The Science Journal of the American Association for Respiratory Care

2002 OPEN FORUM Abstracts

The Utilization of the Frequency to Tidal Volume Ratio and Maximum Inspiratory Pressure as Predictors of Successful Weaning and Extubation in Trauma and Closed Head Injured Patients

Kenneth Miller MEd RRT, Elizabeth Seislove MSN, Richard Shimer MD, Michael Pasquale MD, Joseph Groller RRT. Lehigh Valley Hospital, Allentown, PA

Introduction: The initiation of mechanical ventilation is an integral element of the management of patients with significant trauma or neurological compromise. Ventilatory support is frequently life-saving but represents a significant risk of morbidity. Patient discomfort, airway trauma, ventilator-induced trauma, and pneumonia are some frequent negative side effects from prolonged mechanical ventilation. Mechanical ventilation is also a major source of institutional and patient expense. For these reasons it is prudent to liberate patients from mechanical ventilation as quickly as deemed clinically acceptable. Currently no method of ventilatory weaning has been clearly demonstrated as superior in the medical or surgical literature.1-3 Recently the respiratory frequency to exhaled tidal volume (F/TV) ratio has gained popularity as an excellent barometer of the patient?s ability to perform spontaneous breathing trials.4 Currently, information on the clinical value of these parameters in the ICU has been limited. The goal of our study was to determine if the F/TV ratio <105 and maximum inspiratory pressure (MIP) more negative than ?20 cm H20 followed by a 30-minute spontaneous breathing trial would be indicative of the traumatized and/or neurologically impaired patient?s ability to be liberated from mechanical ventilation in a timely and safe fashion.

Methods: We performed a prospective evaluation of the F/TV and MIP for extubation involving patients age 18 years or older admitted to a level one Trauma-Neuro ICU who received mechanical ventilation for more than 48 hours. Once the patient was deemed clinically stable and a candidate for possible extubation F/TV and MIP measurements were performed. If the F/TV <105 and the MIP was more negative than ?20 cm H20 the patient was given a 30-minute spontaneous breathing trial on 5 cm H20 of CPAP via an internal ventilator flow-by system. During the 30-minute breathing trial the patient was monitored for hemodynamic and pulmonary stability based on acceptable TNICU criteria. If the patient maintained clinical stability, the patient was liberated from the ventilator. If not, the patient was returned to previous ventilator parameters.

Results: 64 patients were enrolled, of which 37 were admitted with the diagnosis of multiple trauma and 22 with the diagnosis of closed head injury; 62 of these patients were successfully liberated from the ventilator with no adverse effects. The two patients who failed the breathing trials were re-intubated within 30 minutes due to upper airway obstruction and not secondary to poor pulmonary mechanics. By utilizing this method of weaning we were able to reduce ventilator duration by 36 hours (7.5 reduced to 6.0 days) and decrease length of stay in the TNICU by 48 hours (9.2 reduced to 7.12 days). Pre-study patient population had an mean age of 42 years?study group mean age same; TRISS 0.71 compared to 0.81; ASCOT 0.71 compared to 0.83; and Glasglow score 9.2 compared to 8.8. These reductions lead to a decrease in patient discomfort and costs.

Conclusion: Our study results demonstrate that utilizing the F/TV and MIP measurements are a reliable indicator of the patient?s ability to maintain acceptable hemodynamic and pulmonary stability during spontaneous breathing trials and post extubation in the TNICU patient population.

1. Bochard L Rauss A, Benito S, et al. Comparison of three methods of gradual withdrawal from ventilatory support during weaning from mechanical ventilation. Am J Respir Crit Care Med 1994; 150:896-903.

2. Esteban A, Frutos, Tobin MJ, et al. A comparison of four methods of weaning from mechanical ventilation. N Engl J Med 1995; 332:345-350.

3. Esteban A, Alia I, Gordo F, et al. Extubation outcome after spontaneous breathing trials with pressure support or T-tube. Am J Crit Care Med 1997; 156:459-465.

4. Epstein SK. Etiology of extubation failure and the predictive value of rapid
shallow breathing index. Am J Respir Crit Care Med 1995;152:545-549.

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