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Expansion of Intravascular Volume

Approximately 60% of asphxiated preterm neonates weighing less than 1500 g are hypovolemic at birth because their umbilical cord was clamped and cut earlier than usual (see Fig. 59-6 ) so that resuscitation could begin. Term neonates are hypovolemic if the umbilical cord is clamped early or if the cord is wound tightly around the neck and must be cut to deliver the neonate. Hypovolemia also occurs with intrauterine asphyxia, with placental abruption, or with transection of the placenta during cesarean section.

Detection of Hypovolemia

Hypovolemia is detected by measuring the arterial blood pressure and by physical examination (i.e., skin color, perfusion, capillary refill time, pulse volume, and extremity temperature) ( Table 59-3 ). After 24 hours of age, urine volume and specific gravity measurements are also helpful.

The arterial pressure can be measured with a Doppler system or an indwelling arterial catheter. Table 59-4 shows the systolic, diastolic, and mean arterial pressures (MAPs) during the first 12 hours after birth. An increase in arterial pressure should occur with increasing gestational age. MAP is a more useful determinant of the adequacy of intravascular volume than the systolic or diastolic pressure. Cordero and coworkers [95] published the mean arterial blood pressures of neonates weighing less than 600 g.

Central venous pressure (CVP) measurements are helpful in detecting hypovolemia and in determining the

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TABLE 59-4 -- Average systolic, diastolic, and mean arterial blood pressures during the first 12 hours of life in normal infants

Blood Pressures (mm Hg) during the First 12 Hours of Life
Blood Pressure Measures by Birth Weight 1 2 3 4 5 6 7 8 9 10 11 12
Birth weight 1001–2000 g











   Systolic 49 49 51 52 53 52 52 52 51 51 49 50
   Diastolic 26 27 28 29 31 31 31 31 31 30 29 30
   Mean 35 36 37 39 40 40 39 39 38 37 37 38
Birth weight 2001–3000 g











   Systolic 59 57 60 60 61 58 64 60 63 61 60 59
   Diastolic 32 32 32 32 33 34 37 34 38 35 35 35
   Mean 43 41 43 43 44 43 45 43 44 44 43 42
Birth weight >3000 g











   Systolic 70 67 65 65 66 66 67 67 68 70 66 66
   Diastolic 44 41 39 41 40 41 41 41 44 43 41 41
   Mean 53 51 50 50 51 50 50 51 53 54 51 50

adequacy of fluid replacement. Changes in CVP are more important than a single CVP determination. The venous pressure of normal neonates is 4 to 8 cm H2 O. If the CVP is less than 4 cm H2 O, hypovolemia should be suspected.

Hypovolemic neonates are usually pale and have poor capillary refill and poor skin perfusion. Their extremities are cold, and their pulses (especially the radial and posterior tibial pulses) are weak or absent. Neonates who are intoxicated with alcohol or magnesium are usually pink, peripherally dilated, and hypotensive and may be acidotic.

Treatment of Hypovolemia

The key to treating hypovolemia is intravascular volume expansion. This can best be done with blood, but plasma and crystalloid are also used for this purpose. Albumin can also be used, but the evidence for its effectiveness is limited. If it is suspected that the neonate will be hypovolemic at birth, maternal blood should be crossmatched against 1 unit of type O, Rh-negative packed red blood cells and 1 unit of type O, Rh negative whole blood. Both units of blood should be brought to the delivery room in separate "cold packs" (i.e., sealed plastic ice chest containing dry ice) just before the neonate is born. If blood is not needed, it can be returned unopened to the blood bank within 4 hours.

If crossmatched blood is not available at the time of delivery, the placenta can be cleansed with iodine and blood can be withdrawn from the umbilical vein and artery with sterile syringes containing 1 to 2 units of heparin per 1 mL of blood collected. These vessels usually contain a large amount of blood, especially if the umbilical cord was clamped immediately after birth.[58] The blood should be passed through a blood filter before it is given to the neonate; this eliminates blood clots and debris. There is no concern about incompatibility of blood types because blood from the umbilical cord was part of the circulating blood volume of the neonate before the umbilical cord was clamped. We usually reserve transfusing placental blood for emergencies for fear of causing an infection, although this has never occurred. If no source of blood is available (or is not required because of an adequate hematocrit level), the intravascular volume can be expanded with 10 mL/kg of normal saline, 1 to 2 g/kg of 25% albumin, or 10 mL/kg of plasma.

Occasionally, enormous volumes of blood are required to raise the arterial blood pressure to normal levels. Rarely, more than 50% of the blood volume (85 mL/kg) in term neonates and 100 mL/kg in preterm neonates must be replaced ( Fig. 59-10 ). This is especially true if the placenta is transected during a cesarean section. However, in most cases, less than 10 to 20 mL/kg can restore a normal MAP.

Besides indicating the absolute arterial blood pressure, the arterial pressure tracing provides other information helpful to the evaluation of the adequacy of intravascular volume. A decrease in systolic pressure of more than 5 mm Hg with each inspiration suggests that the neonate is hypovolemic (see Fig. 59-10 ). It can also be seen that increasing the blood volume eliminates the swings in arterial pressure induced by inspiration.

Care must be taken not to overexpand the intravascular volume and cause hypertension, especially in preterm neonates. Hypertension may disrupt the intracerebral vessels and cause intracranial hemorrhage[96] if cerebrovascular autoregulation is absent,[97] [98] which it usually is in asphyxiated neonates. [99] [100] [101]

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