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* From the Pulmonary and Critical Care Unit (Drs. Schwartz, Malhotra, and Kesselman) and Department of Medicine (Dr. Maroo), Massachusetts General Hospital, Boston, MA.
Correspondence to: David R. Schwartz, MD, Pulmonary and Critical Care Unit, Massachusetts General Hospital, 55 Fruit Street, Bulfinch-148, Boston, MA 02114-2696; e-mail: schwartz{at}massmed.org
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Abstract |
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Key Words: negative pressure pulmonary edema • pulmonary hemorrhage • stress failure
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Introduction |
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Case Report |
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At the end of the procedure, peripheral twitch monitoring showed 4/4 twitches with a train-of-four, and the patient met the standard criteria for extubation without the need for neuromuscular relaxant agent reversal. Following extubation, he became agitated and began to make vigorous inspiratory efforts without significant air movement. He became tachycardic to 120 beats/min, hypertensive to 170/100 mm Hg, and hypoxemic with a pulse oximeter saturation of 88% on a 100% nonrebreather mask. Despite artificial oral and nasal airways and intermittent positive pressure applied with a bag-valve mask, he continued to make inspiratory "crowing" sounds. He became increasingly hypoxemic and was atraumatically reintubated 5 min after extubation. A direct laryngoscopy excluded the presence of supraglottic edema, upper airway bleeding, or laryngospasm. Coarse inspiratory rhonchi were heard bilaterally on auscultation, and copious, pink, frothy sputum was obtained with suctioning. The patient was stabilized and transferred to the postanesthesia care unit.
A chest radiograph revealed asymmetric, right greater than left, fluffy perihilar infiltrates, and a small left pleural effusion. An initial arterial blood gas measurement revealed a pH of 7.35, a PCO2 of 52.9 mm Hg, a PaO2 of 35 mm Hg, and an arterial oxygen saturation of 68% on a fraction of inspired oxygen of 1.0. The patient's endotracheal secretions became progressively bloody, consistent with frank hemorrhage. The clinical impression of the anesthesiologists was that the patient had experienced negative pressure pulmonary edema (NPPE) secondary to UAO; the etiology of the hemoptysis was unknown. Supportive treatment included IV furosemide, supplemental oxygen, and 10 cm H2O positive end-expiratory pressure. Before the patient was transfered to the medical ICU, his oxygenation had improved; the pulse oximeter saturation was 94% on a fraction of inspired oxygen of 0.5, and a repeat arterial blood gas measurement revealed a pH of 7.42, a PCO2 of 40.3 mm Hg, and a PaO2 of 158 mm Hg. The patient received a total of 4,300 mL of crystalloid, and his total urinary output was 2,845 mL.
Following his stabilization, the patient denied having a history of previous cough, hemoptysis, hematuria, or epistaxis, but he did acknowledge a history of loud snoring. He denied any recent use of cocaine or IV drugs, and he had a negative tuberculin skin test within the past year. His only medication was timolol eyedrops, and he had no drug allergies. The family history was noncontributory.
The initial examination revealed an African-American man with blood in his endotracheal tube. His temperature was 39.1°C (102.4°F) with rapid spontaneous defervescence. He had no petechiae, telangiectasias, or oral or mucosal bleeding. There was no jugular venous distention. He had diffuse inspiratory rales, normal heart sounds, and no peripheral edema. The laboratory investigation was notable for a hematocrit of 58%, with a repeat value 7 h later of 46.9%. The WBC count and coagulation profile were normal. The urinalysis revealed 3 to 5 nondysmorphic RBCs/high-power field and 0 to 2 WBCs/high-power field, without casts or proteinuria. A urine toxicology screen was negative for cocaine metabolites.
The bronchoscopy in the medical ICU revealed a small amount of fresh blood in the proximal airways. The endobronchial mucosa was normal and was without masses or an identifiable bleeding source. A BAL was performed to help clarify the origin and chronicity of the bleeding. A lavage of the lingula and the right middle lobe with 6 aliquots of 20 mL normal saline each revealed a progressively bloody return consistent with alveolar hemorrhage. The BAL fluid contained 5.6 x 103 WBC/mL with 99% polymorphonuclear leukocytes and no organisms. The cytology was negative for hemosiderin-laden macrophages, and all cultures were negative. An ECG revealed a sinus tachycardia, and the echocardiography showed normal valves and normal right and left ventricular function. Test results were negative for anti-glomerular basement membrane antibody, antineutrophil cytoplasmic antibody, and HIV. There was no evidence of cryoprotein.
The patient's oxygen requirement decreased progressively over the ensuing 24 h. By hospital day 2, his hematocrit had decreased to 40%, and he was extubated. He remained stable thereafter. Sequential anteroposterior portable chest radiographs revealed the persistence of bilateral acinar disease until an improvement became apparent on hospital day 3. Prior to the patient's discharge on hospital day 4, a chest radiograph showed a slight interval clearing. An ear, nose, and throat evaluation was notable for a mild redundancy of oropharyngeal tissue and normal vocal cords. A sleep study revealed a respiratory disturbance index of 20 events/h that was consistent with obstructive sleep apnea (OSA). The patient was discharged in stable condition, but he did not return for his scheduled follow-up.
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Discussion |
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NPPE has been well-described in cases of acute UAO.2 3 4 5 In children, it has been observed after intubation secondary to croup and epiglottitis.2 In both children and adults, it has been reported as a complication of postanesthetic laryngospasm,2 3 5 strangulation, hanging,6 foreign body airway obstruction, upper airway tumors,3 and OSA.7
NPPE is characterized by a rapid onset (within minutes) and resolution, with a significant clinical and radiographic improvement in 12 to 24 h.5 Most patients require temporary intubation and positive end-expiratory pressure.3 Diuresis and/or fluid restriction are often utilized. Hemodynamic measurements, including pulmonary capillary wedge pressure, pulmonary arterial pressure, and central venous pressure taken following the development of edema, are normal.5
Markedly negative intrathoracic pressure (ITP) augments normal inspiratory hemodynamic physiology (Fig 1 ). Venous return is increased through the combination of reduced right atrial pressure secondary to the transmission of negative ITP and the elevation of the mean systemic pressure (Pms) related to catecholamine-induced venoconstriction from anxiety, hypoxia, and hypercarbia. As the right ventricular volume increases, the interventricular septum may shift leftward, indicative of reduced left ventricular diastolic compliance.8 Negative ITP transmission to the cardiac fossa and a catecholamine-induced elevation of the systemic vascular tone cause an increase in the left ventricular transmural pressure, thus raising ventricular wall tension.9 This increase in afterload depresses left ventricular ejection. The effect of these changes is a net translocation of blood from the systemic to the pulmonary circulation. The formation of edema in this setting requires an increased Ptm: pulmonary capillary hydrostatic pressure (Ppc) minus the pulmonary interstitial hydrostatic pressure (Ppi). The Ppc rises secondary to the increased blood volume and the increased pulmonary vascular tone (due to hypoxia and acidosis). During a Mueller maneuver, the Ppi, approximating the change in the alveolar and pleural pressures, becomes quite negative (around -100 cm H2O),10 contributing to high capillary transmural pressure. These changes predict the formation of a transudative edema free of RBCs. The development of exudative, high-protein edema, however, has been reported following the relief of acute UAO.11 In published reports of NPPE,2 4 5 numerous examples are given of RBC leakage into the edema, including the early description of postobstructive pulmonary edema by Oswalt et al4 describing "pink, frothy fluid" in all three cases.
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Increased pulmonary capillary wall stress (defined as Ptm x radius of curvature/wall thickness) can cause the mechanical disruption of the alveolar-capillary membrane with the subsequent impairment of barrier function, a process termed "stress failure."14 When the alveolar-capillary membrane is viewed under the scanning electron microscope, stress failure is characterized by breaks in the capillary endothelial and alveolar epithelial barriers and, occasionally, in the basement membrane.15 In animal models, stress failure occurs at a Ptm of 40 mm Hg (rabbit), 70 mm Hg (dog), and 100 mm Hg (horse).14 16 17 Ultrastructural evidence of damage to the capillaries exists in both animal models and human cases of high-altitude pulmonary edema18 and neurogenic pulmonary edema19 , and in exercise-induced pulmonary hemorrhage in thoroughbred racehorses.17 Additionally, stress failure may contribute to edema and/or hemorrhage in cases of mitral stenosis and pulmonary veno-occlusive disease,20 and following periods of intense exercise in elite athletes.21
In each of the aforementioned cases, a high Ptm is due to an elevated Ppc. However, the stress failure model predicts that the loss of membrane integrity would also occur when decreased Ppi contributes to a high Ptm, as seen in NPPE. The model allows for the development of a spectrum of abnormalities ranging from transudative edema to pulmonary hemorrhage.22 Although small increases in Ptm result in low-protein edema through alterations in the Starling forces, higher pressures causing ultrastructural changes in the capillary endothelial barrier can lead to exudative edema.14 Extreme elevations in the Ptm break the alveolar-capillary membrane, allowing RBC leakage into the alveoli and, possibly, frank hemorrhage. Rapid changes in the Ptm, independent of the peak pressure, could favor the development of bleeding, as in exercise-induced pulmonary hemorrhage and postexercise hemoptysis.20
Given the relatively high estimated incidence of NPPE following acute airway obstruction, we are surprised that NPPH has not been reported previously. Without further data, we can only surmise the cause of our patient's extreme presentation. In patients with OSA, we speculate that nighttime "inspiratory muscle training" could enable the production of exaggerated negative intrathoracic pressures sufficient to cause hemorrhage. In a study of 10 patients with sleep apnea/obesity-hypoventilation syndrome, intra-alveolar hemorrhage and extensive hemosiderosis were noted that were "disproportionately severe for the morphologic abnormalities present in the left ventricle".23 Alternatively, the intrinsic weakness of the alveolar-capillary membrane could increase the severity of stress failure for a given rise in the Ptm. The use of crack cocaine induces increased alveolar permeability, and pulmonary hemorrhage and edema have been noted in a histopathologic series of cocaine users.24 Bleeding following acute UAO has been observed previously, but it was attributed to the rupture of the bronchial vasculature.11 25 In our patient, the bleeding appeared to originate in the alveoli, indicating that the pulmonary capillaries were the likely source. The dual mechanism for the increased capillary Ptm found in acute UAO would provide ideal conditions for the development of stress failure.
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Footnotes |
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Received for publication May 8, 1998. Accepted for publication October 27, 1998.
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 M Ranta, A J Cain, B Odutoye, and R E Mountain Pulmonary oedema induced by a piece of chicken J R Soc Med, January 8, 2002; 95(8): 404 - 405. [Full Text] [PDF]
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= increased; 
= decreased.