Mesenteric blood flow, glucose absorption and blood pressure responses to small intestinal glucose in critically ill patients older than 65 years

Purpose: To compare nutrient-stimulated changes in superior mesenteric artery (SMA) blood flow, glucose absorption and glycaemia in individuals older than 65 years with, and without, critical illness. Methods: Following a 1-h 'observation' period (t ₀-t ₆₀), 0.9 % saline and glucose (1 kcal/ml) were infused directly into the small intestine at 2 ml/min between t ₆₀-t ₁₂₀, and t ₁₂₀-t ₁₈₀, respectively. SMA blood flow was measured using Doppler ultrasonography at t ₆₀ (fasting), t ₉₀ and t ₁₅₀ and is presented as raw values and nutrient-stimulated increment from baseline (Δ). Glucose absorption was evaluated using serum 3-O-methylglucose (3-OMG) concentrations during, and for 1 h after, the glucose infusion (i.e. t ₁₂₀-t ₁₈₀ and t ₁₂₀-t ₂₄₀). Mean arterial pressure was recorded between t ₆₀-t ₂₄₀. Data are presented as median (25th, 75th percentile). Results: Eleven mechanically ventilated critically ill patients [age 75 (69, 79) years] and nine healthy volunteers [70 (68, 77) years] were studied. The magnitude of the nutrient-stimulated increase in SMA flow was markedly less in the critically ill when compared with healthy subjects [Δt ₁₅₀: patients 115 (-138, 367) versus health 836 (618, 1,054) ml/min; P = 0.001]. In patients, glucose absorption was reduced during, and for 1 h after, the glucose infusion when compared with health [AUC_120-180: 4.571 (2.591, 6.551) versus 11.307 (8.447, 14.167) mmol/l min; P < 0.001 and AUC_120-240: 26.5 (17.7, 35.3) versus 40.6 (31.7, 49.4) mmol/l min; P = 0.031]. A close relationship between the nutrient-stimulated increment in SMA flow and glucose absorption was evident (3-OMG AUC_120-180 and â̂†SMA flow at t ₁₅₀: r ² = 0.29; P < 0.05). Conclusions: In critically ill patients aged >65 years, stimulation of SMA flow by small intestinal glucose infusion may be attenuated, which could account for the reduction in glucose absorption.