False Positive Alarms Research Articles

The Utah anesthesia workstation.

A prototype anesthesia workstation has been developed to demonstrate the feasibility of a computer-assisted anesthesia workplace. The workstation provides a central display of information and aids the user in controlling and monitoring the anesthesia delivery system. The anesthesiologist interacts with the workstation through a Macintosh computer, which is easy for the clinician to understand and to use. Seventeen sensors and monitors transmit information from the anesthesia delivery system to the computer. The computer monitors this information using a set of rules, evaluated once each breath, to detect changes in the delivery system. If an event is detected, the computer alerts the anesthesiologist with a diagram, a text message, and an audible warning. A laboratory test of the monitoring system was performed to see if it properly identified 26 different critical events during simulated low flow and closed circuit anesthesia. Five hundred and eight-three of 660 simulated critical events (88%) were identified with the unique and correct message. On 35 occasions, multiple messages were displayed, including the correct one. Critical events were misidentified or not detected 42 times. Eight false positive alarms occurred during the 20 h of testing; all occurred as a result of baseline drift in a single transducer. These results demonstrate that a sophisticated monitoring system can reliably diagnose specific anesthesia machine failures.

Some Considerations Regarding the Use of the Delta Lev-L-Sentry Low Level Alarm System

The possibility of infusing an air embolus during extracorporeal circulation is of concern to every perfusionist. The perfusionist uses a variety of devices to prevent such an accident. The Delta Lev-L-Sentry alarm system is one such device. It consists of a disposable sensor tape, an electronic sensor head, and a power/control box. The sensor head and tape are attached to the oxygenator. The unit will warn of a low level situation in the oxygenator when the fluid falls below the preset sensor tape position. This paper describes two possible situations where the Delta-L-Sentry alarm system may not activate properly, and one situation in which it will activate improperly. A protein coating from the blood can result in a low sensitivity of the sensor tape. This, combined with a rapid draining of the oxygenator, can produce a false negative alarm. To avoid this false negative alarm mode it is recommended that the sensor tapes be cut and attached at the prescribed 50 degree angle (from the horizontal) regardless of the angle supplied by the manufacture. Another situation which can cause a false negative alarm mode is spilling electrolyte solution on the sensor tape. This can be avoided by protecting the sensor head. The one instance of a false positive alarm mode was caused by electrocautery interference during surgery. The use of a grounding cable will reduce the interference thus avoiding the false positive alarm signals.

Microprocessor-based long term cardiorespirography. I. Heart rate changes and apneic attacks.

Cardiorespirography is a well-known method of continuous monitoring in neonatal intensive care. Apneic attacks, bradycardia and tachycardia are registered. In our experience we connected a cardiorespirography recorder to a microprocessor system. The processor consisted of a hardware part including a program (software) and a printer which provided printouts of alarm events. As alarm situations, which cause an alarm printout, we defined: 1. apneic episodes (duration 10, 20 or 30 seconds) 2. tachycardiac (beat-to-beat rate greater than 180/minute) 3. V-shaped and U-shaped bradycardia (beat-to-beat heart rate less than 80/min) and combinations. The reliability of the system of recognizing and classifying alarm situations was tested by comparing the alarm printouts with the simultaneously recorded cardiorespirograms. Fifty eight 12 hour records of 41 patients were evaluated. Six hundred alarm situations were counted. The alarm printouts were found in concordance with the cardiograms in all tachycardia alarms. Nearly all bradycardia (V-shaped, U-shaped bradycardia, combination of bradycardia and apnea) were correctly classified. A preset apnea duration of 10 seconds resulted in many false positive alarm printouts. With 20 second apnea time only few false positive alarms were seen, but nine apneic attacks were not recognized. Altogether 81.5% of alarm printouts were correct, 16.8% were false alarms, or V-shaped bradycardia were really U-bradycardia. Only 2% of all alarms were not recognized by the microprocessor system. We suggest to combine the microprocessor with a special alarm recorder, which is able to store beat-to-beat heart rate and respiration wave before alarm situations.

Evaluation of a computerized arrhythmia alarm system

A prospective study of a computerized arrhythmia alarm system was carried out in the coronary care unit during 200 patient hours of monitoring. The computer system was designed to activate an alarm on the development of rhythm and conduction disorders including asystole, ventricular tachycardia, atrial tachycardia, sinus tachtcardia, bradycardia, frequent premature ventricular beats, atrial fibrillation and bundle branch block. Study patients were simultaneously monitored by the computer system and a conventional analog heart rate alarm system. All alarms generated by the two systems were evaluated. Of 79 computer alarms, 42 (53 percent) were true positive alarms; during the same period there were 167 analog alarms of which only 13 (8 percent) were true positive alarms. In both systems, false positive alarms were primarily due to patient movement, but they occurred only 25 percent as often with the computer system as with the analog system. These results indicate that computerized arrhythmia monitoring systems offer significant advantages over conventional monitoring techniques.

Detection of ventricular arrhythmias in real-time with a portable analog computer

Recent studies on the occurrence of sudden death emphasize that many patients have ventricular premature contractions as prodromes of lethal arrhyhmlas. A portable, 6 ounce analog computer has been developed to detect tachycardias (heart rate 150 to 190 beats/min), bradycardias (heart rate less than 50 beats/min) and ventricular premature contractions. When preset limits are exceeded, acoustic warnings are sounded, and the patient may transmit his electrocardiogram by telephone, without additional equipment, to a receiving device that graphically reproduces the electrocardiogram in real-time. Hospital studies in 26 ambulatory patients with a variety of arrhythmias have been completed. Tachycardias and bradycardias were detected in every instance during 30 observation periods in six patients. Reproducible warnings were triggered in 19 of the 20 patients with ventricular premature contractions of various configurations during each of 5 observation periods (100 observations). In one patient, the electrical vector of the ventricular premature contraction closely resembled the normal QRS vector and was not detected. Appropriate electrode placement is essential to avoid initial Q waves and to maximize the difference between the vector of ventricular premature contraction and that of the normal QRS complex. No false positive acoustic alarms were sounded. Our results demonstrate that it is possible to detect ventricular premature contractions readily and reproducibly in ambulatory patients. Use of this detector may permit large scale monitoring of patients with a high risk of sudden death.

Tests for hydrocyanic acid: G. C. Sherrard of the U. S. Public Health Service (Pub. Health Rep., 1928, 43, 1016–1022)

The ion mobility behavior of nineteen chemical warfare agents (7 nerve gases, 5 blister agents, 2 lachrymators, 2 blood agents, 3 choking agents) and related compounds including simulants (8 agents) and organic solvents (39) was comparably investigated by the ion mobility spectrometry instrument utilizing weak electric field linear drift tube with corona discharge ionization, ammonia doping, purified inner air drift flow circulation operated at ambient temperature and pressure. Three alkyl methylphosphonofluoridates, tabun, and four organophosphorus simulants gave the intense characteristic positive monomer-derived ion peaks and small dimer-derived ion peaks, and the later ion peaks were increased with the vapor concentrations. VX, RVX and tabun gave both characteristic positive monomer-derived ions and degradation product ions. Nitrogen mustards gave the intense characteristic positive ion peaks, and in addition distinctive negative ion peak appeared from HN3. Mustard gas, lewisite 1, o-chlorobenzylidenemalononitrile and 2-mercaptoethanol gave the characteristic negative ion peaks. Methylphosphonyl difluoride, 2-chloroacetophenone and 1,4-thioxane gave the characteristic ion peaks both in the positive and negative ion mode. 2-Chloroethylethylsulfide and allylisothiocyanate gave weak ion peaks. The marker ion peaks derived from two blood agents and three choking agents were very close to the reactant ion peak in negative ion mode and the respective reduced ion mobility was fluctuated. The reduced ion mobility of the CWA monomer-derived peaks were positively correlated with molecular masses among structurally similar agents such as G-type nerve gases and organophosphorus simulants; V-type nerve gases and nitrogen mustards. The slope values of the calibration plots of the peak heights of the characteristic marker ions versus the vapor concentrations are related to the detection sensitivity, and within chemical warfare agents examined the slope values for sarin, soman, tabun and nitrogen mustards were higher. Some CWA simulants and organic solvents gave the ion peaks eluting at the similar positions of the CWAs, resulting in false positive alarms.