Respiratory Suppression and Swallowing from Introduction of Fluids into the Laryngeal Region of the Lamb

Abstract

Summary: Introduction of 0.9% NaCl or undiluted fetal tracheal fluid into the laryngeal region produced no suppression of breathing in lambs during the perinatal period. As NaCl or tracheal fluid solutions were increasingly diluted with water, progressively greater respiratory suppression associated with rapid swallowing was observed. Introduction of amniotic fluid was associated with variable suppression of respiration. The swallowing induced by the dilute solutions was as rapid as two swallows per sec. Lambs 3 months of age swallowed when water was introduced into the laryngeal region, but were able to alternate swallows between breaths without suppression of breathing. Speculation: The suppression of breathing by presence of certain fluids in the laryngeal region may have important clinical implications. At birth, aspiration of amniotic fluid into the laryngeal area could seriously suppress breathing under certain conditions. In the pre-term or newly born infant, introduction of fluids with low osmolality into the laryngeal region might initiate this detrimental reflex more strongly than in older children. Finally, the aggravated response where life-threatening apnea develops from presence of small amounts of fluid in the laryngeal region might occur especially in neonatal disease states predisposing to apneic episodes. Under such conditions, swallowing could clear the liquid from the laryngeal region so that this area would be free of fluid at subsequent postmortem examination. Death from apnea could occur as terminal hypoxia supervenes, leaving little evidence for the pathologist to define the cause of death.