This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Horstman, D. J. Articles by Carvalho, B. Search for Related Content PubMed PubMed Citation Articles by Horstman, D. J. Articles by Carvalho, B. Related Collections Obstetrics Anesthetic Techniques Regional Anesthesia

---

OBSTETRIC ANESTHESIOLOGY

A Randomized Trial of Maximum Cephalad Sensory Blockade with Single-Shot Spinal Compared with Combined Spinal-Epidural Techniques for Cesarean Delivery

From the Department of Anesthesia, Stanford University School of Medicine, Stanford, California.

Address correspondence to Brendan Carvalho MBBCh, FRCA, Department of Anesthesia, H3580, Stanford University School of Medicine, Stanford, CA 94305. Address e-mail to bcarvalho{at}stanford.edu.

Abstract

BACKGROUND: Previous studies have shown more extensive cephalad sensory blockade in women receiving combined spinal-epidural (CSE) anesthesia compared with single-shot spinal (SSS) anesthesia for elective cesarean delivery. It has been postulated that introduction of the epidural needle during CSE disturbs the negative pressure in the epidural space, resulting in relatively greater cerebrospinal fluid (CSF) pressure and increased spread of intrathecal local anesthetic. We tested the hypothesis that CSE results in more extensive cephalad sensory blockade than SSS anesthesia and that loss-of-resistance during initiation of CSE anesthesia increases CSF pressure compared with SSS.

METHODS: Thirty parturients scheduled for elective cesarean delivery were enrolled in this randomized, double-blind study. Patients received either SSS or CSE anesthesia with equal doses of intrathecal anesthetic (hyperbaric bupivacaine 12 mg, fentanyl 10 µg and morphine 200 µg). Before the intrathecal injection, the CSF pressure was measured with a fiberoptic pressure sensor. Maximum cephalad sensory blockade to pinprick, cold and touch was measured. The total dose of phenylephrine required to maintain baseline arterial blood pressure was also recorded.

RESULTS: There were no significant differences in the median (interquartile range) pinprick sensory block height [T4 (T4–2) vs T3 (T4–1)] or CSF pressures [6 (4–12) vs 9 (8–12) mm Hg] between the SSS and CSE groups. There were no significant correlations between CSF pressure and block height or total dose of phenylephrine.

CONCLUSION: The SSS and CSE techniques inserted in the lateral decubitus position resulted in similar extent of sensory blockade and CSF pressure. These findings suggest that altering the intrathecal dose is not necessary and that any difference in intrathecal pressure associated with initial placement of an epidural needle in the epidural space during CSE anesthesia is clinically inconsequential.

Most elective cesarean deliveries are performed under neuraxial anesthesia using either single-shot spinal (SSS), epidural or combined spinal-epidural (CSE) techniques.1,2 Although many anesthesiologists initiate CSE anesthesia with an intrathecal anesthetic dose similar to what they would use for a SSS technique, previous studies have suggested a smaller dose may be preferable.3 A study in women undergoing elective cesarean delivery found that despite administration of the same intrathecal local anesthetic dose, a CSE technique resulted in significantly higher (5 dermatomes) sensory blockade compared with a SSS technique.3 These findings corroborated a similar study in women undergoing minor gynecological procedures that found a 2 dermatome peak sensory blockade difference between SSS and CSE techniques using equivalent intrathecal doses.4 Both studies controlled for patient positioning and did not site an epidural catheter or administer epidural medication during the CSE anesthetic.

It has been proposed that the differences in the cephalad extent of sensory blockade between the SSS and CSE techniques may be related to disturbances in the normal subatmospheric epidural pressure or by the introduction of air or saline collections while identifying the epidural space using loss-of-resistance to air or saline during initiation of CSE anesthesia. The CSE technique via either or both of these mechanisms may cause dural compression which reduces the lumbrosacral cerebrospinal fluid (CSF) volume and, consequently, increases the spread of intrathecal anesthetics.3,4

We hypothesized that the CSE anesthetic technique results in more extensive cephalad sensory blockade and a concomitant increase in CSF pressure compared with a SSS technique. The primary objective of the study was to compare peak sensory block height to pinprick achieved by SSS and CSE techniques after the administration of the same intrathecal anesthetic dose. Secondary objectives were to compare CSF pressures immediately before the intrathecal injection, determine the relationship between CSF pressure and sensory blockade (pinprick, cold and light touch), and measure the extent of sympathectomy as assessed indirectly by the total dose of phenylephrine required to maintain baseline arterial blood pressure.

METHODS

After IRB approval and written informed consent, 30 ASA Physical Status 1 or 2 parturients, age 18 to 45 yr, scheduled for elective cesarean delivery under neuraxial anesthesia were enrolled in this randomized, double-blind study. Patients were excluded from study participation if they met any of the following criteria: morbid obesity (Body Mass Index >40 kg/m²); height <150 cm; any contraindication to neuraxial anesthesia; history of spinal deformity or spinal surgery; multiple gestations; onset of labor; or severe maternal disease (e.g., preeclampsia, diabetes, cardiac disease). The study was conducted in the Labor and Delivery Suite at Lucile Packard Children’s Hospital, Stanford, California and patients were enrolled over a 2-mo period (August–October 2006).

Study patients received 1000 mL lactated Ringer’s solution plus 500 mL hetastarch after obtaining peripheral IV access. Patients were premedicated with IV metoclopramide 10 mg and ranitidine 50 mg. Fluid infusion and premedication were administered approximately 30 min before the induction of anesthesia. All subjects were placed in a right lateral decubitus position, and after a sterile preparation, 2 mL of 1% lidocaine was infiltrated into the L3–4 interspace. Patients were allocated to receive an intrathecal injection via either a SSS or CSE technique of 0.75% bupivacaine in 8.25% dextrose 12 mg, fentanyl 10 µg and morphine 200 µg. Group allocation was done using computer-generated random number allocation and group assignments were secured in a sealed opaque envelope that was opened at the time of the patient’s arrival in the operating room.

The SSS was performed using a 26G x 12.4 cm Gertie Marx spinal needle (International Medical Development, Huntsville, UT) through a 19G x 3.8 cm spinal introducer needle (Smith Medical, St. Paul, MN) in the L3–4 interspace. After confirming intrathecal placement by free flow of CSF, the CSF pressure was measured with a fiberoptic pressure sensor (Photon Control Inc., Burnaby BC, Canada). The sterile sensor was attached directly to the hub of the spinal needle and the pressure was recorded on a digital monitor (Photon Control Inc., Burnaby BC, Canada) after a 5-s equilibration period. The intrathecal anesthetic was then administered.

The CSE procedure was performed in the L3–4 interspace with a 17G Tuohy needle (B-Braun Medical, Bethlehem, PA) by identifying the epidural space using a loss-of-resistance technique with 1 mL of air. A 26G Gertie Marx spinal needle was then passed through the Tuohy needle until free flow of CSF was observed. Similar to the SSS group, the static CSF pressure was then measured at the hub of the spinal needle after a 5-s equilibration period. After administration of the intrathecal anesthetic, both the Tuohy and spinal needles were removed without placement of an epidural catheter or administration of any epidural medication.

Immediately after intrathecal anesthetic administration, patients from both groups were placed in the supine position with left lateral displacement. An anesthesiologist blinded to the anesthetic technique evaluated the cephalad extent of sensory blockade every 3 min until the same dermatome level was recorded on three consecutive checks. This dermatome level established the peak block height. Sensory blockade was determined using pinprick, cold and light touch modalities. Loss of sharp pinprick sensation was assessed with a 30G needle starting at the left groin and advancing in a cranial direction until the subject perceived the stimulus as sharp. The pinprick sensation was then repeated on the right side. Sensation to cold and light touch was assessed by asking the subject to report when the stimulus (ice and cotton swab) appeared similar to a reference point (forehead skin). The stimulus was advanced in a cranial direction on the abdomen until a sensation similar to the forehead skin was perceived. For all three modalities, the dermatome level below the detected stimulus was recorded as the sensory block height. Intrathecal block success was defined as a bilateral T6 sensory level to pinprick.

Baseline mean arterial blood pressure was taken as the average of three readings in the operating room before block placement. Arterial blood pressure was measured noninvasively in the arm at baseline, 3, 6, 9, 12, 15, 20, and 30 min after the intrathecal injection. IV phenylephrine 50–100 µg was administered every minute as required throughout the cesarean delivery to maintain mean arterial blood pressure within 10% of the patient’s baseline. The anesthesiologist who treated the arterial blood pressures was not blinded to the group assignments.

Statistical Analysis
A previous study in women undergoing minor gynecological procedures demonstrated a 2 dermatome median difference and variability (interquartile range) of 2 dermatomes in peak sensory block heights between a SSS and CSE technique.4 Based on these findings, a priori sample size analysis predicted that we required 14 subjects per study arm to detect a 2-dermatome pinprick level difference in the primary outcome between the SSS and CSE study groups (Wilcoxon’s ranked sum test, Power 0.8, P = 0.05). This was a conservative sample size analysis in light of a study that demonstrated a 5 dermatome difference in peak sensory blockade between a SSS and CSE technique for elective cesarean delivery.3

Descriptive statistics were used to summarize demographic and obstetric data. Outcome measures of interest between the two groups were compared using Student’s t-test for normally distributed variables and Mann–Whitney test for nonparametric comparisons. Normal distribution was determined using QQ plots and the Kolmogorov–Smirnov test. Correlations were assessed with the use of linear regression unless otherwise indicated. Longitudinal data analyses (blood pressure) were performed using repeated measures ANOVA taking time as a repeated measure. Analyses were performed with Microsoft Excel and SPSS 11.0 for Windows statistical package (Chicago, IL) with P < 0.05 considered statistically significant.

RESULTS

Thirty women were enrolled and 15 women were randomized into each study group. Two subjects in the SSS group were excluded from the analysis due to difficulty in block placement in the lateral position. Both patients eventually received spinal anesthetics in the sitting position; however, their data were excluded because of the effects of the hydrostatic column on CSF pressure in the sitting position. In one patient (SSS group) we were unable to obtain CSF pressure due to equipment malfunction; however, all other study end points for that subject were analyzed. Demographic and baseline characteristics were similar between the study groups (Table 1). All patients achieved sensory blockade of T6 or higher. No patients required supplemental anesthesia during the cesarean delivery, and there were no surgical complications. There were no patients lost to follow-up or noncompliance.

Peak sensory blockade to pinprick was similar between the SSS and CSE study groups (Table 2). Similarly, there were no differences in cold or light touch peak sensory blockade between the two study groups. The CSF pressure recorded immediately before intrathecal anesthetic administration was not different between the SSS and CSE groups (Table 2).

Mean baseline mean arterial blood pressure at baseline was 84 ± 12 mm Hg and 78 ± 12 mm Hg in the SSS and CSE groups, respectively (P = 0.14). There were no significant differences with respect to arterial blood pressure over the 30 min period after the intrathecal injection between study groups (P = 0.63). We found no difference in total phenylephrine use between the SSS and CSE groups (Table 2).

There were no significant correlations between CSF pressure and the peak sensory blockade to pinprick (Fig. 1; r² = 0.12, P = 0.07) from the pooled datasets. Subgroup correlation analysis for CSF pressure and peak sensory blockade to pinprick were also not significant (r² = 0.19, P = 0.16 for the SSS and r² = 0.06, P = 0.37 for the CSE study groups). There was no significant correlation between CSF pressure and total phenylephrine dose requirement (Fig. 2; r² = 0.003, P = 0.79).

View larger version (17K): [in this window] [in a new window]   Figure 1. Correlation between cerebrospinal fluid (CSF) pressure and peak sensory blockade to pinprick (r2 = 0.123, P = 0.07). SSS = single-shot spinal; CSE = combined spinal-epidural. Data are missing from one patient in the SSS group.

View larger version (17K): [in this window] [in a new window]   Figure 2. Correlation between cerebrospinal fluid (CSF) pressure and total phenylephrine dose (r2 = 0.003, P = 0.79). SSS = single-shot spinal; CSE = combined spinal-epidural. Data are missing from one patient in the SSS group.

DISCUSSION

Our results demonstrate that there are no clinically or statistically significant differences in peak sensory blockade between the SSS and CSE techniques in women receiving intrathecal anesthesia for elective cesarean delivery. Furthermore, the CSE technique, compared with SSS, did not increase the CSF pressure immediately before the intrathecal injection.

Studies comparing the effect of different neuraxial anesthesia techniques on peak sensory blockade have shown conflicting results. In the present study, the CSE and SSS techniques resulted in similar peak sensory blockade. Our results are similar to Lim et al.5 who reported no difference in the extent of cephalad sensory blockade (T3 vs T3) between CSE and SSS techniques in women in established labor undergoing cesarean delivery. In contrast, Ithnin et al.3 reported a 5-dermatome level difference (C6 vs T3) between patients receiving CSE compared with SSS anesthesia for elective cesarean delivery. These results confirmed the authors’ previous results of a 2-dermatome level difference (T3 vs T5) between the CSE and SSS techniques in women undergoing minor gynecological procedures.4 Although we used the same elective cesarean delivery study population and followed similar methodological study procedures as Ithnin et al.,3 we found no differences in the extent of cephalad sensory blockade. We are unsure of the reasons for the differences in our study findings. One possible explanation is the different intrathecal bupivacaine doses (12 mg vs 10 mg). The relatively larger anesthetic dose in our study may have negated any subtle differences caused by the different anesthetic techniques. In addition, we added fentanyl and morphine to the intrathecal bupivacaine. Intrathecal opioids may change the baricity of intrathecal solutions and may have affected the spread of the local anesthetic.6 However, we believe our intrathecal mixture is more reflective of current clinical practice. The choice of phenylephrine in our study, versus ephedrine in the studies by Ithnin et al.3 and Goy and Sia,4 may confound a direct comparison between the studies. The extent of sensory blockade after intrathecal plain levobupivacaine has been found to be less when hypotension was treated with phenylephrine compared with ephedrine during cesarean delivery, but this difference was not maintained when hyperbaric bupivacaine was used.7,8 Differences in population demographics compared to the Ithnin et al.3 study may also explain differences in our finding. Another possible explanation is that their findings were spurious, and could not be replicated in women in established labor undergoing cesarean delivery, despite an identical methodology.5

The total phenylephrine dose required to keep the mean arterial blood pressure within 10% of baseline was not significantly different between our two study groups. This is consistent with our findings that the CSE and SSS techniques resulted in similar block heights and arterial blood pressure measurements. Previous authors have found that the degree of arterial hypotension after subarachnoid injection of local anesthetics correlates with peak sensory blockade.9,10 Although Lim et al.,5 and Goy and Sia4 reported a larger decline in arterial blood pressure and an increased requirement for ephedrine after a CSE compared with a SSS, Ithnin et al.3 found no difference in the incidence of hypotension nor the dose of ephedrine required to maintain the arterial blood pressure.

Ithnin et al.3 postulated that differences in peak sensory blockade between the SSS and CSE techniques may be attributed to the effect of the CSE technique on CSF pressure. They proposed that "the negative pressure in the epidural space is counterbalanced by the open connection to atmospheric pressure through the epidural needle, possibly resulting in a reduction of the dural sac volume and consequently a higher level of sensory block after a spinal dose of local anesthetic."3 This mechanism is plausible since magnetic resonance imaging studies have shown lumbosacral volume is an important determinant of spinal block height.11 In our study, however, we found no difference in CSF pressure between the SSS and CSE groups.

To minimize the effects of saline on lumbosacral volume, CSF pressure and sensory blockade, we used loss-of-resistance to air. However, we think that the effect of this potential confounder is small and that our findings would likely to be similar even if a small volume of saline instead of air were used. It is important to note that the underlying assumption by Ithnin et al.,3 that epidural pressure is negative, has been challenged. In two separate studies, Okutomi et al.12 and Telford and Hollway13 found that the epidural pressure is actually positive and that negative epidural pressures at the moment of epidural puncture may only represent artifacts induced by tenting of the dural membrane. If the epidural pressure is not negative, then opening the epidural space to atmospheric pressure would not be expected to result in a difference in sensory blockade between the two techniques. Regardless of whether the epidural pressure is negative or positive, both techniques may allow air entry into the epidural space. During advancement of the spinal needle, the needle stylet is occasionally removed to check for the presence of CSF flow before actual dural penetration. Although only a small volume of air is likely to be entrained during this process, it might nonetheless disrupt the baseline equilibrium, making the effect of the two techniques on pressure potentially equivalent.

We found no correlations between the opening CSF pressure and peak sensory blockade or the total phenylephrine dose. Although previous authors have reported that CSF density, volume and velocity correlate with spinal block height,9,11 to our knowledge, no previous studies have evaluated the relationship of opening CSF pressures and the cephalad extent of sensory blockade. Despite our finding of no difference in CSF pressures, we cannot exclude the possibility of changes in lumbrosacral CSF volume. Due to the high capacitance of the CSF-dural sac system, significant CSF pressures changes may not result from small thecal sac volume changes.

A potential limitation of this study is that it was powered to determine our primary end point (sensory block height) and not CSF pressure. The difference between CSE and SSS CSF pressure measurements (6 mm Hg vs 9 mm Hg, P = 0.09) suggests that there may be a trend towards a difference that may achieve significance with a larger sample size. Our study was powered to detect differences in sensory block height because of the availability of previous data and, more importantly, because of its clinical relevance. A difference in CSF pressure between the two techniques alone, without a difference in sensory block height, would not merit altering dose recommendations between the two techniques.

Another potential limitation is the variability in sensory blockade measurements. Previous studies have demonstrated significant variability in the evaluation of sensory blockade between different modalities (cold, pinprick and touch) and within individual patients.14 Furthermore, a survey of anesthesiologists found that 1 in 7 were inaccurate by 2 or more dermatomes when asked to identify the T5 dermatome on an anatomical picture.15 We attempted to minimize these potential pitfalls and confounders by using only one anesthesiologist to determine sensory blockade in all 30 study patients. This anesthesiologist was also blinded to the treatment groups and used a standardized dermatomal sensory map reference. It is noteworthy that, although the study was powered to show a 2 dermatome difference to pinprick, there were no significant differences in any of the sensory modalities (cold, pinprick and touch) tested. A potential bias of the study was that the anesthesiologist measuring CSF pressure and administering phenylephrine was not blinded to group assignments.

In conclusion, we found that the extent of cephalad sensory blockade and CSF pressures were similar between SSS and CSE anesthetic techniques inserted in the lateral decubitus position in women undergoing elective cesarean delivery. These findings suggest that altering the intrathecal dose is not necessary and that any difference in intrathecal pressure associated with initial placement of an epidural needle in the epidural space during CSE is clinically inconsequential.

Footnotes

Accepted for publication September 4, 2008.

This study was conducted at Lucile Packard Children’s Hospital and was funded internally by the Department of Anesthesia, Stanford University School of Medicine, Stanford, California. The authors involved in this study received no external financial support.

Presented in part as an abstract at the Society for Obstetric Anesthesia and Perinatology Annual Scientific Meeting, April 2007, Banff, Canada.

The authors share no relationships with any company or organization with a vested interest in the outcome of this study.

Reprints will not be available from the author.

REFERENCES

1. Jenkins JG, Khan MM. Anaesthesia for caesarean section: a survey in a UK region from 1992 to 2002. Anaesthesia 2003;58:1114–8[Web of Science][Medline]
2. Bucklin BA, Hawkins JL, Anderson JR, Ullrich FA. Obstetric anesthesia workforce survey: twenty-year update. Anesthesiology 2005;103:645–53[Web of Science][Medline]
3. Ithnin F, Lim Y, Sia AT, Ocampo CE. Combined spinal epidural causes higher level of block than equivalent single-shot spinal anesthesia in elective cesarean patients. Anesth Analg 2006;102:577–80[Abstract/Free Full Text]
4. Goy RW, Sia AT. Sensorimotor anesthesia and hypotension after subarachnoid block: combined spinal-epidural versus single-shot spinal technique. Anesth Analg 2004;98:491–6[Abstract/Free Full Text]
5. Lim Y, Teoh W, Sia AT. Combined spinal epidural does not cause a higher sensory block than single shot spinal technique for cesarean delivery in laboring women. Anesth Analg 2006;103:1540–2[Abstract/Free Full Text]
6. Richardson MG, Wissler RN. Densities of dextrose-free intrathecal local anesthetics, opioids, and combinations measured at 37 degrees C. Anesth Analg 1997;84:95–9[Abstract]
7. Cooper DW, Gibb SC, Meek T, Owen S, Kokri MS, Malik AT, Koneti KK. Effect of intravenous vasopressor on spread of spinal anaesthesia and fetal acid-base equilibrium. Br J Anaesth 2007;98:649–56[Abstract/Free Full Text]
8. Cooper DW, Jeyaraj L, Hynd R, Thompson R, Meek T, Ryall DM, Kokri MS. Evidence that intravenous vasopressors can affect rostral spread of spinal anesthesia in pregnancy. Anesthesiology 2004;101:28–33[Web of Science][Medline]
9. Higuchi H, Hirata J, Adachi Y, Kazama T. Influence of lumbosacral cerebrospinal fluid density, velocity, and volume on extent and duration of plain bupivacaine spinal anesthesia. Anesthesiology 2004;100:106–14[Web of Science][Medline]
10. Higuchi H, Adachi Y, Kazama T. The influence of lumbosacral cerebrospinal fluid volume on extent and duration of hyperbaric bupivacaine spinal anesthesia: a comparison between seated and lateral decubitus injection positions. Anesth Analg 2005;101:555–60[Abstract/Free Full Text]
11. 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;89:24–9[Web of Science][Medline]
12. Okutomi T, Watanabe S, Goto F. Time course in thoracic epidural pressure measurement. Can J Anaesth 1993;40:1044–8[Web of Science][Medline]
13. Telford RJ, Hollway TE. Observations on deliberate dural puncture with a Tuohy needle: pressure measurements. Anaesthesia 1991;46:725–7[Web of Science][Medline]
14. Russell IF. A comparison of cold, pinprick and touch for assessing the level of spinal block at caesarean section. Int J Obstet Anesth 2004;13:146–52[Web of Science][Medline]
15. Congreve K, Gardner I, Laxton C, Scrutton M. Where is T5? A survey of anaesthetists. Anaesthesia 2006;61:453–5[Web of Science][Medline]

This article has been cited by other articles:

				D. Benhamou and C. Wong Neuraxial Anesthesia for Cesarean Delivery: What Criteria Define the "Optimal" Technique? Anesth. Analg., November 1, 2009; 109(5): 1370 - 1373. [Full Text] [PDF]

				S. Leo, B. L. Sng, Y. Lim, and A. T. H. Sia A Randomized Comparison of Low Doses of Hyperbaric Bupivacaine in Combined Spinal-Epidural Anesthesia for Cesarean Delivery Anesth. Analg., November 1, 2009; 109(5): 1600 - 1605. [Abstract] [Full Text] [PDF]

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Horstman, D. J. Articles by Carvalho, B. Search for Related Content PubMed PubMed Citation Articles by Horstman, D. J. Articles by Carvalho, B. Related Collections Obstetrics Anesthetic Techniques Regional Anesthesia