|Year : 2008 | Volume
| Issue : 2 | Page : 191-195
Spinal Anaesthesia in Ambulatory Surgery: Dose-Response Characteristics of Constant Volume Bupivacaine
Veena R Shah1, Rupen Mackwana2, Kalpana Vora3
1 Professor, Anaesthesiology, Institute of Kidney Diseases & Research Centre, Institute of Transplantation Sciences, Civil Hospital Campus, Ahmedabad 380016, Gujarat, India
2 Tutor, Anaesthesiology, Institute of Kidney Diseases & Research Centre, Institute of Transplantation Sciences, Civil Hospital Campus, Ahmedabad 380016, Gujarat, India
3 Assistant Professor, Anaesthesiology, Institute of Kidney Diseases & Research Centre, Institute of Transplantation Sciences, Civil Hospital Campus, Ahmedabad 380016, Gujarat, India
|Date of Acceptance||09-Mar-2008|
|Date of Web Publication||19-Mar-2010|
13, Choksi Park, Jivraj Park, Ahmedabad, 380051,Gujarat
Source of Support: None, Conflict of Interest: None
Use of spinal anaesthesia is gradually increasing in ambulatory setting. With the continuing controversy over the use of lidocaine for spinal anaesthesia, other local anaesthetics are being explored to achieve reliable spinal anaesthesia with rapid recovery and minimal side-effects. This study explored the use of long acting local anaesthetic bupivacaine in ambulatory setting. One hundred patients presenting for endoscopic uro-gynaecological surgeries were randomized to four groups according to dose of bupivacaine they received keeping the volume constant. Maximum level of sensory block, intensity of block, time to two segment regression, time to S2 regression and time to discharge were recorded. Results of our study indicate that spinal anaesthesia with 7.5 mg of 0.5% bupivacaine in 8% dextrose diluted with equal volume of saline provides an optimal combination of adequate anaesthesia with recovery profile acceptable for ambulatory endoscopic uro-gynaecological surgeries.
Keywords: Bupivacaine; Spinal anaesthesia; Ambulatory surgery
|How to cite this article:|
Shah VR, Mackwana R, Vora K. Spinal Anaesthesia in Ambulatory Surgery: Dose-Response Characteristics of Constant Volume Bupivacaine. Indian J Anaesth 2008;52:191-5
|How to cite this URL:|
Shah VR, Mackwana R, Vora K. Spinal Anaesthesia in Ambulatory Surgery: Dose-Response Characteristics of Constant Volume Bupivacaine. Indian J Anaesth [serial online] 2008 [cited 2019 Sep 16];52:191-5. Available from: http://www.ijaweb.org/text.asp?2008/52/2/191/60620
| Introduction|| |
Outpatient or ambulatory surgery is becoming popular all over the world due to number of advantages to the patient, hospital and community. An ideal anaesthetic technique for ambulatory surgery should provide a rapid and smooth onset of action, intraoperative analgesia, good surgical condition and short recovery time free from side effects  . Although most ambulatory procedures are performed under general anaesthesia, neuraxial anaesthesia is increasingly becoming popular. Patients receiving central neuraxial blockade are more alert, less nauseated and more comfortable in the recovery room than those receiving general anaesthesia  . Spinal anaesthesia should be ideal for outpatients due to its quick onset, reliable anaesthesia with minimal supplies making it cost-effective technique with rapid turnover time. Such benefits should be weighed against adverse events such as postdural puncture headache, backpain, neurological complications or rare potential for infection and haematoma.
Choice of local anaesthetic is a key element in success of spinal anaesthesia for ambulatory surgery as safe and timely discharge is of prime importance. Lidocaine due to its short duration is ideal for ambulatory setting but its safety has been questioned by reports of permanent and transient neurological symptoms(TNS) ,, . In contrast, bupivacaine has lowest incidence of TNS (0-1.3%)  making it an attractive alternative to lidocaine, the only drawback is its long duration of action delaying the discharge. To overcome this drawback, we decided to study dose response characteristics of hyperbaric bupivacaine keeping the volume constant in uro-gynaecological ambulatory surgery.
| Methods|| |
After obtaining institutional ethical committee approval and written informed consent, 100 patients of ASA physical status I-II scheduled for endoscopic urogynaecological surgeries on ambulatory basis were enrolled in the study. Exclusion criteria included contraindications to spinal anaesthesia and history of allergy to bupivacaine.
On arrival in the operation theatre, routine monitoring was attached and baseline pulse, NIBP, SpO 2 and respiratory rate were recorded. Intravenous line was secured and preloading with 500 ml of 0.9% saline was done. Lumbar puncture was performed in either right or left lateral position under strict asepsis between L 3 -L 4 interspace with 25 gauge pencil-point spinal needle by median route. After confirming free flow of CSF, the study drug was injected over 10 seconds. Patients were randomized by sealed envelope technique to receive one of the following doses of bupivacaine.
Group A : 3 ml of 0.5% bupivacaine (15 mg) in 8% dextrose
Group B : 2 ml of 0.5% bupivacaine (10 mg) + 1 ml of NS ( 0.33% bupivacaine in 5.33% dextrose)
Group C : 1.5 ml of 0.5% bupivacaine (7.5 mg) + 1.5 ml of NS (0.25% bupivacaine in 4% dextrose)
GroupD : 1 ml of 0.5% bupivacaine (5 mg) + 2 ml of NS (0.17% bupivacaine in 2.66% dextrose)
Immediately, patients were turned to supine position. Five minutes after spinal injection, patients were placed in lithotomy position and following observations were recorded from the point of injection of the drug in the CSF. Sensory block was tested by pinprick method and dermatomal level was checked every two minutes till stabilized. Highest level of sensory block and degree of motor blockade assessed by Bromage scale were recorded.
0 - Full flexion of knees and feet
1 - Just able to flex knees, full flexion of feet
2 - Unable to flex knees, but some flexion of feet possible
3 - Unable to move legs or feet.
Surgeons were allowed to operate once adequate anaesthesia was established. Intraoperative patient's judgement of block was categorized by the degree of sensation felt during surgery.
A - Complete absence of sensations
B - Sensation of motion only
C - Mild discomfort
D - Discomfort requiring supplementation in the form of analgesic or anaesthetic agent
At the end of surgery, patients were observed in post anaesthesia care unit (PACU) by an independent observer unaware of the drug being injected till they were discharged. Time taken for two segment regression, S 2 segment wear off time and time to discharge were recorded. Time to urinate was not recorded as all patients were catheterized. Discharge criteria were defined as recovery of sensation to pinprick at S 2 dermatome, ability to walk without assistance and stable vital signs. Patients were discharged with escort, were prescribed oral analgesics and instructed to report any complications like headache, backache or dysaesthesia in buttocks, thigh and lower limb upto one week of surgery.
Statistical analysis was done using analysis of variance for age, weight& height. Intergroup differences were compared by applying repeated measure ANOVA& using nonparametric - Kruskal - Wallis test with post HOC - Dunt test. Results were considered significant if P< 0.05.
| Results|| |
The four groups were identical regarding age, weight, height and duration of surgery [Table 1].
The highest level of sensory blockade was higher in Group A as compared to other three groups, all having median block height of T8. The intensity of motor blockade as judged by Bromage scale progressively decreased with further dilution of bupivacaine. Similar pattern was observed in patient´s judgement of block [Table 2].
Recovery times assessed by two segment regression time, S 2 segment wear off time and time to discharge followed a clear pattern of Group A> GroupB > Group C > Group D, however it did not achieve statistical significance between Group C and Group D [Table 2].
Postoperative followup revealed PDPH in 5 patients which responded to rest and analgesics.There were no incidence of backache or neurological symptoms except discomfort of urinary catheter [Table 3].
| Discussion|| |
The principle finding of our study was that decreasing the dose of bupivacaine 0.5% in 8% dextrose keeping volume constant resulted in progressively diminished intensity of block, shorter times to two segment regression, complete S 2 sensory recovery and ability to discharge. However, cephalad spread of sensory blockade was not affected by saline dilution.
There has been a controversy regarding relationship between volume, concentration and total dose of spinally administered local anaesthetic drugs, however it is not possible to change one of these factors without changing another. Most of the studies suggest that quality as well as duration of spinal block is proportional to the total dose of local anaesthetic rather than volume or concentration , . Ben-David et al demonstrated that increasingly greater dilution of 15mg bupivacaine with 8% dextrose led to a progressively shorter duration of spinal anaesthesia  . Similarly, spinal anaesthesia with 50 mg of 5% lidocaine in dextrose is significantly longer acting than 50 mg of 1.5% lidocaine in dextrose  . Combining these two principles of dose and dilution, we decided to study whether the subarachnoid administration of constant volume, but more dilute solution of bupivacaine would yield spinal anaesthesia of satisfactory quality with shorter recovery times than achieved with 0.5% bupivacaine in 8% dextrose.
Cephalad spread of spinal blockade is generally believed to be influenced by total dose of the local anaesthetic than by the volume , . However, not all the studies have shown a linear relationship between dose and block height . VanZundert and De Wolf  compared spinal anaesthesia using a glucose-free solution of 2.5 ml of 0.5% bupivacaine or 10 mL of 0.125% bupivacaine and found a similar onset, intensity, and spread of anaesthesia, whereas Alston  et al have shown a significant effect of dose only in higher dose range. Results of our study are partially consistent with above studies as we found higher level only in 15mg group. Another factor responsible for cephalad spread is the baricity of solution& position of the patient. When patients are turned to supine position after hyperbaric solutions, there is a tendency for anaesthesia to spread close to T 4 level which approximates the lowest level of thoracic kyphosis. Lowering baricity may achieve less extension of cephalad spread, but most of the evidence shows that any concentration of glucose in excess of 0.8% behaves in a hyperbaric manner  . In our study, saline dilution of bupivacaine produced solutions of progressively lesser dextrose concentration, but it did not influence block height as all solutions were having dextrose concentration of >1%.
Intensity of sensory as well as motor block as judged by patient's judgement of block& Bromage scale decreased by simultaneous increase in dilution and decrease in dose of bupivacaine. The use of a lower dose (5mg) resulted in 40% of patients requiring supplementation due to intraoperative discomfort in contrast to no supplementation required in 7.5mg group. In the previous studies , , when the dose of local anaesthetic was held constant, dilution per se had very little effect on block intensity, only one study showed decreased intensity of motor block with diluted hyperbaric bupivacaine when dose was held constant  .We believe that decreased intensity of block from Group A to Group D is due to decrease in dose rather than different densities of bupivacaine because increased amount of local anaesthetic will result in a relative overdose in relation to minimum concentration required to block the various nerve fibres type. Our results are consistent with VanZundert et al who showed that 70mg of subarachnoid lidocaine as 0.5%,1%,2%,5% or 10% solution resulted in similar degree of motor block& duration of spinal anaesthesia in spite of extremely broad range of volume& concentration  . Similarly, Gentili et al observed a progressive increase in degree of motor& sensory block with increase in dose of hyperbaric bupivacaine from 4mg to 8mg .
The duration of spinal anaesthesia as measured by two segment regression, complete S 2 sensory recovery and ability to discharge decreased steadily with increasing dilution and decrease in dose except that it was not statistically significant between 5mg and 7.5mg group. This may be due to both dilution per se as well as smaller dose of bupivacaine. Huffnagle et al injected 5mg,7.5mg,10mg& 12.5mg of intrathecal bupivacaine for postpartum tubal ligation& observed rapid regression of motor block with decrease in dose& shorter time in PACU with 7.5mg dose  . Tarkkila et al observed early regression of block with 5mg hyperbaric bupivacaine (median 161min) compared to 10mg (median 231min)  whereas Ben-David et al in patients undergoing knee arthroscopy observed an average discharge time of 202 ± 14 min with 7.5mg hyperbaric bupivacaine compared to 260 ± 15 min with 10mg& 471 ± 35 min with 15mg dose  which are comparable to our study.
In the past, the risk of PDPH limited the use of spinal anaesthesia for outpatient surgery. The advent of smaller gauge pencil point needles have reduced the incidence of PDPH to less than 3% even in younger patients  . Though a smaller gauge lowers the incidence of PDPH, failure rate is increased with needles smaller than 27 gauge hence we used 25 gauge needle to achieve optimal balance between technical success and risk of PDPH. We had 5% incidence of PDPH which responded to rest and analgesics which is comparable to study of Eckstein et al . There was no incidence of backpain or neurological symptoms during the follow-up in our study.
To conclude, this study demonstrates that smalldiluted dose of bupivacaine for subarachnoid block can be used for ambulatory surgery of short duration. Recovery from the 5 mg dose was not significantly faster than recovery from the 7.5 mg dose, and it did not provide a reliable degree of motor and sensory blockade. Spinal block using 7.5mg bupivacaine in 4% dextrose provided the optimal combination of adequate anaesthesia for endoscopic urogynaecological surgeries and a recovery profile rapid enough to be appropriate for use in an ambulatory setting.
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[Table 1], [Table 2], [Table 3]