Cerebral arterial air embolism after endobronchial electrocautery: a case report and review of the literature

Background Endobronchial electrocautery is a common and safe therapeutic endoscopic treatment for malignant airway obstruction. Cerebral arterial air embolism (CAAE) is a rare but potentially fatal complication of endobronchial electrocautery. Case presentation We present the first case of cerebral arterial air embolism after endobronchial electrocautery. A 56-year-old male with a pulmonary tumour in the right upper lobe received repeated endobronchial electrocautery. During the procedure, he experienced unresponsiveness, hypoxemia and bradycardia, and he developed tetraplegia. Brain computed tomography showed several cerebral arterial air emboli with low-density spots in the right frontal lobe. He received hyperbaric oxygen therapy with almost full recovery, except for residual left-sided weakness. Conclusions General physicians should realize that CAAE may be a possible complication of endobronchial electrocautery. Several measures, including avoiding positive pressure, lowering ventilatory pressures if possible, avoiding advancing the bronchoscope to occlude the bronchus and using the non-contact technique, should be used to prevent this devastating complication.


Introduction
Therapeutic endoscopic treatment may be considered to be used in malignant airway obstruction, such as endobronchial electrocautery, argon plasma coagulation (APC), thermal laser. Electrocautery is a common and safe bronchoscopy technique. The main complications of electrocautery include bleeding and airway re. Cerebral arterial air embolism is an extremely rare but potentially fatal complication of bronchoscopy. Azzola et al. [1] reported that a frequency of < 0.02% of cerebral air embolism happened after bronchoscopy in their institution. Although cerebral arterial air embolism has been showed as a complication of APC and thermal laser [2], it has never been reported in electrocautery. Herein, we described a patient who developed cerebral arterial air embolism (CAAE) after endobronchial electrocautery.

Case Presentation
A 56-year-old male, never smoker, was transferred to our hospital. Approximately 16 years prior, he had been diagnosed with lung cancer and received lung surgery and chemotherapy. Three years ago, he developed a cough and underwent multiple endobronchial electrocautery therapy in another hospital. With the diagnosis of the recurrence of right lung endobronchial adenocarcinoma, the patient this time was admitted for repeated bronchoscopic thermal ablation procedure to relieve airway obstruction. Bronchoscopy revealed an endobronchial tumor emanating from the posterior segment of the right upper lobe (RUL) bronchus and causing completely obstruction of the bronchus (Fig. 1a). The patient was in supine position without intravenous sedation. The tumor was debulk using endobronchial electrocautery and blunt dissection of devitalized tissues with tooth forceps follows. (Fig. 1b, c). The setting of electrocautery cut mode was at 40W intensity and the coagulation mode was at 30 W intensity for duration of 3 s.
During the procedure the patient showed no cough and no obvious bleeding. At the end of the operation, he suddenly became unresponsive, hypoxemic (SpO 2 88%) and bradycardic (heart rate 58 /min). High ow oxygen administration with mask and uid resuscitation were quickly performed. His heart rate and SpO 2 recovered quickly and the consciousness gradually improved 30minutes later. However, his abnormal neurological symptoms became obvious, including slurred speech, right gaze, paralysis in both extremities. The muscle strength in left limbs was 0/5 while 2/5 in right limbs. His left Babinski sign was positive. Hypoglycemia was excluded. Emergency brain computerized tomography (CT) revealed the presence of cerebral gas embolisms with several millimeter-sized, rounded and low-density spots in the right frontal lobe (Fig. 2).
Hyperbaric oxygen therapy (HBO 2 ) was initiated within 2 hours after bronchoscopy. He was transferred to the intensive care unit. That night, he received another hyperbaric oxygen therapy once again. After this treatment, the patient experienced generalized tonic-clonic seizures which were aborted using phenytoin, phenobarbitone and sodium valproate. A repeated brain CT done 24 h after bronchoscopy showed no signs of air embolism (Fig. 3).
The patient received intensive rehabilitation. His mental status subsequently improved but he still had a mild leftsided hemiparesis with muscle strength 3/5 in left upper limb and power 4/5 in left lower limb.

Discussion And Conclusions
CAAE is a rare but potentially fatal complication of both diagnostic and therapeutic bronchoscopy and often iatrogenic [3]. Knowledge about the etiology of CAAE is limited and case reports therefore are important sources to get information [4]. To our knowledge only four cases of CAAE after thermal ablation have been reported [5][6][7][8].
The pro les of the reported patients, the examination procedures undertaken, the treatments, and the outcomes are shown in Table 1. This is the rst reported case in the literature of CAAE developing after endobronchial electrocautery.
The possible mechanisms responsible for the development of CAAE during the therapeutic bronchoscopy include formation of broncho-vascular stula, occlusion of bronchus by the bronchoscopy and paradoxical embolization [3,4,8,9]. A broncho-vascular stula was formed because of in ammation or heat coagulation and mechanical destruction of the tumor and adjacent tissue [7,10]. In this case, electrocautery ablation of the tumor accompanied by mechanical debridement of the bronchus might result in the formation of the broncho-vascular stula [1,11]. The gas could enter the circulation through stula. Gas embolism can easily enter a bronchovascular stula if the internal airway pressure goes up with the bronchoscopy process or when the patient is accepting positive pressure ventilation, coughing or taking a deep breath during the procedure [7,[12][13][14][15].
Paradoxical embolization occurs when the gas migrates from the venous circulation into the arterial system via an intracardiac shunt (patent foramen ovale) [16]. Actually, the air can be eliminated through diffusion into the alveoli, but if the capacity of the air exceeds 50 mL, it is easily for it to enter the pulmonary veins [16,17]. In an animal study, Feller-Kopman et al. [10,13]found that bronchoscopic thermal ablation with gas ow was associated with the occurrence of gas embolism in a dose-dependent fashion. What they found was consistent with the fact that high ow of coolant gas can lead to vascular air embolism during the use of contact probe [10]. Other possible risk factors for CAAE include patients with chronic obstructive pulmonary disease, a cavity inside the mass, lesions in the upper lobe, left lateral position, semi-recumbent position and bleeding [1,7,18].
Iatrogenic CAAE can be caused by a broad range of procedures, such as central venous catheter, cardiopulmonary bypass, bronchoscopy, lung biopsy, Nd-YAG laser resection of tumor etc. [4,17]. Early in 1979, CAAE is suggested as a complication of transbronchoscopic lung biopsy [12]. This means CAAE should be considered as a possible cause of neurological symptoms after any procedure with a possibility of CAAE. Clinicians should keep in mind the possibility of CAAE after endobronchial electrocautery.
The symptoms of CAAE develop suddenly and are the same as those of cerebral hemorrhage or thromboembolism, including hemiparesis, tetraplegia, seizures and coma with cardiovascular collapse. In some reported cases, the diagnosis of CAAE should be suspected when there was protracted recovery from sedation [8]. In this case, the patient was noted to loss of consciousness. The symptoms of CAAE could be fatal or asymptomatic which indicates that it is important to bear the condition in mind even without symptoms [4].
Because asymptomatic CAAE exists, the actual incidence is higher than previously reported.
Imaging of the brain is useful to visualize air bubble. A CT was done within 2 hours of the symptom onset in this case and air bubbles were showed in the right frontal lobe. Sometimes CT may not reveal the presence of air in the brain as bubbles may be reabsorbed quickly if there is a delay in imaging or using inadaptable window settings on noncontrast CT [19]. And when the air bubble diameter is less than 1.3 cm, it may not be detected by CT [15]. Kanchustambham et al. [8] reported that no air bubbles could be visualized on the CT images and the diagnosis was made by exclusion. A repeated CT after 24 hours showed no signs of air bubbles in this case.
Hence, CAAE cannot be ruled out through normal imaging. The acute infarct can be con rmed by MRI which is more time-consuming than CT and might delay the therapy. Transesophageal echocardiography and precordial doppler are used to detect intravenous and intracardiac air embolism, and end-tidal carbon dioxide may be an early sign of air embolism [9,13]. As a result, clinical evaluation is still preferred for the assessment of CAAE [8].
Hyperbaric oxygen therapy is recommended as the most bene cial treatment of CAAE [9,[16][17][18]20]. The mechanisms of hyperbaric oxygen therapy for CAAE include: reduced air volume, increased diffusion gradient out of the bubbles, reduction in cerebral edema, decreased endothelial damage, promotion of restoration of distal blood ow [3,6,16,20]. In some hospitals, HBO 2 is not available due to the lack of hyperbaric chamber or unable to transport patients [1,7,15,18]. The time to start HBO 2 treatment determines the outcome of the patients. It showed better outcome for patients treated with HBO 2 within ve to seven hours from the symptom onset [3,4,20]. However, there were several reports of good outcomes in patients with delayed onset of treatment from 40 hours to multiple days [4,6,21]. Our patient received the rst HBO 2 treatment within 3 hours and the second time HBO 2 treatment within 24 hours and no signs of air bubbles were showed in a repeated CT. The mortality in CAAE patients without HBO 2 treatment was 93% while 7% with HBO 2 treatment [21]. In conclusion HBO 2 should be initiated as soon as possible after the diagnosis of CAAE to reach the best effect. When there is no available of HBO 2 , normobaric oxygen (NBO 2 ) can be administered as the most frequent non-HBO 2 treatment [8,18].
There are some different opinions on the patient's position to prevent air embolism. Kanchustambham et al. [9] suggested using left lateral decubitus and Trendelenburg position. The Trendelenburg position was reported to reduce the air bubbles going to the brain [20]. However, some studies revealed that Trendelenburg position may worsen cerebral edema and patient should be placed at and supine in cases of arterial air embolism [4,16] The patient suspected of diagnosed with air embolism should be transferred to intensive care unit for careful monitoring and management. Other treatments include endotracheal intubation, volume expansion and extracorporeal membrane oxygenation (ECMO) [9,22]. Targeted temperature management (TTM) may be helpful to prevent the deterioration of cerebral function in the cases of CAAE [23]. Other organs should be examined by echocardiography, electrocardiogram or other examinations when encountering a patient with CAAE, because systemic air embolisms should be considered [24]. This is the rst case of CAAE after endobronchial electrocautery. General physicians should realize that CAAE can be a possible complication of endobronchial electrocautery. Some measures could be used to prevent this devastating complication: avoiding positive pressure, lowering ventilatory pressures if possible, setting the ow to the lowest rate possible when using Nd-YAG or APC, avoiding advancing the bronchoscope to occlude the bronchus, using the non-contact technique etc. Bronchoscopy revealed that the posterior segment of the RUL bronchus was completely obstructed by the tumor (a, arrow). Endobronchial electrocautery was used to debulk the tumor (b). Bronchoscopy showed the posterior segment after the ablation (c).

Figure 2
The cerebral CT scan following bronchoscopy showed multifocal cerebral air embolism in the right frontal lobe (arrows).