Difficult Airway Management in the obese patient

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Obesity airway management remains a challenging problem in operating thea­tres for bariatric surgeries .The results indicate that difficult tracheal intubation is more fre­quent in obese than in lean patients (14.3% vs. 3%.). Difficult intubation was defined as three or more laryngoscopic attempts to place the tracheal tube into the trachea, as lasting >10 min using conventional laryngoscopy, or both. If it is failed, can lead to severe life-threaten­ing complications: decrease in SpO2 level to < 80% during attempts, oedematous airway obstruction, difficulty in face mask ventilation, severe cardiovascular collapse, ventricular ar­rhythmia, aspiration, cardiac arrest, and death.

Causes of difficult intubation included: Inadequate preoperative assessment, inad­equate equipment, experience not enough, poor technique, malfunction of equipment and inexperience assistance.

Fig 3. Preoxygenation is more effective in the 25 degrees head-up position than in the supineposition in severely obese patients

Preoperative airway assessments play a key role in attempt to identify those patients with a potentially difficult airway. No study has ever demonstrated a direct correlation between in­creasing weight and increased difficulty with direct laryngoscopy. Indeed, a Danish cohort study of 91,332 patients showed that high BMI, alone, is a weak predictor for difficult and failed tracheal intubation. However, as­sociation with: a Mallampati score of III or IV (Fig1A), small mouth opening < 3.5 cm, short thyromental distance (less than 6 cm or 3 fin­gerbreadths) (Fig 1B), limited neck movement < 80° and wide neck circumference > 40 cm can highly predict difficulty with direct laryn­goscopy and tracheal intubation in morbidly obese patients.

FIGURE 2.
Cormack grading of laryngeal views during laryngoscopy.
Grade I. Most of the glottis is visible.
B. Grade II. The posterior aspect of the glottis is visible.
C. Grade 3. Only the epiglottis is seen; no part of the laryngeal inlet is visible.
D. Grade IV. The epiglottis is not visible. Patients with grades I and II are usually easy to intubate with direct laryngoscopy,
whereas those with grades III and IV are often difficult; the ability to see the arytenoid cartilage is the important difference

In OR and when morbidly obese patient ly­ing flat will experience significant alterations in the mechanical properties of their pulmo­nary system. Therefore, the supine position produces a splinting effect of the abdominal contents on the diaphragm with progressive reductions in functional residual capacity (FRC), expiratory reserve volume (ERV), and total lung capacity (TLC). This loss of lung vol­ume limits oxygen reserves and results in a very short “safe apnea period” (SAP). SAP is the length of time following paralysis and apnea until oxygen saturation (SpO2) drops to 90% or 92%. Even following adequate pre-oxygen­ation with 100% oxygen, SAP will be only 2-3 minutes in morbidly obese patients compared to 5-8 minutes in normal individuals. Thus, any delay in establishing an airway in an obese patient will result in hypoxemia much soon­er than in other patients. For obese patients the greatest increase in SAP can be achieved when the OR table is tilted into the reverse Trendelenburg (RT) position. RT, by reduc­ing mass loading on the chest, also facilitates bag-mask assisted ventilation. A randomized cohort study showed that preoxygenation in the 25 degrees head-up position achieves 23% higher oxygen tensions, allowing a clinically significant increase in the safe apnea period, greater time for intubation and airway control (Fig 3).

FIGURE 1
A. The Mallampati classification predicts intubation difficulty
based on the visibility of intraoral structures. Classes III and IV
predict difficult intubation.
B. A short thyromental distance (less than 6 cm or 3 fingerbreadths)
when the head is extended predicts difficult intubation.

When potential difficulty with tracheal in­tubation is expected, or if direct laryngoscopy is attempted and is unsuccessful, alternative airway techniques should be considered. Fi­breoptic bronchoscopy has been the “gold standard” for years for tracheal intubation in “difficult” airway patients. However, FOB is in­creasingly being replaced by video-laryngos­copy, (e.g. Glidescope), when direct laryngos­copy is not appropriate or is unsuccessful. For example, in a study involved 2,004 patients, success for Glidescope intubation after failed direct laryngoscopy was 94%. This implies the necessity of availability of such devices.

In conclusion, the airway management in obesity involves special considerations. The patient should be placed, prior to pre-oxygen­ation, in the Head Elevated Laryngoscopy Po­sition (H.E.L.P) or ‘Rapid Airway Management Positioner “ (Ramped) with the OR table tilted in the reverse Trendelenburg position (Fig 4 ) . These manoeuvre facilitate bag-mask ventila­tion, optimize view during direct laryngoscopy by airway axes alignments, and significantly increase the SAP. If direct laryngoscopy is un­successful a Supraglotic airway devices (e.g. Laryngeal mask (LMA) ) can be used as a tem­porary bridging device to oxygenate the pa­tient. A video-laryngoscope or FOB will usually be successful in establishing an airway when a difficult direct laryngoscopy is anticipated or when direct laryngoscopy is attempted and fails. Finaly, alternative invasive methods should be available such Jet ventilation device and emergency cricothyrotomy catheter set.

Fig 4. Head positioning for tracheal intubation. A. Neutral position. B. Head elevated. C. “Sniffing” position with a flexed
neck and extended head. Note that flexing the neck while extending the headlines up the various axes and allows direct
laryngoscopy. D. Morbidly obese patients are best intubated in a “Ramped” position with elevation of the upper part of
the back, neck, and head; the ideal position aligns the external auditory canal and the sternum.

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