Objective: To study in anemic patients with chronic obstructive pulmonary disease (COPD) whether blood transfusion reduces minute ventilation and work of breathing (WOB).
Design: We prospectively evaluated the minute ventilation and WOB in 20 anemic adults (hemoglobin of <11 g/dL). Ten patients had severe COPD and ten patients were without lung disease. Measurements were made before and after receiving red blood cell transfusion; post-transfusion measurements were made 24 to 36 hrs after the last transfusion.
Setting: The study was performed in the intensive care unit of a tertiary referral center for home mechanical ventilation and for patients considered difficult to wean from mechanical ventilation.
Patients: Twenty clinically stable patients (12 female, eight male) with chronic anemia were studied. Ten patients with COPD (mean forced expiratory volume in 1 sec: 0.55+/-0.1 [SD] L) were compared with ten patients without lung disease. All participants had adequate renal and left ventricular function.
Interventions: Patients received 1 unit of packed red blood cells for each g/dL that their hemoglobin value was less than an arbitrarily defined target value of 11.0 to 12.0 g/dL. Each unit was transfused over 2 hrs and < or =3 units in total was given.
Measurements and main results: Esophageal pressure was measured from a catheter which was positioned in the middle of the esophagus. Flow was measured using a pneumotachygraph connected to a mouthpiece while a nose clip closed the nostrils during the measurements. From these data, respiratory rate, minute ventilation, and inspiratory resistive WOB were computed. Arterial blood gas values, oxygen saturation, hemoglobin, and hematocrit were also measured, and oxygen content was calculated before and 24 to 36 hrs after transfusion. In patients with COPD, hemoglobin increased from 9.8+/-0.8 to 12.3+/-1.1 g/dL due to a mean transfusion of 2.2+/-0.4 (SD) units of red blood cells. There was a reduction in the mean minute ventilation from 9.9+/-1.0 to 8.2+/-1.2 L/min (p < .0001); correspondingly, WOB decreased from 1.03+/-0.24 to 0.85+/-0.21 WOB/L (p< .0001). The capillary P(CO2) increased from 38.1+/-6.0 to 40.7+/-6.8 torr (5.1+/-0.8 to 5.8+/-0.9 kPa) (p < .05). Similarly, capillary P(O2) changed from 56.9+/-8.9 to 52.8+/-7.0 torr (7.6+/-1.2 to 7.0+/-0.9 kPa) (p < .05). In anemic patients without lung disease, minute ventilation, WOB, and the capillary blood gas values did not change after increase of the hemoglobin by a similar degree.
Conclusions: We conclude that red blood cell transfusion in anemic patients with COPD leads to a significant reduction of both the minute ventilation and the WOB. In these patients, transfusion may be associated with unloading of the respiratory muscles, but it may also result in mild hypoventilation.