Paper
Friday, July 23, 2004
10:00 AM - 10:30 AM
Friday, July 23, 2004
3:00 PM - 3:30 PM
Work of Breathing During Weaning From Mechanical Ventilation
Weihong Hu, BS, MS, Nursing, The Ohio State University, Columbus, OH, USA, Kathleen S. Stone, PhD, RN, FAAN, College of Nursing, The Ohio State University, Columbus, OH, USA, Susan Frazier, RN, PhD, Ohio State University, Columbus, OH, USA, and Debra K. Moser, DNSc, RN, College of Nursing, University of Kentucky, Lexington, KY, USA.
Introduction: Weaning from mechanical ventilation is a significant clinical problem with 37-45% of patients failing to wean. Long-term mechanical ventilation is associated with complications, mortality and increased cost of care in critically ill patients. Objective: The purpose of this study was to determine the effect of three different weaning modes (continuous positive airway pressure (CPAP), pressure support (PS) and t-piece on work of breathing (WOB) and the relationship of WOB and preload (blood volume) changes on cardiovascular-pulmonary (C-P) function during weaning from mechanical ventilation. Design: Experimental within subject repeated measures design. Subjects: This study was conducted in anesthetized male canines, Group I ([n=24], normal ventricular function) and Group II ([n=18], pace-maker induced heart failure). Methods: Subjects were randomly assigned to the two groups and the three weaning modes. WOB using the Bicore, arterial blood gases (ABGs) and three serial thermodilution cardiac output (CO) measurements at end-expiration were made before and after ventilator manipulation and preload changes (diuresis with lasix). Findings: In Group I,WOB was significantly less with PS (.7 joules/L, p=.007) than CPAP (1.28 joules/L) and T-piece (1.2 joules/L) p=.039. Following diuresis, WOB was significantly less with PS (.68 joules/L p=.000)than CPAP (1.18 joules/L) and T-piece (.98 joules/L) p=.004. In Group II heart failure, there were no statistically significant differences between the modes during hypervolemia. Following diuresis with lasix, WOB was significally less with PS (.58 joules/L p=.001 compared to CPAP (1.1joules/L). Alterations in cardiac output were least with PS and greatest with T-piece in groups I & II. Conclusions: Pressure support decreases the work of breathing with weaning and causes the least changes in cardiac output. T-piece causes marked alterations in CO increasing the risk of weaning failure. Implications: Weaning using pressure support ventilation is preferable in normal and heart failure subjects. Support: NIH NINR 1R01NR; American Nurses Foundation
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