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Respiratory effects of regional anesthesia during acute pain
1Baltimore Veterans Affairs Medical Center, University of Maryland.
Background And Objectives:
It is commonly thought that pain stimulates respiration. The goal of this study was to determine any effect on ventilation caused by acute pain in patients with upper extremity injuries by measuring CO2-response curves before and after regional anesthesia.
Methods:
Four patient volunteers refrained from taking analgesic medications during the study period. Visual analogue scale (VAS) pain scores (10 cm scale), resting ventilation and P(ET)CO2, and steady-state, CO2-response curves (4% and 7% inspired CO2) were determined just before and after axillary block anesthesia.
Results:
Axillary block anesthesia reduced VAS pain scores from 7.1 +/- 1.1 to 0.7 +/- 0.5 (p < 0.05). Resting ventilation and P(ET)CO2 were unchanged. CO2-response curve slopes decreased from 1.84 +/- 0.54 to 1.40 +/- 0.58 l/min-1.mm Hg-1 (p < 0.05), and the curves were displaced 3.2 +/- 1.2 mm Hg to the right at 25 l/min-1 VE (p < 0.05).
Conclusions:
Other causes for the respiratory changes observed are discussed. It is concluded that acute pain stimulates respiration as measured by the steady-state, CO2-response method and that relief of acute pain results in a decrease in CO2-mediated ventilatory drive. More research is needed using both experimental pain models and patients with chronic pain.