acute respiratory distress syndrome (ARDS) a group of symptoms accompanying fulminant pulmonary edema and resulting in acute respiratory failure; called also
shock lung, wet lung, and many other names descriptive of etiology or clinical manifestations. Many etiologic factors have been associated with ARDS, including shock, fat embolism, fluid overload, oxygen toxicity, fluid aspiration, narcotic overdose, disseminated intravascular coagulation, multiple transfusions, inhalation of toxic gases, diffuse pulmonary infection, and systemic reactions to sepsis, pancreatitis, and massive trauma or burns.
ARDS is characterized clinically by
dyspnea,
tachypnea,
tachycardia,
cyanosis, and
hypoxemia. Pa
O2/FI
O2 remains low (below 2 cc) even with oxygen therapy at high oxygen concentrations. The lung compliance is decreased so that the lung is stiffer and more difficult to ventilate. Chest radiographs show signs of bilateral interstitial and alveolar edema. Cardiac filling pressures are normal, and the pulmonary capillary wedge pressure is below 18 torr.
Most authorities consider that the syndrome has three phases or stages that characterize its progression: the
exudative stage, the
fibroproliferative or
proliferative stage, and the
resolution or
recovery stage. The exudative stage comes first, two to four days after onset of lung injury, and is distinguished by the accumulation of excessive fluid in the alveoli with entrance of protein and inflammatory cells from the alveolar capillaries into the air spaces. The fibroproliferative stage comes second and is characterized by an increase in connective tissue and other structural elements in the lungs in response to the initial injury. It begins between the first and third weeks after the initial injury and may last up to ten weeks. Microscopic examination reveals lung tissue that appears densely cellular. The patient is at risk for
pneumonia,
sepsis, and
pneumothorax at this time. The third stage is the resolution or recovery stage. During this stage the lung reorganizes and recovers, although it continues to show signs of
fibrosis. Lung function may continue to improve for as long as six to twelve months or even longer, depending on the precipitating condition and severity of the injury. It is important to remember that there are often different levels of pulmonary recovery in patients with ARDS.
Some authorities refer to a fourth phase or stage of ARDS, the period after the resolution or recovery stage. Some patients continue to experience health problems caused by the acute illness, such as coughing, limited exercise tolerance, and fatigue. Anxiety, depression, and flashback memories of the critical illness may also occur and be similar to
posttraumatic stress disorder.
Treatment and Patient Care. Mechanical
ventilation must be begun at the first signs of
hyperventilation and
hypoxemia, before obvious signs of respiratory distress develop. A cuffed
endotracheal tube or
tracheostomy tube is used to maintain an airway. The patient is ventilated at the lowest oxygen concentration that maintains the arterial oxygen saturation (Sa
O2) at 90 per cent.
positive end-expiratory pressure (PEEP) or
continuous positive airway pressure (CPAP) may be used to increase the number of alveoli that remain open at the end of exhalation and thus decrease pulmonary shunt.
hemodynamic monitoring, using a
swan-ganz catheter, is done to measure cardiac output, pulmonary capillary wedge pressure, and right atrial wedge pressure. An arterial line is placed to continuously monitor
blood pressure and measure arterial
blood gases. A diuretic such as
furosemide (Lasix) may be administered to reduce fluid volume overload and pulmonary edema. If infection develops, antibiotics are administered. Hemodynamic parameters, arterial blood gas levels, intake and output, breath sounds, vital signs, inspiratory pressure, tidal volume, inspired oxygen concentration, and end-expiratory pressure are all continuously monitored.
acute stress disorder an
anxiety disorder characterized by development of
anxiety,
dissociation, and other symptoms within one month following exposure to an extremely traumatic event, the symptoms including reexperiencing the event, avoidance of trauma-related stimuli, anxiety or increased arousal, and some or all of the following: a subjective sense of diminished emotional responsiveness, numbing, or detachment, derealization, depersonalization, and amnesia for aspects of the event. If persistent, it may become
posttraumatic stress disorder.