HIGH-FREQUENCY INTRATRACHEAL PULMONARY VENTILATION - IMPROVED GAS-EXCHANGE AT LOWER AIRWAY PRESSURES

Purpose: Conventional ventilation in the neonatal intensive care unit causes iatrogenic injury to fragile newborn lungs, especially those wi th preexisting pathology or prematurity. Intratracheal pulmonary venti lation (ITPV), developed by Dr Theodor Kolobow and associates at the N ational Institutes of Health (NIH), incorporates a continuous flow of humidified gas through a reverse thrust catheter positioned at the dis tal end of the endotracheal tube. In animal studies ITPV was shown to facilitate gas exchange at low peak pressures by reducing physiologica l dead space, facilitating exhalation, and enhancing CO2, elimination. The specific aims of this project were (1) to invent a new ITPV-speci fic ventilator; (2) to optimize gas exchange in a newborn animal model at law airway pressures using higher frequency ITPV; and (3) to demon strate efficacy and improved ventilation at tower airway pressures in a prematurity model. Methods: (1) A new ventilator had to be construct ed. The first prototype is microprocessor driven, incorporating contro ls for flow, pressures, and concentrations of gases. The ventilator ha s the capability to vary FIO2, respiratory rate (0 to 15 Hz), and insp iratory-expiratory I:E ratio. (2) Prototype testing was performed. New born lambs (n = 3, 6 to 7 kg) underwent tracheotomy and placement of a rterial and venous lines. Lambs were initially supported on convention al mechanical ventilation (CMV). Animals were allowed to achieve stead y state with measurements Of baseline vital signs, arterial blood gase s, and ventilatory settings. ITPV was instituted at a rate of 100 brea ths per minute and flow adjusted to achieve lower peak carinal pressur es than obtainable on conventional ventilation. In a stepwise fashion, respiratory rate, I:E ratio, and ITPV flows were varied while initial ly maintaining PaCO2 constant, and then allowing improvement. (3) Thes e experiments were repeated in preterm lambs (n = 6, 1.8 to 3.6 kg). R esults: At the time of transition from CMV to ITPV (rate, 100, I:E, 1: 3), gas exchange was maintained despite a documented drop in average p eak carinal pressure for the newborn lambs from 28.3 cm H2O on CMV to 10.3 cm H2O on ITPV (P=.028). The average peak carinal pressure fell e ven further at higher ITPV rates with adjustments in I:E ratio. For th e premature lambs, peak carinal pressures also fell significantly on I TPV (44 to 32 cm H2O, P=.002) with corresponding significant improveme nt in ventilation (PaCO2 from 52.2 to 31.9 mm Hg, P=.029). Conclusions : (1) Our new ITPV ventilator operates at rates and I:E ratios previou sly unobtainable. (2) In newborn and premature lambs ITPV functions mo st effectively at higher rates with higher gas flow rates and with lon ger exhalation, providing significantly improved gas exchange at signi ficantly lower peak carinal pressures. (3) ITPV may prove beneficial i n achieving gas exchange in newborns while avoiding barotrauma. Based on these data, we have initiated human clinical studies of ITPV in new borns with congenital diaphragmatic hernia or prematurity to improve g as exchange and reduce barotrauma in the neonatal intensive care unit. Copyright (C) 1997 by W.B. Saunders Company.