Alterations in forearm vascular reactivity in patients with septic shock

Patients with septic shock are haemodynamically unstable and suffer from vasodilation. Studying the human forearm vascular bed in patients with septic shock, we tested the hypothesis that the responses to regionally infused endothelium-(in)dependent vasodilators and vasoconstrictors are uniformly impaired. Forearm blood flow (FBF, venous occlusion plethysmography) and brachial arterial pressure were determined to calculate forearm vascular resistance (FVR) in eight consecutive sedated, mechanically ventilated patients with septic shock (APACHE II Score range 21-34, SOFA Score 11-16) and 11 healthy volunteers. Despite increased baseline FBF in patients with septic shock (6.1 (SD 1.5) ml x min(-1) x (100 ml of tissue)(-1) compared to 4.7 (1.4) in volunteers) the significant decreases in FVR seen in response to exogenous nitric oxide (nitroprusside) and acetylcholine did not differ between groups. However, compared to volunteers, mitigation of endogenous nitric oxide production by a low dose of N(G)-methyl-L-arginine acetate (L-NMMA) caused a significant increase (+6.7 mmHg x min x ml(-1)) in septic patients. Regional vasoconstriction in response to phenylephrine (FVR: +9.9 vs +30.7 mmHg x min x ml(-1) in controls) and angiotensin II (FVR: +9.0 vs +67.4 mmHg x min x ml(-1)) was markedly impaired. In contrast, vasopressin, in dosages evoking no vasoconstriction in volunteers, induced a significant increase in FVR in septic patients (+10.0 mmHg x min x ml(-1)). In the forearm of patients with septic shock, vasoconstriction by alpha1- and angiotensin II receptor agonists is selectively impaired, whereas the vasoconstrictor response to vasopressin is exaggerated. These findings exclude a generalised impairment of vasomotor activity in patients with septic shock and provide a rationale for vasopressin administration.