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 Table of Contents  
Year : 2018  |  Volume : 2  |  Issue : 3  |  Page : 45-50

Modified high-flow nasal cannula in young children with pneumonia: A 3-year retrospective study

Department of Pediatrics, Division of Pediatric Pulmonology, Faculty of Medicine Ramathibodi Hospital, Bangkok, Thailand

Date of Web Publication19-Oct-2018

Correspondence Address:
Dr. Aroonwan Preutthipan
Department of Pediatrics, Division of Pediatric Pulmonology, Faculty of Medicine Ramathibodi Hospital, Bangkok
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/prcm.prcm_2_18

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Objectives: We aimed to report our 3-year experience in modified HFNC (MHFNC) usage in young children with community-acquired pneumonia in infectious diseases ward and to identify factors associated with MHFNC failure. Materials and Methods: A retrospective, cross-sectional study of pediatric patients, aged <5 years, with community-acquired pneumonia, who were treated with MHFNC at infectious diseases from August 2012 to December 2015 were recruited. MHFNC failure was defined as a need for further respiratory support within 48 h after initiating MHFNC. Patients: Ninety-nine patients with community-acquired pneumonia were included in this study. Setting: A tertiary care hospital. Measurements and Results: Ninety-nine children (median age of 14 months, body weight 8.6 + 3.1 kg) were included. Ninety-two children (93%) were successfully treated with MHFNC and only seven (7%) were in the failure group. The maximal flow was 3 L/kg/min. Lower oxygen saturation (SpO2)/fraction of inspired oxygen (FiO2) ratio (<264) and higher FiO2 requirement were found to be associated with failure. Maximum FiO2 requirement >0.5 had high odds ratios (22.25) to develop MHFNC failure. No serious complication from MHFNC was found. Conclusions: MHFNC is a practical respiratory support in young children with pneumonia. SpO2/FiO2 ratio (<264) and FiO2 requirement >0.5 is a risk factor for MHFNC failure.

Keywords: High-flow nasal cannula, high-flow nasal cannula failure, hypoxemia, noninvasive ventilation, pneumonia

How to cite this article:
Vareesunthorn I, Preutthipan A. Modified high-flow nasal cannula in young children with pneumonia: A 3-year retrospective study. Pediatr Respirol Crit Care Med 2018;2:45-50

How to cite this URL:
Vareesunthorn I, Preutthipan A. Modified high-flow nasal cannula in young children with pneumonia: A 3-year retrospective study. Pediatr Respirol Crit Care Med [serial online] 2018 [cited 2023 May 29];2:45-50. Available from: https://www.prccm.org/text.asp?2018/2/3/45/243743

  Introduction Top

High-flow nasal cannula (HFNC) is a relatively new respiratory support modality increasingly used in children and adults.[1] HFNC was reported to be helpful in newborns with respiratory distress compared to continuous positive airway pressure (CPAP),[2] upper and lower respiratory tract diseases, and during bronchoscopic procedures.[3] This device provides a mixture flow of air and oxygen, which were heated and humidified, and thus reduce mucosal inflammation and injury. At present, there is no universal consensus on the definition of HFNC. Some authors define HFNC when flow rates are higher than 2 liter per minute (LPM) and 6 LPM in infants and children, respectively,[4] or the gas flow rate exceed patients' inspiratory flow demand.[5]

Previous studies have proposed the mechanisms of action of HFNC including accurate delivery of up to 100% oxygen,[6] minimizing rebreathing of carbon dioxide,[7] maintaining positive airway pressure during the respiratory cycle, especially in the upper airway,[7] and optimizing mucociliary clearance by heated humidified gas.[8],[9] Adverse effects include noise emissions and air leak syndrome (pneumothorax and pneumomediastinum) and its association with delayed intubation[10],[11] The commercial HFNC is noted to be costly and may not be widely available. Our team of Pediatric Pulmonary Division at Ramathibodi Hospital has developed a modified HFNC (MHFNC) which cost less than half of the commercial HFNC. After introducing MHFNC in May 2011, these devices have been increasingly used in children with various respiratory problems. We conducted this retrospective study to report our experience in using MHFNC in children with community-acquired pneumonia at Ramathibodi Hospital from August 2012 to December 2015. And the second objective was to identify factors associated with MHFNC failure.

  Materials and Methods Top

Study design

This was a retrospective study conducted in a tertiary care center and was approved by the Ethics Committee of Ramathibodi Hospital, Mahidol University.


Medical records of all patients, aged <5 years, admitted to a pediatric infectious diseases ward with a diagnosis of community-acquired pneumonia and treated with MHFNC from August 2012 to December 2015 were evaluated. Patients, who were previously treated with HFNC at home or other wards and whose medical records could not be obtained, were excluded. Patients' data were extracted from the electronic medical record (EMR).

Modified high-flow nasal cannula device

MHFNC device comprises oxygen and air flow from the pipelines, a heated humidifier (MR850, Fisher and Paykel Healthcare®), a single-heated breathing circuit, and a shortened standard oxygen nasal cannula as shown in [Figure 1]. Respiratory nurses prepared MHFNC equipment in advance for use in the ward. Initiation of MHFNC was decided by the residents on duty. The size of the cannula depended on the nostrils. The ratio of cannula to nostril diameters should not exceed 0.7. This would allow leakage of excessive gas flow in order to prevent air leak syndrome. To increase humidity production and loosen secretion, the temperature of the heated humidifier was adjusted clinically by nurses at bedside, that is, temperature mode was adjusted to mask mode if there were droplets observed in the connector between the corrugated tube and nasal cannula and to endotracheal mode if there was no mist in the connector.
Figure 1: Drawing illustration of our modified high-flow nasal cannula.

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Patient monitoring

Heart rate, respiratory rate, oxygen saturation, and respiratory condition of the patients were routinely monitored. Vital signs were recorded at the patient's bedside form every 15 min until stable. Certainly, bedside nurse record forms were not scanned into EMR, so we could not obtain these parameters for statistical analysis. The vital signs recorded in EMR were those at 4 h interval before and after MHFNC was commenced.

Failure of modified high-flow nasal cannula treatment

MHFNC failure was defined as a need for further respiratory support within 48 h after initiating MHFNC. Escalation of respiratory support was decided by on service residents and staffs. Other respiratory support included noninvasive and invasive mechanical ventilation.

Oxygen saturation/fraction of inspired oxygen ratio

SpO2/fraction of inspired oxygen (FiO2) ratio (SF ratio) was the ratio of oxygen saturation and fraction of inspired oxygen which reflects severity of hypoxemia. SF ratio that is ≤264 is alternatively used as a parameter for diagnosis of pediatric acute respiratory distress syndrome (ARDS)[12] when PaO2 is not available. SF ratio was found to be one of the indicators of early noninvasive ventilation failure in children.[13],[14]

Data gathering and outcomes

Data collection included age, sex, weight, height, underlying medical conditions (bronchopulmonary dysplasia (BPD) or chronic lung diseases, congenital heart diseases, liver diseases, neurologic diseases, history of prematurity), supplemental oxygen requirements prior to, initial and maximum total flow rate, initial and maximum total flow rate per kg, initial and maximum FiO2, respiratory viral study results, initial white blood cell count, antibiotics used, initial oxygen saturation (SpO2), initial heart rate and respiratory rate, heart rate and respiratory rate 4 h after MHFNC initiation, and length of stay (LOS).

Initial respiratory rate was classified to more than or less than 90th percentile for age.[15] Initial SpO2 and FiO2 were calculated to yield the SF ratio. Moreover, the ratios were later classified to more than or less than 264 which was the cutoff value used in pediatric ARDS criteria.[12] In the MHFNC failure group, we collected additional information including causes of MHFNC failure, types of respiratory support needed after MHFNC failure, and time in hours to MHFNC failure. Arterial blood gases were not routinely checked and therefore were not included in analysis.

Statistical analysis

All data are expressed as median (interquartile range), mean ± standard deviation (minimum, maximum), or number (percentage). Categorical variables were analyzed with a Chi-square test. Continuous parametric variables were compared using two-sample t-test and nonparametric variables were compared using Mann–Whitney test. Variables that were significantly different between success and failure groups were enter into logistic regression model to determine odds ratios (ORs) and 95% confidence intervals (95% CI) for predicting failure of therapy. For all analyses, P < 0.05 was considered as statistical significance. All data analyses were performed using SPSS Statistical software (version 17.0; SPSS, Chicago, IL, USA).

  Results Top

One hundred and six patients met the inclusion criteria. Seven patients were excluded from the study because four patients' medical records were not found in EMR and the other three patients had been treated with home HFNC. Therefore, 99 patients were included in this study.

Baseline characteristics of all 99 patients were presented in [Table 1]. There was a male predominance (60%). Patients' age ranged from 8 to 26 months with mean age of 14 months old. Mean body weight was 9 kg, ranging from 2 to 20 kg. Most patients had no underlying medical conditions and no viral study done. Eighty-eight percent of patients needed low-flow oxygen nasal cannula before MHFNC therapy. There was a wide range of SF ratio (210-350) with mean value of 280. Half of the patients had SF ratio ≤264. MHFNC settings were showed in [Table 2]. The mean initial flow rate was 1.1 ± 0.3 L/kg/min which was increased later to 1.4 ± 0.4 L/kg/min. Mean initial FiO2 was 0.37 ± 0.08 which was later increased to 0.39 ± 0.09.
Table 1: Baseline characteristics of all patients

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Table 2: Modified high-flow nasal cannula settings

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No major complications from MHFNC were reported. After using MHFNC, 92 of 99 patients (93%) clinically improved and were classified as the success group and 7 (7%) deteriorated and were classified as the failure group. The causes of MHFNC failure were progression of pneumonia (n = 5), excessive secretion (n = 1), and cardiac failure (n = 1). Furthermore, 6 of 7 were intubated after MHFNC failure. The time from starting MHFNC to stepping up to other respiratory support for these seven patients was shown in [Figure 2].
Figure 2: Time in hours when patients needed intubations or noninvasive mechanical ventilation.

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Demographic, laboratory data, SF ratio, initial oxygen therapy, and respiratory rate of both success and failure groups were shown in [Table 3]. There were no differences between both groups for age, sex, body weight, height, and underlying diseases. More than half of the patients did not have viral study results. Positive viral studies, baseline respiratory rate > 90th percentile for age, initial white blood cell count, and antibiotics used did not differ between the two groups. SF ratio, SF ratio <264, and LOS >7 days were the variables that showed significant differences between success and failure groups. In respect to vital signs change over time after MHFNC initiation, there were no significant changes in heart rate and respiratory rate at the first 4 h when comparing between groups [Table 4].
Table 3: Comparison of baseline characteristics between success and failure groups

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Table 4: Changes in heart rate and respiratory rate at 4 h after starting modified high-flow nasal cannula

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Gas flow rate and FiO2 used in both success and failure group were presented in [Table 5]. The mean values of initial and maximum flow rate were 9 L/min (1–1.5 L/kg/min) and 11 L/min (1.3–1.5 L/kg/min), respectively, which did not differ between groups. Mean initial and maximum FiO2 of the failure group were significantly higher than the success group, P = 0.001 and <0.001, respectively. In addition, more patients in the failure groups required maximum FiO2 >0.5, P < 0.001. Logistic regression analysis showed that maximum FiO2 >0.5 was strongly associated with increased risk of MHFNC failure (OR, 22.25; 95% CI, 3.37–146.99; P = 0.01).
Table 5: Comparison of modified high-flow nasal cannula settings between success and failure groups

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  Discussion Top

Our current study findings suggested that MHFNC is a useful respiratory therapy in young children with community-acquired pneumonia with high success rate of 97%. No significant complications such as air-leak syndrome were demonstrated. Our success rate was comparable to previous studies that reported the use of commercial HFNC in children with respiratory distress from other conditions,[10],[16],[17],[18],[19] Air-leak syndrome was not found in our patients possibly due to our practice protocol to choose the size of nasal prong not larger than 0.7 of nare diameter. This provides the space for excessive gas flow to leak to the atmosphere and prevent barotrauma to the lungs. Another benefit of this space is to allow patients to entrain more air from atmosphere when gas flow from HFNC system is less than patients' inspiratory flow rate, especially when crying.

This study confirmed that the MHFNC could be used safely and effectively in children with pneumonia starting at the age of 1 month to 54 months, weighing 2 kg to 20 kg, with various underlying diseases including BPD, congenital heart diseases, neurologic diseases, and liver diseases. Almost all patients required supplemental oxygen before MHFNC application and more than half of the patients had high initial respiratory rate (>90th percentile of age) and half of the patients had SpO2/FiO2 ratio <264 which indicated severe hypoxemia secondary to parenchymal lung injury from pneumonia.

The optimum gas flow rate for each patient was adjusted according to clinical signs and symptoms at bed side. We found that with MHFNC most patients in our study required absolute gas flow rate <2 L/kg/min as recommended by a number of standard guidelines of commercial HFNC.[20],[21],[22] Another component that makes MHFNC differs from commercial HFNC is that a blender is not incorporated in the system. Air and oxygen from wall pipeline are directly connected to a heated humidifier chamber as shown in [Figure 1]. FiO2 can be manually calculated. To remember easily, whenever oxygen flow rate is equal to air flow rate, FiO2 will always be 0.6, which is a cutoff value of oxygen toxicity. Humidification is also necessary to facilitate secretion clearance to prevent mucus plugging and remove purulent material caused by pneumonia. We set the humidifier on 37°C invasive setting to maintain optimal humidity. However, when water droplets or condensation accumulate in the nasal cannula, the humidifier temperature should be decreased temporarily.

We found that oxygenation status assessed by SpO2/FiO2 ratio, initial FiO2, and maximum FiO2 requirement were significantly associated with MHFNC failure. Maximum FiO2 requirement >0.5 had significantly higher odds ratios of 22.25 to develop MHFNC failure. Furthermore, more than half of the patients in the failure group got worsen and needed ventilatory support within the first 12 h. The oxygenation deterioration was most likely related to progression of pneumonia which was found to be the most common etiology of the failure group. Therefore, MHFNC should be used with caution in patients with low baseline SpO2/FiO2 ratio and FiO2 to >0.5 since these are significant predictors identified for MHFNC failure. Close monitoring and clinical observation are important in this group of patients in order to early detect HFNC failure, so that intubation would not be delayed. Previous studies have showed predictors of HFNC failure in children to be absent change in respiratory rate,[16],[17],[18] lower oxygenation,[16] thoracoabdominal asynchrony,[16] higher PRISM III score,[17] lower body weight,[17] respiratory acidosis (low pH with high PCO2),[10],[18] and congenital heart diseases.[19]

Our MHFNC system can be setup without difficulties in any hospitals that have heated humidifiers, air, and oxygen pipelines. The cost of treatment by MHFNC is less than half of the regular commercial HFNC that is available in the market. In our opinion, MHFNC is the most reasonable choice of treatment, especially in low-income countries. At our hospital, MHFNC has been used satisfactorily in various causes of respiratory distress such as pneumonia, bronchiolitis, asthma, croup, postextubation stridor, and tracheobronchomalacia. Nursing care for patients being on MHFNC is similar to commercial HFNC.[22] Insertion of nasogastric tube is needed if the patient develops abdominal distension. In such case, the nasogastric tube is aspirated for air 2–4 hourly. Some children can be fed orally if they do not have breathing difficulty or abdominal distension. Nose care is vital to maintain passageway of high-flow gas which comprises gentle nose suction to remove secretion obstruction and securing nasal prongs to avoid pressure sore to nares.

This retrospective study was limited to community-acquired pneumonia; therefore, our finding might not be generalized to other respiratory disease.

Moreover, arterial blood gases, especially CO2 were not available for analysis. The study used MHFNC, not commercial HFNC. Therefore, the efficacy of both devices could not be compared.

  Conclusions Top

MHFNC is a useful and practical respiratory support in young children with pneumonia. It has not only low failure rate but also much less treatment cost. No major and life-threatening complications occurred. The strong predictor of MHFNC failure identified in this study was maximum FiO2 >0.5 which may reflect progression of pneumonia. Close monitoring of respiratory clinical status is essential, especially within the first 12 h after initiation of MHFNC.


The authors would like to thank Thianchai Bunnalai, MD, for his creative idea on MHFNC; Panida Srisan, MD, for her suggestion; Nattachai Anantasit, MD, for his helpful advices; Umapon Udomsubpayakul, for her statistical analysis advices; Chula Kooanantkul, MD., for his excellent statistic analysis consultant; and Chuenarom Tharawas, for her beautiful drawing illustration.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

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Fleming S, Thompson M, Stevens R, Heneghan C, Plüddemann A, Maconochie I, et al. Normal ranges of heart rate and respiratory rate in children from birth to 18 years of age: A systematic review of observational studies. Lancet 2011;377:1011-8.  Back to cited text no. 15
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  [Figure 1], [Figure 2]

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]

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