Protracted recruitment of patients

Transfusion of stored blood has been associated with increased pulmonary vascular resistance in lambs. The investigators hypothesize that transfusion of one unit of red blood cells stored under standard conditions in intensive care patients will increase pulmonary arterial pressure and pulmonary vascular resistance to a greater extent than will one unit of fresh red blood cells.

Inclusion Criteria:

1. The patient has a pulmonary artery catheter in place
2. Transfusion of 1 unit of packed red blood cells indicated for standard intensive care therapy
3. The patient has an arterial catheter

Exclusion Criteria:

1. Age < 18 years
2. Clinical prediction that the patient will not survive at least 48 hours
3. Acute bleeding: > 2 units of packed red blood cells/hour
4. Vasopressor use: noradrenalin > 0.2 μg/kg/min or any use of adrenalin within 6 hours of inclusion into the study
5. Therapy with inhaled NO, inhaled prostacyclin, or phosphodiesterase-5-inhibitors
6. Sepsis