Abstract
BackgroundIntensive care unit-acquired weakness (ICUAW) is a common complication, associated with significant morbidity. Neuromuscular electrical stimulation (NMES) has shown promise for prevention. NMES acutely affects skeletal muscle microcirculation; such effects could mediate the favorable outcomes. However, optimal current characteristics have not been defined. This study aimed to compare the effects on muscle microcirculation of a single NMES session using medium and high frequency currents.MethodsICU patients with systemic inflammatory response syndrome (SIRS) or sepsis of three to five days duration and patients with ICUAW were studied. A single 30-minute NMES session was applied to the lower limbs bilaterally using current of increasing intensity. Patients were randomly assigned to either the HF (75 Hz, pulse 400 μs, cycle 5 seconds on - 21 seconds off) or the MF (45 Hz, pulse 400 μs, cycle 5 seconds on - 12 seconds off) protocol. Peripheral microcirculation was monitored at the thenar eminence using near-infrared spectroscopy (NIRS) to obtain tissue O2 saturation (StO2); a vascular occlusion test was applied before and after the session. Local microcirculation of the vastus lateralis was also monitored using NIRS.ResultsThirty-one patients were randomized. In the HF protocol (17 patients), peripheral microcirculatory parameters were: thenar O2 consumption rate (%/minute) from 8.6 ± 2.2 to 9.9 ± 5.1 (P = 0.08), endothelial reactivity (%/second) from 2.7 ± 1.4 to 3.2 ± 1.9 (P = 0.04), vascular reserve (seconds) from 160 ± 55 to 145 ± 49 (P = 0.03). In the MF protocol: thenar O2 consumption rate (%/minute) from 8.8 ± 3.8 to 9.9 ± 3.6 (P = 0.07), endothelial reactivity (%/second) from 2.5 ± 1.4 to 3.1 ± 1.7 (P = 0.03), vascular reserve (seconds) from 163 ± 37 to 144 ± 33 (P = 0.001). Both protocols showed a similar effect. In the vastus lateralis, average muscle O2 consumption rate was 61 ± 9%/minute during the HF protocol versus 69 ± 23%/minute during the MF protocol (P = 0.5). The minimum amplitude in StO2 was 5 ± 4 units with the HF protocol versus 7 ± 4 units with the MF protocol (P = 0.3). Post-exercise, StO2 increased by 6 ± 7 units with the HF protocol versus 5 ± 4 units with the MF protocol (P = 0.6). These changes correlated well with contraction strength.ConclusionsA single NMES session affected local and systemic skeletal muscle microcirculation. Medium and high frequency currents were equally effective.
Highlights
Intensive care unit-acquired weakness (ICUAW) is a common complication, associated with significant morbidity
Exclusion criteria were age under 18 years, pregnancy, pre-existing neuromuscular disease, conditions that limit lower limb mobility, pacemakers, and presence of edema or subcutaneous fat that interfered with the application of Neuromuscular electrical stimulation (NMES) or with the assessment of the microcirculation
A total of 31 patients were included in the study (26 men, age 59 ± 11 years, with Acute Physiology and Chronic Health Evaluation Acute physiology and chronic health evaluation II (II) (APACHE II) score 18 ± 6 and Sequential Organ Failure Assessment (SOFA) score 7 ± 2 on the day of the NMES session)
Summary
Intensive care unit-acquired weakness (ICUAW) is a common complication, associated with significant morbidity. Since active mobilization is not feasible for many ICU patients, due to either their illness or sedation, neuromuscular electrical stimulation (NMES) has been proposed as an alternative method of exercise and mobilization This approach was based on clinical experience in patients with chronic obstructive pulmonary disease (COPD) [8,9] and chronic heart failure [10]. Initial application of NMES in septic patients using electrical currents with frequencies in the range of medium (45 to 50 Hz) to high (100 Hz) has shown encouraging results in preventing loss of muscle mass and preserving strength in the critically ill [11,12,13,14,15]
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