Perinatal/Neonatal Casebook ⅢⅢⅢⅢⅢⅢⅢⅢⅢⅢⅢⅢⅢⅢ Umbilical Cord Blood Gases Casebook
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Perinatal/Neonatal Casebook nnnnnnnnnnnnnn Umbilical Cord Blood Gases Casebook Jeffrey Pomerance, MD, MPH, Section Editor d) Umbilical gases are within normal limits—likely presence of Contributed by Jeffrey Pomerance, MD, MPH cystic adenomatoid malformation (CAM); e) Umbilical gases are within normal limits—likely presence of This is the sixth casebook in a series that provides basic informa- Potter’s syndrome with hypoplastic lungs with or without uni- tion designed to be helpful to the clinician responsible for inter- lateral or bilateral pneumothoraces. preting umbilical cord blood gases. The series of umbilical cord blood gases is drawn from actual patients. The information is DENOUEMENT AND DISCUSSION presented in a sequential format to facilitate progress in expertise. Interpreting Umbilical Cord Blood Gases, VI Normal umbilical cord blood gas values are provided again The best interpretation for this case is “e.” Each choice is explained for assistance in interpreting the values in the case presented below. (Table 1). a) This answer is possibly correct; it is just not the best answer. The CASE REPORT history of only a “small amount” of amniotic fluid when the membranes ruptured, together with the presence of variable The mother was a 27-year-old, gravida 2, para 1, aborta 0 with an decelerations, suggests decreased amniotic fluid volume (see intrauterine pregnancy at 40 weeks’ gestation. The mother re- “e”). Poor response to resuscitation should always trigger con- ported spontaneous rupture of membranes 5 hours before admis- sideration of misplacement, dislodgment, or occlusion of the sion. A small amount of clear fluid was said to have passed. The endotracheal tube. fetal heart rate monitor showed mild variable decelerations. Over b) The umbilical cord blood gases are normal. the next several hours, the patient’s cervix became completely c) This answer is possibly correct; it is just not the best answer. The dilated and effaced and the head was at a 12 station. The fetal history of only a “small amount” of amniotic fluid when the heart rate monitor revealed moderate to severe variable decelera- membranes ruptured, together with the presence of variable tions. The infant was delivered vaginally 30 minutes later. Apgar decelerations, suggests decreased amniotic fluid (see “e”). CDH scores were 2, 2, and 3 at 1, 5, and 10 minutes, respectively. is sometimes associated with an increased amount of amniotic Cord blood gases (all given as pH/PCO /PO /base excess) were 2 2 fluid, as the upper gastrointestinal tract may become obstructed as follows: umbilical vein, 7.31/44/19/23; by its malposition in the chest. In infants with CDH, the abdo- umbilical artery, 7.26/53/14/24. men may appear scaphoid when significant amounts of the A pediatric resuscitation team was present at the time of deliv- intestine or liver reside in the chest rather than in the abdomen. ery. The infant was intubated and bag ventilated with 100% oxy- When CDH is on the left side, as it is in 90% of infants,1 the heart gen. After 30 minutes, the infant’s arterial blood gas was 6.92/87/ sounds may be heard better on the right. CDH with or without 19/219. associated unilateral or bilateral pneumothoraces should be Considering this case, pick the single best interpretation of the considered in a baby who presents as in this case. A chest X-ray umbilical cord blood gases from the following choices. with a tube into the stomach is usually diagnostic. a) Umbilical gases are within normal limits—likely esopha- d) This answer is possibly correct; it is just not the best answer. geal intubation; CAM is usually unilateral2 and does not impinge on the con- b) Umbilical artery gas with mild respiratory acidosis and mild tralateral side; therefore, the infant is usually capable of being hypoxemia of short duration—likely esophageal intuba- successfully resuscitated. A small subset of infants with CAM tion; have extensive lung disease and resuscitation may be problem- c) Umbilical gases are within normal limits—likely presence atic.AchestX-rayisessentialtomakethediagnosisofCAM.The of congenital diaphragmatic hernia (CDH); history of only a “small amount” of amniotic fluid when the membranes ruptured, together with the presence of variable decel- Greater Baltimore Medical Center, Baltimore, MD. erations, suggests decreased amniotic fluid volume (see “e”). Address correspondence and reprint requests to Jeffrey Pomerance, MD, MPH, Greater Balti- e) This is the correct answer. Making the diagnosis of hypoplastic more Medical Center, 6701 North Charles Street, Room 2358, Baltimore, MD 21204. lungs in the delivery room is difficult. One must take advantage Journal of Perinatology (1999) 19(8) Part 1, 608–609 © 1999 Stockton Press. All rights reserved. 0743–8346/99 $12 608 http://www.stockton-press.co.uk Umbilical Cord Blood Gases Casebook Pomerance Table 1 Normal Umbilical Cord Blood Gas Values* otic fluid, such as squames and hair intermixed with sebum, form nodules on the placental surface, may rarely extend onto Venous blood Arterial blood the membranes as well, and are never found on the umbilical 3 pH 7.35 6 0.05 7.28 6 0.05 cord surface. These nodules are on the fetal side and may be 6 6 PCO2 38 5.6 49 8.4 dislodged by light pressure with a gloved fingernail. Finding 6 6 PO2 29 5.9 18 6.2 amnion nodosum on the placenta suggests the presence of Base excess† 24 6 2 24 6 2 severe prolonged oligohydramnios and provides a likely expla- 2 6 6 HCO3 20 2.1 22 2.5 nation for the infant’s poor response to resuscitation (i.e., *From Yeomans et al.4 (146 infants born vaginally). Used with permission. Data are mean pulmonary hypoplasia). Unilateral or bilateral pneumothora- values 6 SD. ces are a common sequela of attempting to ventilate hypoplas- †Calculated from data. tic lungs. Whenever an infant does not respond to resuscitation as one would anticipate, one must consider problems with the endotracheal tube, primary pneumothorax, and other less of every clue, including history, physical examination of both common problems such as severe anemia, severe hypovolemia, the infant and the placenta, and response to intervention. In CDH, and a small percentage of infants with CAM, to name a this case, helpful historical clues might have included a de- few. This infant had Potter’s syndrome and oligohydramnios creased fundal height for gestational age in addition to the sequence established at autopsy. The diagnosis was strongly history of decreased amniotic fluid. Historical clues provided by suspected clinically on the basis of a history of a small amount the patient sometimes are given less credence than those pro- of amniotic fluid, amnion nodosum, a Potter’s facies and vided by healthcare professionals. This is not a wise practice. other associated deformations, and a poor response to appro- Rupturing one’s membranes in a public place is a special fear priate resuscitation. of many pregnant women, as it may be very embarrassing. Therefore, it is unlikely that a woman would underestimate the amount of amniotic fluid or simply not pay much attention to References this event. The physical examination of the infant with hypo- 1. Hartman GE, Boyajian MJ, Choi SS, Eichelberger MR, Newman KD, Powell DM. plastic lungs secondary to Potter’s syndrome is usually remark- General surgery. In: Avery GB, Flethcher MA, MacDonald MG, editors. Neonatol- able for a flat facies, low-set and malformed ears, multiple ogy, Pathophysiology, and Management of the Newborn. 5th ed. Philadelphia: contractures, dislocated hips, and clubbed feet. Except for the Lippincott Williams and Wilkins; 1999. p. 1005–44. ear deformities, these findings are a consequence of decreased 2. Miller MJ, Fanaroff AA, Martin RJ. Respiratory disorders in preterm and term room for movement secondary to severe oligohydramnios (oli- infants. In: Neonatal-Perinatal Medicine. 6th ed. Vol 2. St. Louis: Mosby; 1997. p. gohydramnios sequence). Pulmonary hypoplasia is likely sec- 1040–65. ondary to external compression of the chest and the developing 3. Benirschke K, Kaufman P. Pathology of the Human Placenta. 2nd ed. New York: lungs. In addition, careful examination of the placenta may be Springer-Verlag; 1990. p. 160–2. extremely rewarding. Severe, prolonged oligohydramnios re- 4. Yeomans ER, Hauth JC, Gilstrap LC III, Stickland DM. Umbilical cord pH, PCO2, sults in a condition known as amnion nodosum, Greek for and bicarbonate following uncomplicated term vaginal deliveries. Am J Obstet bumps on the amnion. Material normally suspended in amni- Gynecol 1985;151:798–800. Journal of Perinatology (1999) 19(8) Part 1, 608–609 609.