- Email: [email protected]
Spinal anesthesia with hypobaric bupivacaine for knee arthroscopies: Effect of posture on motor block
Spinal Anesthesia With Hypobaric Bupivacaine for Knee Arthroscopies: Effect of Posture on Motor Block Kristiina S. Kuusniemi, M.D., Kalevi K. Pihlajama¨ki, M.D., Ph.D., Olli A. Kirvela¨, M.D., Ph.D., and Jaakko E. Korkeila, M.D. Background and Objectives: The clinical impact of patient positioning on motor block during unilateral spinal anesthesia was the focus of our study. It was assumed that a 45° rotation toward the prone position would minimize blocking the ventral motor roots compared with using the conventional lateral decubitus position. Methods: Spinal anesthesia with 3.4 mL of hypobaric 0.18% bupivacaine via a 27-gauge Whitacre needle was administered to 70 patients undergoing knee arthroscopy. The patients were kept either in a lateral decubitus position (group I) or rotated approximately 45° toward the prone position (group II). No prophylactic vasopressors or infusions were used. The intensity of motor block (modified Bromage scale) was assessed for both the operative and the contralateral side. Results: The patients in group I had a slightly more pronounced motor block, but statistical significance could be shown only 20 minutes following the block. There was no statistical difference between the groups in the need of additional analgesics during the operation. None of the patients needed general anesthesia. The hemodynamics were stable and none of the patients developed postspinal headache or backache. Conclusions: The position of the patient affects the spread of the spinal anesthesia when clearly hypobaric agents are used. However, this small modification in positioning of the patient did not lead to a clinically meaningful difference in the spread of the motor block. Reg Anesth Pain Med 2001;26:30-34. Key Words:
Spinal anesthesia, Ambulatory, Hypobaric bupivacaine.
B
ecause of its simplicity, spinal anesthesia is an easy regional technique to use in a busy ambulatory practice. Using small doses of local anesthetic, common adverse effects (e.g., prolonged motor block, hemodynamic instability, and urinary retention) can be avoided.1 If only nerve roots supplying a specific area are targeted, the anesthetic must be directed to the intended region. In addition to positioning the patient after the injection, a change in the needle aperture orientation with side-hole needles produces a predictable local anesthetic distribution.2 We have previously shown that with a low dose of hypobaric bupivacaine, directional pencil-point From the Department of Anaesthesiology, University of Turku (K.S.K., O.A.K.), and Department of Anaesthesiology, Turku City Hospital (K.K.P., J.E.K.), Turku, Finland. This study was performed at the Turku City Hospital, Turku, Finland. Reprint requests: Kristiina S. Kuusniemi, M.D., Department of Anaesthesiology, Kiinamyllynkatu 4-8, 20520 Turku, Finland. E-mail: [email protected]. © 2001 by the American Society of Regional Anesthesia and Pain Medicine. 1098-7339/01/2601-0007$5.00/0 doi:10.1053/rapm.2001.18181
30
needle, and a lateral decubitus position, a predominantly unilateral spinal block for ambulatory surgery can be achieved.3-5 The position of the patient at the time of injection of the anesthetic and for some time thereafter is crucial when the baricity of the solution differs from that of cerebrospinal fluid (CSF). There are 31 pairs of spinal nerves, and each nerve is formed by the union of a ventral and a dorsal root. Laterally each ventral and dorsal root pierces the arachnoid and dura separately before uniting at or near the intervertebral foramen to form the mixed spinal nerve. The aim of this study was to find out whether the ventral motor roots of the spinal nerves would be affected less when patients were placed on their nonoperated side and rotated 45° toward the prone position when anesthetized with a clearly hypobaric spinal anesthetic agent.
Methods The study was approved by the local Ethics Committee and all patients gave their oral informed consent. We studied 70 American Society of Anesthesiologists (ASA) I or II patients older than 25
Regional Anesthesia and Pain Medicine, Vol 26, No 1 (January–February), 2001: pp 30 –34
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years undergoing knee arthroscopy in which a tourniquet with a pressure of 350 mm Hg was used. Patients with deformities of the spinal column, mental disturbance, neurological disease, or sensitivity to local anesthetics were excluded from the study. Premedication was either 5 or 10 mg diazepam by mouth, depending on the patient’s age and weight.6 A peripheral intravenous (IV) cannula was inserted, but no infusion was begun. Hypotension (systolic arterial pressure decrease ⬍90 mm Hg or ⬎50 mm Hg decrease from baseline) was treated with 3-mg increments of IV etilefrine (Effortil; Boehringer Ingelheim, Ingelheim, Germany). Bradycardia (heart rate ⬍50 beats/min, or a decrease of more than 20% from the initial value if it was initially lower than 50 beats/min) was treated with 0.5 mg IV atropine. Blood pressure and heart rate were recorded at 5-minute intervals before and during induction, surgery, and recovery by an automated oscillotonometer. Arterial oxygen saturation was registered continuously by pulse oximetry. The anesthesia nurse in the operating room was kept unaware of the anesthesia method used by anesthetizing the patients in the separate induction area before entering the operating room. A standardized research form was filled out on all patients. In the induction area, patients were randomly assigned to 1 of the 2 groups by the anesthesia nurse, according to a list of random numbers. Placing the patients in the lateral decubitus with the surgical side uppermost during the injection under fully aseptic conditions, dural puncture was performed at the midline of the L3-L4 interspace. In all patients, a 27-gauge Whitacre needle (Becton Dickinson, Madrid, Spain) with an introducer was used. The dose, volume, and concentration of the hypobaric bupivacaine were kept constant during this study. Once a free flow of clear CSF was obtained, 3.4 mL of 0.18% bupivacaine (6.12 mg) was injected (0.5% bupivacaine 1.8 mL ⫹ sterile distilled water ad 5 mL, density at 25°C 0.997 g/mL). Half of the dose was injected laterally toward the surgical side, and the other half caudally. The injection was made with a 5-mL Luer-Lock syringe which made it possible to inject the 3.4-mL dose in 10 seconds without leakage between the needle and the syringe. The anesthetic solution was administered without barbotage or aspiration at the end or in the beginning of the injection. After injection of the local anesthetic, the patients were kept 20 minutes either in a straight lateral position, operative side nondependent (group I), or asked to roll approximately 45° forward (group II), still in the lateral position. In both groups, the bed was also put in a slight head-down tilt to have the spine in a 10°
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Trendelenburg position. After 20 minutes, all patients were turned on their back. Motor block in the lower limbs was assessed with reference to specific myotomes by an anesthetist unaware of the anesthesia used. It was done by testing the power of a specific joint movement of both lower limbs which were regarded as equivalent to the following five myotomes: L2 hip flexion, L3 knee extension, L4 ankle dorsiflexion, L5 great toe dorsiflexion, and S1 ankle plantar flexion. A score of 0 was assigned for no block and 1 for complete block or for an uncoordinated movement.7 The total score was calculated for each side, the maximum score being 5 points for one side. The motor block was evaluated again at the end of the operation and at 2 hours from the injection. Before the operation began, the anesthesia nurse confirmed that the operation field was adequately blocked. If there was any discomfort induced by the tourniquet, if the patient felt any pain during the operation, or the patient exhibited an obvious need, 100 g of fentanyl was administered IV. The need for fentanyl, atropine, or etilefrine in the operating room was decided by the anesthetic nurse who was unaware of the anesthesia method used. All patients in group I and all but 2 patients in group II who had a contraindication for diclofenac received a preemptive dose of 75 mg diclofenac intramuscularly. Afterward, at the day-surgery unit, a nurse asked for the patient’s opinion of the anesthesia. The possible choices given were good, satisfactory, or poor. The patients were asked to inform the nurses in the day-surgery unit when they felt the anesthesia was completely worn off. The patients were discharged from the hospital, at the earliest in 4 hours after the injection of the anesthetic or when the motor block had completely resolved. Nurses at the day-surgery unit had instructions to verify that vital signs were stable for at least 1 hour, and that patients were well oriented and able to drink, void, dress, and walk before they could be discharged with an escort. We informed the patients about the possibility of experiencing a headache or backache after the operation. They were also given a phone number to call if a headache or backache developed. The power calculations showed that to detect a difference in mean values that would be at least as large as 1 standard deviation of the observations, the power would be 95% if n were 32. The t-test was used for statistical analysis of patients’ height, weight, age, and body mass index (BMI). Wilcoxon signed rank test was used to analyze the difference between the operated and nonoperated side in the motor block. The unilaterality of the motor block between the groups was analyzed using Mann-
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Regional Anesthesia and Pain Medicine Vol. 26 No. 1 January–February 2001 Table 1. Patient Characteristics (mean ⫾ SD) Group I
Group II
No. of patients 32 32 Sex (female/male) 15/17 22/10 Age (yr) 51.5 ⫾ 12.7 48.6 ⫾ 12.2 Weight (kg) 80.0 ⫾ 13.0 74.4 ⫾ 12.3 Height (cm) 173.8 ⫾ 9.6 167.2 ⫾ 7.2 26.2 ⫾ 3.3 26.5 ⫾ 3.6 BMI (kg/m2)
Statistical Significance NS NS NS NS P ⫽ .003 NS
Abbreviations: BMI, body mass index; NS, not significant.
Whitney U-test. The chi-squared test was used when appropriate. A P value of less than .05 was considered significant.
Results The patient characteristics are presented in Table 1. Seventy patients were initially studied, but 4 patients were excluded because the L3-L4 interspace was not used and 2 were excluded because the direction of the injection was not as planned. The results of motor block assessments are shown in Fig 1. The motor block between the operated and nonoperated sides was significantly different at all testing times in both groups. The motor block at the operated side was more pronounced in group I where the patients were kept in the straight lateral position, but statistical significance could be shown only at the 20-minute testing time (P ⬍ .05). After the operation, the motor block was more widespread at the nonoperated side in both groups compared with the values at the 20-minute testing time (P ⬍ .05).
The mean time from the injection to the beginning of the operation was 49 minutes in group I and 48 minutes in group II. The mean duration of the operation was 27 minutes in group I and 34 minutes in group II. The longest time from the injection to the end of the operation was 107 minutes in group I and 150 minutes in group II. The patient’s opinion of the duration of the block was missing in 4 patients’ research forms in group I and in 5 patients’ research forms in group II. The mean duration of anesthesia estimated by the patients in group I was 210 minutes and in group II was 228 minutes. There were 2 patients in both groups (6.3%) who were treated for hypotension. One of these patients received 6 mg of etilefrine and the other 3 received 3 mg each. None of the patients needed treatment for bradycardia. Two patients in group I (6.3%) and 1 patient in group II (3.1%) received treatment for shivering. They were all administered 20 mg of pethidine. There were no reports of urinary retention, postdural puncture headache, or postoperative back and/or leg pain. In group I, there was 1 patient who felt some discomfort in the operative field and 3 patients who felt discomfort induced by the tourniquet. However, all these patients believed that the anesthesia was good. In group II, there were 2 patients who believed that the operation and tourniquet caused some discomfort. In addition, 2 patients felt some discomfort in the operation field and 5 patients felt discomfort induced by the tourniquet. Afterward, 1
Fig 1. The total motor block score (modified Bromage scale; mean ⫾ SD) on the operated and nonoperated side in group I and II. (■), Group I, operated side; (䊐), group II, operated side; (t), group I, nonoperated side; ( ), group II, nonoperated side. EOP, end of operation. * P ⬍ .05.
Spinal Anesthesia With Hypobaric Bupivacaine
patient who received fentanyl judged the anesthesia to be satisfactory, the rest thought it was good. The difference between the groups regarding the need of additional analgesia (4 v 9) was not significant (P ⫽ .214). None of the patients needed general anesthesia. The dose of fentanyl in the patients who needed it was 100 g in group I and in group II, despite 2 patients in group II who needed this dose twice. In group I, all 32 patients found the anesthesia to be good. In group II, 31 patients thought the anesthesia was good and 1 thought it was satisfactory.
Discussion We attempted to produce unilateral spinal anesthesia with a minimal motor block to facilitate patient comfort, because a deep and prolonged motor block may be inconvenient for the patients. Various factors have been reported to affect the spread of local anesthetics in the subarachnoidal space8,9: the volume of CSF,10 the baricity of the local anesthetic solution, the position of the patient during and after injection when using nonisobaric solutions,11-13 the dosage of local anesthetic, and the site of injection.14 In our study, the site of injection and the volume, dose, and concentration of the bupivacaine were constant in order to study the effect of the patient’s position after the injection on the extent of motor block. The 20-minute delay resulting from positioning may be too time consuming in a rapidly working day-surgery unit; however, if the blocks can be performed in a separate induction area the delay may be minimized. The way we positioned the patient after the injection was based on the spinal nerve anatomy. Root filaments emerge from the spinal cord and unite into bundles to form the anterior and the posterior roots of individual spinal nerves. The anterior, ventral root is the motor root and the posterior, dorsal root is the sensory root. In our study, the motor block was more pronounced when the patients were in the straight lateral position, but there was a statistical significance only at the first testing time. After the patient was turned to the supine position for surgery, the block started to spread slightly to the nonoperated side. To our surprise, the study showed that even 20 minutes after the injection when using small doses of bupivacaine, the block can spread. An adequate sensory block of the knee requires an extensive block, because the knee has a nerve supply from both lumbar and sacral nerve roots. For surgery in the knee region, L2-S2 dermatomes need to be anesthetized. The use of a tourniquet requires a block 1 dermatome higher, up to L1. Despite the very limited
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motor block, the sensory block was adequate for these surgical procedures. In all, the patients were quite satisfied with the spinal anesthesia administered because they were able to move the other leg quite normally. We rationalized that by rotating the patient slightly forward, still in the lateral position, the drug would affect mainly the dorsal, sensory root region. However, there were 9 patients in group II and 4 patients in group I who either felt tourniquet-induced discomfort or discomfort in the operation field. The difference between the groups was not statistically significant. In addition to finding no practical advantage in trying to avoid motor block, there was a trend in group II toward lesssatisfactory anesthesia. Another explanation for the lack of statistical significance may be that the number of patients included in this study was insufficient. However, according to power analysis, patient numbers were adequate. Although the position of the patient is considered to affect the spread of the spinal anesthesia when the baricity of spinal anesthetic agent differs from that of CSF, the small modification in the patient’s position did not produce a clinically significant difference in motor block. The 0.18% bupivacaine was selected to assure a hypobaric solution. By definition, the baricity is the ratio of the density of the injectate to the density of CSF. In a recent study, determining the densities of CSF in patients for surgery under spinal anesthesia, the mean CSF density for their study population was 1.00059 ⫾ SD 0.00020 g/mL.15 The baricity of 0.5% bupivacaine solution can be decreased by diluting it with water.16 The density of our 0.18% bupivacaine solution at 25°C is 0.997 g/mL, being hypobaric in any patient. Since both CSF and local anesthetic exhibit a curvilinear decrease in density with increasing temperature,17 our solution is even more hypobaric at the body temperature. Hypotension is the most common cardiovascular side effect of spinal anesthesia18 and primarily the result of a decrease in venous return. Loading the patient with IV fluid is widely used to prevent the decrease in the arterial pressure. In our study, the patients did not receive any preemptive fluid or vasopressor, but hypotension, when encountered, was treated with IV etilefrine. Because the block in our study was mainly unilateral and the position of the patient during the first 20 minutes after the injection included a slight Trendelenburg position, patient hemodynamics were quite stable compared with the percentages usually mentioned in the literature.18 In conclusion, a small modification, i.e., 45° forward axial rotation, did not result in a clinically significant change in motor block when a clearly
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hypobaric anesthetic agent was used for spinal anesthesia.
References 1. Pittoni G, Toffoletto F, Calcarella G, Zanette G, Giron GP. Spinal anesthesia in outpatient knee surgery: 22-gauge versus 25-gauge Sprotte needle. Anesth Analg 1995;81:73-79. 2. Urmey WF, Stanton J, Bassin P, Sharrock NE. The direction of the Whitacre needle aperture affects the extent and duration of isobaric spinal anesthesia. Anesth Analg 1997;84:337-341. 3. Kuusniemi K, Pihlajama¨ki K, Pitka¨nen M, Korkeila J. A low-dose hypobaric bupivacaine spinal anesthesia for knee surgery. Reg Anesth 1997;22:534-538. 4. Kuusniemi KS, Pihlajama¨ki KK, Irjala JK, Jaakkola PW, Pitka¨nen MT, Korkeila JE. Restricted spinal anaesthesia for ambulatory surgery: A pilot study. Eur J Anaesthesiol 1999;16:2-6. 5. Kuusniemi KS, Pihlajama¨ki KK, Pitka¨nen MT, Korkeila JE. Low-dose bupivacaine: A comparison of hypobaric and near isobaric solutions for arthroscopic surgery of the knee. Anaesthesia 1999;54:540-545. 6. Jacobsen H, Hertz JB, Johansen JR, Hansen A, Kolliker K. Premedication before day surgery. Br J Anaesth 1985;57:300-305. 7. Cousins MJ, Bromage PR. Epidural blockade. In: Cousins MJ, Bridenbaugh PO, eds. Neural Blockade in Clinical Anesthesia and Management of Pain. Philadelphia, PA: Lippincott; 1988:253-260. 8. Stienstra R, Greene NM. Factors affecting the subarachnoid spread of local anesthetic solutions. Reg Anesth 1991;16:1-6. 9. Greene N. Distribution of local anesthetic solution within the subarachnoid space. Anesth Analg 1985;64: 715-730.
10. Carpenter RL, Hogan QH, Liu SS, Crane B, Moore J. Lumbosacral cerebrospinal fluid volume is the primary determinant of sensory block extent and duration during spinal anesthesia. Anesthesiology 1998;89: 24-29. 11. Kalso E, Tuominen M, Rosenberg PH. Effect of posture and some C.S.F. characteristics on spinal anaesthesia with isobaric 0.5% bupivacaine. Br J Anaesth 1982;54:1179-1184. 12. Kristoffersen E, Sloth E, Husted JC, Bach AB, Husegaard HC, Zu¨low I. Spinal anaesthesia with plain 0.5% bupivacaine at 19°C and 37°C. Br J Anaesth 1990;65:504-507. 13. Povey HMR, Jacobsen J, Westergaard-Nielsen J. Subarachnoid analgesia with hyperbaric 0.5% bupivacaine: Effect of 60-min period of sitting. Acta Anesthesiol Scand 1989;33:295-297. 14. Sakura S, Sumi M, Morimoto N, Yamamori Y, Saito Y. Spinal anesthesia with tetracaine in 0.75% glucose: Influence of the vertebral interspace used for injection. Reg Anesth Pain Med 1998;23:170-175. 15. Lui ACP, Polis TZ, Cicutti NJ. Densities of cerebrospinal fluid and spinal anaesthetic solutions in surgical patients at body temperature. Can J Anesth 1998;45: 297-303. 16. Covino BG, Scott DB, Lambert DH. Pharmacological considerations. In: Handbook of Spinal Anaesthesia and Analgesia. Singapore: Kin Keon Printing Co Pte Ltd, 1994:71-104. 17. Levin E, Muravchick S, Gold MI. Density of normal human cerebrospinal fluid and tetracaine solutions. Anesth Analg 1981;60:814-817. 18. Carpenter R, Caplan R, Brown D, Stephenson C, Wu R. Incidence and risk factors for side effects of spinal anesthesia. Anesthesiology 1992;76:906-916.
Spinal anesthesia, Ambulatory, Hypobaric bupivacaine.
B
ecause of its simplicity, spinal anesthesia is an easy regional technique to use in a busy ambulatory practice. Using small doses of local anesthetic, common adverse effects (e.g., prolonged motor block, hemodynamic instability, and urinary retention) can be avoided.1 If only nerve roots supplying a specific area are targeted, the anesthetic must be directed to the intended region. In addition to positioning the patient after the injection, a change in the needle aperture orientation with side-hole needles produces a predictable local anesthetic distribution.2 We have previously shown that with a low dose of hypobaric bupivacaine, directional pencil-point From the Department of Anaesthesiology, University of Turku (K.S.K., O.A.K.), and Department of Anaesthesiology, Turku City Hospital (K.K.P., J.E.K.), Turku, Finland. This study was performed at the Turku City Hospital, Turku, Finland. Reprint requests: Kristiina S. Kuusniemi, M.D., Department of Anaesthesiology, Kiinamyllynkatu 4-8, 20520 Turku, Finland. E-mail: [email protected]. © 2001 by the American Society of Regional Anesthesia and Pain Medicine. 1098-7339/01/2601-0007$5.00/0 doi:10.1053/rapm.2001.18181
30
needle, and a lateral decubitus position, a predominantly unilateral spinal block for ambulatory surgery can be achieved.3-5 The position of the patient at the time of injection of the anesthetic and for some time thereafter is crucial when the baricity of the solution differs from that of cerebrospinal fluid (CSF). There are 31 pairs of spinal nerves, and each nerve is formed by the union of a ventral and a dorsal root. Laterally each ventral and dorsal root pierces the arachnoid and dura separately before uniting at or near the intervertebral foramen to form the mixed spinal nerve. The aim of this study was to find out whether the ventral motor roots of the spinal nerves would be affected less when patients were placed on their nonoperated side and rotated 45° toward the prone position when anesthetized with a clearly hypobaric spinal anesthetic agent.
Methods The study was approved by the local Ethics Committee and all patients gave their oral informed consent. We studied 70 American Society of Anesthesiologists (ASA) I or II patients older than 25
Regional Anesthesia and Pain Medicine, Vol 26, No 1 (January–February), 2001: pp 30 –34
Spinal Anesthesia With Hypobaric Bupivacaine
years undergoing knee arthroscopy in which a tourniquet with a pressure of 350 mm Hg was used. Patients with deformities of the spinal column, mental disturbance, neurological disease, or sensitivity to local anesthetics were excluded from the study. Premedication was either 5 or 10 mg diazepam by mouth, depending on the patient’s age and weight.6 A peripheral intravenous (IV) cannula was inserted, but no infusion was begun. Hypotension (systolic arterial pressure decrease ⬍90 mm Hg or ⬎50 mm Hg decrease from baseline) was treated with 3-mg increments of IV etilefrine (Effortil; Boehringer Ingelheim, Ingelheim, Germany). Bradycardia (heart rate ⬍50 beats/min, or a decrease of more than 20% from the initial value if it was initially lower than 50 beats/min) was treated with 0.5 mg IV atropine. Blood pressure and heart rate were recorded at 5-minute intervals before and during induction, surgery, and recovery by an automated oscillotonometer. Arterial oxygen saturation was registered continuously by pulse oximetry. The anesthesia nurse in the operating room was kept unaware of the anesthesia method used by anesthetizing the patients in the separate induction area before entering the operating room. A standardized research form was filled out on all patients. In the induction area, patients were randomly assigned to 1 of the 2 groups by the anesthesia nurse, according to a list of random numbers. Placing the patients in the lateral decubitus with the surgical side uppermost during the injection under fully aseptic conditions, dural puncture was performed at the midline of the L3-L4 interspace. In all patients, a 27-gauge Whitacre needle (Becton Dickinson, Madrid, Spain) with an introducer was used. The dose, volume, and concentration of the hypobaric bupivacaine were kept constant during this study. Once a free flow of clear CSF was obtained, 3.4 mL of 0.18% bupivacaine (6.12 mg) was injected (0.5% bupivacaine 1.8 mL ⫹ sterile distilled water ad 5 mL, density at 25°C 0.997 g/mL). Half of the dose was injected laterally toward the surgical side, and the other half caudally. The injection was made with a 5-mL Luer-Lock syringe which made it possible to inject the 3.4-mL dose in 10 seconds without leakage between the needle and the syringe. The anesthetic solution was administered without barbotage or aspiration at the end or in the beginning of the injection. After injection of the local anesthetic, the patients were kept 20 minutes either in a straight lateral position, operative side nondependent (group I), or asked to roll approximately 45° forward (group II), still in the lateral position. In both groups, the bed was also put in a slight head-down tilt to have the spine in a 10°
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Kuusniemi et al.
31
Trendelenburg position. After 20 minutes, all patients were turned on their back. Motor block in the lower limbs was assessed with reference to specific myotomes by an anesthetist unaware of the anesthesia used. It was done by testing the power of a specific joint movement of both lower limbs which were regarded as equivalent to the following five myotomes: L2 hip flexion, L3 knee extension, L4 ankle dorsiflexion, L5 great toe dorsiflexion, and S1 ankle plantar flexion. A score of 0 was assigned for no block and 1 for complete block or for an uncoordinated movement.7 The total score was calculated for each side, the maximum score being 5 points for one side. The motor block was evaluated again at the end of the operation and at 2 hours from the injection. Before the operation began, the anesthesia nurse confirmed that the operation field was adequately blocked. If there was any discomfort induced by the tourniquet, if the patient felt any pain during the operation, or the patient exhibited an obvious need, 100 g of fentanyl was administered IV. The need for fentanyl, atropine, or etilefrine in the operating room was decided by the anesthetic nurse who was unaware of the anesthesia method used. All patients in group I and all but 2 patients in group II who had a contraindication for diclofenac received a preemptive dose of 75 mg diclofenac intramuscularly. Afterward, at the day-surgery unit, a nurse asked for the patient’s opinion of the anesthesia. The possible choices given were good, satisfactory, or poor. The patients were asked to inform the nurses in the day-surgery unit when they felt the anesthesia was completely worn off. The patients were discharged from the hospital, at the earliest in 4 hours after the injection of the anesthetic or when the motor block had completely resolved. Nurses at the day-surgery unit had instructions to verify that vital signs were stable for at least 1 hour, and that patients were well oriented and able to drink, void, dress, and walk before they could be discharged with an escort. We informed the patients about the possibility of experiencing a headache or backache after the operation. They were also given a phone number to call if a headache or backache developed. The power calculations showed that to detect a difference in mean values that would be at least as large as 1 standard deviation of the observations, the power would be 95% if n were 32. The t-test was used for statistical analysis of patients’ height, weight, age, and body mass index (BMI). Wilcoxon signed rank test was used to analyze the difference between the operated and nonoperated side in the motor block. The unilaterality of the motor block between the groups was analyzed using Mann-
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Regional Anesthesia and Pain Medicine Vol. 26 No. 1 January–February 2001 Table 1. Patient Characteristics (mean ⫾ SD) Group I
Group II
No. of patients 32 32 Sex (female/male) 15/17 22/10 Age (yr) 51.5 ⫾ 12.7 48.6 ⫾ 12.2 Weight (kg) 80.0 ⫾ 13.0 74.4 ⫾ 12.3 Height (cm) 173.8 ⫾ 9.6 167.2 ⫾ 7.2 26.2 ⫾ 3.3 26.5 ⫾ 3.6 BMI (kg/m2)
Statistical Significance NS NS NS NS P ⫽ .003 NS
Abbreviations: BMI, body mass index; NS, not significant.
Whitney U-test. The chi-squared test was used when appropriate. A P value of less than .05 was considered significant.
Results The patient characteristics are presented in Table 1. Seventy patients were initially studied, but 4 patients were excluded because the L3-L4 interspace was not used and 2 were excluded because the direction of the injection was not as planned. The results of motor block assessments are shown in Fig 1. The motor block between the operated and nonoperated sides was significantly different at all testing times in both groups. The motor block at the operated side was more pronounced in group I where the patients were kept in the straight lateral position, but statistical significance could be shown only at the 20-minute testing time (P ⬍ .05). After the operation, the motor block was more widespread at the nonoperated side in both groups compared with the values at the 20-minute testing time (P ⬍ .05).
The mean time from the injection to the beginning of the operation was 49 minutes in group I and 48 minutes in group II. The mean duration of the operation was 27 minutes in group I and 34 minutes in group II. The longest time from the injection to the end of the operation was 107 minutes in group I and 150 minutes in group II. The patient’s opinion of the duration of the block was missing in 4 patients’ research forms in group I and in 5 patients’ research forms in group II. The mean duration of anesthesia estimated by the patients in group I was 210 minutes and in group II was 228 minutes. There were 2 patients in both groups (6.3%) who were treated for hypotension. One of these patients received 6 mg of etilefrine and the other 3 received 3 mg each. None of the patients needed treatment for bradycardia. Two patients in group I (6.3%) and 1 patient in group II (3.1%) received treatment for shivering. They were all administered 20 mg of pethidine. There were no reports of urinary retention, postdural puncture headache, or postoperative back and/or leg pain. In group I, there was 1 patient who felt some discomfort in the operative field and 3 patients who felt discomfort induced by the tourniquet. However, all these patients believed that the anesthesia was good. In group II, there were 2 patients who believed that the operation and tourniquet caused some discomfort. In addition, 2 patients felt some discomfort in the operation field and 5 patients felt discomfort induced by the tourniquet. Afterward, 1
Fig 1. The total motor block score (modified Bromage scale; mean ⫾ SD) on the operated and nonoperated side in group I and II. (■), Group I, operated side; (䊐), group II, operated side; (t), group I, nonoperated side; ( ), group II, nonoperated side. EOP, end of operation. * P ⬍ .05.
Spinal Anesthesia With Hypobaric Bupivacaine
patient who received fentanyl judged the anesthesia to be satisfactory, the rest thought it was good. The difference between the groups regarding the need of additional analgesia (4 v 9) was not significant (P ⫽ .214). None of the patients needed general anesthesia. The dose of fentanyl in the patients who needed it was 100 g in group I and in group II, despite 2 patients in group II who needed this dose twice. In group I, all 32 patients found the anesthesia to be good. In group II, 31 patients thought the anesthesia was good and 1 thought it was satisfactory.
Discussion We attempted to produce unilateral spinal anesthesia with a minimal motor block to facilitate patient comfort, because a deep and prolonged motor block may be inconvenient for the patients. Various factors have been reported to affect the spread of local anesthetics in the subarachnoidal space8,9: the volume of CSF,10 the baricity of the local anesthetic solution, the position of the patient during and after injection when using nonisobaric solutions,11-13 the dosage of local anesthetic, and the site of injection.14 In our study, the site of injection and the volume, dose, and concentration of the bupivacaine were constant in order to study the effect of the patient’s position after the injection on the extent of motor block. The 20-minute delay resulting from positioning may be too time consuming in a rapidly working day-surgery unit; however, if the blocks can be performed in a separate induction area the delay may be minimized. The way we positioned the patient after the injection was based on the spinal nerve anatomy. Root filaments emerge from the spinal cord and unite into bundles to form the anterior and the posterior roots of individual spinal nerves. The anterior, ventral root is the motor root and the posterior, dorsal root is the sensory root. In our study, the motor block was more pronounced when the patients were in the straight lateral position, but there was a statistical significance only at the first testing time. After the patient was turned to the supine position for surgery, the block started to spread slightly to the nonoperated side. To our surprise, the study showed that even 20 minutes after the injection when using small doses of bupivacaine, the block can spread. An adequate sensory block of the knee requires an extensive block, because the knee has a nerve supply from both lumbar and sacral nerve roots. For surgery in the knee region, L2-S2 dermatomes need to be anesthetized. The use of a tourniquet requires a block 1 dermatome higher, up to L1. Despite the very limited
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motor block, the sensory block was adequate for these surgical procedures. In all, the patients were quite satisfied with the spinal anesthesia administered because they were able to move the other leg quite normally. We rationalized that by rotating the patient slightly forward, still in the lateral position, the drug would affect mainly the dorsal, sensory root region. However, there were 9 patients in group II and 4 patients in group I who either felt tourniquet-induced discomfort or discomfort in the operation field. The difference between the groups was not statistically significant. In addition to finding no practical advantage in trying to avoid motor block, there was a trend in group II toward lesssatisfactory anesthesia. Another explanation for the lack of statistical significance may be that the number of patients included in this study was insufficient. However, according to power analysis, patient numbers were adequate. Although the position of the patient is considered to affect the spread of the spinal anesthesia when the baricity of spinal anesthetic agent differs from that of CSF, the small modification in the patient’s position did not produce a clinically significant difference in motor block. The 0.18% bupivacaine was selected to assure a hypobaric solution. By definition, the baricity is the ratio of the density of the injectate to the density of CSF. In a recent study, determining the densities of CSF in patients for surgery under spinal anesthesia, the mean CSF density for their study population was 1.00059 ⫾ SD 0.00020 g/mL.15 The baricity of 0.5% bupivacaine solution can be decreased by diluting it with water.16 The density of our 0.18% bupivacaine solution at 25°C is 0.997 g/mL, being hypobaric in any patient. Since both CSF and local anesthetic exhibit a curvilinear decrease in density with increasing temperature,17 our solution is even more hypobaric at the body temperature. Hypotension is the most common cardiovascular side effect of spinal anesthesia18 and primarily the result of a decrease in venous return. Loading the patient with IV fluid is widely used to prevent the decrease in the arterial pressure. In our study, the patients did not receive any preemptive fluid or vasopressor, but hypotension, when encountered, was treated with IV etilefrine. Because the block in our study was mainly unilateral and the position of the patient during the first 20 minutes after the injection included a slight Trendelenburg position, patient hemodynamics were quite stable compared with the percentages usually mentioned in the literature.18 In conclusion, a small modification, i.e., 45° forward axial rotation, did not result in a clinically significant change in motor block when a clearly
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hypobaric anesthetic agent was used for spinal anesthesia.
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