Hemodynamic Stability During Labor and Delivery with Continuous Epidural Infusion

ORIGINAL CONTRIBUTION

Hemodynamic Stability During Labor and Delivery With Continuous Epidural Infusion

Mark A. Gerhardt, MD, PhD Vit B. Gunka, MD Robert J. Miller, DO

Context: Epidural anesthesia for labor pain is frequently com- Conclusions: Continuous epidural infusion of 0.2% ropiva- plicated by maternal hypotension. caine hydrochloride without bolus administration reduces the incidence of hypotension by 67% and is safer than tradi- Objective: To test whether continuous epidural infusion (CEI) tional bolus dosing for routine labor. This method requires fur- of local anesthetic, without bolus administration, lowers the ther study in high-risk patients, including those with incidence of hypotension in parturient patients. preeclampsia and cardiovascular disease. Methods: In a single-blind clinical study, subjects were ran- J Am Osteopath Assoc. 2006;106:692-698 domly assigned to CEI-only (10 mL/h of 0.2% ropivacaine hydrochloride without bolus) or control (10 mL of 0.2% ropi- ost parturient patients elect to receive epidural anes- vacaine hydrochloride per hour with 10-mL bolus) epidural Mthesia to ease the physical demands and discomfort of dosing groups. The incidence of hypotension (20% decrease childbirth.1 However, epidural anesthesia is frequently asso- in systolic blood pressure or mean arterial pressure (MAP), sys- ciated with hypotension,2,3 requiring intervention with fluid tolic blood pressure lower than 100 mm Hg, or MAP lower and/or vasopressors. Furthermore, the fetus may be com- than 65 mm Hg) was recorded for 2 hours after dosing. Sta- promised because uterine blood flow depends on maternal tistical analysis included a 2ϫ2 ␹2 analysis, the Fisher exact test, perfusion.4 Fetal distress can develop rapidly. Epidural dosing and paired two-tailed t tests. strategies that decrease the incidence of maternal hypotension have clear benefits for the mother and fetus. Results: Fifty subjects were studied, with 25 randomly Epidural anesthesia is routinely administered with bolus assigned to each study group (CEI-only vs control). Baseline dosing of local anesthesia (LA) followed by either continuous blood pressure was not different between groups (CEI-only, epidural infusion (CEI) or repeated bolus doses. Hypotension 127 [11]/ 77 [8.7] mm Hg; control, 131 [14]/ 78 [2]). The inci- may occur as a result of anesthesia-induced sympathectomy, dence of hypotension was lower in the CEI-only group than usually associated with neuraxial administration of LA.5,6 In in the control group (5 [20%] vs 15 [60%]; P=.009), with inter- anticipation of the increase in venous capacitance, preemp- vention required in 1 (20%) of 5 CEI-only subjects and 7 (47%) tive administration of a fluid bolus before LA is delivered. of 15 control subjects. Sensory block reached the T10 der- Although this practice is generally safe, hypotension develops matome in 54.4 (18) minutes in the CEI-only group and 38 (24) in many patients despite the fluid bolus.7,8 minutes in the control group (P=.04). Pain scores and maternal Alternative dosing regimens that decrease the incidence and fetal pulse rates were not different between groups. Anal- and/or extent of the hypotension require development. We gesic supplementation (250 ␮g of epidural fentanyl) was used hypothesized that CEI of LA, without bolus administration, will more frequently in the CEI-only group (72% vs 32%; P=.01), result in a lower incidence of hypotension than the bolus without adverse effects. dosing method. Patients with uncomplicated term pregnancies who requested epidural anesthesia were studied to determine the incidence of hypotension, the time required for the sensory block to reach the T10 dermatomal level, and the patient’s From the Department of Anesthesiology (Dr Gerhardt) at Ohio State University perception of pain with CEI-only vs CEI with bolus dosing. Medical Center in Columbus, the Department of Anesthesiology (Dr Gunka) at the University of British Columbia in Vancouver, and the William Jennings Bryan Dorn Veterans Hospital (Dr Miller) in Columbia, SC. Methods This study was performed without extramural funding. After institutional review board approval, 50 subjects with Address correspondence to Robert J. Miller, DO, William Jennings Bryan Dorn Veterans Hospital, 6439 Garners Ferry Rd, Columbia, SC 29209-1638. term pregnancies (38–42 weeks’ gestation) who requested E-mail: [email protected] epidural anesthesia during labor were enrolled in the study after informed consent. Subjects were excluded if they had Submitted March 23, 2006; revision received June 22, 2006; accepted June 27, 2006. pregnancy-induced hypertension (PIH) (preeclampsia), con-

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comitant cardiovascular disease, documented coagulation abnormality or abnormal bleeding history, evidence of infec- Table 1 tion or anatomic abnormality at the proposed catheter inser- Patient Characteristics (N=50)* tion site, or if they declined study participation or the epidural CEI-Only Group† Control Group‡ anesthesia during labor, were unable to give informed vol- Characteristic (n=25) (n=25) untary consent, or were younger than 18 years. Subjects were also excluded from the study in cases of difficult epidural placement, inadvertent epidural puncture (wet tap), precipi- Age, y 27.6 (6.2) 27.0 (5.6) tous labor, or fetal distress mandating urgent/emergent Height, cm 166 (7) 164 (7) cesarean delivery. Subjects were randomly assigned to the Weight, kg 85 (17) 82 (22) experimental or control group in a single-blind design. A T10 Gestational age, wk 39.8 (1.1) 39.6 (1.1) level of anesthesia was the goal of the dosing regimen. Gravida 2.4 (1.5) 2.4 (2.0) Each subject received a 750-mL crystalloid bolus intra- Para 1.1 (1.2) 0.8 (1.1) venously before placement of a lumbar epidural catheter via the Cervical dilatation, cm 4.2 (1.2) 4.5 (1.1) loss-of-resistance technique. All catheters were placed 6 cm Hematocrit, % 36 (3) 36 (3) into the epidural space without a test dose of LA with Oxytocin infusion, % 84 72 epinephrine. All subjects received 0.2% ropivacaine hydrochloride delivered by a Baxter APII pump (Baxter; Deerfield, Ill). The * Data are given as mean (SD). † Patients who received continuous epidural infusion (CEI) of 0.2% control group received bolus administration of epidural anes- ropivacaine hydrochloride without bolus dosing. thesia (10 mL of 0.2% ropivacaine hydrochloride) followed ‡ Patients who received CEI of 0.2% ropivacaine hydrochloride with bolus dosing. immediately by CEI of 10 mL of 0.2% ropivacaine hydrochloride per hour. subjects assigned to the experimental group received CEI of 0.2% ropivacaine hydrochloride with no bolus. level was 54.4 (18) and 38.0 (24) minutes for the CEI-only and Maternal blood pressure (BP) and maternal and fetal control groups, respectively (P=.04). This level was achieved pulse rates were recorded every 5 minutes for 2 hours. The first in all subjects before the end of the study period. measurement was obtained immediately before epidural The baseline systolic BP, diastolic BP, and MAP were not dosing (baseline) between uterine contractions. Hypotension different between groups (Figure 1). In the control group, all suc- was prospectively defined as (1) a 20% decrease in systolic cessive BP levels were lower than those in the CEI-only group. BP and/or mean arterial pressure (MAP); and/or (2) systolic The difference was statistically significant at 15 minutes (P=.03). BP less than 100 mm Hg or MAP less than 65 mm Hg. A significant difference was noted in systolic BP and MAP at Discomfort was assessed every 5 minutes using a visual 20 minutes (P=.04). The systolic BP readings were significantly analog scale (VAS), where 1 indicated pain free and 5, severe lower in 15 (71%) of 21 control subjects between 20 and 120 pain. In cases of moderate to severe pain ratings on two or more minutes. At 50 minutes, the mean systolic BP in the CEI-only successive evaluations after initiation of epidural anesthesia, group declined 3% (4 mm Hg) compared with baseline levels subjects were given adjunctive fentanyl (250 ␮g) epidurally. The (123 [14]/73 [11] mm Hg) (P=.01), and the control group sys- level of epidural anesthesia was evaluated by pin-prick dis- tolic BP had declined about 11% (117 [13] mm Hg) from base- crimination every 5 minutes. All other aspects of patient care line levels. were unchanged. In the CEI-only group, 5 (20%) of 25 subjects became All data were collected prospectively. The incidence of hypotensive compared with 15 (60%) of 25 subjects in the con- hypotension was tested using a 2ϫ2 ␹2 analysis, with a Fisher trol group. Three subjects had baseline systolic BP readings less exact test for categoric variables. A paired, two-tailed t test than or equal to 110 mm Hg. Of these subjects, 2 in the CEI-only was used to evaluate differences between groups. Significance group had a systolic BP measurement of less than 100 mm was established at an ␣ level of .05. Data are given as mean (SD) Hg, meeting criteria for hypotension. The baseline BP readings unless otherwise indicated. of 104/69 mm Hg and 110/67 mm Hg declined to 99/69 mm Hg and 99/81 mm Hg, respectively. One subject in the control Results group had a baseline BP of 103/52 mm Hg but did not fulfill Fifty subjects completed the study (25 CEI-only and 25 control criteria for hypotension. Thus, the incidence of clinically sig- subjects). No technical complications occurred. There were nificant hypotension may be as low as 12% for the CEI-only 1.2 (0.4) epidural placement attempts (needle and/or catheter method, representing an 80% decrease compared with the removed before completion of catheter insertion) in both bolus technique. groups. Subject characteristics were similar in both groups Treatment for hypotension was administered to 7 of 15 (Table 1). The time for sensory block to reach a T10 dermatomal subjects in the control group and to 1 subject in the CEI-only

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A 150

140

130

120

110

Control

Systolic BP, mm Hg Systolic BP, 100 CEI 90 0 10 20 30 40 50 60 70 80 90 100 110 120

B 100

60 Control

Diastolic BP, mm Hg Diastolic BP, CEI 50 0 10 20 30 40 50 60 70 80 90 100 110 120

C 120

110

100

MAP BP, mm Hg MAP BP, 70 Control CEI 60 0 10 20 30 40 50 60 70 80 90 100 110 120

Time, Min

Figure 1. Maternal systolic blood pressure (BP) (A), diastolic BP (B), and mean arterial pressure (C) during continuous epidural infusion (CEI) of 0.2% ropivacaine hydrochloride with (control group; n=25) and without (CEI-only group; n=25) bolus dosing. Note that 28% of control and 4% of study subjects received therapy for hypotension during the 2-hour observation period. Each data point represents the mean (SD). * Statistically significant (PϽ.05).

group (P=.6). More subjects in the control group had greater common practice to administer fluid or ephedrine immediately and longer-lasting decreases in BP compared with the CEI-only in obstetric patients who complain of nausea/emesis. No group (Figure 1). One subject in the CEI-only group and 5 in the patients met criteria for hypotension secondary to symptomatic control group did not receive intervention for hypotension therapy of nausea/emesis. despite marked (у25% or systolic BP Ͻ100 mm Hg) and/or Maternal pulse rates remained unchanged during the prolonged (у10 minutes) BP decreases. If analyzed on an study in both the CEI-only and control groups. Although sta- intent-to-treat basis, 40% of the CEI-only group and 80% of the tistical significance was demonstrated between the two groups control group would have received treatment (P=.13). It is at three time intervals, no pattern or clinical significance can be

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only and control groups, respectively. There were no associated changes in maternal BP or fetal pulse rate after fentanyl (Table 2). 5 Control CEI One subject from the control group continued to report * pain and requested additional analgesia 15 minutes after the 4 * first rescue dose, which was given at 40 minutes. She received * * a second fentanyl dose (250 ␮g) at 55 minutes and reported 3 * relief after receiving a 20-minute infusion of 500 ␮g of fen- * tanyl. This subject met criteria for hypotension after the second * *

VAS Scores VAS 2 dose of fentanyl, but because she received bolus dosing of LA, it is difficult to conclude what factor(s) contributed to the 1 hypotension. No fetal pulse rate changes were noted, though she did require diphenhydramine hydrochloride for pruritus.

0 Comment Baseline 5 10 15 20 More than half of parturient patients choose to have epidural Time, min anesthesia.1 Typically, dilute LA solutions are administered by bolus dosing of 5 mL to 15 mL followed by CEI.9 In addition Figure 2. Visual analog scale (VAS) pain scores after epidural fentanyl to offering patients pain relief, epidural anesthesia has been (250 ␮g) in patients receiving continuous epidural infusion (CEI) of shown to speed the first and second stages of labor in nulli- 0.2% ropivacaine hydrochloride with (CEI-only group; n=25) and parous women10 and allows obstetricians to perform mid- or without (control group; n=25) bolus dosing. Each data point repre- low-forceps delivery, vacuum extraction, or cesarean delivery.11 sents the mean (SD) score of 18 patients and 8 patients for the CEI and Technical complications associated with epidural anes- control groups, respectively. * Statistically significant difference thesia include inadvertent dural puncture and anatomic fac- (PϽ.05) compared with the baseline. tors that hinder successful catheter placement (eg, morbid obesity). Increased venous capacitance resulting from the inhibited sympathetic outflow12 and maternal hypotension attributed to this observation. Furthermore, these data points are physiologic complications. Because maternal hypotension were not different when compared with the baseline for each is so prevalent, proper positioning and prophylactic intra- group (CEI-only, 83.0 [8.7]; control, 88.9 [16]). Fetal pulse rates venous fluids before dosing of the epidural catheter are mea- were similar over time within and between groups. The base- sures that should be taken for all parturient patients.13,14 Many line fetal pulse rates were 138 (8.3) and 142 (10) beats/min in patients (60% in our control group) will still become hypoten- the CEI-only and control groups, respectively. sive and may require treatment with ephedrine or supple- There was no difference between groups in baseline VAS mental fluid. The safest method of epidural anesthesia during pain scores (CEI-only, 3.9 [1.2]; control, 4.3 [0.88]). Both groups lablor would appear to be placement and initiation of 0.2% ropi- demonstrated progression toward a VAS score of 1. A statis- vacaine hydrochloride infusion without a bolus dose at 3 cm tically significant reduction in VAS score was noted by 5 and of cervical dilatation.15 This method would take advantage of 15 minutes in the CEI-only (P=.001) and control (P=.02) groups, the safety features we observed and limit maternal discomfort. respectively. However, only the 30-, 35-, and 40-minute VAS Maternal hypotension requires rapid treatment. Decreased scores were different between the two groups. perfusion in brainstem structures results in nausea, vomiting, Rescue analgesia was provided by epidural administra- and syncope, and thus, increased risk of aspiration. Anesthe- tion of 250 ␮g of fentanyl. This adjuvant analgesia was used siologists empirically treat patients for nausea and vomiting more frequently (72% vs 32%) and earlier (17.6 vs 32.5 minutes) with ephedrine, often while determining BP.16–18 Difficulties in the CEI-only group. Fifty-eight percent of CEI-only sub- with intubation and aspiration are the leading causes of anes- jects received fentanyl within the first 20 minutes. Figure 2 thesia-related mortality in parturient patients. shows the VAS scores at the time of fentanyl administration The decrease in uterine blood flow also places the fetus at (baseline) and every 5 minutes for 20 minutes. In the CEI-only great risk.19 Maternal hypotension may be more deleterious group, the VAS decreased from 4.2 (1.0) to 3.2 (1.2) at 5 min- than umbilical cord compression, as it may attenuate fetal com- utes (PϽ.001). In the control group, the VAS decreased from pensatory responses.20 Histologic neuronal damage and fetal 3.7 (1.1) to 2.7 (1.0) (P=.007) 5 minutes after fentanyl was cerebral infarction have been associated with the degree of administered. The mean VAS continued to decline over the maternal hypotension but not hypoxia.21–23 Fetal subendocardial next 20 minutes to a nadir of 1.6 (0.60) and 1.6 (0.74) for the CEI- injury is another complication of maternal hypotension.24

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found to reduce the risk of maternal hypotension.8 Table 2 Karinen et al32 observed that administration of Maternal Blood Pressure and Fetal Pulse Rate After Epidural Administration of 250 ␮g Fentanyl* (N=50) the initial bolus in divided doses rather than in a single large dose did not alter the hemodynamic changes associated with epidural initiation. Vari- Maternal Blood Presure Fetal Pulse Rate, Group Systolic Diastolic beats/min ation of the CEI rates of ropivacaine from 2 mL/h to 10 mL/h following bolus dosing did not reduce CEI-Only group† (n=25) the need for top-up doses in parturient patients.29 Baseline 132 (13) 78 (12) 140 (9.5) The technique used in the current study has 5 min 130 (13) 79 (9.9) 136 (8.4) several limitations: lack of a test dose, increased 10 min 129 (13) 75 (11) 139 (8.3) time to effectiveness, and increased need for rescue 15 min 130 (14) 75 (12) 139 (8.0) analgesia. A test dose of LA with epinephrine is 20 min 126 (12) 71 (9.9) 138 (9.8) often used to rule out intravascular and intrathecal Control group‡ (n=25) catheter placement.33,34 This practice is not without Baseline 123 (9.3) 76 (11) 136 (9.4) risk, however, and an epidural test dose is con- 5 min 119 (9.0) 75 (10) 135 (12) troversial in obstetric anesthesiology.35 Also, intra- 10 min 119 (7.1) 74 (11) 138 (13) venous administration of epinephrine reduces 15 min 115 (12) 69 (11) 138 (14) uterine blood flow,35 an adverse effect that is of 20 min 117 (8.3) 76 (9.9) 138 (13) particular importance in patients with PIH. Another limitation of this method of admin- * Data are given as mean (SD). There are no significant differences between the groups in istration is the longer time to effectiveness of the any comparison. Baseline refers to the time at which the fentanyl was administered. Each anesthesia. The time required for the anesthetic succeeding data point represents time following fentanyl administration. † Patients who received continuous epidural infusion (CEI) of 0.2% ropivacaine hydrochloride level to reach T10 was increased from 38 to 54 without bolus dosing. minutes. Because our method of rescue analgesia ‡ Patients who received CEI of 0.2% ropivacaine hydrochloride with bolus dosing. with 250 ␮g of fentanyl is safe and effective, we believe that the benefit of decreased hypotension High-risk parturient patients with PIH may benefit from outweighs the risk of an additional 16 minutes for the anesthetic the no-bolus CEI dosing method. Pregnancy-induced hyper- level to reach T10 when pain scores are similar. tension is observed in about 8% of pregnant women25 and is Subjects in the CEI-only group needed rescue analgesia the leading cause of maternal morbidity.26 Blood pressure more often than control subjects. The adjuvant use of fentanyl control in this population improves both maternal and fetal out- provides an analgesic therapeutic option for anesthesiologists comes.27 who use the no-bolus CEI method. Our data show a reduction Inadvertent intrathecal placement must be considered in VAS from 3.9 to 2.6 during the first 30 minutes in the CEI- when inserting epidural catheters, including established only group and no difference in the control group during the catheters. Slow administration of ropivacaine via CEI allows same period. Studies have shown that patients may require top- greater time to verify correct placement. Furthermore, the iso- up doses even after the desired anesthetic level is established, baric nature of the commercially available 0.2% ropivacaine perhaps as labor progresses and the S2 to S4 nerves become hydrochloride may limit cephalad spread and provide a involved.36–40 One final limitation of our study is that physician margin of safety for inadvertently placed intrathecal catheters. bias may have influenced fentanyl administration. However, A variety of LA types and dosing regimens have been the goal of this study was to evaluate a potentially safer, hemo- used in obstetric anesthesia. Ropivacaine has distinct advan- dynamically stable dosing method for parturient patients. tages with respect to patient safety and pharmacologic prop- The rescue dose of fentanyl, 250 ␮g, delivered epidurally, erties.28,29 Although structurally and pharmacodynamically was used prospectively. Epidural fentanyl (75 ␮g) has been pre- similar to bupivacaine hydrochloride, ropivacaine has greatly viously reported to have no effect on fetal pulse rate.41 In con- reduced cardiotoxic properties compared with bupivacaine.30,31 trast, intrathecal fentanyl may result in decreased fetal pulse Ropivacaine may produce fewer central neurologic symp- rate.42 Most anesthesiologists consider intrathecal adminis- toms compared with lidocaine hydrochloride when administration of opioids to have fivefold to tenfold greater potency.42–44 tered systemically.28,29 Ropivacaine has greater effects on sen- The use of 10 ␮g to 25 ␮g of fentanyl intrathecally has been well sory fibers than on motor fibers.28 Obstetric patients can thus established in obstetric anesthesiology, especially when used be given less concentrated LA solutions so that motor function in combination with an epidural catheter.42–44 A 25-␮g is preserved while analgesia is sustained. Several variations of intrathecal dose translates into a 250-␮g epidural dose. bolus dosing regimens have been evaluated but have not been Pruritus was noted in many patients. However, the inci-

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dence, duration, and severity of these symptoms in patients 12. Goodlin RC. Venous reactivity and pregnancy abnormalities. Acta Obstet receiving intrathecal fentanyl do not correspond to the dose Gynecol Scand. 1986;65:345–348. administered.29 It is reasonable to think that the epidural route 13. Vincent RD, Chestnut DH. Which position is more comfortable for the parturient during identification of the epidural space? Int J Obstet Anesth. may produce a similar adverse effect profile. 1991;1:9–11. In summary, alternative epidural dosing strategies may 14. Andrews PJ, Ackerman WE III, Juneja MM. Aortocaval compression in the improve the safety of anesthetic care for mother and fetus. sitting and lateral decubitus positions during extradural catheter placement We have demonstrated that the incidence of maternal hypoten- in the parturient. Can J Anaesth. 1999;40:320–324. sion can be dramatically reduced (67%) with 0.2% ropivacaine 15. Zlatnik FJ. Normal labor and delivery and its conduct. In: Scott JR, DiSaia hydrochloride CEI without bolus dosing. Furthermore, PJ, Hammond CB, Spellacy WN. Danforth’s Obstetrics and Gynecology. 7th ed. epidural administration of 250 ␮g of fentanyl provides hemo- Philadelphia, Pa: JB Lippincott; 1994:107. dynamically stable, rapidly effective relief for breakthrough 16. Cormack RS, Lehane J. Difficult tracheal intubation in obstetrics. Anaes- pain. We favor the early placement of epidural catheters in par- thesia. 1984;39:1105–1111. turient patients who request epidural anesthesia for labor (ide- 17. Mendelson CL. The aspiration of stomach contents into the lungs during ally, at 3 cm of cervical dilatation). This method allows for obstetric anesthesia. Am J Obstet Gynecol. 1946;52:191–205. greater patient comfort and satisfaction while decreasing the 18. LeFrock JL, Clark TS, Davies B, Klainer AS. Aspiration pneumonia: a ten- issues of onset delay and rescue analgesic use. Further studies year review. 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