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REGIONAL ANESTHESIA

Differing Incidences of Relevant Hypotension with Combined Spinal-Epidural Anesthesia and Spinal Anesthesia

Department of Anesthesiology, Intensive Care Medicine, and Pain Therapy, University Hospital Giessen, Giessen, Germany

Address correspondence and reprint requests to Dr. Med. Bernd Hartmann, Abt. Anaesthesiologie, Intensivmedizin, Schmerztherapie, Universitätsklinikum Giessen, Rudolf-Buchheim-Str. 7, D-35392 Giessen, Germany. Address e-mail to Bernd.A.Hartmann{at}chiru.med.uni-giessen.de

	Abstract

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In this investigation we assessed whether patients receiving spinal anesthesia (SPA) as part of combined spinal-epidural anesthesia (CSE) more often experience relevant hypotension than patients receiving SPA alone. From January 1, 1997, until August 5, 2000, electronic anesthesia records from 1596 patients having received SPA and 1023 patients having received CSE for elective surgery were collected by using a computerized anesthesia record-keeping system. Relevant hypotension was defined as a decrease of mean arterial blood pressure of more than 30% within a 10-min interval and a therapeutic action of the attending anesthesiologist within 20 min after onset. Electronic patient charts were reviewed by using logistic regression with a forward stepwise algorithm to identify independent risk factors that were associated with an increased incidence of hypotension after CSE. Univariate analysis was performed to assess differences in biometric data and relevant risk factors for hypotension between the two procedures. The incidence of relevant hypotension was more frequent with CSE than with SPA alone (10.9% versus 5.0%; P < 0.001). In the multivariate analysis, arterial hypertension (odds ratio, 1.83; 95% confidence interval, 1.21–2.78) and sensory block height >T6 (odds ratio, 2.81; 95% confidence interval, 1.88–4.22) were found to be factors associated with hypotension in the CSE group. Compared with patients receiving SPA alone, patients undergoing CSE had a significantly more frequent prevalence of arterial hypertension and higher sensory block levels (P < 0.01) despite smaller amounts of local anesthetics. In this study, patients receiving CSE had an increased risk for relevant hypotension as compared with patients with SPA alone. Part of this effect seems to be due to the procedure alone and not only because this population is at higher risk.

IMPLICATIONS: This study, based on a large number of patients with a retrospective design by using on-line recorded data, suggests that spinal anesthesia as part of combined spinal-epidural anesthesia may more often lead to relevant hypotension than spinal anesthesia alone. Preexisting arterial hypertension and a sensory block height exceeding T6 are major risk factors for the development of this complication.

	Introduction

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Hypotension after spinal anesthesia (SPA) is a frequent problem, with an incidence of 15.3% (1) to 33% (2). This may cause major adverse outcomes if perfusion pressure decreases to less than the limits for autoregulation of vital organs, and it also may produce minor, but significant, discomfort, e.g., postoperative nausea, vomiting, or dizziness (1).

The lower threshold in blood pressure requiring intervention remains debatable. The risk of major complications (cardiac morbidity or mortality) attributable to hypotension during either regional or general anesthesia is very small. Thus, only patients with profound hypotension during anesthesia have an increased risk of major sequelae.

A confounding factor in defining thresholds for hypotension may be the mode of data recording (automatic versus hand-recorded). Automatic recording of data provides significantly better data quality (3–6).

In contrast to possible prophylaxis and therapy of hypotension, only a few studies have addressed prediction of this event (1,2,7). Furthermore, there are no studies comparing possible incidences of relevant hypotension after combined spinal-epidural anesthesia (CSE) or SPA alone.

The aim of this study was to investigate whether CSE leads more often than SPA alone to relevant hypotension. This was done by using an on-line anesthesia information management system after predictors of relevant hypotension due to CSE anesthesia had been defined.

	Methods

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From January 1, 1997, to August 5, 2000, the anesthesia records of 1596 patients having received SPA alone and 1023 patients with CSE for elective surgery were recorded by using the anesthesia information management system NarkoData (IMESO GmbH, Hüttenberg, Germany). Descriptions of this system have been presented previously (3,8). Only inpatients who received surgery on a scheduled basis were considered eligible for this study. Patients were excluded if a local anesthetic other than bupivacaine was used. Cases of SPA for obstetric surgery or anesthesia for patients younger than 18 yr were not considered for the study.

Puncture techniques for SPA were identical in both patient groups: 25-gauge needle, median approach, lumbar epidural space (L3-4), and the patient in the upright position. In the case of CSE, which was performed with the needle-through-needle technique (Espocan®; Braun Melsungen, Melsungen, Germany), after the typical loss of resistance, a volume of 5–10 mL of saline 0.9% was injected into the epidural space, followed by dural puncture and application of the local anesthetic (plain bupivacaine 0.5%) into the subarachnoid space. After removal of the spinal needle, the epidural catheter was then advanced as soon as possible in a cephalad direction between 3 and 6 cm into the epidural space. However, no additional local anesthetics were applied epidurally until the end of the surgical procedure. Volume preload was applied at the discretion of the anesthesiologist. Generally, in patients without abnormal fluid status, our internal guidelines do not recommend application of large amounts of fluids before SPA. IV sedation was usually achieved with small amounts of midazolam (1–2 mg) as a bolus.

Mean arterial blood pressure (MAP) was recorded at least every 5 min with noninvasive measurement or every 3 min with invasive measurement. Application of one of the two methods was according to clinical criteria deemed appropriate by the attending anesthesiologist. The definition of hypotension comprised the following conditions: occurrence within 30 min after spinal puncture (to preclude an effect of blood loss or the surgical procedure on the incidence of hypotension) and a decrease of more than 30% within 10 min as compared with baseline values. Definition of relevant hypotension additionally required therapeutic intervention by the attending anesthesiologist (the administration of a vasoconstrictor—amezinium metilsulfate [Supratonin®], cafedrine/theodrenaline [Akrinor®], epinephrine, or norepinephrine) and/or the infusion of an additional crystalloid or colloid volume within 20 min after the beginning of the hypotensive episode. According to the internal guidelines of our department, hypotension is usually treated if MAP decreases in a previously normotensive subject to less than 60 mm Hg. The threshold is higher (70 mm Hg) in hypertensive patients. In general, additional volume is first applied, followed by a vasopressor if hypotension persists. All blood pressure recordings for this study were performed with the patient in the supine position.

In a recently published study (7), five variables were found to have a significant predictive value for the incidence of hypotension in SPA: chronic alcoholism, arterial hypertension, body mass index (BMI), peak sensory block height, and urgency of surgery. Accordingly, with the same method, the following variables were tested for a possible effect on the incidence of hypotension after CSE.

Patient-related variables included age, height, weight, BMI, sex, ASA physical status (9), active cigarette smoking, chronic alcohol consumption (defined as more than three alcoholic drinks per day), chronic heart failure (New York Heart Association status I–IV), preoperative history of hypertension (present or absent according to the patient’s medical history) or hypotension, vascular diseases, endocrine diseases, and preoperative antihypertensive treatment (angiotensin-converting enzyme inhibitors, ß-adrenergic blockers, calcium antagonists, or diuretics).

Surgical variables included surgical department (orthopedic and trauma surgery, general surgery, urology, gynecology, and others) and the type of surgical procedure according to the International Classification of Procedures in Medicine. Anesthetic variables included oral premedication with 3.75 or 7.5 mg of midazolam (yes/no), amount of IV crystalloid or colloid preload administered before block, IV sedation after block, and the time interval between CSE puncture and the start of the operation. SPA variables included the site of CSE puncture (L1-2 to L5-S1), number of punctures (1 to 4 or 5), dose of plain bupivacaine 0.5%, sensory block height measured by pinprick 10 min after application of the block, and local complications after CSE puncture (bleeding or paresthesia).

Data were exported from the database into the statistics program SPSS® (SPSS Software GmbH, Munich, Germany) for statistical analysis. Differences in the incidences of hypotension and the risk profiles between the two groups of patients (SPA and CSE) were checked by using univariate analysis. We calculated mean value, SD, median, interquartile range, and 95% confidence interval as metric variables. Metric variables were compared by using the nonparametric Mann-Whitney U-test. Categorical variables were tested by using either ² statistics or Fisher’s exact test. In case of P < 0.05, results were considered statistically significant.

To investigate independent factors with a significant association with relevant hypotension after CSE anesthesia, a multivariate logistic regression was used. For this multivariate analysis, only variables that had been proved to have a significant effect (P < 0.05) were taken into account in the univariate analysis. For statistical evaluation, all categorical variables, including the medical department of surgery, were considered as dichotomous variables, defined as either present or absent.

The model’s discriminative power was tested by cross-validation with the "leaving one out" technique (10). The Hosmer-Lemeshow goodness-of-fit H and C statistical method (11) was used to evaluate the calibration of the customized models, which was considered satisfactory when the P value was >0.05. The discriminative power (ability to discriminate between patients with or without hypotension) was tested with a receiver operating characteristic curve (12).

	Results

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Relevant hypotension occurred in 111 (10.9%) of 1023 patients with CSE. After SPA alone, relevant hypotension was observed in 81 (5.0%) of 1596 patients. This difference was statistically significant (P < 0.001).

Biometric data, identified risk factors for hypotension after SPA and CSE, and their distribution between the two groups are presented in Table 1. Between the SPA and CSE groups, there were statistically significant differences for age (53 ± 19 yr versus 66 ± 11 yr; P < 0.001), BMI (26.3 ± 4.5 kg/m² versus 28.1 ± 5.0 kg/m²; P < 0.001), surgical department (traumatology/orthopedics in 75.9 versus 99.5%; P < 0.001), amount of bupivacaine applied into the subarachnoid space (3.7 ± 0.3 mL versus 3.6 ± 0.3 mL; P < 0.001), sex (40% male versus 65% female; P < 0.001), prevalence of chronic alcoholism (3.2% versus 1.4%; P = 0.003), prevalence of arterial hypertension (25.8% versus 51.8%; P < 0.001), and sensory block height exceeding the T6 level (13.0% versus 25.9%; P < 0.001). No other observed variable showed significant differences between study groups.

The Hosmer-Lemeshow goodness-of-fit test showed good calibration (H statistic: H = 0.36, df = 2, P = 0.83; C statistic: C = 0.36, df = 3, P = 0.94). Hence, the model equation shows good correspondence between the observed and expected values within these groups.

	Discussion

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Central neuraxis block may lead to hypotension. The degree to which this is considered clinically relevant has not been defined. Because SPA is associated with extremely infrequent morbidity or mortality attributable to hypotension, a rigid definition is probably appropriate to predict major adverse outcomes (13). Our goal for this study was to have clear cutoff values of MAP for analysis of data. Thus, the definition of relevant hypotension in our study was rigid. The conjunction between a decrease in MAP and a therapeutic intervention by the anesthesiologist provides evidence that the event was considered potentially harmful. Most other authors consider only a percentage change in blood pressure, which may in the case of abnormally high or low baseline values lead to detection of an artifact. This may be the reason why in our study the incidence of hypotension was less frequent than observed by other authors (1,2).

CSE anesthesia is a relatively new technique that allows for highly effective analgesia for surgery, with small blood concentrations of local anesthetics and satisfactory postoperative analgesia (14). In our retrospective review of electronic anesthesia records, we could see that CSE was associated with more hypotensive episodes considered to be relevant by the attending anesthesiologist. Five factors have predictive value for the incidence of hypotension in SPA: urgency of surgery, chronic alcoholism, higher BMI, arterial hypertension, and sensory block height >T6 (7). Only the last two of these had relevance for CSE in multiple logistic regression. This may be because urgent surgical procedures are rarely performed with the CSE technique and because in the CSE cohort the prevalence of patients with chronic alcoholism was very small (1.4%). In fact, patients in the CSE group had a higher BMI (28.1 versus 26.3 kg/m²), which may have contributed to the increased incidence of hypotension. This result was statistically significant but may not account for the doubled incidence of hypotension among CSE patients. Furthermore, the attending anesthesiologists may have tried to offset the problem of more obese patients in the CSE group by reducing the amount of local anesthetic (18.0 versus 18.5 mg). Statistically significant differences were observed regarding the surgical specialty. Nearly all patients in the CSE group were scheduled for orthopedic surgery (99.5%, as compared with 75.9% of patients in the SPA group). However, because the study time interval was 30 minutes after puncture, surgical variables cannot account for major differences in hypotension.

Data from our study suggest that there are two possible explanations for the increased incidence of hypotension observed with CSE. The first is that patient cohorts were not identical in both groups. Arterial hypertension is a well acknowledged risk factor for the development of hypotension, and its prevalence was twice as frequent in the CSE group as compared with the SPA group. Because indications for the two techniques are not interchangeable, this fact is not surprising. CSE often is used for major orthopedic surgery (e.g., total hip or total knee replacement). These older patients frequently have significant medical conditions, including arterial hypertension.

However, our results can be explained only in part by preoperative risk factors, because sensory block height was significantly higher in the CSE group despite even larger volumes of local anesthetics applied intrathecally in the SPA group. This suggests that the puncture procedure itself has a cephalad spread of the local anesthetic.

Basically, the technique of puncture is identical in CSE and SPA. However, there are minor differences that could result in clinically significant effects. CSE is often performed with the patient in the sitting position, which is important because cephalad spread of the isobaric local anesthetic is more pronounced in the sitting position (15). However, with the CSE technique, placement of the epidural catheter after subarachnoid puncture requires the patient to remain in the sitting position longer, which might affect the higher spread of the surgical block.

Furthermore, 5–10 mL of saline was injected into the epidural space. This increased volume in the lumbar epidural space may lead to an enhanced cephalad spread of the local anesthetic in the subarachnoid space.

Protective measures against hypotension after spinal puncture have not been effective. Prehydration with large amounts of IV fluids has been challenged in the literature (16,17). In our study, more colloid and less crystalloid were administered in the patients receiving SPA as compared with CSE. However, these differences were far from being clinically significant and did not result in different incidences of relevant hypotension.

In general, comparison of two different medical or surgical procedures is best investigated in a prospective study design. However, in this special case, analysis of the underlying clinical problem also has problems. Because the indications for both anesthetic procedures are not identical in our institution, a randomized design would be ethically problematic, at least in our hospital. Furthermore, because the definition of relevant hypotension in our case was rigid, large sample sizes would be required to detect significant results. Further bias in a prospective design might result from data that are not recorded on-line. It is well recognized that on-line recording leads to more reliable data than other forms of data collection (6).

In summary, this study, based on a large number of patients, with a retrospective design using on-line recorded data, suggests that SPA for CSE anesthesia more often leads to relevant hypotension than SPA alone. Furthermore, this study corroborates that major risk factors for hypotension after central neuraxis block are preexisting hypertension and a sensory block height exceeding T6.

The more frequent incidence of hypotension in our CSE patients was partially due to a more frequent prevalence of arterial hypertension as a major risk factor. However, the level of the sensory block after 10 minutes was higher with CSE than with SPA alone, which cannot be sufficiently explained by differing risk factors. This leads to the assumption that the CSE procedure itself may have an increased risk of relevant hypotension compared with SPA alone.

	Acknowledgments

 
Supported by the Department of Anesthesiology, Intensive Care Medicine, and Pain Therapy, University Hospital Giessen, Germany, and IMESO GmbH, Hüttenberg, Germany.

We thank Moredata GmbH, Giessen, Germany, for their help in data management and statistical evaluation.

	References

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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 Web of Science 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 Web of Science (3) Citing Articles via Google Scholar Google Scholar Articles by Klasen, J. Articles by Hempelmann, G. Search for Related Content PubMed PubMed Citation Articles by Klasen, J. Articles by Hempelmann, G. Related Collections Cardiovascular Regional Anesthesia