1Department of Anaesthesiology, Leiden University Medical Center, Albinusdreef 2, 2333 ZA Leiden, The Netherlands 2Present address: Department of Anaesthesiology, Stichting Streekziekenhuis Coevorden-Hardenberg, M. van Thijnensingel 1, 7741 GB Coevorden, The Netherlands*Corresponding author
Accepted for publication: June 12, 2001
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Abstract |
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Br J Anaesth 2001; 87: 73842
Keywords: anaesthetic techniques, subarachnoid; anaesthetics local, bupivacaine; age factors
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Introduction |
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The present study examined the influence of different periods of sitting, before the patient is placed in the supine horizontal position, on the spread of analgesia following subarachnoid administration of a hyperbaric bupivacaine solution in elderly patients.
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Methods |
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Patients were pre-medicated with temazepam 10 mg orally and atropine 0.25 mg i.m., 45 min before the induction of spinal anaesthesia. Before the spinal injection, 500 ml of glucose in saline was administered by rapid i.v. infusion. Dural puncture was performed with the patient in the sitting position by a standard midline approach using a 25-gauge Quincke spinal needle via an 18-gauge introducer. When a free flow of clear cerebrospinal fluid was obtained and after aspiration of 0.2 ml of spinal fluid, 3 ml of 0.5% bupivacaine in 8% glucose (Marcaine Heavy, specific gravity 1.026 at 20°C) was injected at room temperature at a rate of 0.2 ml s1. Patients remained sitting for 2 (group 1, n=15), 5 (group 2, n=15), 10 (group 3, n=15), or 20 (group 4, n=15) min after completion of the subarachnoid injection. They were then placed in the supine horizontal position.
Analgesia was assessed bilaterally in the anterior axillary line by pinprick using a short beveled 25-gauge needle. Assessments were made every 5 min during the first 30 min after the injection and at 45 and 60 min. Analgesia was defined as inability to detect a sharp pinprick. Motor block of the lower limbs was evaluated by asking the patient to raise the extended leg (flexion of the hip), flex the knee, and flex the ankle. It was rated per joint (0=no, 1=partial, 2=complete motor block). The results obtained in both extremities were added, giving a maximum score of 12 (complete motor block). Assessments of motor block were made immediately after the assessment of the analgesia levels. The time to maximum cephalad spread of analgesia, the highest level of analgesia attained and the maximum degree of motor block were recorded. During the first 20 min, all assessments were made by the anaesthetist who performed the lumbar puncture. Assessments at 30, 45, and 60 min (i.e. when all patients were lying supine) were made by another anaesthetist who was unaware of the period of sitting.
Systemic arterial pressure, measured with an automatic cycling device (Accutor 1, Datascope) and heart rate (HR) (from the electrocardiogram) were monitored before the subarachnoid injection, after induction of spinal anaesthesia, during surgery and in the recovery room at 5-min intervals during the first 30 min, then at 15 min intervals until the patients were returned to the ward. If the systolic arterial pressure (SAP) decreased more than 30% below the pre-anaesthetic value or to less than 90 mm Hg, ephedrine 5 mg was given intravenously. Bradycardia (HR <55 beats min1) was treated with atropine sulphate 0.25 mg intravenously.
Group sizes were based on a power analysis, which demonstrated that with a variance s2=3.39 in the upper level of analgesia (as observed in a previous study in elderly patients),2 15 patients would be required per group to have an 80% probability of detecting a difference of two segments between group means at the 0.05 level of significance. Data are presented as mean (SD), mean (95% confidence interval), median (95% confidence interval), or frequencies, as appropriate. Medians and the corresponding 95% confidence intervals were corrected for the presence of tied observations.10 Maximum changes in SAP and HR were analysed using one-way analysis of variance. Changes in analgesia levels, as well as analgesia levels after 20 min, the highest analgesia levels and the times at which maximum analgesia levels and maximum changes in SAP and HR were reached were analysed with the Kruskal Wallis test, followed by the non-parametric Student NewmanKeuls test,10 when indicated. Multiple Fisher exact tests were used to compare the numbers of patients with a complete motor block, and the numbers of patients requiring ephedrine or atropine. To adjust for multiple comparisons in these tests, the sequentially rejective BonferroniHolm method was applied. A P<0.05 was considered significant.
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Results |
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Discussion |
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With shorter periods of sitting (10 min), the upper analgesia level increased by approximately four segments after placing the patient in the supine position. With a longer period of sitting, for example 20 min, the average increase was only two segments. This suggests that with time less local anaesthetic is available for upward spread. This presumably is the result of binding of local anaesthetic to tissue structures within the subarachnoid space, in particular spinal cord.
The effect of the period of sitting on the spread of sensory block following subarachnoid administration of a hyperbaric anaesthetic solution has been studied previously by Povey and colleagues.7 Their study showed that, irrespective of the period of sitting (225 min), analgesia levels increased several segments after the patient had been put into the supine position. Subsequent positioning in a 15° head-down position resulted in a further increase of the analgesia levels by approximately two to three segments. On the other hand, Sinclair and colleagues11 reported that a 15° head-down tilt had minimal effect on the cephalad spread of analgesia. In that study, however, patients were positioned in the head-down position immediately after the injection and were maintained in that position for only 10 min before being placed into the supine horizontal position. Taken together, the observations of both Povey and colleagues and Sinclair and colleagues suggest that the ultimately achieved upper analgesia level is mainly dependent upon the final position of the patient. This is further substantiated by another study of Povey and colleagues,8 which showed that sensory block following injection of a hyperbaric bupivacaine solution may still extend rostrally if the patient is placed supine after sitting for as long as 60 min after subarachnoid injection. This indicates that the fixation time of a hyperbaric solution takes at least 60 min with bupivacaine. In both studies of Povey and colleagues, the increase in the highest level of analgesia was considerably larger than in our study. In part, this may be related to differences in the dose of bupivacaine administered, which amounted to 3 ml of 0.5% bupivacaine in this study and 4 ml of 0.5% bupivacaine in the studies of Povey and colleagues.
Similarly, it has been demonstrated that changes in position can alter the spread of sensory block for at least 1 h following subarachnoid administration of a hypobaric lidocaine solution for perirectal surgery.12 Dermatomal levels remained low (T11L5) while the patients were in the prone (jackknife) position with the head down at 15° from horizontal, but increased two to six dermatomes if the patient was placed in a sitting position in the recovery room after surgery.
Positional changes may also extend the sensory block after subarachnoid administration of glucose-free bupivacaine which is slightly hypobaric at body temperature.13 The level of sensory block increased up to four segments when the patient was placed 30° head up after lying supine for 80115 min after the injection of glucose-free bupivacaine. This is probably related to migration of unbound bupivacaine within cerebral spinal fluid (CSF). If a true isobaric solution is injected, the epicentre of the local anaesthetic concentration in CSF remains at the site of injection regardless of the position of the patient during and after the injection. This was demonstrated clinically by Wildsmith and colleagues, who studied the effects of posture on the spread of isobaric tetracaine and concluded that posture should not be used to control the spread of isobaric solutions.9
Several studies have shown that analgesia levels obtained after subarachnoid injection of a hyperbaric local anaesthetic solution are approximately three to four spinal segments higher in elderly compared with young adult patients.13 The same presumably holds for levels of sympathetic block that are associated with analgesia levels, but are generally two to four segments higher. Conse quently, the highest levels of sympathetic block are often in the upper thoracic region in elderly patients, which may explain the higher frequency of cardiovascular side effects in elderly compared with young adult patients.4 5 Factors that contribute to the more extensive block in the elderly include gradual degeneration of the central and peripheral nervous system,14 15 changes in the anatomical configuration of the lumbar and thoracic spine,16 and possibly a reduction in the volume of the cerebrospinal fluid.6
Recently, we demonstrated that injecting hyperbaric bupivacaine at a lower (L4L5) than the usual (L3L4) lumbar interspace did not reduce cephalad spread of local anaesthetic and did not limit the highest analgesia levels.17 In that study, as well in this study, there was a considerable inter-individual variation in the highest level of analgesia. These observations are in keeping with earlier reports on the spread of analgesia following subarachnoid administration of hyperbaric bupivacaine, in particular in elderly patients.2 3 Because of this profound inter-individual variability, the predictability of the analgesia levels that will be reached in an individual patient is low.2 3 17
In conclusion, this study has demonstrated that during spinal anaesthesia with a hyperbaric bupivacaine solution the period of sitting has little, if any, influence on final analgesia levels and on haemodynamic changes in elderly patients. These results suggest that the use of posture does not allow as much control over the spread of a hyperbaric solution as is thought.
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References |
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