Adding oil to the fire- more on epidurals and cesareans - All About Epidural
oil-to-fire

Adding oil to the fire- more on epidurals and cesareans

Date: July 13th, 2013

As shown in the corresponding chapter of this site, currently available evidence convincingly demonstrates that labor epidurals do not increase the risk of cesarean section. Of course, this does not mean that the research in this area should be closed. Emergency cesarean section is associated with various complications and adverse outcomes, and therefore the factors that may potentially increase the risk of surgical intervention should be continuously monitored. The practice of obstetric analgesia continuously evolves, and new techniques may lead to unexpected problems.

An example of such unexpected complication is the introduction of combined spinal-epidural analgesia (CSE), during which the initial dose of local anesthetic mixture is administered through the small spinal needle. As the result the effect of the block is much faster and the quality of the block is considerably better than with the conventional epidural. Soon it was noticed among women receiving CSE fetal heart rate often dropped to critical levels, leading to emergency cesarean section. After careful analysis it was found that the culprit causing this drop was opioid Fentanyl. As the result, the dose of spinal Fentanyl was reduced to the minimum, and the cesarean rate returned to the baseline.

In regards to epidural and cesareans, the relationship is difficult to study because of methodological difficulties, mostly because it is difficult to randomly assign women to epidural and control groups. Therefore the clinicians are forced to rely on the results of inferior kind of evidence, observational studies. The difference between one and the other is explained in detail here. In short, the problem is that the associations between various factors and outcomes established in observational studies do not necessarily mean that these factors are the causes of such outcomes.

As an example consider this fact: most patients presenting to the emergency rooms with heart attacks are over the age of sixty. Most of them also have gray hair. Technically speaking, the presence of gray hair is associated with the higher incidence of heart attacks and, therefore, gray hair is the risk factor for this condition. Does gray hair cause heart attacks? Of course not, the real problem is the atherosclerosis as the result of wear and tear of the blood vessels that comes with age and is the result of multiple other factors, such as accumulated stress, eating habits, lack of exercise and so on. Gray hair is just another consequence of getting older.

The situation with cesareans and epidurals is somewhat similar, and earlier observational studies have found significant association between them. The most important question that must be asked before interpreting these studies is: how were women selected for epidurals? Typically, in labor wards and in such studies labor epidural is either given on request of the woman or when labor is prolonged, obstructed or complicated in other ways, which are associated with increase pain during the process of childbirth. Wait a minute, complicated labor is also an indication for cesarean section! In other words, women that are likely to get labor epidural are also more likely to require cesarean section. This is called selection bias, which plagues many observational studies and makes the results of these studies less credible. In an attempt to reduce bias the researches apply various methods of statistical manipulation of data in order to exclude other factors that may influence the outcome.

New data (not really)

The study published in December last year in one of midwifery journals repeats the pattern. Danish researchers selected 2,721 healthy nulliparous women from various medical centers. All women had low risk of requiring emergency cesarean section. However, to exclude possible bias researchers identified the sub-group of women with very low risk of cesarean, namely women taller than 160 cm, younger than 35 years old, with BMI less than 30 and expecting to have babies weighing less than 4,000 g. This subgroup was termed “risk profile0” and included 837 women.

According to the results of the study, overall 21.6% of women required epidural analgesia. In the subgroup of risk profile0 epidural was needed by 9.6% of women. Overall frequency of emergency cesarean section was 8.6%. More women with epidurals had cesareans (4.4 vs. 24.5%). Among women with risk profile0 the rate of cesareans was very low, 3.4%. However, in this subgroup also the the frequency of cesarean section was higher among those who used epidural compared to women who choose other methods of analgesia (2.3 vs. 13.8%). Women using epidural group were also more likely to require vacuum extraction.

The small print

At first glance the results are striking, to say the least. However, the devil is in the detail. According to the presented data women who used labor epidural were: of shorter stature, were more advanced in their pregnancies, gave birth to heavier infants. They also tended to be heavier and older. At admission to labor ward they were more frequently in the earlier stages of labor with less cervical dilatation and reported more pain. They were also more frequently treated with opioid drug to reduce pain. In other words, most women who required epidurals had higher risk for cesarean section before they received the block.

In conclusion the authors of the article state: “In this well-defined group of low-risk nulliparous women, we found higher risks of emergency caesarean section… among women using epidural analgesia, even in the very low-risk group… As we have performed an observational study, we are not able to draw any conclusion about causal relations.”

Still no news

This study illustrates several important issues related to reading and interpreting clinical research. Observational studies are not very valuable in establishing causal relationship between risk factors and outcomes. The risk of cesarean section is determined by multiple factors, including various physiological and medical parameters of the woman and clinical standards and methodology accepted at a particular hospital. Many of these factors also determine if the woman is likely to request epidural analgesia. As the result, even sophisticated statistical analysis (read “extensive massage of numbers”) is fairly useless in establishing the relationship between the two.

This study also illustrates how easy it is to misinterpret clinical data and get the wrong impression from the abstract of the article if one does not read the text in full. The results of this study could have easily made it into the media, sensationalizing the findings and adding to the confusion of mothers-to-be.

Overall the study contributes to the existing data and confirms what we already know: labor epidural does not increase the risk of cesarean section.

Reference.
Eriksen LM, Nohr EA, Kjaergaard H. Mode of Delivery after Epidural Analgesia in a Cohort of Low-Risk Nulliparas. BIRTH 38:4 December 2011.

Image from: http://www.freedigitalphotos.net/images/view_photog.php?photogid=3506

Dr. Eugene Smetannikov is a practicing anesthesiologist with the interest in obstetric anesthesia. He is the author of the most comprehensive book on the subject, The Truth About Labor Epidural

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