Abstract
As pain is the subjective sensation itself, a number of difficulties exist in the objective and scientific study of this phenomenon. However, when pain evoked by various degrees of given stimulations is expressed quantitatively, there is a specific relationship observed between the stimulation intensity and the pain sensation magnitude.
The author has attempted to quantitatively compare the changes that occur in pain sensation with changes in nitrous oxide concentration when electric dental stimulation is given under conditions of step-wise altering the pain threshold at specific time intervals in order to investigate the mechanism of nitrous oxide anesthesia via pain by determining pain electrophysiologically and objectively.
Ten adult male volunteers were subjected to electric dental stimulation under various concentrations of nitrous oxide for measurement of somatosensory evoked potentials (SEP) to quantitatively determine the relationship between concentrations of nitrous oxide and pain sensation. The following results were obtained.
(1) In SEP between 50 msec and 500 msec following stimulation, negative-positive-negativepositive-negative latencies were observed in all subjects, and the mean latencies were N 68, p98, N 148, p260 and N 360, respectively.
(2) Upon comparison between nitrous oxide concentrations and the amplitude of SEP, the most significant amplitude decrease was observed at N 150-P260. As compared with the room air, graded reductions in the amplitude of SEP were noted at pre-15% and 30% nitrous oxide, particularly in the latter where the reduction was statistically significant (P>0.001). Furthermore, the amplitude of SEP began increasing with post-15% nitrous oxide, and the changes at N 150-P 260 correlated with the changes in nitrous oxide concentrations.
(3) 30% nitrous oxide significantly delayed all elements of SEP latencies, while 15% nitrous oxide caused significant increases in the early components of N 70, p100 and N 150, and tended to increase other components.
(4) 100% oxygen significantly increased SEP amplitude in N 70-P 100, and tended to increase other elements.
(5) With 100% oxygen, SEP latencies were significantly faster at N 360 but three were no changes in the early components.
(6) Values of pain scale either decreased or increased at intervals as in the SEP amplitude; however, there was no significant difference between these two parameters.
The results as described above suggested the possibility of SEP as a useful index for determination of the optimum depth of nitrous oxide anesthesia.
