Monitor screen display inversion: Potential for risk during anaesthesia.

Sir,

Equipment failure is not new in the operating room despite thorough pre-operative check protocols. These failures are unforeseen and necessitate instant out of the box solutions from the anaesthesiologist. Of all the anaesthesia related problems, anaesthesia equipment failure accounts for 0.1-0.4%.[1] Problems relating to breathing circuits are most common.[12] Monitor malfunctions constitute 30% of equipment related problems[2] and while this frequency is low, the nuisance value of such malfunctions could be very high. Importance of monitoring and interpretation of data are crucial at all stages of anaesthesia. Artefacts in the monitoring equipment not only confound interpretation, but may lead to faulty clinical actions and unwarranted anxiety in the operating room.

We came across transient repetitive malfunction of a multiparameter monitor display. The monitor in use was the Infinity Gamma® Monitor (Drager© Medical AG and Co., KGaA Moislinger Allee 53/55, D-23542 Lubeck, Germany) used in a case of perianal abscess drainage under general anaesthesia in the casualty operation theatre. 5-min after administration of general anaesthesia the patient was positioned in lithotomy position. At this point, the display screen with all the numerical readings and waveforms inverted [Figure 1]. The orientation of the monitor changed with the lowermost window now displayed topmost. Within 15 s, the display reverted to normal only to invert again within the next few seconds. This sequence of events continued throughout in a random and unpredictable manner. Since the capnograph was being monitored on a separate screen (Anaesthesia gas monitor-Vamos®, Drager) that was the only parameter consistently available to the anaesthesiologist apart from the age old ‘hand on pulse.’ Since it was a short 15-min case in the casualty theatre far away from the main operation theatre complex, it was difficult to arrange for an alternate monitor. However, the case management was uneventful.

Figure 1

Inverted display on monitor

On enquiry with the technical expert of Drager© Medical, India, it was concluded that the problem was in the display software of the monitor and such a problem had never been notified to Drager© before. The monitor worked well without any display problems for the next 7 days. However, it continued to malfunction sporadically thereafter and was sent for replacement.

Various factors such as electrosurgical unit interference, motion artefacts, excessive ambient light, shivering, poor contact, sweat, evoked potentials, etc., are known to interfere with the electrocardiography (ECG)[3] and pulse oximeter waveforms. Selvan et al. have reported earthing faults causing ECG artefacts leading to serious haemodynamic consequences secondary to intra-aortic balloon pump trigger failure.[4] According to Takla et al., the current generation of monitors does not eliminate artefacts effectively due to the presence of linear filters.[5] They also suggest that this problem can be overcome by artificial intelligence and advanced signal processing methods.[5] The problem we encountered of display inversion was not related to the artefacts, but was due to software malfunction and may still occur in a monitor with advanced processing methods. In the event of monitor malfunction, a backup monitor should be made available. A defibrillator which is always present in the operation theatre complex can be handy for ECG monitoring until another multipara monitor is arranged. Availability of pulse oximeter module in the defibrillator would be an added advantage.