Clinical Science (1996) 90. 105-111 (Printed in Great Britain) Effects of dobutamine on the relationship between oxygen consumption and delivery in healthy volunteers: comparison with sodium nitroprusside Daniel DE BACKER, Jacques BERRE, Jean Jacques MORAINE, Christian MELOT, Jacques VANFRAECHEM* and jean-Louis VINCENT Deportment of Intensive Care, E.rasme University Hospital, Brussels, Belgium, and *Institute of Sports Medicine, Free University of Brussels, Brussels, Belgium (Received 19 july/16 November 1995; accepted 24 November 1995) 105 1. Dobutamine has been used to study the relation- ship between oxygen consumption (YO:z) and oxygen delivery (DO:z) in critically ill patients, but this has led to concerns that it could consistently increase YO:z in all patients. Although a direct thermogenic effect of the catecholamine has been primarily impli- cated in this increase in YO:z, an increase in blood flow may contribute significantly by increasing the oxygen requirements of the heart and other organs such as the kidney and the liver. If this mechanism is predominant, it should also be observed when blood OQW increases during the infusion of non-adrenergic agents. To separate the two mechanisms, we com- pared the effects of dobutamine with those of sodium nitroprusside on YO:z/DO:z relationships in healthy volunteers. 2. Eight healthy volunteers received infusions of dobutamine at doses of 2,4 and 6pgmin- 1 kg-I and nitroprusside at doses of 0.5, 1 and 2pgmin- 1 kg-I in an alternate order. 3. VO:z was determined by indirect calorimetry and cardiac output by electrical bioimpedance. Data were analysed by analysis of variance for repeated measurements and individual YO:z/DO:z slopes were determined by linear regression. 4. YO:z increased more with dobutamine than with nitroprusside (from 138± 14 to 149± 20ml min- I m-:z, P<O.OOI, and from 131 ± 14 to 138± 17mlmin- 1m-:Z, P<O.OOI, respectively). However, DO:z also increased more with dobutamine than with nitro- prusside (from 531±186 to 702±274mlmin- 1m- 2 , P<O.OOI, and from 523± 107 to 610± 122 mlmin- I m-:Z, P<O.OOI, respectively). Individual YO:z /DO:z slopes were similar with dobutamine and nitroprusside (6.5±3.5 compared with 7.1±4.6%, P not significant). 5. At the doses used, DO:z and YO:z increased more with dobutamine than with nitroprusside in healthy volunteers. However, the YO:z/DO:z slopes were simi- lar for both substances. Thus, an increase in YO:z is not exclusively observed with catecholamines. Studies of the effects of therapeutic interventions on oxygen- derived variables should report not only changes in VO:z but also YO:z/DO:z slopes. INTRODUCTION The study of the relationship between oxygen consumption (V0 2 ) and oxygen delivery (D0 2 ) in the critically ill is a subject of intense interest and continuing controversy. There is a consensus that V0 2 is relatively independent of D0 2 in haemo- dynamically stable patients [1-5] but may be dependent on D0 2 in some critically ill patients with acute circulatory failure [2, 5, 6]. To study this phenomenon, D0 2 could be acutely reduced by the application of positive end-expiratory pressure [1] or acutely increased by fluid infusion [2], erythro- cyte transfusions [2] or the administration of inotropic [2-4, 6] or vasodilating [3, 5] substances. Each of these methods has its drawbacks. The application of positive end-expiratory pressure may be poorly tolerated and induce barotrauma. Fluid infusion carries the risk of fluid overload. Adminis- tration of colloids or crystalloids may decrease haemoglobin levels so that D0 2 may not increase. On the other hand, erythrocyte transfusions carry their own risks of transmitted infectious diseases or acute allergic reactions. Blood transfusions may also be associated with a decrease in cardiac output so that the increase in D0 2 may be limited. Vaso- dilating therapy could induce hypotension in un- stable patients or worsen gas exchange in patients with respiratory failure. Dobutamine administration is particularly con- venient to study the V0 2/D0 2 relationship in critically ill patients because it has no deleterious effects on arterial pressure or blood oxygenation and its effects are easily and fully reversible [3, 4]. We observed that a dobutamine infusion of 5 Jigmin - 1 kg - 1 in patients with sepsis or cardiac Key words: adrenergic agenu, cardiac output, cell metabolism, oxygen uptake. vasodilating agenu. AbbreviatioM: 00,. oxygen delivery; LVET, left ventricular ejection time; SpO,. arterial saturation; VCO" CO, production; VO" oxygen consumption. Correspondence: Prof. Jean-Louis Vintent, Department of Intensive Care. Erasme University Hospital. Route de Lennik 808. 6-1070 Brussels. Belgium.