Background The purpose of this study was to compare the effectiveness and safety of high-flow nasal cannula (HFNC) and conventional oxygen therapy (COT) in fibreoptic bronchoscopy (FB) after congenital heart surgery (CHS) in children.
Methods We did a retrospective cohort study using patients from the electronic medical record system of Fujian Children’s Hospital in China. The study population was children who underwent FB in the cardiac intensive care unit after CHS for 1 year (May 2021–May 2022). Children were classified into HFNC and COT groups according to their oxygen therapy during FB. The primary outcome was oxygenation indices during FB, including pulse oximeter oxygen saturation (SpO2) and transcutaneous oxygen tension (TcPO2) during FB. Secondary outcomes were the number of interruptions during FB and their causes, and complications after FB.
Results We identified 107 children from the electronic medical record system, and 102 children after CHS were finally included in the study (53 in the HFNC group and 49 in the COT group). During the FB examination, TcPO2 and SpO2 were significantly higher in the HFNC group than in the COT group (TcPO2: 90.3±9.3 vs 80.6±11.1 mm Hg; SpO2: 95.6±2.5 vs 92.1%±2.0%, p<0.001) and the transcutaneous carbon dioxide tension was significantly lower than in the COT group (39.6±3.0 vs 43.5±3.9 mm Hg, p<0.001). During the FB, a total of 20 children in the COT group had 24 interruptions, and 8 children in the HFNC group had 9 interruptions (p=0.001). In terms of postoperative complications, eight cases had complications in the COT group and four complications in the HFNC group (p=0.223).
Conclusions Among children undergoing FB after CHS, the application of HFNC was associated with better oxygenation and fewer procedural interruptions compared with COT, without an increased risk of postoperative complications.
Data availability statement
Data are available on reasonable request.
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WHAT IS ALREADY KNOWN ON THIS TOPIC
Pulmonary complications are common comorbidity after congenital heart surgery. Fibreoptic bronchoscopy can determine the lung condition of the patient, aspirate thick sputum that blocks the airway, and stimulate the patient to cough effectively. However, hypoxaemia remains the most common complication during fibreoptic bronchoscopy. High-flow nasal cannula has been widely applied to prevent hypoxaemia during adult fibreoptic bronchoscopy.
WHAT THIS STUDY ADDS
The application of high-flow nasal cannula in infants undergoing fibreoptic bronchoscopy after congenital heart surgery improves oxygenation, reduces procedural interruptions and does not increase the risk of postoperative complications. This indicates that high-flow nasal cannula is effective and safe in the fibreoptic bronchoscopy examination of infants after congenital heart surgery.
HOW THIS STUDY MIGHT AFFECT RESEARCH, PRACTICE OR POLICY
To provide a reference for oxygen therapy for children undergoing fibreoptic bronchoscopy examination after congenital heart disease.
Pulmonary complications are common comorbidity after congenital heart surgery (CHS), leading to hypoxaemia and hypercapnia, increasing the risk of secondary tracheal intubation.1 Fibreoptic bronchoscopy (FB) is useful for assessing airway anatomy and dynamics and obtaining biological samples, as well as for other therapeutic indications such as aspiration of airway secretions and removal of airway foreign bodies.2 However, during FB, the infant has a weak respiratory drive due to procedural sedation and partial obstruction of the airway by the bronchoscope. Thus, despite supplemental oxygen, hypoxaemia remains the most common complication of FB.3 4 Severe and refractory hypoxaemia can interrupt FB procedures, leading to unsatisfactory diagnostic or therapeutic outcomes. Other strategies are sometimes required, including bag-mask ventilation, or even endotracheal intubation and mechanical ventilation.5 Several guidelines recommend mandatory oxygen supplementation for children with dyspnoea, and nasal cannula is a common form of oxygen therapy, but hypoxic events still occur during conventional oxygen therapy (COT).6 7 High-flow nasal cannula (HFNC) is increasingly used as a form of respiratory support. The advantages of HFNC are that the inhalation gas is warmed and humidified (warmed to 34°C–37°C, 100% humidified) for easier secretion removal, improved CO2 ‘wash-out’ by reducing dead space, and reduced respiratory work due to flow-dependent positive end-expiratory pressure effects.8 HFNC has been used to prevent hypoxaemia during FB in adults, with patients showing improved oxygenation and ventilation during and after FB.9–11 However, there are few studies on the use of HFNC for oxygen therapy during FB examination in children.12 There is no relevant research on the application of HFNC during FB in children with congenital heart disease (CHD), and the effect of using HFNC is not yet clear. Therefore, this study aimed to investigate the efficacy and safety of HFNC during FB examination in children after CHS.
Study design and populations
We conducted a retrospective cohort study of patients from the electronic medical record system of Fujian Children’s Hospital in China. The study population was children undergoing FB after simple CHS (ventricular septal defect, atrial septal defect or patent ductus arteriosus) in the cardiac intensive care unit (CICU) from May 2021 to May 2022. Demographic, clinical, laboratory, treatment and outcome data were extracted from electronic medical records. Children who needed FB examination to assist in diagnosis or treatment due to pulmonary complications (lung infection, atelectasis, etc) after extubation of simple CHD were included in the study. Children after CHS with epistaxis, nasal injury or haemodynamic instability before the FB examination were excluded.
Indications for FB are as follows: examination of the airways (persistent stridor, suspicion of a foreign body, persistent wheezing, haemoptysis, persistent/recurring atelectasis, persistent/recurring pneumonia, etc), therapeutic procedures (aspiration of secretions, extraction of foreign bodies, etc), perioperative examination and treatment of tracheal surgery and tracheo-oesophageal fistula surgery, etc. All children are fasted for 6 hour before FB and are sedated in an area with appropriate monitoring and resuscitation equipment. The patient’s pulse oximeter oxygen saturation (SpO2), heart rate (HR), ECG monitoring and mean blood pressure was continuously monitored using a General Electric Dash 3000 monitor (GE Medical Systems). Midazolam 0.1–0.3 mg/kg (total ≤10 mg) or propofol 1–1.5 mg/kg were applied for sedation before the examination. During the operation, 1% lidocaine was used for local spray anaesthesia in the oral cavity and airway (total amount <7 mg/kg). All bronchoscopy procedures were performed by a CICU specialist through the nasal passage using an Olympus BF-N20, BF-XP190 (Olympus, Tokyo, Japan) FB with an outer diameter of 2.8 cm and 3.1 cm. In cases involving bronchoalveolar lavage (BAL), the FB was wedged into the appropriate segmental bronchus, 37°C normal salines (1 mL/kg) was injected through the working bronchoscope working channel and then administered with a negative pressure of 100–200 mm Hg. Aspirate to obtain BAL fluid. The time from the insertion of the bronchoscope to the removal of the bronchoscope was recorded. Both groups were performed by the same physicians and nurses.
Respiratory support during the examination
The choice of oxygen therapy during the examination mainly depends on the attending physician and the condition of the child. The initial flow of the HFNC group (Fisher & Parker AIRVOTM, New Zealand) was set at 2 L/kg/min (maximum flow 25 L/min), the initial FiO2 was 0.4 to maintain the patient’s target SpO2 above 95%, and the humidification temperature was 34°C. Children in the COT group inhaled oxygen through nasal cannula, and the FiO2 values were calculated as 0.24 at 1 L/min, 0.28 at 2 L/min, 0.32 at 3 L/min, 0.36 at 4 L/min, and 0.4 at 5 L/min. The procedure will be stopped if SpO2 drops below 90% or if other cardiovascular events such as hypotension or arrhythmias occur during the examination. The HFNC group increased the flow rate to 3 L/kg/min, and the COT group increased the inhalation flow rate to 3–5 L/min and increased FiO2 to 0.4–0.6 during the examination. If the SpO2 continues to decrease or was accompanied by apnea, bag-mask ventilation should be immediately given.
Data collection and definition
We conducted a detailed retrospective review of medical records and FB checklists through the electronic medical record system. Baseline characteristics included demographics, type of CHD, cardiopulmonary bypass time, aortic cross-clamp time, FB duration, FB examination indications and findings of FB examination were extracted from the medical records. Additionally, the vital signs included: respiratory rate (RR), HR, mean arterial blood pressure (MAP), the fraction of inspiratory oxygen (FiO2), SPO2, TcPO2 and transcutaneous carbon dioxide tension (TcPCO2) 30 min before (T0), during (T1) and 30 min (T2) after the examination was also extracted. The incidence of related complications including hypoxic events, hypotension, bradycardia, arrhythmias, bag-mask ventilation, fever, epistaxis and intubation within 24 hours after FB was also recorded. The electrodes of the TCM4 (Radiometer, Copenhagen, Denmark) are placed on the abdomen or thigh for dynamic monitoring of TcPO2 and TcPCO2 levels. Hypoxaemia is defined as SpO2 less than 90%.
Data were analysed using SPSS software V.25.0 for Windows (IBM SPSS). Independent continuous variables are presented as the mean and SD; counts and percentages described the categorical data. Means were compared using Student’s t-test, and Fisher’s exact test was used for categorical data. The comparison of vital signs, oxygenation parameters and CO2 levels between the two groups at each time point around the FB examination was first analysed using repeated measures analysis of variance and then further simple effects analysis for data with significant interactions. There are no missing data in this study, and prior to conducting this analysis procedure, we used Mauchly’s test to test the sphericity hypothesis, and if the assumption of sphericity is violated, Greenhouse-Geisser correction was applied to the df. A two-sided p<0.05 was regarded as statistically significant.
Patient and public involvement
Patients or the public were not involved in the design, conduct, reporting or dissemination plans of this study.
A total of 107 children were screened between May 2021 and May 2022, of whom 5 did not meet the inclusion criteria due to incomplete data. Ultimately, 102 children were included in the study (53 in the HFNC group and 49 in the COT group).
The baseline characteristics in the two groups are shown in tables 1 and 2. There was no significant difference in the data between the two groups before bronchoscopy (p>0.05). The main indications for FB were pulmonary atelectasis (18/53 vs 15/49), respiratory distress (13/53 vs 14/49), stridor (9/53 vs 8/49), increased oxygen demand (7/53 vs 6/49), suspected airway anomalies (6/53 vs 6/49). The main findings in FB were tracheobronchitis (23/53 vs 25/49), tracheomalacia (13/53 vs 10/49), laryngomalacia (5/53 vs 4/49), subglottic stenosis (5/53 vs 4/49), tracheal stenosis (4/53 vs 4/49) and vocal cord paralysis (3/53 vs 2/49).
The comparison of related parameters at each time point in the two groups of patients is shown in figure 1. During the examination (T1), TcPCO2 in the HFNC group was significantly lower than that in the COT group (39.6±3.0 vs 43.5±3.9 mm Hg, p<0.001), but TcPO2 and SpO2 were significantly higher than that in the COT group (TcPO2: 90.3±9.3 vs 80.6±11.1 mm Hg; SpO2: 95.6±2.5 vs 92.1%±2.0%; p<0.001). There was no significant difference in RR, HR, MAP, SpO2, TcPO2 and TcPCO2 between the two groups 30 min before and after the examination (T0 and T2) (p>0.05). Moreover, there was no significant difference in the duration of the operation between the two groups (12.6±6.0 vs 15.1±7.1 min, p>0.05).
During FB, a total of 20 children in the COT group had 24 interruptions, and 8 children in the HFNC group had 9 interruptions (p=0.001) (table 3). The causes were hypoxia in 24 cases (16 cases in the COT group and 8 cases in the HFNC group), hypotension in 3 cases (both in the COT group), arrhythmia in 3 cases (2 in the COT group/1 in the HFNC group), and bradycardia in 2 cases (COT group). In terms of postoperative complications, eight cases had complications in the COT group (four cases of fever, three cases of epistaxis, and one case of tracheal intubation), and four complications (three cases of fever, one case of epistaxis) in the HFNC group (p=0.223).
In this study, a retrospective analysis of 102 children who underwent FB examination after simple CHS found that children receiving oxygen via HFNC had improved oxygenation, reduced interruption and did not increase the risk of postoperative complications.
Pulmonary complications due to pulmonary oedema, pulmonary hypertension, respiratory tract infection, tracheobronchomalacia, chylothorax and diaphragm injury after CHS can lead to postoperative respiratory distress, increased oxygen demand, and even secondary tracheal intubation which seriously affects the prognosis of children.1 Studies have shown that approximately 6.2%–25.0% of patients have varying degrees of pulmonary complications after cardiac surgery.13–15 Bedside FB examination allows for anatomical and functional assessment of the airway in patients with CHD at the bedside after cardiac surgery. Studies have found that FB examination can help detect CHD complicated with airway abnormalities, improve the lung condition of patients, and help targeted intervention under the guidance of FB, thereby improving prognosis.16 Currently, in most children’s heart centres in China, in order to reduce the adverse reactions and costs caused by general anaesthesia, children who have been extubated after simple CHD often choose to perform bronchoscopy in the CICU under deep sedation or intravenous anaesthesia.17 However, the anaesthetic drugs used during FB may cause respiratory depression and the bronchoscope directly blocks the airway during the examination. Both these factors may contribute to hypoxemia during the procedure.18 It has been reported in the literature that PaO2 decreases by up to 20 mm Hg in patients during bronchoscopy.19 HFNC is a new respiratory support technique that provides a high flow of gas at a relatively constant oxygen concentration, temperature and humidity, and provides a level of positive end-expiratory pressure to reduce upper airway resistance and respiratory work, which has a positive effect on improving oxygenation and CO2 removal.20–22
In this study, patients in both groups underwent FB at different oxygen therapy modalities, and patients in the HFNC group showed improvements in parameters related to oxygenation (TcPO2, SpO2) both during (T1) and after (T2) the examination, and TcPCO2 was significantly lower in the HFNC group than in the COT group during the examination (T1). Other studies have shown similar results. Sharluyan et al in a prospective randomised controlled study of 104 children undergoing FB found that HFNC provided optimised oxygenation during elective FB with significantly lower desaturation compared with conventional nasal catheter oxygen administration and could be considered for oxygen administration, especially when BAL was performed.12 A prospective cohort study conducted by Douglas et al found that the preoperative SpO2 and the lowest intraoperative SpO2 in the HFNC group were significantly higher than those in the standard oxygenation group in adult patients undergoing bronchoscopy.23 Since sedative medication and depth of sedation may affect the occurrence of desaturation, however, there were no significant differences in our study in terms of the type of sedative medication used and the depth of sedation.
The mean examination time of patients in the HFNC group in our study was significantly shorter than in the COT group, and only 3 examinations were interrupted due to hypoxia or hypotension (significantly less than the 20 interruptions that occurred in 13 patients in the COT group), which is similar to the previous studies.24 25 Considering the specific pathophysiological situation after CHS, HFNC treatment helps to reduce the respiratory and cardiovascular afterload by providing positive pressure, while reducing the adverse haemodynamic effects of hypercapnia by flushing CO2.26 27 In this study, hypotension occurred in two COT-supported children during FB, and arrhythmia and bradycardia occurred in one COT-supported child each, but no cardiovascular adverse events occurred in the HFNC group. Furthermore, TcPCO2 was significantly lower in the HFNC group than in the COT group during the FB examination. The MAP, RR and HR increased significantly during the FB examination (T1) in both groups but returned to baseline levels at the end of the examination, which was considered to be due to sympathetic activation during the examination. Additionally, we observed that one infant in the COT group required tracheal intubation and mechanical ventilation support within 24 hours after the FB examination, but no serious complications were found in the HFNC group except for transient fever and epistaxis, which indicated the safety of HFNC.
This study is the first to investigate the effectiveness and safety of oxygen therapy during bronchoscopy in children with simple CHD. But a major limitation of the study is that it was a retrospective single-centre study. As the choice of low or high-flow oxygen depends on the clinical situation, the underlying conditions of the two groups of patients may not be matched. Second, children with complex CHD and pulmonary complications are often in critical condition, so we choose to perform FB in these high-risk children in the operating room. Therefore, the population included in this study was children with simple CHD, and there is a lack of information on children with complex CHD and single ventricular circulation, so the results are only applicable to a population with similar characteristics. Additionally, the sedative drugs used in this study were mainly midazolam and propofol, whether the sedation regimen affects hypoxic events and complications requires further study.
The application of HFNC was associated with better oxygenation and fewer procedural interruptions compared with COT in children undergoing FB examination after CHS and did not increase the risk of postoperative complications. Well-designed prospective, large-sample, multicentre studies are needed in the future to confirm the role of HFNC in FB examination.
Data availability statement
Data are available on reasonable request.
Patient consent for publication
This study involves human participants but this study was approved by the ethics committee of Fujian Children’s Hospital (No. 2022ETKLRD10021), and since the study was a retrospective study, informed consent was waived. Participants gave informed consent to participate in the study before taking part.
We appreciated all doctors and nurses in our centre for fruitful advice and discussions.
Contributors Y-RZ designed the study, performed the statistical analysis, participated in the operation, and drafted the manuscript. X-HC and S-JZ collected the clinical data. All authors read and approved the final manuscript. Y-R Z is responsible for the overall content as the guarantor.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.
Provenance and peer review Not commissioned; externally peer reviewed.