Apneic Oxygenation and Intubation

Educational Objectives

The goal of this program is to improve apneic oxygenation and intubation. After hearing and assimilating this program, the clinician will be better able to:

1. Perform intubation by first visualizing the epiglottis and not removing O2.

2. Insert the laryngeal mask airway without applying cricoid pressure.

3. Implement appropriate positioning during intubation.

Summary

Intubation: speaker’s method to perform epiglottoscopy, followed by laryngoscopy and tube delivery; epiglottis located midway from mouth to larynx, and centered between right and left; previously, O2 removed while patient intubated; speaker believes nasal cannula key part of airway management; O2 administered through nose and mouth at 15 L/min moves soft palate open and increases O2 saturation; key points — first visualize epiglottis; do not remove O2 during intubation; use nose as orifice for oxygenation and ventilation

Mask ventilation: push down on nasal bridge and up on submandibular tissue; ear-to-sternal notch positioning (head elevated until ear at sternal notch) especially indicated in morbidly obese patients; face plane should be parallel to ceiling; in children, not necessary to keep head elevated; risk for aspiration less than risk for critical desaturation if performed with low volume and low pressure ventilation in patent airway; previously thought that muscle relaxants not indicated in difficult airway, but indicated presently to improve intubation; previous irradiation to neck associated with difficulty in mask ventilation; increasing evidence to support that intubation easier than mask ventilation; of 53,000 anesthetic cases, mask ventilation found impossible in 77 cases, and 19 had difficult intubation; historically performed stepwise (thought safer), but increasing evidence that neuromuscular blockade improves ability to perform intubation and mask ventilation; Calder and Yentis reported mask ventilation easier when drugs administered; Waters found bag-mask ventilation easier after administration of rocuronium; laryngeal mask airway (LMA) — essential to safety in emergency airway; cannot use in patient with gag reflex and with cricoid pressure (CP); effective 95% of time when mask ventilation ineffective; muscle relaxants improve face mask ventilation and LMA; avoid overventilation; O2 absorption and ventilation different processes; study with pigs showed that with 12 breaths, 6 of 7 cases resuscitated, but with 20 to 30 breaths, only 1 of 7 cases resuscitated; results explained by decreased venous return when breaths stacked and heart compressed; American Heart Association recommends administrating O2, creating patent airway, and pumping chest (passive apneic oxygenation); speaker believes ventilation and oxygenation with nasal masks will become practice of future (avoiding ventilation through mouth); exercise caution in patients with asthma and chronic obstructive pulmonary disease due to possible drop in blood pressure (BP)

Cricoid pressure: Sellick thought that extreme occipital extension of head needed; however, positioning head lower than chest difficult for obese patients; previously, vomiting reported due to large ventilation volumes used; presently, ventilation at 6 to 7 mL/kg or no ventilation recommended; through magnetic resonance imaging, Smith showed that esophagus moves to side in 9 of 10 cases with CP, and airway compression seen in 4 of 5 cases; as CP applied, 86% of men and 100% of women have impossible ventilation; CP possible reason for high failure rates in emergency airways and obstetric anesthesia; CP detrimental for placement of LMA and no longer recommended

Oxygenation: speaker previously believed that oxygenation related to diaphragmatic flap, but actually no association present; on room air, 912 mL of O2 bound to hemoglobin (Hb); if desaturated to 90%, 838 mL bound to Hb; lung volume of 400 mL on room air decreases to 250 mL; with preoxygenation, lung volume increased by factor of 6; O2 reservoir depleted if patient stops breathing as a result of drugs; O2 pulled in during apnea, and rest of gas in airway pulled down; passive apneic oxygenation requires open alveoli; obese patient must be tilted downward; 180 sec of safe apnea gained with induction in reclining position; if induced in flat position, 60 sec of safe apnea lost, because 50% of lung volume collapses (due to absence of open alveoli, unable to perform passive oxygenation); positioning important and patent alveoli needed; 100 sec of safe apnea present if induction performed in head-elevated position, compared to induction in supine position; time to desaturation — one of key features of patient safety in emergency airway; maximized by upright position before intubation; patient reclined only as much as needed for intubation (sternal notch line)

Pulse oximetry: O2 saturation between 92% and 96% does not mean minutes of safe apnea present (possibly only seconds); on room air, in young patient with cranial bleeding and normal lungs, O2 saturation 100%; if preoxygenated, period of safe apnea increased, particularly if young patient bradycardic due to increased pressure; not applicable to tachycardic young patient with overdose of diphenhydramine (eg, Allermax, Benadryl, Dytuss) and O2 saturation of 95%

Gas solubility and absorption during apnea: CO2 dissolves in tissue and blood, highly soluble, and leaks out slowly; when patient stops breathing, CO2 leaks from blood into alveoli at rate of 10 mL/min; in presence of O2, gas absorption 250 mL/min; when apnea occurs, subatmospheric pressure present at level of alveolus; blood moving past alveoli absorbs O2 passively due to subatmospheric alveolar pressure; as patient stops breathing, possible to maintain arterial saturation if airway patent with O2 flowing by tracheal tube; partial pressure of arterial CO2 rises 3 to 5 mm Hg/min to point where pH 6.72; brain able to tolerate hypercarbia, but not hypoxemia; arterial desaturation prevented by continuous oxygenation as long as alveoli open, patient in upright position, and upper airway patent; with laryngoscopy or video laryngoscopy, flushing upper airway with O2 creates patency down to level of larynx, preventing desaturation; passive oxygenation poor in some patients (eg, obese individuals in supine position; those with fluid in lungs or multilobar pneumonia); in intensive care unit, insert tracheal tube, turn off ventilator, and allow CO2 to rise 20 points (if no breath triggered, then brain death indicated); as fraction of inspired O2 (FIO2) increased in apneic individual, prolonged safe apnea time increases exponentially

Nose: FIO2 in hypopharynx higher if 10 L of O2 run through nose than with use of face mask (also true if running 15 L or 20 L of O2 through nose); using face mask allows rebreathing of CO2, leading to lower FIO2; previously, optimum airway management only provided FIO2 at 56% in hypopharynx; in conscious sedation, small amounts of nasal O2 can mask hypoventilation; speaker inserts nasal cannula on all patients, but not all oxygenated; unless end-tidal volume monitored, minor increases in FIO2 can mask hypercarbia (able to overcome if O2 flow increased enough); with nasal mask creating positive pressure in upper nasopharynx, space behind back of soft palate opened; pushing air and O2 through mouth compresses tongue (should be performed with patient in upright position); passive breathing difficult through mouth; when desaturation occurs, speaker administers O2, pulls patient’s mandible forward, sits patient upright, and increases O2 for rapid correction; if no correction seen, use bag-valve mask (BVM) with patient as upright as possible; laying patient flat distends abdomen and decreases alveolar collapse; head-forward position results in more thyromental space for displacement of tissue and better mouth opening; every Ambu bag or bag-mask unit should have positive end-expiratory pressure (PEEP) valve; every intubated patient has nasal cannula and if awake, O2 administered at 4 to 6 L/min; if unconscious and pulse oximetry results poor, O2 administered at 15 L/min; nonrebreather mask (NRM) applied, then drugs administered; wait for 60 sec and preoxygenate for 4 min if possible, filling hypopharynx with O2; through gas diffusion and apneic oxygenation, O2 pulled down trachea to prevent desaturation

Summary of methods: nasal and face mask for oxygenation; direct laryngoscopy plus alternative device for intubation; mask plus LMA or single-use supraglottic airway (King LT) for ventilation

Readings

Edwin SB, Walker PL: Controversies surrounding the use of etomidate for rapid sequence intubation in patients with suspected sepsis. Ann Pharmacother, 2010 Jul-Aug;44(7-8):1307-13; Gupta D, Rusin K: Videolaryngoscopic endotracheal intubation (GlideScope) of morbidly obese patients in semi-erect position: a comparison with rapid sequence induction in supine position. Middle East J Anesthesiol, 2012 Oct;21(6):843-50; Hiestand B et al: Rocuronium versus succinylcholine in air medical rapid-sequence intubation. Prehosp Emerg Care, 2011 Oct-Dec;15(4):457-63; Jaber S et al: An intervention to decrease complications related to endotracheal intubation in the intensive care unit: a prospective, multiple-center study. Intensive Care Med, 2010 Feb;36(2):248-55; Khan MF et al: Airway management and hemodynamic response to laryngoscopy and intubation in supine and left lateral positions. Middle East J Anesthesiol, 2010 Oct;20(6):795-802; Marsch SC et al: Succinylcholine versus rocuronium for rapid sequence intubation in intensive care: a prospective, randomized controlled trial. Crit Care, 2011 Aug 16;15(4):R199; Mitterlechner T et al: Head position angles to open the upper airway differ less with the head positioned on a support. Am J Emerg Med, 2013 Jan;31(1):80-5; Onyekwulu FA, Nwosu A: Emergency airway management with laryngeal mask airway. Niger J Clin Pract, 2011 Jan-Mar;14(1):95-7; Ramachandran SK et al: Apneic oxygenation during prolonged laryngoscopy in obese patients: a randomized, controlled trial of nasal oxygen administration. J Clin Anesth, 2010 May;22(3):164-8; Sinha A et al: ProSeal™ LMA increases safe apnea period in morbidly obese patients undergoing surgery under general anesthesia. Obes Surg, 2013 Apr;23(4):580-4; Warner KJ et al: Single-dose etomidate for rapid sequence intubation may impact outcome after severe injury. J Trauma, 2009 Jul;67(1):45-50.