The ma- jority of the volunteers were anesthesia and surgery residents. Other participants included nurses and other clinical personnel attending Advanced Cardiac Life Support courses. There were no exclusion criteria. We added a reed whistle as an audible indicator of exhalation to the exhalation port of a standard adult SIMR (1st Response™, Manual Resuscitator; SIMS Portex Inc., Keene, NH) (Fig. 1). The adult facemask provided by the manufacturer with the SIMR was used for the study. The reed whistle can be readily removed from the exhalation port to return the SIMR to its standard configuration. Accepted for publication July 27, 2005. Address correspondence and reprint requests to Samsun Lampo- tang, PhD, Department of Anesthesiology, PO Box 100254, Gaines- ville, FL 32610 – 0254. Address e-mail to slampotang@anest.ufl.edu. DOI: 10.1213/01.ANE.0000181833.23904.4E ©2006 by the International Anesthesia Research Society 168 Anesth Analg 2006;102:168–71 0003-2999/06