We have developed a method t o lower cardiac output (Q) instantaneously, reversibly, and in a controlled, stepwise fashion in conscious lambs, using a balloon tipped (Foley) catheter inflated in the right atrium. The hemodynamic and metabolic effects of selective lowering of Q in the conscious, unsedated lamb has not previously been reported. Under conditions of low Q, we studied lambs at 2 weeks (n=5), 4 weeks (n=6) and 8 weeks (n=5) of age to determine the critical Q necessary t o decrease oxygen consumption (V02) or increase lactate (L) production a t each age. A t each level of balloon inflation we measured: VO C 0 2 production (VC02), venous hemoglobin concentration (Hb?: heart rate, arterial L, and systemic and pulmonary arterial blood gases, % HbO2 and pressures. The actual critical Q varied between lambs at a given age, although it was lower in the older lambs. However, when Q was normalized t o resting cardiac output (Qo), L production increased and V02 decreased in all lambs whenever Q 4 .6 Qo, thereby establishing a critical Q which was similar for a h a g e s . Due to the wide differences with age in Hb and Qo, the critical systemic oxygen transport (SOT) also decreased with age from 15 (2 weeks) t o 11 (8 weeks) m102/min kg.These data provide evidence of a critical Q in the young subject and provide a model for studying the metabolic effects of low Q in the conscious lamb. Furthermore, the relationship between V02 and SOT determined here for low flow states is similar to that established previously for anemia and hypoxemia. LIMITATIONS OF SELF-INFLATING BAGS. Neil F i n e r , Fidel176 El Fadley, Keith Barrington, Kathrine P e t e r s , UniverSi t v of A 1 berta. Roval A1 exandra Hosoi t a l . Deoartment , ..of Neonatology ,-Edmonton, ~i b e r t a , CANADA S e l f -i n f l a t i n g bags a r e frequently used in neonatal and pedia t r i c r e s u s c i t a t i o n . Because of concerns t h a t these devices tend t o be u n r e l i a b l e and i n c o n s i s t e n t we studied a r e p r e s e n t a t i v e number: 12 Ohio (Hope I I ) , 5 Leardal, 5 PMR2 Puritan with and without r e s e r v o i r s (R).These bags were connected to a small test lung v e n t i l a t e d a t r a t e s (RR) from 1 0 Ten children received < 8mg/kg t o t a l morphine dosage f o r the f i r s t nine days of EI. Of t h i s group, only one p a t i e n t developed morphine dependency and only a f t e r receiving > 16mg/kg cumulative morphine dosage over several subsequent weeks of EI.The remaining t h r e e children received >16mg/kg cumulative morphine dosage and each showed s i g n s of dependency. Our conclusion i s t h a t cumulative morphine dosage may help t o i d e n t i f y EI children a t r i s k of withdrawal. PIGTAIL CATHETER TECHNIQUE REDUCES TRAUMA OF CHEST178 TUBE PLACEMENT. B. P. Fuhrman, B. G. Landrum, T. B.F e r r a r a and T. P. Green. P e d i a t r i c C r i t i c a l Care and Neonatology, Univ. of Minnesota, Minneapolis, MN 55455.Chest tube placement f o r drainage of p l e u r a l f l u i d o r evacuat...