Volume 5, No. 4 • Winter 1990

Monitors and More Shown in Exhibits

John H. Eichhorn, M.D.

Patient Safety related technology and concepts were prominently featured in the technical and scientific exhibits at the October ASA Annual Meeting.

As has been the case in the last three years, existing forms of patient monitoring appeared in new “mix-and-match” ‘combinations while there was comparatively little in the way of genuinely new technology. A random survey of pricing policies suggest that there is more manufacturer/ dealer discounting-and flexibility this year and, thus, this may be a relatively good time for capital investments in monitors.

Within the category of monitors, respiratory gas and volatile agent monitors continue to be featured prominently. Several new versions and brands were shown for the first time. Less specific emphasis on the potential safety impact of these instruments was seen this year compared to) last year. Several prototypes of equipment for measuring blood gas and pH monitoring, both intermittent and continuous, were exhibited. Various technologies involving other than traditional electrodes are involved and each manufacturer seems confident of having solved (each in a different way) the potential problem of clot or serum protein obstruction of the device-blood interface. Each company suggested commercial availability “soon.”

‘Real Time’ NIBP

More attempts at non-invasive continuous real-time waveform blood pressure monitoring were demonstrated. One involves a small air bladder that compresses the radial artery against the underlying bone and functions as a tonometer. Another (which is zeroed against a traditional cuff involves somewhat the same concept with a piezoelectric crystal partially compressing the artery and then measuring arterial wall motion. Still another continuous blood pressure monitor shown in prototype last year senses pressure (after zeroing with a standard cuff) by comparing pulse wave velocity* and volume at two separate sites (usually finger and forehead). This latter instrument also can have reflectance plethysmograph/pulse oximetry incorporated.

Respiratory Sensors

Piezoelectric crystals also are the heart of a self contained wireless remote respiratory monitor that senses chest wall movement. The manufacturer claims a minimum of motion artifact because only the bidirectional equal volumes of the chest wall are recognized by the computer. The unit can also sense ECG and can transmit both via radio signals to a base unit. This technology is -suggested for epidural (pain therapy, labor, etc.) and PCA patients.

Hot Finger

There was significant emphasis on temperature monitoring and a wide variety of technologies to prevent heat loss and/or rewarm cold patients. A related concept was the demonstration of a mitten made of heat reflecting fabric intended for use enclosing a hand with a pulse oximeter probe in place on a finger. The goal is to prevent or relieve cold-induced vasoconstriction that can inhibit correct pulse oximeter function while at the same time shielding out potentially interfering ambient light.

At least three new versions and improved existing models of computers automated anesthesia records/patient information data managers were exhibited. Each will connect to existing monitoring equipment and capture patient -monitor output readings automatically at the programmed interval. Other details, such as compatibility with hospital mainframe computers, varied widely. All these manufacturers agreed, however, that they predict dramatically increased interest in and application of this type of technology.

New types of endotracheal tubes for use in laryngeal laser surgery and tubes made of new materials were shown. Each was touted as an advance in the quest for freedom from the threat of intratracheal fire during these procedures.

Vein Finder

One interesting new device was an ultrasound “finder” for central veins, particularly in the neck. The hand-held instrument gives a remarkably dear picture of the vessels in the neck and has on it a guide for the probing” needle who can almost be seen actually puncturing the vein as it is advanced. This type of device may both reduce accidental carotid and pleural punctures and also speed significantly the process of central line insertion.

Coags at the Drop of a Drop

Another new device was a coagulation monitor that uses only a drop of blood and can measure prothrombin time and activated partial thromboplastin time in a few seconds. Proposed use in the operating room to guide coagulation therapy was cited as a safety enhancement.

QA Systems Shown

In the scientific exhibits, them were three examples of anesthesia quality assurance systems. Each involved computer driven data bases, but the details of data collection, processing, display, and reporting varied widely. There was also an exhibit involving* an approach to the prevention and detection of substance abuse by anesthesia personnel. The patient safety implications of these presentations were clear and direct. The history of and benefits from patient monitoring were the subjects of an elaborate exhibit prepared by Leslie Rendell-Baker, M.D. and colleagues. A “hybrid artificial intelligence technique for recognizing and diagnosing abnormal capnograms was demonstrated. The exhibitors from Denver noted that eventually there may be a processing system that also initiates suggestions for remedial action based on the information generated by the capnogram analysis. Finally, the latest improvements in one of the well-recognized anesthesia simulators (on-screen presentations using a personal computer) were demonstrated.

The ‘Next’ Pulse Oximeter

The overall theme of the exhibits was refinement and micro-application of existing basic technology. Several equipment manufacturers were overheard to ask, “What is the next revolutionary technology equivalent in impact to the pulse oximeter?” Observers of these conversations concluded that there appeared to be no answer to this question.

Dr. Eichhorn, Harvard Medical School and Beth Israel Hospital, is Editor of the APSF Newsletter.