Pediatric emergency medicine trisk 617

FIGURE 96.2 Neonatal blood pressure norms based on gestational age. A: Systolic blood
pressure norms. B: Diastolic blood pressure norms. (Reprinted with permission by Springer,
from Zubrow AB, Hulman S, Kushner H, et al. Determinants of blood pressure in infants
admitted to neonatal intensive care units: a prospective multicenter study. J Perinatol
1995;15(6):470–479; permission conveyed through Copyright Clearance Center, Inc.)

Hypertension is confirmed after serial accurate measurements reveal consistent
elevations above 95% for age and weight. The most common causes of neonatal
hypertension include umbilical artery catheterization, renovascular disease,


parenchymal renal disease, and chronic lung disease of prematurity. Additionally,
coarctation of the aorta, hyperthyroidism, congenital adrenal hyperplasia (CAH),
and increased intracranial pressure can cause neonatal hypertension and can be
life threatening if left untreated. Most infants with hypertension are
asymptomatic. When symptoms are present, they are often nonspecific (lethargy,
poor feeding, apnea) and do not necessarily correlate with the degree of
hypertension. Initial evaluation should include blood pressure measurement in all
four extremities, urinalysis, urine culture, blood urea nitrogen, serum creatinine,
electrolytes, and calcium. It is important to note that the absence or presence of
hematuria, proteinuria, or azotemia vary in this age group and cannot be used in
isolation to diagnose renovascular disease. If the history and physical
examination are suggestive of endocrine, neurologic, or intoxication causes of
hypertension, additional testing may be needed. Renal ultrasonography (US) with
Doppler evaluation should also be included to evaluate for renovascular and
parenchymal disease. Echocardiography should be considered to assess left
ventricular function. Determining when to institute pharmacotherapy for
hypertension is based on the underlying etiology, severity of hypertension, and
presence of symptoms. The decision to initiate therapy should be done in
consultation with pediatric nephrologist.

FIGURE 96.3 Neonatal blood pressure norms based on birth weight. A: Systolic blood
pressure norms. B: Diastolic blood pressure norms. (Reprinted with permission by Springer,
from Zubrow AB, Hulman S, Kushner H, et al. Determinants of blood pressure in infants
admitted to neonatal intensive care units: a prospective multicenter study. J Perinatol
1995;15(6):470–479; permission conveyed through Copyright Clearance Center, Inc.)

Hypotension in a neonate can result from volume depletion, hemorrhage,
sepsis, or cardiac failure. Detecting hypotension in the preterm or SGA infant can
be challenging, as noninvasive monitoring can routinely overestimate blood
pressure values. It is imperative to treat hypotension aggressively to prevent end-


organ damage and multisystem organ failure. First-line treatment is to provide
intravascular replacement with iso-osmotic fluids, typically normal saline, or
packed red blood cells in the setting of acute hemorrhage. Typical resuscitation
volumes are 10 mL/kg over 30 minutes, with more judicious use in the premature
infant. Excessive volume expansion in the preterm neonate is associated with
higher morbidity; therefore early administration of pressors is necessary if there is
a limited response to volume. Treatment of hypotension should be directed at
improving perfusion and cardiac function, rather than aiming for a desired blood
pressure value. This is of particular importance in conditions that widen the pulse
pressure, where systolic pressures are adequate but the mean arterial pressure
underestimates perfusion pressure.
Temperature
Rectal thermometry is considered the reference standard for measurement of body
temperature in neonates. However, it is important to note that mechanical trauma
from rectal thermometry in a newborn can result in peritonitis and abscess
formation, and should be performed with caution. It is also contraindicated in
patients with neutropenia. Similarly, infants receiving active intervention for

temperature control require continuous thermometry that is better accomplished
with electronic axillary thermometry. Temperature readings may vary according
to the site measured so that reference ranges should be interpreted with its
specific set of normal values. In general, hypothermia in a neonate occurs when
the temperature is less than 36.5°C, and fever occurs when temperatures exceed
38°C.
Infants have a very large ratio of surface area to body mass, low fat stores, and
immature thermoregulatory centers, all of which leave them at increased risk for
cold stress. Neonates naturally respond to cold stress by becoming
hypermetabolic, vasoconstricted, hyperactive, tachycardic, tachypneic, and
acidotic. Heat loss after a week of life commonly occurs through radiation, and is
greatly influenced by ambient temperature, humidity, and the temperature of
surfaces to which the infant is exposed. Therefore, whenever possible, it is
important for the clinician to minimize exposure to cold air and surfaces during
examination or observation by placing the baby under an open radiant heater.
Hyperthermia or fever is most often noted as a sign of hypermetabolism in a
septic infant. However, hypothermia can also be a sign of sepsis, due to a
markedly diminished response to bacterial pyrogens in neonates (see Chapter 31
Fever ).