Oxygenation is the delivery of oxygen to the body’s cells. The processes involved are ventilation, alveolar gas exchange, oxygen transport and delivery, and cellular respiration. Ventilation is the movement of air into and out of the lungs to deliver fresh air to the alveoli. Ventilation is regulated by respiratory centers in the pons and medulla oblongata of the brain. These centers are stimulated by an increase in carbon dioxide in the blood or a decrease in the blood pH, resulting in faster and deeper ventilation. Hypoxemia (a decrease in blood oxygen concentration) stimulates ventilation to a lesser degree. Inspired air is filtered, humidified, and warmed throughout the upper airway.

Oxygen uptake (external respiration) is the exchange of oxygen from the alveolar space into the pulmonary capillary blood. Oxygen diffuses across the alveolar membrane from an area of greater concentration (alveoli) to an area of lower concentration (pulmonary capillary blood). Likewise, carbon dioxide diffuses from the blood to the alveolar space. The capacity of the blood to carry oxygen depends upon the amount of dissolved oxygen in the plasma, the amount of hemoglobin, and the tendency of the hemoglobin to bind with oxygen. The amount of oxygen in the blood is measured as (1) the partial pressure of oxygen (PaO2) and (2) the percentage of hemoglobin that is saturated with oxygen (SaO2). The normal PaO2 is about 80 to 100 mm Hg. The normal SaO2 is 96% to 98%. The oxyhemoglobin dissociation curve is a representation of the relationship between the partial pressure of oxygen and oxygen saturation.

The oxygen is delivered to the cells through circulation. The cardiac cycle (a single cycle of atrial and ventricular contraction and relaxation) involves both electrical and mechanical events. The cardiac conduction system is responsible for the electrical activity of the heart. The electrical impulse begins at the heart’s pacemaker, the sinoarterial (SA) node in the right atrium, moves to the atrioventricular (AV) node, and finally moves through the ventricular tissue along the bundle of His, right and left bundle branches, and Purkinje fibers.

The mechanical system is the series of four chambers and valves through which the blood passes as it is pumped. Blood leaves the right ventricle through the pulmonary artery, where it is oxygenated, then passes through the pulmonary vein to the left atrium. From the left atrium, the blood passes through the aorta to the circulation, delivering oxygen to the tissues and picking up carbon dioxide. Carbon dioxide returns through the venous system to the vena cavae and then to the right atrium. Blood flow is shifted to the area of greatest need for oxygen through autoregulation. Precapillary sphincters in the arterioles relax or contract according to need. Blood returning through the venous system is regulated by pressure gradients.

The diastole is the process of chamber filling as the right and left atria relax. During diastole, deoxygenated flood flows from the pulmonary capillary bed through the vena cavae into the right atrium, and oxygenated blood flows from the pulmonary capillary bed via the pulmonary veins into the left atrium. During systole, pressure increases in the atria, the right tricuspid and left mitral atrioventricular valves open, the atrial muscle contracts (“atrial kick”) and the blood flows into the ventricles. At this point, intraventricular pressure rises, the tricuspid and mitral valves close, and the ventricular muscle contracts, increasing intraventricular pressure enough to open the right pulmonic valve and left aortic valve. Deoxygenated blood is forced out of the right ventricle into the lungs through the pulmonary arteries and oxygenated blood flows from the left ventricle, through the aorta, and into the systemic circulation. The exchange of oxygen and carbon dioxide at the cellular level takes place through diffusion in response to concentration gradients. This exchange is known as internal respiration.

The factors affecting oxygenation are the individual’s developmental level, environment, and lifestyle. Due to various structural factors, the child’s upper airway is shorter and narrower than an adult’s, leading to an increased potential for obstruction and airway resistance. In contrast, the older adult has less efficient oxygenation due to a loss of lung elasticity, the deterioration of alveoli, slowed cilia movement in the upper airway, and altered circulation. In the environment, air pollution introduces noxious gases to the inhaled air. Additionally, the oxygen in the air is decreased in higher altitudes and hot or cold weather can have detrimental effects on oxygenation. Lifestyle factors include lack of exercise, poor posture, obesity, poor nutrition, emotional stress, drug intake, and smoking.

Oxygenation is also affected by chronic obstructive pulmonary disease (COPD) or chronic airflow limitation (asthma, emphysema, and chronic bronchitis), restrictive pulmonary disease (pneumonia, pulmonary fibrosis, pleural defects, and pulmonary masses), diffusion defects (decrease in the efficiency of gas diffusion from the alveolar space into the pulmonary capillary defect caused by pulmonary edema or obstructive or restrictive pulmonary diseases) ventilation-perfusion (V/Q) mismatching (an imbalance between ventilation and perfusion, resulting in deadspace or shunting), atherosclerosis, heart failure, anemia, and altered oxygen uptake (due to cyanide poisoning or sepsis).

Physiological responses to reduced oxygenation include increased oxygen extraction from the arterial blood, anerobic metabolism, tissue ischemia, and cell death. The cells can extract more oxygen from the arterial blood when circulation is poor or more oxygen is needed. Hypoxia (prolonged oxygen deprivation) leads to cellular death, or infarction. Widespread cellular death results in multi-organ-system failure. Anaerobic metabolism is the utilization of glucose in the absence of oxygen, which occurs only briefly.

The assessment of oxygenation begins with a health history, including the events leading up to a problem, the duration of the problem, the methods used to alleviate symptoms, and the impact of the problem on activities of daily living. The physical examination includes observation of the client’s breathing (anxious appearance, flaring of nostrils, position preferences, and general chest configuration), noting the respiratory rate and rhythm and the signs and symptoms of hypoxia (restlessness, anxiety, dizziness, confusion, agitation, increased pulse, increased rate and depth of respiration, and elevated blood pressure), cyanosis (bluish discoloration of the skin), and clubbing of the fingers.

The physical examination also includes palpation, percussion, and auscultation of the chest. Diagnostic and laboratory data include blood gasses (pH, Pco2, HCO3, PaO2, and SaO2), sputum culture, ventilatory function tests, chest x-ray, computerized tomography (CT) scan and magnetic resonance imaging (MRI) of the thoracic structures, ventilation scan, bronchoscopy, thoracentesis, echocardiography, electrocardiography, and stress test.

The primary nursing diagnoses for clients with oxygenation problems are Ineffective Airway Clearance, Ineffective Breathing Patterns, Impaired Gas Exchange, Decreased Cardiac Output, and Ineffective Tissue Perfusion. The secondary nursing diagnoses for clients with oxygenation problems are Deficient Knowledge, Activity Intolerance, Disturbed Sleep Pattern, Imbalanced Nutrition, and Acute Pain. Individualized expected outcomes for each nursing diagnosis should be derived with input from the client.

Interventions to promote airway clearance include teaching effective coughing, postural drainage, chest physiotherapy, monitoring hydration, administering medications, monitoring environmental and lifestyle conditions, managing artificial airways (nasal, oral, endotracheal, or tracheal), suctioning, and breathing exercises. Interventions to improve oxygen uptake and delivery are oxygen administration, teaching purse-lipped breathing, and elevating the head of the bed. Clients with pneumothorax or hemothorax have chest tubes and need specialized nursing care. Interventions to increase cardiac output and tissue perfusion include managing fluid balance, encouraging activity restrictions, positioning for comfort and ease of respiration, and administering medication. In some cases, emergency obstruction, respiratory arrest, and cardiac arrest occur, requiring emergency cardiopulmonary resuscitation. Interventions to address nursing diagnoses include lifestyle and activity adaptations, modification of the diet, and promotion of client comfort. Evaluation of care is based on how well expected outcomes are met.