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Effect of pain relief on progress of labor

Bhavani Shankar Kodali MD

Epidural analgesia minimally lengthens labor and does not increase the risk of cesarean delivery

 

Pregnant women commonly pose questions such as "Does epidural prolong my labor?" " Do I have increased chances of forceps delivery?" These are simple questions but with a very complex answer. The influence of epidural analgesia on the course of labor continues to generate a debate within the anesthesia community and even more so outside of it. The literature is divided on this issue. Obstetricians, midwives, lay labor personnel, patients, hospital administrators, insurance executives, media reporters, and health care policy makers are all participating in this debate. Despite lack of evidence to support their claims, a vocal minority indict epidural analgesia to be an important cause of cesarean delivery.

There are several confounding factors that prevents the scientific community to determine a real answer to this apparently simple question. Some of them are as follows.

  • Ethical issues

A major factor involves ethical issues.  An ideal study (prospective double blind randomized study) would necessitate women coming for childbirth randomly to be divided into two groups. One would receive epidural for childbirth and the other would not.  However, today, it is unethical to deny epidural anesthesia to a woman who requests this type of pain relief.  Moreover, obstetricians may request epidural analgesia when they encounter a possible difficult labor in a woman. Even if women were randomly allocated to each of the two groups, initially, at the beginning of the study, there is a possibility that women can cross over to the epidural group from the I.V method due to inadequate pain relief during the course of the labor. Ethically, one can not deny this request for the sake of a study. 

  • Inability to perform blinded studies:  

Ideally, the evaluators in a study should be blinded to the method of analgesia to eliminate bias. Insurmountable problem is posed by the practical impossibility of blinding patients, obstetricians, nurses, and anesthesiologists to the presence or absence of a functional epidural block.  Because of proceeding with operative delivery is ultimately a subjective, clinical decision made by the obstetrician, the absence of masking may be important. Obstetricians and midwives may not treat their patients with epidural analgesia the same way that they treat those without it.  For example, forceps-assisted delivery may be more common among patients with epidural analgesia, partly because obstetricians know their patients will be comfortable and have relaxed pelvic musculature for the procedure. 

  • Personality differences among women who seek epidural versus who do not:

This is another factor that makes this issue very complex and probably invalidate retrospective studies (studying the outcome of women who received the type of anesthesia based on their choice rather than random allocation). There are inherent differences in the women who seek epidural anesthesia from those who do not. Woman who select epidural analgesia in labor are frequently nulliparous (first baby), tend to come to the hospital earlier in labor,  have their baby much higher in the abdomen, have a big baby, and may have a slow labor itself.  All of these factors contribute towards increasing the duration of labor with or without epidural analgesia.

  • Power of the studies:  

Some of the studies have been severely underpowered meaning that the number of patients in each group were not sufficient enough to really validate the results of the studies. 

Because of several limitations, one has to view the results of any study presented with a pinch of salt. Nonetheless, even in the absence of truly double blind randomized studies with enough power in them, it is possible to draw some conclusions using sophisticated statistical methods (Meta-analysis).

Meta-analysis

In order to overcome the difficulties of an underpowered study (a study with not enough number to strengthen the results of an individual study) a meta-analysis  of several studies (obtaining answers from analyzing several similar studies) was undertaken that showed the following findings:(1)

 

  • Effect of epidural analgesia on cesarean delivery: Meta-analysis of five randomized trials and two others (one preliminary report and an older European trial) that represent the experience of nearly 2400 pregnant women has found no difference in the risk of cesarean delivery between the epidural or opioid analgesia groups. Moreover, the results are unchanged when analyzing only cesarean delivery for dystocia (abnormal cervical dilation or progress of labor) or when analyzing for nulliparous women (women with first pregnancy).
  • Effect of epidural analgesia on length of labor: The effect of epidural analgesia on cervical dilation in established labor is probably minimal. A meta-analysis of 10 randomized studies of epidural analgesia versus opioid analgesia concluded that the first stage of labor was prolonged by an average of 42 minutes (approximately 8%). The mean duration of second stage of labor was only 14 minutes longer for patients receiving epidural analgesia in a meta-analysis of involving six randomized studies.  This translates to a difference of about an hour of longer labor in women in the epidural group when compared to those in the I.V group.  
  • Epidural analgesia and instrumental (forceps deliveries): The relationship between epidural analgesia and forceps deliveries is complex.  The incidence of instrumental vaginal deliveries may be increased by epidural analgesia, although this practice varies tremendously among obstetricians and hospitals .  Meta-analysis of randomized trials found the total instrumental delivery rate to be doubled for patients receiving epidural analgesia, but with a broad confidence interval indicative of wide variation among studies resulting from variations in practice style and preferences among obstetricians. For example, the obstetrician may more likely to perform forceps-assisted delivery  among patients with epidural analgesia, partly because obstetricians know that their patients will be comfortable.
  •  
  • Oxytocin use: Oxytocin is used more frequently in the women receiving the epidural analgesia when compared to the women in the I.V group. Meta-analysis of studies revealed that oxytocin was required after analgesia nearly twice as frequently  in the epidural group.  
  • Patient satisfaction and neonatal outcome: Patient satisfaction and neonatal outcome are better after epidural than I.V method of providing childbirth pain relief. Meta-analysis of studies has shown that pain was much worse and dissatisfaction was much more common in the opioid groups, and low 1- and 5-minute Apgar scores, low umbilical cord pH, and the need for nalaxone treatment all were much more common among neonates born to mothers receiving opioid analgesia. 

 

The final conclusion, therefore, is as follows:

The appearance of several well-conducted, prospective, randomized trials have helped to confirm the opinion of most anesthesiologists and a growing number of obstetricians, that epidural analgesia only minimally lengthens labor and does not increase the risk of cesarean delivery. 

Patients receiving epidural analgesia have longer labors. A difference on an average of about 60 minutes of longer labor in the epidural group as compared with the systemic I.V method.  However, patient satisfaction and neonatal outcome are better after epidural than I.V method of providing childbirth pain relief.

  1. Table 1: Randomized Trials of Epidural vs. opioid analgesia

First author and citation

Rate of C/S for dystocia1

P

 

Epidural group

Opioid group

 

Philipsen

Eur J Obstet Gynecol Reprod Biol 1989; 30:27-33

10/57 (17%)

6/54 (11%)

NS

Thorp

Am J Obstet Gynecol 1993; 169:851-8

8/48 (16.7%)

1/45 (2.2%)

<.05

Ramin2

Obstet Gynecol 1995; 86:783-9

Current Anesth Rep 2000; 2:18-24

43/664 (6%)

37/666 (6%)

NS

Sharma

Anesthesiology 1997; 87:487-94

13/358 (4%)

16/357 (5%)

NS

Bofill

Am J Obstet Gynecol 1997; 177:1465-70

4/49 (4%)

3/51 (3%)

NS

Clark

Am J Obstet Gynecol 1998; 179:1527-33

15/156 (9.6%)

22/162 (13.6%)

NS

Gambling3

Anesthesiology 1998; 89:1336-44

39/616 (6%)

34/607 (6%)

NS

Loughnan

Br J Anaesth 2000; 84:715-9

36/304 (12%)

40/310 (13%)

NS

Howell

Br J Obstet Gynaecol 2001; 108:27-33

13/184 (7%)

17/185 (9%)

NS

Lucas4

Am J Obstet Gynecol. 2001;185:970-5

46/372 (12%)

54/366 (15%)

NS

Table 2:  Sentinel event studies comparing C/S rate before and after a rapid change in epidural availiability

First author and citation

Rate of C/S (epidural rate)

P

 

Low epidural use period

High epidural use period

 

Bailey

Anaesthesia 1983; 38:282-5

7.1% (0%)

9.3% (27%)

NS

Gribble

Obstet Gynecol 1991; 78: 231-34

9.0% (0%)

8.2% (47%)

NS

Larson

SOAP1 abstracts 1992: 13

27.5% (0%)

22.9% (32%)

NS

Mancuso

SOAP1 abstracts 1993: 13

14.9% (19%)

12.3% (67%)

NS

Johnson

J Fam Pract 1995; 40:244-7

18.4% (21%)

17.2% (71%)

NS

Lyon

Obstet Gynecol 1997; 90: 135-141

11.8% (13%)

10.0% (59%)

NS

Fogel

Anesth Analg 1998; 87:119-23

9.1% (1%)

9.7% (29%)

NS

Yancey

Am J Obstet Gynecol 1999; 180:353-9

19.4% (1%)

19.0% (59%)

NS

Impey

Am J Obstet Gynecol 2000;182:358-63

3.8% (10%)

4.0% (57%)

NS

Further reading:

1. Segal S, Birnbach D. Epidurals and cesarean deliveries: A new look to an old problem. Editorial. Anesthesia and Analgesia 2000;94:775.

2. Halpern SH, Leightonm BL, Ohisson A, Barrett JF, Rice A. Effect of epidural vs parenteral opioid analgesia on the progress of labor. JAMA 1996;280;2105.

3. Segal S. Epidrual analgesia and the progress and outcome of labor and delivery. Problems in Anesthesia. 1999;11:324.

4. Thorp JA, Hu DH, Albin RM, et al. The effect of intrapartum epidural analgesia on nulliparous labor: a randomized, controlled, prospective trial. Obstet Gynecol 1993;169:851-8.

5. Ramin SM, Gambling DR, Lucas MJ, Sharma SK et al. Randomized trial of epidural versus intravenous analgesia during labor. Obstet Gynecol 1995;86:783-9.

5. Philipsen T, Jensen NH. Epidural block or parenteral pethidine as analgesic in labor: a randomized study concerning progress in labor and instrumental deliveries. Eur J Obstet Gynecol Reprod Biol 1989;30:27-33.

6. Sharma SK, Sidawi JE, Ramin SM, Lucas MJ, Laveno KJ, et al. Cesarean delivery; a randomized trial of epidural versus patient-controlled meperidine analgesia during labor. Anesthesiology 1997;87:487-94.

7. Bofill JA, Vincent RD, Ross EL, et al. Nulliparous active labor, epidural analgesia, and cesarean delivery for dystocia. Am J Obstet Gynecol 1997;177:1465-70.

8. Clarke A. Carr D. Loyd G, Cook V, Spinnato J.  The influence of epidural analgesia on cesarean delivery rates: a randomized, prospective clinical trial. Am J Obstet Gynecol 1998;179:1527-33.

9. Wong CA. The influence of analgesia on labor- is it related to primary cesarean rates? Semin Perinatol 2012;36:353-6.

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