Adverse effects of regional anaesthesia in children

True complications of regional block procedures pertain to the performance of the block technique and the local anaesthetic. Such complications include lesions caused by the device used, and many of these complications can be avoided by using specifically designed devices.Complications related to the local anaesthetic solution mainly consist of local and systemic complications. Local toxicity has mainly been reported in adults following spinal administration of 5% lidocaine (lignocaine), a drug that is not usually used in children. Systemic toxicity consists of CNS and cardiovascular complications, methaemoglobinaemia and allergic reactions. Systemic toxicity has special features in children, especially in those <1 year old. Infants have a much higher free serum concentration of local anaesthetics than older children and adults, and are more prone to the deleterious effects of local anaesthetics. Additionally, as regional blocks are usually performed under general anaesthesia in children, signs of CNS toxicity may be concealed. Because of their higher heart rate, newborns and infants are thought to be more prone to the phasic block produced by tertiary amine agents such as bupivacaine than are adults. Serum concentrations at which bupivacaine (and etidocaine) exert cardiac toxicity seem to be similar to those producing CNS toxicity. As there is an increased threshold for CNS toxicity in infants plus an increased (or equal) sensitivity to bupivacaine cardiotoxicity, cardiac signs may not be preceded by any sign of CNS toxicity. Cardiac complications include: (i) arrhythmias with high degree conduction block, major QRS widening, torsade de pointes, and ventricular tachycardia related to re-entry phenomena; and (ii) major vascular collapse favoured by a concomitant decrease in the myocardial contractile force. Other complications of regional block procedures result from poor selection of agent, and inadequate safety precautions and monitoring of the patient, especially during the postoperative period. There are 2 other groups of disorders often reported as complications of regional anaesthetics: (i) effects that were not anticipated by the anaesthetist because of a lack of knowledge of all the consequences of the technique used; and (ii) complications attributed to a concomitant regional block procedure but with no established, sometimes even improbable, causal link with the regional technique. The overall morbidity of regional anaesthesia in children is low. Sound selection of local anaesthetics, insertion routes and block procedures, together with appropriate and careful monitoring, should prevent any major undesirable effects and enable regional anaesthesia to be a well tolerated and effective tool to overcome pain associated with minimal morbidity.

[Conventional techniques for analgesia: opioids and non-opioids. Indications, adverse effects and monitoring]

Morphine dosage must be carefully adapted in patients with renal failure or severe liver failure. The i.v. route is used for morphine titration in the post anaesthesia care unit (PACU), or for analgesia in children. Systematic (not on demand) intramuscular or subcutaneous morphine must be administered at intervals not longer than 4 hours. Dosage is best determined after i.v. titration in the PACU. Codeine, administered orally, is metabolised into morphine. Codeine has almost no effect in 7% of Caucasians and at least 15% of Asians. Nalbuphine, which has a sedative effect and a short half-life, is mainly used in children. Paracetamol (acetaminophen) is used orally or rectally, most often in combination with codeine. Paracetamol dosage is 60-90 mg.kg-1.d-1, including a 20 mg (orally), or 40 mg (rectally) loading dose. Its therapeutic ratio is low, with a potential hepatic toxicity. Dosage must be lowered in alcoholics or in patients under isoniazide therapy. Non-steroidal anti-inflammatory drugs are powerful antinociceptive agents. Their use must be restricted to the first 5 postoperative days. Their major contraindications are kidney failure, risk of gastrointestinal bleeding, coagulation disorders, allergy. They also have a marked morphine sparing effect and reduce therefore the respiratory depression induced by morphine.

Increase in the chronically monitored cerebrospinal fluid pressure after experimental brain injury in rats

The early effects of experimental brain injury with diffuse axonal lesions on intracranial pressure (i.c.p.), mean arterial pressure (MAP) and cerebral perfusion pressure (CPP) in rats have been already studied. The aim of this experiment was to examine the effects of brain injury on ICP, MAP and CPP during the first few days post-injury. In order to do that, an accurate technique of ICP measurement had to be developed. In a series of eight rats, a translumbar intrathecal catheter (TIC) was surgically introduced allowing repeated measurements of cerebrospinal fluid pressure (CSFP). Under anaesthesia, a second series of nine rats were equipped simultaneously with TIC and an intracranial fiberoptic device to measure ICP. Simultaneous measurements of CSFP and ICP were recorded for baseline values, than during and after jugular compression which was intended to induce an acute and significant increase in ICP. A third series of 53 rats having TIC received an experimental severe brain injury. MAP was measured non-invasively and CPP was calculated as CPP-MAP. CSFP, MAP and CPP were intermittently measured during 5-6 post-traumatic days and compared to the values obtained during ten control rats (SHAM). A clinical score was used to compare clinical condition. The results showed that the translumbar CSFP accurately measured ICP in rats having normal or acutely increased ICP. The experimental brain injury induced increased CSFP lasting up to 5-6 days, with increased MAP during the first 6 hours. CPP values were compromised at 24-48 hours. The clinical performance was reduced in the brain-injured rats. The translumbar technique of CSFP measurement reflected exact ICP in normal and acutely increased ICP in rats. Experimental brain injury with diffuse axonal lesions can increase lumbar CSFP in rats for many days.

The effect of pneumoperitoneum on intraocular pressure in rabbits with alpha-chymotrypsin-induced glaucoma

Increased intraperitoneal pressure is associated with physiological changes including alterations of intraocular pressure (IOP). We have previously shown that IOP is not adversely affected by increased intraperitoneal pressure up to 15 mm Hg in women with no preexisting eye disease. The aim of this study was to measure IOP changes associated with increased intraperitoneal pressure (up to 15 mm Hg) of 2 h duration in 12 rabbits with alpha-chymotrypsin-induced glaucoma. A reliable model of glaucoma was created by injecting alpha-chymotrypsin into the posterior chamber of the right eye in 12 rabbits. Thereafter, 5 of the 12 rabbits with glaucomatous eyes were treated with topical timolol. The left eye was used as a control. During pentobarbital general anesthesia, increased intraperitoneal pressure up to 15 mm Hg was created by intraperitoneal CO2 insufflation. Body temperature and expired CO2 were kept constant throughout the study. IOP measurements were made using an electronic pneumotonometer. IOP, mean arterial pressure, heart rate, and central venous pressure were recorded in head-up and head-down positions before, during, and after increased intraperitoneal pressure. The IOP of both eyes, in both treated and untreated rabbits, increased significantly from baseline only when increased intraperitoneal pressure associated with the head-down position resulted in a significant increase in central venous pressure. However, the IOP increase remained within the diurnal range. The major finding of this study is that, in a reliable model of glaucoma, CO2 pneumoperitoneum was associated with an increase in IOP when a head-down position was combined with pneumoperitoneum.

IMPLICATIONS

In rabbits with alpha-chymotrypsin-induced glaucoma, increased intraperitoneal pressure (up to 15 mm Hg) resulted in a significant intraocular pressure increase when pneumoperitoneum was associated with the head-down position. However, the intraocular pressure increase remained within the diurnal range.

Application of HPLC to counting of colored microspheres in determination of regional blood flow

Colored microspheres have become popular compared with radioactive microspheres because they do not use radioactivity. However, they suffer from a much greater variability in their determination. We have developed a new method for assaying the dye using high-performance liquid chromatography (HPLC) with internal standard. This technique permits accurate determination of < or = 400 spheres in rat blood, heart, kidney, liver, and brain with a relative error [coefficient of variation (CV)] < 10%. To date, only three colors (white, yellow, and red) may be used because, of the five colors tested, one (violet) served as internal standard and another (blue) exhibited marked degradation during extraction. Compared with the classical spectrophotometric technique, HPLC allows a three to five times improvement in reproducibility with a relative error significantly lower (P < 0.01) than with direct spectrophotometry. Although this new technique appears to be more time consuming than the classical method, its use seems to be preferable because of the improvement in measurement sensitivity.

Correlation between in vitro and in vivo activity of amoxicillin against Streptococcus pneumoniae in a murine pneumonia model

We studied the relationship between in vitro bacteriological parameters [minimal inhibitory concentration (MIC), minimal bactericidal concentration (MBC) and killing rate, defined as the reduction in the inoculum within 1, 3 or 6 hr] and in vivo activity of amoxicillin against 12 strains of Streptococcus pneumoniae, with penicillin MICs of < 0.01 to 16 micrograms/ml, in a cyclophosphamide-induced neutropenic murine pneumonia model. Dose-response curves were determined for amoxicillin against each strain, and three quantitative parameters of in vivo amoxicillin activity were defined, i.e., maximal attainable antimicrobial effect attributable to the drug [i.e., reduction in log colony-forming units (CFU) per lung, compared with untreated controls], dose required to reach 50% of maximal effect and dose required to achieve a reduction of 1 log CFU/lung. We demonstrated a highly significant correlation between the dose required to reach 50% of maximal effect and MIC (Spearman r = 0.98, P < .0001) or MBC (Spearman r = 0.95, P < .0001) for amoxicillin against strains of S. pneumoniae with a wide range of amoxicillin MICs (0.01-8 micrograms/ml). Significant correlations between the dose required to achieve a reduction of 1 log CFU/lung and MIC (Spearman r = 0.98, P < .0001) or MBC (Spearman r = 0.95, P < .0001) were also observed. In contrast, there were no significant correlations between the maximal attainable antimicrobial effect attributable to the drug and MIC, MBC or killing rate or between killing rate and the dose required to reach 50% of maximal effect or the dose required to achieve a reduction of 1 log CFU/lung. We conclude that in vitro susceptibility test results (MICs and MBCs) correlated well with in vivo amoxicillin activity against pneumococcal strains, including highly penicillin-resistant strains, in this animal model. Furthermore, these data suggest that the estimated MIC breakpoints for amoxicillin against S. pneumoniae would be 2 micrograms/ml for intermediate-resistant and 4 micrograms/ml for resistant, although this remains to be confirmed in clinical studies.

Clonidine and or adrenaline decrease lignocaine plasma peak concentration after epidural injection

Clonidine is an alpha 2-adrenoceptor agonist increasingly used in combination with lignocaine for spinal or epidural anaesthesia because of a prolonged analgesic effect. Life adrenaline, it may decrease lignocaine peak concentration (Cmax), thus leading to decreased toxicity. However, the effects of clonidine on resorption of lignocaine into the systemic circulation from the epidural space remain to be established. We studied the pharmacokinetics of lignocaine after epidural injection of lignocaine with or without clonidine, adrenaline and both drugs. Total body clearance and apparent volume of distribution were similar in the four groups, but the maximum observed concentration (Cmax) was markedly increased in the plain solution group as compared with the other groups; (plain lignocaine: 7.15 +/- 2.04 micrograms ml-1, lignocaine + adrenaline: 3.11 +/- 136 micrograms ml-1, lignocaine + clonidine: 4.48 +/- 1.26 micrograms ml-1, lignocaine + adrenaline + clonidine: 4.06 +/- 1.42 micrograms ml-1 [mean +/- s.d.]). Our results show that, clonidine decreases lignocaine Cmax to the same extent as adrenaline.

Effect of lignocaine in myocardial contusion: an experiment on rabbit isolated heart

1. The reported incidence of myocardial contusion after blunt chest trauma varies from 16 to 76%. Of these patients, about 6% present a severe, life threatening contusion. We used an isolated heart preparation to examine the effect of lignocaine on myocardial performance after contusion. 2. Thirty hearts obtained from male New Zealand rabbits were perfused at constant flow according to the Langendorff technique and were divided into four groups. The following parameters were measured at frequent intervals for 60 min: mean coronary perfusion pressure (CPP), left ventricular diastolic pressure (LVDP), developed pressure (DP), dP/dtmax, dP/dtmin. 3. Group 1 (n = 6) served as control, group 2 (n = 7) received lignocaine for 20 min (15 microM for the first 10 min and 30 microM for the following 10 min), group 3 (n = 9) had a contusion leading to a 30-50% decrease in dP/dtmax and group 4 (n = 8) had the contusion and the lignocaine infusion was started 10 min after the contusion and stopped after 30 min. Lignocaine concentration was measured in the effluent. 4. Lignocaine alone moderately decreased contractility in group 2. In group 3, after contusion, DP, dP/ dtmax, and dP/dtmin were markedly decreased during the 60 min recording period. In group 4, lignocaine infusion rapidly restored contractility. DP, dP/dtmax and dP/dtmin returned towards their basal values. This improvement of contractility remained stable, even after lignocaine infusion was discontinued. 5. In our rabbit isolated heart preparation, lignocaine at a low therapeutic concentration was able to restore contractility after contusion. These results need to be confirmed by other studies but this may lead to promising therapeutic intervention.

Effects of carbon dioxide embolism with nitrous oxide in the inspired gas in piglets

We have compared cardiorespiratory variables in anaesthetized piglets whose lungs were ventilated with oxygen in nitrous oxide (N2O group) or nitrogen (N group) after right ventricular carbon dioxide boluses (0.5 or 1 ml kg-1; n = 12) or slow graded injections (n = 6). Boluses affected all variables studied significantly (P < 0.05) except mean systolic arterial pressure. Significant changes in PE'CO2 (P = 0.012) and PaO2 (P = 0.048) values were observed in the N2O group. Changes in PaCO2 were related to volumes of injected carbon dioxide (P = 0.044). Boluses of 1.0 ml kg-1 induced severe circulatory collapse in two piglets in the N2O group. Slow embolization altered respiratory variables significantly (P < 0.001)). PaO2 decreased significantly in the N2O group (P < 0.0001). Mean pulmonary arterial pressure increased significantly over time (P = 0.001) and lasted longer in the N2O group (P < 0.05). Volumes and time required to induce a 50% increase in mean pulmonary arterial pressure differed significantly between groups (P < 0.05). We conclude that nitrous oxide worsened the effects of rapid and slow carbon dioxide emboli on cardiopulmonary variables. Rapid carbon dioxide embolism altered respiratory and haemodynamic variables, while slow carbon dioxide embolism changed only respiratory variables.

Binding of bupivacaine to human serum proteins, isolated albumin and isolated alpha-1-acid glycoprotein. Differences between the two enantiomers are partly due to cooperativity

Binding parameters of R(+)- and S(-)-bupivacaine were determined for human serum proteins, human alpha-1-acid glycoprotein (AAG) and human serum albumin (HSA), using ultrafiltration. Binding parameters were estimated according to the Scatchard model of the law of mass action using nonlinear regression. A sigmoid (cooperativity) term was added when needed. Both enantiomers exhibited a two site binding profile for human serum and for a solution containing AAG and HSA at physiological concentrations. At concentrations lower than 40 microM (concentrations encountered in clinical situations), the low capacity, high affinity apparent site was predominant and S(-)-bupivacaine exhibited a higher free fraction than R(+)-bupivacaine. At concentrations higher than 60 microM, the opposite situation was observed and the S(-) enantiomer showed much higher binding to AAG than the R(+) enantiomer. Two cooperativity phenomena occurred. Negative cooperativity was observed when AAG and HSA were combined in the same solution. S(-) and R(+) enantiomers exhibited different behavior toward purified AAG and HSA due in part to complex allosteric cooperativity (positive or negative depending on the ligand/protein ratio). In conclusion, we observed stereoselective binding of bupivacaine to AAG and HSA. Moreover, cooperativity occurred, and the behavior of the two enantiomers showed marked differences in this respect.

Can immediate opioid requirements in the post-anaesthesia care unit be used to determine analgesic requirements on the ward?

The aim of this prospective study was to evaluate the efficacy of two dosage regimens of (i.m.) morphine calculated from an initial (i.v.) titrated dose in the early postoperative period. Seventy ASA I-III patients who underwent general anaesthesia (GA) (n = 58), regional anaesthesia (RA) (n = 10) or GA+RA (n = 2) for orthopaedic (n = 54), urological (n = 11) or abdominal surgery (n = 5) received i.v. titrated morphine in the post-anaesthesia care unit (PACU). Titration consisted of 3 mg morphine i.v. every ten minutes until patients had a visual analogue pain scale (VAS) < 3, without marked sedation. Seventeen patients did not complain at all or had good analgesia with an initial i.v. dose < or = 6 mg of morphine followed by paracetamol only. Patients who needed more than 6 mg i.v.morphine were randomly assigned to a "high-dose" or a "low-dose" group and received a systematic i.m. morphine regimen calculated from the initial titrated dose. Pain was assessed by VAS before each i.m. injection and the next morning. One patient had respiratory depression and one marked sedation in the PACU. These patients were excluded from the rest of the study. Only 16 patients were excluded from the rest of the study. Only 16 patients had a VAS > 3 at least once during the study period and only three needed rescue analgesia which was available on request. We conclude that a systematic i.m. morphine regimen adapted from an initial i.v. titration in the PACU provides efficacious and relatively inexpensive postoperative analgesia, applicable to a great majority of patients.

Postoperative pain after local anesthetics for laparoscopic sterilization

OBJECTIVE

To test the effectiveness of intraperitoneal local anesthesia in relieving postoperative pain after laparoscopic sterilization.

METHODS

In a double-blind, placebo-controlled randomized study of two groups of 25 subjects each, women scheduled for tubal sterilization under general anesthesia received 80 mL of 0.5% lidocaine with 1/320,000 epinephrine intraperitoneally in the right subdiaphragmatic quadrant at the beginning of the procedure. At the end of the procedure, they received 10 mL of 2% lidocaine with 1/80,000 epinephrine injected into each mesosalpinx. Controls received saline instead of lidocaine. Shoulder and pelvic pain assessed by visual analogue pain scale, postoperative analgesic requirements, nausea or vomiting, and time to return to normal daily activities were evaluated in the ambulatory unit and after discharge during the first 48 postoperative hours. Blood samples were taken in ten subjects receiving lidocaine to evaluate peak plasma concentrations and time to peak plasma concentrations.

RESULTS

Pain was significantly less in patients who received lidocaine, and the difference lasted for the duration of the study (P < .05). Analgesic requirements and time to return to normal daily activities were significantly reduced in patients who received lidocaine (P < .05). Blood samples revealed no toxic concentrations. The peak plasma concentration was 3.22 +/- 1.21 micrograms/mL, and the time to peak plasma concentration was 42 +/- 15 minutes.

CONCLUSION

Intraperitoneal instillation of lidocaine-epinephrine combined with mesosalpinx infiltration of lidocaine during tubal sterilization produces effective, long-lasting analgesia and improves the postoperative course.

Are pulse oximetry and end-tidal carbon dioxide tension monitoring reliable during laparoscopic surgery?

Cardiorespiratory changes induced by pneumoperitoneum and head-up tilt may generate alveolar ventilation to perfusion ratio changes and increased systemic vascular resistances. The reliability of end-tidal carbon dioxide tension and pulse oximetry in predicting arterial carbon dioxide partial pressure and arterial oxygen saturation may therefore be affected. The 35 ASA 1-2 patients in this study comprised 12 men and 23 women aged 48 (SD 17) years and weighing 71 (SD 14) kg. Twenty-nine were to undergo upper abdominal laparoscopy for cholecystectomy and six hyperselective vagotomy. Intra-abdominal pressure was 1.7 (SD 0.9) kPa and head-up tilt was 5.6 (SD 4.2) degrees. After abdominal insuflation, arterial carbon dioxide partial pressure significantly increased (p < 0.05). However, the arterial carbon dioxide partial pressure-end-tidal carbon dioxide partial pressure gradient remained constant throughout surgery. This gradient was highly correlated with arterial carbon dioxide partial pressure (p < 0.0001), but was not correlated with elapsed time, intra-abdominal pressure or head-up tilt. Arterial oxygen saturation was always greater than 95% in all patients and the arterial oxygen saturation-pulse oximetric saturation gradient was always less than or equal to +4%. In conclusion, end-tidal carbon dioxide partial pressure and pulse oximetric saturation allow reliable monitoring of arterial carbon dioxide partial pressure and arterial oxygen saturation in the absence of pre-existing cardiopulmonary disease and/or acute peroperative disturbance.

Myocardial uptake of bupivacaine: I. Pharmacokinetics and pharmacodynamics of lidocaine and bupivacaine in the isolated perfused rabbit heart

Bupivacaine, but not lidocaine, may cause severe cardiac dysrrhythmias in case of accidental intravascular injection. In an attempt to discriminate between a pharmacokinetic and a pharmacodynamic (or both) origin to these differences, we used an isolated rabbit heart model with constant coronary inflow to compare the myocardial uptake and disposition kinetics of lidocaine and bupivacaine. Drug concentration in the outflow perfusate was assayed and surface electrocardiogram was recorded. Drug uptake and disposition kinetics were modeled with a two-compartment open model. An Emax model was used to describe the increase in QRS duration in relation with drug concentration in the central compartment. Lidocaine and bupivacaine exhibited similar myocardial pharmacokinetics (i.e., a rapid decrease in the outflow concentration upon drug administration discontinuation). Bupivacaine-induced maximum increase in QRS duration (Emax) was 15 times superior to lidocaine Emax. The steady-state perfusate concentration producing half Emax was the same for both drugs. We conclude that bupivacaine-induced QRS widening decreases almost at the same rate as does lidocaine-induced QRS widening when drug administration is terminated. Therefore, the different cardiac effects of lidocaine and bupivacaine are not due to differences in myocardial uptake and disposition kinetics.

Myocardial uptake of bupivacaine: II. Pharmacokinetics and pharmacodynamics of bupivacaine enantiomers in the isolated perfused rabbit heart

The enantiomers of a racemic drug generally differ in their pharmacokinetic and/or pharmacodynamic properties. Because bupivacaine is a mixture of two optical isomers known to exert different toxic properties on isolated nerve preparations, we decided to use an isolated rabbit heart model with constant coronary inflow to compare the myocardial uptake kinetics of the R(+)-, S(-)-enantiomers and the racemic mixture of bupivacaine. The increase in QRS duration was also measured, and the inflow concentration-effect relationship was analyzed for the three drugs. The racemic and the two enantiomers of bupivacaine exhibited similar myocardial pharmacokinetics with a two-compartment profile for all hearts except one. All drugs showed a rapid decrease in the outflow concentration when drug administration was discontinued. The tissue/perfusate concentration ratio at steady state was similar for the three drugs. QRS widening, as well as the occurrence of severe arrhythmias, was much less pronounced in the hearts receiving the S(-) isomer than in the hearts receiving the R(+) isomer or the racemic mixture. Despite the occurrence of arrhythmias, QRS widening was adequately modelled with an Emax model. C50, the inflow perfusate concentration producing half Emax (maximal theoretical increase in QRS duration) was the same for all three drugs. The authors conclude that the S(-)-bupivacaine exerts less detrimental effects on the isolated heart of the rabbit perfused at a constant coronary flow with protein-free buffer.

[Analgesia after thoracotomy by extrapleural administration of continuous bupivacaine]

This study was aimed to assess the efficiency and the side effects of a continuous administration of bupivacaine into the paravertebral space. Twenty patients, ranked ASA 2 or 3, with a mean age of 57.9 years, and having had a posterolateral thoracotomy for resection of lung tissue, were randomly assigned to one of two groups, B or C. At the end of the surgical procedure, a 22 gauge catheter was inserted into the paravertebral extrapleural space, at T4 levels As soon as pain occurred during recovery (T0), the patients were given two-hourly intravenous boluses of buprenorphine. The patients in group B were also given, through the paravertebral catheter, a 20 ml bolus of 0.25% bupivacaine, followed by a continuous steady rate infusion (10 ml.h-1). Group C patients were given normal saline in the same way. All patients could improve their analgesia with 0.05 ml boluses of buprenorphine given by an auto-analgesia pump (Pharmacia). The following parameters were assessed during the 72 h which followed the first injection: pain with a visual analogic scale, quality of sedation (5 grades), heart and breathing rate, systolic and diastolic blood pressure, arterial blood gases. In group B, plasma bupivacaine concentrations were measured throughout the infusion, and for an 8-hour period after its end. The statistical analysis included 15 patients only, as the catheter had moved into the chest cavity in the other 5. Analgesia was qualified to be adequate by all patients, but there was no statistically significant difference in the amounts of self-administered buprenorphine between groups B and C.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of epinephrine and clonidine on plasma concentrations of spinal bupivacaine

ASA II-III patients, scheduled for peripheral vascular surgery, were included in a study designed to assess the effect of spinal epinephrine and clonidine on plasma concentrations of spinally administered 0.5% glucose-free bupivacaine. Patients were allocated randomly to three groups to receive via a spinal catheter 22.5 mg (4.5 ml) of bupivacaine alone (Group B, 9 patients) or combined with 0.3 mg epinephrine (Group BE, 10 patients) or 0.15 mg clonidine (Group BC, 10 patients). Sensory blockade was assessed by pin-prick and motor blockade on the Bromage scale. Bupivacaine plasma concentrations were measured by gas chromatography. A trend to prolongation of local anaesthetic blockade was documented in patients receiving bupivacaine plus epinephrine or clonidine. (Time to regression of sensory blockade to L2: 170 +/- 75 min in Group B, 230 +/- 50 min in Group BE, 232 +/- 64 min in Group BC.) The maximum peak concentration (Cmax), the time to reach Cmax (Tmax) and the time-concentration curve from 0-180 min (AUC) were not different for the three groups (Cmax 228 +/- 112 ng.ml-1 in Group B, 215 +/- 103 ng.ml-1 in Group BE, 234 +/- 159 ng.ml-1 in Group BC; Tmax 41 +/- 34 min in Group B, 59 +/- 31 min in Group BE, 68 +/- 32 min in Group BC; AUC 31.0 +/- 1.7 mg.ml-1.min-1 in Group B, 27.3 +/- 1.1 mg.ml-1.min-1 in Group BE, 27.0 +/- 1.1 mg.ml-1.min-1 in Group BC). The results of this study suggest that epinephrine and clonidine do not decrease blood resorption of spinal bupivacaine.

Serum concentrations of local anaesthetics following intraperitoneal administration during laparoscopy

The present study is a comparison of the pharmacokinetics of four local anaesthetics injected double blind in the right subdiaphragmatic area during outpatient laparoscopy performed under standard general anaesthesia in 28 young women. 80 ml of one of the following solutions was injected: Group A 0.5% plain lidocaine (n = 7), Group B 0.5% lidocaine with 1/320.000 adrenaline (n = 8), Group C 0.5% lidocaine with 1/800.000 adrenaline (n = 7), and Group D 0.125% bupivacaine with 1/800.000 adrenaline (n = 6). Blood samples were collected over 360 min from an iv catheter and serum concentrations were measured by gas chromatography. No adverse effects occurred in the study period. In Group A (plain lidocaine), Cmax was significantly higher and tmax significantly earlier than in Groups B and C (lidocaine with adrenaline). A toxic level was not found after either solution in any patient. The intraperitoneal use of doses of 400 mg lidocaine or 100 mg bupivacaine for perioperative analgesia was safe and solutions of lidocaine containing adrenaline appeared to pose even less risk than plain solutions.

Heart rate response to an i.v. test dose of adrenaline and lignocaine with and without atropine pretreatment

In order to evaluate the sensitivity of an adrenaline test dose for detecting intravascular injection and the effect of atropine pretreatment, 90 ASA physical status I and II patients were allocated randomly to two groups, to receive i.v. saline 1 ml (n = 46) or i.v. atropine 0.5 mg (n = 44). Five minutes later, all patients received an i.v. test dose of 2% lignocaine 3 ml with adrenaline 15 micrograms at a rate of 1 ml s-1. The groups were similar with respect to basal heart rate (HR). HR remained unchanged after saline injection, but increased slightly 5 min after atropine injection (mean 78 (SD 15) beat min-1 vs 87 (20) beat min-1 (P less than 0.05). After the test dose of lignocaine with adrenaline, HR increased significantly in both groups at 30 s, 1 and 2 min, and remained increased at 3 min in the atropine group. The maximum increase in HR was greater in the atropine group than in the saline group (31 (4) beat min-1 vs 26 (11) beat min-1 (P less than 0.05). However, when individual maximum HR changes are considered, five patients in the saline group and four in the atropine group had an increase less than or equal to 10 beat min-1, and three patients in the saline group had no change or a decrease in HR. Defining a positive result to a test dose as an increase in HR of greater than 10 beat min-1, the sensitivity of the adrenaline test dose was 83 (5.5)% in the saline group and 91 (3.5)% in the atropine group (ns).(ABSTRACT TRUNCATED AT 250 WORDS)

Extrahepatic metabolism of morphine occurs in humans

The pharmacokinetics of morphine was studied in six patients in whom a radiologic localization of an insulinoma was to be performed under general anesthesia. Sampling was done in the peripheral artery, the mesenteric vein in five of the six patients, the hepatic vein, and the peripheral vein, as well as in urine. Hepatic blood flow was estimated by an indocyanine green infusion technique at the end of the radiologic procedure. Morphine terminal half-life was 92 +/- 9 minutes, total body clearance was 1260 ml.min-1, and the hepatic extraction ratio was 0.65 +/- 0.11. No concentration gradient was observed between the artery and the superior mesenteric vein, showing that no gut wall metabolism of morphine occurred. The total body clearance exceeded the hepatic clearance by 38%. It was concluded that the extrahepatic extraintestinal clearance of morphine probably occurred through the kidney.

Myocardial uptake of lignocaine: pharmacokinetics and pharmacodynamics in the isolated perfused heart of the rabbit

1. The uptake kinetics and pharmacodynamics of lignocaine were studied in isolated perfused heart of the rabbit. 2. Six hearts were perfused with increasing concentrations of lignocaine in a modified Krebs-Henseleit buffer. The effluent concentration together with the increase in QRS duration were measured during lignocaine infusion and during 20 min after cessation of lignocaine infusion. 3. Lignocaine disposition and elimination were best described by a two-compartment open model. Terminal half-life was 11.0 +/- 2.9 min. The unidirectional transfer was slower from central to peripheral compartment than from peripheral to central compartment (T1/2.12 = 42.6 +/- 10.5 min whereas T1/2.21 = 10.7 +/- 2.8 min). The myocardium/perfusate concentration-ratio was 4.7 +/- 0.4. 4. The pharmacodynamic effect was best described in the central compartment by using the Hill equation. Calculated maximum QRS duration (Emax) was 77 +/- 8 ms. Emax was also directly measured in four additional rabbits by infusing ten times the dose of lignocaine used in the main experiment: the value of Emax measured in these conditions was 92.5 +/- 9.6 ms, i.e. a QRS widening of 150%. The steady-state perfusate concentration producing half the effect (C50) was 15.7 +/- 7.6 micrograms ml-1. 6. In conclusion, the specific lignocaine binding leading to increase in QRS duration appeared to be more closely related to the vascular stream than non specific binding leading to a deeper accumulation process.

Pharmacokinetics of bupivacaine after short and prolonged infusions in conscious dogs

A conscious dog model was used to study pharmacokinetics of bupivacaine after a short infusion (SI) (15 min) and a prolonged infusion (PI) (24 hours). Bupivacaine was infused in six mongrel dogs at least 10 days after implantation of femoral arterial and venous catheters. Each dog received both the SI and the PI in a random crossover design at a one week interval. Bupivacaine concentration was measured in serum sampled during the SI, during the last hour of the PI, and at frequent intervals during eight hours after cessation of infusion. Indocyanine green (ICG) clearance also was measured during the last hour of the PI and 90 min after cessation of both the SI and the PI. The terminal half-life (T1/2Z) of bupivacaine increased after the PI compared with the SI, 167 +/- 86 vs 53 +/- 13 min, respectively (mean +/- SD; P less than 0.05), and total body clearance (Cl) decreased, 3.4 +/- 1.2 vs 9.5 +/- 4.5 ml.min-1.kg-1, (P less than 0.05), although the volumes of distribution (VZ and VSS) did not change. A decrease in hepatic blood flow did not cause the decrease in Cl because ICG clearance did not change during the three sets of measurements. Thus, the observed increase in T1/2Z and decrease in Cl after the PI as compared with the SI are due to a decrease in hepatic intrinsic clearance of bupivacaine. Differences in the kinetic profile of the two enantiomers of bupivacaine cannot be excluded as a cause. We conclude that the extrapolation of kinetic data of bupivacaine obtained after a short infusion (or a bolus injection) to prolonged dosage must be done with care.

Pharmacokinetics of bupivacaine following caudal anesthesia in infants

Pharmacokinetics and protein binding of bupivacaine were studied after caudal injection of 2.5 mg/kg in 13 ASA PS 1 infants (1-6 months of age) scheduled for elective hernia repair. Blood was sampled at frequent intervals from 5 min to 600 min in all but one patients. Additional samples were taken at 720 and 840 min in five patients. Bupivacaine concentration was measured using gas chromatography. Protein binding was measured using ultrafiltration. Peak serum concentrations ranged between 0.55 and 1.93 micrograms/ml. The time to reach the peak ranged from 10 to 60 min. Terminal half-life (T1/2 beta) was 7.7 +/- 2.4h (mean +/- SD), the volume of distribution (Vss) was 3.9 +/- 2.01.kg, and the total body clearance (CL) was 7.1 +/- 3.2 ml.min.kg-1. The free fraction was markedly increased (0.16 +/- 0.07) when compared with published adult values, and showed a highly significant negative correlation with age. Alpha 1 acid glycoprotein measured in the same infants correlated significantly with age. In conclusion, pharmacokinetics of caudal bupivacaine in infants are characterized by Cmax of total drug similar to those observed in adults after epidural injection. The free fraction is increased at least until 6 months of life. This suggests caution in the use of bupivacaine in infants until we understand the clinical significance of this increased free fraction.