Abstract

An 81-year-old male scheduled for debridement of a perianal abscess sustained acute upper airway obstruction with atelectasis of the left lower lobe during induction of anesthesia. Results of a fiberoptic bronchoscopy revealed dorsal bulging and obstruction of the left bronchus. Under the context of tortuous aorta and calcified left border of the heart silhouette, aortic aneurysm was suspected; the diagnosis was confirmed by a computed tomography scan. Aortic aneurysm without specific symptoms cannot be screened by a single preoperative chest X-ray. The anesthesiologist should promptly request further radiographic studies to rule out potential aortic pathology if in doubt.

Keywords

aortic aneurysm; intraoperative complications; oxygen desaturation; pulmonary atelectasis;

1. Introduction

Several cases have been reported on sustaining bronchial or tracheal compression with or without lobar atelectasis by a thoracic aortic aneurysm.1, 2, 3 An enlarged mediastinal mass that causes a compression effect on the tracheobronchial tree and neighboring large vessels such as the pulmonary vein and artery and heart chambers is extremely catastrophic. The clinical presentation includes a variety of symptoms, from asymptomatic, mild cough, hoarseness, and dysphagia to dyspnea, chest pain, and pulmonary effusion.⁴ Chen et al reported a case of a patient in whom a marked increase in airway pressure was encountered after an endotracheal intubation under general anesthesia, which was later found to be due to a compression of the airway by a metastatic tumor mass.⁵ Cone and Stott reported an instance of intermittent airway obstruction during anesthesia due to compression by an undiagnosed anterior mediastinal mass.⁶ We are unaware of any published reports of acute intraoperative O₂ desaturation and atelectasis due to a compression of the airway by an existing aortic aneurysm.

2. Case report

An 81-year-old man presented for emergency debridement of a perianal abscess. He received an extracorporeal shock-wave lithotripsy more than 10 years ago, and was hospitalized 3 years ago because of upper gastrointestinal bleeding. In the past 2 years, he had experienced difficulty in swallowing. Preoperative chest radiography revealed a tortuous aorta with calcification and a clear bilateral lung field (Fig. 1). Spinal anesthesia was attempted initially, but failed due to a technical problem, for which general anesthesia, induced with sevoflurane inhalation, was used as a substitute, followed by the insertion of a laryngeal mask airway (LMA). Pulse oximetry fell to 90% with inspired oxygen fraction of 1.0. Paradoxical breathing by inhalational stridor was noted. The LMA was removed and replaced with endotracheal intubation. The airway pressure was increased with mechanical ventilation, but O₂ saturation did not improve promptly as expected. Arterial blood gas measurement (PO₂) was 67 mmHg.

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Fig. 1. Preoperative posteroanterior view. On the postoperative morning, the radiologist reported that chronic interstitial infiltration over the lower lungs, enlarged cardiac silhouette, and aneurysm over ascending aorta should be ruled out.

Fiberoptic bronchoscopy showed inward bulging of the dorsal part of the trachea, with a narrowing of the distal part of the trachea. After passing the narrowing, we found that the left main stem bronchus was totally invisible (Fig. 2). Portable chest radiography was arranged in the operating theater and the chest X-ray (CXR) taken showed a total collapse of the left lower lobe (Fig. 3), which in our opinion was caused by dorsal compression of an aortic aneurysm. After the surgery had been completed, emergent chest computed tomography (CT) was arranged, which revealed a huge aneurysm in the ascending aorta (diameter: 9 × 11 cm) with a narrowing of the left main bronchus because of external compression (Fig. 4). The patient remained intubated and was mechanically ventilated with positive pressure until the next morning, and received elective surgical repair of the aneurysm on the same day. Postoperatively, the patient recovered well and was discharged from the hospital uneventfully 4 weeks later (Fig. 5).

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Fig. 2. (A) Fiberoptic bronchoscopy showed bulging of dorsal part of trachea, occluding most of the path. (B) While passing the narrowing, the arrow showed the right main stem bronchus and the left main stem bronchus were totally out of vision. (C) After advancing to the right bronchus, the right bronchus gives out three branches, known as upper (a), middle, and lower lobe bronchi (b).

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Fig. 3. Intraoperative anteroposterior view. The radiologist reported chronic interstitial infiltration over the lower lungs, enlarged cardiac silhouette, aneurysm over ascending aorta, consolidation in left lower lobe with left pleural effusion, and endotracheal tube in place.

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Fig. 4. Linear left bronchus (*) caused by a large aneurysm (arrows), measuring 9 cm × 11 cm.

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Fig. 5. Chest X-ray on day of hospital discharge.

3. Discussion

Approximately 1% of males between 55 years and 64 years of age could be affected with an aneurysm, and the likelihood might increase to about 4–6% over the age of 75. Hypertension and arteriosclerotic heart disease could carry the highly risky factors in developing aneurysmal disease. It is a silent killer because most of its victims are free of symptoms until the situation becomes life-threatening, such as sizable compression of the vitals or requiring dissection. The diagnosis of aortic aneurysm is difficult. Most cases have it incidentally unearthed during CXR examination for other purposes. Because aortic aneurysm is a degenerative disorder, it is not uncommon to find a tortuous aorta with calcified wall in aged patients, as evidenced by CXR film. Pooled data from 10 studies place the predictive sensitivity of a widened mediastinum or an abnormal aortic contour for thoracic aortic disease at 64% and 71%, respectively.⁷ Research has not yet established whether these patterns could be equally applied to asymptomatic patients. Physicians should have a low threshold for requesting a chest CT scan for thoracic aortic disease. However, to date no cost–benefit analysis has been conducted for the screening of such patients and no clear guidelines are established for dealing with such abnormalities on preoperative CXR.⁴ In our patient, the findings of the current CXR were similar to the one taken 3 years ago, but the radiologist at that time did not report the finding to be a major concern of a possible aortic aneurysm. The surgery was scheduled as an emergency, and thus no report on preoperative images could be tendered by the radiologist on duty. The growth of aneurysms is estimated at a rate of 0.1 mm per year.⁸ According to this estimate, our patient's concealed aneurysm had already existed for 3 years. The patient reported that he had received gastrointestinal endoscopy and no significant finding was noted at that time. Antón reported a case with an unusual nondissecting ascending aneurysm with a size of 8 × 9 cm, diagnosed 5 years earlier, who developed pulmonary effusion due to pulmonary vessel compression. The aneurysm was 9.5 × 10 cm in size at the time of report.⁹ Therefore, an aneurysm's size does not necessarily parallel the severity of the presenting symptoms or signs.

Our patient did not complain of any discomfort, either while he was awake in the right lateral decubitus position during the spinal anesthesia or while he was in the supine position during the inhalation induction. The first presentations were paradoxical respiratory pattern and upper airway obstructive stridor when the patient lost consciousness during inhalation induction. Phillips et al reported a case of positional dyspnea in the left decubitus position, associated with aneurysm of the thoracic aorta.¹⁰ Spiropoulos et al reported another case with orthopnea affected with a similar disorder.¹¹ Because our patient was free from symptoms of airway compromise, we ventured to speculate that the supine position and inhalation of gas had altered the whole critical balance of keeping airway patency between spontaneous breathing and the compressing effect of the aneurysm. The induction of general anesthesia tends to exacerbate external airway compression upon decreasing lung volume and relaxation of bronchial smooth muscle. In addition, the inadequate position of LMA might contribute to existent obstructive upper airway. The tachycardia and hypertension induced by hypercapnea during the induction phase would further exaggerate the size of the aneurysm, which made the obstruction worse. On the contrary, regional anesthesia induces various degrees of sympathetic block and makes hemodynamics less variable. Theoretically, it is safer to adopt regional rather than general anesthesia for this situation.

Several disastrous fatal complications have been reported during induction or emergence from general anesthesia in pediatric patients with anterior mediastinal mass.¹² The effect is further exaggerated by neuromuscular block and positive pressure ventilation, both of which reduce normal transpleural pressure gradients, causing a narrowing of large-caliber airways.⁶ However, our patient differed from those patients in two ways. First and most striking, he was free of symptoms prior to the operation. Second, the aneurysm was distensible but not as solid as a tumor mass such as lymphoma. For patients with symptomatic anterior mediastinal mass, spontaneous respiration should be maintained during general anesthesia.¹² Our patient started developing upper airway obstruction when he was induced with inhalation anesthesia. We speculated that critical narrowing of the airway was aggravated by an exertion breathing pattern due to inadequate LMA positioning, in addition to decreased lung volume during the induction phase. Oxygenation was improved gradually to some extent later when the patient was paralyzed and mechanically ventilated. It reflects that different sites and underlying pathology as well as patient's posture interact with each other, and cause different responses to paralysis and mechanical ventilation.

Unexpected acute airway obstruction during anesthesia is associated with various situations, including external and internal airway pathologies. Some conditions may have been diagnosed prior to surgery, but some are not. Aortic aneurysm, with or without dissection or leak, constitutes a critical emergency. The condition should be of primary priority over any underlying problem, especially in aged patients or if the CXR indicates abnormality. Fiberoptic bronchoscopic examination is a direct and prompt diagnostic tool to verify and clarify the degree of narrowing at the first consultation. Portable CXR is not really necessary except when desaturation is encountered. CT imaging should follow to clarify the diagnosis and to provide information for decision making. Surgical repair is indicated for aneurysms larger than 5.5 cm in asymptomatic patients (Class I, LOE C).⁶

In conclusion, unexpected upper airway obstruction constitutes a critical emergency situation during the induction phase of anesthesia. Identification of the pathology is essential. Tortuous aorta with calcified wall is a common finding on the CXR of elderly patients. The anesthesiologist should inquire every detail about compressing symptoms or signs, perform circumstantial physical examination, and consult the radiologist preoperatively as much as possible. If in doubt, one should have a low threshold for ordering further radiological studies to define the aortic anomalies. Possible aneurysm compression should be kept in mind when acute upper airway obstruction is encountered during perioperative periods.