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Re: FBS and cord blood pHFrom: ainsron (ainsron@sbcglobal.net)Mon May 8 20:12:26 2006
I haven't done a scalp blood sample for 18 years. Even when we did them, they were rarely useful. It was a clumsy procedure, took too long to get the result - by the time it was back, you already needed to have acted on it if it was abnormal. This is the ACOG position from technical bulletin on intrapartum fetal heart rate monitoring, CLINICAL MANAGEMENT GUIDELINES FOR OBSTETRICIAN-GYNECOLOGISTS, NUMBER 70, DECEMBER 2005: * Are there ancillary tests that reassure fetal status? The false-positive rate of EFM is high. There are some ancillary tests available that help to ensure fetal well-being in the face of a nonreassuring FHR tracing, thereby reducing the false-positive rate of EFM. In the case of an EFM tracing with decreased or absent variability without spontaneous accelerations, an effort should be made to elicit one. A meta-analysis of 11 studies of intrapartum fetal stimulation noted that four techniques are available to stimulate the fetus: 1) fetal scalp sampling, 2) Allis clamp scalp stimulation, 3) vibro-acoustic stimulation, and 4) digital scalp stimulation (34). Each of these tests is a reliable method to exclude acidosis if accelerations are noted after stimulation. Because vibroacoustic stimulation and scalp stimulation are less invasive than the other two methods, they are the preferred methods. When there is an acceleration following stimulation, acidosis is unlikely and labor can continue. When a nonreassuring FHR tracing persists and neither spontaneous nor stimulated accelerations are present, a scalp blood sample for the determination of pH or lactate can be considered. However, the use of scalp pH has decreased (35), and it may not even be available at some tertiary hospitals (36). The sensitivity and positive predictive value of a low scalp pH (defined in the study as less than 7.21 because it is the 75th percentile) to predict umbilical arterial pH less than 7 were 36% and 9%, respectively. More importantly, the sensitivity and positive predictive value of a low scalp pH to identify a newborn with hypoxic-ischemic encephalopathy were 50% and 3%, respectively (37). The use of pulse oximetry has been suggested as a modality to reduce the false-positive rate of a nonreassuring FHR tracing. A multicenter randomized clinical trial reported that among term singleton fetuses with nonreassuring FHR patterns, the use of fetal pulse oximetry along with electronic tracing was associated with a significantly lower rate (4.5%) of cesarean delivery for presumed nonreassuring tracing than the controls (10%), who were managed with FHR monitoring alone (38). However, before proceeding with emergent cesarean delivery, most of the patients had not undergone ancillary tests to assess fetal well-being or intrauterine resuscitation, both of which could have decreased the need to proceed with cesarean delivery. Moreover, the randomized trial decreased neither the overall rate of cesarean delivery nor the rate of umbilical arterial pH less than 7. Because of the uncertain benefit of pulse oximetry and concerns about falsely reassuring fetal oxygenation, use of the fetal pulse oximeter in clinical practice cannot be supported at this time. Additional studies to test the efficacy and safety of fetal pulse oximetry are underway. Ronald E. Ainsworth, MD, FACOG -----Original Message----- From: ob-gyn-l@obgyn.net [mailto:ob-gyn-l@obgyn.net] On Behalf Of GA12L@aol.com Sent: Monday, May 08, 2006 2:11 PM To: Multiple recipients of list OB-GYN-L Subject: FBS and cord blood pH In a message dated 08/05/2006 21:38:29 GMT Daylight Time, rmodugno@aol.com writes: We haven't used fetal scalp blood sampling for some time. We define fetal asphyxia as arterial pH less than 7.0 That's interesting. Why do our docs start sweating when the pH is <7.25? If there is any sign of fetal distress they do FBS. So if you had an iffy trace at what point would you bale out. In fact, to all of you. Do any of you do FBS in the face of an unreassuring CTG? What do you all consider to be an acceptable pH? Thanks
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