Ventilatory response to intractable pain

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Abstract
Patients (52) admitted to a pain relief unit, had a cannula placed in the radial artery to measure the paO2 [arterial partial pressure of O2], paCO2 and pH of arterial blood every 2 h, for periods ranging from 12-24 h. The patients were divided into 3 groups: 14 had low back pain, 21 patients had pain from cancer and 17 had pain from other causes; 20 were male and 32 were female with a mean age of 53 yr (range 16-82 yr). Mean paO2 of these groups was within normal limits. Mean paCO2 and pH for the 3 groups were, low back pain paCO2 4.1 kpa [kilopascals?], pH 7.42, others, paCO2 4.2 kpa, pH 7.42. The finding of a normal pH associated with a low paCO2 suggests that these patients were reset to a low paCO2. Treatment, most commonly nerve blocks, resulted in marked pain relief in 30 patients. Ten of these patients were available for follow-up at least 1 wk later (4 from the low back pain group, 6 from the cancer group), and in every patient, after pain relief, there was a rise in paCO2 which was statistically significant and was not accompanied by a fall in pH. Intractable pain is apparently accompanied by chronic hyperventilation. Relief of pain may be accompanied by a decrease in ventilation.