TYK19
All of the following INCREASE the probability of laryngospasm EXCEPT:
A. Light anesthesia
B. Hypocapnia
C. Hypoxia
D. Hyperthermia
E. Young age
Answer
The answer is C. Hypoxia (finally) is a GOOD thing. Ok, so maybe not but you know what I mean. Infants are particularly susceptible to laryngospasm. This likely relates to some developmental hyper-excitability of the laryngospasm reflex in young patients. Hyperventilation and resultant hypocapnia, as well as light anesthesia, increase the activity of the superior laryngeal nerve, reduce the mean threshold of the adductor reflex, or increase upper airway resistance. Hyperthermia also may decrease the threshold for laryngospasm. Howevere, hypoventilation and resultant hypercapnia, positive intrathoracic pressure, and deep anesthesia increase the threshold of discharge of the superior laryngeal nerve and resultant laryngospasm. Hypoxemia below a Pao2 of 50 mm Hg also lessens the risk of laryngospasm by increasing the threshold of discharge of the superior laryngeal nerve. This is likely a protective mechanism in which sustained hypoxia and hypercarbia will relieve laryngospasm. Animal studies suggest that during a discrete interval after birth and before complete neurologic maturation, there is a period of transient laryngeal hyperexcitability.
Notes
Suzuki, Masafumi, and Clarence T. Sasaki. "Effect of various sensory stimuli on reflex laryngeal adduction." Annals of Otology, Rhinology & Laryngology 86.1 (1977): 30-36. [1]
Ikari, Taketsugu, and Clarence T. Sasaki. "Glottic closure reflex: control mechanisms." Annals of Otology, Rhinology & Laryngology 89.3 (1980): 220-224 [2]