OB Div News March 2009 Several articles in this month s review have come from Canadian institutions. In spite of my pride in being Canadian, which was enhanced during the Olympics, this is purely coincidental. The ones chosen for review are ones which I think are of value to the practicing OB anesthesiologist. Preventing Hypotension As readers of the OB Div News are aware there has been considerable attention by researchers to preventing spinalinduced hypotension. While more recent studies have focused on the use of vasopressors, such as ephedrine and phenylephrine, others have looked at the effects of hydration. While studies have suggested that a preload of colloid has a degree of effectiveness, a preload of crystalloid has not been found to be of any benefit. The concept of coload, administration of intravenous fluid concomitantly with the onset of the spinal block, has been suggested as an alternate technique. Banerjee et al (Can J Anesth 2010;57:24-31) sought RCTS comparing coload and preload prior to cesarean delivery. The researchers found six manuscripts, one of which was eliminated; they also found 3 references in abstract form. There were a total of 518 subjects. The median quality score was 3 (out of 5). The definition of hypotension varied among the studies (5 used a 20% reduction of systolic BP from baseline, either a 20% reduction or a SBP <100 torr in another study and a decrease in SBP of 10% in two studies). The incidence of hypotension in the coload group was 59.3% compared to 62.4% in the preload group. This led the authors to conclude that timing of fluid loading was not an important determinant of hypotension and this applied to colloid or crystalloid.
George et al (Anesth Analg 2010;110:154-8) have done an updown determination of the 90% effective dose of phenylephrine for the treatment of spinal-induced hypotension. They consented 66 subjects but 1 withdrew as she received atropine prior to spinal anesthesia due to a vasovagal reaction. The investigators performed a standard up-down study beginning with a dose of 100 μg of phenylephrine to treat a decrease in SBP of 20% from baseline. The incremental increase or decrease in phenylephrine was 20 μg. Failure of treatment was persistence of hypotension 1 min after administration of the vasopressor. If that occurred, the attending anesthesiologist could use whatever vasopressor they wanted. Results: 69% developed hypotension and so were treated with phenylephrine. The mean time from IT injection to hypotension was 5.8 +/-3.6 min. The ED 90 for phenylephrine was 147 μg. This dose was 50% higher than their anticipated results. At the time of their study their normal treatment dose was 100 μg. They suggest that use of 150 μg might be more efficacious. Tuffier s Line Pysyk et al (Can J Anesth 2010;57:46-9) have once again looked at the relationship between the intercristal (Tuffier s line) and level as determined by ultrasound in a group of volunteers. These investigators 114 adult subjects who were hospital staff or patients who were seen in the pre-admission unit at Ottawa Civic Hospital. The subjects were position in the sitting position as if undergoing a neuraxial block. The iliac crest was then identified and marked. An ultrasound was then used to 2
determine the level. The palpated Tuffier s line was at the L3-4 interspace in 73% of subjects. When the level was palpated at the L2-3 interspace the subject was more likely to be male and to be taller. Although the majority of subjects were found to have the intercristal line at the L3-4 interspace it is important to remember that in several subjects it was higher. As well, no pregnant subjects were included in this study and pregnancy with its physiological changes may lead to a false identification of the L3-4 interspace. Although this may not be significant in the majority of patients it can be important if one is doing a spinal anesthetic at the L2-3 interspace using the intercristal line to determine one s level. In that circumstance one could be one or two levels higher which would increase the chance that the spinal cord may be present at the site of needle insertion. One might want to review the following articles on this subject: Reynolds F. Damage to the conus medullaris following spinal anaesthesia. Anaesthesia 2001;56:238-47; Broadbent CR, et al. Ability of anaesthetists to identify a marked lumbar interspace. Anaesthesia 2000;55:1122-26 and the others listed in the references of this study. Is Epidural Morphine Indicated after Vaginal Delivery? Epidural morphine has become a standard for postoperative analgesia after cesarean delivery under epidural anesthesia. Some anesthesiologists have also administered epidural morphine following forceps delivery. Now, Macarthur et al (Anesth Analg 2010;110:159-64) have published their doubleblind, randomized, placebo-controlled trial of its use following vaginal delivery. The background to this study was a previous 3
study (Macarthur A, Macarthur C. Am J Obstet Gynecol 2004;191:1199-204) done at their institution they found that women reported difficulty with sitting, urinating because of postpartum pain, even if they had minimal perineal trauma. The investigators approached 1110 women with labor epidural analgesia and randomized 231 (those who did not participate declined, or had cesarean delivery or rapid delivery or allergy to analgesics). Three withdrew after randomization leaving 228 in the study. Of these 113 received epidural morphine and 115 placebo. Of those who delivered vaginally, 1/3 had an operative vaginal delivery and 74% had major perineal trauma. The dose of EM used was 2.5 mg diluted in 10 ml of saline; the placebo was saline. Standard EM orders were used in the 24 h postpartum. All subjects received scheduled acetaminophen and ibuprofen. They could also receive oral codeine or IM morphine as required. The primary outcome was the proportion of women who received opioid analgesia in the 1 st 24 h postpartum. There were several secondary outcomes including side effects of the epidural morphine. In addition to standard demographics they also collected information as to type of vaginal delivery, degree of perineal trauma as recorded in the delivery record, neonatal weight, etc. There was a 78% reduction in the need for postpartum opioid analgesics (p<0.001) in the EM group and this was consistent for nullips as well as multips, and for differing degrees of perineal trauma. Of interest, there was no statistical difference in the incidence of side effects between groups, although the incidence in the EM group was double that in placebo. The most common side effect was urinary retention (10% placebo vs 4
18% EM). As the incidence of side effects was not the primary outcome many more subjects would have been needed to prove statistical difference. In the discussion the authors suggest that their study may have underestimated the benefits of EM as the protocol included regular acetaminophen and NSAIDs. In situations where these are provided on a prn basis there might be a greater effect of EM. The downside of EM is that it requires greater monitoring in the immediate postpartum period. To complete a look at treatment of pain after vaginal delivery one should consider the possibility of chronic pain if it is inadequately treated. Kainu et al (Int J Obstet Anesth 2010;19-4-9) used a questionnaire to evaluate persistent pain after caesarean section and vaginal birth. In that study they found that chronic pain was more common one year postpartum after cesarean delivery compared to vaginal delivery (18% v 10%). Of those with chronic pain 55% of women who delivered vaginally had mild pain while 40% had moderate to unbearable pain (5% did not respond). They found that chronic pain was associated with a history of previous pain, chronic disease and pain after delivery. So this would imply that we should treat acute postpartum pain not only in our cesarean delivery patients but also those who deliver vaginally. This latter article is accompanied by an editorial by Lavand homme (IJOA 2010;19:1-2) and is worthwhile reading. Enjoy! SOGC Clinical Practice Guideline A Clinical Practice Guideline titled Obesity in Pregnancy has been published (JOGC 2010;32:165-73). Recommendation #8 5
states Antental consultation with an anesthesiologist should be considered to review analgesic options and to ensure a plan is in place should a regional anesthetic be chosen. In their discussion on this point they state consideration should be given to early epidural in labor. My perspective is that anesthetic consultation should be mandatory for a morbidly obese parturient and an early epidural should be encouraged. Does fentanyl in the epidural affect breastfeeding? Wilson et al (Anaesthesia 2010;65:145-53) have done a secondary analysis on data accumulated from the COMET trial to see whether epidural fentanyl affects early breastfeeding. For details of the COMET trial see Wilson MJ et al (Anesthesiology 2001;97:1567-75). The authors of this retrospective look found that epidural analgesia with or without fentanyl did not affect initiation of breast feeding. Undoubtedly there will be many more studies looking at the effect of analgesia on breastfeeding. Instead of studies, I would suggest that efforts should be made to ensure that there is adequate lactation consultant support. Other Interesting Articles Green LK, Paech MJ. Obstetric epidural catheter-related infections at a major teaching hospital: a retrospective case series. IJOA 2010;19:38-43. Joanne Douglas, MD Vancouver B.C. 6