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  1. Problem. The blood pressure (BP) is >2 standard deviations below normal for age. (For normal BP values, see Appendix C.) It is difficult to state a specific blood pressure for every gestational, postnatal age, and weight of an infant that needs treatment. There is debate over normal blood pressures for extremely premature infants. It is best to treat the patient and not the specific number. Hypotension (diminished BP) is distinct from shock, which is a clinical syndrome of inadequate tissue perfusion with the clinical signs noted below. Hypovolemic shock is the most common cause of shock in a newborn.

  2. Immediate questions

      1. What method of measurement was used? If a cuff was used, be certain that it was the correct width (ie, covering two thirds of the upper arm). A cuff that is too large gives falsely low readings. If measurements were obtained from an indwelling arterial catheter, a "dampened" waveform suggests there is air in the transducer or tubing or a clot in the system, and the readings thus may be inaccurate.

      1. Are symptoms of shock present? Symptoms of shock include tachycardia, poor perfusion, cold extremities with a normal core temperature, lethargy, narrow pulse pressure, apnea and bradycardia, tachypnea, metabolic acidosis, and weak pulse.

      1. Is the urine output acceptable? Normal urine output is ~1–2 mL/kg/h. Urine output is decreased in shock because of decreased renal perfusion. If the BP is low but the urine output is adequate, aggressive treatment may not be necessary, because the renal perfusion is adequate. (Note: An exception involves the infant with septic shock and hyperglycemia who has osmotic diuresis.)

      1. Is there a history of birth asphyxia? Birth asphyxia may be associated with hypotension.

      1. At the time of delivery, was there maternal bleeding (eg, abruptio placentae or placenta previa) or was clamping of the cord delayed? These factors may be associated with loss of blood volume in the infant.

  3. Differential diagnosis. If a blood pressure is felt to be low, evaluate the infant. If the infant is oxygenating, not acidotic, has normal urine output, and good perfusion, treatment is usually not necessary, regardless of the BP. If the infant is symptomatic (acidotic, not oxygenating, poor or decreased urine output, and poor peripheral perfusion) then the infant is probably not perfusing and has a BP that needs to be treated.

      1. Hypovolemic shock may be secondary to antepartum or postpartum blood loss or fluid and electrolyte losses.

          1. Antepartum blood loss (often associated with asphyxia)

              1. Abruptio placentae.

              1. Placenta previa.

              1. Twin-twin transfusion.

              1. Fetomaternal hemorrhage.

          1. Postpartum blood loss

              1. Coagulation disorders (DIC, coagulopathies).

              1. Vitamin K deficiency.

              1. Iatrogenic causes (eg, loss of an arterial catheter).

              1. Birth trauma (eg, liver injury, adrenal hemorrhage, intracranial hemorrhage, intraperitoneal hemorrhage).

              1. Pulmonary hemorrhage.

          1. Fluid and electrolyte losses. Volume depletion is common in premature infants.

      1. Septic shock. Endotoxemia occurs, with release of vasodilator substances and resulting hypotension. It usually involves Gram-negative organisms such as Escherichia coli and Klebsiella spp but can also occur with Gram-positive organisms such as in group B streptococcal and staphylococcal ...

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