Background and Aims To evaluate the influence of bupivacaine baricity and fentanyl on quality of low-dose spinal anesthesia in knee arthroscopy.

Methods The research included patients (BMI>25), who underwent short-term knee surgery under low-dose spinal anesthesia. 3 groups formed: 7 mg/165cm(±1mg/5cm) isobaric bupivacaine +10µg fentanyl intrathecally (IF group); HF – 7 mg/165cm(±1mg/5cm) hyperbaric bupivacaine +10µg fentanyl; H – 7 mg/165cm(±1mg/5cm) hyperbaric bupivacaine alone. Groups compared for sensory/motor blockade extension and duration, haemodynamics, complications, pain-satisfaction rates.

Results The highest superficial[Th7] and deep[Th8-12] sensory blockade levels of operated limb at 60th min recorded in IF and HF groups. Lower sensory blockades[Th9; L1] detected in H group, compared with HF (p=0.003). Shorter (p<0.0001) sensory blockade caused by isobaric bupivacaine (-137.5 min), compared to hyperbaric with fentanyl. Lasting sensory blockade (+80 min) recorded in HF vs H group (p<0.0001). The motor blockade in groups HF and H was deeper (Bromage3), but only Bromage2 in IF group with shorter duration (-122 min vs HF; -59.5 min vs H (p<0.0001)). On the opposite limb sensory blockade was higher in HF than in H group[Th9 vs L4] (p=0.006); in latter – without motor blockade. Pruritus manifested 30% with fentanyl use. One patient developed hypotension, single case of urinary retention and nausea observed (HF group).

Conclusions Isobaric bupivacaine with fentanyl in low-dose spinal anesthesia ensured shorter duration of sensory/motor blockade, but sufficient analgesia – therefore had advantages over hyperbaric bupivacaine. Co-administration of fentanyl to hyperbaric bupivacaine associated with prolonged action, effects on unoperated limb, and we would not recommend for outpatient knee arthroscopy.