The efficacy and safety of modified transbronchial cryobiopsy in the diagnosis of interstitial lung disease

Abstract

The objective of this study is to investigate the efficacy and safety of flexible transbronchial cryobiopsy (TBCB) in the diagnosis of diffuse parenchymal lung disease (DPLD) in a routine bronchoscopy examination room under analgesia and sedation, using neither endotracheal intubation or rigid bronchoscope nor fluoroscopy or general anesthesia. The data from 50 DPLD patients with unknown etiology who were treated in the Affiliated Hospital of Guilin Medical College from May 2018 to September 2020 were collected, and 43 were eventually included. The specimens obtained from these 43 patients were subjected to pathological examination, pathogenic microorganism culture, etc, and were analyzed in the clinical-radiological-pathological diagnosis mode to confirm the efficacy of TBCB in diagnosing the cause of DPLD. Subsequently, the intraoperative and postoperative complications of TBCB and their severity were closely observed and recorded to comprehensively evaluate the safety of TBCB. For the 43 patients included, a total of 85 TBCB biopsies were performed (1.98 [1, 4] times/case), and 82 valid tissue specimens were obtained (1.91 [1, 4] pieces/case), accounting for 96.5% (82/85) of the total sample. The average specimen size was 12.41 (1, 30) mm². Eventually, 38 cases were diagnosed, including 11 cases of idiopathic pulmonary fibrosis, 5 cases of connective tissue–related interstitial lung disease, 5 cases of nonspecific interstitial pneumonia, 4 cases of tuberculosis, 4 cases of occupational lung injury, 3 cases of interstitial pneumonia with autoimmune characteristics, 1 case of lung cancer, 2 cases of interstitial lung disease (unclassified interstitial lung disease), 1 case of hypersensitivity pneumonitis, 1 case of pulmonary alveolar proteinosis, and 1 case of fungal infection. The remaining 5 cases were unclarified. For infectious diseases, the overall etiological diagnosis rate was 88.4% (38/43). With respect to complications, pneumothorax occurred in 4 cases (9.3%, 4/43, including 1 mild case and 3 moderate cases), of which 3 cases (75%) were closed by thoracic drainage and 1 case (25%) was absorbed without treatment. In addition, 22 cases experienced no bleeding (51.2%) and 21 cases suffered bleeding to varying degrees based on different severity assessment methods. TBCB is a minimally invasive, rapid, economical, effective, and safe diagnostic technique.

1. Introduction

Diffuse parenchymal lung disease (DPLD) is a class of lung disease that is composed of more than 200 different types. The incidence of DPLD is estimated to be up to 15% and its clinicopathological features, etiology, treatment, and prognosis vary greatly.^[1,2,4,5] At present, the DPLD diagnostic model, as the core of diagnosis for this disease, is generally a multidisciplinary clinical-radiological-pathological model that combines clinical, imaging, and pathological evidence.^[3,5] Surgical lung biopsy (SLB) is considered the optimal method for obtaining pathological biopsy specimens; however, this technique is costly and traumatic and is subjected to a high morbidity and mortality.^[19,24,25] On the other hand, the tissue specimens obtained by transbronchia forceps biopsy are smaller in size and prone to squeezing artifacts, leading to a low performance of diagnosis.^[31,32] Similarly, percutaneous lung biopsy has the same problems and involves a higher risk of hemopneumothorax and pneumothorax. In general, the commonly used biopsy methods for the time being are all subjected to deficiencies in terms of efficacy and safety, which seriously limits the etiological diagnosability of DPLD.

Transbronchial cryobiopsy (TBCB) as a novel technique has been rapidly developed in the past decade. Researchers have carried out systematic studies on TBCB and applied it widely in monitoring interstitial lung disease,^{[15,16,22,23]} lung tumors,^[26,27] peripheral lung disease,^[28] and post-lung transplantation.^[20,21] The tissue specimens obtained by TBCB are large in size and relatively intact in structure. Besides, TBCB is featured with the advantages of better safety and a higher positive rate of diagnosis, therefore exhibiting great potential in the diagnosis of DPLD. Unfortunately, there is still a lack of a standard protocol for TBCB, leading to significant variations among different medical institutions and operators in terms of technical procedure. The latest international expert consensus^[3] recommends that TBCB should be performed under deep sedation, general anesthesia, endotracheal intubation, or rigid bronchoscope. However, rigid bronchoscopy has stringent technical requirements, and biopsy operation requires assistance from an anesthesiologist, which further increases the difficulty to implement and popularize TBCB. In order to overcome this problem, we made some innovative modifications to the existing TBCB technique, to allow it being completed in a routine bronchoscopy room using only flexible bronchoscope while having the patient breathing independently, with no need for general anesthesia, deep sedation, rigid bronchoscopy, or endotracheal intubation. The outcome of our technique was as satisfactory as the operation implemented under conventional rigid bronchoscopy in the operating room, implying that this achievement may facilitate the widespread promotion of TBCB in China. In this study, we aimed to explore the efficacy and safety of the modified TBCB technique in the etiological diagnosis of DPLD.

2. Materials and methods

2.1. Research subjects

Data were retrospectively collected from 50 DPLD patients who were advised to receive pathological tissue examination through TBCB for diagnosing the cause of disease at the Department of Respiratory and Critical Medicine of the Affiliated Hospital of Guilin Medical College from May 2018 to September 2020. Eventually, 43 patients who met our inclusion and exclusion criteria and successfully completed TBCB were included.

Inclusion criteria: age >18 years and <80 years; partial pressure of arterial oxygen in low flow oxygen inhalation >60 mm Hg (1 mm Hg = 0.133 kPa); lesions in both lung fields or more than 2/3 of the lung fields on HRCT, with manifestations of small flakes, nodules, grids or lines, military shapes, honeycomb shapes, and ground glass shadows of varying sizes; Cause of disease cannot be determined based on high resolution chest CT, laboratory examination or routine bronchoscopy, in combination with clinical manifestations and other related data.

Exclusion criteria: Uncorrected blood metabolic disorders, hemodynamic instability, severe respiratory failure, unstable heart disease, pulmonary hypertension, uncontrolled hypertension or use of anticoagulants, etc; Pulmonary dysfunction: Carbon monoxide diffusing capacity of the lung <35% or forced vital capacity <50%; HRCT shows that the biopsy site is adjacent to medium and large blood vessels or pulmonary vesicles, or indicates pulmonary vascular thickening, pulmonary vascular malformation, hemangioma, or pulmonary vasculitis.

This study is a retrospective study that had been approved by the Medical Ethics Committee of the Affiliated Hospital of Guilin Medical College and exempted from informed consent (ethical approval number: YJSLL202105).

2.2. Freezing equipment

Soft freezing probe: manufactured by Erbo Electronic Medical instrument Company, serial number/batch number 11463160 (diameter 1.9 mm, length 900 mm); disposable guide wire: distributed by German Boko International Medical Trading (Shanghai), batch number 21284777; Hemostatic balloon: distributed by Nanwei Medical Technology Co., Ltd, specification model MTN-SRB-T-16/20, product batch number 200610531.

2.3. Operation procedure

2.3.1. Preoperative preparation

Before the operation, fully communicate with the patient and their family about matters related to the operation, complete HRCT, pulmonary function tests, echocardiography, and other examinations, which are the same as the routine preoperative bronchoscopy examinations. Hemostatic drugs, hemostatic gauze, closed thoracic drainage device, and routine preset hemostatic balloon were prepared as appropriate. Other instruments remained the same as those for routine bronchoscopy. All the operations were performed in a routine bronchoscopy room.

2.3.2. Anesthesia

The upper and lower airways were anesthetized with 2% lidocaine and sedated with midazolam (0.02–0.07 mg·kg⁻¹) and fentanyl (0.5–2 µg·kg⁻1). Based on appropriate clinical judgment, 1 to 3 mg midazolam and 0.1 µg·kg⁻¹ fentanyl were intravenously injected to the patient, followed by intermittent injection of 1 to 3 mg midazolam and 0.1 µg fentanyl to maintain moderate sedation (intervention for keeping the airway unobstructed is not needed during moderate sedation, as the patient had adequate autonomic ventilation and could maintain normal cardiovascular function).

2.3.3. Airway management

For airway management, the modified TBCB technique proposed in this study only enhanced the delivery of oxygen through a nasal catheter placed in the nasal cavity under local anesthesia and moderate sedation. The patient’s heart rate, blood oxygen, respiratory rate, blood pressure, and electrocardiogram were recorded continuously.

2.3.4. Placement of the guide wire and test balloon

The guide wire and test balloon were placed in the following steps: Direct the guide wire to pass through the working channel of the flexible bronchoscope to reach the biopsy site. Then, indwell and fix it, and withdrawal from the bronchoscope; Send the hemostatic balloon to the biopsy site through the guide wire, and inflate the balloon to the size that can completely block the opening by injecting air or saline under direct vision; After testing, deflate the balloon for further use.

2.3.5. TBCB operation and observation

The TBCB operation was performed in the following procedure: Check and confirm in vitro whether the test cryostat and cryoprobe are in normal working condition. Determine the time for the first freezing in vivo based on the time required for the probe to be frozen in vitro on the day of operation. This time should be adjusted appropriately based on the size of specimen (generally, the specimen diameter is recommended to be 5 mm); Send the ultrasound probe (radial EBUS) through the bronchoscopy hole into the target bronchus, directly reaching the most distal end. When encountering an obvious resistance, mark the position of the probe back end at the entrance of bronchoscopy hole as point B. Then, withdrawing the probe to the bronchial opening and fixing the probe position, measure the distance from point B to the bronchoscopy hole, and set this distance as the length from the bronchial opening to the chest wall (this length minus 1 mm is the length of the frozen probe to be sent in). Accordingly, send the frozen probe in for the desired length to perform lung biopsy. No fluoroscopy monitoring is required; After freezing for a specified period of time, pull the cryoprobe, specimen, and bronchoscope as a whole out of the body. In the meanwhile, inflate the preset hemostatic balloon quickly; Once the specimen is taken out, reinsert the flexible bronchoscope immediately to check the hemostatic balloon and the bleeding condition. If there is no blood leakage, deflate the hemostatic balloon slowly. Otherwise, ensure the bronchial opening being blocked by the hemostatic balloon and inject adrenaline saline and snake venom thrombin through the balloon. After the bleeding stops, decide whether to continue frozen lung biopsy based on the size of specimen and the amount of bleeding; During the biopsy operation, auscultate the lung repeatedly and monitor the patient’s condition closely to detect any possible pneumothorax; For cases requiring multiple biopsies, repeat the above process until the end of operation; Perform chest X-ray examination 1 to 2 hours after the operation and monitor the patient’ condition closely for 72 hours to avoid occurrence of delayed pneumothorax (treat the patient immediately if pneumothorax is detected); Monitor the patient’s vital signs closely and return the patient to the ward once the condition is stabilized; Maintain a strictly aseptic environment during the operation process and sterilize the equipment following a high standard after the operation to avoid infection.

2.3.6. Observation of complications

The most common complications of TBCB are pneumothorax and bleeding. For the former, the severity of pneumothorax was classified into “mild,” “moderate,” and “severe” according to the degree of lung compression (<30%, 30%–50%, and ≥50%, respectively) in this study.^[7] For the latter, there has been no exact measure of consensus for the severity of bleeding both at home and abroad. According to the specific hemostatic methods adopted during the operation in previous studies,^{[3,6,9,15,24]} we classified the severity of bleeding as follows: grade 0 or no bleeding (only blood stains, no need for aspiration); grade 1 or mild bleeding (need for aspiration); grade 2 or moderate bleeding (need for hemostatic balloon occlusion or topical use of hemostatic drugs); and grade 3 or severe bleeding (need for vascular intervention or surgery, admission to ICU, and even death).

2.4. Statistical methods

Data analysis was carried out using SPSS22.0 statistical software, with $d^{\overline{x}}\pm \mathrm{s}$, M(Q1, Q3) representing the results of measurement data. The number of cases and proportion in percentage were used to represent the results of count data. The χ² test was used to test the comparison of rates, with the detection level set to α = 0.05. Then, the contingency table was established, and the χ² test (qualitative variables) and t test (normally distributed variables) were used to test the inferences.

3. Results

3.1. Clinical baseline data

Of the 43 patients who successfully completed TBCB, there were 12 females and 31 males, with an average age of 57 (32–78) years; there were 14 cases (32.56%) whose smoking index was higher than 400 cigarettes per year and 28 cases (65.1%) who had an exposure history. The average length of stay was (9.70 ± 5.71) days. See Table 1 for details.

Table 1.

Clinical characteristics of the 43 TBCB patients included.

Item	Category	Result
Age		57.0 ± 9.9
Gender	Male	31 (72.09%)
	Female	12 (27.91%)
Height (cm)		162.7 ± 8.5
Weight (kg)		61.8 ± 8.8
BMI		23.32 ± 2.67
Smoking index*	>400	14 (32.56%)
	≤400	9 (20.93%)
	0	20 (46.51%)
Exposure history†	Yes	28 (65.12%)
	No	15 (34.88%)
Underlying diseases (cases)	No	20
	Autoimmune disease	5
	Hypertension	3
	Diabetes	7
	Hepatitis	2
	Tuberculosis	1
	Coronary heart disease	1
	Others‡	8
Hospitalization days (d)		9.70 ± 5.71

TBCB = transbronchial cryobiopsy.

^*Number of cigarettes smoked per day × years of smoking.

^†Exposure to birds, mold, hay, rural organic dust, war chemicals, welding and occupational dust (such as asbestos, silica, and coal), etc.

^‡Four cases of gastritis, 2 cases of cerebral infarction, 1 case of nasopharyngeal carcinoma, and 1 case of dilated cardiomyopathy.

3.2. TBCB operation and biopsy

All the frozen probes used during the biopsy operation were of a diameter 1.9 mm. The average freezing time was 4.81 (3, 8) seconds, and the average number of freezing times was 1.98 (1, 4) per case. A total of 85 biopsies (4 in the right upper lobe, 68 in the right lower lobe and 13 in the left lower lobe) were performed, and 82 valid specimens were obtained (3 specimens were regarded as invalid due to low diagnostic efficacy as the acquired alveolar lung parenchyma was too small or there was even no alveolar lung parenchyma), with an effective rate of 96.5% (82/85, 1.91 [1, 4] pieces per case). The specimen size was 12.41 (1, 30) mm². See Table 2 for detailed results.

Table 2.

The detailed results.

Biopsy characteristics	N = 43	M (Q1,Q3)
Freezing time (s)		4.81 (3, 8)
Times of freezing/case		1.98 (1, 4)
Number of specimens/case		1.91 (1, 4)
Specimen size (mm2)		12.41 (1, 30)
Biopsy site (times)
Upper right leaf		4/4.7%
Lower right leaf		68/80%
Lower left leaf		13/15.3%

3.3. Diagnosis results

According to the pathological results of TBCB specimens combined with clinical and imaging evidence, 38 of 43 patients (88.4%) were diagnosed with clinical-radiological-pathological, among which 32 had specific pathological diagnosis (i.e., 74.4% of the patients were highly consistent with the final diagnosis). In our study, the most common histological type was idiopathic pulmonary fibrosis/UIP (see Table 3 for specific disease types). As it can be seen in Figure 1, 5 cases were not clearly diagnosed, and all of them showed the symptoms of DPLD. By combining clinical, imaging and laboratory examination evidence, these 5 cases were speculated to involve a high possibility of infectious diseases.

Table 3.

Types of diseases in 43 patients.

Histological type	Cases	Constituent ratio/%
IPF	11	26%
CTD-ILD	5	12%
NSIP	5	12%
Tuberculosis	4	9%
Occupational lung injury	4	9%
IPAF	3	7%
ILD	2	5%
Lung cancer	1	2%
HP	1	2%
PAP	1	2%
Fungal infection	1	2%
Infectious disease	5	12%
Total	43	100%

CTD-ILD = connective tissue-related interstitial lung disease, IPAF = interstitial pneumonia with autoimmune characteristics, IPF = idiopathic pulmonary fibrosis, HP = hypersensitivity pneumonitis, NSIP = nonspecific interstitial pneumonia, PAP = pulmonary alveolar proteinosis.

Figure 1.

Types of diseases in 43 patients. CTD-ILD = connective tissue-related interstitial lung disease, IPAF = interstitial pneumonia with autoimmune characteristics, IPF = idiopathic pulmonary fibrosis, HP = hypersensitivity pneumonitis, NSIP = nonspecific interstitial pneumonia, PAP = pulmonary alveolar proteinosis.

3.4. Complications of TBCB

3.4.1. Bleeding

All the 43 patients included were routinely preset with hemostatic balloon occlusion to prevent and stop bleeding. Out of the 85 biopsies performed, there were 22 cases (51.2%) with no bleeding, 13 cases (30.2%) with mild bleeding, 7 cases (16.3%) with moderate bleeding, and 1 case (2.3%) with severe bleeding. The incidence of moderate or severe bleeding was 18.5%.

3.4.2. Pneumothorax

Four of 43 (9.3%) patients developed pneumothorax, including 1 case of mild pneumothorax (2.3%) and 3 cases of moderate pneumothorax (7.0%). Among the cases with pneumothorax, 3 (75%) received closed thoracic drainage and 1 (25%) recovered without any treatment. Complication rates are shown in Table 4.

Table 4.

Complications of TBCB.

Type of complication	Cases	Constituent ratio/%
Bleeding
Mild	13	30.2%
Moderate	7	16.3%
Severe	1	2.3%
Pneumothorax
Mild	1	2.3%
Moderate	3	7.0%
Severe	0	0%
Postoperative infection	0	0%
Dead	0	0%

TBCB = transbronchial cryobiopsy.

4. Discussion

4.1. Advantages of TBCB compared to SLB

With respect to the applicability of SLB and TBCB in DPLD, a study including 447 patients (150 patients received SLB and 297 patients received TBCB) showed that the diagnosis rate of SLB was significantly higher than that of TBCB (98.7% vs 82.8%); however, when observing the mortality of complications, TBCB was significantly lower than SLB (0.3% vs 2.7%).^[24] Another study found that the 30-day mortality rate after SLB was up to 7.1% and was even higher in elderly patients and patients with comorbidities.^[25] Hagmeyer et al^[12] reported a diagnosis rate of 72% for TBCB, while among patients who received SLB (n = 8), the diagnosis rate was increased to 75%. Compared with SLB, TBCB has the advantages of higher diagnosis rate, reduced trauma and potential complications, as well as larger specimens, less artifacts, more alveolar tissue, higher quality, and lower cost.^{[15,17,18,20–23,29]} Therefore, TBCB exhibits the potential to replace SLB in lung biopsy for unexplained DPLD patients for the purpose of avoiding a tedious surgical biopsy process.

4.2. Sedation type and airway control

To date, the debate on what is the optimal way to perform TBCB operation mainly concentrates on two factors, namely, sedation type and airway control: it is possible to perform TBCB either by establishing a tracheal intubation or using a rigid bronchoscope as an artificial airway under deep sedation, or having the patient conscious without intubation. Regarding the differences between sedation and artificial airway during the TBCB operation, there are currently 15 clinical studies related to frozen lung biopsy.^[9–23] Specifically, for the choice of sedation type: 8 studies adopted deep sedation or general anesthesia^{[9,12,14,17,18,21–23]} and 7 studies^{[10,11,13,15,16,19,20]} adopted moderate anesthesia for sedation and analgesia; for the establishment of artificial airway: 4 studies^{[10,11,16,20]} did not establish artificial airway and the remaining 11 studies^{[9,12–15,17–19,21–23]} established artificial airways in different forms including laryngeal mask, tracheal intubation and rigid bronchoscope. For the time being, a vast majority of the TBCB operations abroad were carried out under general anesthesia or deep sedation, or under rigid bronchoscope or tracheal intubation, with support of flexible bronchoscope. The earliest TBCB operations performed in China (by Professor Guo Shuliang) were also under general anesthesia and rigid bronchoscope.^[33] Although most of the patients with diffuse pulmonary disease need to undergo lung biopsy in China, the low popularity of rigid bronchoscopy has increased the difficulty in implementing and promoting TBCB across the country, leading to a negative impact on the diagnosis and treatment of DPLD. A critical difference between our technique and conventional TBCB is that our technique can be performed using flexible bronchoscope in a routine bronchoscopy room under moderate sedation and local anesthesia. Moreover, the hemostatic balloon preset in the lung lobe bronchus near the biopsy site can be routinely inflated after the biopsy process so as to effectively reduce the risk of bleeding. This improvement is similar to what was reported by Bango-Álvarez et al,^[10] but Bango-Álvarez et al^[10] used 2 flexible bronchoscopes alternately during the biopsy process. Despite that the cryoprobe and flexible bronchoscope must be pulled out together during the TBCB operation and the two flexible bronchoscopes must be repeatedly pulled into and out of the bronchus in alternation, the patients were well tolerated under adequate sedation. Bango-Álvarez et al’s^[10] study had 91 confirmed cases (86%), including 5 cases (4.7%) who developed complications, which were similar to our study (diagnosis rate 88.4%, 4 cases [9.3%] developing pneumothorax). Nevertheless, it is noteworthy that our modified technique did not require intervention or surgery to stop bleeding, and did not cause any death. In contrast, Casoni et al^[18] reported 1 case of death (exacerbated by idiopathic pulmonary fibrosis). Moreover, in a meta-analysis^[24] concerning patients undergoing intubation under deep sedation (including 11 studies, 625 patients), the combined diagnosis rate was 0.81 (95% CI 0.76–0.86), whereas in a study focusing on consciously sedated non-intubated patients (including 3 studies, 142 patients), the combined diagnosis rate was 0.83 (95% CI 0.64–0.97). Compared with other published studies under general anesthesia in the operating room, our technique resulted in fewer complications and achieved a higher diagnosis rate.

4.3. Complication rate

Safety is the most critical factor restricting the popularization of TBCB. With respect to complications of TBCB, bleeding and pneumothorax are the major ones. There is an obvious blind time in the airway during TBCB biopsy. Our modified technique can overcome this problem by presetting a hemostatic balloon. Dhooria et al^[34] reported that the risk associated with this blind time could be minimized by inflating the hemostatic balloon with air/fluid. In the existing literature, there were 4 studies^{[10,11,16,20]} that performed TBCB under moderate sedation without establishing an artificial airway and without presetting a hemostatic balloon, among which the incidence of mild bleeding was up to 84% and the incidence of pneumothorax was up to 19.6%. In our study, 51.2% of the cases had no bleeding and 30.9% suffered only mild bleeding. Our low rate of bleeding was partly attributed to the preventive use of hemostatic balloon, which was inflated immediately after the biopsy operation. This method can effectively protect the remaining bronchial ventilation from bleeding. In addition, local occlusion can help accelerate hemostasis, and the freezing effect of cryoprobe can coagulate the small blood vessels ruptured during the biopsy process, so that the risk associated with the blind time is minimized. Our technique fully demonstrates the importance of hemostatic balloon in preventing and controlling severe bleeding.

In a meta-analysis including 12 studies,^[24] it was found that 16.9% (65/383) of the patients had moderate bleeding after receiving cryobiopsy under general anesthesia and rigid bronchoscope, while the total incidence of moderate bleeding was 0.12 (95% CI 0.02–0.25). In another meta-analysis including 27 studies conducted in 2019,^[35] the incidence of TBCB-related moderate or severe bleeding was up to 14.2%. In comparison, the risk of moderate or severe bleeding in our study was 18.6%, suggesting that the risk of moderate or severe bleeding during TBCB would not be significantly increased in the absence of intubation or rigid bronchoscope and without implementing general anesthesia. Moreover, the preventive use of hemostatic balloon can effectively reduce the incidence of moderate or severe bleeding (1.8% vs 35.7%).^[36]

Pneumothorax, as another common complication of TBCB, is usually caused due to the fact that TBCB may involve the visceral pleura during the operation, and its incidence is ranged from 0% to nearly 30%.^{[7,18–20,23,24]} In a meta-analysis including 994 patients,^[24] the incidence of pneumothorax was up to 10%, while another meta-analysis including 13 studies reported that 9.5% of the patients developed pneumothorax postoperatively.^[39] The incidence of pneumothorax in our study was similar to that reported in the current literature (4/43, with an incidence of 9.3%). A common feature among the 4 cases of pneumothorax in our study is that multiple (≥3) biopsies were carried out in the same segment of the bronchus. Therefore, it is speculated that too many times of biopsy at the same site may be a major risk factor for pneumothorax. In addition, the risk of pneumothorax may also be affected by procedure-related factors, such as the sedation type and/or airway control. Compared with patients under sedation and spontaneous breathing, patients receiving deep sedation and invasive ventilation were associated with a higher incidence of pneumothorax. According to Hagmeyer et al’s results,^[12] TBCB performed under medical sedation and spontaneous breathing showed a reduced risk of iatrogenic pneumothorax relative to that performed under general anesthesia and invasive ventilation. Therefore, our study further demonstrates that, in the absence of tracheal intubation, general anesthesia and establishment of artificial airway through rigid bronchoscope, TBCB is still safe and feasible. Moreover, our technique can not only reduce radiation, but also lower the costs. This finding is of great significance to the popularization of TBCB surgery.

Nevertheless, this study was of a retrospective design with several limitations. First, our sample size was small and all the included cases came from the same center. Second, the operations were performed by different experienced interventional pulmonologists, which might lead to varying diagnosis rates and complication rates. Third, most of the biopsy specimens were taken from the lower lobe of the lung, which might lead to sampling bias. This is due to the restriction that the cryoprobe could not be bent too much during the biopsy process and had difficulty to reach the upper lobe apex bronchus and other sites. In the follow-up research, we aim to target other diseases related to transbronchial cryo-lung biopsy under flexible bronchoscope as controls for further comparative analysis.

5. Conclusions

TBCB under general anesthesia or deep sedation, and with rigid bronchoscope or tracheal intubation, is a mature frozen lung biopsy technique, and its safety and efficacy have been confirmed by many studies abroad. However, in view of China’s national conditions, TBCB under moderate sedation and consciousness using flexible bronchoscope, as a novel type of frozen lung biopsy technology, may be more feasible for widespread promotion for the purpose of improving China’s overall capability in diagnosing the cause of diseases such as diffuse lung disease and interstitial lung disease. For patients with good lung function and involving no related risk factors, we believe there is no need to intubate the patient or use fluoroscopy, or implement general anesthesia during the TBCB process, and it is feasible to perform TBCB in a routine bronchoscopy room under moderate sedation. Overall, the modified TBCB procedure proposed in this paper is a minimally-invasive, rapid, economical and safe technique. Our findings are expected to be further verified following the accumulation of more TBCB operations under flexible bronchoscope.

Author contributions

Writing—original draft: Wenting Long, Jingying Luo, Hui Xiang, Liuyan Hong.

Writing—review & editing: Miao Luo, Jianghong Wei, Libing Ma.