Response of critically ill patients to increased oxygen demand: hemodynamic subsets.
OBJECTIVE
To ascertain how patients with different abnormalities of oxygen transport at rest respond to an acute increase in oxygen demand.


METHODS
Observational study with retrospective assignment to subgroups, based on resting oxygen extraction ratio or increased cardiac output.


METHODS
University hospital surgical intensive care unit (n = 96).


METHODS
Postoperative, mechanically ventilated, critically ill patients (n = 96).


METHODS
Chest physical therapy.


RESULTS
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.


CONCLUSIONS
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.
Weissman
C
C
Department of Anesthesiology, College of Physicians and Surgeons of Columbia University, Columbia-Presbyterian Medical Center, New York, NY 10032.
Kemper
M
M
Harding
J
J
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D002245:Carbon Dioxide / Q000097:blood; D002302:Cardiac Output / Q000502:physiology; D016638:Critical Illness; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D008875:Middle Aged; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption / Q000502:physiology*; D010313:Partial Pressure; D026741:Physical Therapy Modalities; D011182:Postoperative Care; D012044:Regression Analysis; D012121:Respiration, Artificial; D012189:Retrospective Studies
D002245:Carbon Dioxide; D010100:Oxygen