Skin conductance or entropy for detection of non-noxious stimulation during different clinical levels of sedation

Electrodermal Activity Monitoring During Painful Stimulation in Sedated Adult Intensive Care Unit Patients: a Pilot Study

Introduction-Aim: Newer methods, such as infrared digital pupillometry and electrodermal activity (EDA) measurement have been suggested as good alternatives for analgesia monitoring in critically ill patients. This study analyzed EDA changes due to pain stimulus in sedated adult critical care patients Methods: Skin conductance variability, selected hemodynamic and respiratory parameters, Bispectral index (BIS) and ambient noise level, were monitored during 4 hour routine daytime in an adult ICU. 4h-Measurements were divided into 2 groups, based upon the sedation level of the patients: Group A - Ramsay Sedation Score 2-4 and Group B - Ramsay Sedation Score of 5-6. Selected recordings before and after pain stimulus were performed. The stimulus chosen was the pressure applied to nail bed for 10 sec, which was performed routinely during neurological examination. Patients' demographics, laboratory exams and severity scores were recorded. Pain status evaluation before every event was also performed by 2 independent observers via Critical Care Pain Observation Tool (CPOT) and Adult Non Verbal Pain Score (ANVPS) Results: In both groups the rate of EDA changes was greater than other monitoring parameters: more in Group A than in Group B. Yet, the difference between groups was not statistically significant.

CONCLUSION

EDA measurements are greater to pain stimuli, than cardiovascular, respiratory or even BIS monitoring. These encouraging results suggest that, further studies are needed to better define EDA role in ICU.

Acute pain therapy in postanesthesia care unit directed by skin conductance: a randomized controlled trial

Background

After surgery, effective and well-directed acute pain therapy is a necessary and integral part of the overall treatment plan. Generally, the assessment of pain intensity depends on a patient’s self-evaluation using scoring systems such as numeric rating scales (NRS, 0 to 10). Recently, a “Pain Monitor” was commercially provided which is based on measurements of fluctuations of skin conductance (NFSC). In this randomized, controlled, single-blind trial, possible benefits of this certain device were studied.

Methods

Postoperative patients (n = 44) were randomly assigned to a test or a control group during their stay in the postanesthesia care unit (PACU). All patients were treated and monitored according to internal hospital standards. Whereas all patients systematically evaluated their pain each 15 min, test group patients were additionally addressed when NFSC exceeded a predefined level. In cases of NRS≥5 during a routine elevation or in between, pain relief was achieved by standard procedures irrespective of group allocation.

Results

During their stay in PACU, both test and control groups experienced a significant decrease in NRS as a consequence of pain therapy. No significant differences in mean NRS or in NFSC values were found between the test and control groups. No correlation was observed between NRS and NFSC.

Conclusion

Postoperative patients experience diverse stressors, such as anxiety, disorientation, shivering, sickness and pain. Although the application of continuous pain monitoring would be meaningful in this clinical setting, the tested device failed to distinguish pain from other stressors in postoperative adult patients.

Trial Registration

German Clinical Trials Register DRKS00000755.

Sympathetic reactivity in late pregnancy is related to labour onset in women

Stress regulation during pregnancy is considered to be connected to the timing of labour initiation. Although increasing knowledge is emerging on the regulation of parturition, there is currently no way to predict the start of spontaneous labour in women. The main aim of this study was to assess pain threshold and the sympathetic nervous system response to cold pain in relation to the onset of labour in healthy pregnant women. Ninety-three pregnant women were recruited and assessed for skin conductance (SC) activity during a cold pressor test in gestational week 38. Pain threshold and cold endurance were also measured and the results were compared with data obtained from hospital records. Seventy-four women had a spontaneous labour onset and a valid SC measurement. SC activity during the cold pressor test decreased significantly with the number of days left to spontaneous parturition. This may indicate a gradual decrease in sympathetic autonomic nervous system reactivity even during the last weeks of pregnancy. Measuring SC activity during mild stress provocation is a rapid and non-invasive means to study variation in sympathetic reactivity during pregnancy, and may be useful in research on stress regulation in pregnancy and its relation to labour initiation.

Comparison of the surgical Pleth Index™ with haemodynamic variables to assess nociception-anti-nociception balance during general anaesthesia

BACKGROUND

The Surgical Pleth Index (SPI) is proposed as a means to assess the balance between noxious stimulation and the anti-nociceptive effects of anaesthesia. In this study, we compared SPI, mean arterial pressure (MAP), and heart rate (HR) as a means of assessing this balance.

METHODS

We studied a standard stimulus [head-holder insertion (HHI)] and varying remifentanil concentrations (CeREMI) in a group of patients undergoing neurosurgery. Patients receiving target-controlled infusions were randomly assigned to one of the three CeREMI (2, 4, or 6 ng m⁻¹), whereas propofol target was fixed at 3 µg ml⁻¹. Steady state for both targets was achieved before HHI. Intravascular volume status (IVS) was evaluated using respiratory variations in arterial pressure. Prediction probability (Pk) and ordinal regression were used to assess SPI, MAP, and HR performance at indicating CeREMI, and the influence of IVS and chronic treatment for high arterial pressure, as possible confounding factors.

RESULTS

The maximum SPI, MAP, or HR observed after HHI correctly indicated CeREMI in one of the two patients [accurate prediction rate (APR)=0.5]. When IVS and chronic treatment for high arterial pressure were taken into account, the APR was 0.6 for each individual variable and 0.8 when all of them predicted the same CeREMI. That increase in APR paralleled an increase in Pk from 0.63 to 0.89.

CONCLUSIONS

SPI, HR, and MAP are of comparable value at gauging noxious stimulation-CeREMI balance. Their interpretation is improved by taking account of IVS, treatment for chronic high arterial pressure, and concordance between their predictions.

Recent advance in patient monitoring

Recent advance in technology has developed a lot of new aspects of clinical monitoring. We can monitor sedation levels during anesthesia using various electroencephalographic (EEG) indices, while it is still not useful for anesthesia depth monitoring. Some attempts are made to monitor the changes in sympathetic nerve activity as one of the indicators of stress, pain/analgesia, or anesthesia. To know the balance of sympathetic and parasympathetic activity, heart rate or blood pressure variability is investigated. For trend of cardiac output, low invasive monitors have been investigated. Improvement of ultrasound enables us to see cardiac structure and function continuously and clearer, increases success rate and decreases complication of central venous puncture and various kinds of nerve blocks. Without inserting an arterial catheter, trends of arterial oxygen tension or carbon dioxide tension can be monitored. Indirect visualization of the airway decreases difficult intubation and makes it easier to teach tracheal intubation. The changes in blood volume can be speculated non-invasively. Cerebral perfusion and metabolism are not ordinary monitored yet, but some studies show their usefulness in management of critically ill. This review introduces recent advances in various monitors used in anesthesia and critical care including some studies of the author, especially focused on EEG and cardiac output. However, the most important is that these new monitors are not almighty but should be used adequately in a limited situation where their meaning is confirmed.

Prospective study comparing skin impedance with EEG parameters during the induction of anaesthesia with fentanyl and etomidate

Objective

Sympathetic stimulation leads to a change in electrical skin impedance. So far it is unclear whether this effect can be used to measure the effects of anaesthetics during general anaesthesia. The aim of this prospective study is to determine the electrical skin impedance during induction of anaesthesia for coronary artery bypass surgery with fentanyl and etomidate.

Methods

The electrical skin impedance was measured with the help of an electro-sympathicograph (ESG). In 47 patients scheduled for elective cardiac surgery, anaesthesia was induced with intravenous fentanyl 10 μg/kg and etomidate 0.3 mg/kg. During induction, the ESG (Electrosympathicograph), BIS (Bispectral IndeX), BP (arterial blood pressure) and HR (heart rate) values of each patient were recorded every 20 seconds. The observation period from administration of fentanyl to intubation for surgery lasted 4 min.

Results

The ESG recorded significant changes in the electrical skin impedance after administration of fentanyl and etomidate(p < 0.05). During induction of anaesthesia, significant changes of BIS, HR and blood pressure were observed as well (p < 0.05).

Conclusions

The electrical skin impedance measurement may be used to monitor the effects of anesthetics during general anaesthesia.

Pharmacokinetic-pharmacodynamic modeling in anesthesia, intensive care and pain medicine

PURPOSE OF REVIEW

Studies from the anesthesiology literature published in the last 2 years were selected to illustrate the most important developments in the field of pharmacokinetic-pharmacodynamic modeling.

RECENT FINDINGS

The pharmacokinetic models focused on incorporating covariate, especially age for pediatric-geriatric use, and altered physiological states. The pharmacodynamic models studied the effect of rate of anesthetic administration, age, experimental conditions, and delay within the monitor on estimation of drug concentration in the biophase. Models for the surrogate measure of the components of general anesthesia, hypnosis (bispectral index scale, entropy), immobility (limb tetanic stimulus-induced withdrawal reflex) and antinociception (surgical stress index, skin conductance algesimeter) were developed and validated. Response surface models were used to study drug interactions for important end-points during surgery and also to optimize dosing of anesthetic agents to maximize the desired/undesired effect ratio. The models for target-controlled infusions were improved by incorporating more covariates, and the closed-loop system was refined by using adaptive controllers that individualize the pharmacokinetic/pharmacodynamic parameters to the particular patient by using Bayesian, Kalman filters, fuzzy logic or neural networks.

SUMMARY

Progress was made by improving population pharmacokinetic/pharmacodynamic models, developing new indexes to measure drug effect and using them in an adaptive delivery system to the individual patient.

New parameters of skin conductance compared with bispectral index ® monitoring to assess emergence from total intravenous anaesthesia

BACKGROUND

Arousal after total i.v. anaesthesia (TIVA) has been reported to be detectable by monitoring the number of fluctuations per second (NFSC), a parameter of skin conductance (SC). However, compared with monitoring of the bispectral index (BIS), the predictive probability of NFSC was significantly lower. The aim of this study was to determine the value of the two new, not yet published parameters of SC, area under the curve (AUC) methods A and B, for monitoring emergence from TIVA compared with monitoring of NFSC and BIS.

METHODS

Twenty-five patients undergoing surgery were investigated. NFSC, AUC A, AUC B, BIS, and haemodynamic parameters (mean arterial pressure and heart rate) were recorded simultaneously. The performance of the monitoring devices in distinguishing between the clinical states 'steady-state anaesthesia', 'first clinical reaction', and 'extubation' were compared using the method of prediction probability (Pk) calculation.

RESULTS

BIS showed the best performance in distinguishing between 'steady-state anaesthesia' vs 'first reaction' (Pk BIS 0.95; NFSC 0.73; AUC A 0.54; AUC B 0.62) and 'steady-state anaesthesia' vs 'extubation' (Pk BIS 0.99; NFSC 0.73; AUC A 0.71; AUC B 0.67). However, the time from first BIS>60/SC>0 to a first clinical reaction was significantly shorter for BIS (median BIS((R)) 180 s; NFSC 780 s; AUC A 750 s; AUC B 690 s; P < 0.001).

CONCLUSIONS

AUC A and AUC B did not improve accuracy of SC monitoring in patients waking after TIVA.

Comparison of skin conductance with entropy during intubation, tetanic stimulation and emergence from general anaesthesia

BACKGROUND

The number of skin conductance fluctuations (NSCF) expresses sympathetic skin nerve activity. The response entropy (RE) measures electromyographic and electroencephalographic activity in the forehead. The state entropy (SE) measures mainly electroencephalographic activity. When the suppression of frontal muscular activity is complete, RE is equal to SE. RE-Delta is defined as SE minus RE. The purposes of this study were to examine whether NSCF and RE-Delta correlate with signs of clinical stress during intubation and tetanic noxious stimulation and to elucidate how rapidly and accurately entropy and NSCF react during emergence from general anaesthesia.

METHODS

Twenty women scheduled for gynaecological laparotomy were studied. During intubation in remifentanil and propofol general anaesthesia, NSCF and RE-Delta were correlated with the clinical stress score. After a wash-out period, two series of tetanic stimuli were given, the first with (R+) and the second without (R-) remifentanil infusion. The tetanic pre-stimuli periods were compared with the tetanic post-stimuli periods, and R+ was compared with R-. During emergence, the responses of entropy and skin conductance were related to the time of extubation.

RESULTS

NSCF correlated well with the clinical stress score during intubation (r(2)= 0.73, P < 0.0005). RE-Delta showed a weaker correlation (r(2)= 0.33, P= 0.007). During tetanic stimuli, the NSCF pre-stimuli level was lower than the post-stimuli level (P < 0.001), and the NSCF R+ response was lower than the NSCF R- response (P= 0.002). RE-Delta did not show similar differences. During emergence, RE reacted before NSCF and SE (P= 0.003).

CONCLUSION

NSCF was better than RE-Delta for the measurement of clinical stress during intubation, and was sensitive to tetanic stimuli at different opioid analgesic levels, by contrast with RE-Delta. Both modalities were able to predict emergence at the end of anaesthesia, but RE was more rapid.