A rise in pain threshold during labor: A prospective clinical trial

How can the pain sensitivity to be affected by maximal progressive exercise test during pregnancy?

The multidimensional etiology of pain may explain the beneficial effects of regular physical activity, as evidenced by increased pain tolerance. Physically active people find it easier to exert themselves, which enables them to increase their physical activity, which in turn leads to a reduction in pain. However, no study investigated the physical activity and exercise tests as modulators of pain sensitivity in pregnant women. Therefore, this study aimed to investigate the changes in pain perception in pregnant women during pregnancy, with a particular interest in the effects of maximal progressive exercise test (CPET) and self-performed physical activity (PA). Thirty-one women with an uncomplicated singleton pregnancy (aged 23-41 years; M = 31.29, SD = 4.18) were invited to participate in pain sensitivity measurements before and after CPET twice during pregnancy (with an 8-week break). We found that pregnant women had a significantly lower pain threshold after a maximal exercise test than before, regardless of whether the test was performed in the second or third trimester of pregnancy. This effect was most pronounced in women with low levels of physical activity. Second, women with high physical activity had higher pain tolerance than women with moderate and low physical activity. In addition, physical activity levels predicted changes in pain tolerance over the course of pregnancy, with negative changes in women with low physical activity and positive changes in women with moderate physical activity. Finally, these associations were not reflected in differences in the subjective pain experience.

Changes in pain perception during pregnancy after one-time maximal physical exertion and an 8-week high-intensity interval training

Background: Pain, a subjective sensation, poses a great challenge to the human body as a stressor. There is empirical evidence that moderate to intense physical activity increases pain tolerance and this may be critical during pregnancy for optimal pregnancy, fetal development, and delivery. To the best of our knowledge, it is the first study examining the changes in pain perception in pregnant women after a maximal progressive exercise test and after 8 weeks of high-intensity interval training (HIIT). Methods: Thirty-five women with uncomplicated singleton pregnancies between 13 and 28 weeks of gestation participated in the study. The HIIT intervention was developed in accordance with the recommendations and available data on HIIT during pregnancy. The maximal progressive cardiopulmonary exercise test was performed on a cycle ergometer with an electronically controlled load. Pressure pain threshold and pressure pain tolerance were measured with an algometer. Results: We found significant effects of the maximal exercise test and high-intensity interval training, such that the pregnant women had higher pain tolerance after the maximal exercise test than before and after the high-intensity interval training than the baseline. Conclusion: Our results suggest that post-exercise analgesia may be important in pregnant women and that high-intensity interval training appears to be beneficial for pregnant women to improve their pain tolerance while being obstetrically safe. Increased pain tolerance before labor could lead to better management of pain during labor and in the postpartum and lactation periods. Increasing pregnant women's awareness of this issue can improve their wellbeing and provide more comfort during labor.

Beyond Fear: Unveiling the Relationship Between Fear of Childbirth and Pharmacological Pain Relief

BACKGROUND

Pharmacological analgesia is the dominant method for pain relief in labor. Fear of childbirth (FOC) may significantly affect women's preferences for and usage of pharmacological analgesia.

AIM

This study aimed to investigate the relationship between FOC in late pregnancy and preferences for, as well as actual use of, pharmacological analgesia among nulliparous and multiparous women, accounting for confounding factors.

METHODS

A total of 1,300 women participated in the study, completing questionnaires assessing preferences for pharmacological analgesia, FOC, perception of labor pain, social support, coping styles, and demographic variables. The actual use of pharmacological analgesia was followed up. The data were analyzed using univariate and multivariate regression analyses.

RESULTS

Univariate analysis revealed that women with moderate to severe FOC had a stronger preference for pharmacological analgesia compared to those with none to mild FOC. However, multivariate analysis showed no direct association between FOC and actual usage of pharmacological analgesia. Instead, a stronger preference for pharmacological analgesia increased the likelihood of its actual usage during labor.

CONCLUSIONS

Our study underscores the effect of FOC on preferences for pharmacological analgesia and its potential influence on actual usage during labor. Healthcare providers should consider women's FOC and preferences when evaluating pain management options. Targeted interventions focusing on promoting non-pharmacological techniques should be implemented to optimize labor pain management for women, particularly nulliparous women.

The association between adverse childhood experiences and peripartal pain experience

ABSTRACT

Adverse childhood experiences (ACEs) are associated with altered ongoing and evoked pain experiences, which have scarcely been studied for the peripartum period. We aimed to investigate how ACEs affect pain experience in pregnancy and labor. For this noninterventional trial with a short-term follow-up, pregnant women were divided into a trauma group (TG) with ACEs (n = 84) and a control group (CG) without ACEs (n = 107) according to the Childhood Trauma Questionnaire. Pain experience in pregnancy and labor was recorded by self-report and the German Pain Perception Scale. Pain sensitivity prepartum and postpartum was assessed by Quantitative Sensory Testing and a paradigm of conditioned pain modulation (CPM), using pressure pain thresholds (PPTs) and a cold pressor test. The TG showed higher affective and sensory scores for back pain and a more than doubled prevalence of preexisting back pain. Pelvic pain differences were nonsignificant. The TG also exhibited increased affective scores (1.71 ± 0.15 vs 1.33 ± 0.11), but not sensory scores for labor pain during spontaneous delivery. There were no group differences in prepartum pain sensitivity. While PPTs increased through delivery in the CG (clinical CPM), and this PPT change was positively correlated with the experimental CPM (r = 0.55), this was not the case in the TG. The association of ACEs with increased peripartal pain affect and heightened risk for preexisting back pain suggest that such women deserve special care. The dissociation of impaired clinical CPM in women with ACEs and normal prepartum experimental CPM implies at least partly different mechanisms of these 2 manifestations of endogenous pain controls.

Individual Characteristics and Pain Sensitivity during Pregnancy-A Cross-Sectional Study in Pregnant and Non-Pregnant Women

The aim of the study was to describe the characteristics and factors related to pain perception in pregnant women, such as optimism, personality traits, and fear of developing COVID-19 consequences. Sixty-six pregnant women aged 23 to 42 years participated in the study, and the comparison group consisted of n = 59 non-pregnant female students aged 19 to 23 years. Pressure pain threshold and pain tolerance were measured with an algometer. To assess psychological characteristics, the Life-Orientation Test-Revised was used to assess optimism, the Fear of COVID-19 Scale was used to assess COVID-19 anxiety, and the Ten-Item Personality Inventory was applied to assess personality traits in a five-factor model. The main results of the study showed that pain tolerance was significantly lower in both dominant and non-dominant hand pregnant women than in the comparison group. The studied pregnant women had higher scores for conscientiousness, fear of COVID-19, and optimism compared with the non-pregnant women. Regression analysis showed that the variability in pain perception among pregnant women could not be explained by individual differences in personality traits, optimism, and fear of COVID-19.

Effects of non-pharmacological coping strategies for reducing labor pain: A systematic review and network meta-analysis

BACKGROUND

Facilitating the childbirth process is a global issue. Many strategies have been developed to cope with labor pain and improve the delivery experience and satisfaction of pregnant women. The results of different types of medical intervention on women's expectant pain have been varied. Therefore, this systematic review was aimed at summarizing the body of evidence regarding the effects of various non-pharmacological coping strategies for reducing labor pain.

METHODS

The review was conducted according to guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). We systematically searched the articles published between 1989 and 2020 in six electronic databases: PubMed, MEDLINE, CINAHL, WOS, PsycARTICLES, and Airiti Library, and the reference lists of the Clinical Trial Registry. Twenty studies were identified, with eight eligible studies included in the Bayesian network meta-analysis.

RESULTS

Eight studies with 713 participants were included in the meta-analysis with nine different non-pharmacological strategies for reducing labor pain. The traditional meta-analysis demonstrated that the non-pharmacological coping strategies were effective in reducing labor pain. Of these interventional strategies, the ranking probabilities analysis of the network meta-analysis suggested that the Bonapace Method may be the most effective strategy in reducing labor pain, followed by acupressure.

CONCLUSIONS

Non-pharmacological coping strategies can reduce labor pain while maintaining an effective and satisfactory delivery experience. This systematic review, by synthesizing the body of evidence, demonstrated that non-pharmacological coping strategies are effective in reducing labor pain. Furthermore, as demonstrated in the network meta-analysis, the Bonapace Method, modulating birth pain by involving the father, is the most effective non-pharmacological intervention for reducing labor pain.

Mechanisms Underlying Lumbopelvic Pain During Pregnancy: A Proposed Model

Up to 86% of pregnant women will have lumbopelvic pain during the 3rd trimester of pregnancy and women with lumbopelvic pain experience lower health-related quality of life during pregnancy than women without lumbopelvic pain. Several risk factors for pregnancy-related lumbopelvic pain have been identified and include history of low back pain, previous trauma to the back or pelvis and previous pregnancy-related pelvic girdle pain. During pregnancy, women go through several hormonal and biomechanical changes as well as neuromuscular adaptations which could explain the development of lumbopelvic pain, but this remains unclear. The aim of this article is to review the potential pregnancy-related changes and adaptations (hormonal, biomechanical and neuromuscular) that may play a role in the development of lumbopelvic pain during pregnancy. This narrative review presents different mechanisms that may explain the development of lumbopelvic pain in pregnant women. A hypotheses-driven model on how these various physiological changes potentially interact in the development of lumbopelvic pain in pregnant women is also presented. Pregnancy-related hormonal changes, characterized by an increase in relaxin, estrogen and progesterone levels, are potentially linked to ligament hyperlaxity and joint instability, thus contributing to lumbopelvic pain. In addition, biomechanical changes induced by the growing fetus, can modify posture, load sharing and mechanical stress in the lumbar and pelvic structures. Finally, neuromuscular adaptations during pregnancy include an increase in the activation of lumbopelvic muscles and a decrease in endurance of the pelvic floor muscles. Whether or not a causal link between these changes and lumbopelvic pain exists remains to be determined. This model provides a better understanding of the mechanisms behind the development of lumbopelvic pain during pregnancy to guide future research. It should allow clinicians and researchers to consider the multifactorial nature of lumbopelvic pain while taking into account the various changes and adaptations during pregnancy.

The Programmed Cell Death Ligand-1/Programmed Cell Death-1 Pathway Mediates Pregnancy-Induced Analgesia via Regulating Spinal Inflammatory Cytokines

The maternal pain threshold gradually increases during pregnancy, especially in late pregnancy. A series of mechanisms underlying pregnancy-induced analgesia have been reported. However, these mechanisms are still not completely clear, and the underlying molecular mechanisms need further investigation. We examined the relationship between the antinociceptive effect and the expression level of programmed cell death ligand-1 (PD-L1) during pregnancy and further observed the changes in pain thresholds and expression levels of cytokines in late-pregnant mice before and after blockade of PD-L1 or programmed cell death-1 (PD-1).

Non-pharmacological interventions of pain management used during labour; an exploratory descriptive qualitative study of puerperal women in Adidome Government Hospital of the Volta Region, Ghana

Background

Women have experienced labour pain over the years as various attempts have been made to effectively manage this pain. There is paucity of literature on the experiences and perceptions about labour pain management with the contemporary Ghanaian health system. This study explored the perspective of puerperal women on the use of non-pharmacological labour pain management at Adidome Government Hospital.

Methods

The study adopted an exploratory descriptive qualitative approach as data was collected through individual interviews. Informed consent was obtained from all participants who were purposely sampled until data saturation was reached on the 17th participant. Interviews were audio recorded and transcribed immediately. Thematic analysis was engaged in three interrelated stages, namely data reduction, data display, and data conclusion to analyse the transcript and field notes. Results were presented with supporting quotes from the transcripts.

Results

The women described labour pain as very severe, severe and moderate as the pain lasted more than 12 h. The various strategies adopted in managing labour pains included shouting and walking around, crying and screaming and staying calm and snapping the fingers. Other pain management strategies adopted during labour included women engaged in deep breathing exercises, chatting with other people and relatives, diversion therapy, reassurance, taking a shower, assuming side lying positions, and receiving intravenous therapy. The presence of the husband of a labouring woman during labour improved pain bearing ability.

Conclusion

It is important that midwives institute pragmatic protocols in the labour ward that ensure a relaxing atmosphere for women in labour, respond to the sensitivity and specificity of labouring women needs and when possible significant others (e.g., husband) of the labouring women could be allowed to visit. Labour wards should be made sound proof to allow women the ability to express themselves satisfactorily during labour without fear of being heard outside.

During childbirth, women have complained of severe pains as health personnel over the years keep looking for appropriate means to alleviate the pain. We therefore studied women with children less than 42 days to understand their perspective on the use of non-drug methods in relieving pain during birth. With the intention of exploring this phenomenon we had an interview with 17 women in the Adidome government hospital. The women showed that labour is a very painful experience. The methods they adopted in reducing pain included shouting, walking around the hospital, crying or screaming, staying calm and snapping the fingers. These women were generally happy with the care that was rendered by midwives. Other methods used to reduce pain were taking deep breaths, talking with a family member or friend, taking a bath, assuming a lying position and receiving intravenous infusion. Women who had their husband present during labour said it helped their pain endurance. We therefore suggested that midwives should be encouraging and supportive of women who are in labour and if possible, allow their spouses into the birth room to augment the pain adaptation ability. Also, labour wards should have sound resilient so that women can make any sound if they so wish to.

Oxytocin receptor expression in the midbrain dorsal raphe is dynamic across female reproduction in rats

Central oxytocin receptor (OTR) expression is extremely sensitive to circulating steroid hormones and OTRs influence many of the neurobehavioural adaptations associated with female reproduction (e.g., postpartum caregiving, aggression, cognition, affective responses). Changes in central OTR expression across female reproduction have often been studied, but almost all of such research has focused on the forebrain, ignoring hormone-sensitive midbrain sites such as the serotonergic dorsal raphe (DR) that are also critical for postpartum behaviours. To investigate the effects of female reproductive state on OTRs in the DR, we first used autoradiography to examine OTR binding across four female reproductive states in laboratory rats: dioestrous virgin, pregnancy day 10, the day of parturition and postpartum day 7. OTR binding in the rostral DR (but not other DR subregions) was approximately 250% higher in parturient rats compared to dioestrous virgins and dropped back down to virgin levels by postpartum day 7. Given the chemical heterogeneity of the DR, we then examined OTR expression in the three most abundant neuronal phenotypes of the DR (i.e., serotonin, GABA and dopamine) in dioestrous virgins and recently parturient females. Using dual-label immunohistochemistry and in situ hybridisation, we found that twice as many dopaminergic cells in the parturient rostral DR contained OTR immunoreactivity compared to that found in virgins. On the other hand, mothers had fewer rostral DR GABAergic cells expressing OTRs than did virgins. OTR expression in serotonin cells did not differ between the two groups. Overall, these results suggest that the rostral subregion of the midbrain DR is uniquely sensitive to oxytocin around the time of parturition, with subpopulations of cells that become more sensitive (i.e., dopamine), less sensitive (i.e., GABA) and show no change (i.e., serotonin) to this neuropeptide. This dynamic OTR signalling in the female DR may help drive the numerous behavioural changes across female reproduction that are necessary for successful motherhood.

The Need to Consider Pregnancy As a Biological Variable to Reduce Preventable Suffering Related to Pregnancy

Maternal morbidity and mortality constitute a national health crisis, and pain is a significant component of maternal morbidity. One important way to reduce maternal morbidity is to reduce the pain associated with pregnancy. Unfortunately, our understanding of how to reduce pain in women is hampered because, historically, mostly male subjects have been used in the study of pain. However, more recently, females increasingly have been included in pain research studies, and astounding differences in how males and females process pain have been uncovered. Moreover, pain in nonpregnant women differs in many ways from pain experienced by pregnant women. We argue here that to better address maternal morbidity, we must better address the pain associated with pregnancy. Furthermore, just as it is important to include both men and women in pain research to better understand pain in both sexes, conducting pain research in pregnant women is essential to finding ways to reduce pain in pregnant women.

Association of Pain Catastrophizing with Postnatal Depressive States in Nulliparous Parturients: A Prospective Study

PURPOSE

Postnatal depression (PND) is associated with maternal morbidity and socioeconomic burden. Recent studies have shown an association between pain catastrophizing, increased labor pain, and subsequent adverse postnatal adjustment; however, little is known on its role in PND development. We aimed to investigate the association between pain catastrophizing and probable PND.

METHODS

Parturients planning to undergo epidural labor analgesia were recruited. Predelivery questionnaires, including the Pain Catastrophizing Scale (PCS) and Edinburgh Postnatal Depression Scale (EPDS), were administered during early labor. A phone survey at 5- 9 weeks postdelivery was conducted to determine postdelivery EPDS and Spielberger's State-Trait-Anxiety Inventory scores. The primary outcome was a binary variable of postdelivery EPDS with cutoff of ≥10, whereas the secondary outcome was a continuous variable on increases in EPDS score.

RESULTS

Probable PND (EPDS ≥10) occurred in 10.5% (95% CI 8.0%-13.5%, 55 of 525) of women who underwent epidural labor analgesia. We found that high pain catastrophizing (PCS ≥25) was associated with increased postdelivery EPDS scores (adjusted β estimate 0.36, 95% CI 0.15-0.57; p=0.0008), but did not meet significance for increased risk of probable PND (p=0.1770). Additionally, presence of breakthrough pain during epidural analgesia (adjusted β estimate 0.24, 95% CI 0.02-0.46; p=0.0306) and lower BMI at term (adjusted β estimate -0.04, 95% CI -0.07 to -0.01; p=0.0055) were associated with increased postdelivery EPDS scores.

CONCLUSION

No significant association was found between high pain catastrophizing and probable PND; however, high predelivery pain catastrophizing, presence of breakthrough pain during epidural analgesia, and lower BMI at term were associated with increased postdelivery EPDS scores. Further research will be needed to validate this association in the context of the risk of PND development.

Labor pain in women with and without severe fear of childbirth: A population-based, longitudinal study

BACKGROUND

This prospective study aims to investigate whether severe fear of childbirth increases pain perceptions during birth and whether co-occurring maternal health and birth factors as well as length and weight of the child explain the association.

METHODS

The study sample comprised women with a vaginal delivery and was drawn from the Akershus Birth Cohort. Data from the hospital birth's record and questionnaires at weeks 17-19 and 32 of pregnancy and 8 weeks postpartum were used (n = 1649). Analysis of variance and analysis of covariance were conducted to examine whether ratings of labor pain differed significantly between women with and without severe fear of childbirth and which factors explained the difference.

RESULTS

Women with severe fear of childbirth experienced significantly more labor pain than women without severe fear of childbirth (P < .01). However, when controlling for symptoms of maternal depression and anxiety, use of epidural/spinal anesthetic or nitrous oxide gas, and menstrual pain, this difference was no longer significant (P = .09).

DISCUSSION

Although the results show that labor pain is related to multiple physiological and psychological factors in a complex manner, symptoms of maternal depression and anxiety seem to play a central role for the experience of labor pain, and should therefore be focused on by health practitioners.

Changes in birth-related pain perception impact of neurobiological and psycho-social factors

PURPOSE

To analyse post-partum short- and long-term pain sensitivity and the influence of endogenous pain inhibition as well as distinct psycho-social factors on birth-related pain.

METHODS

Pain sensitivity was assessed in 91 primiparous women at three times: 2-6 weeks before, one to 3 days as well as ten to 14 weeks after childbirth. Application of a pressure algometer in combination with a cold pressor test was utilised for measurement of pain sensitivity and assessment of conditioned pain modulation (CPM). Selected psycho-social factors (anxiety, social support, history of abuse, chronic pain and fear of childbirth) were evaluated with standardised questionnaires and their effect on pain processing then analysed.

RESULTS

Pressure pain threshold, cold pain threshold and cold pain tolerance increased significantly directly after birth (all p < 0.001). While cold pain parameters partly recovered on follow-up, pressure pain threshold remained increased above baseline (p < 0.001). These pain-modulating effects were not found for women with history of abuse. While CPM was not affected by birth, its extent correlated significantly (r = 0.367) with the drop in pain sensitivity following birth. Moreover, high trait anxiety predicted an attenuated reduction in pain sensitivity (r = 0.357), while there was no correlation with fear of childbirth, chronic pain and social support.

CONCLUSION

Pain sensitivity showed a decrease when comparing post-partum with prepartum values. The extent and direction of CPM appear to be a trait variable that predicted post-partum hypalgesia without being changed itself. Post-partum hypalgesia was reduced in women with a history of abuse and high trait anxiety, which suggests that individual differences in CPM affect childbirth experience.

The Association Between Progesterone, Estradiol, and Oxytocin and Heat Pain Measures in Pregnancy: An Observational Cohort Study

BACKGROUND

Hormonal action has been implicated as a possible mechanism for pregnancy-induced analgesia. Previous investigators have reported an increase in heat pain tolerance during labor compared with nonpregnant controls and postulated it was because of the hormonal changes during pregnancy. However, these previous reports did not include measurement of hormonal values. The purpose of our study was to quantitatively test if changes in pregnancy hormone concentrations correlated with changes in temperature ratings.

METHODS

This was a prospective cohort study consisting of 32 women scheduled for elective cesarean delivery at term between July 2010 and January 2013. Heat pain threshold and tolerance, estrogen, progesterone, and oxytocin levels were measured twice in each patient at term and again 4 to 8 weeks postpartum.

RESULTS

All hormone levels decreased significantly between term pregnancy and the postpartum visit (all P values < 0.029). However, there were no statistically significant differences between term and postpartum heat pain measurements. The mean baseline heat pain threshold was 40.9°C at term compared with 40.3°C °postpartum (P = 0.47; mean change, -0.6°C; 95% confidence interval of change, -1.8°C to +0.7°C). The mean baseline heat pain tolerance was 46.1°C at term and 46.0°C postpartum (P = 0.59; mean change, -0.1°C; 95% confidence interval of change, -0.8°C° to +0.6°C).

CONCLUSIONS

Our findings show that amounts of estradiol and progesterone changed significantly between the term and the postpartum visit; however, the thermal pain tolerance did not significantly change. In summary, we did not observe an association between hormonal changes and changes in pain threshold measures. This finding argues against the concept of simple progesterone- or estrogen-induced analgesia in humans.

The Effects of Fibromyalgia Syndrome on Physical Function and Psychological Status of Pregnant Females

Objectives

This study aims to investigate the frequency and most common symptoms of fibromyalgia syndrome (FS) among pregnant females and determine the impacts of FS on physical functioning and psychological status.

Patients and methods

A total of 360 pregnant females (mean age 26.5 years, range 19 to 42 years) were included. The subjects were divided into two groups in terms of having (FS group; n=136; mean age 27 years; range 19 to 41 years) or not having FS (control group; n=224; mean age 26.5 years; range 20 to 42 years). The impact of FS on physical functions was evaluated using Fibromyalgia Impact Questionnaire. Psychological statuses of the subjects were evaluated using State-Trait Anxiety Inventory, Wijma Delivery Expectancy/Experience Questionnaire, and Beck Depression Inventory.

Results

Low back pain was the most common complaint while fatigue was the most common symptom in FS group. FS group had higher levels of pain and physical disability (p<0.001) and also higher values of anxiety, fear of childbirth, and depression (p<0.001, for all values) compared to control group. Symptom severity and physical function scores were significantly correlated with increased levels of pain, depression, anxiety, and fear of childbirth (p<0.001, for all values).

Conclusion

Fibromyalgia syndrome is common among pregnant females. The existence of FS in pregnancy is a severe factor contributing to maternal stress, anxiety, and depression. Therapeutic measures for fibromyalgia syndrome should be well-established to support healthy pregnancy and good child health outcome.

The role of maternal attachment in the experience of labor pain: a prospective study

OBJECTIVE

To examine the influence of attachment dimensions and sociodemographic and physical predictors in the experience of labor pain.

METHODS

Eighty-one pregnant women were assessed during their third trimester of pregnancy and during labor. The perceived intensity of pain in the early stages of labor (3 cm of cervical dilatation) and before the administration of patient-controlled epidural analgesia was measured using a visual analog scale. Pain was also assessed indirectly based on anesthetic doses. Attachment was assessed using the Adult Attachment Scale-Revised.

RESULTS

Attachment anxiety and avoidance were positively and significantly correlated with labor pain and anesthetic consumption. In the multivariate models, attachment anxiety was a significant predictor of higher pain at 3 cm of cervical dilatation (β = 0.36, p = .042) and before the administration of patient-controlled epidural analgesia (β = 0.51, p = .002). Older age (β = 0.31, p = .005), a shorter duration of labor (β= -0.41, p = .001), and attachment avoidance (β = 0.41, p = .004) were significant predictors of higher anesthetic use.

CONCLUSIONS

The study findings suggest that perceived labor pain and anesthetic use are strongly associated with attachment, rather than demographic and physical factors. These data support the importance of understanding the experience of labor pain within an attachment theoretical framework.

The effect of post-surgical neuroplasticity on the stability of systemic pain perception: a psychophysical study

BACKGROUND

Surgery-induced neuroplasticity at spinal and supra-spinal levels is assumed to evoke a clinical acute post-operative pain (cAPOP) experience, which is expressed by allodynia and/or hyperalgesia. It remains unclear whether the systemic pain perception measured outside the incision area remains unchanged and whether it is affected by the presence of cAPOP.

AIMS

This study explored whether the systemic perception of experimental pain would be altered towards hypersensitivity following elective gynecological surgery unmasked by opioids.

METHODS

A perioperative psychophysical evaluation of heat pain thresholds (HPT) and pain estimations were obtained in a remote bodily area before and after surgery among 35 women.

RESULTS

The ratings for both pain dimensions of intensity and unpleasantness remained stable following surgery. However, there was a reduction found in HPT the day after surgery (43.6 ± 2.2 °C to 42.2 ± 3.1 °C, p = 0.002). This reduction was associated with lower HPT measured before surgery (r = .56, p < 0.000) and with higher cAPOP intensity obtained at rest (r = -.44, p = 0.008).

CONCLUSIONS

This post-surgical allodynia, as reflected by the systemic enhancement of pain perception, may represent plasticity in the central pain pathways at the supra-spinal level. Pre-surgical assessment of a patient's pain perception profile may predict certain pain dimensions of post-surgical pain plasticity. The evaluation of individual pain profiles may contribute to a mechanism-based approach aimed to attenuate the cAPOP.

The correlation of antepartum upper extremity cuff algometry with epidural analgesic requirements for labor

Background:

Individual parturients experience pain differently, and it is unknown how these differences affect their requirements for labor analgesics.

Materials and Methods:

Cuff algometry of the upper limb was used to determine the pain thresholds and temporal summation of pain scores in nulliparous women about to undergo induction of labor. Analgesia was provided, upon request, with a patient controlled epidural analgesia infusion of bupivacaine and fentanyl. Nurse-administered epidural boluses of bupivacaine or lidocaine were given for breakthrough pain. Partial Spearman correlations were used to correlate the cuff algometry measurements with the amount of analgesic medication required by the patient.

Results:

There was no significant correlation between any of the algometry measurements and the number of patient or nurse administered bupivacaine boluses. There was a correlation of 0.7 (P = 0.001) between the temporal summation scores and the hourly number of nurse-administered epidural lidocaine boluses; however, this was based on only 3 patients who required lidocaine boluses.

Conclusions:

The use of pre-labor cuff algometry of the upper limb does not correlate with the patient epidural analgesic requirements and subsequent analgesia administration.

Influence of estrogen levels on thermal perception, pain thresholds, and pain tolerance: studies on women undergoing in vitro fertilization

We examined the relationship between estrogen and pain in women undergoing in vitro fertilization (IVF). Quantitative sensory tests (QST) were performed twice during the IVF-regimen: once during hormonal down-regulation and once during hormonal up-regulation. A group of healthy men and a group of women using monophasic contraceptives were also examined, to control for session-to-session effects. Among the women undergoing IVF, serum 17β-estradiol levels differed strongly between treatments as expected, and increased from 65.7 (SD = 26) pmol/L during the down-regulation phase, to 5,188 (SD = 2,524) pmol/L during the up-regulation phase. Significant outcomes in the QST were only seen for temperature perception thresholds (1.7 °C versus 2.2 °C; P = .003) and cold pain threshold (11.5 °C versus 14.5 °C; P = .04). A similar change in cold pain threshold was also seen in the 2 control groups, however, and statistical analysis suggested that this change was due to a session-to-session effect rather than being the result of hormonal modulation. Heat pain thresholds, heat tolerance, pressure pain thresholds, and the cold pressor test showed no significant differences between sessions. These data demonstrate that pain perception and pain thresholds in healthy women show little, if any, changes even with major variations in serum estradiol levels.

PERSPECTIVE

This study shows that pain perception and tolerance in women undergoing in vitro fertilization do not vary, despite the dramatic changes in 17β-estradiol levels induced by the treatment regimen. The result thus suggests that in humans, contrary to experimental animals, changes in estrogen levels have little influence on pain sensitivity.

Pregnancy-induced analgesia: a combined psychophysical and neurophysiological study

BACKGROUND

To investigate changes in heat pain threshold and modifications in heat pain processing during pregnancy and labour, seventy-six nulliparous pregnant women were enrolled in two studies.

METHODS

In the first study (psychophysical), 60 pregnant women underwent a quantitative sensory testing (QST) investigating heat perception in two body areas (right forearm and T10 dermatome) according to these groups: 32-33 gestational weeks (GW), 39-40 GW, early stage of active labour and 24 h after the delivery. In the other study (neurophysiological), contact heat-evoked potentials (CHEPs) were recorded in other 16 women at the 32nd GW and in 11 of these also at the 40th GW.

RESULTS

The psychophysical study showed that heat pain threshold was significantly increased at the forearm at 32-33 GW (median ± IQR: 39.6 ± 0.7 °C), at 39-40 GW (40.6 ± 1.1 °C) and at early stage of active labour (40.8 ± 1.5 °C) as compared to 20 non-pregnant controls (p < 0.001). Heat pain threshold tested at T10 level was significantly increased at 32-33 GW (41.0 ± 1.6 °C), at 39-40 GW (42.1 ± 1.8 °C), and at early stage of active labour (42.3 ± 1.3 °C) as compared to the non-pregnant women (p < 0.001). The N2-P2 CHEP amplitude (main negative N2 and positive P2 components of the vertex biphasic potential) recorded from the pregnant women was significantly lower at the 40th than at the 32nd GW, after stimulation of both the forearm (p < 0.001) and the abdomen (p < 0.001).

CONCLUSIONS

In pregnant women, there is a progressive increase of heat pain threshold and a reduction of the CHEP amplitude, suggesting that a general inhibitory mechanism may be involved.

Pharmacokinetics of a loading dose of intravenous paracetamol post caesarean delivery

BACKGROUND

The postpartum period affects drug disposition, but data of intravenous paracetamol loading dose pharmacokinetics immediately following caesarean delivery have not yet been reported.

METHODS

Immediately following caesarean delivery, women received a 2-g loading dose of intravenous paracetamol. Plasma samples were collected at 1, 2, 4 and 6 h. Individual pharmacokinetics were calculated assuming a linear one-compartment model with instantaneous input and first-order output. Data were reported using median and range.

RESULTS

Twenty-eight patients undergoing caesarean delivery were recruited (age 31.5 [20-42] years, weight 79 [57-110] kg, body surface area 1.9 [1.5-2.4]m(2)). Median paracetamol plasma concentrations after 1, 2, 4 and 6 h were 22.5, 15.25, 7.9, and 3.9 mg/L respectively. Paracetamol clearance was 20.3 (11.8-62.8) L/h or 10.9 (7-23.8)L/hm(2), distribution volume 58.3 (42.9-156) L or 0.72 (0.52-1.56) L/kg.

CONCLUSION

Pharmacokinetics of intravenous paracetamol have been estimated following caesarean delivery. Although limited to a loading dose shortly after surgery, the results are clinically relevant since this is the first description in this patient population. These data provide evidence on which to base further integrated pharmacokinetic/pharmacodynamic studies in peripartum analgesia.

The effect of epidural analgesia on labor progress and outcome in nulliparous women

OBJECTIVE

The present study was designed to investigate the influence of epidural analgesia on labor progress and outcome in nulliparous women.

METHODS

A population-based study comparing women with and without epidural analgesia was conducted. Deliveries occurred during 1988-2006 at the Soroka University Medical Center. A multivariable logistic regression model with backward elimination was constructed to control for confounders.

RESULTS

During the study period there were 39 498 deliveries; epidural analgesia was given in 9960 (25.2%) of these. Using a multivariable analysis with backward elimination, the following conditions were significantly associated with the use of epidural analgesia: advanced maternal age, oligohydramnios, premature rupture of membranes, induction of labor, and Jewish (vs. Bedouin) ethnicity. These patients were more likely to deliver by cesarean delivery (CD; OR = 1.4, 95% CI 1.3-1.5; p < 0.001) and vacuum extraction (OR = 1.5, 95% CI 1.4-1.7; p < 0.001). After controlling for possible confounders such as macrosomia, failed induction, hypertensive disorders, gestational diabetes, maternal age, labor dystocia, and ethnicity, epidural analgesia was not found to be an independent risk factor for CD but rather a protective factor (OR = 0.9, 95% CI 0.8-0.9; p = 0.038). When vacuum extraction was the outcome variable, epidural analgesia was documented as an independent risk factor (OR = 1.1, 95% CI 1.01-1.3; p = 0.04).

CONCLUSIONS

Epidural analgesia in nulliparous parturients increases the risk for labor dystocia and accordingly is an independent risk factor for vacuum extraction. Nevertheless, it does not pose an independent risk for cesarean delivery.

Genetic variability of the mu-opioid receptor influences intrathecal fentanyl analgesia requirements in laboring women

Labor initiates one of the most intensely painful episodes in a woman's life. Opioids are used to provide analgesia with substantial interindividual variability in efficacy. mu-Opioid receptor (muOR, OPRM1) genetic variants may explain differences in response to opioid analgesia. We hypothesized that OPRM1 304A/G polymorphism influences the median effective dose (ED(50)) of intrathecal fentanyl via combined spinal-epidural for labor analgesia. Nulliparous women were prospectively recruited around 35 weeks gestation (n=224), and genotyped for 304A/G polymorphism. Those requesting neuraxial labor analgesia were enrolled in one of the two double-blinded trials: up-down sequential allocation (SA, n=50) and a separate confirmatory random-dose allocation trial (RA, n=97). Effective analgesia from intrathecal fentanyl was defined by >or=60 min analgesia with verbal rating score <or=1 (scale 0-10) and was compared between mu OR 304A homozygotes (Group A) and women carrying at least one 304G allele (Group G). OPRM1 304G allele frequency f(-) was 0.18. Using SA, intrathecal fentanyl ED(50) was 26.8 microg (95% CI 22.7-30.9) in Group A and 17.7 microg (95% CI 13.4-21.9) in Group G (p<0.001; 304A homozygosity increased the ED(50) 1.5-fold). RA confirmed that 304A homozygosity significantly increases intrathecal fentanyl ED(50) (27.4 microg in Group A and 12.8 microg in Group G [p<0.002; 2.1-fold]). We demonstrate for the first time that the muOR 304G variant significantly reduces intrathecal fentanyl ED(50) for labor analgesia, suggesting women with the G variant may be more responsive to opioids and require less analgesic drugs. These findings for intrathecal fentanyl pharmacogenetics may have implications for patients receiving opioids in other settings.