HEMODYNAMIC-CHANGES DURING ENDOTRACHEAL SUCTIONING ARE MEDIATED BY INCREASED AUTONOMIC ACTIVITY

Endotracheal suctioning of intubated infants produces profound changes in cardiovascular and cerebral hemodynamics, but the mechanisms regul ating these changes are not fully understood. To determine the role of the autonomic nervous system in regulating these physiologic changes, we investigated the effects of endotracheal suctioning on heart rate (HR), mean arterial blood pressure (MABP), and renal sympathetic nerve activity (RSNA) in nine ventilated newborn lambs. In the first part o f the study (n = 6), ventilation was interrupted for suctioning. With suctioning (15 s), HR decreased by 39 +/- 6% (p < 0.05), whereas MABP and RSNA increased significantly (p < 0.05) by 36 +/- 5% and 68 +/- 8% , respectively. These changes were significantly (p < 0.05) larger tha n changes observed during disconnection from the ventilator (15 s) wit hout suctioning. Administration of atropine (0.02 mg/kg) blocked the H R response to suctioning without altering MABP or RSNA changes. After bilateral vagotomy, suctioning produced no changes in any parameter. W hen a closed tracheal suction system was used and ventilation was main tained, suctioning again resulted in significant (p < 0.05) increases in MABP (+10 +/- 3%) and RSNA (+34 +/- 5%) and a decrease in HR (-15 /- 4%). These data suggest that suctioning stimulates sympathoexcitato ry receptors localized in large airways whose afferent fibers course w ithin the vagus, resulting in increased sympathetic activity, which in duces peripheral vasoconstriction and elevates MABP. In contrast, the HR response appears to be mediated by increased parasympathetic activi ty as this is abolished by atropine.