Effect of sex and pregnancy on the potency of intrathecal bupivacaine: determination of ED50 for motor block with the up–down sequential allocation method:

The Median Effective Dose of Intrathecal Hyperbaric Bupivacaine for Cesarean Section at Moderately High-Altitude

Objective

Alterations in altitude can lead to an augmented requirement for local anesthesia among patients. Nevertheless, the necessity for an elevated dosage of local anesthetic for parturients at moderately high altitudes during spinal anesthesia for cesarean section remains uninvestigated. This up-down sequential study endeavors to determine the ED50 dose of bupivacaine required for spinal anesthesia during cesarean sections at moderately high-altitude.

Methods

Thirty singleton parturients at moderately high altitude underwent elective cesarean section under combined spinal-epidural anesthesia. The up-and-down sequential method was employed, starting with an initial dose of 12mg (1.6mL) of 0.75% hyperbaric bupivacaine for the first participant. The dose for the next case was adjusted up or down by 0.75mg based on the effectiveness of the previous participant. Effectiveness was defined as the bilateral sensory block reaching T6 within 15 minutes after spinal anesthesia injection, without the need for additional epidural anesthesia before fetal delivery. The ED50 dose and 95% confidence interval were calculated using the Dixon sequential method and isotonic regression, respectively. The incidence of maternal hypotension, nausea, and vomiting during the study period was also recorded.

Results

The ED50 of hyperbaric bupivacaine for spinal anesthesia in cesarean section was calculated as 8.23 mg (95% CI, 6.52-9.32 mg) using the Dixon up-and-down method. Further validation using isotonic regression yielded a value of 8.39 mg (95% CI, 7.48-9.30 mg), confirming the accuracy and sensitivity of the conclusion. During the operation, only 6 parturients experienced hypotension, and no adverse reactions such as nausea, vomiting, and shivering were observed.

Conclusion

The ED50 dose of 0.75% hyperbaric bupivacaine for spinal anesthesia during cesarean section at moderately high altitude is 8.23 mg, which exceeds the ED50 dose typically required by parturients at low altitude. Comprehensive investigations are warranted to ascertain the ED90 or ED95 dose of local anesthetics for cesarean section at moderately high altitudes, thereby offering enhanced guidance for clinical practice.

The impact of biological sex in peripheral nerve blockade: A prospective pharmacodynamic, pharmacokinetic and morphometric study in volunteers

STUDY OBJECTIVE

The impact of biological sex in peripheral regional anaesthesia is largely unknown. We therefore designed a prospective study in volunteers to investigate the impact of biological sex on pharmacodynamic, pharmacokinetic and morphometric characteristics for peripheral nerve blockade.

METHODS

The initial study plan was powered to include 90 volunteers to find a difference of 35 min in duration of sensory block (primary outcome variable) with 80% power and alpha error at 5%. After discussions in ethical review, a pilot study of 2 x 12 volunteers from each sex were studied. Female and male volunteers received ultrasound guided nerve blockade with 3.0 mL ropivacaine 7.5 mg mL-1. Sensory duration of blockade, as the primary outcome, was evaluated by pinprick testing. Secondary outcomes were sensory onset time of blockade, pharmacokinetic characteristics and the visibility of ulnar nerves using ultrasound. Analyses included Mann-Whitney U-statistics with P<0.05 (two-sided) as significant.

RESULTS

After 24 participants, the median (IQR) duration of sensory blockade was 450 (420; 503) min in women and 480 (450; 510) min in men (P = 0.49). Sensory onset time of blockade, and ultrasound visibility of nerves were also similar between the study groups. The total drug exposure across time (AUC0-infinity) was significantly higher in women (P = 0.017). After a the planned power re-analysis after these 24 study paticipants, which suggested that > 400 subjects would be required with 80% power and alpha error of 5% to find significance for the primary outcome parameter for marginal differences, we terminated the study at this point.

CONCLUSIONS

We did not detect significant differences between female and male study participants in terms of pharmacodynamic and morphometric characteristics after ultrasound guided ulnar nerve blocks. Women did show significantly greater pharmacokinetic ropivacaine exposures. The results of this study indicate that peripheral regional block pharmacodynamic characteristics are independent of the biological sex, whereas pharmacokinetic parameters are sex-dependent.

Spontaneous spinal epidural hematoma (SSEH) after cesarean section under epidural anesthesia: A case report

Spontaneous spinal epidural hematoma (SSEH) is an uncommon condition that can lead to severe neurological injuries, often accompanied by back pain. Pregnancy is identified as a risk factor for SSEH. Early diagnosis of SSEH presents challenges due to its atypical manifestations and the use of intraspinal anesthesia and analgesic techniques. In this case, we present the instance of a 29-year-old woman who initially received epidural labor analgesia during the first stage of labor but subsequently required a cesarean section under epidural anesthesia according to amniotic fluid turbidity. Unfortunately, the anomalous recovery of neurological function in her left lower extremity was not given sufficient attention at an early stage, and paralysis in the non-puncture segment occurred 45.5 hours after the initial puncture. Interestingly, she did not experience any back pain during these procedures. MRI examination and consultation with neurosurgeons confirmed the diagnosis of SSEH, prompting the patient to undergo emergency decompression surgery. She made an incomplete recovery 17 months after the operation. This case emphasizes the importance of considering the possibility of SSEH in pregnant women undergoing epidural analgesia, highlighting the need for spinal imaging and early neurosurgical interventions to facilitate treatment.

Understanding Research Methods: Up-and-down Designs for Dose-finding

SUMMARY

For the task of estimating a target benchmark dose such as the ED50 (the dose that would be effective for half the population), an adaptive dose-finding design is more effective than the standard approach of treating equal numbers of patients at a set of equally spaced doses. Up-and-down is the most popular family of dose-finding designs and is in common use in anesthesiology. Despite its widespread use, many aspects of up-and-down are not well known, implementation is often misguided, and standard, up-to-date reference material about the design is very limited. This article provides an overview of up-and-down properties, recent methodologic developments, and practical recommendations, illustrated with the help of simulated examples. Additional reference material is offered in the Supplemental Digital Content.

Comparing Imaging Biomarkers of Cerebral Edema after TBI in Young Adult Male and Female Rats

Traumatic brain injury (TBI) is one of the leading causes of death and disability worldwide. Cerebral edema following TBI is known to play a critical role in injury severity and prognosis. In the current study we used multimodal magnetic resonance imaging (MRI) to assess cerebral edema 24 hours after unilateral contusive TBI in male and female rats. We then directly quantified brain water content in the same subjectsex vivo.We found that both males and females had similarly elevated T₂ values after TBI compared with sham controls. Apparent diffusion coefficient (ADC) was more variable than T₂ and did not show significant injury effects in males or females. Brain water was elevated in male TBI rats compared with sham controls, but there was no difference between female TBI and sham groups. Notably, MRI biomarkers of edema were more closely correlated with brain water in male rats; female rats did not show any relationship between brain water and T₂ or ADC. These observations raise questions about the interpretation of radiological findings traditionally interpreted as edema in female TBI patients. A better understanding of sex differences and similarities in the pathophysiology of post-traumatic edema is needed to help improve patient management and the development of effective treatment strategies for men and women.

Comparison of ropivacaine plasma concentration after posterior Quadratus Lumborum Block in Cesarean Section with ropivacaine with epinephrine vs plane

BACKGROUND

The posterior Quadratus Lumborum Block (pQLB) has been used in postoperative pain management after Cesarean Section (CS). However, clinicians have no data about pQLB safety in pregnants, at increased risk of local anesthetic systemic toxicity (LAST). The purpose of the present study was to explore the efficacy and the safety of adding epinephrine to ropivacaine for bilateral pQLB vs. bilateral pQLB performed with ropivacaine alone in CS.

METHODS

in this prospective trial 52 pregnants, ASA 2 physiological status, were consecutively allocated to one of 2 groups, e-pQLB and pQLB; e-pQLB group received 0.375% ropivacaine+100 mcg epinephrine, 20 ml each side; pQLB received 0.375% ropivacaine alone, 20 ml each side. The primary and secondary outcomes were to evaluate if the adjunct of epinephrine to ropivacaine increases efficacy and safety of pQLB, respectively.

RESULTS

Authors found in e-pQLB group vs. p-QLB group: a total mean morphine consumption statistically lower during the first 24 postoperative hours (5.08±3.12, vs 9.11±4.67 SD mg, p=0.0002); NRS values statistically lower at 6 hours from block, both at rest (1,73±1,88 SD vs. 2,88±2,53, p=0.03) and with movement (3,03±1,98 SD vs. 4,23±2,87, p=0.04); a longer time between block and the first opioid request (5.92±2.48 vs 3.78±2.68 SD hrs, p< 0.003); venous ropivacaine concentrations significantly lower at any time of samples but at 120 minutes.

CONCLUSIONS

Adding epinephrine to ropivacaine increases efficacy and duration of pQLB. Moreover it increases block safety, reducing peak and mean venous ropivacaine concentration.

Factors Associated With Minimum Effective Volume of Lidocaine 1.5% for Sciatic Nerve Blocks

OBJECTIVES

The objectives of this study were to investigate the correlations between the minimum effective volume (MEV) of lidocaine 1.5% for an ultrasound-guided popliteal sciatic nerve block and individual factors including the cross-sectional nerve area, sex, age, body mass index, and the depth of the sciatic nerve and to evaluate the safety of combined femoral and sciatic nerve blocks by monitoring the plasma concentration of local anesthetics.

METHODS

Forty patients received combined single-shot femoral and continuous sciatic nerve blocks. The femoral nerve block was performed with an in-plane technique and 15 mL of lidocaine 1.5%. A continuous peripheral nerve block annular tube was positioned between the tibial and peroneal nerves inside the paraneural sheath. Thirty minutes after the femoral nerve block, a loading dose of 5 mL of lidocaine 1.5% was given to block the sciatic nerve after obtaining the maximum compound muscle action potential (CMAP) amplitude using nerve conduction studies. Additional lidocaine 1.5% was pumped at a rate of 30 mL/h through the indwelling annular tube if, after 8 minutes, the CMAP amplitude was still present. The CMAP amplitude monitored by the nerve conduction studies and pinprick tests were recorded every 2 minutes after the administration of lidocaine 1.5%. When the CMAP amplitude decreased to nearly 0 mV, this MEV was recorded. The influences of the cross-sectional area of the sciatic nerve, sex, age, body mass index, and the depth of the sciatic nerve on the MEV were analyzed using stepwise multiple linear regression. Blood samples were collected from 10 patients to evaluate the safety of combined femoral and sciatic nerve blocks by ultra-performance liquid chromatography-tandem mass spectrometry. Blood was drawn at 0 minutes before femoral nerve injection; 0 minutes before sciatic nerve injection; 8 minutes after sciatic nerve injection; and 0, 10, 20, 30, 45, 60, 75, 90, and 120 minutes after the pumping of lidocaine 1.5% stopped.

RESULTS

A significant correlation was found between the MEV of lidocaine 1.5% and the cross-sectional area of the sciatic nerve (r=0.459), with a regression equation of the MEV (mL)=5.969+0.095×(the cross-sectional area of the sciatic nerve). The coefficient of determination was 0.211 (P<0.05). The MEV of lidocaine 1.5% for complete sciatic nerve blocks ranged from 7 to 15 mL. The maximum concentrations of lidocaine, monoethylglycinexylidide, and glycinexylidide were 1672.9 (227.6), 265.7 (32.7), and 42.2 (22.4) ng/mL, respectively.

CONCLUSIONS

There is a positive correlation between the cross-sectional area of the sciatic nerve and the MEV. The regression equation can help to predict the MEV of lidocaine 1.5% for popliteal sciatic nerve blocks. The maximum concentrations of lidocaine and its metabolites did not approach toxic threshold limits in this study.

Sex-dependent prolongation of sciatic nerve blockade in diabetes patients: a prospective cohort study

INTRODUCTION

Diabetes may affect the duration of nerve block after regional anesthesia. This study aimed to compare the durations of sensory and motor block in diabetes versus non-diabetes patients after lower limb nerve block and delineate any sex-based differences in the duration of sensory and motor blocks of both diabetes and non-diabetes patients.

METHODS

This prospective single-blinded cohort study recruited 86 patients who underwent unilateral lower extremity surgery; 52 patients were non-diabetic and 34 were diabetic. Each patient received an ultrasound-guided nerve stimulator-assisted subgluteal sciatic nerve block with 0.75% ropivacaine. Duration of sensory block was assessed with the Semmes-Weinstein monofilament test, and duration of motor block was assessed with dorsal and plantar flexion of the foot.

RESULTS

The sensory and motor block durations of diabetes patients were significantly prolonged versus non-diabetes patients (19.8±6.0 hours vs 15.6±5.1 hours; p<0.05) and (19.5±8.1 hours vs 14.8±5.7 hours, p=0.005), respectively. The durations of sensory and motor block were comparable between male diabetes and non-diabetes patients, but they were significantly longer in female diabetes patients. Multiple regression analysis further revealed that, after adjustment for age and preoperative sensory threshold, diabetes, fasting plasma glucose and HbA1c levels were significantly associated with sensory and motor blocks. Sex analysis showed the association was only present in female diabetes patients, not male diabetes patients.

CONCLUSION

The durations of sensory and motor block are significantly prolonged after subgluteal sciatic nerve block in diabetes patients. Furthermore, the prolonged nerve blockade is present only in diabetes women, not diabetes men.

TRIAL REGISTRATION NUMBER

NCT02482831.

Infant spinal anesthesia: Do girls need a larger dose of local anesthetic?

BACKGROUND

Gender differences in absorption, distribution, and metabolism of a number of anesthetic agents have been identified in adults. Clinically, adult studies suggest women demonstrate slower onset of opioid analgesic effects, lower spinal and epidural dose requirements, and greater sensitivity to neuromuscular blocking agents. Sex-related differences in the pharmacokinetics and pharmacodynamics of local anesthetics in neonates and infants, however, have not been well documented. As a result, it is not known whether modification of the dose of local anesthetic for awake spinal anesthesia in infants is required.

AIMS

Our aim was to determine whether the ED50 and ED95 of local anesthetics used for infant spinal anesthesia are different between sexes.

METHODS

This was a retrospective analysis of data previously collected during dose-response studies of levobupivacaine and ropivacaine spinal anesthetics. The doses were reanalyzed using generalized linear regression analysis to determine whether there is a discernible difference in dose requirements between male and female infants.

RESULTS

One hundred and twenty infant spinal anesthetics were reviewed. For levobupivacaine, the ED50 (95% CI) was 0.69 (0.49-0.88) mg vs 0.49 (0.33-0.65), whereas the ED95(95% CI) was 1.07 (0.73-1.41) vs 0.93 (0.64-1.22) for girls and boys, respectively. For ropivacaine spinal anesthesia, the ED50 (95% CI) was 0.64 (0.35-0.92) mg vs 0.30 (-0.32-0.92), whereas the ED95 (95% CI) was 1.30 (0.73-1.87) vs 1.66 (0.55-2.76) for girls and boys, respectively.

CONCLUSION

There is no evidence that sex differences occur at the ED50 dose range or at the clinically relevant ED95 dose. Modification of spinal anesthetic dose is not required for infant girls.

Is the pharmacokinetics of bupivacaine equivalent after lumbar epidural administration through a needle or a catheter in male and female adults?

We assessed possible pharmacokinetic modifications due to different epidural injection techniques using either a needle or a catheter. Adult patients (n=23) undergoing lower abdominal or lower extremity surgery were randomly assigned a single bupivacaine epidural injection anesthesia (0.5%, 15 mL, 0.3 mL/s) through needle or catheter device. Plasma bupivacaine concentration was quantified using a validated HPLC method and non-compartmental pharmacokinetic parameters estimated. CMAX and TMAX were similar in both groups: 952 ± 346 ng/mL, 0.65 ± 0.5 1h in the needle group; 810 ± 307 ng/mL, 0.43 ± 0.29 h in the catheter group respectively. Plasma AUC₀→∞ was also similar in both groups: 3868 ± 1687 ngh/mL for needle versus 4096 ± 1748 ngh/mL using catheter. The catheter group showed slower disposition than the needle group: t₁/₂=3.9 ± 2.3 h, MRT=6.0 ± 3.1 h versus 2.7 ± 1.03 h and 4.5 ± 1.2 h with needle administration respectively though it did not reach statistical significance, Cl/F and V/F were also similar. Lastly, female patients showed significant longer t1/2 after administration through catheter (5.7 ± 2.0 h) than needle (2.7 ± 0.6 h) group (P=0.0279). The device type does not affect the pharmacokinetics which is similar in both groups although sex-based differences might exist.

[Gender aspects in anesthesia : modified approach in research and treatment?]

Gender differences can have a relevant influence on the perioperative outcome as male and female patients are affected differently by adverse events, e.g. side effects of drugs. Furthermore, differences relating to specific drug effects, comorbidities and outcome after anesthesia or intensive care have been demonstrated. There seems to be a gender bias in diagnosis and therapy. While the knowledge regarding this field is still growing certain aspects have already been integrated into clinical practice: prevention of postoperative nausea and vomiting (PONV), target controlled infusion (TCI) model and male only policy with production of blood products. There is a need to study the influence of gender, age and race in order to optimize treatment towards a more individualized therapy. This article highlights already identified differences and discusses potential underlying mechanisms.

Sex-related differences of patient-controlled epidural analgesia for postoperative pain

Gender differences in pain modulation are evident but data are rare with regard to perioperative regional analgesia. The aim of the present analysis was to assess gender-related differences in pain ratings, analgesic consumption, and adverse events in a large group of patients treated with patient-controlled epidural analgesia (PCEA) after major surgery. Data from 14,988 adult patients (6506 women; 8482 men) receiving a PCEA between January 1998 and December 2009 were examined. Demographic data and postoperative measurements assessed by the Acute Pain Service, including total PCEA consumption, pain scores, and complications, were analyzed by using PASW Statistics (18.0; SPSS Inc, Chicago, IL, USA). Beyond standard descriptive analyses, gender-related differences were investigated using a stepwise multivariate analysis of variances. Postoperative pain scores during rest and movement were almost equal between men and women. However, women showed lower total PCEA consumption consistently throughout the 5-day observation period (relative reduction by 1.7%-10.2% compared to men; P=0.00). Total PCEA consumption did not interact with surgical site (abdomen, thorax, extremity) (P=0.379) or age (<50, 50-75, >75 years; P=0.330), but was influenced by body mass index (P=0.017) and vomiting (P=0.011). Furthermore, motor blockade was greater in females compared to males (P=0.000). In patients treated with PCEA, gender differences in numeric rating scale scores exist but are not clinically relevant. However, reduced total PCEA consumption in women might be a consequence of an increased incidence of motor blockade and vomiting; the latter point towards an opioid-free PCEA solution in female patients at high risk for vomiting.