Warren D. Smith

Ergonomic problems associated with laparoscopic surgery.

AbstractBackground: The Society of American Gastrointestinal Endoscopic Surgeons (SAGES) Task Force on Ergonomics conducted a subjective and objective assessment of ergonomic problems associated with laparoscopic instrument use. The goal was to assess the prevalence, causes, and consequences of operational difficulties associated with the use of laparoscopic instruments. Methods: A questionnaire was distributed asking respondents to rate the frequency with which they experienced pain, stiffness, or numbness in several body areas after laparoscopic operations. An ergonomics station was assembled to quantify forearm and thumb muscle workload. Processed electromyogram (EMG) signals were acquired from 27 volunteer surgeon subjects while they completed simulated surgical tasks using a hemostat and an Ethicon® laparoscopic grasper, with the aid of an endoscopic trainer and video monitoring system. Results: Of 149 surgeons responding to the questionnaire, 8% to 12% reported frequent pain in the neck and upper extremities associated with laparoscopic surgery. The ergonomics station demonstrated that the peak and total muscle effort of forearm and thumb muscles were significantly greater (p < 0.01) when the grasping task was performed using the laparoscopic instrument rather than the hemostat. Conclusion: These findings indicate that laparoscopic surgical technique is more taxing on the surgeon.

Performance of the ARX-derived auditory evoked potential index as an indicator of anesthetic depth: a comparison with bispectral index and hemodynamic measures during propofol administration.

Background Autoregressive modeling with exogenous input of middle-latency auditory evoked potential (A-Line autoregressive index [AAI]) has been proposed for monitoring anesthetic depth. The aim of the current study was to compare the accuracy of this new index with the Bispectral Index (BIS), predicted effect-site concentration of propofol, and hemodynamic measures. Methods Twenty female patients scheduled for ambulatory gynecologic surgery received effect compartment controlled infusion of propofol. Target effect-site concentration was started at 1.5 &mgr;g/ml and increased every 4 min by 0.5 &mgr;g/ml. At every step, sedation level was compared with monitoring values using different clinical scoring systems and reaction to noxious stimulus. Results Bispectral Index, AAI, and predicted propofol effect-site concentration were accurate indicators for the level of sedation and loss of consciousness. Hemodynamic variables were poor indicators of the hypnotic-anesthetic status of the patient. BIS correlated best with propofol effect-site concentration, followed by AAI. Hemodynamic measurements did not correlate well. No indicators predicted reaction to noxious stimulus. Poststimulus, BIS and AAI showed an increase as a result of arousal. This reaction occurred more rapidly with the AAI than with BIS. Conclusion Bispectral Index, AAI, and predicted propofol effect-site concentration revealed information on the level of sedation and loss of consciousness but did not predict response to noxious stimulus.

Simulator training to automaticity leads to improved skill transfer compared with traditional proficiency-based training: a randomized controlled trial.

Objective:We hypothesized that novices will perform better in the operating room after simulator training to automaticity compared with traditional proficiency based training (current standard training paradigm). Background:Simulator-acquired skill translates to the operating room, but the skill transfer is incomplete. Secondary task metrics reflect the ability of trainees to multitask (automaticity) and may improve performance assessment on simulators and skill transfer by indicating when learning is complete. Methods:Novices (N = 30) were enrolled in an IRB-approved, blinded, randomized, controlled trial. Participants were randomized into an intervention (n = 20) and a control (n = 10) group. The intervention group practiced on the FLS suturing task until they achieved expert levels of time and errors (proficiency), were tested on a live porcine fundoplication model, continued simulator training until they achieved expert levels on a visual spatial secondary task (automaticity) and were retested on the operating room (OR) model. The control group participated only during testing sessions. Performance scores were compared within and between groups during testing sessions. Results:Intervention group participants achieved proficiency after 54 ± 14 and automaticity after additional 109 ± 57 repetitions. Participants achieved better scores in the OR after automaticity training [345 (range, 0–537)] compared with after proficiency-based training [220 (range, 0–452; P < 0.001]. Conclusions:Simulator training to automaticity takes more time but is superior to proficiency-based training, as it leads to improved skill acquisition and transfer. Secondary task metrics that reflect trainee automaticity should be implemented during simulator training to improve learning and skill transfer.

The effect of laparoscopic instrument working angle on surgeons' upper extremity workload.

BackgroundLaparoscopic surgery may be kinder to the patient, but it is more demanding on the surgeon. Fixed trocar positions often require the surgeon to work with instruments at awkward angles to their body. We studied the effect of horizontal and vertical laparoscopic instrument working angle on the surgeon’s thumb, forearm, and shoulder muscle work.MethodsElectronyographic (EMG) signals were collected from the thenar compartment (TH), flexor digitorum superficialis (FDS), and deltoid (DEL) muscles of the dominant arm of eight surgeons while they were closing a standard pistol-grip disposable laparoscopic grasper against a fixed resistance of 3 N. With the aid of a special testing bench, the instruments’ position was randomly changed among 15°, 45°, and 75° of horizontal angulation relative to the surgeons’ sagital plane, and 15°, 45°, and 75° degrees of vertical angulation relative to a horizontal plane. EMG signals were rectified and smoothed using analogue circuitry and digitally sampled at 10 Hz using a National Instruments DAQCard-700 connected to a Macintosh PowerBook 5300c running LabVIEW software. Statistical analysis was carried out by analysis of variance (ANOVA).ResultsThe effects of vertical and horizontal working angles on the muscle effort were as follows: TH (horizontal, N.S.; vertical, N.S.), FDS (horizontal, p<0.001; vertical, N.S.), and DEL (horizontal, p<0.001; vertical, p<0.01).ConclusionThese results suggest that working with laparoscopic instruments at a horizontal angle of >45° to the surgeon’s sagital plane significantly increases the workload of the flexor digitorium superficialis and deltoid muscles. The deltoid muscle is also adversely affected by vertical angulation of the instrument. The instrument working angle has no effect on the thenar muscles. Whenever possible, laparoscopic surgeons should strive to place their instruments and trocars so as to minimize extreme horizontal or vertical displacement of their hands away from a resting position of comfort.

A measure of association for assessing prediction accuracy that is a generalization of non-parametric ROC area.

There is a need for a measure of prediction accuracy that generalizes non-parametric receiver operating characteristic (ROC) area to polytomous ordinal patient state. We describe such a measure, prediction probability PK derived from Kims measure of association. We show that the value of PK equals the value of non-parametric ROC area for dichotomous patient state and is a meaningful generalization of non-parametric ROC area for polytomous state.

Increased stress levels may explain the incomplete transfer of simulator-acquired skill to the operating room.

BACKGROUND Proficiency-based simulator training in laparoscopic suturing leads to improved operative performance, but the skill transfer is incomplete. The objective of this study was to examine the stress level of trainees during the transition from the simulator to the operating room (OR) and its impact on performance. METHODS Novices (n = 20) were randomized into training and control groups. After the training group achieved proficiency in laparoscopic suturing, both groups were tested on a live porcine, laparoscopic Nissen fundoplication model. Participant performance was assessed using an objective score. Stress level was evaluated by recording beat-to-beat heart rate (BBHR) and short-term heart rate variability (STHRV) at baseline, after achieving proficiency (only the training group) and in the OR. Repeated measurement analysis of variance (ANOVA) and t test were used for analysis. RESULTS Baseline simulator performance and data for heart rate variability were similar for both groups. After achieving simulator proficiency, the trained group demonstrated the anticipated decrease in performance (mean average + or - SEM) in the OR (524 + or - 17 vs 290 + or - 95; P < .001), and an increase in BBHR (98 + or - 14 vs115 + or - 18; P < .001) but not STHRV (4.1 + or - 0.8 vs 3.7 + or - 0.9; P = .5). A similar but lesser increase of the BBHR was observed in the control group compared to the study group. CONCLUSION BBHR was a more sensitive measure of stress level compared with STHRV. The increased BBHR observed in the OR that reflects stress and performance anxiety may explain the incomplete transfer of simulator-acquired skill in novice learners.

Forty-hertz Midlatency Auditory Evoked Potential Activity Predicts Wakeful Response during Desflurane and Propofol Anesthesia in Volunteers

BACKGROUND Suppression of response to command commonly indicates unconsciousness and generally occurs at anesthetic concentrations that suppress or eliminate memory formation. The authors sought midlatency auditory evoked potential indices that successfully differentiated wakeful responsiveness and unconsciousness. METHODS The authors correlated midlatency auditory evoked potential indices with anesthetic concentrations permitting and suppressing response in 22 volunteers anesthetized twice (5 days apart), with desflurane or propofol. They applied stepwise increases of 0.5 vol% end-tidal desflurane or 0.5 microg/ml target plasma concentration of propofol to achieve sedation levels just bracketing wakeful response. Midlatency auditory evoked potentials were recorded, and wakeful response was tested by asking volunteers to squeeze the investigators hand. The authors measured latencies and amplitudes from raw waveforms and calculated indices from the frequency spectrum and the joint time-frequency spectrogram. They used prediction probability (PK) to rate midlatency auditory evoked potential indices and concentrations of end-tidal desflurane and arterial propofol for prediction of responsiveness. A PK value of 1.00 means perfect prediction and a PK of 0.50 means a correct prediction 50% of the time (e.g., by chance). RESULTS The approximately 40-Hz power of the frequency spectrum predicted wakefulness better than all latency or amplitude indices, although not all differences were statistically significant. The PK values for approximately 40-Hz power were 0.96 during both desflurane and propofol anesthesia, whereas the PK values for the best-performing latency and amplitude index, latency of the Nb wave, were 0.86 and 0.88 during desflurane and propofol (P = 0.10 for -40-Hz power compared with Nb latency), and for the next highest, latency of the Pb wave, were 0.82 and 0.84 (P < 0.05). The performance of the best combination of amplitude and latency variables was nearly equal to that of approximately 40-Hz power. The approximately 40-Hz power did not provide a significantly better prediction than anesthetic concentration; the PK values for concentrations of desflurane and propofol were 0.91 and 0.94. Changes of 40-Hz power values of 20% (during desflurane) and 16% (during propofol) were associated with a change in probability of nonresponsiveness from 50% to 95%. CONCLUSIONS The approximately 40-Hz power index and the best combination of amplitude and latency variables perform as well as predictors of response to command during desflurane and propofol anesthesia as the steady-state concentrations of these anesthetic agents. Because clinical conditions may limit measurement of steady-state anesthetic concentrations, or comparable estimates of cerebral concentration, the approximately 40-Hz power could offer advantages for predicting wakeful responsiveness.

Necessary and sufficient conditions in the tracer determination of compartmental system order.

Two assumptions inherent in common tracer techniques of determining the order of steady state compartmental systems are examined: (i) that experimental access to the compartmental system is adequate to reveal all compartments, and (ii) that the compartments can be counted by resolving tracer transients into sums of non-positive exponentials. Linear systems theory is applied to a matrix formalization of the tracer kinetics to derive necessary and sufficient conditions under which assumption (i) is valid. Examples of how to test for adequate experimental access are given for general classes of compartmental systems, as well as for specific structures. Both direct insertion and “natural” absorption of tracer into a system are considered. General methods of obtaining linear system order are related to the tracer analysis of compartmental systems. Assumption (ii) is valid only when the characteristic roots of the tracer system matrix are non-positive, real, and distinct. These roots are always non-positive; necessary and sufficient conditions on the compartmental structure are described under which they are also real and distinct. Also, the relations between the number of exponentials in a tracer transient and compartmental system order are derived for general compartmental structures.

Craniofacial Electromyogram Activation Response: Another Indicator of Anesthetic Depth

Objective. After finding that craniofacial EMG preceding a stimulus was a poor predictor of movement response to that stimulus, we evaluated an alternative relation between EMG and movement: the difference in anesthetic depth between the endpoint of EMG responsiveness to a stimulus and endpoint of movement responsiveness to that stimulus. We expressed this relation as the increment of isoflurane between the two endpoints. Methods. We measured EMG over the frontalis muscle, over the corrugator muscle, and between the Fp2 and the mastoid process as patients emerged from general anesthesia during suture closing of the surgical incision. Anesthesia was decreased by controlled washout of isoflurane while maintaining 70% N2O, and brain isoflurane concentrations (CisoBrain) were calculated. We studied a control group of 10 patients who received only surgical stimulation, and 30 experimental patients who intermittently received test stimuli in addition to the surgical stimulation. Patients were observed for movement responses and EMG records were evaluated for EMG activation responses. We defined an EMG activation response to be a rapid voltage increase of at least 1.0 µV RMS above baseline, with a duration of at least 30 s, in at least one of the three EMG channels. Patient responses to stimuli were classified as either an EMG activation response without a move response (EMG+, a move response without an EMG activation response (MV+), both an EMG activation response and a move response (EMG+MV+), or no response. We defined the EMG+ endpoint to be the threshold between EMG+ response and nonresponse to a stimulus, and estimatedC isoBrain at this endpoint. We similarly defined the move endpoint and estimated the move endpointC isoBrain. We then calculated the increment ofC isoBrain at the EMG+ endpoint relative to the move endpoint. Main results. For the 30 experimental patients, the initial response to a test stimulus was an EMG+ in 14 patients (47%), an EMG+MV+ in 12 patients (40%), and a MV+ in 1 patient (3%); no response occurred by the time surgery was completed in 3 patients (10%). No response occurred in 7 of the control patients (70%). Of the 14 patients with an initial EMG+ response to a test stimulus, 9 patients later had a move response. For these 9 patients, the increment of CisoBrain between the EMG+ endpoint and move endpoint was 0.11 ± 0.04 vol% (mean ± SD). Conclusions. Our results suggest that, given the circumstances of our study, an EMG activation response by a nonmoving patient indicates that the patient is at an anesthetic level close to that at which movement could occur. However, because the first EMG activation response may occur simultaneously with movement, the EMG activation response cannot be relied upon to always herald a move response before it occurs. Our results also suggest that EMG responsiveness to a test stimulus may be used to estimate the anesthetic depth of an individual patient.

EEG Predicts movement response to surgical stimuli during general anesthesia with combinations of isoflurane, 70% N2O, and fentanyl.

Objective. Our objective was to evaluate the performance of the EEG as an indicator of anesthetic depth by measuring EEG prediction of movement response to surgical stimuli.Methods. While using 5 different combinations of isoflurane, 70% N2O, and fentanyl, we measured the EEG of 246 patients during pelvic laparoscopy and observed their movement responses to opening stimuli (defined as skin incision, CO2 needle insertion, or trocar insertion) and also to closing stimuli (defined as sutures during incision closure). The EEG was expressed asF95, the frequency in hertz below which resides 95% of the power in the EEG frequency spectrum. The relations betweenF95 and movement response were expressed as logistic regression curves.F95-response logistic regression curves, which are analogous to dose-response curves, were calculated for each of the 2 stimuli administered during each of the 5 anesthetic techniques. The prediction of patient responsiveness byF95 was tested using β (beta), a measure of the slope of anF95-response logistic curve. The presence of shifts among theF95-response logistic curves was tested using the differences inF95 values between curves. Hypothesis tests used a level of significance ofP = 0.05.Main Results. The slopes of theF95-response logistic regression curves showed a statistically significant ability to predict movement response to stimuli for 9 of the 10 combinations of stimuli and anesthetic techniques. We did not calculate anF95-response logistic curve for the tenth combination because it contained burst suppression, which our EEG analysis method was not designed to process. TheF95-response logistic curves were shifted relative to each other, and the shifts were affected by the type of stimulus and the combination of anesthetic agents. Referenced to opening curves, the mean shift of the closing curves was ± 4.2 ± 0.3 Hz (mean ± SD). With increasing doses of fentanyl, the use of 70% N2O, or both, the curves shifted to higher values ofF95; the range in shifts was 0.2 to 8.1 Hz. The slope β values of theF95-response logistic curves and the shifts among the curves were similar to the β values and shifts that might be expected from changes in anesthetic agent doses.Conclusions. The EEG, expressed asF95, predicted movement response to surgical stimuli during combinations of isoflurane, 70% N2O, and fentanyl. TheF95-response curves shifted upward on the frequency scale for the less intense stimuli and for anesthetic techniques using 70% N2O, fentanyl, or both.F95 prediction of movement response appeared to be related to anesthetic agent doses. OurF95-response curves may provide helpful guidelines for usingF95 to titrate the administration of anesthetic agents and for assessing the depth of general anesthesia.