Journal of Obstetric Anaesthesia and Critical Care

: 2022  |  Volume : 12  |  Issue : 1  |  Page : 1--4

High flow nasal cannula (HFNC) and video laryngoscope (VL) as essential adjuncts in management of obstetric difficult airway: Efficacious tools or simply an industry push!

Anjan Trikha, Manpreet Kaur 
 Department of Anaesthesiology, Pain Medicine and Critical Care, All India Institute of Medical Sciences (AIIMS), Delhi, India

Correspondence Address:
Dr. Manpreet Kaur
Department of Anaesthesiology, All India Institute of Medical Sciences (AIIMS), Room No. 5007, 5th Floor Teaching Block, New Delhi - 110 029

How to cite this article:
Trikha A, Kaur M. High flow nasal cannula (HFNC) and video laryngoscope (VL) as essential adjuncts in management of obstetric difficult airway: Efficacious tools or simply an industry push!.J Obstet Anaesth Crit Care 2022;12:1-4

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Trikha A, Kaur M. High flow nasal cannula (HFNC) and video laryngoscope (VL) as essential adjuncts in management of obstetric difficult airway: Efficacious tools or simply an industry push!. J Obstet Anaesth Crit Care [serial online] 2022 [cited 2022 May 21 ];12:1-4
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Full Text

General anesthesia (GA) administration in a pregnant woman is very challenging primarily because of three things – first, the airway is inherently difficult; second, any hypoxemic event during intubation has the potential to affect the wellbeing/appearance, pulse, grimace, activity, and respiration (APGAR) score of the newborn and lastly, it is rarely carried out nowadays. Failed intubation incidence is 1 in 390 for all types of obstetrical surgeries.[1] Further, maternal mortality from failed intubation in the caesarean section is 2.3 per 100000.[1] Hence, the administration of safe GA is of utmost importance for both maternal and fetal safety. Recent guidelines regarding difficult airway management in non-obstetrics with regard to newer gadgets necessitates the need to reconsider the Obstetric Difficult Airway Guidelines and include new gadgets to enhance the safety of a parturient.[2],[3]

Lately, two devices have been promoted for the management of non-obstetric difficult airway – high flow nasal cannula (HFNC) and video laryngoscope (VL). The former decreases the time required for adequate preoxygenation and increase the apnea time available for intubation. The latter is a useful tool to make intubation easier and quicker in a difficult airway setting. There is a need to evaluate critically the published advantages of both the devices in a setting of difficult obstetric airway. Currently, the question is, whether it is the right time to include HFNC and VL in Obstetric Airway management in existing guidelines or it is simply an industry push.[4]

Preoxygenation is administration of a high fraction of inspired oxygen (Fio2) before anesthetic induction to prolong the safe apnea time. Ideally, end points of maximal preoxygenation are targeting end-tidal oxygen concentrations (EtO2) more than 90%. Safe apnea time is the time interval following interruption of ventilation after which critical arterial desaturation (SaO2 88–90%) occurs. Apneic oxygenation is mostly done with nasal cannula with an oxygen flow rate of 15 L/min. The flow acts as an oxygen reservoir by filling the pharynx with a higher concentration of oxygen in the air–oxygen mixture.

The Obstetric Anaesthetists Association (UK) and Difficult Airway Society (DAS, UK) guidelines, in 2015,[2] recommend preoxygenation with a tight-fitting facemask in parturients undergoing GA. They also recommend “considering a nasal cannula with an oxygen flow rate of 5 L/min for pre-oxygenation to maintain the bulk flow of oxygen.”[2] The guidelines mention “New systems for nasal oxygenation that deliver humidified oxygen at high flow, such as the OptiflowTM system is under development but they have only been assessed in non-pregnant patients.”[2] This is just a passing remark and has not been incorporated in the guidelines. All India Difficult Airway Association (AIDAA) recommends administering oxygen at 15 L/min through a nasal cannula in obstetric patients as an additional precaution till a definitive airway has been secured but does not mention HFNC or any device per se.[3] Further AIDAA does not refer to any study for advocating such high flows through the nasal cannula in parturient.

HFNC has been evaluated as a preoxygenation device in the intensive care unit (ICU) and the operating room in non-obstetric patients. It can deliver a flow of 60 L/min and an inspired fraction of oxygen of up to 100%.[5] Preoxygenation with HFNC would be considered useful if it can increase the apnea time as compared to conventional time-tested facemask preoxygenation for 3–5 min. Nasal oxygenation with optiflow nasal cannula at the rate of 70 L/min for 10 min increases the apnea time in non-pregnant patients but not in parturients.[6] There is already ample evidence supporting the utility of HFNC for preoxygenation in a non-obstetric patient.[7],[8],[9],[10] However, there is limited literature on its utility in a parturient. This aids in apneic ventilation throughout the intubation and has been envisaged that this would allow an increase in apnea time. Delivery of high-flow oxygen continuously through the nose can increase end-expiratory volume and improve inspiratory flow dynamics.[11]

A PubMed search with HFNC and preoxygenation revealed 15 studies out of which 3 were meta-analysis.[7],[12],[13] The results of these three meta-analyses recommended HFNC for preoxygenation, apneic oxygenation during intubation, and concluded that HFNC lowers the risk of intubation-related complications like desaturation.[7],[12],[13] All these meta-analyses were multicentric trials in critically ill patients or in patients with acute hypoxemic respiratory failure, none of them included subjects with difficult airway or parturients.

There are only two randomized controlled trials regarding preoxygenation with HFNC in parturients.[14],[15] Tan et al. used HFNC with a flow of 30 L/min for 30 s, and then 50 L/min for 150 s (total 3 min) for preoxygenation in parturients. This protocol for preoxygenation did not achieve the target EtO2 ≥90% for the first expired breath.[14] The authors attributed this failure to the need for higher flows for a longer duration due to already physiologically compromised functional residual capacity and increased oxygen consumption in pregnancy. The only advantage as per the authors of using HFNC over tightly fitting face mask for preoxygenation was that HFNC was comfortable for pregnant women compared to a facemask.[14] In the second study by Shippam et al., preoxygenation using HFNC (30–70 L/min oxygen flow) via nasal prongs was compared with standard 15 L/min oxygen delivered through a tight-fitting facemask. In this study, HFNC did not reliably achieve EtO2 ≥90% which is a marker of optimal preoxygenation in a parturient.[15]

In our opinion, using HFNC has some limitations. First is the high cost of the equipment, limiting its routine use all over the world. Preoxygenation of a parturient with such high flows may cause gastric insufflation, potentially increasing the risk of regurgitation and aspiration in an unprotected airway in the parturient. Two reports in literature by Mc Lellan and Lodenius et al. have shown that gastric insufflation does not take place with HFNC.[16],[17] However, extrapolating this finding to incompetent lower esophageal sphincter or reflux in pregnancy is questionable. Another limitation derived from personal experience is the air gushing out of patient's oral cavity on the face of the anesthesiologists during intubation. Besides, during the COVID19 pandemic, HFNC use has increased tremendously in the Indian subcontinent and lot of new innovations with regard to its utility for oxygenation has come up in a huge way. To add to it, HFNC usage has been hyped as a device by the medical industries as well.

In short preoxygenation with HFNC would be considered better than facemask if it scores well on three criteria. First, if HFNC achieves the desired EtO2 faster than the mask resulting in decreasing anesthesia induction time in category I caesarean section. Second, if HFNC gives significantly more apnea time. Third, if HFNC offers more comfort compared to tight-fitting facemask which is claustrophobic.

VL had been promoted for the management of non-obstetric difficult airway management and the COVID 19 pandemic has further increased its popularity. Practice guidelines for management of difficult airway by American society of Anesthesiologists task force has recommended VL as the first-line strategy for airway management of the known or suspected Difficult Airway in known or suspected COVID19 patients.[18] Before such a recommendation can be made for obstetric patients, there is a need to critically evaluate the published evidence of the device in this population.

VL has been one of the major advances in anesthesia over the recent years. It enables the operator to visualize the glottis indirectly on a video screen without need of alignment of line of sight to oral–pharyngeal–laryngeal axis. It offers lesser lifting force of laryngoscopy, lesser cervical spine movement, lesser sore throat, and has a faster learning curve. It reduces intubation failure and makes intubation easier in patients with an anticipated difficult airway. VL has been used extensively in anesthesia practice, however, there is limited literature in obstetrics where there is a higher risk of failed tracheal intubation.[19] VL has been shown to reduce failed intubations and complications like airway trauma among patients with difficult airway.[19],[20] A variety of videolaryngoscopes are available including the McGrath and C-MAC to disposable devices such as Airtraq (prodol, Meditec, Guecho, Spain), and King vision (Ambu). Choosing one particular videolaryngoscope would depend on: individual cost of the device, evidence available from the literature comparing various devices in various settings, both obstetric and non-obstetric. One such study by Blajic et al. has shown that the C-MAC was easier to use and needed fewer additional maneuvers than the King Vision in obstetric patients.[21]

Once a new device (VL) is acquired, familiarity of the device by the team members including the lead anesthesiologist is essential. Unless the new device is used regularly in non-difficult airway setting, it is not prudent to utilize it in difficult airway scenarios. Further, routine simulation-based training in manikins with difficult airway using VL should be promoted at various stages of training in laryngoscopy for enhancing the familiarity with the device. Universal videolarngoscopy adoption in anesthesia and intensive care setting was perceived beneficial to patient safety, team dynamics, human factors, quality of care, and quality of training.[22]

There are inherent difficulties in airway research in obstetric patients. A PubMed search with the terms “videolaryngoscopy,” “difficult airway” and “obstetric” revealed only five results with one meta-analysis, two studies, one survey, and one case report.[23],[24],[25],[26],[27] The above meta-analysis by Howle et al.[23] was a mixed-method systemic review and the remaining four results of the PubMed search were already covered by it. The principal findings of this meta-analysis showed no difference between videolaryngoscopy and direct laryngoscopy in parturients without difficult airway. However, the authors reported that a few observational studies and case reports highlight the importance of videolaryngoscopy as a primary intubating device in difficult airway setting in this sub group of patients. They further suggested that there was evolving evidence supporting the increased adoption of VL as a first-line device in obstetrics.

Research needs to continue for utility of videolaryngoscope as first-line device in patients with features of difficult airway rather than keeping it as a rescue device. Besides, to increase the familiarity of the device, it must be freely available to be used as a first-line device in non-obstetric cases. It could be suggested that instead of reserving VL as a rescue tool for failed intubation in parturients, it should be made a routine first-choice option for all parturient even without predictors of difficult airway. Only after using videolaryngoscope as first-line device in normal airway, it can become a device of routine use and thereby it can be easily adopted in parturients with difficult airway predictors.

Thus, to conclude, and in our opinion, VL is a device that should find an important place in the management of obstetric difficult airway but with a rider that cost, availability, and familiarity with the device must be discounted. As far as HFNC is concerned, more studies and trials regarding its efficacy and safety are needed in the obstetric population before it can be incorporated into obstetric difficult airway guidelines.


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