Mechanism of pain caused by the nerve-root tension test in patients with sciatica.

We describe 2 instances where sciatic nerve block prevented pain in the sciatic nerve distribution caused by the nerve-root tension test in patients with radiculopathy. We hypothesize that antidromic activation of nociceptors from the injured root is a mechanism underlying sciatica.

Sympathetic blockade increases tactile sensitivity.

To determine whether tactile sensitivity of the normal skin is altered by suppression of sympathetic efferent activity, the effect of stellate ganglion block and epidural sympathetic block on touch threshold was studied. The study was performed on ten individuals with various chronic pain syndromes. Tactile sensitivity was measured in the normal skin area with the use of von Frey filaments and a two-alternative forced-choice procedure with a staircase presentation of touch stimuli. With stellate ganglion block, touch threshold decreased on the side of the block by 48.8 +/- 8.% (P = 0.002) without any significant change in the threshold on the healthy, nonblocked side (P = 0.003 for the difference between the sides). With epidural sympathetic block, touch threshold decreased to the same extent on the diseased and healthy sides, which were both affected by the block (46.2 +/- 11.4%, P = 0.027 and 47.7 +/- 12.5%, P = 0.032, respectively). The results show that sympathetic blockade increases tactile sensitivity. They also suggest that sympathetic efferent activity modulates the function of tactile receptors. It is hypothesized that the sympathetic modulation makes tactile receptors less sensitive to touch, less specific, and probably more prone to code tactile stimuli in such a way that the brain recognizes this code as pain.

Barbiturates inhibit stress-induced analgesia.

The effect of pentobarbitone and thiopentone on stress-induced analgesia was studied in 40 male Sprague-Dawley rats. Antinociception was determined by measuring motor reaction threshold to the noxious pressure on the tail with the use of an "Analgesymeter." Stress was induced by placement of a clamp on the hind paw. The stress procedure was found to cause an increase in reaction threshold, which was partially suppressed by naloxone 0.5 mg X kg-1. Pentobarbitone in a subanaesthetic dose of 25 mg X kg-1, SC, almost completely abolished the stress-induced increase in the reaction threshold (an increase in reaction threshold from 329 +/- 33 g to 486 +/- 62 g in control group, and from 250 +/- 26 g to 273 +/- 35 g in pentobarbitone group, p less than 0.02 for the difference in the threshold changes). Thiopentone used in a dose of 25 mg X kg-1, IV, caused a loss of the righting reflex for 37 +/- 10 minutes; stress procedure applied ten minutes after regaining the righting reflex did not cause any increase in the reaction threshold (with an increase in the reaction threshold in control group from 355 +/- 50 g to 540 +/- 26 g, p less than 0.001 for the difference between the groups). The results suggest that the barbiturates in subanaesthetic doses inhibit stress-induced analgesia. Thiopentone used in an anaesthetic dose has the potential for inhibition of stress-induced analgesia in the period of recovery from anaesthesia.

Blood microaggregates and ultrafilters.

The report presents three studies of post-traumatic pulmonary insufficiency (PTPI). In the first no significant pulmonary hemodynamic or ventilatory changes in severely shocked baboons resuscitated with shed fresh blood or stored blood were observed over 48 or 84 hours. Second, a post-mortem study of patients receving more than 5 units of blood within 24 hours of death showed sme microemboli in the lungs in about two thirds. Patients with multiple microthrombi had received an average of 20.6 units of blood; patients with some or no microemboli 15.5 and 6.3, respectively. Third in a review of the respiratory complications of 153 multiple-trauma patients, it was shown that the formerly severe problems with PTPI were now well managed clinically, that persistent respiratory failure was now occurring much later after injury, and occurred almost exclusively in patients with sepsis. Relation of the above data to previous reports in the literature led to the conclusion that the clinical significance of microaggregates in stored blood, if any, is low, and that ultrafiltration to remove microemboli only makes sense if it does not impede the rate of blood infusion and does not increase cost.

Oxygen consumption changes with stored blood infusions.

Stored blood contains microaggregates, often implicated in the pathogenesis of post-traumatic pulmonary insufficiency. This study was an attempt to further elucidate the effect of autologous stored, filtered and non-filtered blood infusions and homologous stored and fresh blood infusions on pulmonary function and hemodynamics. Inconsistent changes in pulmonary hemodynamics and blood oxygenation were noted. The one significant finding was an increase in oxygen consumption, which occurred with unfiltered autologous or homologous blood but not with fresh or filtered blood. Since an increased oxygen consumption results in an oxygen demand which is difficult to meet in the face of multiple other injuries, it is conceivable that this observation implicates massive stored blood transfusion as a major contributing factor in the development of so-called irreversible shock.