Fatal Apnea in Piglets by way of Laryngeal Chemoreflex: Postmortem Findings as Anatomic Correlates of Sudden Infant Death Syndrome in the Human Infant

Objectives/Hypothesis: Intrathoracic petechiae are a prominent diagnostic finding in sudden infant death syndrome (SIDS) victims. In this study, the laryngeal chemoreflex (LCR) was elicited experimentally to discover whether intrathoracic petechiae would be produced by way of the LCR. The hypothesis was that water stimulation of the larynx in piglets, leading to death by prolonged apnea, would produce postmortem findings similar to those found in SIDS victims. Study Design: Using the piglet as an animal model, the LCR was initiated by way of water stimulation of the larynx, resulting in death. Normoxic and hypoxic conditions were established before the stimulation. The piglets were studied postmortem to determine the relationship between the physiologic mechanisms of the LCR and characteristic pathologic findings in SIDS. Methods: Using protocols approved by animal care, 14 mixed‐breed piglets aged 7 to 14 days were sedated with a ketamine/xylazine mixture. Respiratory and pressure‐monitoring devices were affixed and light anesthesia maintained with Surital infusion. In 10 of the piglets, a small catheter was placed between the arytenoid cartilages, and 5 mL of tap water was introduced over 1 second. The LCR ensued, producing periods of central apnea bordered by gasping efforts and resulting in hypoxemia and death in all cases. Four piglets underwent this manipulation in normoxic conditions. Six breathed a hypoxic gas mixture for 1 hour to bring their Po 2 down to below 50 torr before water was introduced into the larynx. Four control piglets breathed the hypoxic gas mixture for 1 hour (without water stimulation or LCR) before Surital overdose. Within 24 hours of death, all piglets underwent thoracoabdominal autopsy by a blinded evaluator experienced in SIDS pathology. Results: The autopsies revealed nothing remarkable in the abdominal viscera of any of the experimental animals. Thymus, heart, and lungs were graded 0 to 4 to indicate the degree of petechiae on external surfaces. Average cumulative scores (ACS) were applied to each animal. The control (hypoxic) piglets had no petechiae (ACS 0.0). The normoxic experimental piglets had moderate petechiae (ACS 3.5). The hypoxic experimental piglets had more prominent petechiae (ACS 6.3). Conclusions: Stimulation of the LCR, leading to death by prolonged apnea, produces postmortem findings in piglets similar to those found in SIDS victims. Petechiae were more severe among piglets pretreated with a hypoxic mixture of gases. This study supports the hypothesis that initiation of the LCR may produce pathologic features often prominent in SIDS.