W. John Russell

Advanced Patient Monitoring Displays: Tools for Continuous Informing

We reviewed the use of advanced display technologies for monitoring in anesthesia. Researchers are investigating displays that integrate information and that, in some cases, also deliver the results continuously to the anesthesiologist. Integrated visual displays reveal higher-order properties of patient state and speed in responding to events, but their benefits under an intensely timeshared load is unknown. Head-mounted displays seem to shorten the time to respond to changes, but their impact on peripheral awareness and attention is unknown. Continuous auditory displays extending pulse oximetry seem to shorten response times and improve the ability to timeshare other tasks, but their integration into the already noisy operative environment still needs to be tested. We reviewed the advantages and disadvantages of the three approaches, drawing on findings from other fields, such as aviation, to suggest outcomes where there are still no results for the anesthesia context. Proving that advanced patient monitoring displays improve patient outcomes is difficult, and a more realistic goal is probably to prove that such displays lead to better situational awareness, earlier responding, and less workload, all of which keep anesthesia practice away from the outer boundaries of safe operation.

Monitoring with Head-Mounted Displays: Performance and Safety in a Full-Scale Simulator and Part-Task Trainer

BACKGROUND: Head-mounted displays (HMDs) can help anesthesiologists with intraoperative monitoring by keeping patients’ vital signs within view at all times, even while the anesthesiologist is busy performing procedures or unable to see the monitor. The anesthesia literature suggests that there are advantages of HMD use, but research into head-up displays in the cockpit suggests that HMDs may exacerbate inattentional blindness (a tendency for users to miss unexpected but salient events in the field of view) and may introduce perceptual issues relating to focal depth. We investigated these issues in two simulator-based experiments. METHODS: Experiment 1 investigated whether wearing a HMD would affect how quickly anesthesiologists detect events, and whether the focus setting of the HMD (near or far) makes any difference. Twelve anesthesiologists provided anesthesia in three naturalistic scenarios within a simulated operating theater environment. There were 24 different events that occurred either on the patient monitor or in the operating room. Experiment 2 investigated whether anesthesiologists physically constrained by performing a procedure would detect patient-related events faster with a HMD than without. Twelve anesthesiologists performed a complex simulated clinical task on a part-task endoscopic dexterity trainer while monitoring the simulated patient’s vital signs. All participants experienced four different events within each of two scenarios. RESULTS: Experiment 1 showed that neither wearing the HMD nor adjusting the focus setting reduced participants’ ability to detect events (the number of events detected and time to detect events). In general, participants spent more time looking toward the patient and less time toward the anesthesia machine when they wore the HMD than when they used standard monitoring alone. Participants reported that they preferred the near focus setting. Experiment 2 showed that participants detected two of four events faster with the HMD, but one event more slowly with the HMD. Participants turned to look toward the anesthesia machine significantly less often when using the HMD. When using the HMD, participants reported that they were less busy, monitoring was easier, and they believed they were faster at detecting abnormal changes. CONCLUSIONS: The HMD helped anesthesiologists detect events when physically constrained, but not when physically unconstrained. Although there was no conclusive evidence of worsened inattentional blindness, found in aviation, the perceptual properties of the HMD display appear to influence whether events are detected. Anesthesiologists wearing HMDs should self-adjust the focus to minimize eyestrain and should be aware that some changes may not attract their attention. Future areas of research include developing principles for the design of HMDs, evaluating other types of HMDs, and evaluating the HMD in clinical contexts.

Monitoring with Head-Mounted Displays in General Anesthesia: A Clinical Evaluation in the Operating Room

BACKGROUND:Patient monitors in the operating room are often positioned where it is difficult for the anesthesiologist to see them when performing procedures. Head-mounted displays (HMDs) can help anesthesiologists by superimposing a display of the patients vital signs over the anesthesiologists field of view. Simulator studies indicate that by using an HMD, anesthesiologists can spend more time looking at the patient and less at the monitors. We performed a clinical evaluation testing whether this finding would apply in practice. METHODS:Six attending anesthesiologists provided anesthesia to patients undergoing rigid cystoscopy. Each anesthesiologist performed 6 cases alternating between standard monitoring using a Philips IntelliVue™ MP70 and standard monitoring plus a Microvision Nomad™ ND2000 HMD. The HMD interfaced wirelessly with the MP70 monitor and displayed waveform and numerical vital signs data. Video was recorded during all cases and analyzed to determine the percentage of time, frequency, and duration of looks at the anesthesia workstation and at the patient and surgical field during various anesthetic phases. Differences between the display conditions were tested for significance using repeated-measures analysis of variance. RESULTS:Video data were collected from 36 cases that ranged from 17 to 75 minutes in duration (median 31 minutes). When participants were using the HMD, compared with standard monitoring, they spent less time looking toward the anesthesia workstation (21.0% vs 25.3%, P = 0.003) and more time looking toward the patient and surgical field (55.9% vs 51.5%, P = 0.014). The HMD had no effect on either the frequency of looks or the average duration of looks toward the patient and surgical field or toward the anesthesia workstation. CONCLUSIONS:An HMD of patient vital signs reduces anesthesiologists’ surveillance of the anesthesia workstation and allows them to spend more time monitoring their patient and surgical field during normal anesthesia. More research is needed to determine whether the behavioral changes can lead to improved anesthesiologist performance in the operating room.

Visual and auditory attention in patient monitoring: a formative analysis

We investigate the effectiveness of sonification (continuous auditory display) for supporting patient monitoring while reducing visual attentional workload in the operating theatre. Non-anaesthetist participants performed a simple continuous arithmetic task while monitoring the status of a simulated anaesthetised patient, reporting the status of vital signs when asked. Patient data were available either on a monitoring screen behind the participant, or were partially or completely sonified. Video captured when, how often and for how long participants turned to look at the screen. Participants gave the most accurate responses with visual displays, the fastest responses with sonification and the slowest responses when sonification was added to visual displays. A formative analysis identifying the constraints under which participants timeshare the arithmetic and monitoring tasks provided a context for interpreting the video data. It is evident from the pattern of their visual attention that participants are sensitive to events with different but overlapping temporal rhythms.

Phaeochromocytoma: Intraoperative changes in blood pressure and plasma catecholamines

The aim of this study was to assess the relationship between changes in plasma catecholamine concentrations and intraarterial blood pressure (BP) measured simultaneously during resection of phaeochromocytoma (n = 14). Arterial plasma concentrations of noradrenaline (NA), adrenaline (A) and dopamine (DA) were measured by a radio-enzymatic method. Arterial NA concentrations (pmol/ml; median and Wilcoxon 95% CI) were 71.8 (46,162) before induction of anaesthesia, 113.0 (79,231) after intubation, 375.0 (285,931) during tumour handling and 32.5 (18,88) following tumour removal. Simultaneous mean BP values (mmHg; Mean ± SEM) were 119 ± 8, 114 ± 7, 159 ± 7 (p = 0.0001) and 72 ± 6 (p < 0.0001) respectively. At the time of tumour handling there was a weak correlation between plasma NA and A combined and mean BP (r = 0.583,p = 0.029) and a stronger correlation between log plasma NA and A combined and pulse pressure (r = 0.749,p = 0.008). The very large rises in plasma catecholamine concentrations and in BP are likely to have been causally related. Individual patients maintained a constant ratio of NA to A in plasma from pre-induction to tumour handling (r = 0.916,p < 0.0001). The maintenance of a constant NA: A ratio suggests that the pattern of catecholamine synthesis and release may be a characteristic of the individual tumour.

Preoperative Risk Assessment and Intraoperative Monitoring

In emergency surgical settings, opportunities for optimization of the patient are usually limited due to the lack of time and often the hours during which surgery is required. However, in elective surgical settings, especially with higher-risk patients who have multiple comorbidities, preoperative evaluation and optimization are important considerations to reduce the risk of adverse events and to improve clinical outcomes. This chapter aims to provide information on perioperative assessment and intraoperative monitoring in an effort to reduce the rates of complications, risks, and consequences associated with surgery. For other associated procedures, refer to the relevant chapter or volume.