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 Table of Contents  
REVIEW ARTICLE
Year : 2020  |  Volume : 3  |  Issue : 1  |  Page : 13-18

Patient positioning and glottic visualisation: A narrative review


1 Department of Anaesthesiology, Mahatma Gandhi Medical College and Research Institute, Sri Balaji Vidyapeeth Deemed-to-be University, Puducherry, India
2 Department of Anaesthesiology, Super Speciality Cancer Institute and Hospital, Lucknow, Uttar Pradesh, India
3 Department of Anaesthesiology, Jawaharlal Institute of Postgraduate Medical Education and Research, Puducherry, India

Date of Submission01-Feb-2020
Date of Acceptance29-Mar-2020
Date of Web Publication30-May-2020

Correspondence Address:
Dr. Nandhakumar Janani
Department of Anaesthesiology, Mahatma Gandhi Medical College and Research Institute, Sri Balaji Vidyapeeth Deemed-to-be University, Puducherry - 607 402
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ARWY.ARWY_3_20

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  Abstract 


Optimal glottic view is a prerequisite for successful endotracheal intubation. Several factors such as height of pillow, head position, backup position and head-elevated laryngoscopy position (HELP) have been attributed to improve glottic view. This review of existing literature was conducted to summarise current evidence on the influence of different head positions on glottic view. The search engines used were PubMed, Cochrane Library, Google Scholar and ResearchGate. Keywords used for the search were sniffing position, HELP, backup position and glottic view. The two components of optimal sniffing position used traditionally for laryngoscopy include neck flexion of 35° and face-plane extension of 15° which is supposed to align three axes (oral, pharyngeal and laryngeal axes). Optimal height of pillow used to achieve sniffing position was found to be 9 cm. Since it is difficult to align all the three axes, the two-curve theory was proposed. Advantage of the sniffing position was questioned by various authors who projected the HELP and 25° backup position as better options. Our narrative review suggests that 25° backup and HELP position improves glottic view in comparison to supine sniffing position. To achieve alignment of external auditory meatus to the sternal notch, a small child required a small pillow, an older child or an adult required a bigger pillow and obese patients needed the ramped position/25° head-up position.

Keywords: Backup position, glottic view, head-elevated laryngoscopic position, sniffing position


How to cite this article:
Kumar V R, Janani N, Indubala M, Jaya V. Patient positioning and glottic visualisation: A narrative review. Airway 2020;3:13-8

How to cite this URL:
Kumar V R, Janani N, Indubala M, Jaya V. Patient positioning and glottic visualisation: A narrative review. Airway [serial online] 2020 [cited 2020 Oct 1];3:13-8. Available from: http://www.arwy.org/text.asp?2020/3/1/13/285428




  Introduction Top


Optimal glottic view is a precondition for successful endotracheal intubation. It is dependent on proper positioning of head and neck during direct laryngoscopy. The supine sniffing position, based on the three axes alignment theory, has traditionally been considered the optimal head position for direct laryngoscopy.[1],[2],[3] Since it is difficult to align all the three axes, the two-curve theory was proposed to explain the airway configuration.[4] The superiority of the sniffing position over other head and neck positions was debated because elevating the head higher than the conventional sniffing position improved laryngeal exposure.[5],[6] Head-elevated laryngoscopy position (HELP) has been found to significantly improve the glottic view and preoxygenation in obese patients when compared to the sniffing position.[6] The impact of a 25° backup position on intubating conditions was recently analysed by several authors.[7],[8] There were conflicting results in literature about optimal head position for direct laryngoscopy despite the fact that endotracheal intubation is a frequently performed critical skill for anaesthesiologists and emergency physicians.[9],[10] The aim of this review is to discuss the influence of various head positions on optimal glottic visualisation for readers to have a clear concept in this area.


  Description of Various Positions Top


Head-extension position [Figure 1] is attained by maximal head extension with no flexion of neck where the patient is placed supine with no pillow under the head.[2],[3],[11]
Figure 1: Head-extension position created by extending the head in the supine position with no pillow under the head

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Conventional sniffing position [Figure 2] is achieved by placing a 9-cm high non-compressible pillow under the head targeting to obtain a 35o neck flexion and 15o face-plane extension at the atlanto-occipital joint.[12]
Figure 2: Sniffing position achieved by placing the patient in supine position with a 10-cm pillow under the head to attain 15° face-plane extension and 35° neck flexion

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Head-elevated laryngoscopy position/ramped position [Figure 3] is achieved by elevating the patient's upper body and head using blankets or rapid airway management positioner such that the line from the sternal notch to external auditory meatus is at the same horizontal level.[5],[13],[14],[15],[16]
Figure 3: Head-elevated laryngoscopy position/rapid airway management positioner position obtained by placing the patient in supine position with pillows or blankets under the head and shoulders to align the external auditory meatus and sternal notch to the same horizontal level

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The backup position [Figure 4] is achieved by flexing the patient's torso at the level of hips using the controls on the operating table.[7],[16],[17]
Figure 4: Backup position created by placing the patient in supine position with 20° to 25° backup obtained by flexing the patient's torso at the level of hips using operating table controls

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  Influence of Height of Pillow on Axes and Glottic View Top


Probable theories for improved glottic view by increasing height of pillow are an increase of the occipito–atlanto–axial (OAA) angle produced by additional flexion. This increase on OAA angle supports posterior movement of the larynx during laryngoscopy, thereby decreasing the angle between line of vision and the laryngeal axis. Increase in height of pillow also causes caudal movement of the mandible and downward movement of the larynx, which enlarges the submandibular space.[18],[19],[20]

Several authors have studied heights of pillow ranging from 3 cm to 9 cm. Schmitt and Mangobserved head and neck elevation beyond sniffing improved glottic view in case of difficult direct laryngoscopy.[5] Park et al. supported thisstatement by stating that head elevation with a 9-cm pillow provided better laryngoscopic view.[20] However, in patients with a short neck, a pillow whose height is less than 9 cm provided better laryngeal view. In contrast, Hong et al. compared head elevation with an 8-cm pillow to that with a 4-cm pillow and observed that there was no improvement in laryngeal view.[21] It has been recommended that use of a pillow to align head and neck position has to be individualised based on head and neck anatomy and weight of the patient.[22],[23]


  Influence of Sniffing Position and Simple Extension Top


In 1936, Magill suggested that sniffing position aligns oral, laryngeal and pharyngeal axes to the line of vision during direct laryngoscopy [Figure 5] and is considered as the traditional position for intubation.[1],[24],[25] The three axes theory supporting sniffing position proposed by Bannister and Macbeth in 1944 stated that neck flexion aligned pharyngeal and laryngeal axes, while extension at atlanto–occipital joint aligned these two axes with the oral axis, facilitating line of sight to fall on the glottis.[24] Horton et al. standardised the sniffing position as 35° neck flexion and 15° face-plane extension at the atlanto–occipital joint.[26]
Figure 5: The oral, pharyngeal and laryngeal axes

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When compared to simple extension, the sniffing position was found to be advantageous in obese patients and those with limitation of neck extension but not in patients with normal airway.[2] This was supported by various authors who observed that patients in whom simple head extension was used had increased difficulty in intubation, needed more lifting force,[27] external laryngeal manipulation and use of alternate intubation techniques.[3],[11],[19],[28],[29] As compared to the sniffing position, simple extension resulted in a greater need to use a stylet,[11] higher intubation scores and increased need for the anaesthesiologist to stoop forward during intubation.[30],[31],[32]

Changes in the configuration of normal airways with different head positions were studied by Greenland et al.[4] The airway was considered to have two curves (oropharyngeal and pharyngo–glotto–tracheal) and not as three-axes alignment because it was difficult to achieve. Magnetic resonance imaging (MRI) was obtained in four positions: neutral position, head lift by 35° neck flexion, head extension with no head elevation and sniffing position. Sniffing position had the smallest primary curve making it the optimal position for direct laryngoscopy. Sniffing position, head extension and head lift positions significantly reduced the area between the line of sight and airway curve than the head flat position. Using MRI, Adnet et al. studied the alignment of oral, pharyngeal and laryngeal axes in the neutral, simple extension and the sniffing positions. They concluded that the sniffing position does not align these axes.[10] They found in a randomised study that the sniffing position does not offer advantage over simple extension.[2] The sniffing position was found to be advantageous in patients with obesity and restricted neck extension. This could be the probable reason why there was good glottic visualisation without a pillow or with pillow of different sizes. It is recommended that sniffing position improves glottic view in patients with difficult airway, but simple extension may be enough in patients with a normal airway. Hence, the restricted extension at the atlanto–occipital joint during manual in line stabilisation prevents the alignment of pharyngeal and laryngeal axes, thereby worsening the glottic view.


  Influence of Cricoid Pressure on Glottic View Top


Reviewing the effect of cricoid pressure (CP) on glottic visualisation, Salem et al. reported a worsening of glottic visualisation ranging between 14% and 45% of the patients with use of CP. Neck flexion due to application of CP may be the cause for this worsening of glottic view. Neck support and application of bimanual CP prevents neck flexion due to CP by exerting counter pressure, thereby preventing the worsening of glottic view.[33] Studies also showed that CP of more than 44 N was associated with worsening of glottic view and this was not seen when CP was less than 30 N.[34]


  Influence of Head-Elevated Laryngoscopy Position/Ramped Position Top


Probable theories for improved glottic view by applying HELP are neck flexion >35° which increases atlanto–occipital angulations facilitating greater extension and better glottic visualisation. This can be achieved by the sniffing position in non-obese patients. In obese individuals, the anteroposterior diameter of the chest is increased, which makes cervical flexion of 35° impossible to attain. Hence, ramping helps in better alignment of pharyngeal and laryngeal axes compared to sniffing position.[35],[36] Similar findings were observed by Khandelwal et al. who retrospectively observed less intubation complications in head-elevated position by applying MACOCHA score.[13] Advantage of HELP was exemplified by Pinchalk et al. who studied the number of attempts taken to intubate a simulated trauma patient with cervical immobilisation.[14] The average time taken for intubation in supine was longer when compared to head-elevated position. A cadaveric study done by Levitan et al.[6] had significant improvement in percentage of glottic opening (POGO) score with HELP. In morbidly obese, HELP has also been found to improve POGO significantly when compared to sniffing position.[35] Furthermore, Rao et al. suggested that HELP achieved by configuring the operating table is an equivalent alternative to the use of blankets.[15] This was supported by Lebowitz et al. who showed that ramping improved glottic view in obese and non-obese patients.[37] The ease of intubation was better with further neck flexion as there was lesser use of external laryngeal manoeuvres and lifting force.[38]

In contrast, a multicentric trial done by Semler et al. concluded that ramped position attained by elevating the bed to 25° did not improve arterial oxygenation and worsened the glottic view in critically ill patients.[39] This could probably be due to the fact that intubations were performed outside the operating room under non-standard intubating conditions by non-anaesthesiologists. Besides, this patient population also had compromised cardiorespiratory systems.

It is recommended that HELP should be advocated in obese patients and non-obese patients. It may be preferable to align an imaginary horizontal line between sternal notch and external auditory meatus in all patients for optimal glottic view.


  Influence of Head-Up/Backup Position on Glottic View Top


One probable theory for improved glottic view using 25° backup is that increasing elevation of head decreases directional force required for laryngoscopy. It is an easy way to make line of sight of anaesthesiologist fall onto the glottis. In addition, it increases lung volume during preoxygenation. Lee et al. had done a crossover study to see whether laryngeal exposure during laryngoscopy is better in the 25° backup position than in supine position where the laryngoscopic view was recorded with 0° rigid endoscope with patients lying in flat supine position and in 25° backup position.[17] The collected images were graded using POGO scores by a different anaesthesiologist who had been blinded to the positional change and the allocated study group.[40],[41],[42] Comparing the two positions, POGO scores increased significantly from 42.2% in supine position to 66.8% in 25° backup position.[17] The above findings were reinforced by Reddy et al. who applied HELP in addition to 25° backup positions.[7] They inferred that intubation time was less with senior anaesthesiologist when compared to trainees in supine position while intubation time was significantly shorter with both senior and trainee anaesthesiologists in backup position. The use of ancillary laryngeal manoeuvres was also less with the backup position.


  Effect of Horizontal Alignment of External Auditory Meatus to the Sternal Notch on Alignment of Airway Axes Top


Based on MRI studies, Greenland et al. concluded that the external auditory meatus and sternal notch reflect the positions of the clivus and glottic opening respectively in non-obese volunteers. In the neutral position, the nasopharynx is below the glottis, which leads to poor alignment of the oral, pharyngeal and laryngeal axis. The sniffing position (35° neck flexion and 15° face-plane extension) aligning external auditory meatus to sternal notch raises the clivus and therefore the nasopharynx above the glottis. Hence, the sniffing position aligns the pharyngeal and laryngeal axes to the oral axis. Ramping is required to align external auditory meatus and sternal notch in few patients, especially the obese.[4] To achieve alignment of external auditory meatus and the sternal notch, a small child required a small pillow, an older child and adult required a bigger pillow and obese patients needed the ramped position/25° head-up position.[43]


  Conclusion Top


Our literature review suggests that head-elevated laryngoscopic position and 25° backup position improves glottic visualisation when compared to the sniffing position. Furthermore, 25° backup position also improves the line of sight for the intubating anaesthesiologist. In this position, less force is required to elevate and move the tongue and other tissues out of the line of sight. This avoids laryngeal manipulation and minimises the need to stoop by the intubating anaesthesiologist. Apart from patient positioning, many other factors influence the final degree of glottic exposure. These include type and size of the blade, videolaryngoscope, laryngoscope lifting force, operator experience and the patient's airway anatomy. Although multiple manoeuvres such as jaw thrust, adjusting height of table, removing dentures, easing CP, avoiding neck flexion with neck support and using external laryngeal manipulation may improve the glottic view, adjusting the head position is a crucial step in situ ations of difficult glottic exposure.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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