Volume 1, No. 4 • Winter 1986

Safety Technology Shown at ASA

Charles E. Whitcher, M.D.

Many devices shown by technical exhibitors at the October, 1986 ASA Annual Meeting can enhance patient safety.

An impressive array of pulse oximeters was shown, probably reflecting increased demand and a perceived relationship to a standard of cam This is no surprise, since oximeters address a fundamental point, oxygen availability to tissues, and are considered sufficiently reliable and practical for routine use Prospective purchasers wig find significant differences among the many brands shown differences which have not been dearly evaluated in the peer-reviewed literature As with any such purchase, considerations should include the available documentation, as well as anticipated ease of servicing. Probe design is a critical feature which merits careful thought, including ease of application, secureness during use, and ease of removal at the end of the case. Most oximeters retain undesired features such as susceptibility to artifacts due to motion and electrocautery interference.

Standard of Care

Many capnometers were shown, some offering improved me of use and ease of calibration. This is another monitor approaching standard of care status. The capability of multi-system assessment (metabolic, cardiovascular, and respiratory), and a one-breath assessment of endotracheal intubation, are important patient safety features. Esophageal intubation can be reliably and rapidly detected. A useful, if not indispensable, feature to he considered is the C02 wave form display-to verify important features of the capnogram, return to zero and alveolar plateaus for each breath. This feature is provided built-in to certain capnographs, and as an accessory for others.

A new generation of multi-gas monitors was displayed by several manufacturers. The primary analyses Of C02, N20, and anesthetic halocarbons were most frequently based on the infrared absorption principle. Response is rapid, breath-by-breath. End-tidal N20 analysis may be useful in verifying the effects attributable to this agent. End-tidal halocarbon values are useful in assessing anesthetic depth. Inhaled concentration only, measured by certain analyzers, does protect patient safety. Infrared analyzers do not usually differentiate among anesthetic halocarbons; the agent being used must be manually entered. Thus, this method would not readily recognize unexpected mixtures or substitutions of agents.

Several of the new multigas analyzers were capable of in-circuit 02 analysis, using conventional polarographic or fuel cell technologies (with

anticipated needs of frequent calibration and maintenance). An alternative is an updated version of the paramagnetic 02 analyzer. Reported advantages are: breath-by-breath -response, high -liability, raggedness and minimal need for maintenance and calibration.

Other multigas monitors are capable of the rapid analysis of A gases of interest based on mass spectrometry or Raman photospectrometry. Selected units are capable of the specific recognition of halocarbons in mixtures. N2 is also readily measured and this is useful in the recognition of air embolism and the inward leakage of room air into the deadspace of face masks or patient sampling lines. Lack of N2 measurement may lead to the misinterpretation of gas analyses. Direct N2 measurement offers the most protection, but the summing Of 02, N20, C02, and halocarbon would estimate N2. This feature has not yet been offered among infrared analyzers.

An advance shown in central, time-shared mass spectrometer systems was the integrated display of gas analyses with other physiologic monitors e-S., oximeters and automatic sphygmomanometers. In one case, a relatively low cost, quantitative, real time, integrated capnograph with wave form display was shown. This equipment functions continuously in each room during the time the central system is examining other rooms, and even in case of system shutdown. This feature may substantially reduce the objection to central, time-shared systems.

New Type of Mass Spec

Mass spectrometers designed for stand alone use were shown. They are more compact and less expensive than units designed for time-sharing systems, although the per room cost would depend on the size of the suite. An obvious advantage is the near-re-al-time analysis and data display. Like the mass spectrometer, the Raman photospectrometer, a compact gas analyzer designed for stand alone use, directly measures ad respiratory gases on a breath-by-breath basis. This unit is claimed to be nearly ready for marketing.

Automatic noninvasive sphygmomanometers with appropriate alarms are considered by many anesthesia practitioners to contribute materially to patient safety. Regular, frequent measurements are obtained, regardless of the anesthetist’s activities. The available units appear to function in a broadening range of patient age groups and conditions. Updating may be adjusted to short intervals, but measurements remain intermittent.

A potentially significant advance in sphygmomanometry was shown in an automatic, noninvasive, finger-cuff sphygmomanometer based on the Penaz principle. There is an arterial waveform and pressure readings are displayed on a beat-bybeat basis.

Noninvasive cardiac output monitors based on Doppler shift or transthoracic impedance plethysmography were shown. These could be promising monitors in selected cases.

Several different electronic stethoscopes were displayed. They are capable of amplifying distant heard sounds and breath sounds, and of selectively altering relative volumes. Note, however, that they retain the deficiencies of conventional stethoscopes: the total dependence on the attention of the anesthetist, and the absence of alarms.

Automated Records

Several computer implemented, automated record keepers were presented. These devices are indirectly related to patient safety. Vital signs from attached monitors are automatically recorded at frequent intervals regardless of activities of the anesthesiologist, without bias. Other data are precisely timed when manually entered. intraoperative and postoperative care review is facilitated; the effectiveness of treatment is apparent. Selected problems of these devices are the cumbersomeness of data entry and the possibility of the recording of artifacts. Acceptance of the concept among anesthesia practitioners remains to be seen.

Significant development in anesthesia machines include built-in, integrated patient monitoring systems. One manufacturer combined built-in monitors with an integral central alarm system. These improvements may contribute to patient safety by reducing confusion otherwise imposed by multiple monitors and alarms.

At least three sophisticated, new-generation ventilators were shown, intended primarily for use in the intensive care unit. In the realm of the operating room, recently, only minor ventilator improvements have been offered.

Other monitors and equipment shown at the meeting could merit mention in the context of patient safety, but the above illustrate the potential major role of advances in instrumentation in the effort to reduce preventable anesthesia morbidity and mortality.

Dr. Whitcher is Professor of Anesthesia (Clinical), Stanford University School of Medicine.