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 )