Yasser A Sowb, PhD; David M Gaba, MD, Steven K Howard, MD
VAPAHCS and Stanford University School of Medicine

Introduction: 80% of serious accidents in complex systems where humans and machines interact involve human error. Anesthesiology is a complex domain with a similar proportion of accidents attributed to human error.¹ Anesthesiologists are usually positioned among an array of controls and monitors which cover up to 270 degrees horizontally and 120 degrees vertically. In this abstract, we examine anesthesiologists’ interaction with an important equipment, the anesthesia machine (AM), used to manage patient’s ventilation during a simulated crash OB C-section scenario.

Methods: A crash OB C-section scenario was simulated using a comprehensive patient simulator. At the beginning of the scenario and prior to the subject entering the simulated operating room, electric power of the Ohmeda Modulus II AM was purposefully turned OFF by placing its power switch in the STANDBY position. Turning OFF electric power of this particular AM causes shut down in fresh gas delivery while oxygen flush delivery remains functional. The responses of 10 anesthesia residents to this scenario were captured on video and analyzed. Subjects’ response time to restoring electric power to the AM by turning its power switch to the ON position were measured.

Results: Seven subjects recognized that the AM’s power switch was in the OFF position and correctly restored its electric power. The average time it took these seven subjects to restore electric power to the AM from the time when the subject stood by the patient’s head is 100.71 seconds. Three subjects failed to detect that the AM’s electric power is OFF, and two of those subjects were aided to restore its electric power by comments from the surgeon while one subject received help from an anesthesia technician. The average time it took all 10 subjects to restore electric power to the AM is 235.16 seconds.

Discussion: Most subjects failed to detect the AM’s STANDBY electric power mode or shut down in its fresh gas delivery system by looking at it. Eight subjects manipulated the oxygen flow control knob and one subject attempted to deliver oxygen to the patient by squeezing the breathing circuit’s bag before detecting shut down in fresh gas delivery. After detecting the shut down in the AM’s fresh gas delivery, most subjects failed to recognize the root cause of their failing to deliver oxygen in a timely manner. This is shown by the subjects’ relatively long response time to restoring electric power to the AM (101 seconds on average) and list of tested hypotheses. Five subjects (50%) either assessed oxygen pipeline or tank supply and requested an external oxygen tank or needed help from an anesthesia technician or another clinician before restoring electric power to the AM. We contribute subjects’ difficulty to recognize the root cause of shut down in fresh gas delivery to their failure to detect the AM’s STANDBY electric power mode because the AM’s front panel does not provide strong visual indicators of its electric power mode. The AM’s electric power switch is small and located on the lower part of the AM’s front panel making it difficult to detect or recognize its functionality by the subjects. Also, some of the subjects did not completely understand the functional relationship between the AM’s electric power mode and the functionality of its fresh gas and oxygen flush delivery systems. Three subjects repeatedly filled the AM’s breathing circuitry and ventilated the patient by pressing the oxygen flush switch before restoring electric power to the AM. We believe that the AM power switch size, location, and functionality should be more apparent given its relative importance, and the functional relationship between the AM’s electric power mode and fresh gas and oxygen flush delivery systems should be apparent in the design of the AM.²

References:

1. Gaba, DM (1989). International Anesthesiology Clinics; 27:137-47.

2. Sowb, YA; Loeb, RG (In Press). Cognition, Technology, and Work: Human Error in Medicine.