The Potential for Dissemination of Mycobacterium tuberculosis Through the Anesthesia Breathing Circuit* Paul B. Langevin, MD; Kenneth H. Rand, MD; and A. Joseph Layon, MD, FCCP Background: Respiratory pathogens that pass through the anesthesia breathing system potentially can infect other patients. This study was designed to determine if bacteria can pass through contemporary anesthesia breathing systems and if the environment within the machine is hostile to these organisms. Methods: Staphylococcus aureus, Pseudomonas aeruginosa, and Mycobacterium tuberculosis were nebulized into the expiratory limb of an anesthesia breathing circuit and collected from the inspiratory and expiratory limbs in an impinger system that provided a quantitative determina- tion of the number of organisms entering the circuit and the number that would reach the patient in the inspiratory gas. Bacteria were collected before, during, and after nebulization. A second experiment determined if a saturated solution of soda lime was bactericidal. Results: When the gas flow through the circuit was interrupted for < 1 h following the nebulization period, large numbers of microorganisms (1  10 3 to 1  10 5 , around 100% of the nebulized organisms) were collected from the inspiratory gas. Soda lime itself was not bacteri- cidal for any of the organisms tested, but solutions of this material with a pH of 12 were bactericidal. Conclusion: Cross contamination between patients may occur unless the gas flow through the anesthesia breathing system is interrupted for > 1 h. (CHEST 1999; 115:1107–1114) Key words: anesthesia breathing circuit; contamination; Mycobacterium tuberculosis; Pseudomonas aeruginosa; respiratory pathogens; Staphylococcus aureus Abbreviations: BHI = brain-heart infusion; MHA = Mueller-Hinton agar; PBS = phosphate-buffered saline solution; TB = tuberculosis R espiratory pathogens can be transmitted through breathing circuits used to provide anesthesia 1 or respiratory therapy. 2 Although infrequently docu- mented events do not exclude their occurrence, the low frequency of documented cross-infections via the anesthesia machine may suggest that current infection control standards 3,4 are adequate. Never- theless, recent changes in the patient population may warrant renewed concern. Reports from the Centers for Disease Control and Prevention indicate that the rate of decline in the number of tuberculosis (TB) cases reported has decreased since 1984. 5 The num- ber of virulent, multidrug-resistant organisms is in- creasing 6–9 simultaneously with an escalation in the number of immunocompromised patients presenting for operation. Although viral contamination of the anesthesia circuit has heretofore been regarded as inconsequential, clinical transmission of hepatitis C has recently been attributed to a contaminated an- esthesia machine. 10 Before the breathing circuit can serve as a vector for respiratory infections, a patient must aerosolize a *From the Departments of Anesthesiology (Drs. Langevin and Layon), Pathology (Dr. Rand), Surgery (Dr. Layon), and Med- icine (Dr. Layon), University of Florida College of Medicine, Gainesville, FL. Supported in part by a grant from Pall Biomedical Products Co, East Hills, NY. The company received a draft of the article but did not proof or edit it. Manuscript received June 25, 1998; revision accepted November 13, 1998. Correspondence to: Paul B. Langevin, MD, c/o Editorial Office, Department of Anesthesiology, PO Box 100254, Gainesville, FL 32610-0254 laboratory and animal investigations CHEST / 115 / 4 / APRIL, 1999 1107