Online Companion: Fundamentals of Nursing Standards and Practice 2E

Frequently Asked Questions

What information can be provided by the oxyhemoglobin dissociation curve and how can this be utilized in clinical practice?

The oxyhemoglobin dissociation curve provides a graphic representation of the relationship between partial pressure of oxygen (PaO2) and oxygen saturation (SaO2). The relationship is based on affinity or the ability of hemoglobin to hold onto oxygen in the body. The affinity of hemoglobin for oxygen is highest when the PaO2 is 70 mm Hg or higher due to rapid uptake in the pulmonary circulation. Hemoglobin loses it affinity for oxygen in the body as the PaO2 drops below 60 mm Hg in the body due to release of dissolved oxygen as the blood circulates to the peripheral capillary beds.
The oxyhemoglobin dissociation curve can be utilized in clinical practice for it is affected by physiological factors occurring the body that cause it to “shift” thereby affecting affinity. A shift to the right leads to decreased affinity and increases the release of oxygen to the tissues and occurs in response to acidosis, hyperthermia, and in the presence of the enzyme 2,3 DPG. A shift to the left leads to increased affinity where the oxygen is held on tighter and occurs in response to alkalosis, hypothermia, a decrease in the enzyme 2,3 DPG or after massive blood transfusions. The recognition and correction of physiological factors affecting the client’s oxygen transport and delivery mechanisms can be used in the clinical setting to assess and monitor response to therapeutic treatments.

How do the factors of age, environmental and lifestyle factors and disease processes affect oxygenation?

The age of the client can affect the process of oxygenation as elderly clients have reduced ability to fight off respiratory infections as a result of diminished cilia activity and structural changes of the chest leading to decreased gas exchange. Environmental and lifestyle factors can affect the process of oxygenation due to exposure of potential allergens, occupational exposure to allergens, smoking and second hand smoke, emotional as well as physiological stress and weight issues such as malnutrition (obesity as well as underweight). Disease processes can dramatically affect the process of oxygenation as a result of defects in ventilation (obstructive and restrictive pulmonary disease), gas exchange (ventilation-perfusion mismatch), circulation (atherosclerosis, heart failure and anemia) and oxygen uptake (sepsis).

How can the administration of oxygen lead to potential harm and tissue damage in a client?

Oxygen is considered a medication and even though oxygen can be administered initially in the clinical setting by the nurse at 2 L to assist a client who is having difficulty breathing, a physician order should be obtained for ongoing oxygen therapy and the physician should be advised as to the change in client status that required O2 therapy. The administration of oxygen at high levels on a sustained basis can lead to the development of oxygen toxicity. The physiological effects of oxygen toxicity can lead to alveoli collapse and inefficient surfactant production leading to atelectasis and eventually the development of ARDS (adult respiratory distress syndrome) which can be life threatening. In addition, the administration of oxygen at high levels to clients who have chronic lung disease can lead to dramatic problems as low oxygen levels provide the primary stimulus for breathing (due to disease compensation) and once high levels of oxygen are administered this leads to a decrease in their ventilatory drive effort. It is critical for the nurse to understand that oxygen administration is considered a form of drug therapy and that its use should be based on sound physiological principles based on the client’s health status.

Why is it so difficult for clients with impaired oxygenation to rest even though they are clearly experience fatigue?

Clients with impaired oxygenation are unable to rest even though they suffer from fatigue due to a variety of factors affecting their sleep pattern. They may be unable to find a position of comfort leading to tossing and turning and sleeping in an upright position that may not be comfortable. They may experience paroxysmal nocturnal dyspnea – PND during the night that can awaken them from sleep leading to increased exhaustion and anxiety. They also can experience sleep apnea especially if they are overweight leading to interrupted sleep patterns resulting in daytime fatigue even though they did sleep. Clients who experience sleep apnea may have to be placed on CPAP during the night to treat this clinical disorder.