title: Acute microcirculatory effects of medium frequency versus high frequency neuromuscular electrical stimulation in critically ill patients - a pilot study.
abstract: BACKGROUND
  Intensive 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.
  
  
  METHODS
  ICU 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.
  
  
  RESULTS
  Thirty-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.
  
  
  CONCLUSIONS
  A single NMES session affected local and systemic skeletal muscle microcirculation. Medium and high frequency currents were equally effective.
authors.forename: Epameinondas
authors.initials: E
authors.lastname: Angelopoulos
authors.forename: Eleftherios
authors.initials: E
authors.lastname: Karatzanos
authors.forename: Stavros
authors.initials: S
authors.lastname: Dimopoulos
authors.forename: Georgios
authors.initials: G
authors.lastname: Mitsiou
authors.forename: Christos
authors.initials: C
authors.lastname: Stefanou
authors.forename: Irini
authors.initials: I
authors.lastname: Patsaki
authors.forename: Anastasia
authors.initials: A
authors.lastname: Kotanidou
authors.forename: Christina
authors.initials: C
authors.lastname: Routsi
authors.forename: George
authors.initials: G
authors.lastname: Petrikkos
authors.affiliation: First Critical Care Department, National and Kapodistrian University of Athens School of Medicine, Evangelismos General Hospital, Ypsilantou 45-47, Athens 106 75, Greece. a.icusn@gmail.com.
authors.forename: Serafeim
authors.initials: S
authors.lastname: Nanas