Relative potencies of bupivacaine and ropivacaine for analgesia in labour

We have used the technique of randomized, double-blind sequential allocation to compare the minimum local analgesic concentrations (MLAC) of epidural bupivacaine and ropivacaine for women in the first stage of labour. The test bolus was 20 ml of local anaesthetic solution. The concentration was determined by the response of the previous woman to a higher or lower concentration of local anaesthetic, according to up-down sequential allocation. Efficacy was assessed using a 100-mm visual analogue pain score (VAPS). The test solution had to achieve a VAPS of 10 mm or less to be judged effective. For bupivacaine, MLAC was 0.093 (95% CI 0.076-0.110)% w/v, and for ropivacaine, 0.156 (95% CI 0.136-0.176)%w/v (P < 0.0001, 95% CI difference 0.036-0.090). The analgesic potency of ropivacaine was 0.60 (0.47-0.75) relative to bupivacaine. Claims for reduced toxicity and motor block must be considered with differences in analgesic potency in mind.

Epidural pain relief in labour: potencies of levobupivacaine and racemic bupivacaine

We have compared the minimum local analgesic concentrations (MLAC) of levobupivacaine relative to racemic bupivacaine in a prospective, randomized, double-blind, sequential allocation study. Women in labour were given a 20-ml bolus of epidural levobupivacaine or bupivacaine diluted to a concentration determined by up-down sequential allocation. The initial concentration was 0.07% w/v for both drugs. Efficacy was defined using a visual analogue pain score (VAPS) at 10 mm or less within 30 min. The MLAC of levobupivacaine was 0.083% w/v (95% CI 0.065-0.101) and the MLAC of bupivacaine 0.081% w/v (95% CI 0.055-0.108). In molar terms, the MLAC of levobupivacaine was 2.87 mmol litre-1 (95% CI 2.25-3.49) and the MLAC of bupivacaine 2.49 mmol litre-1 (95% CI 1.69-3.32). With regard to the commercial preparations, the potency ratio levobupivacaine: bupivacaine was 0.98 (95% CI 0.67-1.41), and this is unlikely to be of clinical relevance. In molar terms, the ratio was 0.87 (95% CI 0.60-1.25). With regard to toxicity, the evidence should be evaluated in the light of a possible 13% potency difference in molar concentration in favour of racemic bupivacaine.

Visual problems following dural puncture

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Minimum local analgesic concentration of extradural bupivacaine increases with progression of labour

We have used the technique of double-blind sequential allocation to quantify the minimum local analgesic concentration (MLAC) of extradural bupivacaine for women in early (median cervical dilatation 2 cm) and late (median cervical dilatation 5 cm) labour. The first bolus was 20 ml of the bupivacaine test solution. The concentration was determined by the response of the previous woman to a higher or lower concentration of bupivacaine according to up and down sequential allocation. Efficacy was assessed using a 100-mm visual analogue pain score (VAPS). The test solution had to achieve a VAPS of 10 mm or less to be judged effective. In early labour, the MLAC of bupivacaine was 0.048% w/v (95% confidence intervals (CI) 0.037-0.058% w/v), and 0.140% w/v (95% CI 0.132-0.150% w/v) in the late group. The MLAC of bupivacaine in late labour was greater by a factor of 2.9 (95% CI 2.7-3.2) compared with the MLAC in early labour (P < 0.0001, 95% CI difference 0.08-0.11). We conclude that advancing labour requires an increased concentration of extradural bupivacaine for pain relief.

Extradural pain relief in labour: bupivacaine sparing by extradural fentanyl is dose dependent

The minimum local analgesic concentration (MLAC) of bupivacaine in labour is defined as the effective concentration in 50% of subjects (EC50). We have used the technique of double-blinded sequential allocation to quantify the bupivacaine sparing effect of the addition of four different doses of extradural fentanyl in 223 labouring women. There were five groups: (1) plain bupivacaine (control); (2) bupivacaine with fentanyl 1 microgram ml-1; (3) bupivacaine with fentanyl 2 micrograms ml-1; (4) bupivacaine with fentanyl 3 micrograms ml-1; and (5) bupivacaine with fentanyl 4 micrograms ml-1. The MLAC of bupivacaine were 0.069% w/v, 0.057% w/v, 0.048% w/v, 0.031% w/v and 0.015% w/v, respectively. We observed a reduction in MLAC of 18%, 31% (P = 0.03%), 55% (P < 0.0001) and 72% (P < 0.0001) with fentanyl 1, 2, 3 and 4 micrograms ml-1, respectively, demonstrating a significant negative linear trend (P < 0.0001) with increasing fentanyl dose. The incidence of pruritus was increased significantly with fentanyl 4 micrograms ml-1 (P = 0.0015). Because of this, fentanyl 3 micrograms ml-1 may be the optimal dose when the aim is bupivacaine sparing extradural analgesia during labour.

Cardiac arrest complicating spinal anaesthesia for caesarean section

We present a 36-year-old multiparous woman who developed intractable hypotension and cardiac arrest during spinal anaesthesia for elective caesarean section. Cardiopulmonary resuscitation was successful and both mother and baby made a good recovery. Postoperative investigation revealed a dilated cardiomyopathy related to pregnancy. This case highlights the importance of expediting delivery of the neonate during maternal cardiopulmonary resuscitation, the prompt use of adrenaline as inotropic support, and preoperative assessment in apparently healthy parturients.

Determination of the minimum local analgesic concentration of epidural chloroprocaine hydrochloride in labor

The aim was to determine the effective concentration in 50% of patients (EC(50)) of chloroprocaine in the first stage of labor. A constant dose modification of a model where EC(50) was previously defined as the minimum local analgesic concentration (MLAC) was used. Parturients (n = 36) requesting epidural analgesia in labor, at cervical dilatation not exceeding 7 cm, were enrolled into this prospective, double-blinded study. After placing a lumbar epidural catheter, chloroprocaine 150 mg diluted to the concentration being evaluated was given. The concentration was determined by up-down sequential allocation. The volume of the bolus ranged from 15 to 50 ml. Efficacy was assessed using 100 mm visual analogue pain scores with 10 mm or less within 30 min defined as effective. MLAC (95%CI) was 0.42%w/v (0.34 to 0.5) using the formula of Dixon & Massey and as a sensitivity test was 0.4%w/v (0.35 to 0.46) using probit regression analysis. In conclusion, MLAC of chloroprocaine was 0.42%w/v in these parturients, equivalent to 14 millimolar solution. This study confirmed that concentration rather than dose could be used as a measure of efficacy in this constant dose model.

The effect of intrathecal midazolam on post-operative pain

Intrathecal midazolam for use as a post-operative analgesic when given alone and in conjunction with intrathecal diamorphine was assessed. Fifty-two patients scheduled for elective Caesarean section under spinal anaesthesia were randomly allocated to receive either bupivacaine (B), bupivacaine with diamorphine (BD), bupivacaine with midazolam (BM) or all three (BMD) by intrathecal injection. Post-operatively, no differences in visual analogue score (VAS), sedation or post-operative nausea and vomiting (PONV) could be demonstrated between groups. Patient-controlled analgesia system (PCAS) usage was significantly greater in group B when compared with the other groups. Pruritus was commoner in patients receiving diamorphine (BMD & BD). No side effects attributable to midazolam were identified. Intrathecal midazolam at this dose appears safe and has clinically detectable analgesic properties. The duration of useful analgesia appears to be short-lived.

The effect of epidural fentanyl on the minimum local analgesic concentration of epidural chloroprocaine in labor

The minimum local analgesic concentration (MLAC) has been defined as the median effective local analgesic concentration (EC50) in a 20-mL volume in the first stage of labor. The aim of this study was to determine the local anesthetic sparing efficacy of epidural fentanyl by its effect on the MLAC of chloroprocaine. Fifty-six parturients, not exceeding 7 cm cervical dilation, who requested epidural analgesia were allocated to one of two groups in this double-blind, randomized, prospective study. After placing a lumbar epidural catheter, 20 mL of the solution being tested was given: chloroprocaine (n = 28) or chloroprocaine with fentanyl 3 micrograms/mL (60 micrograms) (n = 28). The concentration of chloroprocaine was determined by the response of the previous patient to a higher or lower concentration using up-down sequential allocation. Analgesic efficacy was assessed using 100-mm visual analog pain scores with 10 mm or less within 30 min defined as effective. The MLAC of chloroprocaine was reduced from 0.43% wt/vol to 0.26% wt/vol by fentanyl (P = 0.023). Thus, the addition of epidural fentanyl 3 micrograms/mL (60 micrograms resulted in a significant 40% reduction in the MLAC of chloroprocaine in the first stage of labor.

MEF2B is a potent transactivator expressed in early myogenic lineages

There are four members of the myocyte enhancer binding factor 2 (MEF2) family of transcription factors, MEF2A, -B, -C, and -D, that have homology within an amino-terminal MADS box and an adjacent MEF2 domain that together mediate dimerization and DNA binding. MEF2A, -C, and -D have previously been shown to bind an A/T-rich DNA sequence in the control regions of numerous muscle-specific genes, whereas MEF2B was reported to be unable to bind this sequence unless the carboxyl terminus was deleted. To further define the functions of MEF2B, we analyzed its DNA binding and transcriptional activities. In contrast to previous studies, our results show that MEF2B binds the same DNA sequence as other members of the MEF2 family and acts as a strong transactivator through that sequence. Transcriptional activation by MEF2B is dependent on the carboxyl terminus, which contains two conserved sequence motifs found in all vertebrate MEF2 factors. During mouse embryogenesis, MEF2B transcripts are expressed in the developing cardiac and skeletal muscle lineages in a temporospatial pattern distinct from but overlapping with those of the other Mef2 genes. The mouse Mef2b gene maps to chromosome 8 and is unlinked to other Mef2 genes; its intron-exon organization is similar to that of the other vertebrate Mef2 genes and the single Drosophila Mef2 gene, consistent with the notion that these different Mef2 genes evolved from a common ancestral gene.

Failed intubation revisited: 17-yr experience in a teaching maternity unit

We have reviewed 5802 Caesarean sections performed during general anaesthesia. Our use of general anaesthesia had decreased from 83% in 1981 to 23% in 1994. Despite this, the incidence of failed intubation has increased from 1 in 1984 to 1 in 250 in 1994. The problems associated with general anaesthesia in the obstetric population are increasing. Asians and African/Afrocaribbeans were represented disproportionately because of the increased use of general anaesthesia in these patients. Exposure of trainees to obstetric general anaesthetics has decreased by one-third.

Lessons from in vitro testing of spinal needles

In vitro testing of spinal needles is intended to identify a best buy, but such tests are not necessarily good indicators of clinical performance and some bench tests appear to conflict with mock clinical assessments. Discrepancies can be explained by examining the role of the hub. The Visual Probability Test, which assesses the needle as a complete unit, would appear to be more useful than the more complex measurements of shaft flow. Not all needle manufacturers use the same gauge, creating confusion when comparisons are made. Packaging frequently fails to give adequate information. Changes in hub design could permit earlier identification of dural puncture.

Determination of the minimum local analgesic concentrations of epidural bupivacaine and lidocaine in labor

The aim of this study was to devise a clinical model to determine the effective concentrations in 50% of patients (EC50) for bupivacaine and lidocaine in the first stage of labor and define EC50 as the minimum local analgesic concentration (MLAC). This should allow the determination of relative analgesic potency and, subsequently, the local anesthetic sparing efficacy of other epidural analgesics. Parturients not exceeding 5 cm cervical dilation who requested epidural analgesia were enrolled. The two studies involved 81 women (bupivacaine n = 41, lidocaine n = 40). After a lumbar epidural catheter was placed, 20 mL of the concentration of local anesthetic being tested was given. The concentration was determined by the response of the previous patient to a higher or lower concentration using double-blinded, up-down sequential allocation. Efficacy was assessed using 100-mm visual analog pain scores with less than 10 mm within 1 h defined as effective. MLAC was determined using the formula of Dixon and Massey. Results show MLAC bupivacaine 0.065% (95% confidence interval [CI] 0.045-0.085), MLAC lidocaine 0.37% (95% CI 0.32-0.42), equivalent to 2 and 14 mmol solutions, respectively. Thus bupivacaine was 5.7 times more potent than lidocaine in weighted and 7 times more potent in molar ratios at analgesic EC50, in the volume of local anesthetic studied.

Lignocaine test dose to detect intravenous injection

The accidental intravascular injection of bupivacaine or etidocaine epidurally has resulted in several maternal deaths. To be effective, a test dose must allow detection of intravenous catheter placement and prevent accidental intravenous injection. This study was designed to determine the dose of lignocaine required for this purpose. Sixty healthy gynaecological patients were allocated randomly to receive an intravenous dose of normal saline (group 1), lignocaine 0.5 mg.kg-1 (group 2) or 1 mg.kg-1 (group 3) 3 min prior to induction of anaesthesia. At 1 min intervals the patients were asked about subjective symptoms produced by this 'test dose'. In group 2 only 50% of patients reported a positive test dose, whereas in the patients of group 3, a significantly greater percentage (95%) had a positive test dose (p < 0.01). This suggests that the use of 1 mg.kg-1 lignocaine as a test dose would result in a significantly higher sensitivity for detecting intravascular injection than the use of 0.5 mg.kg-1.

Early and long-term results after completion pneumonectomy

From January 1, 1978 to December 31, 1992, 37 patients underwent a completion pneumonectomy after a previous lobectomy (36 men and 1 woman; mean age, 60 years; range, 41 to 77 years). These account for 4.8% of 758 pneumonectomies. The purpose of the present study was to evaluate the operative results of completion pneumonectomy and long-term survival in patients with bronchogenic cancer. The initial lung resection had been performed for primary bronchogenic cancer in 23, metastatic thyroid adenocarcinoma in 1, and benign diseases in 13 (tuberculosis in 11, aspergilloma in 1, and bronchiectasis in 1). Completion pneumonectomy was required for bronchogenic cancer in 32 (15 stage I, 6 stage II, 11 stage III). One patient had relapsing metastatic thyroid carcinoma, 2 had bronchiectasis, and 2 had a venous infarction after lobectomy. Four patients (10.8%) died perioperatively of the following causes: 1 fatal intraoperative bleeding, 1 fatal postoperative bleeding, 1 pneumonia, and 1 malignant hypercalcemia. Median operative blood loss was 1,000 mL, and 19 patients experienced bleeding exceeding 1,000 mL (51%). Six patients had intraoperative vascular injury. Nonfatal surgical complications occurred in 9 patients (24%), including 5 clotted hemothoraces, 3 empyemas, and 1 bronchopleural fistula. Four patients had medical complications (2 pulmonary edemas, 1 sinus tachycardia, and 1 unexplained fever). Twenty-three had an uneventful straightforward recovery (62%).(ABSTRACT TRUNCATED AT 250 WORDS)

Cloning of tropomodulin cDNA and localization of gene transcripts during mouse embryogenesis

Tropomodulin (Tmod) is a tropomyosin-binding protein involved in the structuring of actin filaments. This report describes Tmod expression in distinct patterns during embryonic development in a wider variety of adult and embryonic vertebrate tissues than previously reported. Identical Tmod cDNAs were cloned from mouse brain, skeletal muscle, heart, and hematopoeitic cells. Genomic blotting demonstrates that Tmod is encoded by a single gene, which has a 1077-bp open reading frame that is highly homologous to that of the human erythrocyte. The spatial and temporal expression of the Tmod gene was examined during mouse embryogenesis using in situ hybridization. Tmod mRNA is present by 9.5 days postcoitum (p.c.) in the developing rostral somites, coincident with expression of contractile protein genes in myotomes, suggesting that Tmod may play an important role in sarcomeric thin filament organization in skeletal muscle. While the expression of Tmod mRNA in cardiac muscle is earlier than that in skeletal muscle, its appearance in the heart also coincides with the expression of genes for thin filament proteins and correlates with initial myocardial contractions at 8.0 days p.c. Tmod mRNA is not detected in developing smooth muscle of the gut, but Tmod mRNA is expressed in hematopoeitic cells in yolk sac and developing liver. The sensory ganglia and epithelia of the inner ear express Tmod mRNA as do other sensory neurons such as those in the olfactory epithelium. Expression levels in the brain are much lower prenatally than postnatally. These findings show that Tmod expression in many cell types is developmentally regulated, suggesting that the interaction of actin filaments with this tropomyosin binding protein is an important process in tissue and cell differentiation.