A 38-year-old man fell 15 ft from a ladder while trying to rescue a cat. During the evaluation at the hospital, he was found to have a closed fracture of the right femur, a fracture of the right radius and ulna, and soft tissue contusions and abrasions. The patient underwent open reduction and internal fixation of his femur and external fixation of his forearm without apparent complications. On postinjury day 2, he began to complain of difficulty in breathing. On physical examination, his temperature is found to be 38.4°C (101°F), pulse rate 120 beats/min, blood pressure 148/86 mm Hg, respiratory rate 34 breaths/min, and Glasgow Coma Score 15. The patient appears anxious and complains of difficulty breathing but is without chest pain. Auscultation of the chest reveals diminished breath sounds bilaterally with scattered rhonchi. The results of a cardiac examination are unremarkable. The abdomen is nondistended and nontender. Examination of the extremities reveals postinjury soft tissue swelling. Laboratory studies reveal the following: white blood cell (WBC) count 16,000/mm3, hemoglobin 10.8 g/dL, platelet count 185,000/mm3. Arterial blood gas (ABG) studies reveal pH 7.4, Pao2 55 mm Hg, PaCo2 40 mm Hg, and HCO324 mEq/L. A chest radiograph (CXR) reveals bilateral nonsegmental infiltrates and no effusion or pneumothorax.
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ANSWERS TO CASE 23: Postoperative Acute Respiratory Insufficiency
Summary: A previously healthy young man develops acute respiratory insufficiency after being injured in a fall and undergoing operative repair of traumatic orthopedic injuries.
• Next steps: Administration of supplemental oxygen and transfer to the intensive care unit for closer observation and possible mechanical ventilation if the patient’s condition does not improve or deteriorates.
• Diagnosis: Acute respiratory insufficiency caused by acute lung injury (ALI).
Learn the presentations and differential diagnosis of acute respiratory insufficiency in surgical patients.
1. Learn the pathophysiology of ALI.
2. Know the types of invasive and noninvasive modes of pulmonary support.
The timing of the development of respiratory insufficiency is compatible within the timeframe of pulmonary embolism (PE) and within the expected time frame for ALI. The patient’s pulmonary examination reveals diminished breath sounds and scattered rhonchi, nonspecific findings that are compatible with ALI. The CXR reveals bilateral nonsegmental infiltrates, and an ABG study shows moderate hypoxemia. PE typically presents with a relatively normal CXR. By strict definition, ALI requires the respiratory insufficiency to be acute in onset, associated with a PaO2:FIO2 value less than 300, bilateral infiltrates, and a pulmonary capillary wedge pressure (PCWP) of less than 18 mm Hg. Although many features of this case suggest a diagnosis of ALI, other potential diagnoses must be considered and excluded, including aspiration pneumonitis, atypical pneumonia, atelectasis, and PE. During the initial evaluation of any patient with acute respiratory insufficiency, it is important to consider the diagnosis, but the primary consideration should be to determine the most appropriate level of respiratory support. For this patient, even though he does not appear to require immediate mechanical ventilatory support, his oxygenation and pulmonary compliance defects may progress and cause further respiratory embarrassment.
APPROACH TO: Acute Respiratory Insufficiency
ASPIRATION: Spillage of gastric contents into the bronchial tree causing direct injury to the airways, which can progress to a chemical burn or pneumonitis (especially when ) and predispose to bacterial pneumonia. When the aspirated gastric contents contain particulate matter, bronchoscopy may be helpful in clearing the airway. Half of affected patients develop subsequent pneumonia not prevented by empirical antibiotics.
PNEUMONIA: Pulmonary infection caused by impairment of the lung’s defense mechanisms. Incisional pain frequently affects the patient’s ability to clear airway mucus, leading to small airway obstruction and ineffective bacteria clearance. Most commonly, nosocomial organisms are those that colonize patients during hospitalization.
PULMONARY EMBOLISM: A major source of morbidity and mortality in surgical patients. The prophylaxis, diagnosis, and treatment of PE are continuous concerns for the surgeon. Bed rest, cancer, and trauma increase the risk of deep vein thrombosis (DVT) and PE occurrence. PE may be clinically silent or symptomatic. In high-risk surgical patients, the risk of developing a clinically significant PE is 2% to 3%, and the risk of developing a fatal PE approaches 1%. The clinical hallmarks include acute-onset hypoxia associated with anxiety leading to tachypnea and hypocarbia without significant CXR abnormalities.
LUNG CONTUSION: Blunt trauma to the chest is a common cause of pulmonary dysfunction resulting from direct parenchymal injury and impaired chest wall function. An injured chest wall leads to impaired breathing mechanics that can range from splinting secondary to a rib fracture to the severe impairment of a flail chest. The morbidity from lung contusion is attributed to direct parenchymal injury and bronchoalveolar hemorrhage, causing ventilation/perfusion (V/Q) mismatch leading to hypoxia. This condition is worsened by chest wall injury pain, leading to atelectasis in the uninvolved lung.
ACUTE RESPIRATORY DISTRESS SYNDROME (ARDS): The most severe form of , this condition encompasses a spectrum of lung injuries characterized by increasing hypoxia and decreased lung compliance. Initially, an injury to the pulmonary endothelial cells leads to an intense inflammatory response. Inhomogeneous involvement of the lung occurs, with interstitial and alveolar edema, loss of type II pneumocytes, surfactant depletion, intra-alveolar hemorrhage, hyaline membrane deposition, and eventual fibrosis. These changes manifest clinically as severe hypoxia, decreased lung compliance, and increased dead space ventilation.
ATELECTASIS: The collapse of alveolar units in patients who undergo general anesthesia, which causes a reduction in functional residual capacity that is further reduced because of incisional pain. The subsegmental atelectasis may progress to obstruction and inflammation, leading to larger airway obstruction and segmental collapse. Most patients have only a low-grade fever and mild respiratory insufficiency.
CARDIOGENIC PULMONARY EDEMA: Myocardial dysfunction most frequently resulting from ischemia can produce left ventricular dysfunction, fluid overload, and pulmonary interstitial edema. The increase in the amount of interstitial water compresses the fragile bronchovascular structures, thereby increasing the V/Q mismatch and producing hypoxia.
VENTILATOR BUNDLE: Consists of a combination of patient care strategies that have been demonstrated to reduce ventilator days, ICU length of stay, and mortality of mechanically ventilated patients. These interventions include head of bed elevation, stress ulcer and DVT prophylaxis, daily sedation interruption, and daily assessment of the readiness for weaning and removal from ventilator support.
VENTILATOR-INDUCED LUNG INJURY (VILI): Positive-pressure-ventilation–associated mechanical ventilator produces a variety of injury effects secondary to overinflation, distension, and repetitive opening and closing of the alveoli. High-oxygen content delivery to the lungs also produces oxygen-free-radical–associated lung injuries. Strategies to minimize VILI include low tidal volume ventilation (5-7 mL/kg), reducing FIO2 below 60% within 48 to 72 hours, and the application of positive end expiratory pressure (PEEP).
In treating patients with acute respiratory insufficiency, the first priority is to assess and stabilize the airway, breathing, and circulation (ABCs). Patients with lethargy and diminished mentation may benefit from immediate endotracheal intubation to protect against aspiration. The assessment of each patient should be directed toward the immediate status as well as toward the anticipated future status of the patient’s ventilation and oxygenation. The adequacy of oxygenation is evaluated by pulse oximetry or Pao2 measurement by ABG studies. The inability to maintain a Pao2 of 60 mm Hg or an oxygen saturation of more than 91% with a supplemental non-rebreathing O2mask is indicative of a significant alveolar-arterial (A-a) gradient, and intubation and mechanical ventilation may be needed. Hypoxemia frequently causes agitation and confusion, and an uncooperative patient can contribute to delays in diagnosis. The adequacy of ventilation is generally assessed by observing the patient’s respiratory efforts and subjective symptoms, and quantified by the measurement of Paco2 by ABG analysis. It is important to bear in mind that ventilation assessment requires the use of all these data and should not be made on the basis of a blood gas value alone.
Pathophysiology of Acute Lung Injury
Acute lung injury (ACI) encompasses a spectrum of lung disease from mild forms to severe lung injury or ARDS. The inciting event can be a direct or indirect pulmonary insult (Figure 23–1). The resultant cascade of events includes both cellular and humoral components that produce an inhomogeneous injury. The inflammatory response involves activated polymorphonucleocytes that generate oxygen radicals, cytokines, lipid mediators, and nitric oxide. The complement, kinin, coagulation, and fibrinolytic systems are also involved. Endothelial damage ensues with an increase in microvascular permeability leading to the accumulation of extravascular lung water. This soon results in diminished lung volume and decreased lung compliance. Lung compliance is further hampered because of the sloughing of type I pneumocytes and a decrease in surfactant production by type II pneumocytes. The process continues, further aggravating interstitial edema, alveolar collapse, and lung consolidation. In the pathogenesis, inflammatory cells and fluid are sequestered within the lungs, leading to a decrease in pulmonary compliance and an increase in the work of breathing. During the prodromal phase of ALI, patients may simply complain of difficulty in catching their breath, leading to tachypnea. Ventilation is reflected by the Paco2, but the patient’s appearance, respiratory rate, and respiratory efforts are equally important endpoints. Hypercapnia is not associated with anxiety or agitation; therefore, patients with an altered level of consciousness should have Paco2 (by ABG) or end-tidal CO2 (by capnography) monitoring to assess ventilation.
Figure 23–1. Chest radiography revealing the bilateral dense pulmonary infiltrates typical of acute respiratory disease syndrome. (Reproduced, with permission, from Mattox KL, Feliciano DV, Moore EE, eds. Trauma. 4th ed. New York, NY: McGraw-Hill; 2000:526.)
Noninvasive Pulmonary Support
Patients with acute postoperative respiratory insufficiency can be provided with supplemental oxygen and noninvasive respiratory support, including a continuous positive airway pressure mask (useful for atelectasis) and chest physiotherapy, including bronchodilators and mucolytic agents (useful for atelectasis, pneumonia, and reactive airway disease). Patients with a significant A-a gradient may benefit from mechanical ventilator support for oxygenation. Noninvasive ventilation strategies were found to be successful in avoiding intubation in 43% of patients in a trial where patients were randomized to invasive ventilation or noninvasive ventilation.
MECHANICAL VENTILATION MODES
Conventional ventilation or positive-pressure ventilation fills the lungs via supra-atmospheric pressure applied through an endotracheal tube to the airways. This creates a positive transpulmonary pressure that ensures inflation of the lungs. Exhalation is passive and occurs after release of the positive pressure. The major settings are volume and pressure controlled, where the tidal volume delivery is based on either volume- or pressure-limiting settings.
High-frequency ventilation also uses an endotracheal tube to facilitate gas exchange; however, it delivers very small tidal volumes, on the order of 1 mL/kg body weight at a very high rate, approximately 100 to 400 breaths/min. Although this mode has an important role in the treatment of respiratory insufficiency in neonates, it has not had the same success in adults.
The theoretical advantage of liquid ventilation lies in its ability to reduce the amount of energy necessary to overcome surface tension at the gas-liquid interface of alveoli. Because diseased lungs have less surfactant, liquid ventilation can improve lung compliance. Studies are needed to document the clinical benefits of this ventilation mode.
Extracorporeal Life Support
Cardiopulmonary bypass or extracorporeal life support uses a heart-lung machine to take over pulmonary and/or cardiac function. If cardiac function is adequate, a venovenous circuit can be used to remove CO2 and oxygenate the blood. As in the case of high-frequency ventilation, the early success achieved in neonates has not been duplicated in adult populations.
23.1 A 57-year-old woman develops an acute onset of respiratory distress 7 days following colectomy for adenocarcinoma of the colon. She had been doing well up until this time. The physical examination reveals diminished breath sounds at the lung bases. The CXR reveals atelectasis of the left lower lobe segment. Which of the following is the most appropriate treatment at this time?
A. Provide supplemental oxygen and begin chest physiotherapy.
B. Provide supplemental oxygen and initiate chest physiotherapy and antibiotic therapy.
C. Begin antibiotic therapy and immediate bronchoscopy to open up the lungs.
D. Provide supplemental oxygen, obtain venous duplex scans of the lower extremities and a lung V/Q scan, and consider starting heparin therapy.
E. Encourage early ambulation.
23.2 Diagnostic bronchoscopy is most appropriate in which of the following patients?
A. A 33-year-old man with right lower lobe hospital-acquired pneumonia
B. A 40-year-old man with AIDS who develops fever, acute respiratory distress, and bilateral pulmonary infiltrates
C. A 66-year-old man with dementia who develops a right upper lobe infiltrate following an episode of aspiration
D. A 30-year-old man who develops ARDS associated with fever and a loculated right pleural effusion
E. A 63-year-old man with tuberculosis, a right upper lobe cavitary lesion, and hemoptysis
23.3 A 34-year-old woman is hospitalized for septic shock caused by toxic shock syndrome. She is treated with intravenous nafcillin and noted to have hypoxemia. A CXR reveals diffuse infiltrates in bilateral lung fields. Which of the following would most likely differentiate ARDS from cardiogenic pulmonary edema?
A. Pulmonary artery catheter readings
B. Serum colloid osmotic pressure
C. Urinary electrolytes and partial excretion of sodium
D. V/Q scan
E. Bronchoscopy and bronchoalveolar lavage
23.4 A 46-year-old man sustained multiple left rib fractures after having fallen off a horse. He is otherwise healthy and has a one pack a day smoking history for the past 24 years. Approximately 1 hour after arrival to the emergency room, the patient’s breathing appears to be more labored, and despite having received several doses of morphine sulfate for pain, he continues to complain of severe chest pain. At this time, his respiratory rate is 36 breaths/min and shallow, blood pressure is 160/100 mm Hg, pulse rate is 115 beats/min, and the pulse oximeter monitor indicates 92% saturation on 40% oxygen face mask. His breath sounds are diminished bilaterally but significantly less audible on the left. Which of these options is most appropriate for this patient at this time?
A. Administer a loop-diuretic.
B. Perform endotracheal intubation and initiate mechanical ventilation.
C. Replace his oxygen mask with a continuous positive airway pressure mask.
D. Obtain an ABG value, and intubate patient if the Pao2 is less than 50 mm Hg and/or if the Paco2 is greater than 50 mm Hg.
E. Obtain a chest x-ray.
23.5 A 34-year-old man slipped and fell in the bathroom at home and struck his anterior neck on the edge of some shelves. When he arrived in the emergency center, he had significant anterior neck pain, soft tissue crepitance, and stridor. He was successfully intubated after several difficult attempts. His chest x-ray immediately following intubation demonstrated satisfactory endotracheal tube placement, diffuse bilateral nonsegmental infiltrates, and no evidence of pneumothorax or pleural effusions. Which of the following is the most appropriate treatment option at this time?
A. Bronchoscopy to identify injury to the tracheal-bronchial tree
B. Supportive care including mechanical ventilation, fluid management
C. Initiate antimicrobial therapy for aspiration pneumonia
D. Consult a thoracic surgeon
23.1 D. Provide supplemental O2, perform a workup for PE, and consider empirical treatment. This patient develops a sudden onset of respiratory distress 7 days postoperatively. The clinical presentation is highly suggestive of PE. The diagnosis of atelectasis as the primary cause of this patient’s clinical picture should not be readily accepted until PE can be ruled out.
23.2 B. Diagnostic bronchoscopy and bronchoalveolar lavage are indicated in an immunocompromised individual with new-onset fever and bilateral pulmonary infiltrates.
23.3 A. The PCWP approximates the left ventricular end-diastolic pressure. A low-normal pulmonary artery wedge pressure (<18 mm Hg) supports leaky capillaries (ARDS) as the etiology, whereas a high PCWP suggests a hydrostatic mechanism, cardiogenic pulmonary edema.
23.4 E. This patient’s current clinical picture is one of worsening respiratory insufficiency that could be contributed by pneumothorax, pulmonary contusion, or atelectasis. A change in his respiratory status at this time requires reevaluation of the ABC, which indicates diminished breath sounds bilaterally, with less audible breath sounds on the left. A chest x-ray is very useful at this time to help determine the cause of his clinical deterioration. Endotracheal intubation and mechanical ventilation would be most appropriate if the patient’s clinical picture is one of impending respiratory failure. ABG values are helpful in guiding treatment for patients with respiratory diseases; however, the ABG results need to be considered within the proper clinical context. Diuretic administration is not inappropriate for this patient exhibiting hyperdynamic clinical parameters and no clear evidence of intravascular fluid overload.
23.5 B. This patient’s findings are compatible with ACL secondary to forced inspiration against a closed or narrow airway, resulting in “negative-pressure pulmonary edema”; negative-pressure pulmonary edema is an unusual variant of ACL and is often self-limiting with supportive care that includes mechanical ventilation and IV fluids.
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Mendez-Tellez PA, Dorman T. Postoperative respiratory failure. In: Cameron JL, ed. Current Surgical Therapy. 9th ed. Philadelphia, PA: Mosby Elsevier; 2008:1196-1201.
Peters CW, Yu M, Sladen RN, Gabrielli A, Layon AJ. Acute lung injury and acute respiratory distress syndrome. In: Gabrielli A, Layon AJ, Yu M, eds. Civetta, Taylor, & Kirby’s Critical Care. 4th ed. Philadelphia, PA: Wolters Kluwer/Lippincott Williams & Wilkins; 2009:2061-2080.