Skin Temperature During Regional Anesthesia of the Lower Extremity

Infrared thermographic assessment of spinal anaesthesia-related cutaneous temperature changes during caesarean section

INTRODUCTION

Assessment of adequacy of spinal anaesthesia prior to obstetric surgery is extremely important but can be problematic because currently available clinical assessment methods are indirect and subjective. As the sympathectomy associated with spinal anaesthesia is known to cause vasodilation and heat redistribution, we sought to assess whether spinal anaesthesia led to significant and consistent cutaneous temperature changes as measured by infrared thermography.

METHODS

Following ethics committee approval, this observational study was conducted in a tertiary level obstetric centre. Participants included women undergoing elective caesarean section under spinal anaesthesia. Following consent, a Flir T540 infrared camera captured thermographic images over the feet, patella, buttock, iliac crests, xiphisternum and axilla. Temperature was measured prior to spinal needle insertion (T0) and following clinical assessment when the block was deemed adequate.

RESULTS

Thirty patients were included. Baseline temperature varied considerable by site. Spinal anaesthesia altered skin temperature in all areas of interest: right and left hallux (mean of differences (MD) +4.0°C and 5.2°C respectively, P <0.0001), right and left plantar (MD +6.1°C and 6.8°C respectively, P <0.0001), patella (MD -0.33°C, P=0.0445), buttock (MD -0.5°C, P=0.009), iliac crest (MD -0.7°C, P=0.0004), xiphisternum (MD -0.95°C, P <0.0001) and axilla (MD -0.71°C, P=0.0002).

CONCLUSIONS

Following spinal anaesthesia thermographic imaging identified different patterns of skin temperature changes, with pronounced temperature increases measured in the feet and cooling of a lesser amplitude in the thoracic and lumbar dermatomes. Infrared thermography has the potential to provide objective measurement of sympathectomy.

Skin temperature changes after ultrasound-guided supra-inguinal fascia iliaca block: a prospective observational study

PURPOSE

Ultrasound-guided supra-inguinal fascia iliaca block (SFIB) is widely used as regional anesthesia of the hip and thigh. It is difficult to judge the blocking effect and the spreading local anesthesia. We hypothesize that the effect and spread of the block could be proven objectively by a rise in the temperature. In this prospective observational study, the broad regional rise in skin temperature of twenty patients who were scheduled for hip surgery was measured using an infrared thermographic camera at multiple intervals following ultrasound-guided SFIB.

METHODS

Infrared thermographic imaging of skin temperature at the femoral, obturator, and lateral femoral cutaneous nerve sites was performed before and at 5-min intervals after ultrasound-guided SFIB for up to 15-min post-injection. The primary outcomes are skin surface temperature. Sensory block was assessed immediately after the final infrared thermographic image acquisition using the cold test.

RESULTS

Compared to pre-injection baseline, temperature increased by 1.2 °C [95% confidence interval (CI) 0.4-2.0 °C] after 5 min, 1.2 °C (95% CI 0.4-2.0 °C) after 10 min, and 0.9 °C (95% CI 0.4-2.1°C) after 15 min. The cold test response was reduced in all cases at the femoral and lateral femoral cutaneous nerve sites and in 13 cases at the obturator nerve site. The sensitivity and specificity of the temperature increase to cold loss were 96% and 63%, respectively when we defined >0°C as the clinical threshold.

CONCLUSIONS

Successful SFIB significantly enhanced skin temperature at the hip and thigh in all cases, suggesting that infrared surface thermography can be used as an objective assessment tool for adequate analgesia.

TRIAL REGISTRATION

University Hospital Medical Information Network Clinical Trials Registry ( UMIN 000037866 ). Registered 31 August 2019.

Use of high-resolution thermography as a validation measure to confirm epidural anesthesia in mice: a cross-over study

BACKGROUND

Effective epidural anesthesia is confirmed in humans by sensory assessments but these tests are not feasible in mice. We hypothesized that, in mice, infrared thermography would demonstrate selective segmental warming of lower extremities following epidural anesthesia.

METHODS

We anesthetized 10 C57BL/6 mice with isoflurane and then inserted a PU-10 epidural catheter under direct surgical microscopy at T11-12. A thermal camera (thermal sensitivity ±0.05°C, pixel resolution 320x240 pixels, and spatial resolution 200 μm) recorded baseline temperature of front and rear paws, tail and ears. Thermography was assessed at baseline and 2, 5, 10, and 15 min after an epidural bolus dose of 50 μL bupivacaine 0.25% or 50 μL saline (control) using a cross-over design with dose order randomized and investigators blinded to study drug. Thermal images were recorded from video and analyzed using FLIR software. Effect over time and maximal effect (E_max) were assessed by repeated measures ANOVA and paired t-tests. Comparisons were between bupivacaine and control, and between lower vs upper extremities.

RESULTS

Epidural bupivacaine caused progressive warming of lower compared with upper extremities (P <0.001), typically returning to baseline by 15 min after administration. Mean (±SD) E_max was +3.73 (±1.56) °C for lower extremities compared with 0.56 (±0.68) °C (P=0.03) for upper extremities. Following epidural saline, there was no effect over time (E_max for lower extremities -0.88 (±0.28) °C compared with the upper extremities -0.88 (±0.19) °C (P >0.99).

CONCLUSIONS

Thermography is a useful tool to confirm epidural catheter placement in animals for which subjective, non-noxious, sensory measures are impossible.

Assessment of skin temperature during regional anaesthesia-What the anaesthesiologist should know

Body temperature homeostasis is accurately regulated by complex feedback-driven neuronal mechanisms, which involve a multitude of thermoregulatory pathways. Thus, core temperature is constantly maintained within a narrow range. As one of the most effective regulatory systems skin temperature is dependent on skin blood flow. Skin blood flow in turn is highly dependent on sympathetic activity. Regional anaesthesia leads to blockade not only of somatosensory and motor nerve fibres but also of sympathetic fibres. As a consequence, vasoconstrictor tonic activity is abrogated and a vasodilation leads to an increase in skin blood flow and temperature. The aim of this review was to summarize the general physiology of thermoregulation and skin temperature as well as the alterations during regional anaesthesia. The main focus was the usefulness of measuring skin temperature as an indicator of regional anaesthesia success. According to the available literature, assessment of skin temperature can indeed serve to predict success of regional anaesthesia. Hence, it is important to realize that relevant and reliable temperature increase is only seen in the most distal body parts, ie fingers and toes. More proximally, temperature changes are frequently small and inconsistent, which means that assessment of block levels is not possible by temperature measurement. Furthermore, relevant skin temperature increases will only be observed in patients, which are initially vasoconstricted. In conclusion, measurement of skin temperature represents a reliable and feasible diagnostic tool to assess and predict the success or failure of regional anaesthesia procedures, especially in patients in which sensory testing is impossible.

Thermographic skin temperature measurement compared with cold sensation in predicting the efficacy and distribution of epidural anesthesia

Due to the high rates of epidural failure (3-32%), novel techniques are required to objectively assess the successfulness of an epidural block. In this study we therefore investigated whether thermographic temperature measurements have a higher predictive value for a successful epidural block when compared to the cold sensation test as gold standard. Epidural anesthesia was induced in 61 patients undergoing elective abdominal, thoracic or orthopedic surgery. A thermographic picture was recorded at 5, 10 and 15 min following epidural anesthesia induction. After 15 min a cold sensation test was performed. Epidural anesthesia is associated with a decrease in skin temperature. Thermography predicts a successful epidural block with a sensitivity of 54% and a PPV of 92% and a specificity of 67% and a NPV of 17%. The cold sensation test shows a higher sensitivity and PPV than thermography (97 and 93%), but a lower specificity and NPV than thermography (25 and 50%). Thermographic temperature measurements can be used as an additional and objective method for the assessment of the effectiveness of an epidural block next to the cold sensation test, but have a low sensitivity and negative predictive value. The local decrease in temperature as observed in our study during epidural anesthesia is mainly attributed to a core-to-peripheral redistribution of body heat and vasodilation.

Thermography as an early predictive measurement for evaluating epidural and femoral-sciatic block success in dogs

OBJECTIVE

To evaluate skin temperature increase as an early predictive measure for evaluating epidural and femoral-sciatic block success in dogs.

STUDY DESIGN

Prospective clinical trial.

ANIMALS

A total of 29 dogs undergoing orthopaedic surgery on one hindlimb.

METHODS

Dogs were anaesthetized and placed into lateral recumbency with the affected limb uppermost and the coat was clipped. Baseline infrared thermographic images (T0) of the affected limb, of the paw pad of the affected leg and of the ipsilateral paw pad were taken. Subsequently, dogs were administered either an epidural (EPI; n=11) or a femoral-sciatic block (FS; n=18) using bupivacaine 1 mg kg^-1. Then, 2 minutes after placement of the block, thermographic images were obtained every 3 minutes for a total of four measurements (T1-T4) and surgery was commenced. Rescue analgesia consisting of fentanyl 1 μg kg^-1 was administered if needed. A regional block was considered successful if the dose of fentanyl administered was less than the lower 95% confidence interval of the geometric mean of the total fentanyl used in each group. A ≥ 1 °C increase of skin temperature was considered as the minimum increase required for detection of a successful block.

RESULTS

A total of 12 out of 18 blocks in the FS and eight of 11 in the EPI group were considered successful based on fentanyl consumption. Out of these, only four of 12 in the FS and one of eight in the EPI group developed an increase in temperature of ≥ 1 °C. Contrarily, four of six of the nonsuccessful cases in the FS and three of three in the EPI group developed an increase in temperature of ≥ 1 °C.

CONCLUSIONS AND CLINICAL RELEVANCE

Contrary to reports in humans, thermography did not indicate regional block success prior to surgery in dogs. However further studies under more controlled conditions are needed to determine whether thermography can be used to indicate failure of regional blockade.

Skin temperature measured by infrared thermography after ultrasound-guided blockade of the sciatic nerve

BACKGROUND

In the present study, we assessed the relationship between subgluteal sciatic nerve blocking and skin temperature by infrared thermography in the lower extremity. We hypothesized that blocking the sciatic nerve will lead to an increase in temperature, and that this will correlate with existing sensory block tests.

METHODS

We studied 18 healthy individuals undergoing orthopaedic surgery of the foot under ultrasound-guided subgluteal blockade of the sciatic nerve with 30 ml ropivacaine 7.5 mg/ml. Skin temperature was measured on the toes, the dorsal and plantar side of the foot, the malleoli, and the lateral side of the lower leg, just before sciatic nerve blockade and at 10-min intervals thereafter.

RESULTS

Baseline skin temperatures showed a significant distal-to-proximal gradient. After sciatic block, temperatures on the blocked side increased significantly in the toes and foot. When comparing pinprick to skin temperature in a receiver operating curve, there was an AUC of 85.9% (95% confidence interval = 83.7-88.2%, P < 0.001). The medial malleolus (not being innervated by the sciatic nerve) showed no significant difference to the lateral.

CONCLUSIONS

After sciatic nerve block, temperatures of the foot increased significantly. There was a good correlation between pinprick testing and infrared temperature measurement. This makes infrared skin temperature measuring a good test in determining block success when sensory testing is impossible.

Assessment of pulse oximeter perfusion index in pediatric caudal block under basal ketamine anesthesia

Whether pulse oximeter perfusion index (PI) may be applied to detect the onset of caudal block in pediatric patients under ketamine intravenous basal anesthesia is investigated. 40 ASA I, 2–8-year-old boys scheduled for elective circumcision surgery were randomized into two groups. Group I: 20 patients were anesthetized by 2 mg·kg⁻¹ ketamine intravenous injection (IV) followed by caudal block using 1 mL·kg⁻¹ lidocaine (1%); Group II: 20 patients were anesthetized by 2 mg·kg⁻¹ ketamine IV only. PI on the toe in Group II decreased by 33 ± 12%, 71 ± 9% and 65 ± 8% at 1 min, 15 min, and 30 min after ketamine injection. The maximum increase in MAP and HR after ketamine IV was 11 ± 6% at 3 min and 10 ± 6% at 2 min. Compared to the PI value before caudal injection of lidocaine, PI in Group I increased by 363 ± 318% and 778 ± 578% at 5 min and 20 min after caudal block, while no significant changes in MAP and HR were found compared to the baseline before caudal block. Thus, PI provides an earlier, more objective, and more sensitive indicator to assess the early onset of caudal block under basal ketamine anesthesia.

Temperature measurement

For many decades the measurement of body core temperature has been ubiquitously established in medical and non-medical applications, e.g., in hospitals, occupational medicine, sports medicine, military and other settings. However, there are still numerous challenges, such as the precise definition of the body core temperature, establishing the clinical importance of the measured temperature and the lack of a reliable, non-invasive and fast measurement method for body core temperature. After an introduction to the topic, the medical aspects from a user point of view are presented, i.e., the needs for temperature measurements, as well as possible measurement sites and clinical specifications and needs are highlighted. Subsequently, technical methods are presented which are used for temperature measurement. The analysis of the technical methods is divided into two sections: the first deals with the standard methods, which are currently used and the second describes methods, which are currently under development. Although temperature measurement appears very easy and is very common in daily use, it has many constraints, which are considered later. The need for further research is deduced from the above-mentioned sections and is finally followed by the conclusions section.

Noninvasive tissue oxygen saturation determined by near-infrared spectroscopy following peripheral nerve block

BACKGROUND

Noninvasive physiologic measurement of cutaneous tissue oxygenation using near-infrared spectroscopy (NIRS) has become increasingly common in cardiovascular and plastic surgery. The aim of this study was to determine whether clinically available NIRS-based monitors could detect changes in tissue oxygen saturation (rSO(2)) following a variety of peripheral nerve blocks. We hypothesize that peripheral nerve blocks will produce detectable changes in cutaneous tissue oxygenation levels that can be measured by noninvasive NIRS-based oximetry.

METHODS

Forty adult patients scheduled for pre-operative peripheral nerve block placement were enrolled. Prior to block placement, NIRS sensors were placed on the operative and nonoperative (control) limb. Baseline tissue oxygen saturation values were obtained prior to dosing of the nerve block, and measurements were recorded every 5 min thereafter.

RESULTS

Initial rSO(2) values were higher in the operative vs. control limbs prior to nerve block placement. Tissue oxygen saturation increased in the blocked, but not control, limbs with time. Subgroup analysis suggested statistically significant differences in rSO(2) values in blocked vs. control limbs for cervical paravertebral, infraclavicular, and femoral nerve blocks.

CONCLUSIONS

Our results demonstrated sustained increases in tissue rSO(2) values following peripheral nerve block placement, in addition to higher initial rSO(2) values in operative limbs prior to block placement. Further investigations are necessary to define the expected baseline rSO(2) values in operative and control limbs. Future efforts utilizing NIRS-based detection of tissue ischemia should consider the small but significant changes in rSO(2) resulting from a successful nerve block.

The effects of sympathectomy on finger photoplethysmography and temperature measurements in healthy subjects

BACKGROUND

Photoplethysmography uses light transmission to measure changes in tissue volume. The resulting photoplethysmogram is composed of AC and DC components. Limited data are available on the effects of vasodilation on the AC and the DC components of the photoplethysmograph signal. The aims of our study were (1) to investigate the effects of sympathectomy on different components of the photoplethysmogram, and (2) to compare sympathectomy-induced changes in the photoplethysmogram with changes in peripheral temperature.

METHODS

In 10 healthy subjects, sympathectomy-induced peripheral vasodilation was achieved using an axillary brachial plexus block. The nonblocked arm served as control. We obtained measurements of bilateral continuous measurements of finger blood volume (by photoplethysmography) and finger temperature. We separated the finger photoplethysmogram into its AC and DC components. In addition, we calculated the ratio of AC to DC (AC/DC). All data were recorded until 30 minutes after the end of brachial plexus block. Repeated-measures analysis of variance followed by the Dunnett post hoc test determined the effect of brachial plexus block on the finger photoplethysmogram and finger temperature.

RESULTS

The DC component of the finger photoplethysmogram decreased (vasodilation) significantly (P < 0.0001) after brachial plexus block in the blocked arm starting 2.7 minutes after the block. Average decrease in DC values was -51% ± 19% (95% confidence interval: -61% to -42%) at 30 minutes after the block. None of the other photoplethysmogram components changed significantly from preblock baseline values. On average, the finger temperature increased significantly (P < 0.0001) starting 5.7 minutes after brachial plexus block in the blocked arm. Average increase in temperature was 7.1°C ± 3.8°C (95% confidence interval: 5.1°C-9.0°C) 30 minutes after the block. The DC component of the photoplethysmogram had the highest sensitivity and specificity to predict a successful block.

CONCLUSIONS

This study characterizes sympathectomy-induced changes in the AC and DC components of the finger photoplethysmogram. In this experimental model, we found the DC component to be most sensitive in detecting peripheral vasodilation.

Pulse oximeter perfusion index as an early indicator of sympathectomy after epidural anesthesia

BACKGROUND

The pulse oximeter perfusion index (PI) has been used to indicate sympathectomy-induced vasodilatation. We hypothesized that pulse oximeter PI provides an earlier and clearer indication of sympathectomy following epidural anesthesia than skin temperature and arterial pressure.

METHODS

Forty patients received lumbar epidural catheters. Patients were randomized to receive either 10 ml 0.5% bupivacaine or 10 ml 0.25% bupivacaine. PI in the toe, mean arterial pressure (MAP) and toe temperature were all assessed at baseline and at 5, 10 and 20 min following epidural anesthesia. The effect of epidural anesthesia over time was assessed by repeated measures analysis of variance. Additionally, we defined clinically evident sympathectomy criteria (a 100% increase in the PI, a 15% decrease in MAP and a 1 degrees C increase in toe temperature). The numbers of patients demonstrating these changes for each test were compared using the McNemar test for each time point.

RESULTS

Twenty-nine subjects had photoplethysmography signals that met a priori signal quality criteria for analysis. By 20 min, PI increased by 326%, compared with a 10% decrease and a 3% increase in MAP and toe temperature, respectively. For PI 15/29, 26/29 and 29/29 of the subjects met the sympathectomy criteria at 5, 10 and 20 min, respectively, compared with 4/29, 6/29 and 18/29 for MAP changes and 3/29, 8/29 and 14/29 for toe temperature changes.

CONCLUSIONS

PI was an earlier, clearer and more sensitive indicator of the development of epidural-induced sympathectomy than either skin temperature or MAP.