Restoring arterial pressure with norepinephrine improves muscle tissue oxygenation assessed by near-infrared spectroscopy in severely hypotensive septic patients

Abstract

To examine the consequences of administration of norepinephrine on muscle tissue oxygenation in severely hypotensive septic shock patients. This was a prospective observational study conducted in a medical intensive care unit of a university hospital. We included 28 septic shock patients that received early volume resuscitation. All were eligible for receiving norepinephrine because of life-threatening hypotension and low diastolic arterial pressure. Muscle tissue oxygen saturation (StO₂) and its changes during a vascular occlusion test were measured at the level of the thenar eminence using a near-infrared spectroscopy (NIRS) device. Transpulmonary thermodilution cardiac index (CI) and NIRS-derived variables were obtained before and after the mean arterial pressure (MAP) was increased by norepinephrine. The baseline StO₂ and the vascular occlusion test-derived variables of 17 healthy volunteers were measured and served as controls. In healthy volunteers, StO₂ ranged between 75 and 90% and StO₂ recovery slopes ranged between 1.5 and 3.4%/s. Administration of norepinephrine, which was associated with an increase in MAP from 54 ± 8 to 77 ± 9 mmHg (p < 0.05), also induced increases in CI from 3.14 ± 1.03 to 3.61 ± 1.28 L/min/m² (p < 0.05), in StO₂ from 75 ± 9 to 78 ± 9% (p < 0.05) and in StO₂ recovery slope from 1.0 ± 0.6 to 1.5 ± 0.7%/s (p < 0.05). Norepinephrine administration aimed at achieving a MAP higher than 65 mmHg in septic shock patients with life-threatening hypotension resulted in improvement of NIRS variables measured at the level of the thenar eminence.