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A randomised, double-blind comparison of three different volumes of hypobaric intrathecal bupivacaine for orthopaedic surgery.

The difference in density between the cerebrospinal fluid (CSF) and local anaesthetic solutions should be considered as a means of restricting drug distribution in the subarachnoid space. Conventional spinal anaesthesia may not be suitable for routine use in outpatients and anaesthetists should familiarise themselves with techniques that are associated with a rapid recovery profile. Using a small dose of either hypobaric or hyperbaric local anaesthetic injected at low speed through a directed needle in patients lying in the lateral position for 15 to 30 minutes can result in preferential development of spinal anaesthesia on the operated side. Unilateral spinal anaesthesia may be indicated for short procedures involving only one of the lower limbs.

Potential haemodynamic benefits have increased interest in methods achieving unilateral spinal anaesthesia, because hypotension is a common complication of spinal anaesthesia with larger doses of local anaesthetic'. When haemodynamic change was compared between bilateral and unilateral spinal block from the same dose of hyperbaric bupivacaine (8 mg), the frequencies of hypotension were 22.4% and 5%, respectively (2). The advantages of unilateral or selective versus conventional subarachnoid anaesthesia are better haemodynamic stability (1,2,5,6), faster motor and sensory recovery (2-4) and decreased urinary retention (3,4,6,7). Unilateral spinal anaesthesia is associated with a lower rate of cardiovascular complications due to less sympathetic block than bilateral spinal anaesthesias. The patients' satisfaction with the unilateral technique appears high (3,4,8,9).

The rationale behind our approach was to produce spinal anaesthesia restricted to the operative side alone and to obtain surgical anaesthesia just sufficient for the duration of surgery. The primary objective of this randomised clinical study was to evaluate the frequency of unilateral block when different doses of hypobaric bupivacaine solution were used for single limb orthopaedic surgery. The efficacy of the block, recovery from the block and haemodynamic effects were also evaluated.


The study protocol was approved by the institutional Ethics Committee and signed informed consent was obtained after the procedure was explained to the patient. Exclusion criteria included hypovolaemia, pre-existing neurological disease, coagulation disorders, administration of thrombosis prophylaxis less than eight hours prior to the procedure, infection at the puncture site, agitation and delirium and bladder catheterisation. One hundred and fifty patients, aged 20 to 60 years, ASA physical status I and II, who did not receive premedication in the ward and were scheduled for elective unilateral orthopaedic surgery under subarachnoid anaesthesia, participated in the study. After subarachnoid anaesthesia was given, a tourniquet was placed on the operating thigh of every patient and inflated to 350 mmHg. Patients were randomly divided using a computer-generated schedule and following preparation of coded envelopes into three groups of 50 patients. The types of surgery included knee videoarthroscopy, correction of tibial and ankle fractures with or without ligamentous lesions and removal of synthetic material below the knee.

Prior to anaesthesia the patient had an intravenous cannula placed and was monitored with continuous electrocardiography, pulse oximetry and a noninvasive blood pressure device. No preload volume of intravenous fluid was given before the block. All patients received fentanyl 1.0 [micro]g.[kg.sup.-1] intravenously (IV). If systolic blood pressure showed a reduction of greater than 30% from baseline it was initially treated with IV Ringer's lactate. If the patient did not respond, 2 mg of IV ethylephrine was administered and repeated until a satisfactory response was achieved. Bradycardia was defined as the reduction of heart rate below 50 bpm and was treated with atropine 0.75 mg IV The patient received oxygen (21.[min.sup.-1]) by Hudson mask and midazolam (1 to 2 mg) after the first evaluation, 20 minutes after initiation of subarachnoid anaesthesia. Supplemental intravenous analgesia was administered if the patient complained of pain or discomfort. Failure of subarachnoid anaesthesia was defined as absence of analgesia in the perineal region.

Hypobaric bupivacaine 0.15% (specific gravity at 37[degrees]C of 0.9964 g/ml) was prepared using 7.5 mg (1.5 ml) 0.5% isobaric bupivacaine (specific gravity at 37[degrees]C of 0.9995 g/ml) in 3.5 ml sterilised distilled water. The isobaric solutions were prepared for the study by Cristalia Produtos Quimicos and Farmaceuticos Ltda (Brazil). Patients were randomly assigned to receive one of three hypobaric bupivacaine doses: Group 1 received 4.5 mg (3 ml) of 0.15% hypobaric bupivacaine; Group 2 6 mg (4 ml) and Group 3 7.5 mg (5 ml).

Patients were placed on the side that was not to be operated on. After cleansing the skin with alcoholic chlorhexidine, the skin of the puncture site was infiltrated with 1% lignocaine. The puncture was paramedian, at the L3-L4 interspace, with a disposable 27 gauge Quincke needle (B. Braun Melsungen SA) without an introducer. Spinal solutions were administered at the rate of 1 m1.15 [s.sup.-1]. The bevel of the needle was directed upwards and the patient remained in the same position for 20 minutes before being placed in the supine position.

Assessment of sensory and motor blockade was performed by an anaesthetist who was unaware of group allocation. The level of the sensory block, defined as lack of pinprick sensation, was determined bilaterally at the midclavicular line, while the motor block was assessed by the modified Bromage scale (0 to 3): 0=free movement of the lower limb; 1=unable to raise extended limb; 2=unable to bend the knee; 3=unable to move the ankle. Motor and sensory block were evaluated on both limbs at 20, 40 and 60 minutes after subarachnoid anaesthesia and again at the end of the procedure. The duration of anaesthesia was determined by the time to regain sensation in the dermatome corresponding to the subarachnoid puncture site. Haemodynamic parameters were evaluated at five-minute intervals. Data regarding the time to recovery from sensory and motor block, as well as to the first urine voided, to ambulation and the conditions for hospital discharge were recorded. Complications in the recovery room, the need for bladder catheterisation, pain and its treatment were recorded by an observer. The time to commence walking was determined by the surgeon and postoperative analgesia consisted of IV tenoxicam 40 mg and dipirone 3 g. The first dose of tenoxicam was administered at the end of the surgical procedure, when all patients received a lumbar (psoas compartment) block or parasacral (sciatic nerve block) block with 40 ml of 0.25% bupivacaine, using an insulated needle and a nerve stimulator.

On leaving the operating room, patients recorded their opinion about the technique employed as good, satisfactory or bad. Patients were followed up for three days postoperatively by phone regarding the presence of headache, neurological symptoms or back pain. Headache was classified as postdural puncture headache if it worsened when the patient was in the sitting position, was located in the occipital or frontal region and was increased by coughing, straining or sneezing. Back pain was considered a transitory neurological symptom if the patient experienced pain and/or decreased sensitivity in the back, buttocks and legs after recovery, with resolution within 72 hours.

Means of age, weight, height and duration of the block were compared according to group by one-way analysis of variance, while the level of the sensory and motor block were analysed by the Mood test for medians. The intra-group unilateral nature of subarachnoid anaesthesia was analysed by examining differences for median dispersion using the Wilcoxon test. The frequencies of the other categorical variables were compared using the Chi-square test for independent samples. A level of significance of [alpha]=0.05 was adopted.



The random distribution produced balanced groups in all demographic data (Table 1). Figure 1 shows the evaluation of the sensory block. At all evaluation times the sensory block in the operated limb was significantly higher than that in the non-operated limb (Table 2). The sensory block after the lowest dose (4.5 mg) was lower than in the other two groups, which did not differ, at all evaluation times except 40 minutes. The mode was T12 with 4.5 mg, T10 with 6 mg and T8 with 7.5 mg. An increase of 1.5 mg in the dose corresponded to an increase of two segments in sensory block. During the time the patient was kept in the lateral decubitus position (20 minutes), the sensory blockade was exclusively unilateral in 46 (92%) patients after 4.5 mg, 39 (78%) patients after 6.0 mg and 39 (78%) patients after 7.5 mg (Table 2). The increase in dose (from 4.5 mg to 6 mg or 7.5 mg) corresponded to a significant loss of unilaterality.

Table 3 shows the evaluation of the motor block. On the operated side complete motor block (BM =3) occurred in 40 (80%) of the patients after 4.5 mg; in 48 (96%) after 6 mg and in 50 (100%) after 7.5 mg (no significant difference between groups receiving 4.5 and 6 mg). This confirmed that the dose increase increased motor block score. On the non-operated side, an absence of motor block (BM=0) occurred in 46 (92%) patients who received 4.5 mg and 39 (78%) of those who received 6 mg and 7.5 mg, confirming that the smallest dose resulted in a higher incidence of unilateral block (no difference between groups receiving 4.5 and 6 mg). At the end of the surgery, complete motor block was maintained in four (8%) patients of those receiving 4.5 mg, 41 (82%) of those receiving 6 mg and 43 (86%) of those receiving 7.5 mg, while on the non-operated side motor block was absent in all patients with 4.5 mg, in 39 (78%) after 6 mg and in 40 (80%) after 7.5 mg. There was no difference in the latency time or surgical duration (Table 4). The increase of the dose correlated with the duration of the sensory block, being a mean ([+ or -] SD) of 1:55 [+ or -] 00:20 hours, 2:15 [+ or -] 00:22 hours and 3:15 [+ or -] 00:31 hours in Groups 1 to 3 respectively Table 4.

No patient needed treatment for hypotension. Seven patients had bradycardia and responded to atropine doses of no more than 0.75 mg (Group 1 n=0, Group 2 n=2, Group 3 n=5). All patients were satisfied with the technique. Three patients had postdural puncture headache but none had micturition difficulties. No patient complained of backache or pain in the buttocks or legs over the three subsequent days.


We obtained adequate levels of subarachnoid anaesthesia for surgery in a single lower extremity limb, using 4.5, 6 or 7.5 mg of 0.15% hypobaric bupivacaine. The onset of action was rapid and duration of action was dose dependent.

When creating unilateral or selective spinal anaesthesia with low doses of intrathecal drug, the injection technique becomes especially important. [Enk.sup.10] emphasised the importance of "low-dose, low-volume and low-flow" for producing unilateral spinal anaesthesia. Low-dose hypobaric 0.15% bupivacaine, administered at 1 m1.15 [s.sup.-1] through a 27 gauge Quincke needle to a patient in the lateral decubitus position, blocked only the uppermost lower limb in 90%, 80% and 75% of those receiving 4.5, 6 and 7.5 mg, confirming that unilateral distribution of drug is influenced by the mass of the drug injected in the subarachnoid space. Specifically, all doses of hypobaric 0.15% bupivacaine studied provided effective unilateral subarachnoid anaesthesia for all patients. No patient felt pain during the surgery, none required supplementation and most (84%) had no motor block in the contra lateral limb. The highest sensory block obtained (Group 3 after 7.5 mg) was due to the larger dose and volume administered.

The objective of achieving unilateral subarachnoid anaesthesia was to prevent clinically important haemodynamic change and to induce unilateral motor block only, thus improving patient comfort, since prolonged bilateral motor blockade can be inconvenient. Several factors have been associated with poor results from unilateral subarachnoid anaesthesia, including the position of the patient, the design of the needle, the speed of administration, the amount of local anaesthetic injected and the density of the anaesthetic solution compared to the CSF (11). Large doses (12 to 20 mg) of bupivacaine are associated with important movement of the block distribution, even after one hour in the lateral decubitus position 12, while small doses (5 to 8 mg) result in a restricted block only after 10 to 15 minutes in the lateral decubitus position (13). A low dose of 0.15% hypobaric bupivacaine (5 mg) has been used previously and the best unilateral block was obtained when the patient remained in the lateral decubitus position for at least 20 minutes (3). In this study, the puncture site and the dose were different, and every patient remained in the lateral decubitus for 20 minutes, leading to unilateral subarachnoid anaesthesia in 70% of patients, the incidence showing dose-dependency.

Intrathecal bupivacaine is considered a long-acting drug. Greene (14) reported 25 factors that could affect the distribution of the local anaesthetic in the CSF, but not all of them have clinical relevance. These factors can be classified into four subgroups: characteristics of the patient, of the CSF, of the local anaesthetic and the injection technique used. Besides the drug dose, the position of the patient at the time of injection and thereafter, together with the baricity of the anaesthetic, are the most important factors affecting the level of subarachnoid anaesthesia (10,15). By definition, baricity is the ratio between injected solution density and CSF density. The mean density of the CSF is 1.00059 [+ or -] 0.00020 g.[ml.sup.1] (16). Local anaesthetic density may be decreased by water dilution. The density of bupivacaine at 0.15% is 0.9964 g/ml at 37[degrees]C, making it hypobaric in all patients. This fact was confirmed by the presence of unilateral block in 98/120 of patients, with only 19 experiencing some degree of sensory block in the non-operated limb. Great variations in volume and concentration of local anaesthetics have little role in dispersion in the subarachnoid space (15), while the total amount of molecules injected is more important. In this study, varying doses from 4.5 mg to 7.5 mg resulted in a wider distribution of anaesthesia. Because the dose of the local anaesthetic seems to be the most important factor influencing unilateral distribution, the dose chosen is critical, although an excessive reduction in dose could increase failure rates (5).

The present study reflected the good circulatory stability of the technique, with bradycardia proving infrequent and arterial hypotension absent despite no preload with Ringer's lactate. Small doses of subarachnoid local anaesthetic cause minimal haemodynamic changes. The fact that the sensory block in this study was limited to a lumbosacral or lower thoracic distribution could have been one factor contributing to the lack of clinically significant hypotension.

A number studies confirm that hypobaric bupivacaine is unlikely to cause a transitory neurological symptom (3,17-19). In the present study, no such case was observed and a possible factor that may have contributed to this was the absence of complete motor block in the lower limbs. The needle type can affect the spread of intrathecal drugs. A high success rate of unilateral subarachnoid anaesthesia has been reported using 25 gauge Whitacre (15) and 29 gauge Quincke (20) needles. In a recent study, 66% of the patients achieved unilateral sensory block when a Whitacre needle was used compared to 16% after the use of a Quincke needle (21). Our success rate of 70% with a 27 gauge Quincke needle demonstrated that it can be used successfully for this type of spinal block. The gauge of the needle is a more important determinant of the incidence of headache and lumbar pain. In this study we had an incidence of 2.5% of postdural puncture headache, but no patient needed a blood patch.

In conclusion, in this study a unilateral block was achieved in 70% of patients. The smallest dose of 0.15% hypobaric bupivacaine (4.5 mg) resulted in a higher rate of unilateral spinal block, with narrower distribution and shorter duration. We consider that doses 6 mg and 7.5 mg should be reserved for surgery that is anticipated to be of longer duration. Potential advantages of unilateral subarachnoid anaesthesia include haemodynamic stability, high patient satisfaction and a low risk of transitory neurological symptoms.

Address for reprints: Dr L. E. Imbelloni, Av. Epitacio Pessoa, 2356/203, 22411-072 - Rio de Janeiro, Brasil.

Accepted for publication on October 8, 2008.


(1.) Carpenter RL, Caplan RA, Brown DL, Stephenson C, Wu R. Incidence and risk factors for side effects of spinal anesthesia. Anesthesiology 1992; 76:906-916.

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(4.) Imbelloni LE, Beato L, Cordeiro JA. [Unilateral spinal anesthesia with low 0.5% hyperbaric bupivacaine dose]. Rev Bras Anestesiol 2004; 54:700-706.

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(14.) Greene NM. Distribution of local anesthetic solutions within the subarachnoid space. Anesth Analg 1985; 64:715-730.

(15.) Stienstra R, Greene NM. Factors affecting the subarachnoid spread of local anesthetic solutions. Reg Anesth 1991; 16:1-6.

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(19.) Imbelloni LE, Vieira EM, Gouveia MA, Netinho JG, Cordeiro JA. [Hypobaric 0.15% bupivacaine versus hyperbaric 0.5% bupivacaine for posterior (dorsal) spinal block in outpatient anorectal surgery]. Rev Bras Anestesiol 2006; 56:571-582.

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(21.) Casati A, Fanelli G, Cappelleri G, Aldegheri G, Leoni A, Casaletti E et al. Effects of spinal needle type on lateral distribution of 0.5% hyperbaric bupivacaine. Anesth Analg 1998; 87:355-359.


Institute for Regional Anesthesia, The Base Hospital, Sao Jose do Rio Preto, Sao Paulo, Brazil

* M.D., Director.

([dagger]) Ph.D., Professor, Faculty of Medicine of Sao Jose Rio Preto.

Demographic variables: mean (SD) and number

Variable Dosage
 4.5 mg 6.0 mg 7.5 mg

Age (y) 38.6[+ or -]13.3 41.6[+ or -]9.7 38.4[+ or -]11.1
Weight (kg) 67.0[+ or -]8.1 68.5[+ or -]8.7 67.9[+ or -]11.5
Gender (F/M) 27/23 23/27 22/28

Variable P value

Age (y) 0.30
Weight (kg) 0.73
Gender (F/M) 0.66


Median sensory level

Evaluation Limb Dosage * P value
 4.5 mg 6.0 mg 7.5 mg

20 min Operated T12-T11 T10 T9 <0.001

20 min Non-operated L4-L3 L4-L3 L4-L3 0.059
 P value <0.001 <0.001 <0.001

40 min Operated T11 T10 T9 <0.001

40 min Non-operated L4-L3 L4-L3 L4-L3 0.059
 P value <0.001 <0.001 <0.001

60 min Operated T12 T11 T11 0.021

60 min Non-operated L4-L3 L4-L3 L4-L3 0.087
 P value <0.001 <0.001 <0.001

End Operated L2 L1-T12 L1 <0.001

End Non-operated L4-L3 L4-L3 L4-L3 1.0
 P value <0.001 <0.001 <0.001


Number of patients with motor block on the operated and the
non-operated side, according to group

 20 min 20 min 40 min 40 min
 Operated Non-operated Operated Non-operated

4.5 mg BM3=31 BM3=0 BM3=31 BM3=0

 BM2=9 BM2=0 BM2=9 BM2=0

 BM1=0 BM1=4 BM1=0 BM1=4

 BMO=0 BMO=36 BMO=0 BMO=36

6 mg BM3=38 BM3=0 BM3=38 BM3=0

 BM2=2 BM2=3 BM2=2 BM2=3

 BM1=0 BM1=3 BM1=0 BM1=3

 BMO=0 BMO=34 BMO=0 BMO=34

7.5 mg BM3=40 BM3=0 BM3=40 BM3=0

 BM2=0 BM2=4 BM2=0 BM2=4

 BM1=0 BM1=5 BM1=0 BM1=5

 BMO=0 BMO=31 BMO=0 BMO=31

 60 min 60 min End End
 Operated Non-operated Operated Non-operated

4.5 mg BM3=23 BM3=0 BM3=3 BM3=0

 BM2=15 BM2=0 BM2=13 BM2=0

 BM1=2 BM1=0 BM1=16 BM1=0

 BMO=0 BMO=40 BMO=8 BMO=40

6 mg BM3=38 BM3=0 BM3=32 BM3=0

 BM2=2 BM2=3 BM2=6 BM2=1

 BM1=0 BM1=3 BM1=2 BM1=5

 BMO=0 BMO=34 BMO=0 BMO=34

7.5 mg BM3=38 BM3=0 BM3=34 BM3=0

 BM2=2 BM2=4 BM2=5 BM2=1

 BM1=0 BM1=5 BM1=1 BM1=7

 BMO=0 BMO=31 BMO=0 BMO=32


Latency, duration of surgery and duration of sensory block

 4.5 mg 6.0 mg 7.5 mg P value

Latency (min) 1.8 (0.6) 1.7 (0.4) 1.6 (0.3) 0.13

Surgery duration 1:25 1:19 1:30 0.73
(h:mm) (0:19) (0:21) (0:34)

Blockade duration 1:55 2:15 3:15 <0.001
(h:mm) (0:20) (0:22) (0:31)

Values are median (interquartile range).
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Article Details
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Title Annotation:Original Papers
Author:Imbellonv, L.E.; Gouveia, M.A.; Vieira, E.M.; Cordeiro, J.A.
Publication:Anaesthesia and Intensive Care
Article Type:Clinical report
Geographic Code:3BRAZ
Date:Mar 1, 2009
Previous Article:Some scientific reflections on possible mechanisms of general anaesthesia.
Next Article:The pulmonary artery catheter sleeve--protective or infective?

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