Critical care - Age-related changes: Nursing

Normal, age-related physiologic changes occur gradually over time, resulting in a decrease in reserve capacity, which is the functional ability of the body’s organs to function beyond what’s needed for normal day-to-day activities. These changes can decrease the ability of the critically ill older adult to adapt to illness, which can increase the risk of complications. As the nurse, you’ll recognize these age-related changes and consider complications that can develop in your critically ill older adult patient as a result.

Starting with the cardiovascular system, there’s an age-related tendency for a decrease in the number of contractile cells in the heart, called cardiomyocytes, along with an accumulation of collagen and fibrosis. The cardiomyocytes also tend to hypertrophy, or increase in size, resulting in a slight thickening of the left ventricular wall with no significant change in the size of the left ventricular cavity.

There are also alterations with calcium signaling within the myocardium during contraction, leading to delayed relaxation during diastole and prolonged contraction during systole. Together, these changes can make the heart a less efficient pump, leading to reduced cardiac output.

Additionally, a loss of cells in the sinoatrial node, which is responsible for generating impulses that stimulate a heartbeat, is associated with a reduced maximal heart rate, which is the highest number of times the heart can beat per minute during physical activity. These age-related changes reduce cardiac functional reserve, impairing the heart’s ability to meet increased demands that can occur during a critical illness.

Other age-related vascular changes include dysfunction of the endothelial cells lining blood vessels. These cells become less effective in balancing substances that cause vasodilation and vasoconstriction. As a result, arteries tend to stiffen, blood flow decreases, and there’s an increased risk of atherosclerosis and thrombosis.

Arterial wall stiffness also contributes to increased afterload and an increase in systolic blood pressure.

Lastly, an impaired baroreflex, which helps maintain blood pressure during position changes, can result in orthostatic hypotension and an increased risk of falls.

Moving on to the pulmonary system, the overall work of breathing increases as an individual ages, making it more difficult to meet increased oxygen demands. The size of the thoracic cavity tends to decrease, due to loss of intervertebral disk height and narrowed rib spaces, which can limit the available space for the lungs to expand. Also, rib cage cartilage begins to calcify, contributing to stiffening of the chest wall and decreasing its compliance, or its ability to expand as lungs fill with air.

Additionally, the primary muscles of respiration, the diaphragm and intercostal muscles, decrease in strength, so older patients may require the use of accessory muscles, like the sternocleidomastoid, scalene, and trapezius muscles, when respiratory demands are increased.

Other changes include diminished elastic recoil in the lungs, leading to alveolar distension, a decreased ability to move air out of the lungs, and an increased residual volume, or the amount of air remaining in the lungs after exhalation. On top of that, a decreased alveolar surface area and reduced capillary blood volume can limit gas exchange, leading to a decrease in the partial pressure of oxygen, or PaO2, in the blood, and hypoxemia.