Infants and older adults are at a greater risk from surgery than are children and young or middle-aged adults. The infant has a lower total blood volume, making even a small loss of blood a serious concern because of the risk for dehydration and the inability to respond to the need for increased oxygen during surgery. In addition, the airway is small, soft, and pliable and infants and small children frequently have upper respiratory infections, such as colds, that can cause airway obstruction and hypoxia. This patient population can quickly develop bronchospasm, stridor, and respiratory arrest. If a child exhibits signs of even mild respiratory infections on the day of surgery, their procedure will be postponed until it resolves. The infant also has difficulty maintaining stable body temperature during surgery because the shivering reflex is not well developed, making hypothermia or hyperthermia more likely. Their lower glomerular filtration rate and creatinine clearance can lead to a slower metabolism of drugs that require renal biotransformation. Because the liver is immature until after the first year of life, the effects of muscle relaxants and narcotics may be prolonged. Physiologic changes associated with aging increase the surgical risk for older patients.These changes decrease older adults’ ability to respond to the stress of surgery, alter the effects of preoperative and postoperative medications and anesthesia, and prolong or alter wound healing processes. With an increasing older adult population, assessing physiologic changes is crucial to providing knowledgeable, safe, holistic nursing care to older surgical patients. Chronic illnesses, more common in the older population, also increase surgical risk and may require alterations in usual perioperative procedures. For example, a patient with congestive failure may be more easily fatigued and thus unable to be up and about as rapidly after surgery.