J Oral Max~llofac 49.353-358.
Surg
1991
Long-Term Memory of Acute Postsurgical Pain ALLEN L. SISK, DDS,* BOBBIE GROVER, RN,t AND DAVID E. STEFLIK,
EDDS
The long-term memory of acute postoperative pain intensity was evaluated in a population of patients who had undergone the removal of impacted third molar teeth. The results suggest a positive correlation between experienced and remembered intensities of postsurgical pain for up to 3 years after surgery. They also suggest that males and females do not differ significantly in their reports of postsurgical pain intensity, nor do they differ significantly in their memories of pain intensity. Pain recall using verbal pain descriptors was more reliable than recall with visual analog scales. Patient reports of intensity of past postsurgical acute pain, particularly those reports obtained with verbal descriptors, may be useful in the planning of treatment and in the selection and evaluation of analgesic regimens.
tant to assess the reliability of this memory. As pointed out by Reading,* reliance on the patient making retrospective comparisons may be fraught with bias. Results of recent studies show a lack of agreement about accuracy of memory of both acute and chronic pain. Hunter et al3 assessed recall of acute head pain in 16 neurosurgical patients; one group recalled pain 5 days after surgery, and the other group recalled pain 1 day after surgery and then again after 5 days. In this study, using the McGill Pain Questionnaire, there was little decay in memory of intensity or quality of acute pain over the 5-day period. Patients all performed recall while in a pain-free state. There was a subgroup of patients who remembered their pain intensity as more intense and having more affective and sensory qualities than did the other patients. High affect at the time of initial registration of memory at the time of pain may interfere with recall and exaggerate the recalled pain. Personality features also may contribute to variations in the recall of acute pain. Bond and Pearson4 reported that neurotic and extroverted women experienced more pain, communicated more symptoms, and were more willing to complain of pain than other personality groups. The sex of the patient may also be a factor in recall of pain. Females have been shown to overestimate perceived intensity of pain more than males5 This tendency of fe-
The memory of pain plays an important role in the practice of dentistry. Memory of acute pain following certain dental surgical procedures contributes to t.he reluctance of patients to seek preventive dental care. Pain memory may also result in postponement of treatment until the patient is compelled by pain from neglected or unrecognized dental disease.’ Also, patient reports of the intensity of past pain are often used in diagnosis, planning of treatment, and the selection of appropriate analgesic regimens for future surgical procedures. Patient recall of pain intensity is also used by the dentist to evaluate the success of a prescribed analgesic regimen. If recall of the level of acute pain intensity is not accurate, then retrospective evaluation of analgesic efficacy will lead to erroneous conclusions. Because many diagnostic and therapeutic decisions are affected by patient memory of pain, it is impor-
Received from the Medical College of Georgia, Augusta. * Associate Professor, Department of Oral and Maxillofacial Surgery. t Senior Staff Nurse, Department of Oral and Maxillofacial Surgery. $ Senior Research Scientist, Department of Oral Pathology. Address correspondence and reprint requests to Dr Sisk: Department of Oral and Maxillofacial Surgery, Medical College of Georgia, Augusta, GA 30912. 0 1991 geons
American
Association
of Oral
and Maxillofacial
Sur-
0278-23g1/91/4904-0006$3.00/O
353
LONG-TERM
354 males to exaggerate pain intensity may also occur during recall. As stated previously, the inability to recall accurately past acute pain may have diagnostic and therapeutic implications. Using ischemic pain as a model for acute pain and rheumatoid arthritis as a model for chronic pain, Roche and Gijsber$ compared memory of acute pain with that of surgically treated chronic pain at 7 days. Memory for acute pain was better than for chronic pain. Hunter et al3 also reported the shortterm memory of acute pain intensity was reasonably accurate, with the intensity of pain recalled more accurately than its affective qualities. Kent’ evaluated longer-term memory of acute pain in patients undergoing a variety of dental procedures in the office of a general dental practitioner. Reports of acute pain given 3 months after a dental appointment were often different from reports given immediately after the appointment. Patients with high anxiety levels tended to report greater pain intensity at 3 months than that reported immediately following their dental procedures. In addition to being affected by anxiety level, overestimation or underestimation of past pain intensity may vary depending upon the present pain state of the patient. Eich et al8 reported that patients with chronic myofascial headaches reported prior pain as being more severe when their present pain intensity was high. Patients also tended to underestimate their previously recorded levels of pain when their present pain intensity was low. Data from previous studies suggest that memory for pain can vary considerably. Variables in recall of pain include whether the pain is acute or chronic, the level of pain at time of recall, age9*” and sex of the patient, anxiety level and other emotional variables both initially and at the time of recall, and the nature of the painful event. Because of these variable aspects, resuits of studies of memory of pain are difficult to compare. No study to date has assessed the recall of acute pain intensity in a population of postsurgical dental patients who have undergone standardized surgical procedures, nor has acute pain memory been assessed beyond 3 months. The purpose of the present study was to evaluate the long-term memory of acute pain intensity in a population of patients who had undergone a standard oral surgical procedure, the removal of impacted third molar teeth. Methods Patients who had participated in two studies at the Medical College of Georgia from 5 months to more than 36 months before this study, and who had experienced no postoperative complications,
MEMORY
OF ACUTE POSTSURGICAL
PAIN
such as alveolar osteitis, were the potential subjects in this study.‘*,‘* From these 58 patients, 116 sets of postoperative pain intensity data had been collected. Each set included hourly and global intensity ratings of pain following the removal of impacted third molar teeth on one side of the mouth. The data included pain intensity assessments using four-point category rating scales (0, no pain; 1, slight pain; 2, moderate pain; 4, severe pain) and 100-mm horizontal visual analog scales (VAS). The VAS had the left end labeled as “no pain,” and the right end labeled as “pain as much as it could possibly be.” To minimize the role of reinforcement and the potential for unwanted record keeping by the patient, no patient had been made aware at the time of participation in previous studies that memory of pain intensity would be assessed. Each of 55 patients for whom a mailing address was available was sent a questionnaire to complete. A cover letter from the principal investigator and research nurse informed each potential subject that the purpose of the questionnaire was to evaluate the ability of patients to recall the greatest level of pain experienced during the time immediately following oral surgery to remove impacted teeth. Each patient who did not return the questionnaire within 2 weeks was contacted by telephone, when possible, and urged to return the questionnaire. Questionnaires returned by the post office as nondeliverable were readdressed and mailed using a current address, when a new address could be learned by telephone. Questionnaires mailed to each patient asked them to recall their maximum pain intensity during the 8 hours following each of their oral surgical procedures, and to rate this remembered pain intensity on category and VAS similar to those used in the immediate postsurgical period. Analysis of data from previous studies showed that maximum pain intensity usually occurred between 7 and 8 hours postoperatively, just before patients received a dose of a narcotic analgesic. The maximum postsurgical pain intensity recorded in the immediate postoperative period was compared with the recalled pain intensity for the same period. The strength of the relationship between actual pain intensity and recalled pain intensity was assessed using the Spearman rank correlation coefficient for ordinal data, and the Pearson product-moment correlation for interval data. In addition, demographic data and pain intensity levels of nonresponders to the survey were compared with data from responders. Case by case analyses of actual pain intensity and remembered pain intensity were performed to obtain frequency data for underrecall of pain intensity, overrecall of pain intensity, and correct recall. Overrecall was defined as a recalled pain intensity
355
SISK ET AL
that exceeded actual pain intensity by more than 10 points on the VAS. or that exceeded the rating of actual pain intensity on the category rating scale. Underrecall was defined as a recalled pain intensity that was more than 10 points lower than actual pain intensity on the VAS, or that was lower than actual pain intensity on the category rating scale. A correct recall on the VAS was defined as recalled pain intensity that differed from actual pain intensity by no more than 10 points. Data from respondents were also divided into three groups based on a tercile split on reported pain from each surgical procedure to permit caseby-case analysis of frequency of overrecall, underrecall, and correct recall versus severity of actual pain. Group I included those patients reporting mild pain (defined as 0 to 33 on the lOO-mm VAS), group II included patients reporting moderate pain (defined as 34 to 66 on the lOO-mm VAS), and group III included patients reporting severe pain (defined as 67 to 100 on the lOO-mm VAS). Data were also grouped to allow case-by-case analysis of frequency of overrecall, underrecall, and correct recall compared with the sex of the respondent. Case-by-case analysis was also performed to compare recall accuracy and the time between surgery and recall of pain intensity. Group A was defined as those patients whose recall data were obtained from 5 to 12 months after surgery, group B as those patients whose recall data were obtained between 12 months to 24 months after surgery, and group C as those patients whose recall data were collected between 24 months and 36.3 months after surgery. Results Completed questionnaires were received from 39 of 55 possible subjects, a response rate of 71%. Responses permitted analysis of 78 events of recall of surgical pain intensity. The mean age of the 39 responders was 19.30 years (SD = 4.76), and the mean age of the nonresponders was 20.75 years (SD = 3.77). Student’s t test demonstrated no significant age difference between respondents and nonrespondents (t = - 1.0786, P = .2857). Responders included 15 males (38%) and 24 females; nonresponders included 4 males and 12 females (62%). x2 Analysis showed no significant difference in sex distribution between responders and nonresponders (P = .26), although there was a tendency for fewer females to respond. A partial explanation of this lower response rate in females is that the marriage rate was relatively high in this group, last names had changed, and forwarding addresses were therefore available for females in fewer cases than males.
For the 39 responders, the means and standard deviations of experienced pain intensity from the first surgical procedures were 1.15 + 0.77 versus 1.94 + 0.85 for the 16 nonresponders (category rating scales). For the second surgical procedure reported pain intensity was 1.17 t 0.82 for responders and 1.81 ? 0.91 for nonresponders. Differences in reported pain intensity of responders versus nonresponders were analyzed using Wilcoxon sign rank tests for category rating data, and paired t tests for VAS data. Although the responders tended to have lower experienced pain intensity than nonresponders, the differences in groups are not significant (surgery 1, category rating scales, z = 1.2944, P = .1955: surgery 2, category rating scales, z = 1.78211, P = .0747; surgery 1, VAS, t = - 1.6042, P = .1310; surgery 2, VAS, t = - 1.6234, P =
.1267). For the first surgical procedures, mean maximum pain intensity reported on the category rating scale was 1.64 (SD = .80). Mean recalled maximum pain intensity was 1.51 (SD = .87). These groups were compared using Spearman’s rank order correlation analysis (r = .5872, P < .OOl). Mean maximum pain intensity reported on the VAS was 39.06 (SD = 27.48). Mean recalled pain intensity was 38.54 (SD = 28.46). Analysis was performed using Pearson’s product moment correlation (r = .5077, P < .OOl, Fig 1). For the second surgical procedures, mean maximum pain intensity reported on the category rating scale was 1.36 (SD = .89) Mean recalled maximum pain intensity was 1.22 (SD = .87). Spearman’s rank order correlation analysis showed significant correlation between actual pain and recall of pain (r = .3824, P < .05, Fig 1). Mean maximum pain intensity reported on the VAS was 27.30 (SD = 26.35). Mean recalled maximum pain intensity was 32.86 (SD = 26.29). Pearson’s analysis of VAS for the second surgery did not show significant correlation (r = .2925, P < .lO, Fig 2). Surgery
1
Sur-gery2
FIGURE 1. Maximum actual pain intensity versus recalled pain intensity, category rating scale.-, Actual;m, recalled.
356
LONG-TERM MEMORY OF ACUTE POSTSLJRGICAL PAIN
Surgery
1
Group
Surgery2
A
Group
B
Group
C 63
FIGURE 3. Percentage of underrecall, overrecall, and accurate recall of pain intensity with category rating scale for group A (5 to 12 months), group B (12 to 24 months), and group C (24 to 36 months).-, Underrecall;m, overrecall;m, accurate.
FIGURE 2. Maximum actual pain intensity versus recalled pain intensity, VAS.m, Actual;m, recalled.
Case-by-case data analysis of memory of intensity of postoperative pain with category rating scales showed that for surgery 1, 18% of subjects underrecalled pain intensity, 18% overrecalled pain intensity, and 64% had correct recall. For the second surgical procedure, 22% underrecalled pain intensity, 29% overrecalled pain intensity, and 49% had correct recall. Combining category rating data for both surgical procedures showed overall 20% underrecall, 24% overrecall, and 56% correct recall. Case-by-case data analysis of memory of intensity of postoperative pain from surgery 1 with VAS showed that 24% of subjects underrecalled pain intensity, 24% overrecalled pain intensity, and 52% had correct recall. For the second surgical procedure, 16% underrecalled, 47% overrecalled, and 37% recalled accurately. Combined VAS data from both surgical procedures showed 20% underrecall, 36% overrecall, and 44% correct recall. Forty percent of recall data (N = 31) was collected between 5 and 12 months after surgery (group A), 32% of recall data (N = 25) was collected between 12 and 24 months after surgery (group B), and 28% (N = 22) was collected between 24 months and 36.3 months after surgery (group C). Analysis of category rating scale data showed that 22% of patients in group A underrecalled their level of pain intensity, 22% overrecalled pain intensity, and 56% accurately recalled pain intensity. Visual analog scale data for group A showed 28% underrecall, 41% overrecall, and 31% accurate recall. Group B category rating scale data showed 23% underrecall, 23% overrecall, and 54% correct recall. Visual analog data for group B showed 18% underrecall, 33% overrecall, and 56% accurate recall. Category rating scale data for group C showed 16% underrecall, 21% overrecall, and 63% accurate recall. Visual analog scale data for group C showed 10% underrecall, 45% overrecall, and 45% accurate recall (Figs 3 and 4). Comparison of accuracy of pain recall to level of
intensity of postsurgical pain included data from 45 cases with mild postsurgical pain (group I), 24 cases with moderate postsurgical pain (group II), and 6 cases with severe postsurgical pain (group III). Pain was recalled as less severe than initially reported in 2% of cases in group I (2 of 45), more severe than initially reported in 47% (2 1 of 45), and accurately recalled in 49% (22 of 45). Cases in group II included 37% (9 of 24) underrecall, 2 1% (5 of 24) overrecall, and 42% (10 of 24) accurate recall. Cases in group III showed 50% underrecall (3 of 6), 33% overrecall (2 of 6), and 17% accurate recall (1 of 6, Fig 5). The mean surgical pain intensity as assessed with the category rating scale for the first surgical procedure was 1.63 (SD = .76) for males, and 1.62 (SD = .83 for females. Comparison of these data with a Mann-Whitney test showed no significant difference (U = .0260, P = .9793). Mean pain intensity for the second surgery (category rating scale) was 1.39 (SD = 90) for males and 1.30 (SD = .88) for females. The Mann-Whitney test showed no significant difference between males and females in these groups (U = .3894, P = .6970). Mean VAS scale Group
A
Group
6
Group
C
70
60
c
50
11;
a
20
10 0
FIGURE 4. Percentage of underrecall, overrecall, and accurate recall of pain intensity with VAS for group A (5 to 12 months), group B (12 to 24 months), and group C (24 to 36 months. m, Underrecakm, overrecall; @%Zl,accurate.
357
SISK ET AL
Group
I
Group
II
Group
III
60
50
0
4o
+F 30 s $ a 20
10
0
FIGURE 5. Comparison of accuracy of recall of pain intensity to the actual pain intensity reported on VAS (group I, 0 to 33: group II, 34 to 66; group III, 67 to lOO).m, Underrecall;m. overrecall; m. accurate.
pain intensity for surgery 1 was 41.26 (SD = 26.46) for males and 36.13 (SD = 29.12) for females. A t test showed no significant difference (t = .6399, P = .5240). Visual analog scale data for surgery 2 showed a mean reported pain intensity of 27.37 (SD = 27.96) for males and 25.44 (SD = 22.90) for females. Analysis with a r test showed no significant difference (t = .2752, P = .7842). Case by case analysis of accuracy of recall of pain by sex of the patient showed a possible tendency of female patients to overrecall pain when compared to male patients. Category rating scale data showed 18 cases of overrecall of pain (5 males:13 females). Visual analog scale data showed overrecall of pain in 27 cases (10 male: 17 female). xz Analysis of data showed no significant differences between male and female patients in overrecall of pain (P = .615). Discussion Results of this study suggest that there is a positive correlation between experienced and remembered intensities of acute postsurgical pain. The results also suggest that patients such as those in this study, who averaged approximately 20 years of age and who were primarily students, are able to retain accurate memory of acute pain intensity for periods of time ranging from 5 months to greater than 3 years. This long-term memory for acute pain intensity differs from the finding reported by Roy et al that pain memory is short-lived,” and from the assertation of Jones13 that pain is hard to imagine or recall due to repression of the painful event. Pain intensity memory was accurate with both a category rating scale and with a VAS for the pain of the first of two surgical procedures. For the second surgical procedure, a significant correlation between actual and recalled pain was seen with the category
rating scale, but not with the VAS. Subjects using the VAS tended to overrecall the intensity of pain experienced following the second surgical procedure; the first of the two painful events was remembered accurately. The memory of the second surgical procedure, rather than being repressed, was remembered accurately with the category rating scale and overrecalled using the VAS. The implication of Jones that forgetting of unpleasant experiences is a universal and crucial aspect of mental functioning is not supported by the results of the present study. The data from the present study support the null hypothesis that there is no significant difference in the accuracy of recall of perceived postoperative pain intensity between male and female subjects. From the data collected in this study, it also appeared that males and females did not differ significantly in their reports of postsurgical pain intensity. In fact, pain reports of females using both category rating scales and VAS showed that slightly less pain was perceived by females than males. This finding differs from Petrie’s statement’ that females tend to exaggerate perceived pain intensity. The memory of acute postoperative pain intensity associated with third molar extraction reported in the present study was reasonably accurate, similar to the memory for acute pain intensity reported in other studies.3.6,7 Data further suggest that mild and moderate levels of pain intensity are more accurately recalled than severe pain intensity. Fifty percent of the patients in this study who reported severe pain following third molar removal later recalled less pain than they actually experienced. This underrecall of severe pain would complicate any attempt to retrospectively evaluate analgesic effectiveness in this subgroup of patients. The pain assessment techniques used in this study compound the sensory and nonsensory aspects of pain, and it has been suggested that these types of scales, particularly VAS, are particularly vulnerable to memory distortion. This is a possible explanation for the more accurate pain recall shown in this study by category rating scales, which are based on verbal pain descriptors. Pain assessment and pain recall are affected by variable emotional components, which were not assessed in the present study. While patients in this study were undergoing what are usually considered threatening surgical procedures, they also were being treated in a research environment, which may differ significantly from the typical clinical setting. The results of this study suggest that postsurgical pain intensity can be recalled accurately for months to 3 years after surgery, and that there is little decay of accuracy of memory for up to 3 years. Patient
358
DISCUSSION
reports of intensity of past acute postsurgical pain, particularly those reports obtained with verbal pain descriptors, may be useful in planning of treatment, and in the selection and evaluation of analgesic regimens. References 1. Dionne RA: Pain control in dentistry: The basis for rational therapy. Compend Contin Educ 6:15, 1985 2. Reading AE: Testing pain mechanisms in persons in pain, in Wall PD, Melzack R: Textbook of Pain. New York, Churchill Livingstone, 1989. pp 269-280 3. Hunter M, Philips C, Rachman S: Memory for pain. Pain 6:35, 1979 4. Bond MR, Pearson IB: Psychological aspects of pain in women with advanced cancer of the cervix. J Psychosom Med 13:13, 1969
J Oral MaxMofac
5. Petrie A: Some psychological aspects of pain and the relief of suffering. Ann NY Acad Sci 86:13, 1960 6. Roche PA, Gijsbers K: A comparison of memory for induced ischaemic pain and chronic rheumatoid oain. Pain 25:337. 1986 _ 7. Kent G: Memory of dental pain. Pain 21: 187. 1985 8. Eich E, Reeves JL, Jaeger B, et al: Memory for pain: Relation between nast and oresent oain intensitv. Pain 23:375. 1985 . ’ . 9. Rabinowitz JC, Craik FIM, Ackerman BP: A processing re-
source account of age differences in recall. Can J Psycho1 361325,I982 10. Roy R, Thomas M, Makarenko P: Memories of pain: Comparison of “worst pain ever” experienced by senior citizens and college students. Clin J Pain 5:359, 1989 11. Sisk AL, Mosley RO, Martin RP: Comparison of preoperative and postoperative diflunisal for suppression of postoperative pain. J Oral Maxillofac Surg 47:464,1989 12. SiskAL, Grover BJ: A comparison of preoperative and postoperative naproxen sodium for suppression of postoperative pain. J Oral Maxillofac Surg (accepted) 13. Jones E: Pain. Int J Psychoanal 38:255, 1957
Surg
492X78-359, 1991
Discussion Long-Term Memory of Acute Postsurgical Pain Stephen Medical
W. Harkins, PhD College
of Virginia,
Richmond
Sisk and colleagues report that intensity of postsurgical pain can be reliably recalled for up to 3 years. Studies of memory for pain are relatively recent. Much attention has been paid to questions of whether pain is a special sense, to what happens when we feel pain, and what can be done to reduce it, but little thought has been given to the mechanism subserving the processes of memory for pain. The findings of Sisk and his associates are interesting and contrast with several studies suggesting a tendency for amplification of pain intensity during recall,1‘4 which may be the result of situational and personality factors.4Xs What is memory for pain? Where are the pains of yesteryear? The study of pain intensity represents one possible dimension of memory for pain, and even memory for pain intensity may be more complex than first apparent. Many individuals can, when properly instructed, distinguish between the experience of first (epicritic) and second (protopathic) pains.6,7 First pain is thought to be subserved by A and second pain by C fibers. First pain is a sharp, tingling, or pricking sensation that is easily localized on the skin’s surface. It tends to adapt to repeated stimulation of the same location, particularly for heat in the nociceptive range. Second pain is poorly localized within the skin surface, may have a burning and/or aching quality, and can long outlast the evoking stimulus. Second pain tends to become more intense with repeated stimulation and can evoke segmental reflexive responses in humans (Harkins, unpublished data). Given the substantial differences in qualities of first and second pain evoked in the laboratory, it is reasonable to expect that
recall of intensity for these two sensory experiences will be equally accurate. More interesting yet is the question of whether memories for these different nociceptive experiences are formed, stored, and retrieved in a similar fashion. These are questions that can be answered in the laboratory. Is it reasonable to expect that intensity of different types of pain are recalled equally well? Certainly, there are considerable differences between types of clinical pain. Experimental pain produced under controlled conditions by brief, noxious stimuli may share some properties with certain types of acute procedures that produce pain (eg, inoculation or injections), but these pains, although sharing temporal characteristics of brevity, certainly can have quite different meanings to the individual. That experimental pain, brief procedural pain, postsurgical pain, pain caused by disease or illness (acute myocardial infarct, kidney stone), recurrent pain (eg, arthritis, headache, sickle cell trait), and chronic pains differ on multiple dimensions makes the study of memory of pain complex. The differences between types of pain will influence memory for intensity as well as memory for quality and suffering. The importance of memory of pain has been basically ignored and Sisk et al are to be commended for drawing our attention to the topic. They appear to realize that there are many types of pain and there is no necessary reason to expect that memory processes are the same for each type of “sensory” event. Perhaps it is appropriate for researchers interested in the basic processes of memory to begin collaborating with clinicians and researchers aware of pain mechanisms and the factors influencing individual variablity of response to different types of painful experiences. We know a considerable amount about verbal memory and about nonverbal memory processes involving the auditory and visual modalities. Procedures for study of
Surg
1991
Long-Term Memory of Acute Postsurgical Pain ALLEN L. SISK, DDS,* BOBBIE GROVER, RN,t AND DAVID E. STEFLIK,
EDDS
The long-term memory of acute postoperative pain intensity was evaluated in a population of patients who had undergone the removal of impacted third molar teeth. The results suggest a positive correlation between experienced and remembered intensities of postsurgical pain for up to 3 years after surgery. They also suggest that males and females do not differ significantly in their reports of postsurgical pain intensity, nor do they differ significantly in their memories of pain intensity. Pain recall using verbal pain descriptors was more reliable than recall with visual analog scales. Patient reports of intensity of past postsurgical acute pain, particularly those reports obtained with verbal descriptors, may be useful in the planning of treatment and in the selection and evaluation of analgesic regimens.
tant to assess the reliability of this memory. As pointed out by Reading,* reliance on the patient making retrospective comparisons may be fraught with bias. Results of recent studies show a lack of agreement about accuracy of memory of both acute and chronic pain. Hunter et al3 assessed recall of acute head pain in 16 neurosurgical patients; one group recalled pain 5 days after surgery, and the other group recalled pain 1 day after surgery and then again after 5 days. In this study, using the McGill Pain Questionnaire, there was little decay in memory of intensity or quality of acute pain over the 5-day period. Patients all performed recall while in a pain-free state. There was a subgroup of patients who remembered their pain intensity as more intense and having more affective and sensory qualities than did the other patients. High affect at the time of initial registration of memory at the time of pain may interfere with recall and exaggerate the recalled pain. Personality features also may contribute to variations in the recall of acute pain. Bond and Pearson4 reported that neurotic and extroverted women experienced more pain, communicated more symptoms, and were more willing to complain of pain than other personality groups. The sex of the patient may also be a factor in recall of pain. Females have been shown to overestimate perceived intensity of pain more than males5 This tendency of fe-
The memory of pain plays an important role in the practice of dentistry. Memory of acute pain following certain dental surgical procedures contributes to t.he reluctance of patients to seek preventive dental care. Pain memory may also result in postponement of treatment until the patient is compelled by pain from neglected or unrecognized dental disease.’ Also, patient reports of the intensity of past pain are often used in diagnosis, planning of treatment, and the selection of appropriate analgesic regimens for future surgical procedures. Patient recall of pain intensity is also used by the dentist to evaluate the success of a prescribed analgesic regimen. If recall of the level of acute pain intensity is not accurate, then retrospective evaluation of analgesic efficacy will lead to erroneous conclusions. Because many diagnostic and therapeutic decisions are affected by patient memory of pain, it is impor-
Received from the Medical College of Georgia, Augusta. * Associate Professor, Department of Oral and Maxillofacial Surgery. t Senior Staff Nurse, Department of Oral and Maxillofacial Surgery. $ Senior Research Scientist, Department of Oral Pathology. Address correspondence and reprint requests to Dr Sisk: Department of Oral and Maxillofacial Surgery, Medical College of Georgia, Augusta, GA 30912. 0 1991 geons
American
Association
of Oral
and Maxillofacial
Sur-
0278-23g1/91/4904-0006$3.00/O
353
LONG-TERM
354 males to exaggerate pain intensity may also occur during recall. As stated previously, the inability to recall accurately past acute pain may have diagnostic and therapeutic implications. Using ischemic pain as a model for acute pain and rheumatoid arthritis as a model for chronic pain, Roche and Gijsber$ compared memory of acute pain with that of surgically treated chronic pain at 7 days. Memory for acute pain was better than for chronic pain. Hunter et al3 also reported the shortterm memory of acute pain intensity was reasonably accurate, with the intensity of pain recalled more accurately than its affective qualities. Kent’ evaluated longer-term memory of acute pain in patients undergoing a variety of dental procedures in the office of a general dental practitioner. Reports of acute pain given 3 months after a dental appointment were often different from reports given immediately after the appointment. Patients with high anxiety levels tended to report greater pain intensity at 3 months than that reported immediately following their dental procedures. In addition to being affected by anxiety level, overestimation or underestimation of past pain intensity may vary depending upon the present pain state of the patient. Eich et al8 reported that patients with chronic myofascial headaches reported prior pain as being more severe when their present pain intensity was high. Patients also tended to underestimate their previously recorded levels of pain when their present pain intensity was low. Data from previous studies suggest that memory for pain can vary considerably. Variables in recall of pain include whether the pain is acute or chronic, the level of pain at time of recall, age9*” and sex of the patient, anxiety level and other emotional variables both initially and at the time of recall, and the nature of the painful event. Because of these variable aspects, resuits of studies of memory of pain are difficult to compare. No study to date has assessed the recall of acute pain intensity in a population of postsurgical dental patients who have undergone standardized surgical procedures, nor has acute pain memory been assessed beyond 3 months. The purpose of the present study was to evaluate the long-term memory of acute pain intensity in a population of patients who had undergone a standard oral surgical procedure, the removal of impacted third molar teeth. Methods Patients who had participated in two studies at the Medical College of Georgia from 5 months to more than 36 months before this study, and who had experienced no postoperative complications,
MEMORY
OF ACUTE POSTSURGICAL
PAIN
such as alveolar osteitis, were the potential subjects in this study.‘*,‘* From these 58 patients, 116 sets of postoperative pain intensity data had been collected. Each set included hourly and global intensity ratings of pain following the removal of impacted third molar teeth on one side of the mouth. The data included pain intensity assessments using four-point category rating scales (0, no pain; 1, slight pain; 2, moderate pain; 4, severe pain) and 100-mm horizontal visual analog scales (VAS). The VAS had the left end labeled as “no pain,” and the right end labeled as “pain as much as it could possibly be.” To minimize the role of reinforcement and the potential for unwanted record keeping by the patient, no patient had been made aware at the time of participation in previous studies that memory of pain intensity would be assessed. Each of 55 patients for whom a mailing address was available was sent a questionnaire to complete. A cover letter from the principal investigator and research nurse informed each potential subject that the purpose of the questionnaire was to evaluate the ability of patients to recall the greatest level of pain experienced during the time immediately following oral surgery to remove impacted teeth. Each patient who did not return the questionnaire within 2 weeks was contacted by telephone, when possible, and urged to return the questionnaire. Questionnaires returned by the post office as nondeliverable were readdressed and mailed using a current address, when a new address could be learned by telephone. Questionnaires mailed to each patient asked them to recall their maximum pain intensity during the 8 hours following each of their oral surgical procedures, and to rate this remembered pain intensity on category and VAS similar to those used in the immediate postsurgical period. Analysis of data from previous studies showed that maximum pain intensity usually occurred between 7 and 8 hours postoperatively, just before patients received a dose of a narcotic analgesic. The maximum postsurgical pain intensity recorded in the immediate postoperative period was compared with the recalled pain intensity for the same period. The strength of the relationship between actual pain intensity and recalled pain intensity was assessed using the Spearman rank correlation coefficient for ordinal data, and the Pearson product-moment correlation for interval data. In addition, demographic data and pain intensity levels of nonresponders to the survey were compared with data from responders. Case by case analyses of actual pain intensity and remembered pain intensity were performed to obtain frequency data for underrecall of pain intensity, overrecall of pain intensity, and correct recall. Overrecall was defined as a recalled pain intensity
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that exceeded actual pain intensity by more than 10 points on the VAS. or that exceeded the rating of actual pain intensity on the category rating scale. Underrecall was defined as a recalled pain intensity that was more than 10 points lower than actual pain intensity on the VAS, or that was lower than actual pain intensity on the category rating scale. A correct recall on the VAS was defined as recalled pain intensity that differed from actual pain intensity by no more than 10 points. Data from respondents were also divided into three groups based on a tercile split on reported pain from each surgical procedure to permit caseby-case analysis of frequency of overrecall, underrecall, and correct recall versus severity of actual pain. Group I included those patients reporting mild pain (defined as 0 to 33 on the lOO-mm VAS), group II included patients reporting moderate pain (defined as 34 to 66 on the lOO-mm VAS), and group III included patients reporting severe pain (defined as 67 to 100 on the lOO-mm VAS). Data were also grouped to allow case-by-case analysis of frequency of overrecall, underrecall, and correct recall compared with the sex of the respondent. Case-by-case analysis was also performed to compare recall accuracy and the time between surgery and recall of pain intensity. Group A was defined as those patients whose recall data were obtained from 5 to 12 months after surgery, group B as those patients whose recall data were obtained between 12 months to 24 months after surgery, and group C as those patients whose recall data were collected between 24 months and 36.3 months after surgery. Results Completed questionnaires were received from 39 of 55 possible subjects, a response rate of 71%. Responses permitted analysis of 78 events of recall of surgical pain intensity. The mean age of the 39 responders was 19.30 years (SD = 4.76), and the mean age of the nonresponders was 20.75 years (SD = 3.77). Student’s t test demonstrated no significant age difference between respondents and nonrespondents (t = - 1.0786, P = .2857). Responders included 15 males (38%) and 24 females; nonresponders included 4 males and 12 females (62%). x2 Analysis showed no significant difference in sex distribution between responders and nonresponders (P = .26), although there was a tendency for fewer females to respond. A partial explanation of this lower response rate in females is that the marriage rate was relatively high in this group, last names had changed, and forwarding addresses were therefore available for females in fewer cases than males.
For the 39 responders, the means and standard deviations of experienced pain intensity from the first surgical procedures were 1.15 + 0.77 versus 1.94 + 0.85 for the 16 nonresponders (category rating scales). For the second surgical procedure reported pain intensity was 1.17 t 0.82 for responders and 1.81 ? 0.91 for nonresponders. Differences in reported pain intensity of responders versus nonresponders were analyzed using Wilcoxon sign rank tests for category rating data, and paired t tests for VAS data. Although the responders tended to have lower experienced pain intensity than nonresponders, the differences in groups are not significant (surgery 1, category rating scales, z = 1.2944, P = .1955: surgery 2, category rating scales, z = 1.78211, P = .0747; surgery 1, VAS, t = - 1.6042, P = .1310; surgery 2, VAS, t = - 1.6234, P =
.1267). For the first surgical procedures, mean maximum pain intensity reported on the category rating scale was 1.64 (SD = .80). Mean recalled maximum pain intensity was 1.51 (SD = .87). These groups were compared using Spearman’s rank order correlation analysis (r = .5872, P < .OOl). Mean maximum pain intensity reported on the VAS was 39.06 (SD = 27.48). Mean recalled pain intensity was 38.54 (SD = 28.46). Analysis was performed using Pearson’s product moment correlation (r = .5077, P < .OOl, Fig 1). For the second surgical procedures, mean maximum pain intensity reported on the category rating scale was 1.36 (SD = .89) Mean recalled maximum pain intensity was 1.22 (SD = .87). Spearman’s rank order correlation analysis showed significant correlation between actual pain and recall of pain (r = .3824, P < .05, Fig 1). Mean maximum pain intensity reported on the VAS was 27.30 (SD = 26.35). Mean recalled maximum pain intensity was 32.86 (SD = 26.29). Pearson’s analysis of VAS for the second surgery did not show significant correlation (r = .2925, P < .lO, Fig 2). Surgery
1
Sur-gery2
FIGURE 1. Maximum actual pain intensity versus recalled pain intensity, category rating scale.-, Actual;m, recalled.
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Surgery
1
Group
Surgery2
A
Group
B
Group
C 63
FIGURE 3. Percentage of underrecall, overrecall, and accurate recall of pain intensity with category rating scale for group A (5 to 12 months), group B (12 to 24 months), and group C (24 to 36 months).-, Underrecall;m, overrecall;m, accurate.
FIGURE 2. Maximum actual pain intensity versus recalled pain intensity, VAS.m, Actual;m, recalled.
Case-by-case data analysis of memory of intensity of postoperative pain with category rating scales showed that for surgery 1, 18% of subjects underrecalled pain intensity, 18% overrecalled pain intensity, and 64% had correct recall. For the second surgical procedure, 22% underrecalled pain intensity, 29% overrecalled pain intensity, and 49% had correct recall. Combining category rating data for both surgical procedures showed overall 20% underrecall, 24% overrecall, and 56% correct recall. Case-by-case data analysis of memory of intensity of postoperative pain from surgery 1 with VAS showed that 24% of subjects underrecalled pain intensity, 24% overrecalled pain intensity, and 52% had correct recall. For the second surgical procedure, 16% underrecalled, 47% overrecalled, and 37% recalled accurately. Combined VAS data from both surgical procedures showed 20% underrecall, 36% overrecall, and 44% correct recall. Forty percent of recall data (N = 31) was collected between 5 and 12 months after surgery (group A), 32% of recall data (N = 25) was collected between 12 and 24 months after surgery (group B), and 28% (N = 22) was collected between 24 months and 36.3 months after surgery (group C). Analysis of category rating scale data showed that 22% of patients in group A underrecalled their level of pain intensity, 22% overrecalled pain intensity, and 56% accurately recalled pain intensity. Visual analog scale data for group A showed 28% underrecall, 41% overrecall, and 31% accurate recall. Group B category rating scale data showed 23% underrecall, 23% overrecall, and 54% correct recall. Visual analog data for group B showed 18% underrecall, 33% overrecall, and 56% accurate recall. Category rating scale data for group C showed 16% underrecall, 21% overrecall, and 63% accurate recall. Visual analog scale data for group C showed 10% underrecall, 45% overrecall, and 45% accurate recall (Figs 3 and 4). Comparison of accuracy of pain recall to level of
intensity of postsurgical pain included data from 45 cases with mild postsurgical pain (group I), 24 cases with moderate postsurgical pain (group II), and 6 cases with severe postsurgical pain (group III). Pain was recalled as less severe than initially reported in 2% of cases in group I (2 of 45), more severe than initially reported in 47% (2 1 of 45), and accurately recalled in 49% (22 of 45). Cases in group II included 37% (9 of 24) underrecall, 2 1% (5 of 24) overrecall, and 42% (10 of 24) accurate recall. Cases in group III showed 50% underrecall (3 of 6), 33% overrecall (2 of 6), and 17% accurate recall (1 of 6, Fig 5). The mean surgical pain intensity as assessed with the category rating scale for the first surgical procedure was 1.63 (SD = .76) for males, and 1.62 (SD = .83 for females. Comparison of these data with a Mann-Whitney test showed no significant difference (U = .0260, P = .9793). Mean pain intensity for the second surgery (category rating scale) was 1.39 (SD = 90) for males and 1.30 (SD = .88) for females. The Mann-Whitney test showed no significant difference between males and females in these groups (U = .3894, P = .6970). Mean VAS scale Group
A
Group
6
Group
C
70
60
c
50
11;
a
20
10 0
FIGURE 4. Percentage of underrecall, overrecall, and accurate recall of pain intensity with VAS for group A (5 to 12 months), group B (12 to 24 months), and group C (24 to 36 months. m, Underrecakm, overrecall; @%Zl,accurate.
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Group
I
Group
II
Group
III
60
50
0
4o
+F 30 s $ a 20
10
0
FIGURE 5. Comparison of accuracy of recall of pain intensity to the actual pain intensity reported on VAS (group I, 0 to 33: group II, 34 to 66; group III, 67 to lOO).m, Underrecall;m. overrecall; m. accurate.
pain intensity for surgery 1 was 41.26 (SD = 26.46) for males and 36.13 (SD = 29.12) for females. A t test showed no significant difference (t = .6399, P = .5240). Visual analog scale data for surgery 2 showed a mean reported pain intensity of 27.37 (SD = 27.96) for males and 25.44 (SD = 22.90) for females. Analysis with a r test showed no significant difference (t = .2752, P = .7842). Case by case analysis of accuracy of recall of pain by sex of the patient showed a possible tendency of female patients to overrecall pain when compared to male patients. Category rating scale data showed 18 cases of overrecall of pain (5 males:13 females). Visual analog scale data showed overrecall of pain in 27 cases (10 male: 17 female). xz Analysis of data showed no significant differences between male and female patients in overrecall of pain (P = .615). Discussion Results of this study suggest that there is a positive correlation between experienced and remembered intensities of acute postsurgical pain. The results also suggest that patients such as those in this study, who averaged approximately 20 years of age and who were primarily students, are able to retain accurate memory of acute pain intensity for periods of time ranging from 5 months to greater than 3 years. This long-term memory for acute pain intensity differs from the finding reported by Roy et al that pain memory is short-lived,” and from the assertation of Jones13 that pain is hard to imagine or recall due to repression of the painful event. Pain intensity memory was accurate with both a category rating scale and with a VAS for the pain of the first of two surgical procedures. For the second surgical procedure, a significant correlation between actual and recalled pain was seen with the category
rating scale, but not with the VAS. Subjects using the VAS tended to overrecall the intensity of pain experienced following the second surgical procedure; the first of the two painful events was remembered accurately. The memory of the second surgical procedure, rather than being repressed, was remembered accurately with the category rating scale and overrecalled using the VAS. The implication of Jones that forgetting of unpleasant experiences is a universal and crucial aspect of mental functioning is not supported by the results of the present study. The data from the present study support the null hypothesis that there is no significant difference in the accuracy of recall of perceived postoperative pain intensity between male and female subjects. From the data collected in this study, it also appeared that males and females did not differ significantly in their reports of postsurgical pain intensity. In fact, pain reports of females using both category rating scales and VAS showed that slightly less pain was perceived by females than males. This finding differs from Petrie’s statement’ that females tend to exaggerate perceived pain intensity. The memory of acute postoperative pain intensity associated with third molar extraction reported in the present study was reasonably accurate, similar to the memory for acute pain intensity reported in other studies.3.6,7 Data further suggest that mild and moderate levels of pain intensity are more accurately recalled than severe pain intensity. Fifty percent of the patients in this study who reported severe pain following third molar removal later recalled less pain than they actually experienced. This underrecall of severe pain would complicate any attempt to retrospectively evaluate analgesic effectiveness in this subgroup of patients. The pain assessment techniques used in this study compound the sensory and nonsensory aspects of pain, and it has been suggested that these types of scales, particularly VAS, are particularly vulnerable to memory distortion. This is a possible explanation for the more accurate pain recall shown in this study by category rating scales, which are based on verbal pain descriptors. Pain assessment and pain recall are affected by variable emotional components, which were not assessed in the present study. While patients in this study were undergoing what are usually considered threatening surgical procedures, they also were being treated in a research environment, which may differ significantly from the typical clinical setting. The results of this study suggest that postsurgical pain intensity can be recalled accurately for months to 3 years after surgery, and that there is little decay of accuracy of memory for up to 3 years. Patient
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reports of intensity of past acute postsurgical pain, particularly those reports obtained with verbal pain descriptors, may be useful in planning of treatment, and in the selection and evaluation of analgesic regimens. References 1. Dionne RA: Pain control in dentistry: The basis for rational therapy. Compend Contin Educ 6:15, 1985 2. Reading AE: Testing pain mechanisms in persons in pain, in Wall PD, Melzack R: Textbook of Pain. New York, Churchill Livingstone, 1989. pp 269-280 3. Hunter M, Philips C, Rachman S: Memory for pain. Pain 6:35, 1979 4. Bond MR, Pearson IB: Psychological aspects of pain in women with advanced cancer of the cervix. J Psychosom Med 13:13, 1969
J Oral MaxMofac
5. Petrie A: Some psychological aspects of pain and the relief of suffering. Ann NY Acad Sci 86:13, 1960 6. Roche PA, Gijsbers K: A comparison of memory for induced ischaemic pain and chronic rheumatoid oain. Pain 25:337. 1986 _ 7. Kent G: Memory of dental pain. Pain 21: 187. 1985 8. Eich E, Reeves JL, Jaeger B, et al: Memory for pain: Relation between nast and oresent oain intensitv. Pain 23:375. 1985 . ’ . 9. Rabinowitz JC, Craik FIM, Ackerman BP: A processing re-
source account of age differences in recall. Can J Psycho1 361325,I982 10. Roy R, Thomas M, Makarenko P: Memories of pain: Comparison of “worst pain ever” experienced by senior citizens and college students. Clin J Pain 5:359, 1989 11. Sisk AL, Mosley RO, Martin RP: Comparison of preoperative and postoperative diflunisal for suppression of postoperative pain. J Oral Maxillofac Surg 47:464,1989 12. SiskAL, Grover BJ: A comparison of preoperative and postoperative naproxen sodium for suppression of postoperative pain. J Oral Maxillofac Surg (accepted) 13. Jones E: Pain. Int J Psychoanal 38:255, 1957
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492X78-359, 1991
Discussion Long-Term Memory of Acute Postsurgical Pain Stephen Medical
W. Harkins, PhD College
of Virginia,
Richmond
Sisk and colleagues report that intensity of postsurgical pain can be reliably recalled for up to 3 years. Studies of memory for pain are relatively recent. Much attention has been paid to questions of whether pain is a special sense, to what happens when we feel pain, and what can be done to reduce it, but little thought has been given to the mechanism subserving the processes of memory for pain. The findings of Sisk and his associates are interesting and contrast with several studies suggesting a tendency for amplification of pain intensity during recall,1‘4 which may be the result of situational and personality factors.4Xs What is memory for pain? Where are the pains of yesteryear? The study of pain intensity represents one possible dimension of memory for pain, and even memory for pain intensity may be more complex than first apparent. Many individuals can, when properly instructed, distinguish between the experience of first (epicritic) and second (protopathic) pains.6,7 First pain is thought to be subserved by A and second pain by C fibers. First pain is a sharp, tingling, or pricking sensation that is easily localized on the skin’s surface. It tends to adapt to repeated stimulation of the same location, particularly for heat in the nociceptive range. Second pain is poorly localized within the skin surface, may have a burning and/or aching quality, and can long outlast the evoking stimulus. Second pain tends to become more intense with repeated stimulation and can evoke segmental reflexive responses in humans (Harkins, unpublished data). Given the substantial differences in qualities of first and second pain evoked in the laboratory, it is reasonable to expect that
recall of intensity for these two sensory experiences will be equally accurate. More interesting yet is the question of whether memories for these different nociceptive experiences are formed, stored, and retrieved in a similar fashion. These are questions that can be answered in the laboratory. Is it reasonable to expect that intensity of different types of pain are recalled equally well? Certainly, there are considerable differences between types of clinical pain. Experimental pain produced under controlled conditions by brief, noxious stimuli may share some properties with certain types of acute procedures that produce pain (eg, inoculation or injections), but these pains, although sharing temporal characteristics of brevity, certainly can have quite different meanings to the individual. That experimental pain, brief procedural pain, postsurgical pain, pain caused by disease or illness (acute myocardial infarct, kidney stone), recurrent pain (eg, arthritis, headache, sickle cell trait), and chronic pains differ on multiple dimensions makes the study of memory of pain complex. The differences between types of pain will influence memory for intensity as well as memory for quality and suffering. The importance of memory of pain has been basically ignored and Sisk et al are to be commended for drawing our attention to the topic. They appear to realize that there are many types of pain and there is no necessary reason to expect that memory processes are the same for each type of “sensory” event. Perhaps it is appropriate for researchers interested in the basic processes of memory to begin collaborating with clinicians and researchers aware of pain mechanisms and the factors influencing individual variablity of response to different types of painful experiences. We know a considerable amount about verbal memory and about nonverbal memory processes involving the auditory and visual modalities. Procedures for study of
