You've been managing an 82-year-old female with respiratory distress for nearly half an hour. She has wheezes in all fields of her lungs and a long history of smoking, asthma and COPD. Even after the third 2.5 mg albuterol nebulizer treatment, she does not appear to have improved at all. The last time you gave albuterol, a single 2.5 mg dose completely relieved a 10-year-old child's asthma attack. Why did these patients respond so differently to the same drug? This article reviews anatomical and physiological differences specific to drug administration for geriatric and obstetric patients and explains drug safety for obstetrical patients.
There are more than 35 million Americans over age 65.1 This population is responsible for more than half of all EMS requests for transport, during which time they may be given a variety of drugs, often forgetting that they are frequently already on several different drugs. The more drugs they are taking, the greater the risk for dangerous drug interactions. Furthermore, biological changes as we age change how drugs act in our bodies.
As people age, they develop atherosclerosis (hardening of the vessels), and, at the same time, the myocardial or heart tissue begins to atrophy, or weaken. This can lead to a decreased left ventricular compliance, then blood pressure changes and increased risk of dysrhythmias.2 The end result is decreased blood circulation, which also means a decrease in the efficiency of drug circulation. Over time, the concentration of plasma proteins in the blood also decreases, leading to an increase in free drug availability. This means that the same amount of drug may be more effective in a geriatric patient than in a young adult.
Consider the following actual patient presentations. The first was a healthy 22-year-old, 200-lb. male who avulsed his thumb on a table saw. After bleeding was controlled and ice applied, he rated his pain at 8 on a 0-10 scale. Morphine was administered in 4 mg increments every 10 minutes. He required 16 mgs of morphine before his pain was rated at 2 out of 10.
A day later, an otherwise healthy 200-lb., 84-year-old male complained of 10 out of 10 hip pain after falling in his kitchen. The physical exam revealed outward rotation and 3-inch shortening of his right leg, and he was immobilized in a position of comfort. He was also given 4 mg morphine for pain management, which reduced his pain to 5 out of 10. Another 4 mg 15 minutes later completely relieved his pain and resulted in mild sedation. These two cases demonstrate how blood changes alter drug availability within the body, changing how elderly patients respond to like doses of drugs.
A decrease in lung elasticity occurs, along with a loss of pulmonary muscle strength, resulting in a smaller tidal volume for each breath. When combined with alveolar dilation, which can increase the lung's surface area by up to 20%2 and a one-third decrease in pulmonary circulation,1 a slowing of carbon dioxide and oxygen occurs. This can lead to carbon dioxide retention, also known as hypercapnia, and hypoxia. 2 Essentially, this also increases dead air space within the lungs. This means when an inhaled drug like albuterol is given, the drug's effects are reduced, because more of the drug remains in the dead airspace. An increased dose may be needed to reach the same effect as a smaller dose in a younger patient.
Diseases like emphysema also destroy the alveolar walls, decreasing the surface area available for gas exchange and exacerbating hypoxemia and hypercapnia.
A few neurologic changes occur with age that affect how drugs interact in the body. Neurons, nerves and nerve fibers all decrease in size and number, and there is slowing of conduction across synapses. This all can lead to a delayed onset of therapeutic action once drugs reach their target cells. Many drugs commonly taken by elderly patients can cause them to become depressed. Examples of these drugs include: analgesics/anti-inflammatory agents, anticonvulsants, antihypertensives, antimicrobials, anti-Parkinson agents, hormones, immunosuppressive agents and tranquilizers.