Previous research has shown that the Inferior Vena Cava Collapsibility Index (IVCCI) can be used to assess volume status. One limitation of the previous work is that changes in intra-thoracic pressure can influence this measurement, and the magnitude of this effect has never been described. The investigators aim is to correlate the degree of change in IVCCI with the set degree of change in intra-thoracic pressure in a heterogeneous population of critically ill patients.

Initially eligible patients will be those admitted to the OSU MICU and 8ICU within the prior 48 hours. These patients will be screened for predetermined exclusion criteria. Eligible patients will have their IVCCI measured and baseline peak and plateau pressures noted. For those patients meeting a second set of criteria, a common ventilator maneuver will be preformed. The positive end-expiratory pressure will be increased by 5-10 cm/H20 pressure. This procedure will be aborted if ANY safety criteria are exceeded. During the interval, the IVCCI will be re-measured, the ventilator settings will be recorded, and the ventilator will be return to the initial settings. Since changes of these same magnitude are made daily in clinical practice, the risks to the patients in this study will be minimal and no more than that experienced in the course of usual care.

Inclusion Criteria:

1. Age>17 years
2. Current use of mechanical ventilation through an endotracheal tube.
3. Admitted to ICU within last 48 hours

Exclusion Criteria:

1. Severe COPD by history (documented FEV1<50% predicted or CT evidence of emphysema)
2. Current suspected Asthma Exacerbation
3. Profound Hypoxia defined as a FiO2 requirement >90% or a PEEP >10 mmHg
4. Patient-ventilator desynchrony or active agitation
5. Unstable O2 requirement as determined by the primary clinical team.
6. Prisoners
7. Bedside clinician refusal (physician or treating nurse).

Exclusion Criteria for ventilator changes:

1. Cardiovascular instability (any increase in rate of vasopressors or i.v. fluid bolus for hypotension within the last four hours)
2. Current PEEP requirements of >15cmH2O
3. Current SpO2 of <88%.

InpatientSample