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OBSTETRIC ANESTHESIA

Sensorimotor Anesthesia and Hypotension After Subarachnoid Block: Combined Spinal-Epidural Versus Single-Shot Spinal Technique

From the Department of Anesthesia, KK Women’s and Children’s Hospital, Singapore

Address correspondence and reprint requests to Raymond W. Goy, Department of Anesthesia, KK Women’s and Children’s Hospital, 100 Bukit Timah Road, Singapore 229 899. Address email to raygoywl{at}singnet.com.sg

	Abstract

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The extent of the intrathecal compartment depends on the balance between cerebrospinal fluid and subatmospheric epidural pressure. Epidural insertion disrupts this relationship, and the full impact of loss-of-resistance on the qualities of subarachnoid block is unknown. In this study we sought to determine if subarachnoid block, induced by combined spinal-epidural (CSE) using loss-of-resistance to air could render higher sensory anesthesia than single-shot spinal (SSS) when an identical mass of intrathecal anesthetic was injected. Sixty patients, scheduled for minor gynecological procedures, were randomly allocated into three groups all receiving 10 mg of 0.5% hyperbaric bupivacaine. In the SSS group, intrathecal administration was through a 27-gauge Whitacre spinal needle inserted at the L3-4 level. For the CSE group, the epidural space was identified with an 18-gauge Tuohy needle using loss-of-resistance to 4 mL of air. After intrathecal administration, a 20-gauge catheter was left in the epidural space. No further drug or saline was administered through the catheter. The procedure was repeated in group CSE _{(no-catheter)} except without insertion of a catheter. Sensorimotor anesthesia was assessed at regular 2.5-min intervals until T10 was reached. In all aspects, there was no difference between CSE and CSE _{(no-catheter)}. Peak sensory level in SSS was lower than CSE and CSE _{(no-catheter)} (median T5 [max T3–min T6] versus (T3 [T1–4] and (T3 [T2–5]) (P < 0.01). During the first 10 min postblock, dermatomal thoracic block was the lowest in SSS (P < 0.05). Time for regression of sensory level to T10 was also shortest in SSS. Hypotension, ephedrine use and period of motor recovery were more pronounced in CSE and CSE _{(no-catheter)}. We conclude that subarachnoid block induced by CSE produces greater sensorimotor anesthesia and prolonged recovery compared with SSS. There is also a more frequent incidence of hypotension and vasoconstrictor use despite using identical doses and baricity of local anesthetic.

IMPLICATIONS: This study confirms that induction of subarachnoid block by a combined-spinal epidural technique produces a greater sensorimotor anesthesia and results in prolonged recovery when compared with a single-shot spinal technique. There is a more frequent incidence of hypotension and vasoconstrictor administration despite identical doses of intrathecally administered local anesthetic.

	Introduction

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The spinal canal has been described as a rigid, cylindrical channel enclosing a semi-fluid dural sac (1). The extent of the intrathecal compartment is dependent on the balance between cerebrospinal fluid (CSF) and subatmospheric epidural pressure (2). It has been suggested that these opposing Starling’s forces are in a constant equilibrium, preventing the collapse of the flexible CSF compartment. It could be argued that the insertion of the Tuohy needle in search of the epidural space using the "loss-of-resistance" technique during the institution of combined spinal epidural (CSE) anesthesia may disrupt this equilibrium. Indeed, magnetic resonance imaging has demonstrated residual epidural air pockets extending up to three lumbar vertebral segments after the use of air for loss-of-resistance during the insertion of the epidural needle (3). Significantly, these air pockets have been observed to compress the lumbar thecal sac dorsally and laterally. These findings could be clinically relevant as a reduction of the lumbosacral CSF volume could possibly enhance the extent and duration of sensory anesthesia after spinal injections (4).

The effects of epidurally administered solutions on the extension of sensory blockade after subarachnoid injection are well documented (5–7). However, the full impact of loss-of-resistance on the qualities of subarachnoid block induced by CSE is relatively unknown. We hypothesize that the potential of this repercussion could be less marked in the single-shot spinal technique (SSS), which uses a small-gauged pencil-point spinal needle without the deliberate attempt to obtain loss-of-resistance. Therefore, in this study, our chief aim was to determine if subarachnoid block induced by CSE (using loss-of-resistance to air) could render a higher level of sensory anesthesia than SSS when an identical mass of intrathecal anesthetic was injected. In addition, the contribution of an indwelling 20-gauge epidural catheter in influencing this outcome was also investigated.

	Methods

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After institutional ethics committee approval and written informed consent, 60 female patients (age, 20–40 yr; weight, 50–70 kg; height, 1.5–1.8 m; gestation, <16 wk; ASA physical status I–II) scheduled for minor gynecological procedures (termination of pregnancy and evacuation of uterus) were randomly allocated into 3 groups. Patients with a history of hypertension, diabetes mellitus, systemic infection, and bleeding dyscrasias were excluded.

Randomization was achieved by means of the opaque sealed envelope technique. Each envelope contained one of the three codes: SSS, CSE, and CSE _{(no-catheter)} (CSE without indwelling epidural catheter). To avoid interoperator variability, all the blocks were performed by the principal author. All patients received the same intrathecal dose, consisting of 2 mL of 0.5% bupivacaine (10 mg) in 8% glucose solution, (Marcain, AstraZeneca, Södertälje, Sweden). The test solution was injected over 15 s in each instance with the orifice of the spinal needle in the cephalad direction.

In the SSS group (n = 20), the subarachnoid space was entered using a 27-gauge Whitacre spinal needle (BD, Franklin Lakes, NJ) at the L3-4 interspace. After confirming free flow of CSF, the designated dose of bupivacaine was administered. The patient was maintained in the right lateral position for 1 min to simulate the time taken to insert the epidural catheter in the CSE group. Thereafter, the patient was turned onto the supine horizontal position.

In the CSE group (n = 20), the epidural space was identified with a 18-gauge Tuohy needle (Espocan, B. Braun, Melsungen, Germany) at the L3-4 interspace using the loss-of-resistance to air technique, whereby 4 mL of air was injected. Through the epidural needle, a long 27-gauge pencil-point spinal needle was introduced. On puncturing the dural, the spinal needle was securely docked and the same dose of local anesthetic was administered intrathecally. Before removing the Tuohy needle, a 20-gauge epidural catheter was inserted 3 cm into the epidural space. No further manipulation or injection of any solution was effected through this catheter for the entire period of study. The epidural catheter and filter were firmly taped to the patient’s back and hidden from view of the observer throughout the study. As for the CSE _{(no-catheter)} cohort (n = 20), the entire procedure was identical to the CSE group with the exception that no epidural catheter was inserted through the Tuohy needle after intrathecal drug administration. The patients were all turned supine the next minute after injection.

Electrocardiogram, heart rate and oxygen saturation were monitored preblock and continuously throughout the study. Arterial blood pressure was recorded preblock and at 5 min intervals postblock for 30 min by using an automated noninvasive blood pressure device (Dinamap, Critikon, FL) over the patient’s right upper arm. All patients received 500 mL of warmed lactated Ringer’s solution over 15 min before neuraxial block. All the blocks were performed with the patient in the right lateral position. The patients were kept supine for 10 min postblock before the lithotomy position was assumed for the gynecological procedure.

Time of start of monitoring was defined as t = 0. The level of sensory anesthesia was assessed at regular 2.5-min intervals for the first 30 min by an independent physician who was unaware of the therapy received by the patient using loss of sensation to a standard nontraumatic pinprick stimulus. Similarly, the degree of motor blockade was scored on a Bromage scale of 0 to 3 (0 = no motor effects; 1 = a decrease in muscle strength with ability to move the limb against pressure; 2 = inability to move the limb against pressure without complete paralysis; and 3 = complete paralysis of the limb). After an initial 30 min, assessment was continued every 5 min in the recovery area by an independent anesthetic nurse who was also unaware of the anesthetic technique until a recession to T10 level was achieved. At this point, the study was concluded and the patient was discharged from anesthetic care to the postoperative ward. At this time, the indwelling epidural catheters were removed from patients in the CSE group.

The following data were collected:

1. S_max, defined as the maximal sensory block achieved during the period of study.

2. t_max, defined as the period from t = 0 to the time when S_max was first reached.

3. t _(max-2), defined as the period for 2-segment regression of sensory block from the time when S_max was first achieved until the block regressed to two thoracic dermatomal levels below that.

4. t_{(max -T10)}, defined as the period when S_max was first achieved to time when a recession of block to T10 occurred.

Hypotension was defined as a 25% decrease in systolic blood pressure from initial values and in this event, the patients received boluses of IV ephedrine, 5 mg, up to 25 mg in titrated doses. As all the patients were expected to have a maximum Bromage score of 3, the time when Bromage score first reached 3 to the time when it regressed to a score of 2 was also recorded.

Demographic data between the groups were compared using analysis of variance and post hoc Bonferroni’s correction if applicable. S_max, t_max, t_(max-2), t_{(max -T10)}, maximum decrease in systolic blood pressure from the baseline during the first 10 min postblock (expressed as % reduction from the baseline), and the total amount of ephedrine used in the first 10 min postblock (mg) were analyzed by using Kruskal-Wallis and post hoc Mann-Whitney U-tests for pairwise comparison with the application of Bonferroni’s inequality if applicable. Hemodynamic data (blood pressure and heart rate) were not analyzed beyond 10 min postblock because in all subjects, the maximal reduction of blood pressure occurred before that. Moreover, the change from supine to lithotomy position could in itself introduce changes to the hemodynamic variables and obviate meaningful comparisons. Log-rank testing was used for Kaplan-Meier survival analysis of recovery of lower motor block, as some patients did not achieve a Bromage score of 2 at the conclusion of the study. The sample size was computed with = 0.05 and ß = 0.1 to detect a 2-segment difference of S_max between the groups.

	Results

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There were no statistical differences among the three groups with regards to age, weight, height, gestation, and initial vital variables (Table 1). S_max in SSS was significantly lower than CSE and CSE _{(no-catheter)} (median T5 [maximum T3–minimum T6] versus (T3 [T1–4] and (T3 [T2–5]), respectively (P < 0.01) (Fig. 1). There was no difference in S_max between CSE and CSE _{(no-catheter)}. Similarly, during the entire first 10 min postblock, the dermatomal thoracic block to pinprick was the lowest in SSS, although there was no difference between CSE and CSE _{(no-catheter)}(P < 0.05) (Fig. 2). In addition, t_{(max -T10)} was also the shortest in SSS although there was no difference between CSE and CSE _{(no-catheter)}. However, there were no significant differences in t_max, and t_(max-2) among the three groups (Table 2).

View larger version (18K): [in this window] [in a new window]   Figure 1. Maximal sensory block achieved. Error bars show 95% confidence interval of mean. P < 0.05 Single-Shot Spinal (SSS) versus Combined Spinal-Epidural (CSE) and CSE(no catheter). P = not significant for CSE versus CSE(no catheter).

View larger version (20K): [in this window] [in a new window]   Figure 2. Progression of sensory block versus time. P < 0.05 Single-Shot Spinal (SSS) versus Combined Spinal-Epidural (CSE) and CSE(no catheter). P = not significant for CSE versus CSE(no catheter).

The recovery of motor block was also the fastest in SSS (P < 0.05), but no difference was found between CSE and CSE _{(no-catheter)} (Fig. 3).

View larger version (16K): [in this window] [in a new window]   Figure 3. Recovery of motor block—time taken Bromage score 3 to 2. Log-rank statistics. P < 0.05 Single-Shot Spinal (SSS) versus Combined Spinal-Epidural (CSE) and CSE(no catheter). P = 0.13 for CSE versus CSE(no catheter).

	Discussion

Top Abstract Introduction Methods Results Discussion References

We established that the CSE technique resulted in higher maximal sensory block when compared with SSS. Notably, the time taken for the maximal sensory block to regress to T10 and recovery of lower limb motor block were also prolonged when CSE was used. CSE also resulted in a larger decline of systolic blood pressure postblock, hence the use of more ephedrine compared with SSS. Our findings suggest that subarachnoid block rendered by CSE is generically dissimilar to SSS under otherwise identical circumstances.

The absolute mass of intrathecally-administered local anesthetic has been found to be of great importance in determining the extent as well as the duration of sensory block (9,10). As such, a seemingly appropriate dose to provide optimal anesthesia for SSS may potentially result in a relative "overdose" when used in CSE. This and the flexibility of epidural supplementation of anesthesia afforded by CSE may justify using a smaller dose of intrathecal anesthetic in CSE than SSS. However, the magnitude of dose adjustment in this respect will require further investigation. We are also unable to comment if the use of saline instead of air in loss-of-resistance could further contribute to the discrepancy of block characteristics between CSE and SSS. Nevertheless, attempting to insert the epidural catheter after intrathecal injection did not appear to have a major influence on block characteristics, although we did not seek to verify the anesthetic functionality of these catheters.

The actual mechanism that accounts for block differences between SSS and CSE is not known. The use of loss-of-resistance could possibly disrupt the equilibrium of forces and introduce residual air collections within the epidural space. This could, in turn, result in dural compression and reduction of lumbosacral CSF volume. As an extrapolation, the presence of an increased intrathecal drug concentration resulting from a reduced lumbosacral CSF volume could explain the differences between SSS and CSE. Indeed, Carpenter et al. (4) have demonstrated the inverse relation between lumbar CSF volume and peak sensory block level during spinal anesthesia.

A recent retrospective analysis of electronic records has also suggested that the CSE procedure itself may result in an increased frequency of clinically relevant hypotension compared with the SSS technique (11). The level of sensory anesthesia was found to be significantly higher with sCSE. Similarly, Kumar (12) has also anecdotally reported that a parturient undergoing cesarean delivery with CSE anesthesia often experienced a greater degree of hypotension as compared with those given spinal anesthesia with the same local anesthetic dose. These findings are consistent with our current controlled randomized trial that has evidently highlighted the clinical difference between subarachnoid blocks induced by CSE versus SSS.

In conclusion, this study confirms that the induction of subarachnoid block by CSE produces greater sensorimotor anesthesia and prolonged recovery compared with SSS. There is also a more frequent incidence of hypotension and vasoconstrictor use. This finding was evident despite the use of an identical dose and baricity of intrathecally administered local anesthetic. Further trials are required to investigate the clinical impact of this discrepancy of block characteristics on patient care and outcome.

	References

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1. Hogan Q, Toth J. Epidural anatomy: new observations. Can J Anaesth 1998; 45: 40–4.
2. Hogan Q, Toth J. Anatomy of soft tissues of the spinal canal. Reg Anesth Pain Med 1999; 24: 303–10.[ISI][Medline]
3. Gaur V, Gupta RK, Agarwal A, et al. Air or nitrous oxide for loss-of-resistance epidural technique? Can J Anaesth 2000; 47: 503–5.[Abstract/Free Full Text]
4. Carpenter RL, Hogan QH, Liu SS, et al. Lumbosacral cerebrospinal fluid volume is the primary determinant of sensory block extent and duration during spinal anesthesia. Anesthesiology 1998; 89: 24–9.[ISI][Medline]
5. Blumgart CH, Ryall D, Dennison B, et al. Mechanism of extension of spinal anaesthesia by extradural injection of local anesthetics. Br J Anaesth 1992; 69: 457–60.[Abstract/Free Full Text]
6. Stienstra R, Dahan A, Alhadi BZ, et al. Mechanism of action of an epidural top-up in combined spinal epidural anesthesia. Anesth Analg 1996; 83: 382–6.[Abstract]
7. Mardirosoff C, Dumont L, Lemedioni P, et al. Sensory block extension during combined spinal and epidural. Reg Anesth Pain Med 1998; 23: 92–5.[ISI][Medline]
8. Greene NM. Distribution of local anesthetic solutions within the subarachnoid space. Anesth Analg 1995; 64: 715.
9. Gentili M, Senlis H, Houssel P, et al. Single-shot spinal anesthesia with small doses of bupivacaine. Reg Anesth 1997; 22: 511–4.[ISI][Medline]
10. De Simone CA, Leighton BL, Norris MC. Spinal anesthesia for cesarean delivery: a comparison of two doses of hyperbaric bupivacaine. Reg Anesth 1995; 20: 90–4.[ISI][Medline]
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12. Kumar CM. Combined subarachnoid and epidural block for caesarean section. Can J Anaesth 1987; 34: 329–30.[ISI][Medline]

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Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999