Weissman C, Kemper M, Harding J
Department of Anesthesiology, College of Physicians and Surgeons of Columbia University, Columbia-Presbyterian Medical Center, New York, NY 10032.
Crit Care Med. 1994 Nov;22(11):1809-16.
To ascertain how patients with different abnormalities of oxygen transport at rest respond to an acute increase in oxygen demand.
Observational study with retrospective assignment to subgroups, based on resting oxygen extraction ratio or increased cardiac output.
University hospital surgical intensive care unit (n = 96).
Postoperative, mechanically ventilated, critically ill patients (n = 96).
Chest physical therapy.
Metabolic, hemodynamic, and respiratory measurements were made during an initial rest period and then during chest physical therapy. During chest physical therapy, patients (n = 10) having low resting oxygen extraction ratios (< or = 0.20) increased oxygen extraction, without changing oxygen delivery (DO2); while those patients (n = 19) with high resting oxygen extraction ratios (> or = 0.30) increased DO2, but not oxygen extraction. Patients (n = 46) with oxygen extraction ratios between 0.2 and 0.3 had an intermediate response; both DO2 and oxygen extraction increased. The group (n = 19) with increased resting cardiac output (> 9 L/min) and associated low resting oxygen extraction ratios and high DO2 values, increased their extraction of oxygen during chest physical therapy.
The response to an acute increase in oxygen demand was influenced by resting conditions and was characterized by the use of "reserve" capacity. Patients with a resting hyperdynamic state (high DO2 and low oxygen extraction) were able to further increase oxygen extraction during the increase in oxygen demand.
