The CBET exam assesses knowledge on such a wide range of topics. Yet, rarely do I find CBET preparation information on fetal monitoring. This article will explore a little more on this technology.
Before I discuss this technology, I would like to say thank you to J. Scot Mackeil, CBET, at the MGH anesthesia clinical engineering department for his recent comments he sent me about the last “ICC Prep” article on the basics of anesthesia. Mr Mackeil stated, “Anesthesia service is little different from supporting most other modalities in our field. There is an undeserved mystique surrounding the service of this modality. Anesthesia service is really quite elementary once you get over the initial barriers and ‘join the club.’ The same service problems happen all the time. Use errors, replaceable sensors, leaks, and user damage are the bulk of the issues.” It has been my experience that Mr Mackeil is correct in his assessment of servicing this very important clinical equipment modality. To perform well on the CBET exam, one must know some basics of anesthesia service, as most exams will ask a couple of questions about anesthesia machines. Once again, thank you, Mr Mackeil.
The Purpose of Fetal Monitoring
Clinicians perform fetal monitoring to analyze the condition of the fetus during labor, and, it represents a major determining factor in whether or not to perform a cesarean section. Two major parameters are monitored to determine if the labor process is putting the fetus in distress: fetal heart rate and uterine contractions (or uterine activity). Fetal monitors will graph these two parameters on a single sheet of thermal recording paper at an extremely slow speed, usually 3 cm per minute. Heart rate is determined using an ultrasound transducer or by direct fetal ECG monitoring using a scalp electrode, and uterine contractions by using a tocodynamometer—or toco—transducer, which is a stain gauge transducer.
As the primary way to establish fetal heart rate, ultrasound technology sends ultrasound waves to the fetus in utero and it is determined by Doppler shifts in the sound wave created by the beating of the fetal heart. As the heart expands and contracts during the pumping of blood, it creates the Doppler shift in the ultrasound wave. Each Doppler shift detected is a fetal heartbeat and is much higher than a normal adult resting heart rate. A “normal” adult heart rate is around 72 beats per minute, while a normal fetus heart rate should run in the range of 120 to 160 beats per minute. This range of fetal heart rate is referred to as “variability” in fetal monitoring and is normal during labor—as long as the heart rate does not decrease or increase out of this normal range for extended periods such as 15 minutes or more. If the heart rate does change for extended periods, this will be referred to as a shift in fetal heart rate baseline, which can change clinical treatment of the labor process. Change in the fetal heart rate can be an indication of fetal hypoxia, which can create neurological disorders in the fetus and is the greatest reason for using this technology during child labor.
The other technology used to determine fetal heart rate is by direct fetal monitoring using a scalp electrode. The scalp electrode is inserted vaginally and is attached to the scalp of the fetus by a tiny metal electrode, which is screwed into the skin on the fetus’ head and is then attached to a leg plate, which is strapped to the mother’s leg.
Contractions are measured in mm/Hg using the toco transducer and are referred to as uterine activity or uA. As contractions are experienced, the mother’s abdomen becomes very rigid and pushes against the toco transducer, which is attached to the mother’s abdomen by a Velcro strap. Changes in the resistivity of this type of transducer are in direct proportion to the pressure of the contraction. This uA waveform is printed on the thermal paper under the fetal heart rate waveform and is used to determine fetal distress.
Clinicians are looking for changes in heart rate in relationship to contractions to determine the fetus’ overall condition and health during labor. Conditions evaluated on fetal monitors are tachycardia, variability, and early and late decelerations in heart rate compared to contractions. Tachycardia is associated with decreased variability and can be an indication of a lack of fetal nourishing blood supply. Late decelerations are when the fetus heart rate decreases right after a contraction and can be an indication of a potentially dangerous condition for the fetus.
Early decelerations are small decreases in heart rate associated with the onset of a contraction or fetal movement, and are normal as long as the fetal heart rate stays in the normal heart rate ranges or no abnormal “variability” is present.
The information provided here is more than likely all the information you may need to answer any certification question about fetal monitoring. I hope you find this information helpful.
John Noblitt, MAEd, CBET, is the BMET program director at Caldwell Community College and Technical Institute, Hudson, NC. For more information, contact .