CHANGES IN INTRATHORACIC FLUID VOLUMES DURING WEANING FROM MECHANICALVENTILATION IN PATIENTS AFTER CORONARY-ARTERY BYPASS-GRAFTING

Purpose: Although it is known that weaning from mechanical ventilation is associated with alterations in intrathoracic pressure, lung volume , and venous return, changes in intrathoracic fluid volumes during wea ning are not reported. Especially in patients with impaired cardiac fu nction, the development of pulmonary edema during weaning has been des cribed, Thus, we investigated changes in intrathoracic fluid volumes i n patients after coronary artery bypass grafting after changing the ve ntilatory pattern from mechanical to spontaneous ventilation. Material s and methods: Intrathoracic blood volume index (ITBVI), pulmonary blo od volume index (PBVI), and extravascular lung water (EVLW) were calcu lated during mechanical ventilation (T1), T-piece breathing (T2), and spontaneous breathing after extubation of the trachea (T3) in 72 conse cutive patients after coronary artery bypass grafting using a combined dye-thermal dilution method. Results: Changing from mechanical ventil ation to T-piece breathing resulted in an increase in ITBVI from 880 /- 22 mL/m(2) to 970 +/- 22 mL/m(2) (P < .01), and in PBVI from 162 +/ - 6 mL/m(2) to 173 +/- 6 mL/m(2) (P < .01). After extubation of the tr achea, both parameters decreased again (ITBVI, 879 +/- 20 mL/m(2); PBV I, 160 +/- 7 mL/m(2)), EVLW remained unchanged after transition to T-p iece breathing (T1, 5.8 +/- 0.3 mL/kg; T2, 6.0 +/- 0.3 mL/kg), but inc reased to 6.6 +/- 0.5 mL/kg (P < .01) after extubation of the trachea. However, pathological values of EVLW were not observed. Conclusions: In patients after coronary artery bypass grafting, changes in intratho racic intravascular fluid volumes during weaning are restricted to the period of T-piece breathing and reflect an increased venous return. T he maintenance of EVLW in the normal range during weaning indicates th at cardiac function was matched to this elevated preload. Copyright (C ) 1997 by W.B. Saunders Company.