Hemodynamic and catecholamine responses to laryngoscopy with vs. without endotracheal intubation

To study the relationship between the intensity of the stimulus exerted against the base of the tongue during direct laryngoscopy and the magnitude of associated hemodynamic and catecholamine responses, a study was conducted in 40 ASA I or II patients. Laryngoscopy lasting 40 s was performed with a size 3 Macintosh blade connected to a force-displacement transducer. The intensity of the stimulus exerted during laryngoscopy is expressed by the product of its average force (N) and duration (s) and given as impulse in Ns. Highly significant relationships were found between the impulse during laryngoscopy and the maximal hemodynamic and catecholamine responses. Also, when laryngoscopy was followed by orotracheal intubation, significant relationships were found with steeper slopes of the regression lines for systolic blood pressure, heart rate and plasma epinephrine concentrations. A more rapid regression of hemodynamic data was seen in intubated patients, whereas their plasma catecholamine concentrations regressed more slowly. The mechanisms of the responses to laryngoscopy and orotracheal intubation are proposed to be by somato-visceral reflexes. Stimulation of proprioceptors at the base of the tongue during laryngoscopy induces impulse-dependent increases of systemic blood pressure, heart rate and plasma catecholamine concentrations. Subsequent orotracheal intubation recruits additional receptors that elicit augmented hemodynamic and epinephrine responses as well as some vagal inhibition of the heart.