To compare a new mode of mechanical ventilation, Automatic Tube Compensation (ATC) with a traditional one, Continuous Positive Airway Pressure(CPAP), on its effectiveness for detecting patients no longer needing mechanical ventilation.

The ultimate goal of this proposal is to find the best way to rapidly and safely discontinue mechanical ventilation in patients recovering from respiratory failure.

It is common practice in these patients to perform trials of "spontaneous" breathing while still connected to the ventilator in order to assess their readiness to breathe without assistance. To help with this assessment, new mechanical modes have been incorporated to modern ventilators. A recently developed mode, called Automatic Tube Compensation, is designed for this purpose ("spontaneous" breathing). Whether this method is superior to traditional ones has not been established and the investigators intend to address this question.

The investigators aim to:

1. compare Automatic Tube Compensation vs. our traditional mode (Continuous Positive Airway Pressure) during spontaneous breathing trials in their efficacy to identify patients ready be successfully removed from mechanical ventilation
2. study which physiologic variables better predict successful discontinuation of mechanical ventilation in these two modes.

The investigators plan to prospectively randomize patients on mechanical ventilation at the point of weaning evaluation, to undergo spontaneous breathing trials with our current ventilatory mode (Continuous Positive Airway Pressure) or the new mode (Automatic Tube Compensation). Based on predefined physiologic and clinical variables, clinicians will decide whether patients are ready to be removed from mechanical ventilation. The proportions of successful discontinuation (no need to reinstitute mechanical ventilation) and the duration of the weaning period in both groups will be compared. During the spontaneous breathing trials, respiratory variables will be measured and compared between patients with successful vs. non successful discontinuation in order to evaluate their predictive value for successful outcome.

Mechanical ventilation is being used increasingly given our growing population with advanced age and multiple co morbidities and the rising volume of aggressive medical procedures. It is well known to be associated with medical complications and high health care costs. Reducing the duration of unnecessary mechanical ventilation while minimizing the risk of premature removal of needed assistance is the final objective of this project. Approaching this goal will decrease the adverse effects of this treatment and the cost of critical care.

Inclusion Criteria:

• patients 18 years of age or older
• on mechanical ventilation at Thomason Hospital Intensive Care Unit for more than 24 hours
• about to undergo SBT by the current institutional protocol for weaning assessment ordered by their treating physician
• availability of informed consent from patient or next of kin

Exclusion Criteria:

• patients for whom a decision has been made not to reinstitute ventilatory assistance under any circumstance
• pregnancy
• patients not considered for discontinuation of mechanical ventilation on the day of SBT

General ICU population.

Two subjects in each group were randomized and data collected but were not included in analysis per protocol due to needing re-intubation for upper airway obstruction.