An air embolism, is an obstruction in a vein or artery caused by a bubble of gas. Air enters the circulatory system when the pressure gradient favors movement of air or gas from the environment into the blood. A venous air embolism is the most common form of air embolism. It occurs when air enters the venous circulation, passes through the right side of the heart, and then proceeds to the lungs. In relatively small amounts, the lungs can filter the air; it is absorbed without complications. When large amounts of air (80 to 100 mL) are introduced into the body, however, the lungs no longer have the capacity to filter the air, and the patient has serious or even lethal complications. One of the most serious complications is when the large air bubble blocks the outflow of blood from the right ventricle into the lungs, preventing the blood from moving forward.
The patient develops cardiogenic shock because of insufficient cardiac output. Experts have found that the risk from air embolism, increases as both the volume and the speed of air injection increase. An arterial embolism occurs when air gains entry into the pulmonary venous circulation and then passes through the heart and into the systemic arterial circulation. An arterial embolism can also form in the patient who has a venous embolism and a right-to-left shunt (often caused by a septal defect in the heart) so that the air bubble moves into the left ventricle without passing through the lungs. Pulmonary capillary shunts can produce the same effect. The arterial embolism may cause serious or even lethal complications in the brain and heart. Scientists have found that as little as 0.05 mL of air in the coronary arteries can cause death.
Causes of Air Embolism
The two major causes of air embolism are iatrogenic and environmental. Iatrogenic complications are those that occur as a result of a diagnostic or therapeutic procedure. Situations in which iatrogenic injury is a possibility include insertion, maintenance, or removal of the central line. The risk is highest during catheter insertion because the large-bore needle, which is in the vein, is at the hub while the catheter is threaded into the vein. Air can be pulled into the circulation whenever the catheter is disconnected for a tubing change or the catheter-tubing system is accidentally disconnected or broken. When the catheter is removed, air can also enter the fibrin tract that was caused by the catheter during the brief period between removal and sealing of the tract. Other procedures that can lead to air embolism are cardiac catheterization, coronary arteriography, transcutaneous angioplasty, embolectomy, and hemodialysis. Some surgical procedures also place the patient at particular risk, including orthopedic, urologic, gynecologic, open heart, and brain surgery, particularly when the procedure is performed with the patient in an upright position. Conditions such as multiple trauma, placenta previa, and pneumoperitoneum have also been associated with air embolism.
Environmental causes occur when a person is exposed to atmospheric pressures that are markedly different from atmospheric pressure at sea level. Two such examples are deep-sea diving (scuba diving) and high-altitude flying. Excessive pressures force nitrogen, which is not absorbable, into body tissues and the circulation. Nitrogen accumulates in the extracellular spaces, forms bubbles, and enters into the bloodstream as emboli.
Nursing care plan Physical Assessment and Examination
The patient may have been scuba diving or flying at the onset of symptoms. Usually patients who develop an iatrogenic air embolism are under the care of the healthcare team, who assesses the signs and symptoms of air embolism as a complication of treatment. Some patients have a gasp or cough when the initial infusion of air moves into the pulmonary circulation. Suspect an air embolism immediately when a patient becomes symptomatic following insertion, maintenance, or removal of a central access catheter. Patients suddenly become dyspneic, dizzy, nauseated, confused, and anxious, and they may complain of substernal chest pain. Some patients describe the feeling of “impending doom.”
On inspection, the patient may appear in acute distress with cyanosis, jugular neck vein distension, or even seizures and unresponsiveness. Some reports explain that more than 40% of patients with an air embolism have central nervous system effects such as altered mental status or coma. When auscultating the patient’s heart, listen for a “millwheel murmur” produced by air bubbles in the right ventricle and heard throughout the cardiac cycle. The murmur may be loud enough to be heard without a stethoscope but is only temporarily audible and is usually a late sign. More common than the mill-wheel murmur is a harsh systolic murmur or normal heart sounds. Most patients have a rapid apical pulse and low blood pressure. You may also hear wheezing from acute bronchospasm. The patient may have increased central venous pressure, pulmonary artery pressures, increased systemic vascular resistance, and decreased cardiac output.
Most patients respond with fear, confusion, and anxiety. The family or significant others are understandably upset as well. Evaluate the patient’s and family’s ability to cope with the crisis and provide the appropriate support.
Nursing care plan intervention and treatment
Several strategies can help prevent development of air embolism. First, maintain the patient’s level of hydration because dehydration predisposes the patient to decreased venous pressures. Second, some clinicians recommend that you position the patient in Trendelenburg’s position during central line insertion because the position increases central venous pressure. Third, instruct the patient to perform Valsalva’s maneuver on exhalation during central line insertion or removal to increase intrathoracic pressure and thereby to increase central venous pressure.
Prime all tubings with intravenous fluid prior to connecting the system to the catheter. Immediately apply an occlusive pressure dressing after catheter removal, and maintain the site with an occlusive dressing for at least 24 hours. To prevent air embolism during surgical procedures, the surgeon floods the surgical field with liquid in some situations so that liquid rather than air enters the circulation.
If an air embolus occurs, the first efforts are focused on preventing more air from entering the circulation. Any central line procedure that is in progress should be immediately terminated with the line clamped. The catheter should not be removed unless it cannot be clamped. Place the patient on 100% oxygen immediately to facilitate the washout of nitrogen from the bubble of atmospheric gas. Place the patient in the left lateral decubitus position. This position allows the obstructing air bubble in the pulmonary outflow tract to float toward the apex of the right ventricle, which relieves the obstruction. Use Trendelenburg’s position to relieve the obstruction caused by air bubbles. Other suggested strategies are to aspirate the air from the right atrium, to use closed-chest cardiac compressions, and to administer fluids to maintain vascular volume. Hyperbaric oxygen therapy may improve the patient’s condition as well: This therapy increases nitrogen washout in the air bubble, thereby reducing the bubble’s size and the absorption of air. Note that if the patient has to be transferred to a hyperbaric facility, the decrease in atmospheric pressure that occurs at high altitudes during fixed-wing or helicopter transport may worsen the patient’s condition because of bubble enlargement or “bubble explosion.” Ground transport or transport in a low-flying helicopter is recommended, along with administering 100% oxygen and adequate hydration during transport.
If the patient suddenly develops the symptoms of an air embolism, place the patient on the left side with the head of the bed down to allow the air to float out of the outflow track. Notify the physician immediately, and position the resuscitation cart in close proximity. Initiate 100% oxygen via a nonrebreather mask immediately before the physician arrives, according to unit policy.
Be prepared for a sudden deterioration in cardiopulmonary status and potential for cardiac arrest. The patient and family need a great deal of support. Remain in the patient’s room at all times, and if the patient finds touch reassuring, hold the patient’s hand. Provide an ongoing summary of the patient’s condition to the family. Expect the patient to be extremely frightened and the family to be anxious or even angry. Ask the chaplain, clinical nurse specialist, nursing supervisor, or social worker to remain with the family during the period of crisis.