1Department of Anaesthetics and Intensive Care Medicine, The Queens University of Belfast, Whitla Medical Building, 97 Lisburn Road, Belfast BT9 7BL, UK. 2Department of Anaesthetics, Musgrave Park Hospital, Stockmans Lane, Belfast, UK. 3AstraZeneca R&D, Sodertalje, Sweden*Corresponding author
Accepted for publication: June 12, 2001
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Abstract |
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Br J Anaesth 2001; 87: 7437
Keywords: anaesthetic techniques, regional; anaesthetic techniques, spinal; anaesthetics, local; ropivacaine; total hip replacement
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Introduction |
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Although several studies have examined the effects of intrathecal ropivacaine in both labouring women5 and patients undergoing minor surgery,6 no studies have evaluated its use in anaesthesia for major surgery. This study was designed to investigate the safety and efficacy of two concentrations of intrathecal isobaric ropivacaine (7.5 and 10 mg ml1) in patients undergoing primary total hip arthroplasty.
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Methods |
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Oral pre-medication consisted of diazepam 10 mg and ranitidine 150 mg. Following arrival in the anaesthetic room, i.v. access was established, full non-invasive monitoring applied and the patient placed in the lateral position with the affected hip uppermost. Following skin infiltration with 1% lignocaine, a 20-gauge introducer needle was inserted at the L2/3 or the L3/4 interspace through which a 25-gauge pencil-point needle with its opening uppermost was passed. Correct needle placement was identified by free flow of cerebrospinal fluid and 2.5 ml of study drug was injected. The spinal needle was removed and the patient placed supine to perform the initial assessments. Following completion of the initial assessments and before the commencement of surgery, patients were returned to the lateral position and a continuous i.v. infusion of 1% propofol commenced. The rate of this infusion was adjusted to render the patients drowsy but rousable. Surgery was commenced within 45 min of the administration of the study drug.
The upper and lower spread of sensory block was determined bilaterally using loss of cold sensation to ice. The dermatomes were identified by reference to a standard diagram. Sensory block was assessed at 2 and 5 min post-injection and at 5-min intervals thereafter until two consecutive levels of sensory block were identical. Assessments were continued at 30-min intervals following the completion of surgery until normal sensation returned. The degree of motor block in the non-operative leg was assessed at the same time points as sensory block using a modified Bromage scale (0=no motor block, 1=inability to raise extended legs, 2=inability to flex knees, 3=inability to flex ankle joints). Assessment of motor block ceased once normal motor function returned. Heart rate and arterial pressure were recorded using standard non-invasive techniques/monitors before intrathecal injection and thereafter at 5, 10, 15, 20, 25, 30, 45, and 60 min, then hourly until 8 h post-injection.
The quality of anaesthesia (judged by the anaesthetist), the quality of muscle relaxation (opinion of the surgeon) and the degree of intraoperative comfort (judged by the patient) were recorded as excellent, satisfactory or unsatisfactory. Intraoperative blood loss, the time to first request for post-operative analgesia and the total morphine consumption in the first 24 h following surgery were also noted. Patients were followed up daily for adverse events (defined as any unintended or unfavourable sign, symptom, or disease temporally associated with the use of intrathecal ropivacaine) and serious adverse events (defined as any adverse event which requires a prolonged hospital stay, results in permanent disability or incapacity, is life-threatening or results in death) for the duration of their hospital stay and again by telephone 1421 days post-surgery.
A difference of 45 min in the duration of sensory block at T10 was taken to be clinically significant. An estimated 22 patients per group were necessary to detect a 45 min difference in the duration of sensory block at T10 with an 80% power, based on a simple unstratified two-sample 95% t-based confidence interval for group comparison, under normality assumptions. The Stratified Wilcoxon (mid) rank sum test was used for comparison between the two groups. A P value of less than 0.05 was considered statistically significant.
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Results |
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Whilst there was a trend towards a longer duration of sensory block at different dermatome levels in the ropivacaine 10 mg ml1 group, this difference was not statistically significant. The duration of sensory block in each group is shown in Figure 1. There was no significant difference in either the maximum upper or lower spread of sensory block before or after surgery (Fig. 2). Anaesthesia was judged to be excellent in all patients, except for one in the ropivacaine 7.5 mg ml1 group who complained of deep wound pain approximately 5 min after skin incision despite a pre-operative sensory block to T10. General anaesthesia was instituted, the patient was pain free post-operatively with a sensory block level at T7 and motor block of 3 on the modified Bromage Scale in the recovery ward. This patient had no recall of any intraoperative pain.
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The median time to first analgesic request was similar in both groups (7.5 mg ml1=3.3 h, 10 mg ml1=3.9 h). Median morphine requirements (7.5 mg ml1=50 mg (range 094 mg), 10 mg ml1=42 mg (range 17120 mg)) in the first 24 h following surgery were similar.
Intrathecal ropivacaine produced an initial moderate decrease in arterial pressure. Intraoperative hypotension requiring treatment with i.v. ephedrine occurred in 24% of patients in both the 7.5 and 10 mg ml1 ropivacaine groups. No patients in the ropivacaine 7.5 mg ml1 group required treatment for intraoperative bradycardia. Three patients in the ropivacaine 10 mg ml1 group required i.v. atropine 0.6 mg to correct symptomatic bradycardia in the intraoperative period. The most commonly reported adverse events during the first 24 h were pyrexia, nausea, vomiting, hypotension, and oliguria. These events were similarly distributed between groups. There was no significant difference in the blood loss between the two groups (median 480 ml in the ropivacaine 7.5 mg ml1 group, median 370 ml in the ropivacaine 10 mg ml1 group).
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Discussion |
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To our knowledge, this study is the first study to evaluate intrathecal ropivacaine for use as a sole agent in patients undergoing major surgery. The efficacy and safety of two glucose-free solutions of ropivacaine, 7.5 and 10 mg ml1, were assessed for intrathecal anaesthesia in patients undergoing total hip replacement. Both solutions produced similar results in terms of onset and spread of analgesia. In a previous study which compared 3.0 ml of 5 and 7.5 mg ml1 glucose-free ropivacaine in patients undergoing lower limb surgery, only 32% and 50%, respectively, of patients achieved a sensory block of at least T10.6 This contrasts with our study in which virtually all patients achieved adequate sensory block. Furthermore, the upper extent of sensory block was much higher in this study with approximately 10% of patients with sensory anaesthesia in the cervical dermatomes compared with a maximum sensory block at the T4 dermatome in the study carried out by van Cleef and colleagues. This may be because of a difference in the characteristics of the populations studied, the use of a higher dose of ropivacaine, or the difference in the position of the patient during the institution of intrathecal anaesthesia. Furthermore, sensory block in our study was tested using loss of sensation to ice rather than loss of sensation to pinprick, which may produce a significant discrepancy in the assessment of sensory block following intrathecal anaesthesia.10 The subgroup of patients with sensory anaesthesia in the cervical dermatomes did not demonstrate any upper limb motor weakness, respiratory distress, decrease in oxygen saturation, or cardiovascular compromise. This suggests a significant separation in the extent of motor and sensory block when loss of sensation to ice is used.
The one patient in whom a loss of cold sensation to ice at the T10 dermatome did not produce adequate anaesthesia may have had a surgical incision with an upper limit above this level. Furthermore, this patient was pain free in the recovery ward with a sensory level of T7 and motor block of modified Bromage Scale 3 suggesting that the spinal anaesthetic may have had a slow onset.
In common with a previous study,6 an increase in the dose of intrathecal ropivacaine administered led to an increased duration of profound motor block. The variation in spread of sensory block may be attributed to the use of an isobaric solution.
In terms of safety, both doses of intrathecal ropivacaine provided a high degree of cardiovascular stability with a low incidence of bradycardia. The degree of hypotension was as expected for an elderly population undergoing an operative procedure under a combination of spinal anaesthesia and propofol sedation with an ongoing blood loss; the hypotension seen was associated with the commencement of the i.v. infusion of 1% propofol rather than the institution of spinal anaesthesia. The most commonly reported adverse events were those commonly seen in connection to major surgery.
A significant finding was the absence of symptoms of post-dural puncture headache compared with an incidence of 25% in a previous study.6 Although spinal anaesthesia was performed using a larger gauge needle in our study (25-gauge as opposed to 26-gauge), the difference in incidence may be accounted for by the use of a pencil-point needle as opposed to a Quinke needle and again by the difference in the age of the two patient groups. This suggests that intrathecal ropivacaine is not associated with an increased incidence of post-dural puncture headache. No patient reported symptoms of neurological problems post- operatively.
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Acknowledgements |
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References |
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