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Anesth Analg 2006;103:959-964 © 2006 International Anesthesia Research Society doi: 10.1213/01.ane.0000231831.00032.97
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Abstract |
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 Top Abstract IntroductionMETHODSRESULTSDISCUSSIONAPPENDIXREFERENCES |
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BACKGROUND: Sequential (Seq) combined spinal epidural (CSE) may provide better cardiovascular stability than standard (Std) CSE for cesarean delivery. We compared the cardiovascular stability of both techniques using suprasternal Doppler.
METHODS: Healthy women (n = 40) scheduled for elective cesarean delivery were randomized into two groups; Std or Seq CSE. Serial measures of cardiac output indices, including minute distance, stroke distance, stroke volume, peak velocity, and corrected flow time, were recorded before and after intravascular fluid administration and after CSE. Women received either hyperbaric bupivacaine 10 mg (Std) or 5 mg (Seq) with intrathecal fentanyl 15 µg. An epidural top-up with bupivacaine 0.5% w/v (5 mL at 20 min in the Std group and 10 mL at 15 min followed by 5 mL at 25 min in the Seq group) was given if predefined sensory targets were not met. Data were collected every 5 min after intrathecal injection. Hypotension was treated with ephedrine. Statistical analyses included repeated measures analysis of variance, analysis of covariance and Student’s t-test. P < 0.05 denoted significance.
RESULTS: Results showed no difference in cardiac output, minute distance, stroke distance, stroke volume, peak velocity, or corrected flow time between groups over the first 20 min after spinal injection. For whole measurement periods, mean lowest values for these same measures showed no group differences.
CONCLUSION: We therefore found no benefit in terms of cardiovascular stability of Seq to Std CSE for elective cesarean delivery in the healthy pregnant population.
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Introduction |
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TopAbstractIntroductionMETHODSRESULTSDISCUSSIONAPPENDIXREFERENCES |
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Combined spinal epidural anesthesia (CSE) is a common technique used for elective cesarean delivery. Maternal hypotension and fetal acidemia are more commonly associated with spinal than epidural anesthetic techniques (1,2) and have an incidence of up to 83% using traditional spinal doses (3). Epidural techniques cause less hemodynamic disturbance (1) but are associated with poorer surgical analgesia (4) and inadequate muscle relaxation (5) and take longer to achieve surgical anesthesia. It has been suggested that sequential (Seq) CSE anesthesia using a small initial spinal dose followed by epidural top-ups may offer significant advantages over traditional spinal or epidural techniques by reducing the incidence of hypotension while preserving the quality of analgesia (6,7). Although avoidance of hypotension is important for all patients, this technique may be particularly advantageous for high-risk parturients with cardiac disease, where changes in hemodynamic status are less well tolerated.
Maternal symptoms of dizziness, nausea, vomiting, and associated decreases in arterial blood pressure (BP) exceeding 20% baseline are commonly used to indicate significant changes in cardiovascular status after spinal anesthesia. However, because of changes in systemic vascular resistance, BP alone can only provide limited information about cardiac output (CO), which has shown to be a better predictor of organ and placental perfusion than BP (1). Few studies have measured CO specifically after regional anesthesia in the obstetric population. This is largely attributable to the lack in availability of reliable noninvasive measurement techniques. More commonly, studies have continued to focus on BP variables together with fluid and ephedrine requirements as surrogate markers of cardiovascular status, as these are more easily measured (3,8).
The suprasternal measurement of aortic blood flow is a simple, noninvasive method of assessing CO, as described by Light (9). This is a valid technique, providing linear measures of CO consistent with volumetric measures derived from thermodilution (10) and has been used successfully to assess cardiac function in a range of physiological and pathological states including pregnancy (11,12). Technical issues have limited the availability of this technique in general over the years, but signal processing has continued to develop and the SupraQ Cardiac Function Monitor® (Deltex Medical Limited, Chichester, UK) is a currently available, improved suprasternal device. This model measures CO via a handheld stationary probe directing a continuous 2-MHz ultrasound beam at blood flowing in the ascending or aortic arch. The frequency shift of ultrasound waves reflected back from the moving blood is translated into a real-time display of velocity against time using fast Fourier transform spectral analysis. A range of cardiac variables can be derived from this waveform, without the need to know aortic size, giving information on left ventricular flow. Linear measures of CO (which are independent of body size) can be calculated directly from the velocity-time complex and volumetric measures derived from a nomogram incorporated into the software.
We hypothesized that Seq CSE is a more cardiovascular stable technique than standard (Std) CSE in women undergoing cesarean delivery, and we compared the hemodynamic effect of both techniques by measuring CO changes using a suprasternal device, the SupraQ Cardiac Function Monitor®. To our knowledge there are no published data comparing maternal CO after these regional anesthetic techniques.
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METHODS |
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TopAbstractIntroductionMETHODSRESULTSDISCUSSIONAPPENDIXREFERENCES |
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After ethics committee approval and written informed consent, 49 patients scheduled for elective cesarean delivery under regional anesthesia were enrolled in this prospective, randomized, single-blinded study. Exclusion criteria included gestational age <37 wk, multiple pregnancy, cardiac disease, pre-eclampsia, insulin-dependent diabetes mellitus, sepsis, weight <30 kg or >150 kg, height <149 cm or >212 cm, and subject refusal.
Patients were randomly allocated to either Std or Seq CSE groups using a computer-generated randomization method via a sealed envelope system. Both CSE techniques were performed in the sitting position at L3–4 by a single operator using a 16-gauge epidural needle (Smiths Medical, Hythe, Kent, UK) and a 27-gauge, 119 mm Whitacre spinal needle (Becton Dickinson, Franklin Lakes, NJ). In both groups an 18-gauge, closed end, multiport epidural catheter (Smiths Medical) was inserted 4 cm into the epidural space. All subjects received 1000 mL lactated Ringer’s solution via a 14-gauge cannula before spinal injection, followed by a further 500 mL over 20 min during development of the block. Subjects were unaware of group allocation.
Std CSE subjects received a spinal injection of 2 mL (10 mg) hyperbaric bupivacaine hydrochloride 0.5%w/v, glucose 80 mg/mL (AstraZeneca, King’s Langley, Herts, UK), with 15 µg fentanyl (Janssen-Cilag, High Wycombe, Bucks, UK) followed by a further 5 mL plain 0.5%w/v bupivacaine hydrochloride (AstraZeneca) at 20 min via the epidural catheter if predefined sensory and motor criteria were not met, this being a loss of cold sensation to T4 using ethyl chloride and a modified Bromage motor block score of at least 3 (1 = able to raise legs, 2 = able to flex knees, 3 = able to move feet only, 4 = no movement in legs or feet).
Seq CSE subjects received a spinal injection of 1 mL (5 mg) hyperbaric bupivacaine hydrochloride 0.5%w/v, glucose 80 mg/mL with 15 µg fentanyl followed by an epidural top-up of 10 mL plain 0.5%w/v bupivacaine hydrochloride at 15 min and a further 5 mL at 25 min for the same predefined sensory and motor criteria as the Std group. CSE injections in both groups were performed by a single operator.
Before spinal injection, baseline measures of heart rate (HR), Spo2, noninvasive BP, and CO variables were taken in the sitting and 15 degree left tilt positions, before and after intravascular fluid administration. These were recorded at 5-min intervals in the left 15 degree tilt positions after spinal injection together with sensory levels to cold/touch (using ethyl chloride spray) and motor block. All measures were continued for 20 to 35 min depending on epidural top-up requirements. Reductions in systolic BP (SBP) exceeding 20% of baseline were treated with 6-mg IV boluses of ephedrine. None of these measurements for the purposes of the study were continued into the surgical period.
CO measures were taken from the aortic arch and performed by a single operator, trained over a 3-mo period in suprasternal Doppler techniques, using the SupraQ®, as described previously. These are shown in Appendix 1.
All measures were taken from the aortic arch and transferred in real time onto a remote storage disk for subsequent analysis of the velocity time complexes. Complexes were examined for clarity and interference, the best of which were used for data analysis. Each CO variable used for statistical analysis represented the mean of 3 measures derived from 3 consecutive complexes at each time interval.
After delivery of the fetus, umbilical cord blood was taken for arterial and venous gas analysis. Apgar scores were also recorded. Further analgesia was provided with 2.5 mg epidural diamorphine (Evans, Leatherhead, Surrey, UK) in all subjects immediately after delivery. Additional intraoperative requirements were treated with 5-mL epidural boluses of plain 0.5%w/v bupivacaine at the discretion of the attending anesthesiologist. Postoperatively subjects were asked to score any pain during the procedure on a scale of 0 to 3, indicating "no pain" to "severe pain," respectively. Attending anesthesiologists used the same scale to objectively score the quality of intraoperative analgesia.
Data are presented as mean (sd), median [interquartiles] and count as appropriate. Statistical analysis included repeated-measures of analysis of variance, Dunnett’s post-tests, analysis of covariance, Fisher’s exact test, Mann-Whitney U-test, and Student’s t-test. Analyses were performed using the following software: Excel 2000 (Microsoft, Redmond, VA), Number Crunching Statistical System 2000 (NCSS Inc., Kaysville, UT), and GraphPad Prism 3.02 (GraphPad Software Inc., San Diego, CA). Statistical significance was defined for P < 0.05 (two-sided). To detect a 20% difference between groups in CO measures, with a coefficient of variation of 0.20, 16 subjects would be required per group for 80% power and P < 0.05.
We report mainly the volumetric measures of CO, as these are more familiar to the clinician.
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RESULTS |
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TopAbstractIntroductionMETHODSRESULTSDISCUSSIONAPPENDIXREFERENCES |
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Final data analysis was performed on 40 subjects (20 in each group) after 9 exclusions. Four of these were attributable to technical problems, specifically: failure to site the spinal, blood in the epidural catheter, a leaking spinal needle and delay between intravascular fluid administration and siting the spinal. Five others were excluded because of poor-quality Doppler recordings.
Age, weight, height, gestation, and parity were similar in both groups. In the Std group, 16 subjects did not require epidural supplementation after spinal injection and 4 subjects required a single top-up. In the Seq group, 3 subjects did not require epidural supplementation, 15 required one top-up, and 2 subjects required a second. Table 1 shows the effects of positional change (moving from sitting to 15° left tilt) and intravascular fluid administration (1000 mL lactated Ringer’s solution) on CO variables. Analysis of pooled data, prespinal injection, showed that moving from sitting to left tilt position significantly increased stroke volume (SV) (P = 0.0015), stroke distance (SD) (P = 0.0035), and peak velocity (PV) (P = 0.0004) and decreased heart rate (HR) (P < 0.0001). CO and minute distance (MD) were unchanged. Intravascular fluid administration increased all variables, CO, SV, stroke distance, minute distance, corrected flow time (P < 0.0001), and peak velocity (P < 0.01), except HR (P = 0.93) and SBP (P = 0.31), which remained unchanged.
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Figures 1 and 2 show serial changes in CO, SV and SBP in both groups over the first 20 min. Baseline values represent measures in the 15° left tilt position before intravascular fluid administration. Although there was no difference in measures between groups at any point, there were significant time-dependent variations over this period (Figs. 1 and 2).
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As not all subjects had measurements continued beyond 20 min, we were unable to directly compare values beyond this time point. Instead, we compared the mean lowest recorded values (for each CO variable) recorded over the entire measurement period (which varied among subjects) as a comparison of overall cardiovascular stability in the groups. There was no significant difference in mean lowest recorded values between the Std and Seq groups over the whole study period (Table 2).
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Table 3 shows maximum sensory levels to cold and touch together with motor block in both groups. Results are shown at the 15-min interval; i.e., before any epidural supplementation in either group and for maximum block heights at the end of the study period after epidural top-ups as required.
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In the Std group sensory levels to cold were significantly higher than those in the Seq group at the 15-min interval, with median maximum sensory levels of T3.5 and T5, respectively (P = 0.002). Median maximum sensory levels were equal after epidural supplementation, reaching T3 in both groups. Similarly in the Std group, sensory levels to touch were significantly higher than those in the Seq group at 15 min with median maximum sensory levels of T4 and T5, respectively (P = 0.002). Median maximum sensory levels to touch reached T4 in both groups after epidural supplementation. Bromage scores for motor block were also higher in the Std group at 15 min with median maximum Bromage scores of 4 and 2.5 in Std and Seq groups, respectively (P = 0.002). After epidural top-up median maximum levels were equal, scoring 4 in both groups, indicating complete motor block.
There was no difference between groups regarding the number of subjects requiring supplemental analgesia during surgery or in scores for quality of analgesia (Table 3). Both patients and anesthesiologists scored quality of analgesia highly.
There were no differences in the incidences of hypotension, ephedrine requirements, nausea scores, or fetal outcome data between groups (Table 3).
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DISCUSSION |
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TopAbstractIntroductionMETHODSRESULTSDISCUSSIONAPPENDIXREFERENCES |
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This study compares the hemodynamic effect of Std versus Seq CSE for cesarean delivery using suprasternal Doppler as a measure of CO.
Although serial measures of CO appeared to be sensitive to both changing position and to an IV fluid administration, we were surprised to find no difference in cardiovascular stability between Std and Seq techniques at any time point. Both techniques appeared equally stable and were successful in achieving sensory and motor blockade adequate for cesarean delivery; however, this took longer to achieve in the Seq group.
Changes in CO after positional change and fluid administration are comparable to findings from previous authors (13) and suggest that our methodology and technique are adequately sensitive for the purposes of our study.
As the length of study period varied among subjects from 20 to 35 minutes depending on the need for epidural top-up, we were only able to directly compare measures for the first 20 minutes after spinal injection (Figs. 1 and 2). Measures over this period showed that the two CSE techniques did not result in any difference in CO variables at any point. Overall, CO (Fig. 1) decreased at 5 minutes after spinal injection, recovered, and was increased with respect to baseline at 20 minutes. This can be explained by acute vasodilation secondary to spinal anesthesia followed by increases in SV (Fig. 1) and HR resulting from fluid and ephedrine administration.
This study was not specifically designed to examine BP changes; however, we feel it is worth commenting on the changes that were found in relation to those of CO. By the 20-minute interval, SBP (Fig. 2) had decreased 7% below baseline. This was in contrast to CO, which had increased by 19%. This illustrates that changes in BP poorly reflect those in CO, particularly when associated with changes in systemic vascular resistance that accompany spinal anesthesia.
Length of the study period varied among subjects, as Doppler recordings were discontinued at 20 min for those women (in either group) who did not require a top-up, as we considered it unethical to continue measures and delay the start of surgery purely for the purposes of our study. We therefore compared mean lowest values for each CO variable, over entire study periods, to assess overall hemodynamic stability. These measures remain within 20% baseline in both groups and illustrate the cardiovascular stability of both techniques.
Under the conditions of this study it is difficult to distinguish between the effects on CO of IV fluid and ephedrine usage from regional blockade. Prophylactic administration of ephedrine has been shown to increase CO as a result of increases in myocardial contractility, SV, and more variable changes in HR (13,14). In addition, we are unable to comment on the duration of effect of the initial fluid administration or magnitude of effect of additional fluid administered over the first 20 min. Both confounding variables, however, are likely to contribute independently to the changes in CO measures we found.
The spinal dose (10 mg hyperbaric bupivacaine) in the Std group is consistent with standard protocol at our institution for CSE in healthy women undergoing cesarean delivery. We expected this to provide adequate sensory blockade for cesarean delivery at 20 minutes in the majority of subjects, without epidural top-up. The spinal dose (5 mg hyperbaric bupivacaine) in the Seq group was based largely on a study by Fan et al. (7), who suggested this to be the optimum dose, as part of a sequential technique, for providing the best surgical conditions combined with least cardiovascular instability.
Ideally the first epidural top-up should have been administered simultaneously in both groups; i.e., at 20 minutes after spinal injection. A small pilot study we performed showed the incidence of perineal discomfort was unacceptably high for those women in the Seq group who received the first top-up at 20 minutes, despite a sensory level to cold at T4 or above. We attributed this to regression of the spinal component as a result of the smaller dose combined with longer study period (up to 35 minutes). In this study therefore, women in the Seq group received the first top-up earlier, at 15 minutes. This technique is consistent with previous authors using a sequential technique (7).
As the timing of top-ups was inconsistent between groups, it was not possible to blind the operator performing the Doppler measures to group allocation.
Both Std and Seq techniques provided sensory and motor blockade adequate for cesarean delivery in all subjects; however, this was achieved more readily in the Std group. Supplemental analgesia was required during surgery in 30% and 40% of subjects in Std and Seq groups respectively. Confounding variables were duration of surgery and experience of the surgeon. Despite this, subjects and anesthesiologists in both groups were highly satisfied with the quality of analgesia throughout surgery (Table 3).
The SupraQ is a valid technique for measuring CO, as evidenced by the significant body of evidence validating the suprasternal technique in general (10–12) combined with the Deltex nomogram, which has been equally well validated against thermodilution and other methodologies (15,16).
The technique relies on the fact that aortic cross-sectional area does, however, remain constant between measurements. This has been shown to vary with BP in pregnancy but not to an extent that is clinically relevant (17).
Signal acquisition is possible in most subjects with some user training. Our operator gained experience over a 3-month period before commencement of the study. To optimize reproducibility all Doppler measures were performed by a single operator at the same aortic site; i.e., descending aorta (18). We emphasize that the aim of our study was to compare serial measures of CO rather than to focus on absolute measures in individuals.
In summary, and in response to the main objective of the study, we have successfully compared for the first time the hemodynamic effect of Std CSE versus Seq CSE for cesarean delivery using Suprasternal Doppler (SupraQ®) as a measure of CO.
We did not demonstrate any difference in CO between the two techniques and could therefore find no benefit in terms of cardiovascular stability of Seq over Std CSE in the healthy population. Both Std and Seq CSE techniques provided cardiovascular stability and achieved sensory and motor blockade adequate for cesarean delivery, although this took longer to achieve in the Seq group.
Any difference in cardiovascular stability between the two techniques may have been partially obscured by the administration of fluid and ephedrine. In healthy parturients, therefore, any potential differences in hemodynamics are easily overcome by the routine practice of monitoring and treatment of changes in BP. It is possible that women in a high-risk population in whom the use of fluid or ephedrine may be restricted (e.g., pre-eclampsia, cardiac failure, and fixed CO states) may still benefit from a Seq CSE technique.
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APPENDIX |
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TopAbstractIntroductionMETHODSRESULTSDISCUSSIONAPPENDIXREFERENCES |
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Stroke Distance (SD)
The distance (in cm) moved by a column of blood through the aorta during systole. It is derived by calculating the area under the waveform during systole.
Minute Distance (MD)
The distance moved (in cm) by a column of blood through the aorta in one minute, calculated as:
MD = SD x Heart rate
Stroke Volume (SV)
The volume of blood ejected from the heart during systole, calculated as:
SV = SD x C;
Where C is a calibration constant derived from a nomogram incorporated into the software.
Peak Velocity (PV)
The maximum velocity of blood in cm/s during systole.
Flow Time Corrected (FTc)
Flow time (FT) in msec corrected for variations in heart rate using Bazett’s equation, FTc = FT/
(Cycle time). It is often used an indicator of venous return.
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Footnotes |
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Accepted for publication May 30, 2006.
Sources of financial support: Johanna Bray supported by a research fellowship grant from Portex Inc, Keen, NH, USA. Nisa Patel supported by a research fellowship grant from the Obstetric Anaesthetists’ Association, London, United Kingdom (registered charity 272190). SupraQ Cardiac Function Monitor® on loan from Deltex Medical Limited, Chichester, UK.
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REFERENCES |
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- Bray JK, Patel N, Fernando R, Columb MO. Reproducibility of linear cardiac output measurements in the pregnant and non-pregnant populations using suprasternal Doppler ultrasound. Br. J. Anaesth. 2003;90:413P.
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