 Cardiac Workload: o Right ventricle before birth does approximately two thirds of the cardiac work resulting in increased size and thickness of the right ventricle at birth. o After birth right ventricle does a larger sum of work so it increases in size and thickness. o Left sided defects less tolerated and become symptomatic after birth. o Righ ventricular output reflects systemic venous return, and left ventricular output reflects pulmonary venous return. o Systemic blood volume and pulmonary blood volume are not equal in the newborn. o The newborn’s combined cardiac output is greater per unit of body weight than it will be in later childhood.  Temperature Regulation: o Maintenance of thermal balance by losing heat to the environment at a rate equal to heat production. o Newborns are homeothermic: attempting to stabilize their internal body temperatures within a narrow range in spite of significant temperature variations in their environment. o Fetus moves from warm, moist intrauterine environment to colder, drier extrauterine environment.

OB study guide 57 o Term newborns increase their metabolic rate by 200% to 300% after birth in an attempt to accelerate heat production.  Neutral thermal environment (NTE): the rates of oxygen consumption and metabolism are minimal and internal body temperature is maintained because of thermal balance. o Unclothed full-term newborn temperature is about 32 degrees Celsius to 34 degrees Celsius (89.6 to 93.2) o Thermal stability controlled by: the newborn having less fat than an adults. Blood vessels are closer to the skin in the newborn. The flexed posture of the term infant decreases the surface area exposed to the environment, thereby reducing heat loss.  Heat Loss: o Newborns poor thermal stability is due primarily to excessive heat loss rather than to impaired heat production. o Due to the risk of hypothermia and possible cold stress, minimizing heat loss in the newborn after birth is essential. o Two major routes:  Internal core of the body to the body surface and external body surface too the environment.  Core temperature is higher than the skin temperature, and the greater the difference in temperatures between core and skin, the more rapidly heat transfer occurs.  The transfer is accomplished through an increase in oxygen consumption, depletion of glycogen stores, and metabolizing of brown fat. o Heat loss from the body surface to the environment takes place in four ways: o Convection: loss of heat from the warm body surface to the cooler air currents. i.e. air conditioned rooms, air currents with a temperature below the infant’s skin temperature, unwarmed oxygen by mask, an infant being removed from incubator. o Radiation: losses occur when body heat is transferred to cooler surfaces and objects not in direct contact with the body. i.e. walls of a room or of an incubator are potential causes of heat loss by radiation.