Electrosurgery and Temperature Increase in Tissue With a Passive Metal Implant.

Importance: During monopolar electrosurgery in patients, current paths can be influenced by metal implants, which can cause unintentional tissue heating in proximity to implants. Guidelines concerning electrosurgery and active implants such as pacemakers or implantable cardioverter defibrillators have been published, but most describe interference between electrosurgery and the active implant rather than the risk of unintended tissue heating. Tissue heating in proximity to implants during electrosurgery may cause an increased risk of patient injury. Objective: To determine the temperature of tissue close to metal implants during electrosurgery in an in-vitro model. Design, Setting, and Participants: Thirty tissue samples (15 with a metal implant placed in center, 15 controls without implant) were placed in an in vitro measurement chamber. Electrosurgery was applied at 5-60 W with the active electrode at three defined distances from the implant while temperatures at four defined distances from the implant were measured using fiber-optic sensors. Main Outcomes and Measures: Tissue temperature increase at the four tissue sites was determined for all power levels and each of the electrode-to-implant distances. Based on a linear mixed effects model analysis, the primary outcomes were the difference in temperature increase between implant and control tissue, and the estimated temperature increase per watt per minute. Results: Tissues with an implant had higher temperature increases than controls at all power levels after 1 min of applied electrosurgery (mean difference of 0.16°C at 5 W, 0.50°C at 15 W, 1.11°C at 30 W, and 2.22°C at 60 W, all with p < 0.001). Temperature increase close to the implant was estimated to be 0.088°C/W/min (95% CI: 0.078-0.099°C/W/min; p < 0.001). Temperature could increase to above 43°C after 1 min of 60 W. Active electrode position had no significant effect on temperature increases for tissues with implant (p = 0.6). Conclusions and Relevance: The temperature of tissue close to a metal implant increases with passing electrosurgery current. There is a significant risk of high tissue temperature when long activation times or high power levels are used.

Comparison between the AC and DC measurement of electrodermal activity.

Recording electrodermal activity is a well-accepted physiological measurement for clinical approaches and research. Historically, applying a DC (direct current) signal to the skin to measure the conductance is the most common practice for exogenous recordings. However, this method can be subject to error due to electrode polarization even with "nonpolarizing" electrodes-a problem that can be eliminated with alternating current (AC) methodology. For that reason, Boucsein et al. () called for research demonstrating an AC method that is validated by comparison to standard DC methodology. Additionally, the complex structure of human skin has electrical properties that include both resistance and capacitance, and AC recording enables the measurement of skin susceptance (associated with current flow through capacitors). Finally, AC recording permits the simultaneous recording of the endogenous skin potential. In this paper, the results from a direct comparison between both methods are presented, which has not been reported previously. The results demonstrated excellent agreement between a 20 Hz AC method and a standard DC method, supporting the validity of the AC recording methodology employed. The results also showed that an applied voltage of 0.2 V is sufficient for DC recordings.

Estimation of skin conductance at low frequencies using measurements at higher frequencies for EDA applications.

Using low-frequency (LF) alternating current skin conductance (SC) has recently been recommended for electrodermal activity (EDA) measurement, but the method may imply some limitations in sampling rate, which are insufficient for capturing the complete SC waveform. The aim of this study was to assess whether LF SC can be estimated based on skin admittance (SA) measurements at higher frequencies allowing higher sampling rates. SA measurements from 1 Hz to 70 kHz were gathered from 20 healthy human participants, and an interval from 500 Hz to 10 kHz was used to fit a Cole model to the measured SA by means of the nonlinear least squares method. The LF extrapolation of this fit was used to estimate the LF SC at 1, 10, 22 and 30 Hz. The method produced an overestimation of SC by approximately 20%, and the variation in LF SC was preserved by approximately 95%. The overestimation is most likely due to different frequency dependence behavior (dispersion) of SC at the lowest frequencies, which is not accounted for by a single dispersion model. In conclusion, the SA method using high frequency is unsuitable for estimation of the LF SC level, but can probably be used in EDA measurements, which are scored based on the variations in SC.

Bioimpedance-based respiration monitoring with a defibrillator.

Defibrillators often use an ac measurement to ensure safe electrode placement. Some defibrillators also utilize impedance measurements for ventilation monitoring. This paper investigates how such measurements can be optimized for high respiration sensitivity and finds that it is beneficial to add two extra electrodes in addition to the two defibrillator electrodes. This four electrode setup increases sensitivity and also allows respiration measurements at lower frequencies than the two electrode setup.

Tumescent suction curettage vs. curettage only for treatment of axillary hyperhidrosis evaluated by subjective and new objective methods.

The main purpose of this study was to compare the effect of the 2 minimally invasive surgical techniques for treating axillary hyperhidrosis: superficial tumescent suction curettage and curettage only. A total of 22 patients diagnosed with axillary hyperhidrosis received one type of treatment at each side, randomized. Examinations were performed pre-operatively and at 3, 6 and 12 months following treatment. Sweating was measured by gravimetry and a new skin conductance method. Subjective rating of sweating was assessed by a visual analogue scale. Skin conductance was recorded during a stress-test including acoustic, mental and physical stressors. Five patients withdrew or did not meet for any follow-up examination, giving 17 subjects in total for data analysis. Significant reduction in sweating after surgery lasting at least 12 months was found based on skin conductance, gravimetry and visual analogue scale scoring. Comparison between types of treatment revealed a significantly better effect of tumescent suction curettage than curettage only.

Waveform difference between skin conductance and skin potential responses in relation to electrical and evaporative properties of skin.

The shapes of skin conductance (SC) and skin potential (SP) responses are often similar, but can also be very different due to an unexplained cause. Using a new method to measure SC and SP simultaneously at the same electrode, this difference was investigated in a new way by comparing their temporal peak differences. SC, SP, skin susceptance (SS), and transepidermal water loss (TEWL) were recorded from 40 participants during relaxation and stress. The SP response could peak anywhere between the onset of an SC response to some time after the peak of an SC response. This peak time difference was associated with the magnitude of the SCR, the hydration of the skin, and the filling of the sweat ducts. Interpretation of the results in light of existing biophysical theories suggests that this peak difference may indicate the hydraulic capacity state of the sweat ducts at the time of a response.

Improved estimation of sweating based on electrical properties of skin.

Skin conductance (SC) has previously been reported to correlate strongly with sweat rate (Swr) within subjects, but weakly between subjects. Using a new solution for simultaneous recording of SC, skin susceptance (SS) and skin potential (SP) at the same skin site, the aim of this study was to assess how accurately sweat production can be estimated based on combining these electrical properties of skin. In 40 subjects, SC, SS, SP and Swr by skin water loss was measured during relaxation and mental stress. SC and Swr had high intraindividual correlations (median r = 0.77). Stepwise multilinear regression with bootstrap validation lead to a sweating estimation model based on the sum of SC increases, the SP area under the curve and the SS area under the curve, yielding an interindividual accuracy of R(2) = 0.73, rmse = 12.9%, limits of agreement of +27.6, -30.4% and an intraclass correlation coefficient of 0.84. Bootstrapping of training and test-sets gave median rmse = 15.4%, median R(2) = 0.66. The model was also validated for intraindividual variability. The results show that estimation of sweating is significantly improved by the addition of SS and SP measurement.

Publication recommendations for electrodermal measurements.

This committee was appointed by the SPR Board to provide recommendations for publishing data on electrodermal activity (EDA). They are intended to be a stand-alone source for newcomers and experienced users. A short outline of principles for electrodermal measurement is given, and recommendations from an earlier report (Fowles et al., ) are incorporated. Three fundamental techniques of EDA recording are described: (1) endosomatic recording without the application of an external current, (2) exosomatic recording with direct current (the most widely applied methodology), and (3) exosomatic recording with alternating current-to date infrequently used but a promising future methodology. In addition to EDA recording in laboratories, ambulatory recording has become an emerging technique. Specific problems that come with this recording of EDA in the field are discussed, as are those emerging from recording EDA within a magnetic field (e.g., fMRI). Recommendations for the details that should be mentioned in publications of EDA methods and results are provided.

Bioimpedance for pain monitoring during cutaneous photodynamic therapy: Preliminary study.

BACKGROUND: Pain is a well-known problem associated with light exposure during topical photodynamic therapy (PDT). Different methods for dealing with the pain have been developed over the past years, ranging from cooling with air or water to nerve blocking. However, the mechanisms responsible for the pain induction have not yet been fully understood. AIM: This study aims to evaluate bioimpedance in situ measurements of human skin as a method to shed light on pain-inducing real-time changes during light exposure during topical PDT. METHODS: Cream containing 20% aminolevulinic acid (ALA) was applied on forearms of ten healthy human volunteers. After 24h incubation, the cream was removed and the spots were exposed to red laser light (636nm, 300mW/cm(2)). During light exposure bioimpedance measurements with a 4-electrode set-up were taken at two frequencies (10Hz and 100kHz). RESULTS: A significant drop in skin impedance at high and low frequencies coincided with onset of pain during light exposure of spots treated with ALA. A similar drop was not observed for controls. CONCLUSIONS: Bioimpedance spectroscopy can provide valuable data for real-time observation of changes in skin, and may contribute to an increased understanding of the mechanisms responsible for induction of pain during topical PDT. Future studies are needed.

New method for separation of electrode polarization impedance from measured tissue impedance.

In this paper we have shown that electrode polarization impedance (EPI) can be separated from measured tissue impedance as long as the characteristic frequencies of EPI and tissue are not too close, so that the EPI is largely displayed as a separate dispersion. In 2-electrode measurements the EPI and sample are physically connected in series, and commonly modelled by equivalent components in series. We have calculated the parallel equivalent elements and converted the series connected EPI and sample to a parallel admittance model. By curve fitting on the converted model we have shown that this provides a new method for estimating the EPI with enhanced accuracy compared to similar techniques used on the impedance model.

Evaluation of algorithms for calculating bioimpedance phase angle values from measured whole-body impedance modulus.

This paper addresses the problem of calculating the bioimpedance phase angle from measurements of impedance modulus. A complete impedance measurement was performed on altogether 20 healthy persons using a Solatron 1260/1294 system. The obtained impedance modulus (absolute impedance value) values were used to calculate the Cole parameters and from them the phase angles. In addition, the phase angles were also calculated using a Kramers-Kronig approach. A correlation analysis for all subjects at each frequency (5, 50, 100 and 200 kHz) for both methods gave R(2) values ranging from 0.7 to 0.96 for the Cole approach and from 0.83 to 0.96 for the Kramers-Kronig approach; thus, both methods gave good results compared with the complete measurement results. From further statistical significance testing of the absolute value of the difference between measured and calculated phase angles, it was found that the Cole equation method gave significantly better agreement for the 50 and 100 kHz frequencies. In addition, the Cole equation method gives the four Cole parameters (R(0), R(∞), τ(z) and α) using measurements at frequencies up to 200 kHz while the Kramers-Kronig method used frequencies up to 500 kHz to reduce the effect of truncation on the calculated results. Both methods gave results that can be used for further bioimpedance calculations, thus improving the application potential of bioimpedance measurement results obtained using relatively inexpensive and portable measurement equipment.

Electrodermal activity by DC potential and AC conductance measured simultaneously at the same skin site.

BACKGROUND: For a long time, DC conductance has been the most important parameter in electrodermal routine measurements. However, DC current flow polarizes the electrodes, electrolyzes the skin, disturbs the measurement of conductance by possible varying electromotive forces (EMFs) in the circuit, and impedes the registration of the skin endosomatic DC potential. METHODS: We therefore present a measuring system where DC current was replaced by a small AC current in a monopolar system, enabling the DC potential and AC conductance to be measured simultaneously at the same skin site. RESULTS: We have also found examples of skin potential (SP) response waveforms with diphasic sharp edges not appearing in the conductance waveforms. The potential responses were found to be more robust with respect to movement artifacts, and the instrumentation could discern whether the indifferent electrode actually was on an inactive skin site. CONCLUSION: In order to study the generating mechanisms of EDA in detail, the SP must be measured without DC current flow and compared with AC conductance results.

A study on electrode gels for skin conductance measurements.

Low-frequency skin conductance is used within several clinical applications and is mainly sensitive to sweating and the moisture content of the stratum corneum, but also how electrodes introduce changes in the electrical properties. Four electrode gels were investigated with regard to sorption characteristics and electrical properties. Skin conductance time series were collected from 18 test subjects during relaxation, exercise and recovery, wearing different pairs of electrodes contralaterally on the hypothenar and the T9 dermatome. Pressure test was applied on the T9 electrodes. Impedance frequency sweeps were taken on the T9 electrodes the same day and the next, parameterized to the Cole model. ANOVA on the initial skin conductance level change, exercise response amplitude, recovery offset and pressure-induced changes revealed significant differences among gel types. The wetter gels caused a higher positive level change, a greater response amplitude, larger recovery offset and greater pressure-induced artifacts compared to the solid gels. Sweating on the T9 site led to negative skin conductance responses for the wetter gels. Correlations were found between the desorption measurements and the initial skin conductance level change (hypothenar: R = 0.988 T9: R = 0.901) RM-ANOVA on the Cole parameters revealed a significant decrease in R(s) of the most resistive gel. Clinical implications are discussed.

Early detection of cardiac ischemia using a conductometric pCO(2) sensor: real-time drift correction and parameterization.

For detection of cardiac ischemia based on regional pCO(2) measurement, sensor drift becomes a problem when monitoring over several hours. A real-time drift correction algorithm was developed based on utilization of the time-derivative to distinguish between physiological responses and the drift, customized by measurements from a myocardial infarction porcine model (6 pigs, 23 sensors). IscAlert conductometric pCO(2) sensors were placed in the myocardial regions supplied by the left anterior descending coronary artery (LAD) and the left circumflex artery (LCX) while the LAD artery was fully occluded for 1, 3, 5 and 15 min leading to ischemia in the LAD-dependent region. The measured pCO(2), the drift-corrected pCO(2) (DeltapCO(2)) and its time-derivative (TDpCO(2)) were compared with respect to detection ability. Baseline stability in the DeltapCO(2) led to earlier, more accurate detection. The TDpCO(2) featured the earliest sensitivity, but with a lower specificity. Combining DeltapCO(2) and TDpCO(2) enables increased accuracy. Suggestions are given for the utilization of the parameters for an automated early warning and alarming system. In conclusion, early detection of cardiac ischemia is feasible using the conductometric pCO(2) sensor together with parameterization methods.

A new approach for an estimation of the equilibrium stratum corneum water content.

BACKGROUND/PURPOSE: Water content is the most vital parameter governing the overall function of the epidermal stratum corneum (SC). Thus, knowledge of the in vivo absolute water content of the SC is of great interest. METHODS: We have investigated a non-invasive method for the estimation of in vivo SC water content based on transepidermal water loss measurements combined with desorption studies of SC in vitro, by means of a dynamic vapour sorption setup where relative humidity (RH) and temperature are controlled. RESULTS: The SC equilibrium water content of the volar forearm in our study was estimated to be 80+/-7 microg/cm2. The estimate of the water content seems to decrease slightly with increasing ambient RH. CONCLUSION: The estimated water content is a bit lower than what can be expected to be realistic. A calibration against ambient RH is most probably needed if our method is to be applied over a broad range of values of the RH in the ambient air.

Electrical impedance of stainless steel needle electrodes.

We present experimental findings regarding variability and stability of the electrical impedance properties of medical grade stainless steel needle electrodes in vitro. Monopolar impedance spectra (1 Hz to 1 MHz) were measured and scanning electron microscope images were obtained for five needle types with active electrode area from 0.28 to 0.7 mm(2). A saline tank (0.9% NaCl) was used as tissue model. Measurements were done before and after electrolytic treatment with anodic and cathodic DC currents of 1 muA. With active electrode areas below 1 mm(2), high influence from electrode polarization impedance (EPI) was expected at low frequencies (LF). For higher frequencies (HF) the EPI decreases and the impedance of the surrounding tissue is more pronounced. The hypothesis tested was that the EPI at LF would depend upon contact area, alloy composition, surface structure, and treatment of the active electrode, and at HF upon the electrode area geometry, and the specific resistivity of saline. Our results show large differences in electrical properties between needle types. After electrolytic treatment the EPI decreased. After 5-48 h of saline exposure the EPI increased, both for treated and untreated needles. Cathodic treatment gave lower impedance and drift than anodic or no treatment.

Invasive electrical impedance tomography for blood vessel detection.

We present a novel method for localization of large blood vessels using a bioimpedance based needle positioning system on an array of ten monopolar needle electrodes. The purpose of the study is to develop a portable, low cost tool for rapid vascular access for cooling and controlled reperfusion of cardiac arrest patients. Preliminary results show that localization of blood vessels is feasible with this method, but larger studies are necessary to improve the technology.

Current threshold for nerve stimulation depends on electrical impedance of the tissue: a study of ultrasound-guided electrical nerve stimulation of the median nerve.

BACKGROUND: Understanding the mechanisms causing variation in current thresholds for electrical nerve stimulation may improve the safety and success rate of peripheral nerve blocks. Electrical impedance of the tissue surrounding a nerve may affect the response to nerve stimulation. In this volunteer study, we investigated the relationship between impedance and current threshold needed to obtain a neuromuscular response. METHODS: Electrical nerve stimulation and impedance measurements were performed for the median nerve in the axilla and at the elbow in 29 volunteers. The needletip was positioned at a distance of 5, 2.5, and 0 mm from the nerve as judged by ultrasound. Impulse widths of 0.1 and 0.3 ms were used for nerve stimulation. RESULTS: A significant inverse relationship between impedance and current threshold was found at the elbow, at nerve-to-needle distances of 5 and 2.5 mm (P = 0.001 and P = 0.036). Impedance values were significantly lower in the axilla (mean 21.1, sd 9.7 kohm) than at the elbow (mean 36.6, sd 13.4 kohm) (P < 0.001). Conversely, current thresholds for nerve stimulation were significantly higher in the axilla than at the elbow (P < 0.001, P < 0.001, P = 0.024). A mean ratio of 1.82 was found for the measurements of current thresholds with 0.1 versus 0.3 ms impulse duration. CONCLUSIONS: Our results demonstrate an inverse relationship between impedance measurements and current thresholds and suggest that current settings used for nerve stimulation may require adjustment based on the tissue type. Further studies should be performed to investigate the clinical impact of our findings.

Impedance-based tissue discrimination for needle guidance.

Measurement of electrical impedance can discriminate between tissues of different electrical properties. A measurement system with adequate spatial resolution focused on a volume around the tip of a needle or other invasive clinical equipment can be used to determine in which type of tissue the tip is positioned. We have measured the sensitivity zone of a needle electrode with an active electrode area of 0.3 mm(2), and measured impedance spectra in porcine tissue in vivo. Small electrode impedance data will be influenced by electrode polarization impedance (EPI) at low frequencies. To refine existing methods for needle guidance with higher spatial resolution, we have used multivariate analysis and new interpretations of EPI, and tissue data gathered with selected needle electrodes. The focus of this study is on discrimination between muscle and fat/subdermis for drug administration, but our results also indicate that these refinements will facilitate new clinical applications for impedance-based needle guidance in general.

Electrical measurement of sweat activity.

A multichannel logger for long-term measurements of sweat activity is presented. The logger uses skin surface electrodes for unipolar admittance measurements in the stratum corneum. The logger is developed with emphasis on clinical use. The portability of the logger enables recording of sweat activity under circumstances such as daily errands, exercise and sleep. Measurements have been done on 24 healthy volunteers during relaxation and exercise with heart rate monitoring. Recordings of sweat activity during sleep have been done on two healthy subjects. Early results show good agreement with the literature on sweating physiology and electrodermal activity. Results are presented showing measurements related to physical exercise, dermatomes, distribution of sweat glands and sympathetic activity. This study examines the normal sweating patterns for the healthy population, and we present results with the first 24 healthy volunteers. Comparing these results with similar measurements on hyperhidrosis patients will make it possible to find the most useful parameters for diagnosis and treatment evaluation.