Pharmacokinetics and protein binding of bupivacaine in postoperative epidural analgesia

Thoracic Epidural Anesthesia After a Transversus Abdominis Plane Block With Liposomal Bupivacaine in a Patient With Chronic Opioid Use: A Case Report

Liposomal bupivacaine is a long-acting local anesthetic drug that provides extended analgesia. A 45-year-old man with metastatic colon cancer and an intrathecal morphine pump for chronic pain underwent a transverse colectomy for a malignant transverse colon obstruction in this case report. The patient reported severe pain despite preoperative fascial plane blocks with liposomal bupivacaine and postoperative pain management strategies. As a result, an exploratory laparotomy was performed to rule out any underlying causes, but no new injuries were discovered. On postoperative day 1, a thoracic epidural catheter was inserted to provide better pain relief for the patient. The patient's pain was well-controlled by postoperative day 4, allowing the epidural catheter to be removed. On postoperative day 5, the patient was discharged home without complications. This case highlights the difficulties in managing post-laparotomy pain as well as the potential benefits of combining multiple analgesic modalities. It also emphasizes the pharmacokinetic properties of liposomal bupivacaine, emphasizing the need for caution due to its prolonged systemic presence and potential for systemic anesthetic toxicity.

Plasma bupivacaine levels (total and free/unbound) during epidural infusion in liver resection patients: a prospective, observational study

INTRODUCTION

Liver resection patients may be at an increased risk of local anesthetic (LA) toxicity because the liver is essential for metabolizing LA and producing proteins (mainly α1-acid glycoprotein (AAG)) that bind to it and reduce the free (and pharmacologically active/toxic) levels in circulation. The liver resection itself, manipulation during surgery, and pre-existing liver disease may all interfere with normal hepatic protein synthesis and result in an attenuation of the increased AAG (a positive acute-phase protein) that normally occurs postoperatively. The purpose of this study was to determine whether the AAG response is attenuated postoperatively following liver resection and whether patients approach toxicity thresholds with continuous postoperative epidural infusion of bupivacaine.

METHODS

Prospective, observational study with blood drawn preoperatively, in the postanesthetic care unit, on postoperative day (POD) 2, and prior to discontinuation of epidural analgesia on POD3/POD4. Plasma was analyzed for total and unbound bupivacaine via liquid chromatography-mass spectrometry and AAG via ELISA. Signs/symptoms of local anesthetic systemic toxicity (LAST), pain, and sedation scores were also recorded.

RESULTS

For the 19 patients completed, total plasma bupivacaine was correlated with total administered, but unbound levels were not associated with the total administered. Unlike non-hepatectomy surgery where unbound LA plasma levels remain stable (or decrease) with continuous postoperative epidural administration, we observed an overall increase. Several patients approached toxicity thresholds and 47% reported at least one symptom of LAST, but no epidurals were discontinued because of LAST. In contrast to the AAG response reported following major non-liver surgery where AAG levels increase twofold, we observed a reduction until POD2 and the magnitude was proportional to resection weight.

DISCUSSION

Our results are supported by the literature in suggesting that major liver resection patients may be at an increased vulnerability for LAST. Factors such as the extent of liver disease, resection and intraoperative blood loss should be considered when using continuous postoperative epidural infusion of bupivacaine and vigilance should be used in monitoring, for signs/symptoms of LAST, even for those subtle and non-specific. Future research will be required to verify these findings.

TRIAL REGISTRATION NUMBER

NCT03145805.

Determination of bupivacaine tissue concentration in human biopsy samples using high-performance liquid chromatography with mass spectrometry

In the present study, we developed a simple and rapid analytical method for the quantification of bupivacaine hydrochloride in human biopsy samples of adipose, muscle, neural, connective and cartilage tissue using liquid chromatography-mass spectrometry. Anesthetics were extracted from the tissue samples using 0.1% formic acid in acetonitrile for protein denaturation and hexane for removal of lipophilic impurities. Analytes were separated adequately on Phenomenex Luna Omega polar C18 column using a gradient mobile phase 0.1% formic acid in water and 0.1% formic acid in acetonitrile. The lower limits of quantification were ≤ 97 ng g^-1 tissue for all studied tissues. Intra-day recoveries were between 48.2% and 82.1% with relative standard deviations (RSDs) between 1.47% and 14.28%, whereas inter-day recoveries were between 52.2% and 77.6% with RSDs between 2.98% and 14.79%. The calibration curve showed a linear fit with R² higher than 0.99 in the concentration range from 0.16 to 100 μg g^-1 . Lidocaine hydrochloride was tested as internal standard because its recoveries and matrix effects were comparable to bupivacaine hydrochloride. Post-analytical corrections of measured bupivacaine tissue concentrations can accordingly be made based on recovery of lidocaine as internal standard, with recoveries between 51.2% and 86.9% and RSDs between 1.99% and 16.88%. The developed method could be used to study time-dependent spread of bupivacaine locally or to more distant locations across tissue barriers.

Bupivacaine Pharmacokinetics and Breast Milk Excretion of Liposomal Bupivacaine Administered After Cesarean Birth

Very little plasma bupivacaine was transferred into breast milk after liposomal bupivacaine wound infiltration in patients who had undergone cesarean delivery.

To evaluate bupivacaine concentrations in maternal plasma and transfer into breast milk in women undergoing liposomal bupivacaine infiltration in the transversus abdominis plane after cesarean birth.

Thoracic epidural catheter for postoperative pain control following an ineffective transversus abdominis plane block using liposome bupivacaine

A 24-year-old female with a history of ulcerative colitis underwent colectomy. The patient received an ineffective transversus abdominis plane (TAP) block with liposome bupivacaine (Exparel) intraoperatively and was started on a hydromorphone patient-controlled analgesia 5 hours after the TAP block, which did not relieve her pain. A continuous thoracic epidural (CTE) was then placed after blood levels of bupivacaine were drawn, and the patient immediately experienced significant pain relief. The combined use of liposome bupivacaine and bupivacaine CTE infusion in the postoperative management of this patient demonstrated no safety concerns, provided excellent analgesia and plasma concentrations of bupivacaine remained far below toxic levels.

Local infiltration analgesia in knee and hip arthroplasty efficacy and safety

Background

This is a secondary publication of a PhD thesis. Local infiltration analgesia (LIA) is a new multimodal wound infiltration method for treating postoperative pain after knee and hip arthroplasty. This method is based on systematic infiltration of a mixture of ropivacaine, a long acting local anaesthetic, ketorolac, a cyclooxygenase inhibitor (NSAID), and adrenalin around all structures subject to surgical trauma in knee and hip arthroplasty.

Aims

Paper I: to assess whether pain relief after LIA in total knee arthroplasty (TKA) is as effective as femoral block. Paper II: to assess whether the plasma concentration of ropivacaine and ketorolac after LIA in TKA reaches levels linked to toxicity. Paper III: to assess whether the plasma concentration of unbound ropivacaine after LIA in THA reaches levels linked to toxicity and if it is higher in THA as compared to TKA. Paper IV: to assess whether the plasma concentration of ketorolac after LIA in THA reaches levels linked to toxicity, and whether administration of ketorolac in LIA is safer as compared to the intramuscular route.

Methods

Two patient cohorts of 40 patients scheduled for elective total knee arthroplasty (TKA) and 15 patients scheduled for total hip arthroplasty (THA) contributed to this work. In a randomized trial the efficacy of LIA in TKA with regard to pain at rest and upon movement was compared to femoral block.

Results

Both methods result in a high quality pain relief and similar morphine consumption during the 24 h monitoring period. In the same patient cohort the maximal total plasma concentration of ropivacaine was below the established toxic threshold for most patients. All patients in the THA cohort were subjected to the routine LIA protocol. In these patients both the total and unbound plasma concentration of ropivacaine was determined. The concentration was below the established toxic threshold. As ropivacaine binds to α–1 acid glycoprotein (AAG) we assessed the possibility that increased AAG may decrease the unbound concentration of ropivacaine. A 40% increase in AAG was detected during the first 24 h after surgery, however the fraction of unbound ropivacaine remained the same. There was a trend towards increased C max of ropivacaine with increasing age and decreasing creatinine clearance but the statistical power was too low to draw any conclusion. Administration of 30 mg ketorolac according to the LIA protocol both in TKA and THA resulted in a similar C max as previously reported after 10 mg intramuscular ketorolac. Neither age, nor body weight or BMI, nor creatinine clearance, correlates to maximal ketorolac plasma concentration or total exposure to ketorolac (AUC).

Conclusion

LIA provides good postoperative analgesia which is similar to femoral block after total knee arthroplasty. The plasma concentration of ropivacaine seems to be below toxic levels in most TKA patients. The unbound plasma concentration of ropivacaine in THA seems to be below the toxic level.

Implication

The use of ketorolac in LIA may not be safer than other routes of administration, and similar restrictions should be applied in patients at risk of developing side effects.

Systemic Levels of Local Anaesthetic after Intra-Peritoneal Application – a Systematic Review

There is a lack of cohesive reports on the systemic levels of local anaesthetic after intraperitoneal application. A comprehensive systematic review with no language restriction was conducted. Eighteen suitable articles were identified. Data were compiled and presented according to local anaesthetic agent. Intraperitoneal local anaesthetic has been studied in many different procedures, including open and laparoscopic surgery. A total of 415 patients were included for analysis. There were no cases of clinical toxicity. There were 11 (2.7%) cases with a systemic level above or close to a safe threshold (as determined by the report authors) in three trials utilising intraperitoneal local anaesthetic after laparoscopic cholecystectomy. Intraperitoneal lignocaine doses varied from 100 to 1000 mg, mean Cmax ranged from 1.01 to 4.32 μg/ml and mean Tmax ranged from 15 to 40 minutes. Intraperitoneal bupivacaine doses varied from 50 to 150 mg (weight based doses also reported), mean Cmax ranged from 0.29 to 1.14 μg/ml and mean Tmax ranged from 15 to 60 minutes. Intraperitoneal ropivacaine doses varied from 100 to 300 mg, mean Cmax ranged from 0.66 to 3.76 μg/ml and mean Tmax ranged from 15 to 35 minutes. The addition of adrenaline to intraperitoneal local anaesthetic almost halves systemic levels and prolongs Tmax. Intraperitoneal local anaesthetic results in detectable systemic levels in the perioperative setting. Despite a lack of clinical toxicity, careful attention to dose is still required to prevent potential systemic toxic levels. Clinicians should also consider the addition of adrenaline to intraperitoneal local anaesthetic solutions to further add to the systemic safety profile.

Plasma Ropivacaine Levels Following Scalp Block for Awake Craniotomy

The plasma levels of ropivacaine HCl with 5 mcg/mL epinephrine were measured in 10 patients following scalp blockade for awake craniotomy. A mean dose of 260 mg (3.6 mg/kg) resulted in peak plasma concentrations of 1.5 +/- 0.6 mcg/mL, with a median time to peak plasma concentration of 15 minutes. The pattern of rise of plasma level was similar in all patients and rapid compared with other regional blocks (epidural, intercostal, and axillary brachial plexus block). Despite this rapid rise of plasma level, no signs of cardiovascular or central nervous system toxicity were observed. In this group of patients undergoing awake craniotomy for excision of lesions in the eloquent areas of the cerebral cortex, ropivacaine HCl with epinephrine appeared to be a safe and effective local anesthetic agent in the dosages used.

Plasma concentration of ropivacaine after intercostal blocks for video-assisted thoracic surgery

BACKGROUND

Absorption of local anaesthetics following intercostal blocks is rapid. Therefore, plasma concentrations of ropivacaine during intercostal blocks with ropivacaine 2, 5, 7.5 and 10 mg ml-1 (ropivacaine 5 ml injected into each of four intercostal spaces) in patients undergoing video-assisted thoracic surgery were determined.

METHODS

After informed consent and ethics committee approval, 64 patients were randomly allocated to four groups for intercostal nerve block (ropivacaine 2, 5, 7.5 or 10 mg ml-1 at the end of surgery). Central (mixed) venous and arterial plasma samples were collected before the start of intercostal application, and 2, 5, 10, 15, 20, 30, 45, 60 and 90 min afterwards. Plasma concentrations of ropivacaine were measured by high performance liquid chromatography.

RESULTS

Maximum venous plasma concentrations occurred after the mean times of 10.7 (range, 5-15), 10.8 (5-20), 11.3 (5-20) and 12.2 (5-45) min, respectively for each group. The groups had mean concentrations of 1.3 (SD, 0.6; range, 0.3-2.3), 2.1 (1.0; 0.5-4.5), 2.4 (1.0; 1.2-5.1) and 2.5 (0.9; 1.7-5.6) micrograms ml-1, respectively. Maximum arterial plasma concentration following 1.0% ropivacaine occurred after 16 (5-45) min with a mean of 2.3 (0.6; 1.5-3.6) micrograms ml-1. No signs of central nervous system or cardiac toxicity were observed.

CONCLUSIONS

After intercostal blocks the absorption of ropivacaine is rapid compared with other techniques for regional anaesthesia and results in relatively high venous and arterial plasma concentrations, especially if a dose of 100 mg or more is used.

Lidocaine with fentanyl, compared to morphine, marginally improves postoperative epidural analgesia in children

PURPOSE

To compare the epidural administration of fentanyl (1 microg/mL) combined with lidocaine 0.4% to preservative-free morphine for postoperative analgesia and side effects in children undergoing major orthopedic surgery.

METHODS

In a prospective, double-blind study, 30 children, ASA I-II, 2-16-yr-old, were randomly allocated to receive immediately after surgery either epidural F-L (epidural infusion at a rate of 0.1-0.35 mL/kg/hr of 1 microg/mL of fentanyl and lidocaine 0.4%) or epidural M (bolus of 20 microg/kg of morphine in 0.5 mL/kg saline every eight hours). Both groups received 40 mg/kg of iv metamizol (dipyrone) every six hours. In the F-L Group, blood samples were taken on the second and third postoperative day to determine total lidocaine concentrations. Adequacy of analgesia using adapted pediatric pain scales (0-10 score) and side-effects were assessed every eight hours postoperatively.

RESULTS

Resting pain scores were under 4, 95% of the time in the F-L Group and 87% of the time in the M Group (Chi square=4.674, P <0.05). The frequency of complications was very similar in both groups. The F-L Group total plasma lidocaine concentrations were directly related to the dose received, and below the toxic range in all patients.

CONCLUSIONS

Postoperative epidural fentanyl with lidocaine infusion provides slightly better analgesia than conventional bolus administration of epidural morphine. Side-effects or risk of systemic toxicity were not augmented by the addition of lidocaine to epidural opioids.

Ropivacaine plasma concentrations during 120-hour epidural infusion

The pharmacokinetics of ropivacaine were evaluated during long-term continuous epidural analgesia (CEDA) for about 120 h. The total and free plasma concentrations of ropivacaine and the alpha1-acid glycoprotein (AAG) concentration were measured in 12 patients after total knee arthroplasty. The infusion rate was adjusted according to patients' analgesic needs or side effects. The mean (SD) rate of infusion of ropivacaine (Naropin 2 mg ml(-1)) was 14.6 (3.2) mg h(-1) on the day of surgery and was increased after surgery to 15.4 (4.4) mg h(-1) on days 1-5. This was equivalent to an absolute dose of 1786 (553) mg of ropivacaine over the entire infusion period. After an initial increase, the mean free ropivacaine plasma concentration nearly plateaued and than decreased slightly after approximately 70 h. The individual peak free plasma concentration was 0.096 (0.034) microg ml(-1). The highest individual free plasma concentration was 0.16 microg ml(-1). The individual peak total plasma concentration, 4.1 (1.2) microg ml(-1), was achieved after 67.7 (16.5) h, although the AAG concentration increased throughout the observation period. Our data support the safety and efficacy of long-term ropivacaine CEDA.

What concentration of sufentanil should be combined with ropivacaine 0.2% wt/vol for postoperative patient-controlled epidural analgesia?

In this randomized double-blinded study, we sought to determine an optimal dose-combination of sufentanil with ropivacaine 0.2% wt/vol as postoperative epidural analgesics. One hundred twenty patients undergoing major abdominal surgery under general and thoracic epidural anesthesia (T9-11) were assigned to groups receiving patient-controlled epidural analgesia with ropivacaine 0.2% wt/vol (R), ropivacaine 0.2% wt/vol + sufentanil 0.5 microg/mL (R+S0.5), 0. 75 microg/mL (R+S0.75), 1.0 microg/mL (R+S1). A visual analog score of less than 40 was considered effective, and all side effects were recorded. In randomized subgroups (10 patients per group), plasma pharmacokinetic data were obtained for both epidural drugs. Four patients in Group R and two in Group R+S0.5 were excluded because of inadequate analgesia. The drug infusion rates (range of means: 5.4-5. 9 mL/h) were similar in all patients. Analgesia was superior for sufentanil 0.75 microg/mL with no further enhancement by the larger sufentanil concentration of 1 microg/mL. Sufentanil plasma levels were within the range of the minimal effective concentrations (highest in R+S1), and there was no covariation between plasma levels and pain relief. Free ropivacaine plasma concentrations remained stable for 96 h. No severe side effects were detected, although pruritus correlated with an increasing dose of sufentanil. We conclude that the combination of ropivacaine 0.2% wt/vol and 0.75 microg/mL sufentanil provided the best analgesia with the fewest side effects of the three combinations tested.

IMPLICATIONS

Sufentanil is added to epidural infusions of ropivacaine 0.2% wt/vol to improve the effectiveness of postoperative pain management. Regarding the risk of side effects, however, it is still unclear what concentration of sufentanil should be added to the local anesthetic. For postoperative thoracic epidural analgesia after major abdominal surgery, the combination of ropivacaine 0.2% wt/vol and 0.75 microg/mL sufentanil resulted in an appropriate cost:benefit ratio between good analgesia and side effects.

Pharmacokinetics of ropivacaine during extradural anesthesia for total hip replacement

STUDY OBJECTIVE

To determine plasma concentrations of ropivacaine during epidural anesthesia with ropivacaine 10 mg/mL in patients undergoing elective total hip replacement.

DESIGN

Phase III prospective study.

SETTING

Orthopedic surgical unit of the University Hospital in Kiel, Germany

PATIENTS

11 ASA physical status I, II, and III patients undergoing elective total hip replacement after premedication with a benzodiazepine.

INTERVENTIONS

Peripheral venous plasma samples were collected prior to and 10, 15, 20, 30, 45, 60, 90, and 120 minutes following the epidural dose.

MEASUREMENTS AND MAIN RESULTS

After solid phase extraction, plasma concentrations of ropivacaine were measured by high-performance liquid chromatography (HPLC). Free unbound concentrations were determined after ultracentrifugation. In 9 of 11 patients excellent epidural anesthesia was achieved with an initial dose of 144 +/- 13 mg (120 to 150 mg) of ropivacaine corresponding to a dose of 1.9 +/- 0.4 mg/kg body weight. We suspected inadvertent intravascular catheter malposition in one case. Peak plasma concentrations occurred after 20 minutes (10 to 30 min) with a mean of 1.38 +/- 0.42 micrograms/mL (range 0.95 to 2.26 micrograms/mL). Maximum unbound free plasma concentrations of ropivacaine were 0.05 +/- 0.03 microgram/mL (range 0.02 to 0.13 microgram/mL).

CONCLUSION

Ropivacaine 10 mg/mL proved to be suitable for epidural anesthesia for total hip replacement. The plasma concentrations after 120 to 200 mg of its epidural application were not associated with signs of local anesthetic toxicity in patients pretreated with benzodiazepines, even in one case of suspected inadvertent intravascular application.

Pharmacokinetics and efficacy of long-term epidural ropivacaine infusion for postoperative analgesia

The aim of this study was to evaluate the pharmacokinetics and efficacy of the new local anesthetic ropivacaine when used for epidural infusion for up to 72 h after major orthopedic surgery. Immediately after surgery, an epidural infusion of ropivacaine 2 mg/mL was begun at a rate of 6 mL/h in 11 patients. The infusion rate was then adjusted according to patient analgesic needs or side effects. Blood samples were taken during and after the infusion to determine total and unbound ropivacaine and alpha1-acid glycoprotein (AAG) concentrations. Patients were assessed regularly for sensory and motor block and pain using a visual analog scale (VAS) score (0-100 mm). Ten patients received 63-72 h of infusion. Total plasma concentrations of ropivacaine and binding protein (AAG) increased during the infusion such that free concentrations plateaued or began to fall over time. VAS values during mobilization were less than 40 mm in 93% of patients. The majority of patients had no measurable motor block once the surgical block had regressed. When epidural ropivacaine was titrated to achieve a stable sensory block, there was a low incidence of motor block, and free plasma ropivacaine levels were well below the toxic range.

IMPLICATIONS

The pharmacokinetics of continuous epidural infusions of ropivacaine are described in patients for up to 72 h postoperatively. Clinical efficacy and side effects are also reported. An understanding of the plasma concentrations obtained and modes of elimination during prolonged epidural infusion is important for safe, routine clinical use in postoperative analgesia.

High-performance liquid chromatographic method for an automated determination of local anaesthetics in human plasma

A method is described that allows the rapid and precise determination of the local anaesthetics bupivacaine and etidocaine from biological fluids. This method uses a fully automated system with solid-phase extraction in combination with a column-switching technique. Both sample extraction on a LiChrocart pre-column and elution onto the analytical LiChrospher column, were performed automatically and concomitantly using conventional HPLC equipment in conjunction with an OSP-2 on-line sample preparator from Merck combined with UV detection. Recoveries were found to be 96.7 and 96.4% for 2 micrograms/ml bupivacaine and etidocaine, respectively. Lower limits of quantification were found to be 0.05 microgram/ml plasma for both of the compounds.

Central nervous system toxicity in a patient receiving continuous intrapleural bupivacaine

A patient developed signs of central nervous system (CNS) toxicity during treatment of postthoracotomy pain with a continuous intrapleural bupivacaine infusion. This incident occurred after the patient's chest tube was clamped, without any decrease in the bupivacaine infusion rate. This is the first reported case of CNS toxicity in a patient receiving a continuous intrapleural bupivacaine infusion. Possible etiologies of this complication are discussed, as are ways to avoid such a complication in the future.

Intraperitoneal application of bupivacaine during laparoscopic cholecystectomy--risk or benefit?

We investigated, in a double-blind study, the effects of intraperitoneal local anesthetics during laparoscopic cholecystectomy. In Part A of the study 30 patients received 50 mL saline 0.9% (A 0), bupivacaine 0.125% (A 125), or bupivacaine 0.25% (A 25) intraperitoneally at the end of surgery. Mean maximum plasma concentrations of bupivacaine reached 0.48 mg/L (range 0.15-0.90 mg/L) in Group A 125 and 1.0 mg/L (0.35-2.10 mg/L) in Group A 25 within 15 min (range, 5-30 min). There was no significant difference in pain scores or opioid consumption (patient-controlled analgesia with piritramid): 24, 28, and 13 mg/24 h among the study groups, respectively (not significant). Postoperative respiratory function deteriorated in comparison to preoperative values in all study groups, but the forced vital capacity was significantly more impaired in Group A .25. In Part B, 24 patients received placebo (B 0) or bupivacaine 0.25% (B 25). Postoperative hypoxemic periods (oxygen saturation < 92%) were significantly more frequent in Group B 25. Considering the questionable benefits and the potential risks, we would not recommend the application of intraperitoneal bupivacaine during laparoscopic cholecystectomy.

Effect of interpleural administration of bupivacaine or lidocaine on pain and morphine requirement after esophagectomy with thoracotomy: a randomized, double-blind and controlled study

The purpose of the present study was to investigate the efficacy of interpleural (IP) analgesia with bupivacaine or lidocaine after esophageal surgery and to measure the plasma concentrations of bupivacaine and lidocaine after intermittent IP administrations. Two IP catheters were inserted percutaneously in the seventh intercostal space during operation. Patients in the bupivacaine group (Gr B) received 1 mg/kg of 0.5% bupivacaine with epinephrine 1:200000 in 20 mL of saline 0.9%, patients in the lidocaine group (Gr L) received 3 mg/kg of 2% lidocaine with epinephrine in 20 mL of saline 0.9%, and patients in the placebo group (Gr P) received 20 mL of saline 0.9% every 4 h during 2 days. Pain was assessed by visual analog scale (VAS) every 4 h at rest (VASR), after a deep breath or cough (VASC), at the thoracotomy (VAST), and at the laparotomy (VASL). Morphine consumption using a patient-controlled analgesia (PCA) device was recorded. There was no significant difference in the mean VASR, VASC, and VASL scores among the three groups. VAST scores were significantly lower in Gr B at 12, 16, 28, and 32 h when compared with Gr P and Gr L (P < 0.05). There was no statistical difference in mean VAST between Gr L and Gr P. Total consumption of morphine was lower in Gr B than in Gr P and Gr L (41.2 +/- 13 mg vs 66.1 +/- 21 mg in Gr P (P < 0.02) and 75.5 +/- 27 mg in Gr L (P < 0.01)), but were similar in Gr L when compared with Gr P.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma protein binding of bupivacaine in pregnant women at term

The increased toxicity of bupivacaine in parturients is a well-known phenomenon. The reduced plasma protein binding of bupivacaine is one of the possible reasons. Therefore, we measured the free fraction of bupivacaine in plasma samples of parturients and non-pregnant volunteers. The free fraction was significantly higher in parturients (8.2% vs 5.4%) associated with a lower concentration of the alpha-1-acid glycoprotein (0.42 vs 1.01 g/l) and a higher concentration of progesterone (156 vs 0.4 ng/ml). The addition of progesterone to plasma samples of non-pregnant volunteers did not influence the free fraction of bupivacaine, whereas the addition of alpha-1-acid glycoprotein to the plasma of parturients decreased the free fraction significantly. Therefore, the lower concentration of this protein is the principal reason for the higher free fraction of bupivacaine in pregnancy and possibly one of the causes of the higher incidence of toxic side effects of bupivacaine in obstetric use.

A randomised double-blind study of interpleural analgesia after cholecystectomy

Continuous interpleural analgesia provided by 4 hourly injections of 20 ml bupivacaine 0.5% with adrenaline 5 micrograms/ml was compared with placebo in a randomised, double-blind study after cholecystectomy. All patients self-administered intravenous morphine using a patient-controlled analgesia device. There was a highly significant difference in mean morphine consumption between the groups (72 mg as compared with 22 mg). Visual analogue pain scores tended to be lower in the bupivacaine group throughout and this was significant at 2 hours. Respiratory function measurements were not significantly different between the groups. The mean peak venous plasma bupivacaine concentration after the sixth dose was 3.03 micrograms/ml and no symptoms suggestive of local anaesthetic toxicity occurred. It is concluded that this regimen can provide effective and continuous analgesia after cholecystectomy and that combined administration of interpleural bupivacaine and systemic morphine is more effective than morphine alone in the immediate postoperative period. The doses of bupivacaine required for optimal use of the technique lead to significant total plasma bupivacaine concentrations within 24 hours.