High blood pressure is prevalent in obesity and in diabetes, both conditions with insulin resistance. To test whether hypertension is associated with insulin resistance independently of obesity and glucose intolerance, we measured insulin sensitivity (using the euglycemic insulin-clamp technique), glucose turnover (using [3H]glucose isotope dilution), and whole-body glucose oxidation (using indirect calorimetry) in 13 young subjects (38 +/- 2 years [+/- SEM]) with untreated essential hypertension (165 +/- 6/112 +/- 3 mm Hg), normal body weight, and normal glucose tolerance. In the postabsorptive state, all measures of glucose metabolism were normal. During steady-state euglycemic hyperinsulinemia (about 60 microU per milliliter), hepatic glucose production and lipolysis were effectively suppressed, and glucose oxidation and potassium disposal were normally stimulated. However, total insulin-induced glucose uptake was markedly impaired (3.80 +/- 0.32 vs. 6.31 +/- 0.42 mg per minute per kilogram of body weight in 11 age- and weight-matched controls, P less than 0.001). Thus, reduced nonoxidative glucose disposal (glycogen synthesis and glycolysis) accounted for virtually all the defect in overall glucose uptake (1.19 +/- 0.24 vs. 3.34 +/- 0.44 mg per minute per kilogram, P less than 0.001). Total glucose uptake was inversely related to systolic or mean blood pressure (r = 0.76 for both, P less than 0.001). These results provide preliminary evidence that essential hypertension is an insulin-resistant state. We conclude that this insulin resistance involves glucose but not lipid or potassium metabolism, is located in peripheral tissues but not the liver, is limited to nonoxidative pathways of intracellular glucose disposal, and is directly correlated with the severity of hypertension.

Indirect calorimetry is the method by which metabolic rate and substrate utilization are estimated in human beings starting from respiratory gas exchange measurements and urinary nitrogen excretion. This method is based on some models and assumptions that must be known and taken into consideration to correctly interpret the results obtained. Recent advances in technology and the availability of precise and portable metabolic carts have made this technique practical at the beside even in critically ill patients. It must be considered that, particularly in the ICU, there may be several sources of error and many technical difficulties in applying this methodology. Taking into account the relevant clinical studies related to the outcomes of critically ill patient, this article defines when the assessment of energy expenditure by indirect calorimetry may provide useful and valid information. Review of the literature suggests that the clinical application of indirect calorimetry in critically ill patients, although promising, requires further evaluation. Currently, the potential useful clinical applications of indirect calorimetry in this category of patients can be summarized as follows: (1) assessment of energy expenditure in patients who fail to adequately respond to the estimated nutritional needs; (2) assessment of energy expenditure in patients with single- or multiple-organ dysfunction who need prolonged ICU care and artificial nutritional support; (3) assessment of the effects induced by artificial nutrition on the cardiocirculatory and respiratory systems in mechanically ventilated patients with acute respiratory failure; and (4) monitoring of VO2 during weaning from mechanical ventilation.

In mechanically ventilated multiple trauma patients the energy expenditure is not correlated to the severity of injury and illness indices but is dependent on the Harris-Benedict equation in addition to heart rate and minute ventilation. Furthermore, this patient population is characterized by a moderate state of hypermetabolism, and the Harris-Benedict prediction modified with correction factors for trauma systematically overestimates the total energy expenditure.