The measurement of lignocaine at low concentrations in plasma, a comparison of gas liquid chromatography with enzyme immunoassay

Absorption of lidocaine following topical application in microvascular procedures on rabbits

Fifty rabbits were used to investigate the absorption of lidocaine following its topical application to blood vessels. The lidocaine level in the blood was determined by gas chromatography and the enzyme immunoassay. Animals were divided into five groups according to anatomic site (femoral vs iliac) and according to whether vessels were intact or anastomosed. In the last group (E), a water-tight sleeve was placed on the anastomosed femoral artery so that the lidocaine contacted only a small segment of the artery. In each group, 0.4 and 1 ml of 10% lidocaine were used. Our results revealed that absorption of lidocaine from topical usage was rapid. The absorption peak occurred within 5-15 min. The serum concentration of lidocaine was significantly higher in groups with intact vessels than in those with anastomosed ones. The peak level of lidocaine in the serum occurred sooner in the iliac area than in the femoral area. Absorption in group E was very low due to only a small segment of the artery being immersed with lidocaine. The main absorption site of lidocaine was not through the vessel but through the perivascular area. Toxicity may develop clinically if a high concentration of lidocaine is applied on a vessel during microsurgery.

Pharmacokinetics of lidocaine in children with congenital heart disease

The purpose of this study was to determine the pharmacokinetics of lidocaine in children with congenital heart disease (CHD). Fifteen children with left to right intracardiac shunting of blood (acyanotic group) and 15 children with right to left intracardiac shunting of blood (cyanotic group) were studied and compared with 15 children without CHD (control group). Lidocaine (1.5 mg.kg-1) was injected into a peripheral vein over 30 sec and serial samples of arterial blood were obtained up to 120 min after completion of the infusion. Total and free lidocaine were analyzed by enzyme immunoassay. The serum concentration of alpha 1-acid glycoprotein (alpha 1-AGP) at induction of anaesthesia was measured in the three groups by radial immunodiffusion. The percent free lidocaine (100 x [free lidocaine]/[total lidocaine]) was greater at 30 sec post-infusion in all three groups (35-37%) than it was at any other time but was not significantly different among the three groups (P less than 0.05). There was no significant difference in either the percent free or the total lidocaine concentration at any sample time or in any of the pharmacokinetic variables among the three groups. The serum concentration of alpha 1-AGP did not differ significantly among the three groups of patients. We conclude that the presence of intracardiac shunts does not alter the pharmacokinetic behaviour of intravenous lidocaine (1.5 mg.kg-1) in children. The percent free lidocaine is greatest immediately post-injection and this may mitigate against rapid bolus administration of intravenous lidocaine in children.

Alpha 1-acid glycoprotein and the binding of lidocaine in children with congenital heart disease

The purpose of this study was to evaluate the effect of congenital heart disease (CHD) on the serum concentrations of alpha 1-acid glycoprotein (alpha 1-AGP) and the serum binding of lidocaine. Thirteen children with acyanotic CHD and 12 children with cyanotic CHD were studied and compared with 28 children without heart disease (control). The mean (+/- SD) serum concentration of alpha 1-AGP, as determined by radial immunodiffusion, did not differ significantly among the three groups. Five minutes after administration of 1.5 mg.kg-1 intravenous lidocaine, the free fraction of lidocaine correlated inversely and linearly with the serum concentration of alpha 1-AGP in children with acyanotic CHD (r2 = 0.74; P less than 0.001) cyanotic CHD (r2 = 0.57; P less than 0.005), and control (r2 = 0.63; P less than 0.001). The slopes and intercepts of the linear regressions did not differ significantly among the three groups. We conclude that the serum concentration of alpha 1-AGP in children with CHD does not differ quantitatively or qualitatively from that in children without CHD.

Modification of lidocaine protein binding with CO2

Using new, specially designed ultrafiltration devices and an enzyme immunoassay technique, the authors determined the effect of carbon dioxide tension on the fractional binding of lidocaine to human plasma proteins. Identical samples of serum at therapeutic (2.2 micrograms X ml-1) and toxic (6.8 micrograms X ml-1) lidocaine concentrations were tonometered at 37 degrees C to CO2 tensions between 0.13 and 10.7 kPa (1.0 to 80.5 mmHg). The fraction of unbound lidocaine increased linearly with increasing pCO2 (r = 0.93, p less than 0.001). These changes help to explain the increased central nervous system toxicity of lidocaine associated with hypercarbia.

Quantitative analysis of common anaesthetic agents

A summary of chromatographic (e.g. gas chromatography, high-performance liquid chromatography) and non-chromatographic (e.g. radioimmunoassay, enzyme-multiplied immunoassay) analytical techniques suitable for the quantitative analysis of the most popular inhalational (halothane, methoxyflurane, enflurane, isoflurane and nitrous oxide), intravenous (barbiturate, benzodiazepines, etomidate, althesin, morphine, fentanyl, alfentanil, sufentanil, droperidol and ketamine) general and amide-type local (lidocaine, mepivacaine, etidocaine and bupivacaine) anaesthetic agents and some of their metabolites, in biological material, is described. In the case of inhalational anaesthetics attention is also payed to pollution measurement and breath-to-breath monitoring.

Drug level monitoring: cardiovascular drugs

Methods for the determination of cardiovascular drugs in blood and plasma are critically reviewed with emphasis on gas and liquid chromatographic techniques. The importance of the various procedures is discussed, in particular sample work-up where the conditions for isolation and derivatization of the compounds are decisive for the accuracy and precision of the methods. Compared with other assay techniques chromatographic methods are generally to be preferred owing to their better selectivity. In the review the following groups are discussed: digitalis glycosides, antiarrhythmic agents, beta-adrenoceptor antagonists, vasodilating agents, antihypertensive compounds, and diuretics.

Spinal cord and cerebral blood flow responses to subarachnoid injection of local anesthetics with and without epinephrine

Subarachnoid anesthesia with lidocaine, mepivacaine, or tetracaine with and without added epinephrine (1:100 000) produced no demonstrable changes in average cerebral (CBF) or segmental spinal cord blood flow (SCBF) in 38 cats anesthetized with pentobarbital. Blood flow was measured by the injection of radioactive microspheres. Seven groups of cats received either lidocaine 15 mg, lidocaine 15 mg with epinephrine, mepivacaine 10 mg, mepivacaine 10 mg with epinephrine, tetracaine 5 mg, tetracaine 5 mg with epinephrine, or saline with epinephrine 1:100 000. Mean arterial pressure (MAP) decreased significantly (P less than 0.05) in Groups I-VI. Added epinephrine had no effect on the decrease in MAP. Amplitude of the somatosensory cortical evoked response decreased significantly in Groups I-VI, but did not change from control in Group VII. No significant change in CBF or SCBF was demonstrated in any group at any time. Plasma lidocaine and mepivacaine levels were significantly less at 5 min after subarachnoid injection in the groups receiving epinephrine compared to those not receiving epinephrine (P less than 0.05). The data appear to support the hypothesis of a vasoconstrictive reduction in systemic absorption of intrathecal local anesthetics, but suggest that significant segmental spinal cord ischemia does not occur. Maintenance of total flow in the face of a decrease in MAP suggests that autoregulation in brain and spinal cord may be maintained. Changes in regional SCBF or CBF may have been present but were not examined in this study. Further studies of brain and spinal cord blood flow dynamics, regional flow changes, and regulation of flow after intrathecal agents are necessary.

Gas-powered jet injection compared with conventional methods of injection using lignocaine and technetium-99m

Plasma concentrations of lignocaine and the clearance rates of technetium-99m were compared in 10 healthy volunteers after injection with a gas-powered jet system and a needle and syringe. The dosage was highly accurate with jet injection. Bioavailability was comparable for both methods.