The obese patient. Anaesthetic issues: airway and positioning.
Abstract: The authors have combined experience of over forty years working within the NHS and private hospitals as registered operating department practitioners.

It is widely accepted that obesity is a growing problem in the populations of all developed and, increasingly, developing countries. It is also agreed that this sector of the population present specific challenges when required to undergo general anaesthesia. What is not so evident is a universal approach to assessing, predicting and overcoming these challenges. Furthermore, where there is the presentation of a clearly high risk patient, there can be limitations in optimizing the environment for reasons such as saving time, a lack of resources or sheer apathy. This article reviews the challenges, assessment and solutions available to the clinician faced with a high BMI patient with particular reference to the technique of ramping.

KEYWORDS Obesity / Anaesthesia / Ramping
Article Type: Report
Subject: Obesity (Care and treatment)
Anesthesia (Methods)
Anesthesia (Management)
Patients (Positioning)
Patients (Methods)
Patients (Management)
Authors: Bale, Emma
Berrecloth, Richard
Pub Date: 08/01/2010
Publication: Name: Journal of Perioperative Practice Publisher: Association for Perioperative Practice Audience: Academic Format: Magazine/Journal Subject: Health; Health care industry Copyright: COPYRIGHT 2010 Association for Perioperative Practice ISSN: 1750-4589
Issue: Date: August, 2010 Source Volume: 20 Source Issue: 8
Topic: Event Code: 200 Management dynamics Computer Subject: Company business management
Geographic: Geographic Scope: United Kingdom Geographic Code: 4EUUK United Kingdom
Accession Number: 235631936
Full Text: The standard classification of bodyweight according to the body mass index (BMI) is described in the table below:

Current statistics from the Department of Health show almost a quarter (24.5%) of adults in England are obese. If no action is taken this equates to 60% of men, 50% of women and 25% of children being obese by 2050 (DH 2009).

'As a result of the obesity epidemic, anesthetists are more commonly confronted with the challenge of anesthetizing severely obese patients. The technical challenges and risks in obese individuals are appreciably higher than those of healthy weight individuals.' (Dixon et al p1111)

Anatomy and physiology: implications and associated risks

Morphologically patients fall into two broad categories: android and gynaecoid. In the android the fat is carried mainly in the trunk: they have a fat face and cheeks, large breasts, a short, large neck with an associated restricted cervical spine and atlanto-occipital flexion and extension. Abdominal fat tends to be intraperitoneal. The respiratory tract might include a large tongue, excessive palatal and pharyngeal soft tissue and high anterior larynx. These factors alone could indicate difficult mask ventilation and tracheal intubation, with the incidence of difficult intubation at 13% (Adams & Murphy 2000). With the gynaecoid patient, the fat is mainly in the arms, legs and buttocks with the abdominal fat mainly extraperitoneal (Bellamy & Struys 2007). The problem for clinicians is that many patients will lie somewhere in the spectrum between these two groups and require individual assessment.

Although attitudes are changing it is still occasionally heard that obese patients are thought to be 'fine because they have more padding,' when in fact the opposite is true. The sheer force of the weight on their trunk and limbs during surgery compresses the intervening tissues against the table or attachments and can compromise perfusion. External pressures of 23-32mm/Hg can interfere with normal tissue perfusion and, in patients with peripheral vascular disease, tissue damage can occur at even lower pressures (Beckett 2010 p27). The results are two-fold: Poor arterial capillary perfusion can result in ischaemia and poor venous return can result in oedema thus raising pressures within the tissues further. Furthermore, as the byproducts of continued local cell metabolism are not removed due to ineffective circulation, osmosis causes even further oedema and local tissue pressure. The result of this is pressure sores, with accompanying breakdown in tissue leading, untreated, to necrosis (Beckett 2010). Patient perception is that pressures sores are preventable and directly attributable to poor nursing care which raises the spectre of litigation (Dimond 2003).

As well as pressure sores, neural injuries are more common in high and very high BMI patients especially if they are diabetic (Adams & Murphy 2000). Ogunnaike et al (2002 p1797) describe the risks comprehensively: 'Brachial plexus and sciatic nerve palsies have been reported. Stretch injuries may be caused by extreme abduction of the arms, thereby stretching the lower roots of the brachial plexus. The upper roots are most likely stretched by excessive rotation of the head to the opposite side. Sciatic nerve palsy may be caused by prolonged ischemic pressure from tilting the table sideways. Lateral femoral cutaneous nerve injury may occur if the lower limb falls and hangs freely. Ulnar neuropathy has been associated with increased BMI. A retrospective study by Warner et al (1994) documented such an association because 29% of patients with ulnar neuropathy in their series had a BMI equal to or greater than 38 compared with 1% of control patients.'

Physiologically many factors contribute to put high BMI patients' pulmonary and cardiovascular systems under strain. Obese patents have an increased oxygen consumption and carbon dioxide production due to their increased metabolic activity. They have reduced functional residual capacity (FRC) associated with reduced lung compliance as a result of an increase in pulmonary blood volume. FRC is also affected by the reduction in chest wall compliance due to the fat within the wall. Combining these restrictions with the fat within the abdomen, FRC is further reduced and airway resistance increased by mechanical compression of the diaphragm and lungs (Adams & Murphy 2000).

Positioning an obese patient in the supine position for induction exacerbates these complications as described by Brodsky (2010 p86): 'The supine position causes a marked increase in intra-abdominal pressure, which results in a splinting effect of abdominal contents on the diaphragm. Supine obese patients have relative hypoxemia and significant alterations in the mechanical properties of their respiratory system with marked reductions in lung volume.'... 'The supine morbidly obese (MO) patient experiences a proportionally greater decrease in FRC, total respiratory system and pulmonary compliance, and a larger ventilation/perfusion (V/Q) mismatch than a normal weight patient and all changes increase with increasing BMI.'

FRC is shown to fall by 50% in the supine obese patient on induction in comparison to 20% in the normal population. This has been shown to decrease the effectiveness of preoxygenation and tolerance to any period of apnoea (Adams & Murphy 2000). Combining the effect of reduced pulmonary compliance with upper airway obstruction, the anaesthetic clinician will almost certainly experience more difficulty with face mask ventilation (Altermatt et al 2005).

Brodsky (2002 p753) describes more darkly the consequence of physiological compromise in the supine obese patient: 'Some morbidly obese patients cannot tolerate the supine position. In a study of cardiovascular changes in obese patients scheduled for gastric stapling surgery, changing from the sitting to supine position caused significant increases in oxygen consumption, cardiac output and pulmonary artery pressure. By lying down, a decrease in already poor chest wall compliance, further V/Q mismatch, and a sudden shift of blood to an already hyperactive, borderline hypoxic heart occurred. For some obese patients with inadequate cardiac reserve, these changes can lead to fatal cardio-respiratory decompensation, termed Obesity Supine Death Syndrome.'


Within the population of high BMI patients the key question of who is likely to present critical problems during induction and intubation is much debated. The criteria used to indicate potential problems vary from paper to paper. For example some will cite obstructive sleep apnoea (OSA) amongst other co-morbidities usually associated with difficult intubation as an indicator of airway difficulties (Adams & Murphy 2000), where others claim it has no significance (Juvin et al 2003).

Others simply cite a high BMI per se (with or without pregnancy) as being an indicator of difficult intubation (Dixon et al 2005, Cattano et al 2009, Walls 2002), while others dispute this (Brodsky et al 2002).

It is fair to say that the debate between the correlation of obesity and difficult intubation arises for two reasons. Firstly there seems to be the lack of an objective definition of difficult intubation. Adnet in Juvin validated an objective scoring system, the Difficult Intubation Score (DIS). This is comprised of giving a point per variable that deviates from the optimum: i.e. number of attempts, number of additional clinicians, number of alternative techniques, glottis exposure Cormack & Lehane definition, lifting force applied during laryngoscopy, need for cricoid pressure, and position of vocal cords at intubation. A score of 0 would represent intubation achieved at first attempt by one clinician using one technique with minimal force and full view. A score over 5 could be classed as difficult intubation (Juvin et al 2003). This was used by Juvin et al in their study to ascertain factors to predict difficult intubation in obese patients but could only conclude that Mallampati of III or IV was a risk factor. They added however that it had questionable value in clinical practice due to its lower sensitivity, specificity and negative predictive value with obese patients. They felt that jaw mobility limited by fat was more pertinent. Moreover BMI was not a predictor; the higher the BMI does not mean the greater the difficulty of intubation (Juvin et al 2003).

The usual five variables to predict intubation difficulty are: Modified Mallampati, range of head and neck motion, width of mouth opening, presence of overbite, presence of mandibular recession. Abnormalities e.g. tumours, and co-morbidities e.g. OSA were not found to be reliable indicators of difficult intubation (Juvin et al 2003).

The second reason that a dispute arises is because some studies that showed a positive correlation between obesity and difficult intubation, and those that showed no correlation, were of questionable methodology. For example they did not use a control group, used a small number of patients or failed to distinguish between difficult intubation and difficult laryngoscopy (Juvin et al 2003).

Based on the findings of the literature it seems that the most reliable indicator of potential difficult intubation is neck circumference (Juvin et al 2003, Brodsky et al 2002, Gonzalez et al 2008). Brodsky et al (2002) found in a population of 100 patients that 12 presented difficulty with intubation. Only high Mallampati scores and neck circumference were shown to be reliable predictors of problematic intubation. He cites the chance of encountering problems with intubation is about 5% with a neck circumference of 40cm and 35% with a neck circumference of 60cm. All the patients were ramped.

Gonzalez et al also confirmed that intubation was more difficult in the obese patient but that neck circumference and Mallampati of >3 were the most reliable predicting factors (Gonzalez et al 2008)


Where no difference in intubating obese patients has been found, this seems to have been due to the use of 'ramping' the patient so that the head and shoulders are considerably raised. The results of Rao et al (2008 p1917) were so positive that they state, 'on the basis of our results we propose that positioning patients in the head-elevated position by elevating the back or trunk section of the table can be considered by clinicians as part of their pre-formulated strategy in their daily clinical practice in managing the airways of obese patients.'

Cattano et al (2009) reinforce that great care should be taken to ensure that the head and neck is ramped up to establish a patent airway.

One method of evaluating laryngeal view is via the Percentage Of Glottal Opening Score. Lee et al (2007) found that it improved significantly in the 25 degree back-up position compared with supine. Their study of 40 patients showed that, if difficult intubation is associated with poor visibility of the larynx, then the 25% improvement in the view in the 25 degree head up position may be significant in how clinicians approach potentially difficult intubations.

Collins et al (2004) studied 60 morbidly obese patients to compare laryngoscopy and facemask ventilation in the neutral position and then ramped. They found that ventilation and laryngoscopy was significantly improved when the patients were in the ramped position.

The study by Dixon et al (2005) also showed preoxygenation to be more effective in the 25 degree head up position.

Brodsky et al (2002) refer frequently to the importance of ramping the patient so that an imaginary horizontal line connects the patient's sternal notch with the external auditory meatus (Figures 1 and 2). In their study to ascertain the factors which might adversely affect the laryngoscopy and intubation of obese patients they experienced an intubation success rate of 99% compared with a similar rate of 97% demonstrated in the Keller et al (2002) study. However in the Keller et al study 15% required a bougie and only 33% had a grade 1 Cormack view. In the Brodsky et al study no one was reported to need a bougie and 75% had a grade 1 view. It was implied that this discrepancy was due to the patients in the Keller et al study being raised up by only 8 cm (Brodsky et al 2003). They emphasize that the head and trunk must be elevated.



In the normal population head-up positions can have a potentially negative haemodynamic effect if venous return to the heart is reduced, with any beneficial effects on oxygenation being offset if cardiac output is decreased. However, Perilli et al (2000) found that no adverse cardiovascular changes occurred in a study of morbidly obese patients placed in the reverse Trendelenburg's position. Furthermore in a study of normal BMI patients induced at a 20[degrees] angle, none needed intervention for hypotension (Lane et al 2005).

The head elevated position also has implications from an ergonomic point of view. It has been reported as being more comfortable for the clinician: 'he did not need to lower his head or bend his back or his knees to see the larynx because the visual field was improved and the optimal position of the clinician's eye was moved upward' (Lee et al 2007 p585).

How the ramping technique is achieved

There are various methods used by clinicians to achieve the ramping effect of positioning a high BMI patient. One method is to use a stack of linen and pillows as shown in figure 3 but while this does effectively align the sternal notch with the external auditory meatus, it is inadequate in other ways. The overall effect is inelegant and clearly has no scientific means of ensuring the required degree of elevation. Secondly, it is notoriously difficult in operating departments to get hold of surplus linen and pillows. They would then all have to be put into the laundry for washing at the end of the procedure which is a waste of resources. Thirdly, and probably reflective of the former point, there is no support for the arms thereby risking neural damage to the brachial plexus through stretching. Fourthly, if for any reason the patient had to be laid supine post-intubation it would be very cumbersome to remove the stack and would undoubtedly put strain on attending members of staff and the patient (Nissen et al 2007). Finally, there is bound to be some rucking up of the linen as the patient was positioned, which predisposes her to pressure sores.


The other problem with the stacking method as more clearly demonstrated in figure 4 is that the patient frequently ends up with too much neck flexion which can inhibit face mask ventilation as well as making laryngoscopy more difficult. Moreover, restricted access to the neck makes cricoid pressure more difficult to achieve.

The other point to mention about the positioning of patients like that in figure 4 is that laryngoscopy is only likely to be more comfortable from the clinician's point of view if they are sufficiently tall. If the clinician is of medium or short stature then they will require a standing stool and will have to lean over which is going to apply stress to their back. This is an increasingly relevant point as many anaesthetists are female and from regions where people are of shorter stature for example Asia.


The patient position illustrated in figure 4 is achieved on electrically controlled equipment. Bellamy and Struys (2007) reported that automated equipment has failed due to sheer weight of the patient.

Other clinicians have proposed using a stack of three litre irrigation bags but similar problems arise as with the linen. They are also heavy to manoeuvre as well as there being clear issues regarding the stability of the patient. Irrigation bags would not have product liability indemnity if they are used as patient support devices.

There are also inflatable devices used to achieve the ramp effect however the brachial plexus is still not supported and it is not clear whether these devices are powerful enough to withstand the pressure of hyper obesity.

So far, the most effective method of achieving the head elevated laryngoscopy position is by using a pre-manufactured device as described by Rich (2004 p265), '(it) eases the work of breathing for those patients who cannot lay flat secondary to obesity-induced orthopnea. Therefore, the patient is better able to tolerate the pre-induction period or longer period of time when required... The elevation pillow can be prepositioned inserted and removed much faster and with less difficulty than that required to build and dismantle a ramp made of hospital linen.'

There are a number of such pillows on the market. One available in the UK is a component of the Oxford HELP (Head Elevating Laryngoscopy Pillow) positioning system for difficult airway and high BMI (30-80+) anaesthesia. As per the ramping technique the base pillow and headrest (Figure 5) realign the patient's anatomy so that they function, physiologically, like a patient with a normal BMI while maintaining them in a conventional induction position. Pre-induction anxiety (and thereby oxygen consumption) in the patient is reduced as they breathe more easily, normal facemask ventilation is facilitated by the reduced airway pressures, pre-oxygenation is effective thus improving their tolerance to periods of apnoea, the laryngeal view is improved thereby facilitating intubation and good tidal volumes and ventilation pressures can be achieved throughout anaesthesia (Figure 6).




Without the integral Velcro found on other elevation pillows, the headrest can be easily moved to accommodate the head falling back into a 'sniffing the morning air' position where laryngoscopy and cricoid manipulation are easily simultaneously achieved (Figure 7).

This system comprises two colour-coded angulated pillows. Figure 5 depicts the yellow base pillow with an angle of approximately 15[degrees]. This is appropriate for patients of BMI up to 50. It reduces a potentially high risk patient to a low risk patient which benefits all clinicians but in particular inexperienced staff anaesthetising high BMI patients out of hours or in remote clinical areas (Cooper & McClure 2004).

An upper red pillow (Figure 8) can be added to reproduce a 25[degrees] angle which is generally recommended for patients in the super to hyper obese range and has been proven to be effective with a patient of BMI 81.2. The patient shown in figure 6 has a BMI of 49.2 and is therefore on the cusp of needing greater elevation to achieve the anatomical marker described above. Although depicted on both pillows in figure 10, her fat distribution indicates that the lower pillow only is adequate for optimum positioning.



The system comes with a colour-coded BMI chart (Figure 9) specifically designed for high BMI patients. It provides a guide to help clinicians choose the right components for their specific patient although as discussed above, fat distribution can vary enormously between patients of similar BMIs so clinicians must use their professional judgement.


The associated problems of pressure sores and neuropathy have been discussed at length but Brodsky's (2008 p306) caveat sums up the issues: 'Patient position during surgery is extremely important. Pressure points must be carefully padded to reduce the risk of pressure sores, neurologic injury, and rhabdomyolysis (RML); figure 10 shows the ancillary support devices of the system designed to reduce the risks. The patient has support posterior to her scapula and the arm supports take the weight of her arms; both these reduce the risk of stretch to the brachial plexus. There is also support posterior to her knee to prevent strain associated with hyperextension.'

Figures 11 and 12 show the stability of a head elevation pillow once it is in situ, however all clinicians must be aware that high BMI patients are inherently unstable and extreme caution must be used when moving or tilting them.



In terms of the solutions available for dealing with the challenges of high BMI patients undergoing surgery and anaesthesia, there is a comprehensive and safe methodology available to the clinician which seems to obviate the inherent risks associated with this patient category and as such there should be no reason for anaesthetic staff to attempt a conventional induction on a patient who is improperly positioned. The studies on ramping patients are compelling if not indisputable, and the existence of such devices as the Oxford HELP afford an immeasurable degree of patient comfort and safety.


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Atermatt FR, Munoz HR, Delfino AE, Cortinez LI 2005 Pre-oxygenation in the obese patient: effects of position on tolerance to apnoea British Journal of Anaesthesia 95 (5) 706-709

Beckett AE 2010 Are we doing enough to prevent patient injury caused by positioning for surgery? Journal of Perioperative Practice 20 26-29

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Juvin P, Lavaut E, Dupont H et al 2003 Difficult tracheal intubation is more common in obese than in lean patients Anesthesia & Analgesia 97 595-600

Keller D, Briacombe J, Kleinsasser A, Brimacombe L 2002 The laryngeal mask airway as a temporary ventilator device in grossly and morbidly obese patients before laryngoscopy-guided tracheal intubation Anesthesia & Analgesia 94 737-40

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Lee BJ, Kang JM, Kim DO 2007 Laryngeal exposure during laryngoscopy is better in the 25 degree back-up position than in the supine position British Journal of Anaesthesia 99 (4) 581-586

Nissen MD, Gayes JM 2007 An inflatable, multichambered upper body support for the placement of the obese patient in the head-elevated laryngoscopy position Anesthesia & Analgesia 104 1305-1306

Ogunnaike BO, Jones SB, Jones DB et al 2002 Anesthetic considerations for bariatric surgery Anesthesia & Analgesia 95 1793-1805

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Rich JM 2004 Use of an elevation pillow to produce the head-elevated laryngoscopy position for airway management in morbidly obese and large-framed patients Anesthesia & Analgesia 98 (1) 264-265

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Warner MA, Warner ME, Martin JT 1994 Ulnar neuropathy: incidence, outcome and risk factors in sedated or anesthetized patients Anesthesiology 81 1332-40

Wong AB, Moore MSR 2007 Positioning of obese patients in out-of-operating room locations Anesthesia & Analgesia 104 1306-10

Provenance and Peer review: Unsolicited submission; Peer reviewed; Accepted for publication May 2010.

Correspondence address: Emma Bale, Alma Medical Products, 24a Monument Park, Chalgrove, OX44 7RW. Email:

Emma Bale

RODP, BA(Hons)

Marketing Director, Alma Medical Products, Chalgrove

Richard Berrecloth


Managing Director, Alma Medical Products, Chalgrove

Declaration of interests:

The Oxford HELP featured in this article is a product of Alma Medical.

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BMI           Class
<20           Underweight
20-24.9       Normal
25-29.9       Overweight
30-39.9       Obese
40-49.9       Morbidly obese
35-49.9 + co-mMorbidly obese
50-59.9       Super obese
60-69.9       Super super obese
>70           Hyper obese

(Adapted from Bellamy & Struys 2007)
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