Assessment of Neurological Toxicity of Hydroxyethyl Starch 130/0.4 Injected in the Intrathecal Space in Rats

Objective

Epidural blood patch is the procedure of choice to relieve postdural puncture headache. Hydroxyethyl-starch (HES) has been proposed as a patch in some circumstances such as in the case of hematological disease due to the theoretical risk of neoplastic seeding to the central nervous system. Acute neurological HES toxicity has been excluded by a previous animal study, but the long-term neurological toxicity has not been evaluated.

Methods

Rats were randomly assigned to one of three groups: no intrathecal injection, 20 μL of intrathecal saline, or a 20-μL intrathecal HES (6% hydroxyethyl starch 130/0.4) administered via a cervical puncture. Clinical daily rat activity was measured before and after dural puncture by actinometry. The rats were killed at day 28, and the spinal cord was surgically removed and stained with hematoxylin-phloxine-saffron for gross and microscopic examination.

Results

Eleven rats underwent dural puncture without injection, 11 were injected with normal saline, and 12 received intrathecal HES. No clinical or actimetric changes (total distance traveled, number of direction changes, and number of rearings) were observed up to one month after injection. Nonspecific histopathological changes were equally observed in all groups.

Conclusions

The results of the current study indicate that intrathecal injection of HES in rats does not induce any clinical or histopathological evidence of long-term neuronal toxicity. Further safety studies in animals are warranted before HES might be considered a safe alternative to the classic epidural blood patch.

Neurotoxicity of intrathecal 6% hydroxyethyl starch 130/0.4 injection in a rat model

Epidural blood patch is the gold standard treatment for post-dural puncture headache, although hydroxyethyl starch may be a useful alternative to blood if the latter is contraindicated. The aim of this experimental study was to assess whether hydroxyethyl starch given via an indwelling intrathecal catheter resulted in clinical or histopathological changes suggestive of neurotoxicity. The study was conducted in rats that were randomly allocated to receive three 10-μl injections on consecutive days of either saline or hydroxyethyl starch administered via the intrathecal catheter. Eight rats were given injections of saline 0.9% and 11 were given 6% hydroxyethyl starch 130/0.4 derived from thin boiling waxy corn starch in 0.9% sodium chloride (Voluven). Daily clinical evaluation, activity measured by actimetry and neuropathological analysis of the spinal cord were subsequently performed to assess for signs of neurotoxicity. No clinical or actimetric changes were observed in either group following intrathecal saline or hydroxyethyl starch administration. Histopathological examination showed non-specific changes with no differences between the two groups. This experimental study in the rat suggests that repeated intrathecal injection of hydroxyethyl starch is not associated with neurotoxicity.

Protection against ventricular and atrial fibrillation by sotalol

Sotalol is not only a beta blocker but a class III antiarrhythmic drug. Its possible antifibrillatory activity was therefore investigated in both the ventricles and atria of dog heart in situ, since vulnerability to fibrillation is not the same in both these parts of the myocardium. Fibrillation threshold was measured concurrently with the duration and amplitude of monophasic action potential, the effective refractory period, the conduction time in the contractile fibres, and after fibrillation had been triggered the fibrillation rate. Variables were measured at 5 and 10 min after sotalol had been given intravenously in closed chest dogs in three doses (1, 1, and 2 mg X kg-1) at 15 min interval. Sotalol produced a rise in fibrillation threshold that occurred simultaneously with a prolongation in monophasic action potential duration and effective refractory period of the contractile fibres and a slowing in fibrillation rate, whereas conduction time was not affected. The changes appeared, however, to be less pronounced in the ventricles than in the atria, in which vulnerability to fibrillation, normally increased by vagal tone, had been previously enhanced by acetylcholine. Sotalol antagonised the changes due to acetylcholine. In both the atria and the ventricles the first dose (1 mg X kg-1), which produced plasma concentrations of approximately 2 micrograms X ml-1 10 min after injection, produced a submaximal effect. Nevertheless, subsequent administrations increased the beneficial effects but not in proportion to the dose and plasma concentrations.

Blockade by verapamil of cholinergic effects on atrial specialised tissue in the anaesthetised dog

The effects of verapamil were studied in anaesthetised dogs administered dextromoramide intrathecally to provide background vagal tone. Measurements were made of spontaneous heart rate, and, in paced hearts, of conduction times in atrial muscle, the atrioventricular node (A-V node) and His-Purkinje system by means of His bundle potential recording. The effective refractory period (ERP) of A-V node was measured by the extrastimulus method. In atropinised and vagotomised animals, verapamil reduced sinus rate and increased A-V nodal conduction time. In dogs high vagal tone after dextromoramide, however, verapamil increased sinus rate and reduced A-V nodal ERP. After dextromoramide alone, A-V block was observed at an atrial pacing rate of 150 beats X min-1, but after verapamil 1:1 A-V conduction was restored. The decrease in conduction velocity in the A-V node due to ACh was neither attenuated nor enhanced by verapamil.

Influence of the restoration of vagal tone by intracisternal injection of dextromoramide on the cardiac effects of the antiarrhythmic drugs

The effects of four antiarrhythmic drugs, quinidine, procainamide, amiodarone and verapamil were studied on sinus rate, conduction time and, when possible, effective refractory period (ERP) in atrioventricular node (AV node), and finally atrial muscle ERP. This study was made under two types of conditions, vagal tone being absent or present after restoration in the anesthetized dog by a new technique, the intracisternal injection of dextromoramide. Quinidine and procainamide which tend to slow down sinus rate and conduction in the former case accelerate them considerably in the latter by opposing the effects of acetylcholine released by vagal endings. The prolongation of atrial ERP also induced by these drugs results from both this process and their own capacity. Amiodarone and verapamil, usually responsible for bradycardia, notable delay in AV node conduction and lengthening of AV node ERP are, however, liable to elicit opposite effects, especially amiodarone when vagal tone is very high. The reduction of vagal influence is, in the case of these drugs, the only factor in the prolongation of atrial ERP. In any case, the response of both specialized and common tissue of the heart to antiarrhythmic drugs should not be interpreted unless the degree of vagal tone is known.

Effects of mild hyperkalemia on conduction velocity and effective refractory period in various parts of the dog heart in situ

Effects of mild hyperkalemia on conduction velocity, effective refractory periods (ERPs) and sinus rate were studied on 16 anesthetized dogs, using endocavitary His bundle recordings, the extrastimulus method and standard electrocardiogram. Six dogs were placed under acetylcholine infusion (300 micrograms/kg/min) (ACh group), 10 received atropine sulfate 0.2 mg/kg intravenously (atropine group). Intraventricular conduction time, ventricular ERP and QRS duration of the EKG were studied on 7 other open-chested dogs (ventricular group). During a 60 min potassium chloride infusion (0.025 mmol/kg/min, 30 min, then 0.05 mmol/kg/min, 30 min), following observations were made: - In the ACh group, AV node conduction time (A-H interval) decreased by 20% and AV node ERP by 17%, whereas, in the atropine group, the former parameter was not affected and atrial ERP increased by 29%. - At the same time, sinus rate increased in the ACh group and was unaffected in the atropine group. - Conduction times in atrial contractile tissue (S-A interval), His-Purkinje system (H-V interval) and ventricular contractile tissue, like ventricular ERP, exhibited no variation or very slight, occasionally biphasic variations under both conditions. These results can be accounted for by an "anticholinergic" effect of mild hyperkalemia which is discussed.