A lady with repeated respiratory failure.

To the Editor: Upper airway diseases resulting in obstruction can be caused by blockage secondary to tumor or cyst inside the larynx, compression of trachea by a goiter or airway collapse seen in obstructive sleep apnea. Failure to recognize the etiology and correct the condition promptly can be disastrous because upper airway obstruction (UAO) is a life-threatening emergency.

Recently, a 62-year-old woman was brought to the emergency center after onset of acute dyspnea. She had been discharged two days before admission after treatment for respiratory failure. She was using a CPAP machine for obstructive sleep apnea. This was the third time in a month patient presented with respiratory failure and the first respiratory failure episode happened during a sleep study. The patient had a respiratory failure eight months ago after she was admitted to the hospital for hypoglycemia. Bronchoscopy after the respiratory failure did not find significant pathology except for mild bronchitis. On arrival, at this admission, the patient was in moderate respiratory distress. Abnormal vital signs included respiration 24, pulse 140 and pulse oximetry 96% on 100% oxygen. Lung examination revealed diminished breath sounds bilaterally. Some inspiratory wheeze and stridor were noted for the first time. Her heart sounds were distant. An arterial blood gas before intubation revealed a pH of 7.20, PaC[O.sub.2] 62, Pa[O.sub.2] 84, bicarbonate 24.4, [O.sub.2] saturation 93% on Fi[O.sub.2] of 50%. Chest x-ray again showed right midlung atelectasis and chronic right hemidiaphragm elevation. A 2D echocardiography showed left ventricular hypertrophy with an EF of 40 to 45% and mild to moderate pulmonary hypertension. A bronchoscopy showed a band of tissue in the subglottic area and a granulation tissue mass in the adjacent area functioning as a ball valve causing obstruction. The band and the mass were resected under the guidance of direct laryngoscopy. No further obstruction episode occurred ever since.

Respiratory failure can be caused by both intrapulmonary and extrapulmonary conditions. Extrapulmonary causes include a number of different etiologies and can be divided into those caused by 1) decreased respiratory force seen in the central and peripheral nervous system and respiratory muscle dysfunction, and 2) increased impedance to airflow like those seen in diseases of the chest wall, pleural membrane and upper airways. Upper airway diseases causing acute obstruction in adults result from airway edema, compression, space occupation, stenosis, vocal cord paralysis or airway collapse (eg, obstructive sleep apnea). Stridor is a salient feature for all but sleep apnea and tracheal stenosis. Because hypoventilation is associated with all these etiologies, arterial blood gas uniformly shows hypoxemia plus hypercapnia. Our patient was no exception. Obstruction to upper airway is also associated with pulmonary hypertension, (1) congestive heart failure and noncarcinogenic pulmonary edema. (2) In our patient, all episodes of respiratory failure started after the patient fell into sleep. We believe that the followings are responsible for the characteristic sleep time onset. First, it is the recumbent position that brings the subglottic tissue band and the granulation tissue ball together causing obstruction of the airway. Second, airway diameter narrows significantly in individuals both with and without obstructive sleep apnea after sleep onset. (3) Third, the benzodiazepine the patient was taking at night inhibits the respiratory drive and/or respiratory muscle preferentially, and thus contributed to the process when she fell into sleep. (4) Fourth, the diaphragm contributes significantly to normal breathing in the recumbent position but our patient has idiopathic right diaphragmatic weakness/paralysis. This might have led to right mid-lung collapse secondary to insufficient airflow.

In the pediatric population, subglottic cyst has been reported as a rare, nonmalignant cause of UAO. (5) These cysts are the result of intubation in the neonatal period. In adults, benign tumors or malignancies of the vocal cords or larynx often cause UAO. Congenital malformation causing UAO in adult patients however is very rare. In our patient, the subglottic tissue band most likely represents a congenital malformation although endotracheal intubation could have stimulated the growth of the granulation tissue ball. Of all the etiologies mentioned above, which cause upper UAO, obstructive sleep apnea is the only one that does not result in acute respiratory failure. Since acute respiratory failure is a life-threatening emergency, etiologies of acute respiratory failure should be carefully sought and corrected before hospital discharge. Here, meticulous physical examination by the emergency physicians before intubation to look for stridor, and communication with the consultants about their findings are of pivotal importance.

Zhonglin Hao, MD, PhD

Douglas Farman, MD, FACCP

Edwin Grimsley, MD

Raj M. Patel, MD

Department of Internal Medicine

Mercer University, School of Medicine

Macon, GA

References

1. Weibley RE, Maldonado L. Proximal airway disorder in the pediatric patient. In: Shoemaker WC, Ayres SM, Grenvik A, et al (eds). Textbook of Critical Care, 4th ed. Philadelphia, W B Saunders Company. 2000, pp 1477-1481.

2. Kollef MH, Pluss J. Noncardiogenic pulmonary edema following upper airway obstruction. 7 cases and a review of the literature. Medicine (Baltimore) 1991;70:91-98.

3. Kathe GH. Mechanisms and anatomical sites of upper airway obstruction in obstructive sleep apnea in adults. UpToDate Online V14.2, 2006.

4. Issa FG, Sullivan CE. Alcohol, snoring and sleep apnea. J Neurol Neurosurg Psych 1982;45:353-359.

5. Lim J, Hellier W. Harcourt J, et al. Subglottic cysts: the Great Ormond Street experience. Int J Pediatr Otorhinolaryngol 2003;67:461-465.