A decreased risk of medical error or injury resulting from communication delay was reported among users of mobile telephones, compared to anesthesiologists who used pagers (RR = 0.78; 95% CI, 0.6234–0.9649; Table 4). Overall, 14.9% of anesthesiologists reported observing medical error or injury as a result of communication delay. The population-attributable percentage risk of medical error or injury attributable to communication delay from pager use is 19%.
The test-retest reliability of the survey instrument indicates substantial agreement with repeated measurements, with an overall Kappa of 0.75 (95% CI, 0.56–0.94) (4). The individual Kappa coefficients for each survey item are presented in Table 5.
There have been no studies that estimate the prevalence of cellular telephone interference with medical equipment and examine the impact of specific modes of communication on patient safety. This study conducted a cross-sectional survey of a large cohort of anesthesiologists in an attempt to answer these questions. The results of this study suggest that the use of mobile telephones in the OR or ICU decreases the incidence of medical errors or injury in patient care (RR = 0.78). The population-attributable percentage of medical error or injury as a result of communication delay from pager use is 19%. The most likely explanation for this phenomenon is that less time is required to relay important information by telephone, whereas anesthesiologists who rely on pagers must wait for the page to be answered.
The data also indicate that the overall prevalence of anesthesiologist-observed interference between cellular telephones and medical equipment is very infrequent (2.4% ± 0.5%). Although there is some association between observed interference and use of a mobile telephone by an anesthesiologist (RR = 1.6; 95% CI, 0.99–2.4), the result is not statistically significant. A post hoc power analysis using the difference of proportions test indicates that this study has over 90% power to detect the observed difference in interference rates between cellular telephone users and pager users (3.7% versus 2.4%), assuming an α (probability of committing a type I error when the H0 is true) of 0.05. One reason for this observation is that exposure risk may not be entirely anesthesiologist-dependent. It is increasingly common to observe family members, other non-anesthesiologist physicians, and even patients themselves using cell phones in the perioperative setting. These factors may contribute to the interference observed by anesthesiologists who did not use cell phones.
This study has several weaknesses that should be addressed in future research. The primary weakness is that the data were gathered through a retrospective survey instrument. Recall bias is a possible confounder in this type of study design. However, the primary outcome measures (patient injury as a result of communication delay and cell phone interference with medical equipment) are sentinel events that are likely to be recalled accurately by most anesthesiologists. The questionnaire used in this study did not define the terms “medical error” or “injury.” These factors make it difficult to assess the severity of medical errors that may have occurred as a result of delayed communication. The data generated by this study do not necessarily indicate whether improved communication has a beneficial effect on outcome, although it seems logical that decreasing the incidence of medical errors would have this effect.
The survey in this study was designed to assess modes of communication used by anesthesiologists in the OR/ICU as well as instances of communication delays and medical errors resulting from the delays. “Content validity” describes the ability of a survey to measure the outcomes of interest, in this case the incidence of observed EMI with medical equipment in the perioperative setting and the incidence of clinical errors associated with various methods of communication. Based on extensive discussion within the EMIT committee and consultation with other anesthesiologists and clinical engineering experts, the survey adequately covers the domain of the construct being measured and has appropriate content validity for this study.
Another potential weakness of the survey instrument is the possibility that members of the survey population did not understand the questions. Test-retest reliability reflects the ability of a survey to consistently measure the outcomes of interest over repeated measurements (assuming there is no substantial change in the construct being measured over the testing interval). Test-retest reliability was assessed using unweighted Cohen’s Kappa statistic with 95% confidence intervals (5). Skewed binomially-distributed data can sometimes lead to erroneously low values of Kappa (3,6). Accordingly, the percentage agreement was also calculated as the proportion of concordant ratings over the total number of ratings. The Kappa and proportion of concordant ratings indicate that this survey instrument has excellent test-retest reliability. In this study, the test-retest reliability assessment did not evaluate inter-subject reproducibility of the definitions of medical error, injury, and EMI.
Finally, there is the possibility that selection bias affected the results of the survey. The survey was distributed to all attendees of the 2003 ASA annual meeting, the largest annual meeting of anesthesiologists in the United States. The very large sample size makes it very unlikely that the sample could not be generalized to reflect the larger population of anesthesiologists practicing in the United States. Attendees were asked to complete the survey as part of the registration process, ensuring a high response rate. This also minimizes the possibility of bias and supports the validity of the survey method. It is, therefore, unlikely that selection bias is a significant confounder of the survey results.
Although the results suggest that the use of mobile telephones decreases the incidence of errors, this benefit must be weighed against the potential risk of interference with life-support devices such as ventilators, IV infusion pumps, and monitoring equipment. The reported prevalence of interference is 2.4%, which is much less than the risk of observed medical error or injury resulting from a delay in communication (14.9%), and there were no life-threatening events reported. These data represent a reported prevalence and are subject to recall bias, and the survey does not quantify the level of interference or the magnitude of the medical error. This finding does, however, agree with most published studies, in which disruption of a medical device was reversible and occurred only when the handset was operated within several centimeters of poorly shielded areas (e.g., unconnected data ports). It is also supported by studies that have investigated the impact of wireless communications devices with this equipment. An obvious follow-up study would be to conduct a prospective cohort study of the incidence of medical errors and cellular telephone interference in two similar practice environments in which either mobile telephones or pagers are used.
The infrequent prevalence of interference in this study and others is probably attributable, in part, to improvement in cellular telephone technology. Modern mobile telephones use “cellular” technology to provide high-quality communications using very low levels of emitted radiofrequency energy. This technology divides metropolitan areas into small loci, or cells, each of which is equipped with a low-power transmitter and sensitive receiver on a tall tower. Digital cellular telephones make use of several different standards that increase efficiency and allow many handsets to share a single frequency. The most commonly used protocol in the United States is called CDMA (Code-Division Multiple Access), which allows the base station to control the transmitter power used by the handset. In most other parts of the world, mobile handsets use the GSM (Global Standard for Mobile Communications) standard.
Three factors determine whether the energy that is emanated by wireless communications devices will cause disturbances in medical equipment: proximity, power, and shielding. Wireless devices are much more likely to interfere with a given piece of equipment if the frequency of the radiated energy is close to a resonant frequency of the equipment’s circuits. This effect increases with the radiated power of the wireless device. Because field strength decreases with the square of distance, doubling the distance between a handset and medical device decreases the field strength and, presumably, the risk of interference, fourfold. The power output of a typical handheld cellular telephone is typically only 600 mW and is lower in many cases. Institutions that make use of cellular telephones in clinical areas can install “micro-cells” that provide dense signal coverage while causing mobile telephones in the area to use the minimum power output. Some areas within hospitals, especially ORs, are electrically noisy or are located away from outside walls. Installation of micro-cells also permits mobile telephone use in these areas, in which coverage would otherwise be poor or nonexistent.
Nearly every new medical device is shielded against radiofrequency interference. Improvements in medical devices contribute further to the relatively low risk of EMI. An FDA standard created in 1979 provides guidance for shielding of electronic medical devices in an attempt to reduce the incidence of EMI (7). Although compliance is voluntary, medical equipment manufacturers are encouraged to adhere either to this standard or to IEC 60601-1-2, a widely recognized standard issued by the International Electrotechnical Commission, Geneva, Switzerland. Shielding can be accomplished by constructing an outer case from an electrically conductive material. This conductive case then prevents stray radiofrequency energy from entering the device. Grounding the shield provides an added layer of protection against nearly all radiofrequency energy.
Some devices, such as telemetry equipment, must admit electrical or radio signals and must therefore rely on filtering and insensitivity to radiofrequency energy at other frequencies. Cellular telephones transmit and receive ultra-high frequency (UHF) signals. In the United States, handsets transmit in the 850 MHz and 1900 MHz bands; in Europe and Asia, 900 MHz and 1800 MHZ are used for cellular telephony. Wireless local area computer networks using the Institute of Electrical and Electronic Engineers (IEEE) 802.11 specification transmit in the 2.4 GHz band. Modern telemetry equipment uses an assigned frequency range that is not near those used for wireless communication devices.
The IEEE was early to recognize the possibility that mobile telephones may interfere with medical equipment and published a Technical Information Statement recommending that medical life-support equipment be shielded to prevent the entry of stray signals (8). The FDA issued a warning in 1994 stating that portable communications devices might affect electronic medical devices (9). In 1993 and 1996, ECRI issued two reports warning against EMI between medical devices and telephones (10,11). The original 1993 wording was softened in the 1996 report, but still contained the warning: “We have therefore relaxed our previous position calling for prohibition of the use of transmitting devices (particularly cellular telephones) by patients and visitors throughout the hospital. Our new suggestions for a policy are based on a principle that calls for restricting the use of transmitting devices by patients, visitors, and staff in patient areas that are characterized by intensive instrumentation.” In 1999 the issue was revisited, and ECRI found that “Although interference between these communications devices and medical devices has been demonstrated, the risk to patients appears to be minimal, as well as manageable. Based on the evidence available to date, we believe that restrictive policies can be relaxed to allow the use of cell phones and walkie-talkies in certain situations” (12). This was reinforced in the 2001 update (13), with guidelines for creating and implementing policies covering the use of wireless technologies in hospitals.
In 2001, Tri et al. (14) tested 17 medical devices used for cardiopulmonary monitoring against 5 portable telephones (4 digital, 1 analog) to examine the risk of EMI. Although some EMI was noted, especially when close, it was noted that the interference would rarely be clinically important. Shaw et al. (15) performed a similar study with cellular telephones and 14 ventilator models. Although some of the ventilators malfunctioned as a result of EMI, all malfunctions occurred when the telephones were within 15–30 cm of the ventilator. The authors concluded that “it is reasonably safe to permit the use of cellular phones in the intensive care unit, as long as they are kept ≥3 feet from all medical devices.” Tri et al. (16) recently studied the use of wireless local area network technology in clinical areas, specifically using a Compaq personal digital assistant (Compaq, Palo Alto, CA), and found that there was no interference with pacemakers and implantable cardiac devices. ECRI and others have also confirmed that wireless networks do not interfere with medical devices (17–19).
Why the change in findings and recommendations from both ECRI and others? Modern handsets (and wireless networks) use much lower power, and most new medical devices are shielded to prevent entry of unwanted radiofrequency energy. As technology improves the risk of interference decreases. Unfortunately, policies regarding communications technology in the health care environment frequently do not keep pace with other industries.
The Massachusetts General Hospital has adopted a practical and evidence-based approach to the issue of personal communications devices (PCDs). Portions of their policy have been reproduced and paraphrased below (20):
- PCDs may be used safely in most areas of the hospital and near life-support and diagnostic laboratory equipment where wireless antenna systems are available.
- Untrained staff and employees, patients, visitors, and outside personnel may not use PCDs any closer than 3 feet, or roughly one arm’s length, from any medical device or diagnostic laboratory medical device.
- PCDs may be left in “standby mode,” i.e., they do not need to be turned completely off, when closer than 3 feet. However, the user must move the device to the 3-foot limit to use it. For example, if the cell phone rings, the user should move the cell phone away from the medical devices and answer the call.
- Use of hand-held radios (i.e., walkie-talkies) shall be limited to no closer than 10 feet from any medical device.
Clinical care often requires rapid communication between health care providers who may not be co-located. The increasing requirement for anesthesia services in locations such as interventional radiology or endoscopy suites underscores the need for efficient, reliable telecommunication. Commercial beeper systems that are commonly used to alert care team members may not be reliable for instantaneous communication (hospital service contracts often specify transmission delay times as long as 15 minutes as acceptable performance) and usually require the recipient to make a telephone call to complete the delivery of a message. Recent alternative technologies such as cellular or mobile telephones and wireless networking to personal digital assistants provide a potentially advantageous shift from one-way communication to synchronous, two-way communications.
In conclusion, the use of mobile telephones decreases the time required to relay an important message and thus may reduce the risk of committing an error in patient care. The benefits of improved hospital communications offered by cellular handsets appear to outweigh the exceedingly low risks of EMI from cellular telephones. Through the use of procedural and technical controls, hospitals can provide a safe health care environment while still allowing clinicians to take advantage of modern communication technology, and ultimately, improve patient care.
1. Klein A, Djaiani G. Mobile phones in the hospital: past, present, and future. Anaesthesia 2003;58:353–7.
2. Cohen J. Weighted kappa: nominal scale agreement with provision for scaled disagreement or partial credit. Psychological Bulletin 1968;70:213–20.
3. Feinstein AR, Cicchetti DV. High agreement but low kappa. II. Resolving the paradoxes. J Clin Epidemiol 1990;43:551–8.
4. Landis JR, Koch GG. The measurement of observer agreement for categorical data. Biometrics 1977;33:159–74.
5. Cohen J. A coefficient of agreement for nominal scales. Educational and Psychological Measurement 1960;20:37–46.
6. Feinstein AR, Cicchetti DV. High agreement but low kappa. I. The problems of two paradoxes. J Clin Epidemiol 1990;43:543–9.
7. United States Department of Health, Education and Welfare, Public Health Service, Food and Drug Administration, Bureau of Medical Devices, Electromagnetic Compatibility Standard For Medical Devices, FDA MDS-201-0004, October 1979.
8. Radiofrequency interference with medical devices: a technical information statement. IEEE Engl Med Biol Mag 1998;17:111–4.
9. Food and Drug Administration. Electromagnetic interference may cause problems with some medical devices. FDA Medical Bulletin. 1994;24:2
10. Electromagnetic interference and medical devices: an update on the use of cellular telephones and radio transmitters in healthcare facilities. Health Devices. 1996;25:263.
11. Cellular telephones and radio transmitters: interference with clinical equipment. Health Devices 1993;22:416–8.
12. Cell phones and walkie-talkies: is it time to relax your restrictive policies? Health Devices 1999;28:409–13.
13. Wireless communication devices and electromagnetic interference. ECRI’s updated recommendations. Health Devices 2001;30:403–9.
14. Tri JL, Hayes DL, Smith TT, Severson RP. Cellular phone interference with external cardiopulmonary monitoring devices. Mayo Clin Proc 2001;76:11–5.
15. Shaw CI, Kacmarek RM, Hampton RL, et al. Cellular phone interference with the operation of mechanical ventilators. Crit Care Med 2004;32:928–31.
16. Tri J, Trusty J, Hayes D. Potential for personal digital assistant interference with implantable cardiac devices. Mayo Clin Proc 2004;79;1527–30.
17. Wireless LA Ns in healthcare. Health Devices 2001;30:237–47.
18. Wallin MK, Wajntraub S. Evaluation of Bluetooth as a replacement for cables in intensive care and surgery. Anesth Analg 2004;98:763–7.
19. Hanada E, Hoshino Y, Oyama H, et al. Negligible electromagnetic interaction between medical electronic equipment and 2.4 GHz band wireless LAN. J Med Syst 2002;26:301–8.
© 2006 International Anesthesia Research Society
20. Massachusetts General Hospital internal policy on Personal Communications Devices. December 2004.