The Effects of Bupivacaine on the Laryngeal Chemo- and Diving-reflex in the Newborn Lamb:

Bupivacaine is frequently administered to produce analgesia during labor and can be shown to be present in the neonate, indicating that bupivacaine crosses the placenta. Neurobehavioral studies have been unable to detect any effect upon the neonate of bupivacaine. This study looks specifically at the changes in laryneal chemo(L.C.R.) and diving(D.R.) reflex responses in newborn lambs. Stimulation of L.C.R. produces apnoea and re-distribution of bloodflow with subsequent rise in blood pressure and fall in heart-rate, the afferent pathway being the superior laryngeal nerve. The D.R. produces a similar response, the afferent pathway being through the trigeminal nerve. Six, awake, unanesthetized newborn lambs were stimulated by retrograde injection of water and normal saline (N.S.) into the larynx, the airway remaining patent through an endotracheal tube. D.R. was initiated by placing an ice-pack on the lamb's nose. Measurements of ventilation were made using a thermistor probe inserted into the endotracheal tube and cardiovascular parameters determined by arterio-venous cannulation. A series of four stimulations were Imade to elicit the L.C.R. and D.R. as a baseline. 10 mg of bupivacaine was injected into the lamb intravenously and the studies repeated. The results were expressed as a % change from base-line.