High frequency jet ventilation through mask contribute to oxygen therapy among patients undergoing bronchoscopic intervention under deep sedation

doi:10.21203/rs.3.rs-56432/v2

Background: High frequency jet ventilation (HFJV) is an open ventilating technique to maintain ventilation for emergency or difficult airway. However, whether jet ventilation or conventional oxygen therapy (COT) is more effectively and safe in maintaining adequate oxygenation, is unclear among patients with airway stenosis during bronchoscopic intervention (BI) under deep sedation.

Methods: A prospective randomized cohort study was conducted to compare HFJV with normal frequency jet ventilation (NFJV) and COT (high flow oxygen) in oxygen supplementation during BI under deep sedation from March 2020 to August 2020. Patients receiving BI under deep sedation were randomly divided into 3 parallel groups of 50 patients each: the COT group (fractional inspired oxygen (FiO₂) of 1.0, 12 L/min), the NFJV group (FiO₂ of 1.0, driving pressure of 0.1MPa, and respiratory rate (RR) 15bpm) and the HFJV Group (FiO₂ of 1.0, driving pressure of 0.1MPa, and RR of 1200bpm). Pulse oxygen saturation (SpO₂), mean blood pressure and heart rate were recorded during the whole procedure. Arterial blood gas was examined and recorded 15 minutes after the procedure was initiated. The procedure duration, dose of anesthetics, and adverse events during BI in the three groups were also recorded.

Results: A total of 161 patients were enrolled, with 11 patients excluded. The clinical characteristics were similar among the three groups. The PaO₂ of the HFJV group was significantly higher than that of the COT and NFJV groups (P<0.001). PaO₂ was significantly correlated with ventilation mode (P<0.001), body mass index (BMI) (P=0.019) and procedure duration (P=0.001). Multiple linear regression showed that only BMI and procedure duration were independent influencing factors of arterial blood gas PaO₂ (P=0.040 and P=0.002, respectively). The location of airway lesions and the severity of airway stenosis were not statistically correlated with PaCO₂ and PaO₂.

Conclusions: HFJV could effectively and safely improve the intra-operative PaO₂ among patients with airway stenosis during BI in deep sedation, and it did not increase the intra-operative PaCO₂ and the risk of hypercapnia. The location of airway lesions and the severity of airway stenosis may not affect oxygenation maintenance during basic and some advanced BI.

Anesthesiology & Pain Medicine

Bronchoscopic intervention

Conventional oxygen therapy

Normal frequency jet ventilation

High frequency jet ventilation

Bronchoscopic intervention (BI) has become the preferred method for the diagnosis and treatment of airway lesions. It plays an important role in improving the patient’s quality of life, especially by relieving airway obstructions[1]. Different procedures require different methods of anesthesia and different airway management. Various oxygen delivery routes include nasal catheter; face mask; laryngeal mask airway (LMA); and supraglottic tubes, such as Wei nasal jet tube; endotracheal tube; and rigid bronchoscope[2, 3]. Endoscopic face mask is one of the most commonly used oxygen delivery routes for BI because of its high comfort and non-influence on bronchoscope insertion. Different ventilation modes, including conventional oxygen therapy (COT), intermittent ventilation, controlled mechanical ventilation, and jet ventilation could be utilized for conducting differentiated airway management, which has its own advantages and disadvantages[4-6].

Hypoxemia is a major complication and focus of anesthesia during deep sedation especially among patients undergoing BI[7, 8]. The main mechanisms of hypoxemia in BI are ventilation/blood flow imbalance and decreased ventilation in accordance with airway stenosis especially after sedation. With the continuous development of modern medicine, the method for oxygen supply has changed, and the traditional oxygen therapy was no longer the classic and only method available. High-flow oxygen through nasal cannula or mask was used among patients infected with COVID-19 associated with severe hypoxemia, and it showed reductions in the need for therapeutic escalation and intubation among patients who received high-flow oxygen[9]. Supraglottic jet ventilation (SJV) was also superior to conventional means of oxygen delivery among patients with obesity who were under intravenous anesthesia [10]. However, whether jet ventilation is superior to COT in maintaining intra-operative oxygenation is unclear among patients with airway stenosis during BI under deep sedation.

This cohort study aimed to assess the efficacy and safety of oxygen supplementation, and the carbon dioxide (CO₂) concentration and its effects on patients in three ventilation modes including COT, normal-frequency jet ventilation (NFJV), and high-frequency jet ventilation (HFJV), during BI under deep sedation.

2.1. Study design

This is a prospective randomized cohort study compared COT, NFJV and HFJV in oxygen supplementation during BI under deep sedation.

This study was approved by the Medical Research Ethics Committee of Emergency General Hospital in Beijing, China (K20-9). All the patients or their relatives signed informed consent prior to the commencement of the study program. This study was registered in Chinese Clinical Trial Registry on March 22, 2020 (Registration number: ChiCTR2000031110). It also followed the Consolidated Standards of Reporting Trials (CONSORT) guidelines.

2.2. Study population

All patients were selected by the Center of BI, Emergency General Hospital, to undergo BI under deep sedation from March 2020 to August 2020. Inclusion criteria were as follows: (1) Underwent electric flexible bronchoscope; (2) Duration of operation, between 20 and 60 minutes; (3) Age, 18-80 years. Exclusion criteria were as follows: (1) Diagnosed with cardiac respiratory failure and coma; (2) T-tube, endotracheal intubation, and tracheotomy, or SpO₂< 90% in the room air before the surgery; (3) History of mental and neurological disorders, sedative or hypnotic drugs and alcohol abuse; (4) Change the method of anesthesia during the operation; (5) Intra-operative massive hemorrhage；(6) Patients transferred back to ICU with endotracheal intubation after operation.

BI procedures were advanced diagnostic and therapeutic procedures, which included laser, electrocautery, cryotherapy, balloon dilation, argon plasma coagulation and photodynamic therapy. All BI procedures were performed by experienced endoscopists using electric flexible bronchoscope (Pentax, Japan).

2.3. Anesthetic settings and maintenance

Upon entrance to the operating room, the patient underwent electrocardiogram (ECG), pulse oximetry (SpO₂), and blood pressure monitoring. Lidocaine (1%, 10ml) was administered via the spray-as-you-go technique before therapy. An endoscopic face mask was provided for oxygen. An intermittent drip of remifentanil (1µg/kg) was injected. Then, propofol (1mg/kg) was injected 2min after remifentanil was administered during the induction of anesthesia. Continuous injection of remifentanil (0.10～0.15µg·kg^-1·min^-1) and propofol (30～50µg·kg^-1·min^-1) by microinjection pumps was performed in accordance with the patient's vital signs. The fluctuation of the patient’s mean blood pressure (MBP) was controlled at 20% of the baseline. If the fluctuation of MBP was more than 20%, the depth of anesthesia was adjusted or vasopressor was given. The patients maintained a Ramsey sedation scale (RSS) score of 3～4. They breathed spontaneously during BI. When the SpO₂value was<95%, the anesthesiologists increased the driving pressure by 0.05MPa, and when the SpO₂value was<90%, the anesthesiologists performed mask-bag ventilation.

PaO₂ was seen as the primary outcome in this study. The mean ± standard deviation (SD) of PaO₂ was 164.00 ±73.38mmHg, 220.20 ±86.51mmHg, and 210.20 ± 65.11mmHg of the COT, NFJV and HFJV groups according to a pilot study of 5 patients, respectively. The sample size was calculated by the formula of n= (μ_α + μ_β)²σ²/δ²with a standard deviation of 0.8, and bilaterally equalto 0.05, or even 0.2 (power = 0.8). The results showed the value of each group was 35 cases. In accordance with different ventilation modes, the eligible patients were randomized in a 1:1:1 ratio into three parallel groups of 50 patients each by a physician unaware of the study. The three groups were the COT group, the NFJV group, and the HFJV group. The oxygen for COT was provided at fractional inspired oxygen (FiO₂) of 1.0 with a flow rate of 12 L/min through a ventilator (Drager, Germany). The oxygen for NFJV was provided at FiO₂ of 1.0 with a driving pressure (DP) of 0.1MPa, respiratory rate (RR) of 15bpm, and I/E ratio of 1:1.5 through jet ventilation (Twin Stream^TM, Austria). The oxygen for HFJV was provided at FiO₂ of 1.0 with a DP of 0.1MPa, RR of 1200bpm and I/E ratio of 1:1.5 through jet ventilation (Twin Stream^TM, Austria). The flow diagram of this study was shown in Figure 1.

2. 4. Data collection

The following parameters were continuously monitored during anesthesia: pulse SpO₂, MBP, heart rate (HR) and ECG. Meanwhile, the patients’ SpO₂, MBP and HR were recorded at baseline (T₀), the beginning of procedure (T_Beg), 15min after the initiation of procedure (T₁₅), and the end of procedure (T_End). Arterial blood gas (ABG) was examined and recorded 15 minutes after the initiation of procedure. The procedure duration and dose of anesthetics during BI in the three groups were also recorded. Adverse events including intra-operative hypoxemia (SpO₂<90%), intra-operative hypercapnia (PCO₂≥50mmHg), intra-operative severe hypercapnia (PCO₂≥100 mmHg), post-operative hypoxemia (SpO₂<90%), post-operative hypercapnia (PCO₂≥50mmHg), post-operative severe hypercapnia (PCO₂≥100 mmHg), and post-operative agitation, were recorded by an investigator. The statistician and investigator were independent and blinded to the treatment. The location and severity of airway stenosis were recorded. The location of airway lesions was divided into four types: 1) upper and middle parts of the main airway, 2) middle and lower parts of the main airway, 3) left or right main bronchial, and 4) distal bronchial. The severity of airway stenosis was graded to three levels: 1 for 0%～59%, 2 for 60%～89%, and 3 for above 90%. The primary outcomes were the data of ABG in the three groups, while the secondary outcomes were the influencing factors of blood gas indicators PaO₂ and PaCO₂.

SPSS 20.0 software was used for data collation and statistical analysis. The continuous data were expressed as mean ± SD, and the count data were presented as the number and percentage. Chi-square test was used to compare the counting data of different groups (the P value was directly calculated using Fisher’s exact probability method if necessary). Univariate analysis of variance (ANOVA) was used for overall comparison among groups, and least significance difference (LSD) was used for multiple comparison between groups. Pearson analysis was used to investigate the correlation between blood gas indicators of PaO₂ and PaCO₂ and the clinical indicators of patients. Multiple linear regression analysis was used to explore the independent influencing factors of PaO₂ and PaCO₂. P<0.05 was considered statistically significant.

A total of 161 patients were enrolled. Three patients in the COT group, four patients in the NFJV group and another four patients in the HFJV group were excluded because of change to rigid bronchoscope and general anesthesia during operation. All the remaining patients tolerated the BI well. Two patients in the COT group (lowest SpO₂ values were 79% and 85%, lasted for 2 min and 1min), three patients in the NFJV group (lowest SpO₂ values were 81%, 83%, and 87%, lasted for 1 min, 1 min, and 2min, respectively) and two patients in the HFJV group (lowest SpO₂ values were 87% and 88%, both lasted for 1 min) developed hypoxemia, respectively. No other adverse events such as severe hypercapnia and postoperative agitation occurred.

The clinical characteristics of patients are represented in Table 1. No significant differences were found among the three groups in terms of age, height, weight, body mass index (BMI), gender, pathological type, ASA classification, lesion site and stenosis degree. However, significant differences were observed among the three groups in terms of the following comorbidities: cerebrovascular disease; other tumors (such asesophageal cancer and thyroid cancer); and chronic lung disease (including tuberculosis pneumonia, and COPD, etc.)(P=0.011, P=0.029, P=0.017). The number of patients with cerebrovascular disease in the COT group was significantly higher than that in the NFJV and HFJV groups (P=0.011). The number of patients with other tumors in the NFJV group was significantly higher than that in the HFJV group (P=0.029). The number of patients with chronic lung disease in the COT group was significantly higher than that in the NFJV group (P=0.017).

The blood gas values and procedure duration are shown in Table 2. PaO₂, lactic acid and procedure duration significantly differed among the three groups (P<0.001, P=0.005, and P=0.038, respectively). The PaO₂ in the HFJV group was significantly higher than that in the COT and NFJV groups. Moreover, the lactic acid in the HFJV group was significantly higher and procedure duration was significantly. No significant differences in PaCO₂, blood glucose and pondus hydrogenii (PH) were found among the three groups.

The MAP, HR, and SpO₂ of each period time (Figure 2) and anesthetic dose (Figure 3) among the three groups did not significantly differ.

All peri-operative related factors associated with PaO₂ were detected via Pearson analysis. The result showed that PaO₂ was significantly correlated with ventilation mode (P<0.001), BMI (P=0.019) and procedure duration (P=0.001). The ASA level, location of airway lesions, and severity of airway stenosis had no statistical correlation with PaO₂. Multiple linear regression showed that BMI and procedure duration were independent influencing factors of arterial blood gas PaO₂ (P=0.040, P=0.002), and ventilation mode was not the independent factor of arterial blood gas PaO₂. The details are shown in Tables 3 and 4.

All the factors associated with PaCO₂ were also detected via Pearson analysis, as shown in Table 5. No statistical correlation was found between blood gas PaCO₂ and ventilation mode, lesion location, stenosis degree, and procedure duration. Multiple linear regression demonstrated that the above indices were not independent influencing factors of blood gas PaCO₂, as shown in Table 6. The location of airway lesions and the severity of airway stenosis had no statistical correlation with PaCO₂.

BI has shown remarkable advancements in pulmonary medicine diagnostics and therapy in recent years. Monitored anesthesia care (MAC), as moderate sedation, was performed in basic and some advanced BI[11]. By maintaining spontaneous breathing, without the need for LMA or intubation, MAC could meet the surgical needs and alleviates the patient’s discomfort[1]. The commonly used ventilation modes included COT, intermittent ventilation, controlled mechanical ventilation, and jet ventilation (manual or automatic, high or normal frequency)[11, 12]. Ventilation mode is the most direct factor affecting the oxygenation of patients, especially in MAC[6, 13]. In the present study, endoscopic face mask and three ventilation modes were used to provide oxygen to patients[14].

HFJV has become a technique for maintaining ventilation after Klain and Smith developed it[5, 6]. Gas enters the breathing path at low pressure through a narrow jet tube. Open system, high frequency and low tide are the three characteristics of HFJV. This technique has become one of the most important ventilation modes in airway management, especially in emergency airway in the ASA guide[7]. In the present study, the effect of oxygenation maintenance in COT, NFJV, and HFJV was compared via face mask during BI under MAC. The PaO₂ in the HFJV group increased to 251.70mmHg, higher than that in the COT and NFJV groups. HFJV had a certain PEEP effect, which could open the airway, reduce the anatomical inefficiency of the nasopharyngeal cavity, improve the final expiratory volume of the lung, and increase the effective ventilation of the alveoli[15, 16]. The PaO₂ in the NFJV group was 191.98mmHg, higher than that in the COT group (176.28mmHg), but no statistical difference was found. The mechanism of NFJV was similar with that of HFJV. In addition, NFJV may cause asynchronous breathing, resulting in less significant oxygenation improvement than that in HFJV. The results indicated that HFJV is an effective and safe oxygen supplementation for patients under MAC in BI.

In addition to PaO₂, another point of concern was the patient’s PaCO₂. A previous review proved that NFJV was more suitable for BI than HFJV, which may cause CO₂ accumulation when jet frequency was above 150/min[17]. The PaCO₂ values in the COT, NFJV, and HFJV groups were 59.20mmHg, 59.84mmHg, and 59.60mmHg, respectively, and no significant difference was found among them. Although the PaCO₂ value was higher than the upper limit of the normal value, no delayed awakening occurred. Pearson analysis showed no important factors affecting PaCO₂ and certainly no independent factors, neither. Mild hypercapnia may not cause brain injury and only worsen the brain’s condition when PaCO₂ is above 100mmHg[8, 18, 19]. Thus anesthesiologists did not provide any treatment when the PaCO₂ was a little above 50 mmHg.

The key of MAC in BI is how to maintain the patient’s oxygenation in open airway and ensure the feasibility of the procedures. Pathological airways often caused restricted ventilation dysfunction, resulting in decreased respiratory power, increased elastic resistance, decreased alveolar compliance, and limited lung expansion, which were all important factors affecting PaO₂[4]. Meanwhile, the extent and location of the lesions, and whether the open airway aggravates its effect on PaO₂, are problems worth solving. In the present study, the location of airway lesions, which was divided into four types, and the severity of airway stenosis, which was graded to three levels, was speculated to be the important factors related to PaO₂. However, Pearson analysis showed that both were not important factors affecting PaO₂, and certainly were not independent factors.

In this research, the incidence of adverse events was lower than that previous reported[10, 20]. Among the 150 patients, only seven developed intra-operative hypoxemia, which was relatively short and the oxygenation was effectively improved after treatment. Hypoxemia mainly occurred at two stages: one was after induction of anesthesia and the other was in the period of balloon dilation. Rapid anesthesia induction may lead to respiratory depression, as manifested by decreasing RR and tidal volume, the absence of spontaneous breathing and even the occurrence of apnea. SpO₂ was effectively returned to normal after the anesthesiologist reduced the depth of anesthesia to restore spontaneous breathing or with the assistance of bag-mask ventilation. Balloon dilatation resulted in transient complete airway obstruction. After balloon dilatation, normal ventilation could be restored, and SpO₂ could quickly return to normal[21, 22].

Many deficiencies in this study that deserve further research. First, the dose and speed of anesthetic administration during MAC determined the depth of anesthesia and the degree of respiratory depression which directly determined PaO₂. No statistically significant difference was found in the anesthetic doses among the three groups. However, PaO₂ may still be affected due to the differences in the patients’ conditions and the operating habits of the anesthesiologists. Second, the ABG collection time was set at 15min after the operation, when the patient was basically in a stable state of anesthesia. At this time, the airway obstruction was mostly treated already. Finally, only the sedation score of 3–4 was recorded, and bispectral index and neuromonitoring were not performed.

HFJV via endoscopic face mask could effectively and safely improve the intra-operative PaO₂ in patients with airway stenosis during BI in deep sedation. BMI and procedure duration were independent influencing factors of arterial blood gas PaO₂, but all the preoperative factors were not independent influencing factors of blood gas PaCO₂. The location and severity of airway stenosis did not affect the oxygenation maintenance and CO₂ exhalation during basic and some advanced BI.

COT: conventional oxygen therapy; NFJV: normal frequency jet ventilation; HFJV: high frequency jet ventilation; BI: bronchoscopic intervention; RR: respiratory rate; LMA: laryngeal mask airway; SJV: supraglottic jet ventilation; ECG: electrocardiogram; SpO₂: pulse oximetry; RSS: Ramsey Sedation Scale; FiO₂: fractional inspired oxygen; DP: driving pressure; MBP: mean blood pressure; HR: heart rate; ABG: Arterial blood gas; ANOVA: univariate analysis of variance; LSD: least significance difference; BMI: body mass index; MAC: monitored anesthesia care.

Ethics approval and consent to participate

This study was approved by the Medical Research Ethics Committee of Emergency General Hospital in Beijing, China (K20-9). All the patients or their relatives signed informed consent prior to the commencement of the study program.

Consent for publication

Not applicable.

Availability of data and materials

The datasets used and/or analyzed during the current study are available from the corresponding author.

Competing interests

All authors have no potential competing interests to declare.

Funding

The authors declare that they have no funding.

Authors’ contributions

Study conception: HW, YZ, QC. Study design: MY, LL, HW, QC. Study conduct: MY, BW, QH, NL, YZ. Data analysis: MY. Data interpretation: MY, YZ, HW, QC. Drafting of the manuscript: MY, QC. All authors approved the final version of the manuscript.

Acknowledgements

Not applicable.

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Table 1 Comparison of preoperative patient characteristics among three groups

Characteristic	Group COT(n=50)	Group NFJV(n=50)	Group HFJV(n=50)	P Value
Age, mean±SD, years	49.12±14.44	54.24±15.54	51.6±14.39	0.227
Height ,mean±SD, (cm)	165.02±7.74	167.16±7.13	167.04±8.71	0.316
Weight, mean±SD, (Kg)	61.26±8.33	63.46±11	63.59±10.33	0.423
Body Mass Index, mean±SD(%)	22.60±3.38	22.66±3.37	22.74±2.71	0.976
Male, n (%)	33(66)	32(64)	34(68)	0.915
ASA score				0.157
ClassⅠ, n (%)	0(0)	0(0)	2(4)
ClassⅡ, n (%)	20(40)	26(52)	27(54)
Class Ⅲ, n (%)	30(60)	24(48)	21(42)
Comorbidities
Cardiovascular history, n (%)	9(18)	12(24)	11(22)	0.757
Cerebrovascular disease, n (%)	5(10)^bc	0(0)^a	0(0)^a	0.011
Other tumors, n (%)	5(10)	9(18)^c	1(2)^b	0.029
Diabetes mellitus, n (%)	3(6)	6(12)	10(20)	0.108
Chronic pulmonary disease, n (%)	6(12)^c	0(0)^a	1(2)	0.017
Tracheal esophageal fistula, n (%)	1(2)	2(4)	5(10)	0.277
Lobectomy, n (%)	10(20)	6(12)	6(12)	0.426
Pathology
Non-tumor, n (%)	20(40)	23(46)	18(36)	0.592
Tumor, n (%)	30(60)	27(54)	32(64)	0.592
lesion location				0.074
Upper main airway, n (%)	17(34)	14(28)	10(20)
Lower main airway, n (%)	12(24)	22(44)	16(32)
Left and right bronchus, n (%)	8(16)	10(20)	9(18)
Others, n (%)	13(26)	4(8)	15(30)
Degree of stenosis				0.837
0-59%, n (%)	28(56)	33(66)	32(64)
60-89%, n (%)	12(24)	10(20)	9(18)
≥90%, n (%)	10(20)	7(14)	9(18)

Data were expressed as mean ± standard deviation or as numbers and percentages. ^a was statistically significant compared with COT group, ^bwas statistically significant compared with HFJV group, ^c was statistically significant compared with NFJV group.

The number of patients with cerebrovascular disease in the COT group was significantly higher than that in the NFJV and HFJV groups (P=0.011). The number of patients with other tumors (including esophageal cancer, thyroid cancer, etc) in the NFJV group was significantly higher than that in the HFJV group (P=0.029). The number of patients with chronic lung disease (including tuberculosis pneumonia, COPD, etc) in the COT group was significantly higher than that in the NFJV group (P=0.017).