Cord Blood Gases Made Easy
Why draw Cord Blood Gases?
Basically, the reason we draw cord blood gases (CBG) is in case there is a lawsuit years down the road accusing the delivering doctor of causing an anoxic brain injury that resulted in disorders such as cerebral palsy.
The cord blood can prove that neurological deficits that develop in infants were caused by an anoxic brain injury that occurred after delivery or before delivery and was not the result of an anoxic episode at birth. The cord blood gas has been shown to be proof positive in about 80% of the cases (According to PubMed.com), and has in many cases cleared physicians from litigation.
When should a Cord Blood Gas be drawn?
A cord blood gas does not need to be drawn unless a baby is born and has a low APGAR score within 5 minutes of delivery, such as a 3 or less. When the APGAR score is low a cord blood gas should automatically be drawn.
What is a Cord Blood Gas?
When we refer to cord blood we are referring to blood drawn from the placenta after delivery. If you look at a placental cord (see picture below) you will see one large vein surrounded by two arteries that wrap around the vein.
According to PubMed.com, the Umbilical Vein delivers freshly oxygenated blood from the mom to the baby. Since an anoxic brain injury in the baby in not likely to change the pH of the Umbilical Vein, this is not where you will want to draw a cord gas from.
The Umbilical Artery is where the baby's venous circulation dumps unoxygenated blood. This is blood that was on its way back to the mom's heart and lungs to pick up oxygen. Thus, when you draw a cord gas for litigation purposes you will want to draw from one of the two Umbilical Arteries.
Blood from the Umbilical Artery is called a Cord Arterial Blood Gas (CABG), and basically shows how the baby was doing prior to birth.
From this blood we want to watch for acidosis. Since anaerobic metabolism occurs during the absence of oxygen, the acid base balance (pH) of the baby's body increases due to an increase in the amount of lactic acid produced. Therefore pH is the most important indicator in the CABG.
What are acceptable CABG values?
If the pH of the CABG is above 7.10, then we know that the baby was not hypoxic during the delivery, and if there was a hypoxic episode it occurred prior to the delivery process. You know this because the pH had time to normalize.
The anoxic episode may have occurred weeks or months prior to birth, or it may have occurred hours before birth. Either way, this proves the episode did not occur as a result of the delivery and should clear the physician of litigation.
What are critical CABG values?
If the pH is less than 7.10 the episode was more likely acute and the episode may have occurred during the delivery. You know this because the pH did not have time to normalize.
According to obgyn.org, some experts believe a pH of 7.0 with a significant metabolic component is a more significant sign of asphyxia at birth, and may lead to significant neurological dysfunction during life, or possibly even death.
Also according to obgyn.org, "Even when this low pH threshold is used to define significant acidemia, most newborns in this category will be neurologically normal, with no apparent morbidity."
What baby’s are at greatest risk for anoxic brain injuries?
The baby's at greatest risk of anoxic brain injury are premature infants, according to obgyn.org. They are at higher risk of "intracranial hemorrhage and subsequent neurological dysfunction, such as cerebral palsy.
Without umbilical cord blood gas analysis, these neurological complications could be incorrectly attributed to intrapartum or birth asphyxia, especially if the latter is solely based on APGAR scores.
Normal umbilical cord blood values in the premature infant virtually eliminate the diagnosis of significant intrapartum hypoxia or birth asphyxia."
Can you just draw an arterial cord blood gas?
Most experts recommend drawing both arterial and venous gas for the purpose of comparison. One physician suggested “that the cost of approximately $2 per delivery should be absorbed by the hospital as a risk-management measure.
How do draw Cord Blood Gases?Immediately following the delivery of the infant and before placental separation, obtain cord blood gases as follows (refer to pictures below):
· A 6 inch segment of the cord should be isolated between 2 clamps (See figure 2 Below)
· Select two 1cc heparinized blood gas syringes
· Label the two syringes with the patient name and date of birth
· Write on one syringe umbilical vein and the other umbilical artery
· Identify the umbilical vein and umbilical artery
· Grasp one end of the umbilical cord to prevent it from moving
· With your other hand hold the syringe marked umbilical artery as you would hold a pencil
· Prepare to insert the syringe parallel to the artery to avoid passing through the narrow vessel (this is demonstrated in figure 3 below).
· Insert syringe into umbilical artery at a 45 degree angle (Be careful not to go all the way through the artery)
· Pull back slowly on the syringe to allow it to fill with blood
· Ideally we would like at least 1cc, however we need at least 0.3cc of blood
· Remove the needle from the umbilical artery
· Carefully discard the needle
· Remove any air bubbles from the syringe
· Follow the same above steps for drawing blood from the umbilical vein
· Call respiratory therapy to run the samples as soon as possible
What do you do with a cord gas once it is drawn?
Once a CABG and a CAVG has been drawn, hospital policy requires that they be placed on ice, and respiratory therapy should be paged as soon as possible. The samples should ideally be run through the ABG machine within 30 minutes of the draw
What are normal CABG values? What are normal CAVG results?
· pH: 7.27 (range 7.22–7.32) ph: 7.34 (range 7.28–7.40
· pCO2: 50 (range 42–58) PCO2: 40.7 (range 32.8–38.6)
· pO2 18 (range 12–24) pO2: 30 (range 28-32)
· HCO3: 22 (range 24-26) HCO3: 21.4 (range 19-24)
· BE: -2.7 (range –5.5– 0.1) BE: -2.4 (range –4.4-0.4)
The following are conditions that would warrant a CABG:
· Any abnormality during delivery process (prolonged pushing, difficult delivery)
· Low 5 minutes APGAR score (less than 3)
· Any abnormality in patient condition that occurs within 1st 5 minutes after birth
· Premature birth
· Post term birth
· Meconium in amniotic fluid
· Positive pressure ventilation (Neo-puff or bag mask ventilation)
· Severe growth retardation
· Abnormal fetal heart rate tracing
· Maternal thyroid disease
· Intrapartum fever
· multifetal gestation
Conclusion: Essentially, a CABG with a pH of 7.1 or greater can prove the infant was well oxygenated at time of birth, and can clear the delivering physician from litigation.
Umbilical cord blood gases: routine measurement may exonerate ob.gyns
(From OB/GYN News) Dr. Hankins said that following the birth of a baby with Cerebral Palsy (CP), there are many factors that are beyond obstetricians' control in the cascade of events that spiral toward litigation--but doing cord blood studies is not one of them."This is something that is within our hands, but once it escapes you, it is gone. The only opportunity the obstetrician has to obtain this information is going to be right at the moment of birth," said Dr. Hankins, professor of ob.gyn.at the
He recommended that immediately following delivery a segment of the umbilical cord be doubly clamped and placed aside to remain stable for 30 minutes for pH and blood gas assessment.
"[Neither] ACOG nor anyone else has suggested that every baby that's delivered should have cord blood studies, but I say it would be a tremendously positive thing to do and it should get rid of some of this frivolous litigation."
He recommended drawing both arterial and venous gas for the purpose of comparison, and he suggested that the cost of approximately $2 per delivery should be absorbed by the hospital as a risk-management measure.
"It's not subjective; it's pure objective data. If you have a pair of blood gases--arterial and venous--by that alone, and with no other data, I can tell you much of what was happening in that delivery room," he said.
The task force document set the following criteria for the precise definition of an acute intrapartum event sufficient to cause cerebral palsy:
· Evidence of metabolic acidosis in fetal umbilical cord arterial blood obtained at delivery (pH less than 7 and a base deficit of 12 mmol/L).
· Early onset of severe or moderate neonatal encephalopathy in infants born at 34 or more weeks' gestation.
· Cerebral palsy of the spastic quadriplegic or dyskinetic type.
· Exclusion of other identifiable etiologies, such as trauma, coagulation disorders, infectious conditions, or genetic disorders.
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