Author: Lewis Coleman, MD
Anesthesiology News recently reported on a study that promoted the laryngeal mask (LM) in prone position to “avoid intubation, reduce use of relaxants and minimize airway trauma.”1 This study reflects increasing confusion in a complex subject that can be understood best in terms of anesthesia history.
Lacking IV access, early practitioners evolved a sophisticated technique that combined Jackson’s “closed circuit” anesthesia machines with intramuscular morphine and scopolamine premedication, mask induction, CO2 supplementation and ether anesthesia.2-5 The combination of morphine and CO2 accelerated induction and inhibited laryngospasm. Mask induction avoided bolus IV agent toxicity and anatomic airway disasters.
The technique produced excellent outcomes but was bedeviled by airway obstruction, aspiration, muscle tension, unexpected movements, prone position incompatibility and constrained ENT access. Overenthusiastic CO2supplementation occasionally caused CO2 asphyxiation disasters that were incorrectly attributed to CO2 toxicity.6
Ralph Waters, MD, became alarmed by the asphyxiation disasters. He performed crude animal and human experiments, whereupon he incorrectly concluded that CO2 possesses both toxic and narcotic properties.7,8 He characterized CO2 as a “toxic waste gas, like urine,” and ignored its essential role in oxygen delivery and its therapeutic benefits.9 Advancing needle technology enabled him to introduce a practical technique that utilized IV hypnosis that was pleasant for patients, paralysis that facilitated surgical convenience and elective endotracheal intubation that eliminated aspiration, laryngospasm and airway obstruction. Dr. Waters became the first chairman of a university anesthesia department, implemented board certification, trained the first generation of anesthesiologists and guided them to influential positions.10 Elective intubation became the gold standard of airway management, and mask skills were abandoned in training and practice.
The Waters technique conferred practical advantages but it introduced fresh problems. Intravenous hypnosis induction can cause unexpected cardiorespiratory arrest.11 Induction paralysis can precipitate unexpected anatomic airway predicaments regardless of careful preoperative preparation.12Residual paralysis and reversal agent side effects are commonplace. Worst of all, the Waters technique introduced the harmful habit of hyperventilation to rid the body of mythical toxic and narcotic CO2 effects.
Hyperventilation confers no benefits. It damages lung tissues, depletes CO2tissue reserves, induces abnormal “respiratory alkalosis” that paralyzes respiratory chemoreceptors, inhibits oxygen release from hemoglobin, exaggerates capillary flow resistance and undermines respiratory drive, cardiac efficiency, tissue perfusion, tissue oxygenation and opioid clearance.
It invites asthma, atelectasis, pneumonia, PONV and postoperative respiratory depression.13 The uncritical acceptance of the Waters technique caused hazardous respiratory alkalosis to become regarded as normal and even beneficial, while normal respiratory acidosis became confused with metabolic (i.e., lactic) acidosis, which often occurs secondary to dangerous conditions. Helpful opioids came to be avoided as the cause of unexpected respiratory depression. CO2 therapy was banished from fire trucks, physician’s offices and hospitals, as well as from anesthesia practice.
The LM is a vital “rescue” device that can save lives in the event of “can’t intubate, can’t ventilate” crises, but it is otherwise inferior to elective endotracheal intubation. LM and open airway techniques have become accepted alternatives to the problematic Waters technique, but they invite disaster if emergency intubation becomes necessary during difficult circumstances, particularly in the presence of anatomic airway abnormalities.12
I recall two pertinent LM disasters. In the first case, an inexperienced anesthesiologist elected to use the LM for arthroscopic shoulder surgery in the “beach chair” position, wherein the patient was covered with sterile drapes. Lethal airway obstruction due to LM malposition remained undetected until the patient was beyond resuscitation.
In the second, an experienced anesthesiologist resorted to the LM after failed intubation, whereupon the elderly patient was placed in the lateral position for hip replacement surgery, with subsequent lethal airway failure. The same principles apply to conduction anesthesia, analgesic blocks and propofol sedation for endoscopies.14 Airway disasters and fires are common in dental procedures where open airway techniques are employed.15
It is time for reassessment of professional airway management standards. The safety and utility of mask management was appreciated in the past, but is now neglected. Elective endotracheal intubation is safer than alternative methods of airway management. Mask induction and intubation with judicious opioid premedication and CO2 supplementation optimizes its safety, efficiency and practicality.
- anesthesiologynews.com/?Clinical-Anesthesiology/?Article/?01-17/?Use-of-Supraglottic-Airways-in-Patients-in-the-Prone-Position-You-Must-Be-Careful/?38973. Accessed March 1, 2017.
- Jackson Anesthesia equipment from 1914 to 1954 and experiments leading to its development. Anesthesiology. 1955;16:953-969.
- Crile GW. Anoci-association. Philadelphia, PA: W.B. Saunders; 1914.
- Lundy J S. Carbon dioxide as an aid in anesthesia. JAMA. 1925;85:1953-1955.
- Coleman SA, McCrory JW, Vallis CJ, et al. Inhalation induction of anaesthesia with isoflurane: effect of added carbon dioxide. Br J Anaesth. 1991;67:257-261.
- Lundy JS. Convulsions associated with general anesthesia. Surgery. 1937;1:666..
- Waters RM. Toxic effects of carbon dioxide. JAMA. 1933;519:219-224.
- Leake CD, Waters The anesthetic properties of carbon dioxide. J Pharmacol Exp Ther.1928:33:280-281.