Lewis S. Coleman, MD
Drs. Muller and Healy have provided an excellent review that illustrates the inherent shortcomings of prevailing induction practice, but they overlooked the utility of mask induction (Anesthesiology NewsAirway Management 2015;s17-s23).
Elective mask induction and intubation without paralysis optimize anesthetic safety by incorporating preoxygenation and denitrogenation, eliminating unexpected airway collapse and obstruction due to airway muscle paralysis, avoiding lethal bolus hypnotic agent toxicity, eliminating unnecessary residual relaxation,1 and enabling safe retreat from unexpected airway difficulties by ventilating with pure oxygen.
Today, many practitioners presume that IV hypnosis and paralysis are essential to ensure patient comfort and prevent dental or vocal cord damage during elective intubation. These assumptions are unfounded.2 Sevoflurane (Ultane, AbbVie) with modern monitoring and synthetic opioids have revolutionized mask induction, and it deserves a fresh look.3
The dangers and difficulties of elective intubation with paralysis have inspired many practitioners to employ “open airway” techniques with IV propofol infusions, but such techniques sacrifice respiratory assistance and invite occult hypoventilation, carbon dioxide (CO2) asphyxiation, fire, aspiration, and unanticipated airway obstruction that necessitates emergency intubation under difficult and dangerous circumstances.
Like methane and nitrogen, CO2 is an asphyxiant gas that disrupts oxygen uptake in pulmonary alveoli. Pulmonary physiology efficiently expels CO2 in conscious patients at normal atmospheric levels of 0.03%, but occult CO2 asphyxiation occurs at fraction of inspired CO2 concentrations at least as low as 5%, and becomes lethal at concentrations above 30%.4,5 Capnography cannot measure CO2 in the absence of endotracheal intubation, and pharyngeal gas sampling cannot assess occult alveolar CO2 accumulation.
Thus, occult alveolar CO2 accumulation due to toxic respiratory depression explains sudden, unexpected oxygen desaturation that frequently occurs during open airway techniques despite oxygen supplementation and pharyngeal gas sampling.
Combinations of surprise and paralysis invariably accompany induction airway disasters.6 I came to appreciate how fatigue, hunger and hubris readily paralyze preoperative evaluation and awake intubation as a means to avoid airway disasters after my close encounter with a bearded, overweight, diabetic, middle-aged man who presented as an emergency “add-on”.7,8 Thankfully, the laryngeal mask airway averted disaster.
I subsequently embraced routine sevoflurane mask induction and nasal intubation without paralysis to avoid similar predicaments in outpatient dental clinics where anatomic airway problems were common, and preoperative assessment was problematic. Risk-free induction resides in the realm of the unicorn, but mask induction and intubation obviate most induction emergencies and are inherently safer than presently prevailing IV induction techniques.
Intravenous catheter installation is fast, easy and painless after patients are anesthetized. Emergency agents such as epinephrine can be administered via the endotracheal tube. After performing routine sevoflurane mask induction and nasal intubation without paralysis on hundreds of patients, young and old, I found intubating conditions adequate, vocal cord damage nil, dental damage unremarkable, patient satisfaction excellent, efficiency acceptable and safety superior. The technique was surprisingly successful and problem free, and I trained nurses to perform it under supervision.
A Bullard laryngoscope was successfully employed without paralysis for difficult intubations. Failed intubation was rare, and the only consequence was optimized awake intubation or hospital referral. As Drs. Muller and Healy ruefully acknowledged, the inherent hazards of presently prevailing induction techniques cannot be eliminated, if only because of human shortcomings. Mask induction, mask maintenance, and intubation without paralysis are hardly new. They were essential skills before Dr. Ralph Waters introduced elective intubation with rapid IV induction and paralysis as a means to facilitate surgical convenience and eliminate aspiration, obstruction and CO2 asphyxiation. Since then, the utility of mask induction has been largely forgotten.
Mask induction and intubation without paralysis offer a comfortable and safe means to assess and avoid anticipated problems. Better yet, routine mask induction can largely eliminate induction disasters caused by unsuspected airway problems and occult pathology. Sevoflurane mask induction supplemented with short-acting synthetic opioids and complemented by modern monitoring is safer than presently prevailing practice, and nearly as efficient.
Must safety forever remain secondary to expedience?
- Bermudez EA, Chen MH. Cardiac arrest associated with intravenous propofol during transesophageal echocardiography before DC cardioversion. Heart Dis. 2002;4(6):355-357.
- Smith TE, Elliott WG. Routine inhaled induction in adults: a safe practice? Anesth Analg. 2006;102(2):646-647; author reply 7.
- van den Berg AA, Chitty DA, Jones RD, et al. Intravenous or inhaled induction of anesthesia in adults? An audit of preoperative patient preferences. Anesth Analg. 2005;100(5):1422-1424, table of contents.
- Brown E. Physiological effects of high concentrations of carbon dioxide. U S Nav Med Bull. 1930;28:721-734.
- Eisele JH, Eger EI II, Muallem M. Narcotic properties of carbon dioxide in the dog. Anesthesiology. 1967;28(5):856-865.
- Beecher HK, Todd DP. A study of the deaths associated with anesthesia and surgery: based on a study of 599,548 anesthesias in ten institutions 1948-1952, inclusive. Ann Surg. 1954;140(1):2-35.
- Benumof JL. Management of the difficult adult airway. With special emphasis on awake tracheal intubation. Anesthesiology. 1991;75(6):1087-1110.
- Benumof JL. Awake intubations are alive and well. Can J Anaesth. 2015;62(7):723-726.