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Year : 2020  |  Volume : 14  |  Issue : 4  |  Page : 632-637  

Effect of use of high-flow nasal cannula during fiberoptic intubation under general anesthesia: A randomized controlled trial

Department of Anesthesia and Critical Care, Dr. Ram Manohar Lohia Institute of Medical Sciences, Lucknow, Uttar Pradesh, India

Date of Submission09-Apr-2021
Date of Acceptance15-Apr-2021
Date of Web Publication27-May-2021

Correspondence Address:
Dr. Manoj Tripathi
Department of Anesthesia and Critical Care, Dr. Ram Manohar Lohia Institute of Medical Sciences, Lucknow, Uttar Pradesh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/aer.aer_55_21

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Background: Oxygenation by high-flow nasal cannula (HFNC) is being widely studied in the intensive care unit and operation theater settings. Aims and Objectives: The aim of this study is to determine the effect of HFNC during fiberoptic intubation in terms of time taken and ease of intubation. Settings and Design: Randomized, prospective, and controlled study. Materials and Methods: In this study, we have recruited 40 patients according to the inclusion criteria (patient's body mass index [BMI] >22.99 kg.m−2 and patients with a history of stridor and/or obstructive sleep apnea) and after randomization divided them into two groups of 20 each – Group C: Intubation done with conventional fiberoptic after muscle relaxation and Group S: Intubation done with high flow nasal cannula during fiberoptic after muscle relaxation. We have observed and compared between the groups time taken for intubation, oxygen saturation during fiberoptic intubation, need of jaw thrust and difficulty in gliding endotracheal tube over fiberscope. Results: No significant difference was found in time taken for intubation, oxygen saturation, and need of jaw thrust (P > 0.05). We have found a significant difference in gliding of endotracheal tube over fiberscope (P = 0.001). Conclusion: We found high flow nasal cannula better and beneficial in patients with high BMI and having a history of stridor/obstructive sleep apnea for fiberoptic intubation after muscle relaxation.

Keywords: Fiberoptic intubation, high-flow nasal cannula, jaw thrust, oxygen saturation

How to cite this article:
Rao S, Rai S, Das PK, Kumar S, Malviya D, Tripathi M. Effect of use of high-flow nasal cannula during fiberoptic intubation under general anesthesia: A randomized controlled trial. Anesth Essays Res 2020;14:632-7

How to cite this URL:
Rao S, Rai S, Das PK, Kumar S, Malviya D, Tripathi M. Effect of use of high-flow nasal cannula during fiberoptic intubation under general anesthesia: A randomized controlled trial. Anesth Essays Res [serial online] 2020 [cited 2021 Jun 17];14:632-7. Available from:

   Introduction Top

We have precise algorithm for airway management and preoxygenation sequence and practical response for these algorithms is quite appreciable. However, anticipated difficult intubation (DI) remains a frequent challenge and a major cause of hypoxemia during anesthesia. To reduce desaturation during anticipated DI, two options can be used for airway management that is rapid sequence intubation or awake fiberoptic intubation (FOI).[1],[2] During FOI despite well-conducted preoxygenation, DI increases first-attempt failure, long-lasting procedure incidence, and leads to frequent oxygen desaturation.[3]

High-flow oxygenation by nasal cannula (HFNC) has been studied in the intensive care unit (ICU) and in the operating room as a preoxygenation device with controversial results. Few studies have suggested the ability of HFNC to extend safe apnea time during DI and to be held during FOI. This device can deliver up to 60 L.min−1 with an inspired fraction of oxygen of up to 100% and generate a moderate positive supraglottic end expiratory pressure.[4],[5] HFNC allows the insertion of fiberscope in the patient's nostril to perform intubation while continuing the oxygenation and may be better tolerated.[6] High-flow nasal cannulation is used successfully for preoxygenation, awake FOIs, acute hypoxic respiratory failure, during bronchoscopy, postextubation, and to avoid invasive ventilation in respiratory failure. Its use allows delivery of oxygen at flow rates up to 70 l.min−1, extending apneic time, facilitating carbon dioxide elimination, reducing the work of breathing, and providing positive end-expiratory pressure. This extension of apnea time is useful where airway patency is at risk and time would be required for intervention.[7],[8],[9] The present study was designed to evaluate the efficacy of high flow nasal cannula (HFNC) during fiberoptic intubation under general anesthesia.

Aims and objectives

  1. To determine whether the use of high flow nasal cannula eases FOI in term of time taken for intubation in patients with h/o strider and/or high body mass index (BMI) following general anesthesia with muscle relaxation and other parameters
  2. To compare the level of decrease in oxygen saturation during the process of FOI after stopping mask ventilation in patients supported with high flow nasal cannula versus patients not supported with high flow nasal cannula.

   Materials and Methods Top

This was a prospective, randomized controlled study conducted at a tertiary care hospital and research center for a period of 18 months between June 2019 and November 2020 after obtaining the approval from the Institutional Ethical Committee (IEC No. 63/18). A written informed consent was taken from all the patients. This study was enrolled in clinical trial registry (CTRI/2021/04/032516) and followed the ethical principles for medical research involving human subjects according to Helsinki Declaration 2013.

Inclusion criteria

Age 18–65 years of either gender, BMI >22.99 kg.m−2, patients with a history of stridor and or obstructive sleep apnea (OSA), and patients of American Society of Anesthesiologists (ASA) Class I and II were included in the study.

Exclusion criteria

Age <18 years or >65 years, patients with known airway pathology, morbid obesity and pregnancy, and patients of ASA Class III and IV were excluded from the study.


Randomization sequence was drawn using a computer-generated random number table. The patients were randomized into the study arm (Group C) and control arm (Group S) using this random number table.


Allocation concealment (blinding) was done using sequentially numbered opaque envelopes. The names of patients fulfilling inclusion/exclusion criteria and consenting for participation in the study were sequentially entered on the cover of the opaque envelope and after that the envelope was opened to reveal the study arm for the patient. The patient was blind regarding his/her allocation of study arm.

We have recruited 40 patients in our study according to the inclusion criteria and after randomization divided them into two groups of 20 each.

Group C

Intubation done with conventional fiberoptic after muscle relaxation.

Group S

Intubation done with fiberoptic using high flow nasal cannula after muscle relaxation.

After preoperative evaluation, consent and premedication of Tab Rantac 150 mg night before surgery, we have transferred patient onto preoperative room at the morning of surgery. 18G intravenous (i.v.) access in the preoperative room was taken and i.v. fluid infusion was started. Xylometazoline 0.01% nasal drop was instilled in each nostril. Patients were taken into the operating room, and standard monitors such as pulse oximeter, noninvasive blood pressure, and 5 lead ECG were attached. After giving injection fentanyl 1 μ−1 and preoxygenating with O2 @ 10 l.min−1, anesthesia was induced with injection propofol 2–2.5−1. After loss of verbal command and confirmation of ability to ventilate, injection Vecuronium 0.1−1 was given to facilitate tracheal intubation. After ventilating patient for 3 min in Group C, fiberoptic oral intubation was done. In Group S patients, all the above steps were followed along with institution of HFNC with flow rate @ 60 litres.min−1 after ventilating for 3 min and thereafter fiberoptic oral intubation was done. Time taken for intubation is calculated as time taken from the tip of the fiberscope at the opening of mouth to insertion of tube in the glottic opening. Need of jaw thrust and difficulty in passing of the tube over fiberscope that is, not passing in a single attempt, or need rotation were noted. Heart rate, mean arterial pressure, SPO2 were measured before, just after and 5 min after intubation.

In our study, in both groups, we used bite blocker in the oral cavity to facilitate passage of fiberoptic bronchoscope in the oral cavity. Due to bite block, we did not use lingual traction as maneuver to clear the airway passage.

Statistical analysis

Sample size

The study was planned to compare the ease of intubation using fiberoptic bronchoscope alone and fiberoptic bronchoscope with high flow nasal cannula considering the total time of intubation being inversely proportional to ease of intubation. In a previous study by Mohammadzadeh et al.,[10] the time of intubation by bronchoscope alone was 176 + 56 s if the true difference in the time taken for intubation by fiberoptic with the use of high flow nasal cannula is 89 s we will need to study nine patients in each group to be able to reject the null hypothesis that the time taken in both these groups is equal with a power of 0.8. In our institute, there was a sufficient number of patients, out of which only 40 patients were took for this study.

zα/2@95% c.i. = 1.96, zβ @80%power = 0.84, σ = variance, d = difference expected

The results are presented in frequencies, percentages, and mean ± standard deviation. The Chi-square test was used to compare the categorical variables between the groups. The unpaired t-test was used to compare the continuous variables between the groups. P < 0.05 was considered statistically significant. All the analysis was carried out on SPSS 16.0 software version (Chicago, Illinois, Inc., USA).

   Results Top

As shown in [Table 1], patients were comparable in both groups in terms of age, sex, ASA physical status class, and BMI (P > 0.05). [Table 2] shows that no significant difference was found between Group C and S in any of airway parameters (P > 0.05). We compared for time taken in intubation between both the groups. No significant difference was found between Group C and S (106.55 ± 5.01 vs. 106.40 ± 4.95, P = 0.92) [Table 3]. On comparing the jaw thrust required to facilitate intubation, we have found no significant difference between the groups (P > 0.05) [Graph 1]. [Table 4] shows the comparison of difficulty in passing ET tube over fiberscope and statistically significant difference between Group C and S was found (P = 0.001). In Group C, more number of patients had difficulty in passing ET tube through fiberscope than Group S. As shown in [Table 5], we have also compared heart rate, mean arterial pressure and SPO2 before intubation, after intubation and 5 minutes after intubation. No significant difference was found in all above parameters at all time periods between the groups.
Table 1: Comparison of demographic profile between the groups

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Table 2: Comparison of airway parameters between the groups

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Table 3: Time taken for intubation in both the groups

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Table 4: Comparison of difficulty in passing endotracheal tube over fiberscope

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Table 5: Comparison of hemodynamic parameters at different time periods

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   Discussion Top

This prospective, randomized controlled study was conducted with the objective to determine whether the use of high flow nasal cannula eases fiberoptic intubation in patients in terms of time taken for intubation, jaw thrust requirement, difficulty in passing ET tube, and hemodynamic with h/o strider and/or high BMI following general anesthesia with muscle relaxation.

The use of sedative agents can lead to hypoventilation and apnea. In addition, in those patients with pathology-related chronically obstructed upper airways who become apneic, the rate of desaturation will be greater because they may have a lower initial alveolar O2 tension and higher work of breathing. In addition, the application of lidocaine to the upper airway has been shown to reduce dynamic inspiratory airflow and there are case reports linking total airways obstruction with local anesthetic topicalization alone.[11] The conventional forms of oxygen delivery used for AFOI are low-flow variable performance devices; nasal cannula, facemasks, nasal sponges, suction catheters placed in the nostril, or via the working channel of the fiberscope. The patient's peak inspiratory flow rate exceeds the oxygen flow and ambient air entrained to dilute the fractional inspired oxygen (FIO2). Nasal cannula can comfortably supply up to an FIO2 of only 0.36. A study of healthy nonsedated volunteers undergoing AFOI, who received oxygen through standard low-flow nasal cannula, found the incidence of desaturation below 80% to be 1.5%.[12]

In the present study, the demographic variables, Mallampatti grade, inter-incisor gap, hyomental distance, thyromental distance, and neck circumference were comparable between the groups. We have found that jaw thrust required was in all patients of Group C and in 95% of Group S. That was not significant statistically (P > 0.05). During general anesthesia, posterior displacement of tongue, soft palate, and epiglottis tend to close the airway. When performing oral FOI perhaps the first maneuver to try is jaw thrust with the mouth open, as this is the simplest and least invasive approach. Durga et al. in 2001[13] also observed that after giving muscle relaxant, muscle tone reduced and the soft palate, base of tongue, and epiglottis all approximate to the posterior pharyngeal wall which may make FOI more difficult. He found jaw thrust very effective in clearing the airway passage.

Time of intubation was marginally lower in Group S (106.40 ± 4.95 s) than Group C (106.55 ± 5.01 s) in this study, but this difference was found to be insignificant on the statistical analysis (P > 0.05).

In this study, we defined difficulty in passing ET tube over fiberscope if we required rotation of ET tube to glide ET tube over fiberscope or we required additional attempts to glide ET tube over fiberscope. In a study by Asai and Shingu in 2004,[14] they observed that after successful insertion of fiberscope into trachea despite considerable difficulty in a patient with a difficult airway, it is still difficult to advance ET tube over the scope into the trachea and the oxygen saturation starts to decrease. In Group C, we faced difficulty in 75% of patients and in Group S, we faced difficulty in 20% of patients which is significantly higher in Group C (P = 0.001).

High-flow nasal cannula provides an increased FiO2 because the higher flow rates are capable of matching or exceeding the patient's peak inspiratory flow, preventing room air entrainment. Naso- and oropharyngeal dead space is washed out with oxygen-rich gas and acts as a reservoir. Flows of 35 l.min−1 with mouth closure have been shown to create positive expiratory nasopharynx pressure of up to 5.3 cm H2O. At flow rates of 70 l.min−1, this is the only available technique to deliver 100% FiO2 continuously throughout an oral or nasal awake FOI. The humidification of the gases counteracting the drying effect of high flow has been shown to lead to greater patient comfort and higher tolerance compared with conventional methods and to help with mucociliary clearance (Roca et al. 2010,[4] Hasani et al., 2008[15]). Hence, as we have discussed earlier also that after giving GA to the patient, posterior displacement of tongue, soft palate, and epiglottis tend to close the airway and HFNC create positive expiratory nasopharynx pressure of up to 5.3 cm H2O. It tends to open the upper airway in a better way, that can be a reason with other favorable factors discussed in above studies, that is why jaw thrust was less required in Group S and only 20% patient had got difficulty in gliding ET tube over fiberscope in Group S in comparison to Group C where 75% patients got difficulty. Parke and McGuinness[16] also demonstrated that HFNC generates positive pressure in the nasopharynx throughout the respiratory cycle, more so in the expiratory phase.

In our study, SPO2 in Group S was 100% throughout during the procedure and at 1 min and after 5 min. Of intubation, in Group C, there was desaturation of one patient during intubation, patient saturation went down to 89% but recovered in 1 min time and again reached to 100%. Because in our research institute, we used to do FOI at regular basis and we have taken less time for intubation, oxygen saturation was not found significantly different between both the groups. Apneic oxygenation describes the process whereby high flow rates allow continuous delivery of oxygen to the alveoli and participate in gaseous exchange despite the absence of active breathing. Patel and Nouraei have shown that HFNC increased apnea time, therefore buying time to secure a definitive airway.[17] Ramachandran et al.[18] also found that HFNC prolongs time before desaturation and reduces the incidence of significant life-threatening desaturation.

We observed increase in heart rate, systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP) in both the group during intubation and returned to pre intubation level within 5 min after intubation. Increase in heart rate, SBP, DBP, and MAP was found statistically insignificant between the groups (P > 0.05). During FOI, there is stress response in patients due to which there is increase in heart rate, SBP, DBP, and MAP. In a study by Jakuðenko et al. in 2008[19] observed hemodynamic changes in FOI and observed that hemodynamic changes disappeared just in 5 min.

These features suggest that HFNC may be particularly beneficial in delivering oxygen during respiratory or anesthetic procedures. During bronchoscopy and in sedated patients undergoing dental procedures, the use of humidified transnasal oxygenation has yielded higher SpO2 and oxygenation characteristics compared with conventionally used nasal cannulae or venturi masks (Lucangelo et al. 2012;[20] Sago et al., 2015[21]). HFNC has been explored as an adjunct for difficult airway management. It has been described to optimize oxygenation in patients planned for awake FOI. HFNC also reduced significant desaturation in obese patients during induction of anesthesia. Trials are being conducted to evaluate HFNC against standard preoxygenation in anticipated difficult airways. However, HFNC should not be the sole device used for the management of a difficult airway as apnea after induction can result in a slow desaturation (Vourc'h et al.[22] 2019; Lodenius et al.[23] 2018).

One of the most significant criticism of HFNC is the potential for delaying intubation when clinically indicated. A study of patients intubated after a trial of HFNC therapy found that delay of intubation led to poorer outcomes in the ICU. It is hypothesized that the comfort provided by HFNC devices may delay the onset of respiratory distress, confounding the physician's assessment of the patient's respiratory status. Another issue with HFNC is the cost. HFNC is more expensive than COT devices and is therefore less accessible in resource-poor countries.[24]

   Conclusion Top

We concluded that using high flow nasal cannula in oral FOI in patients with high BMI with a history of stridor or OSA makes intubation easier without hypoxia. Hence, we recommend to use high flow nasal cannula during oral FOI in these patients.


One of the limitations of this study was small sample size. The studies with larger sample size with a long duration of study period are required to have more robust findings.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

   References Top

Apfelbaum JL, Hagberg CA, Caplan RA, Blitt CD, Connis RT, Nickinovich DG, et al. Practice guidelines for management of the difficult airway: An updated report by the American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Anesthesiology 2013;118:251-70.  Back to cited text no. 1
Frerk C, Mitchell VS, McNarry AF, Mendonca C, Bhagrath R, Patel A, et al. Difficult Airway Society 2015 guidelines for management of unanticipated difficult intubation in adults. Br J Anaesth 2015;115:827-48.  Back to cited text no. 2
Workeneh SA, Gebregzi AH, Denu ZA. Magnitude and predisposing factors of difficult airway during induction of general anaesthesia. Anesthesiol Res Pract 2017;2017:1-6.  Back to cited text no. 3
Roca O, Riera J, Torres F, Masclans JR. High-flow oxygen therapy in acute respiratory failure. Respir Care 2010;55:408-13.  Back to cited text no. 4
Vargas F, Saint-Leger M, Boyer A, Bui NH, Hilbert G. Physiologic effects of high-flow nasal cannula oxygen in critical care subjects. Respir Care 2015;60:1369-76.  Back to cited text no. 5
Russotto V, Cortegiani A, Raineri SM, Gregoretti C, Giarratano A. Respiratory support techniques to avoid desaturation in critically ill patients requiring endotracheal intubation: A systematic review and meta-analysis. J Crit Care 2017;41:98-106.  Back to cited text no. 6
Ashraf-Kashani N, Kumar R. High-flow nasal oxygen therapy. BJA Educ 2017;17:57-62.  Back to cited text no. 7
Hernández G, Vaquero C, Colinas L, Cuena R, González P, Canabal A, et al. Effect of postextubation high-flow nasal cannula vs. noninvasive ventilation on reintubation and postextubation respiratory failure in high-risk patients: A randomized clinical trial. JAMA 2016;316:1565-74.  Back to cited text no. 8
Poignant S, Moënne-Loccoz J, Cohen B, Laffon M. Acute postoperative hypoxemic respiratory failure as a result of Chilaiditi's syndrome: Contribution of high flow oxygen through nasal cannula. Br J Anaesth 2017;118:465-6.  Back to cited text no. 9
Mohammadzadeh A, Haghighi M, Naderi B, Chaudhry A, Khan ZH, Rasouli MR, et al. Comparison of two different methods of fiber-optic nasal intubation: Conventional method versus facilitated method (NASAL-18). Ups J Med Sci 2011;116:138-41.  Back to cited text no. 10
Ho AM, Chung DC, To EW, Karmakar MK. Total airway obstruction during local anesthesia in a non-sedated patient with a compromised airway. Can J Anaesth 2004;51:838-41.  Back to cited text no. 11
Woodall NM, Harwood RJ, Barker GL. Complications of awake fibreoptic intubation without sedation in 200 healthy anaesthetists attending a training course. Br J Anaesth 2008;100:850-5.  Back to cited text no. 12
Durga VK. Milln JP, Smith JE. Manoeuvres used to clear the airway during fibreoptic intubation. Br J Anaesth 2001;87;207-11.  Back to cited text no. 13
Asai T, Shingu K. Difficulty in advancing a tracheal tube over a fibreoptic bronchoscope: Incidence, causes and solutions. Br J Anaesth 2004;92:870-81.  Back to cited text no. 14
Hasani A, Chapman TH, McCool D, Smith RE, Dilworth JP, Agnew JE. Domiciliary humidification improves lung mucociliary clearance in patients with bronchiectasis. Chron Respir Dis 2008;5:81-6.  Back to cited text no. 15
Parke RL, McGuinness SP. Pressures delivered by nasal high flow oxygen during all phases of the respiratory cycle. Respir Care 2013;58:1621-4.  Back to cited text no. 16
Patel A, Nouraei SA. Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE): A physiological method of increasing apnoea time in patients with difficult airways. Anaesthesia 2015;70:323-9.  Back to cited text no. 17
Ramachandran SK, Cosnowski A, Shanks A, Turner CR. Apneic oxygenation during prolonged laryngoscopy in obese patients: A randomized, controlled trial of nasal oxygen administration. J Clin Anesth 2010;22:164-8.  Back to cited text no. 18
Jakuðenko N, Kopeika U, Mihelsons M, Nagobade D, Putniòa AV, Pavârs A. Comparison of stress response performing endotracheal intubation by direct laryngoscopy, fibreoptic intubation and intubation by the glidescope laryngoscope. Proc Latvian Acad Sci Sec B 2008;62:176-81.  Back to cited text no. 19
Lucangelo U, Vassallo FG, Marras E, Ferluga M, Beziza E, Comuzzi L, et al. High-flow nasal interface improves oxygenation in patients undergoing bronchoscopy. Crit Care Res Pract 2012;2012:506382.  Back to cited text no. 20
Sago T, Harano N, Chogyoji Y, Nunomaki M, Shiiba S, Watanabe S. A nasal high-flow system prevents hypoxia in dental patients under intravenous sedation. J Oral Maxillofac Surg 2015;73:1058-64.  Back to cited text no. 21
Vourc'h M, Baud G, Feuillet F, Blanchard C, Mirallie E, Guitton C, et al. High-flow nasal cannulae versus non-invasive ventilation for preoxygenation of obese patients: The PREOPTIPOP randomized trial. EClinicalMedicine 2019;13:112-9.  Back to cited text no. 22
Lodenius Å, Piehl J, Östlund A, Ullman J, Jonsson Fagerlund M. Transnasal humidified rapid-insufflation ventilatory exchange (THRIVE) vs. facemask breathing pre-oxygenation for rapid sequence induction in adults: A prospective randomised non-blinded clinical trial. Anaesthesia 2018;73:564-71.  Back to cited text no. 23
Kang BJ, Koh Y, Lim CM, Huh JW, Baek S, Han M, et al. Failure of high-flow nasal cannula therapy may delay intubation and increase mortality. Intensive Care Med 2015;41:623-32.  Back to cited text no. 24


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


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