Airway Pearls for Intubating the Obese Patient.

AIRWAY PEARLS

• Consider every case a difficult Intubation due to effects on anatomy and physiology
• Normal airway techniques may not be effective.
• Positioning of the patient is critical- aim for head up.
• Pre-oxygenation techniques are crucial
• Appropriate medication dosing is important
• Video laryngoscopy may provide an edge
• Mechanical Ventilation needs to be tailored

Anatomy and Physiology in the obese patient can make every case difficult

• A BMI greater than 30 kg/m2 is considered obese. BMI’s greater than 40 kg/m2 considered severely CLASS III obese.
• For example a 168cm person weighing 85kg is considered obese. We need to keep some perspective on these. It’s not just the absolute weight. I know a lot of rugby players that fall into that range.
• Obese patients have a decreased overall, lung capacity and an increase in metabolic activity. This results on increased oxygen consumption and an increased work of breathing.
• The adipose tissue produces increased metabolic activity as well as increasing airway resistance and potentially causes increased risk of pharyngeal wall collapse with paralysis.
• The ability to adequately pre-oxygenate give safe apnoea times is affected as the functional residual capacity is also decreased. Safe apnoea times are decreased to one to two minutes.
• The displacement of the diaphragm makes ventilation in the supine position more difficult and can lead to desaturation more readily, in this position.
• Obese patients are more difficult to ventilate and they desaturate far more rapidly.

Normal Airway techniques may not be effective.

• The airway in the obese patient must always be assumed to be a difficult airway. The risk of rapid desaturation is high and the increase in airway resistance makes BVM ventilation more difficult (1,2); a 2 hand technique (2 operator) being required.
• Use a PEEP valve at 10cm H20.
• The use of airway adjuncts, such as nasopharyngeal and oropharyngeal (unless contraindicated) may help with ventilation (3)
• Laryngoscopy can prove difficult due extra adipose tissue resulting in an alteration of the anatomy.
• A predictor of difficult intubation is a large neck circumference and a high Mallampati Score (4).
• Laryngeal masks can be used in the obese patient (5)
• Performing a surgical airway on these patients is extremely difficult due to the inability to identify important anatomical landmarks (6). Bedside ultrasound may assist in identifying the anatomy (7,8)

Patient positioning is critical

• Patients should be placed in the upright position, to allow the diaphragm to fall and allow greater ventilation of the lungs.
• If it’s not possible to sit the patient upright eg., in trauma, with cervical precautions, a reverse Trendelenburg position is recommended.
• In preparation for intubation, the ramped, head-up position where the auditory canal is aligned with the sternal notch, provides a better position for visualisation of the glottis. (9,10), with improvements of over 50% when head elevation is used, as compared to supine positioning (11).

Pre-oxygenation is crucial

• Given that obese patients desaturate very rapidly, adequate pre-oxygenation is imperative, if time allows.
• Non-Invasive ventilation such as CPAP can improve oxygenation (12,13). A minimum of 5-10 minutes may be needed.
• Apnoeic Oxygenation via high flow nasal prongs should also be used during the procedure.

Appropriate medication dosing

The pharmacokinetics of some medications is altered by obesity. Obese patients have a higher glomerular filtration rate, causing renally excreted drugs to have shorter half-lives.

We need to which medications should be given according to ideal body...