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From the Department of Anaesthesia, KK Women's and Children's Hospital, Singapore.
Address correspondence to: Dr. Alex T.H. Sia, Department of Anaesthesia, KK Women's and Children's Hospital, 100 Bukit Timah Road, Singapore 229899. Phone: 65-3941081; Fax: 65-2912661; Email: athsia{at}kkh.com.sg
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Abstract |
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Methods: Forty-eight parturients in early labour received combined spinal epidural (CSE) analgesia to evaluate a) the effect of adding 1.25 mg of bupivacaine to intrathecal (IT) fentanyl 25 µg on the duration of analgesia and b) the effect of baricity of intrathecal local anesthetic on the duration and quality of the block. Patients were randomly allocated to receive: IT fentanyl 25 µg plus normal saline (Group f, n=16), IT fentanyl 25 µg plus plain bupivacaine 1.25 mg (Group f+pb, n=16) and IT fentanyl 25 µg plus heavy bupivacaine 1.25 mg (Group f+hb, n=16). The two components of the IT injectate (total of 2.25 mL) were given sequentially.
Results: Group f+hb had the lowest sensory dermatomal block (T7 vs T4 (Group f), T5 (Group f+pb), P <0.01). There were no differences in the duration of analgesia and incidence of side effects among the groups.
Conclusion: We found no advantage of adding 1.25 mg bupivacaine to fentanyl 25 µg. At this dose, the baricity of bupivacaine has no effect on the duration of analgesia.
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Introduction |
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Although the effect of baricity of IT opioids has been studied, the effect of IT hyperbaric local anesthetics in labour analgesia is less known. The aim of this study is twofold: a) to evaluate the effect of adding 1.25 mg of bupivacaine to IT fentanyl 25 µg on the duration of analgesia in our Asian population and b) to examine if baricity of local anesthetic at this dose has any bearing on the duration and quality of the block.
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Methods |
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CSE block was performed by the principal investigator (EHLL) in the sitting position using the midline approach at L3, 4 intervertebral space after prehydration with 500–1000 mL Hartman's solution. The epidural space was identified using the loss of resistance to saline technique with a 17G Weiss needle. A 120-mm 27G Whitacre needle (Durasafe BD, USA) was then passed through the epidural needle and correct placement of the tip in the subarachnoid space confirmed by free flow of cerebrospinal fluid. 25 µg of fentanyl were diluted with preservative free normal saline solution to a total volume of 2 mL and administered intrathecally over 30 sec. This was followed immediately by 0.25 mL of normal saline, plain 0.5% bupivacaine or hyperbaric 0.5% bupivacaine over ten seconds for Group f, Group f+pb and Group f+hb, respectively. All drugs were prepared by another investigator who was not involved in the intrathecal injection or the subsequent evaluation of the parturient. The intrathecal injection was accomplished with the aperture of the Whitacre needle directed cephalad. The epidural catheter was then positioned 2.5–3.0 cm in the epidural space and aspirated for blood but no drugs were administered via the catheter until the patient requested further analgesia. The patient was placed with the torso elevated at 15 for 30 min after subarachnoid administration to minimize cephalad migration of hyperbaric bupivacaine.
The assessment of the parturient was done by the principal investigator. The preblock systolic blood pressure was measured with a right brachial non-invasive blood pressure monitor (Dinamap, Critikon, Florida, USA) in the 15 elevated position and monitored every five minutes for the first 30 min after spinal anesthesia. The extent of motor blockade was assessed using the modified Bromage scale: 0=able to move hip, knee, ankle, and toes; 1=unable to move hip, able to move knee, ankle and toes; 2=unable to move hip and knee, able to move ankle and toes; 3=unable to move hip, knee and ankle, able to move toes; 4=unable to move hip, knee, ankle or toes. A Bromage scale of 0 was ensured prior to CSE and the degree of motor block was assessed five, 15 and 30 min after the block. The level of sensory loss was ascertained by loss of sensation to cold with an ice pack five, 15 and 30 min after the block. Similarly, pain scores were assessed at five minutes, 15 min and 30 min after the intrathecal administration of the drugs The presence of pruritus, nausea or vomiting, shivering and sedation were also assessed at the same time intervals. Sedation was graded as 0=none; 1=easily rousable by light touch; 2=rousable with loud speech and shaking; 3=rousable with painful stimulation; 4=not rousable by any means. The other side effects were noted as present or absent. Parturients who still experienced pain 15 min after spinal anesthesia were categorized as ‘analgesic failure’ and their epidural catheters injected with 3 mL aliquots of 0.2% ropivacaine. Fetal heart rate changes were monitored 30 min before and after subarachnoid drug administration by the on-call obstetrician (not involved in the study) and managed according to the existing labour ward protocol. Any changes requiring intervention such as drugs or emergency Cesarean section were noted as non-reassuring fetal status. Type I decelerations and variable decelerations that resolved spontaneously with patient in the left lateral position were not considered non-reassuring. The use of oxytocin prior to subarachnoid block was noted.
Hypotension was defined as a systolic blood pressure less than 90 mmHg and treated with 6 mg boluses of ephedrine. The side effects (shivering, nausea and pruritus) if they occurred, would be treated only when requested by the patient.
Prospective power analysis indicated that with 
=0.05 and ß=0.2, 16 patients per group would be able to detect clinically significant 
hour differences in the duration of analgesia between the three groups. Continuous data are expressed as mean ± SD and were compared using analysis of variance (ANOVA). Non-parametric data were compared using the Kruskal-Wallis and Chi squared tests as appropriate. Pain scores were analyzed using analysis of variance for repeated measures. A P value of <0.05 was considered significant.
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Results |
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The duration of analgesia for Group f+hb was 129.5 ± 48.5 min vs 100.1 ± 57.2 min for Group f, and 100.4 ± 50.0 min for Group f+pb (Figure 1
). This difference was not statistically significant. There was one anesthetic failure in Group f. Pain scores were not different between the three groups for all patients who obtained satisfactory pain relief (Figure 2). A distinct anesthetic level could be discerned for every patient. The median height of sensory block to cold for Group f+hb was T7, as opposed to T4 for Group f, and T5 for Group f+pb (Figure 3). The difference in block height between Group f+hb and the other two groups was statistically significant (P <0.01), but not between Group f and Group f+pb.
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). None of fetal heart changes required emergent obstetric intervention. None of the parturients delivered before the request for epidural supplementation of analgesia.
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Discussion |
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Intrathecal fentanyl 25 µg has been shown to provide adequate pain relief in the first stage of labour when used as the sole agent.1 To improve the duration and quality of labour analgesia, particularly in the later part of the first stage of labour5 when the intensity of pain increases and the quality of the pain changes to assume a greater somatic component,6 various combinations of local anesthetics and opioids have been studied. Indeed, synergism between these two groups of drugs has been demonstrated.3 Studies in Asian women to exploit this synergistic relationship have resulted in an increase in the incidence of hypotension and motor blockade when IT 2.5 mg bupivacaine was used in combination with either fentanyl 25 µg or sufentanil 5 µg for labour analgesia. 4,7 For this reason, we undertook the present study using a lower dose of IT bupivacaine although, eventually, this did not produce a significant degree of synergism. From this, we could infer that the use of an intermediate dose of IT bupivacaine (i.e., between 1.25 mg and 2.5 mg range) may, theoretically, optimize the balance between analgesia and side effects.
Baricity refers to the ratio of the density of a solution to that of CSF measured at 37°C.8 It (with the effects of gravity determined by patient posture and the curves of the vertebral column) is recognized as an important factor in determining the spread of a solution when injected intrathecally. The effect of baricity on intrathecal opioids has been studied. Cage et al. demonstrated that the use of IT hyperbaric sufentanil administered in the sitting position shortened the duration of labour analgesia.9 Similarly, Kang et al. found that hyperbaric fentanyl administered intrathecally in a sitting position resulted in reduced quality and duration of labour analgesia.10 The underlying mechanism postulated is that dextrose restricts the cephalad spread of intrathecal opioid, thereby preventing sufficient concentrations from reaching the lower thoracic region of the spinal cord and brainstem where it binds to opioid receptors and produces the desired analgesic effect. In our investigation, we sought to study only the effects of hyperbaric bupivacaine and not hyperbaric fentanyl. Therefore, we administered the local anesthetic solution and the opioid separately, in an attempt to preserve the effects due to the baricity of the solutions. We intended that, with the parturients in the sitting position, the administration of IT fentanyl (being a hypobaric preparation)11 first would allow sufficient amounts to reach the site of opioid action and would not be affected by the baricity of the subsequent injectate. This manoeuvre was successful, apparently, since all our patients in the hyperbaric bupivacaine group obtained adequate labour analgesia of at least the same quality and duration as the fentanyl and fentanyl plus plain bupivacaine groups despite a lower level of highest sensory block height. On the other hand, the effect of baricity of local anesthetics was evident from the lower levels of sensory blockade of the hyperbaric bupivacaine group when compared with the others. The finding that a distinct block height was obtained for all patients, even those who did not get bupivacaine, was not surprising as sensory changes in patients who received IT sufentanil12 and IT fentanyl2 alone have been reported previously. We were unable to determine if the quality of the sensory block was different between groups. We can only conclude that the duration and quality of analgesia produced was indistinguishable among the three groups in our study. We can also infer that, with the regimens described, the level of spinal blockade to cold is not an indication of the duration of analgesia.
Our study shows that the currently employed regimens were effective for early labour analgesia. There were also no serious side effects. As there was one case of analgesic failure in the fentanyl only group, a further reduction of the dosage of IT fentanyl 25 µg should be undertaken cautiously as this could predispose to a higher analgesic failure rate. In this event, the rationale of performing dural puncture in the CSE technique may not be fully justified, as it is not without potential risks.13
In summary, our study indicated that there was no significant advantage of adding 1.25 mg of bupivacaine to fentanyl 25 µg intrathecally for women in early labour in our Asian population. There was also no significant advantage of administering hyperbaric bupivacaine intrathecally at the dose of 1.25 mg in early labour. We administered intrathecal drugs sequentially in an attempt to preserve the effects due to the baricity of the drugs. Further research is required to investigate the effects of higher intrathecal doses of hyperbaric bupivacaine and its use in late labour.
Revision received September 26, 2001. Accepted for publication July 4, 2001.
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References |
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2 Palmer CM, Van Maren G, Nogami WM, Alves D. Bupivacaine augments intrathecal fentanyl for labor analgesia. Anesthesiology 1999; 91: 84–9.[Medline]
3 Maves TJ, Gebhart GF. Antinociceptive synergy between intrathecal morphine and lidocaine during visceral and somatic nociception in rats. Anesthesiology 1992; 76: 91–9.[Medline]
4
Lee BB, Ngan Kee WD, Hung VYS, Wong ELY. Combined spinal-epidural analgesia in labour: comparison of two doses of intrathecal bupivicaine with fentanyl. Br J Anaesth 1999; 83: 868–71
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Honet JE, Arkoosh VA, Norris MC, Huffnagle HJ, Silverman NS, Leighton BL. Comparison among intrathecal fentanyl, meperidine, and sufentanil for labor analgesia. Anesth Analg 1992; 75: 734–9.
6 Viscomi CM, Rathmell JP, Pace NL. Duration of intrathecal labor analgesia: early versus advanced labor. Anesth Analg 1997; 84: 1108–12.[Abstract]
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Sia ATH, Chong JL, Chiu JW. Combination of intrathecal sufentanil 10 µg plus bupivacaine 2.5 mg for labor analgesia: is half the dose enough? Anesth Analg 1999; 88: 362–6.
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Connolly C, Wildsmith JAW. Intrathecal drug spread. Can J Anaesth 1998; 45: 289–92.
9 Cage JC, D'Angelo R, Miller R, Eisenach JC. Does dextrose affect analgesia or the side effects of intrathecal sufentanil? Anesth Analg 1997; 85: 826–30.[Abstract]
10 Kang M, Orebaugh S, Ramanathan S. The analgesia efficacy of hyperbaric subarachnoid fentanyl in parturients.Anesthesiology 1996; 85: A862 (abstract).
11 Richardson MG, Wissler RN. Densities of dextrose-free intrathecal local anesthetics, opioids, and combinations measured at 37C. Anesth Analg 1997; 84: 95–9.[Abstract]
12
Cohen SE, Cherry CM, Holbrook RH Jr, El-Sayed YY, Gibson RN, Jaffe RA. Intrathecal sufentanil for labor analgesia–sensory changes, side effects, and fetal heart rate changes. Anesth Analg 1993; 77: 1155–60
13
Douglas MJ. Walking epidural analgesia in labour (Editorial). Can J Anaesth 1998; 45: 607–11.
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  W. H. L. Teoh and A. T. H. Sia Hyperbaric Bupivacaine 2.5 mg Prolongs Analgesia Compared with Plain Bupivacaine When Added to Intrathecal Fentanyl 25 {micro}g in Advanced Labor Anesth. Analg., September 1, 2003; 97(3): 873 - 877. [Abstract] [Full Text] [PDF]
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