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ORIGINAL CONTRIBUTION |
From the Department of Anesthesiology (Dr Gerhardt) at Ohio State University 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.
Address correspondence to Robert J. Miller, DO, William Jennings Bryan Dorn Veterans Hospital, 6439 Garners Ferry Rd, Columbia, SC 29209-1638. E-mail: robert.miller5{at}va.gov
Context: Epidural anesthesia for labor pain is frequently complicated by maternal hypotension.
Objective: To test whether continuous epidural infusion (CEI) of local anesthetic, without bolus administration, lowers the incidence of hypotension in parturient patients.
Methods: In a single-blind clinical study, subjects were randomly assigned
to CEI-only (10 mL/h of 0.2% ropivacaine hydrochloride without bolus) or
control (10 mL of 0.2% ropivacaine hydrochloride per hour with 10-mL bolus)
epidural dosing groups. The incidence of hypotension (20% decrease in systolic
blood pressure or mean arterial pressure (MAP), systolic blood pressure lower
than 100 mm Hg, or MAP lower than 65 mm Hg) was recorded for 2 hours after
dosing. Statistical analysis included a 2x2 
2 analysis,
the Fisher exact test, and paired two-tailed t tests.
Results: Fifty subjects were studied, with 25 randomly assigned to each study group (CEI-only vs control). Baseline blood pressure was not different between groups (CEI-only, 127 [11]/77 [8.7] mm Hg; control, 131 [14]/78 [2]). The incidence of hypotension was lower in the CEI-only group than in the control group (5 [20%] vs 15 [60%]; P=.009), with intervention required in 1 (20%) of 5 CEI-only subjects and 7 (47%) of 15 control subjects. Sensory block reached the T10 dermatome in 54.4 (18) minutes in the CEI-only group and 38 (24) minutes in the control group (P=.04). Pain scores and maternal and fetal pulse rates were not different between groups. Analgesic supplementation (250 µg of epidural fentanyl) was used more frequently in the CEI-only group (72% vs 32%; P=.01), without adverse effects.
Conclusions: Continuous epidural infusion of 0.2% ropivacaine hydrochloride without bolus administration reduces the incidence of hypotension by 67% and is safer than traditional bolus dosing for routine labor. This method requires further study in high-risk patients, including those with preeclampsia and cardiovascular disease.
Epidural anesthesia is routinely administered with bolus dosing of local anesthesia (LA) followed by either continuous epidural infusion (CEI) or repeated bolus doses. Hypotension may occur as a result of anesthesia-induced sympathectomy, usually associated with neuraxial administration of LA.5,6 In anticipation of the increase in venous capacitance, preemptive administration of a fluid bolus before LA is delivered. Although this practice is generally safe, hypotension develops in many patients despite the fluid bolus.7,8
Alternative dosing regimens that decrease the incidence and/or extent of the hypotension require development. We hypothesized that CEI of LA, without bolus administration, will result in a lower incidence of hypotension than the bolus 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 perception of pain with CEI-only vs CEI with bolus dosing.
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Methods |
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Each subject received a 750-mL crystalloid bolus intravenously before placement of a lumbar epidural catheter via the loss-of-resistance technique. All catheters were placed 6 cm into the epidural space without a test dose of LA with epinephrine. All subjects received 0.2% ropivacaine hydrochloride delivered by a Baxter APII pump (Baxter; Deerfield, Ill). The control group received bolus administration of epidural anesthesia (10 mL of 0.2% ropivacaine hydrochloride) followed 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.
Maternal blood pressure (BP) and maternal and fetal pulse rates were recorded every 5 minutes for 2 hours. The first measurement was obtained immediately before epidural dosing (baseline) between uterine contractions. Hypotension was prospectively defined as (1) a 20% decrease in systolic BP and/or mean arterial pressure (MAP); and/or (2) systolic BP less than 100 mm Hg or MAP less than 65 mm Hg.
Discomfort was assessed every 5 minutes using a visual analog scale (VAS), where 1 indicated pain free and 5, severe pain. In cases of moderate to severe pain ratings on two or more successive evaluations after initiation of epidural anesthesia, subjects were given adjunctive fentanyl (250 µg) epidurally. The level of epidural anesthesia was evaluated by pin-prick discrimination every 5 minutes. All other aspects of patient care were unchanged.
All data were collected prospectively. The incidence of hypotension was
tested using a 2x2 2 analysis, with a Fisher exact test
for categoric variables. A paired, two-tailed t test was used to
evaluate differences between groups. Significance was established at an
level of .05. Data are given as mean (SD) unless otherwise
indicated.
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Results |
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The baseline systolic BP, diastolic BP, and MAP were not different between groups (Figure 1). In the control group, all successive BP levels were lower than those in the CEI-only group. The difference was statistically significant at 15 minutes (P=.03). A significant difference was noted in systolic BP and MAP at 20 minutes (P=.04). The systolic BP readings were significantly lower in 15 (71%) of 21 control subjects between 20 and 120 minutes. At 50 minutes, the mean systolic BP in the CEI-only group declined 3% (4 mm Hg) compared with baseline levels (123 [14]/73 [11] mm Hg) (P=.01), and the control group systolic BP had declined about 11% (117 [13] mm Hg) from baseline levels.
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Treatment for hypotension was administered to 7 of 15 subjects in the
control group and to 1 subject in the CEI-only group (P=.6). More
subjects in the control group had greater and longer-lasting decreases in BP
compared with the CEI-only group
(Figure 1). One
subject in the CEI-only group and 5 in the control group did not receive
intervention for hypotension despite marked (
25% or systolic BP <100 mm
Hg) and/or prolonged (10 minutes) BP decreases. If analyzed on an
intent-to-treat basis, 40% of the CEI-only group and 80% of the control group
would have received treatment (P=.13). It is common practice to
administer fluid or ephedrine immediately in obstetric patients who complain
of nausea/emesis. No patients met criteria for hypotension secondary to
symptomatic therapy of nausea/emesis.
Maternal pulse rates remained unchanged during the study in both the CEI-only and control groups. Although statistical significance was demonstrated between the two groups at three time intervals, no pattern or clinical significance can be attributed to this observation. Furthermore, these data points were not different when compared with the baseline for each group (CEI-only, 83.0 [8.7]; control, 88.9 [16]). Fetal pulse rates were similar over time within and between groups. The baseline fetal pulse rates were 138 (8.3) and 142 (10) beats/min in the CEI-only and control groups, respectively.
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Rescue analgesia was provided by epidural administration of 250 µg of fentanyl. This adjuvant analgesia was used more frequently (72% vs 32%) and earlier (17.6 vs 32.5 minutes) in the CEI-only group. Fifty-eight percent of CEI-only subjects received fentanyl within the first 20 minutes. Figure 2 shows the VAS scores at the time of fentanyl administration (baseline) and every 5 minutes for 20 minutes. In the CEI-only group, the VAS decreased from 4.2 (1.0) to 3.2 (1.2) at 5 minutes (P<.001). In the control group, the VAS decreased from 3.7 (1.1) to 2.7 (1.0) (P=.007) 5 minutes after fentanyl was administered. The mean VAS continued to decline over the next 20 minutes to a nadir of 1.6 (0.60) and 1.6 (0.74) for the CEI-only and control groups, respectively. There were no associated changes in maternal BP or fetal pulse rate after fentanyl (Table 2).
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One subject from the control group continued to report pain and requested additional analgesia 15 minutes after the first rescue dose, which was given at 40 minutes. She received a second fentanyl dose (250 µg) at 55 minutes and reported relief after receiving a 20-minute infusion of 500 µg of fentanyl. This subject met criteria for hypotension after the second dose of fentanyl, but because she received bolus dosing of LA, it is difficult to conclude what factor(s) contributed to the hypotension. No fetal pulse rate changes were noted, though she did require diphenhydramine hydrochloride for pruritus.
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Comment |
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Technical complications associated with epidural anesthesia include inadvertent dural puncture and anatomic factors that hinder successful catheter placement (eg, morbid obesity). Increased venous capacitance resulting from the inhibited sympathetic outflow12 and maternal hypotension are physiologic complications. Because maternal hypotension is so prevalent, proper positioning and prophylactic intravenous fluids before dosing of the epidural catheter are measures that should be taken for all parturient patients.13,14 Many patients (60% in our control group) will still become hypotensive and may require treatment with ephedrine or supplemental fluid. The safest method of epidural anesthesia during lablor would appear to be placement and initiation of 0.2% ropivacaine hydrochloride infusion without a bolus dose at 3 cm of cervical dilatation.15 This method would take advantage of the safety features we observed and limit maternal discomfort.
Maternal hypotension requires rapid treatment. Decreased perfusion in brainstem structures results in nausea, vomiting, and syncope, and thus, increased risk of aspiration. Anesthesiologists empirically treat patients for nausea and vomiting with ephedrine, often while determining BP.16–18 Difficulties with intubation and aspiration are the leading causes of anesthesia-related mortality in parturient patients.
The decrease in uterine blood flow also places the fetus at great risk.19 Maternal hypotension may be more deleterious than umbilical cord compression, as it may attenuate fetal compensatory responses.20 Histologic neuronal damage and fetal cerebral infarction have been associated with the degree of maternal hypotension but not hypoxia.21–23 Fetal subendocardial injury is another complication of maternal hypotension.24
High-risk parturient patients with PIH may benefit from the no-bolus CEI dosing method. Pregnancy-induced hypertension is observed in about 8% of pregnant women25 and is the leading cause of maternal morbidity.26 Blood pressure control in this population improves both maternal and fetal outcomes.27
Inadvertent intrathecal placement must be considered when inserting epidural catheters, including established catheters. Slow administration of ropivacaine via CEI allows greater time to verify correct placement. Furthermore, the isobaric nature of the commercially available 0.2% ropivacaine hydrochloride may limit cephalad spread and provide a margin of safety for inadvertently placed intrathecal catheters.
A variety of LA types and dosing regimens have been used in obstetric anesthesia. Ropivacaine has distinct advantages with respect to patient safety and pharmacologic properties.28,29 Although structurally and pharmacodynamically similar to bupivacaine hydrochloride, ropivacaine has greatly reduced cardiotoxic properties compared with bupivacaine.30,31 Ropivacaine may produce fewer central neurologic symptoms compared with lidocaine hydrochloride when administered systemically.28,29 Ropivacaine has greater effects on sensory fibers than on motor fibers.28 Obstetric patients can thus be given less concentrated LA solutions so that motor function is preserved while analgesia is sustained. Several variations of bolus dosing regimens have been evaluated but have not been found to reduce the risk of maternal hypotension.8 Karinen et al32 observed that administration of the initial bolus in divided doses rather than in a single large dose did not alter the hemodynamic changes associated with epidural initiation. Variation of the CEI rates of ropivacaine from 2 mL/h to 10 mL/h following bolus dosing did not reduce the need for top-up doses in parturient patients.29
The technique used in the current study has several limitations: lack of a test dose, increased time to effectiveness, and increased need for rescue analgesia. A test dose of LA with epinephrine is often used to rule out intravascular and intrathecal catheter placement.33,34 This practice is not without risk, however, and an epidural test dose is controversial in obstetric anesthesiology.35 Also, intravenous administration of epinephrine reduces uterine blood flow,35 an adverse effect that is of particular importance in patients with PIH.
Another limitation of this method of administration is the longer time to effectiveness of the anesthesia. The time required for the anesthetic level to reach T10 was increased from 38 to 54 minutes. Because our method of rescue analgesia with 250 µg of fentanyl is safe and effective, we believe that the benefit of decreased hypotension outweighs the risk of an additional 16 minutes for the anesthetic level to reach T10 when pain scores are similar.
Subjects in the CEI-only group needed rescue analgesia more often than control subjects. The adjuvant use of fentanyl provides an analgesic therapeutic option for anesthesiologists who use the no-bolus CEI method. Our data show a reduction in VAS from 3.9 to 2.6 during the first 30 minutes in the CEI-only group and no difference in the control group during the same period. Studies have shown that patients may require top-up doses even after the desired anesthetic level is established, perhaps as labor progresses and the S2 to S4 nerves become involved.36–40 One final limitation of our study is that physician bias may have influenced fentanyl administration. However, the goal of this study was to evaluate a potentially safer, hemodynamically stable dosing method for parturient patients.
The rescue dose of fentanyl, 250 µg, delivered epidurally, was used prospectively. Epidural fentanyl (75 µg) has been previously reported to have no effect on fetal pulse rate.41 In contrast, intrathecal fentanyl may result in decreased fetal pulse rate.42 Most anesthesiologists consider intrathecal administration of opioids to have fivefold to tenfold greater potency.42–44 The use of 10 µg to 25 µg of fentanyl intrathecally has been well established in obstetric anesthesiology, especially when used in combination with an epidural catheter.42–44 A 25-µg intrathecal dose translates into a 250-µg epidural dose.
Pruritus was noted in many patients. However, the incidence, duration, and severity of these symptoms in patients receiving intrathecal fentanyl do not correspond to the dose administered.29 It is reasonable to think that the epidural route may produce a similar adverse effect profile.
In summary, alternative epidural dosing strategies may improve the safety of anesthetic care for mother and fetus. We have demonstrated that the incidence of maternal hypotension can be dramatically reduced (67%) with 0.2% ropivacaine hydrochloride CEI without bolus dosing. Furthermore, epidural administration of 250 µg of fentanyl provides hemodynamically stable, rapidly effective relief for breakthrough pain. We favor the early placement of epidural catheters in parturient patients who request epidural anesthesia for labor (ideally, at 3 cm of cervical dilatation). This method allows for greater patient comfort and satisfaction while decreasing the issues of onset delay and rescue analgesic use. Further studies will need to be performed to determine the efficacy of this technique in high-risk obstetric populations.
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Footnotes |
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Submitted March 23, 2006; revision received June 22, 2006; accepted June 27, 2006.
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References |
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2. Christianson RE. Studies on blood pressure during pregnancy. I. Influence of parity and age. Am J Obstet Gynecol.1976; 125:509 –513.[Medline]
3. Pyorala T. Cardiovascular response to the upright position during pregnancy. Acta Obstet Gynecol Scand.1966; 45:(suppl 5):1 –116.[Medline]
4. Assali NS, Prystowsky H. Studies on autonomic blockade. I. Comparison between the effects of tetraethylammonium chloride (TEAC) and high selective spinal anesthesia on blood pressure of normal and toxemic pregnancy. J Clin Invest. 1950;29:1354–1366. Available at: http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=14778899. Accessed November 25, 2006.
5. Grundy EM, Zamora AM, Winnie AP. Comparison of spread of epidural anesthesia in pregnant and nonpregnant women. Anesth Analg. 1978;57:544 –546.[Medline]
6. Sharrock NE. Recordings of, and an anatomical explanation for,
false positive loss of resistance during lumbar extradural analgesia.
Br J Anaesth.1979; 51:253
–258.
7. Kalas DB, Senfield RM, Hehre FW. Continuous lumbar peridural
anesthesia in obstetrics. IV. Comparison of the number of segments blocked in
pregnant and nonpregnant subjects. Anesth Analg.1966; 45:848
–851.
8. Grunewald C, Nisell H, Carlstrom K, Kublickas M, Randmaa I, Nylund L. Acute volume expansion in normal pregnancy and preeclampsia. Effects on plasma atrial natriuretic peptide (ANP) and cyclic guanosine monophosphate (cGMP) concentrations and feto-maternal circulation. Acta Obstet Gynecol Scand. 1994;73:294 –299.[Medline]
9. Crawford JS. Some maternal complications of epidural analgesia for labour. Anaesthesia.1985; 40:1219 –1225.[Medline]
10. Leighton BL, Halpern SH, Wilson DB. Lumbar sympathetic blocks speed early and second stage induced labor in nulliparous women [published correction appears in Anesthesiology. 1999;91:602]. Anesthesiology.1999; 90:1039 –1046.[Medline]
11. Hagadorn-Freathy AS, Yeomans ER, Hankins GD. Validation of the 1988
ACOG forceps classification system. Obstet Gynecol.1991; 77:356
–30.
12. Goodlin RC. Venous reactivity and pregnancy abnormalities. Acta Obstet Gynecol Scand.1986; 65:345 –348.[Medline]
13. Vincent RD, Chestnut DH. Which position is more comfortable for the parturient during identification of the epidural space? Int J Obstet Anesth. 1991;1:9 –11.[Medline]
14. Andrews PJ, Ackerman WE III, Juneja MM. Aortocaval compression in the sitting and lateral decubitus positions during extradural catheter placement in the parturient. Can J Anaesth.1999; 40:320 –324.
15. Zlatnik FJ. Normal labor and delivery and its conduct. In: Scott JR, DiSaia PJ, Hammond CB, Spellacy WN. Danforth's Obstetrics and Gynecology. 7th ed. Philadelphia, Pa: JB Lippincott;1994 : 107.
16. Cormack RS, Lehane J. Difficult tracheal intubation in obstetrics. Anaesthesia.1984; 39:1105 –1111.[Medline]
17. Mendelson CL. The aspiration of stomach contents into the lungs during obstetric anesthesia. Am J Obstet Gynecol.1946; 52:191 –205.
18. LeFrock JL, Clark TS, Davies B, Klainer AS. Aspiration pneumonia: a ten-year review. Am Surg.1979; 45:305 –313.[Medline]
19. Venuto RC, Cox JW, Stein JH, Ferris TF. The effect of changes in perfusion pressure on uteroplacental blood flow in the pregnant rabbit. J Clin Invest. 1976;57:938–944. Available at: http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=947960. Accessed November 27, 2006.
20. Cottle MK, Van Petten GR, van Muyden P. Maternal and fetal cardiovascular indices during fetal hypoxia due to cord compression in chronically cannulated sheep. II. Responses to promazine. Am J Obstet Gynecol. 1983;146:686 –692.[Medline]
21. Gunn AJ, Parer JT, Mallard EC, Williams CE, Gluckman PD. Cerebral histologic and electrocorticographic changes after asphyxia in fetal sheep. Pediatr Res.1992; 31:486 –491.[Medline]
22. Mallard EC, Gunn AJ, Williams CE, Johnston BM, Gluckman PD. Transient umbilical cord occlusion causes hippocampal damage in the fetal sheep. Am J Obstet Gynecol.1992; 167:1423 –1430.[Medline]
23. De Haan HH, Gunn AJ, Williams CE, Gluckman PD. Brief repeated umbilical cord occlusions cause sustained cytotoxic cerebral edema and focal infarcts in near-term fetal lambs. Pediatr Res.1997; 41:96 –104.[Medline]
24. Gunn AJ, Maxwell L, De Haan HH, Bennet L, Williams CE, Gluckman PD, et al. Delayed hypotension and subendocardial injury after repeated umbilical cord occlusion in near-term fetal lambs. Am J Obstet Gynecol. 2000;183:1564 –1572.[Medline]
25. Cunningham FG, Lindheimer MD. Hypertension in pregnancy [review]. N Engl J Med.1992; 326:927 –932.[Medline]
26. Grimes DA. The morbidity and mortality of pregnancy: still risky business. Am J Obstet Gynecol.1994; 170(5 pt 2):1489 –1494.[Medline]
27. Sibai BM. Treatment of hypertension in pregnant women [review].
N Engl J Med.1996; 335:257
–265.
28. Markham A, Faulds D. Ropivacaine. A review of its pharmacology and therapeutic use in regional anaesthesia. Drugs.1996; 52:429 –449.[Medline]
29. Cascio MG, Gaiser RR, Camann WR, Venkateswaran P, Hawkins J, McCarthy D. Comparative evaluation of four different infusion rates of ropivacaine (2 mg/mL) for epidural labor analgesia. Reg Anesth Pain Med. 1998;23:548 –553.[Medline]
30. Santos AC, Arthur GR, Pedersen H, Morishima HO, Finster M, Covino BG. Systemic toxicity of ropivacaine during ovine pregnancy. Anesthesiology.1991; 75:137 –141.[Medline]
31. Moller R, Covino BG. Cardiac electrophysiologic properties of bupivacaine and lidocaine compared with those of ropivacaine, a new amide local anesthetic. Anesthesiology.1990; 72:322 -329.[Medline]
32. Karinen J, Makarainen L, Alahuhta S, Jouppila R, Jouppila P. Single bolus compared with a fractionated dose injection technique of bupivacaine for extradural Caesarean section: effect on uteroplacental and fetal haemodynamic state. Br J Anaesth. 1996;77:140–144. Available at: http://bja.oxfordjournals.org/cgi/reprint/77/2/140. Accessed November 27, 2006.
33. Moore DC, Batra MS. The components of an effective test dose prior to epidural block. Anesthesiology.1981; 55:693 –696.[Medline]
34. Norris MC, Fogel ST, Dalman H, Borrenpohl S, Hoppe W, Riley A. Labor epidural analgesia without an intravascular "test dose." Anesthesiology.1998; 88:1495 –1501.[Medline]
35. Mulroy M, Glosten B. The epinephrine test dose in obstetrics: note the limitations. Anesth Analg. 1998;86:923–925. Available at: http://www.anesthesia-analgesia.org/cgi/reprint/86/5/923. Accessed November 27, 2006.
36. Phillips KC, Thomas TA. Second stage of labour with or without extradural analgesia. Anaesthesia.1983; 38:972 –976.[Medline]
37. Johnsrud ML, Dale PO, Lovland B. Benefits of continuous infusion epidural analgesia throughout vaginal delivery. Acta Obstet Gynecol Scand. 1988;67:355 –358.[Medline]
38. Chestnut DH, Bates JN, Choi WW. Continuous infusion epidural analgesia with lidocaine: efficacy and influence during the second stage of labor. Obstet Gynecol.1987; 69(3 pt 1):323 -327.[Medline]
39. Chestnut DH, Vandewalker GE, Owen CL, Bates JN, Choi WW. The influence of continuous epidural bupivacaine analgesia on the second stage of labor and method of delivery in nulliparous women. Anesthesiology.1987; 66:774 –780.[Medline]
40. Chestnut DH. Epidural anesthesia and instrumental vaginal delivery. Anesthesiology.1991; 74:805 –808.[Medline]
41. Viscomi CM, Hood DD, Melone PJ, Eisenach JC. Fetal heart rate
variability after epidural fentanyl during labor. Anesth
Analg. 1990;71:679
–683.
42. Honet JE, Arkoosh VA, Norris MC, Huffnagle HJ, Silverman NS,
Leighton BL. Comparison among intrathecal fentanyl, meperidine, and sufentanil
for labor analgesia. Anesth Analg.1992; 75:734
–739.
43. Gaiser RR, Cheek TG, Gutsche BB. Comparison of three different doses of intrathecal fentanyl and sufentanil for labor analgesia. J Clin Anesth. 1998;10:488 –493.[Medline]
44. Rawal N, Van Zundert A, Holmstrom B, Crowhurst JA. Combined spinal-epidural technique [review]. Reg Anesth.1997; 22:406 –423.[Medline]
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