We conclude that a decrease in respiratory muscle strength may contribute to the decrease in FVC observed at high altitude.

Measurements of toe temperature and transcutaneous PO2 (PtcO2) have been both suggested for non-invasive assessment of peripheral blood flow in acute circulatory failure. The underlying principle of the two methods is that cutaneous vasoconstriction occurs early when tissue perfusion is altered. In 15 patients, we compared the two measurements during cardiogenic shock (27 measurements) or septic shock (29 measurements). Toe-ambiant temperature gradient and PtcO2 correlated well together (r = 0.66, p less than 0.001) especially in hyperkinetic septic shock (r = 0.79, p less than 0.001). In cardiogenic shock, toe-ambiant temperature correlated well with cardiac index (r = 0.63), stroke index (r = 0.64) and oxygen transport (r = 0.65), and these correlations were stronger than for PtcO2. In septic shock, both techniques were poor indicators of blood flow indexes but PtcO2 rather correlated with arterial pressure (r = 0.66) and left ventricular work (r = 0.66). Trend evaluation of data revealed in cardiogenic shock that the increase in toe temperature usually preceded the increase in PtcO2. Since measurement of PtcO2 is technically more complicated, correlates less well with standard hemodynamic parameters and later reflects cardiovascular improvement, it has no advantage over measurement of toe temperature in circulatory shock. In cardiogenic shock, measurements of toe temperature can reliably track cardiac output changes. In septic states, however, non-invasive assessment of skin perfusion is of limited interest.

1. Dobutamine has been used to study the relationship between oxygen consumption (VO2) and oxygen delivery (DO2) in critically ill patients, but this has led to concerns that it could consistently increase VO2 in all patients. Although a direct thermogenic effect of the catecholamine has been primarily implicated in this increase in VO2, 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 flow increases during the infusion of non-adrenergic agents. To separate the two mechanisms, we compared the effects of dobutamine with those of sodium nitroprusside on VO2/DO2 relationships in healthy volunteers. 2. Eight healthy volunteers received infusions of dobutamine at doses of 2, 4 and 6 μg min−1 kg−1 and nitroprusside at doses of 0.5, 1 and 2 μg min−1 kg−1 in an alternate order. 3. VO2 was determined by indirect calorimetry and cardiac output by electrical bioimpedance. Data were analysed by analysis of variance for repeated measurements and individual VO2/DO2 slopes were determined by linear regression. 4. VO2 increased more with dobutamine than with nitroprusside (from 138 ± 14 to 149 ± 20 ml min−1 m−2, P < 0.001, and from 131 ± 14 to 138 ± 17 ml min−1 m−2, P < 0.001, respectively). However, DO2 also increased more with dobutamine than with nitroprusside (from 531 ± 186 to 702 ± 274 ml min−1 m−2, P < 0.001, and from 523 ± 107 to 610 ± 122 ml min−1 m−2, P < 0.001, respectively). Individual VO2/DO2 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, DO2 and VO2 increased more with dobutamine than with nitroprusside in healthy volunteers. However, the VO2/DO2 slopes were similar for both substances. Thus, an increase in VO2 is not exclusively observed with catecholamines. Studies of the effects of therapeutic interventions on oxygen-derived variables should report not only changes in VO2 but also VO2/DO2 slopes.

No abstract

No abstract