INFLUENCE OF DIFFERENT METHODS OF SYNCHRONIZED MECHANICAL VENTILATIONON VENTILATION, GAS-EXCHANGE, PATIENT EFFORT, AND BLOOD-PRESSURE FLUCTUATIONS IN PREMATURE NEONATES

We studied the effects of two methods of synchronized mechanical venti lation [synchronized intermittent mandatory Ventilation (SIMV) and ass ist/control (A/C)] on ventilation, gas exchange, patient effort, and a rterial blood pressure (ABP) fluctuations. SIMV and A/C were applied i n random order in 12 preterm neonates (gestational age, 29.7 +/- 2.3 w eeks; birth weight, 1,217 +/- 402 g). We measured total (Ve(tot)) and mechanical (Ve(mech)) minute ventilation, spontaneous (Vt(spont)) and ventilator supported (Vt(mech)) tidal volume, transcutaneous oxygen sa turation (Sp(O2)), transcutaneous P-O2 (TcPO2), and P-CO2, (TcPCO2), m ean airway pressure (Paw), phasic esophageal pressure deflections (Pe) as an estimate of inspiratory effort, mean arterial blood pressure (A BP), and beat-to-beat ABP fluctuations. The measurements obtained duri ng conventional intermittent mandatory Ventilation (IMV) were compared with the recordings during SIMV and A/C. To make the measurement cond itions comparable and to prevent hyperventilation, peak inspiratory pr essure was reduced during the A/C mode so that Ve(tot), remained in th e same range as during the IMV mode. Whereas Ve(tot) was similar in al l three conditions by study design, Ve(mech) was larger during SIMV an d A/C than during IMV. Vt(mech) increased during SIMV and by study des ign was smaller during AIC than during IMV. Pe decreased during SIMV a nd A/C compared with IMV, and Paw was higher during A/C than during IM V or SIMV. Beat-to-beat ABP fluctuations were reduced during SIMV and A/C compared with IMV and showed a close positive correlation with Pe changes. We conclude that SIMV increases Ve(mech) and reduces Pe compa red with IMV, resulting in smaller intrathoracic and ABP fluctuations. During A/C, a substantial portion of the spontaneous respiratory effo rt is shifted to the ventilator, resulting in a further decrease in Pe and ABP fluctuations. (C) 1996 Wiley-Liss, Inc.