Population Women calling emergency ambulance for pelvic pain.
Methods Women were randomised in two groups: resistive heating (group 1) or passive warming (group 2), each treatment was initiated at the emergency site.
Main outcome measures Pain on visual analogue scale (VAS), anxiety and nausea, given as mean (SD).
Results Prior to the interventions, all women were vasoconstricted and had comparable pain scores. Then, group 1 showed a significant (P < 0.01) reduction in pain (VAS: 72.2 [10.5] mm to 32.4 [18.0] mm), anxiety (VAS: 59.0 [10.9] mm to 37.5 [24.1] mm), nausea (VAS: 42.7 [6.2] mm to 21.6 [5.0] mm) and heart rate (101  beats per minute [bpm] to 59  bpm), as well as in the number of vasoconstricted women (from 19/19 constricted/dilated to 2/19 constricted/dilated), whereas scores in group 2 remained unchanged. There were no significant changes in blood pressure in either group.
Conclusions Local warming is an effective emergency care measure for acute pelvic pain.
In Europe, pain is the most frequently cited reason (72%) for calling an ambulance.1 Acute pelvic pain experience as the reason in 3–5% of these calls is mainly due to underlying acute salpingitis (22.8%), pelvic adhesions (22.9%) and ovarian cysts (14.2%).2 Although the various therapeutic treatments are the best options for pain control, women with non-life-threatening illnesses are usually transported to the hospital in an ambulance without an emergency physician, and the accompanying paramedics are not permitted by law to administer any drug.
Alternatively, noninvasive procedures like acupuncture can potentially be administered, but there is still no consistent data to support its use. However, our recent preliminary data suggested that warming women with minor trauma can provide analgesic and anxiolytic effects.3
Consequently, we conducted a prospective, randomised study to test this hypothesis that local active warming of the abdomen for women with acute pelvic pain would be an effective treatment in the prehospital setting. Second, we predicted that warming would reduce anxiety and sympathetic hyperactivity and increase patient wellbeing and satisfaction. Finally, we wanted to determine whether this would also reduce nausea.
This randomised, single-blinded study was conducted by the Vienna Red Cross and the University Hospital Vienna.
All women who called the emergency ambulance service for pelvic pain were potentially included in the study. The institutional ethics committee of the Vienna Red Cross approved the study. Women were excluded if they had a positive human chorionic gonadotrophin (hCG)-based pregnancy urine test at the emergency site, having taken any analgesics during the last 3 weeks and having pain from any other than gynaecological causes, verified by clinical examination, X-ray, ultrasound or tomography. The final diagnosis was communicated via fax and/or phone directly to the principal investigator, who then excluded these women from the study analysis.
At the emergency site, an investigator determined whether the women were suitable for this study and obtained informed consent. An electric heating blanket (ThermaMed GmbH, Bad Oeynhausen, Germany) covered with a woollen blanket was placed over the abdomen of all women. The cover measured 80 × 200 cm with the actively heated section of the electric blanket measuring 40 × 148 cm. Women were randomly assigned to two groups: resistive heating (group 1) or passive warming (group 2). Computer-generated codes were used for the randomisation. The heating blankets were set to 42°C in group 1 and left inactivated for group 2. The control unit was locked in a plastic box for blinding. Once positioned, the covers remained untouched until arrival at the hospital. Women were monitored with a tympanic thermocouple (core temperature), skin thermosensors on the lower abdominal skin and intramuscular thermosensors above the rectus abdominis muscle to a depth of 6 mm. An additional skin sensor was placed on the forearm and finger to detect indirect signs of vasodilatation (T°finger > T°forearm) or vasoconstriction (T°forearm > T°finger).
Measurements were taken immediately after entering the ambulance (T1) and upon arrival at the hospital (T2). The same independent investigator, blinded to the treatment, recorded all measurements, abstaining from physical contact with both the woman and blanket. Temperature, heart rate and oscillometric blood pressure were monitored. The women were asked to rate their pain, nausea and anxiety levels using visual analogue scales (VAS) (0–100 mm). The VAS, initially developed as a measure for wellbeing, has been established as a reproducible and accurate method to measure pain.4 A thermocouple, level with the women’s head, recorded the ambient temperature.
The intention was to perform a per-protocol analysis of the study data. The primary outcome was the amount of pain relief between the groups upon arrival at the hospital. The total number of women needed was 54 to reach a power of 90% with P < 0.05, a two-tailed t test, and a 30% reduction in pain VAS with a common SD equal to the difference. After normal distribution of the baseline data was confirmed, data analysis was performed using the SPSS statistical package for Macintosh (SPSS, Chicago, IL) and were presented as mean (SD).
Characteristics of study subjects
One hundred and twenty-four women who called emergency ambulance for pelvic pain were screened for this study, 24 refused informed consent and the remaining 100 women who met the defined entry criteria were randomised (50 per group). Thirty-eight women were excluded because of a final diagnosis other than gynaecological (Table 1). Twenty-nine women in group 1 and 33 women in group 2 entered the final data analysis (Figure 1).
Table 1. Diagnoses entailing post hoc exclusion from data analysis based on hospital diagnosis
Active warming (n= 21)
Passive warming (n= 17)
Diagnosis is based on findings in the hospital within 24 hours after the emergency.
Rectal trauma after sexual intercourse
No organic reason found
Woman characteristics were comparable before treatment (T1): the hCG-based pregnancy test was negative in all cases. None of the women showed any adverse event during the treatment period. There were no significant differences in potential confounding factors such as age, weight, height, initial core temperature, skin and intramuscular temperature, blood pressure and heart rate between groups; neither did the pain, nausea and anxiety levels differ significantly between the groups before treatment (Table 2).
Table 2. Demographic characteristics, potential confounding factors and baseline parameters
Active warming (n= 29)
Passive warming (n= 33)
Data are shown as means ± SD. None of these factors differed significantly.
24.2 ± 5.1
26.3 ± 3.8
166.2 ± 8.0
172.9 ± 9.5
82.6 ± 11.1
79.7 ± 8.6
Pain before treatment (VAS)
72.2 ± 10.5
68.8 ± 13.2
Nausea before treatment (VAS)
42.7 ± 6.2
40.1 ± 6.1
Anxiety before treatment (VAS)
59.0 ± 10.9
56.7 ± 8.5
Systolic arterial pressure (mmHg)
143.9 ± 16.4
138.7 ± 11.1
Diastolic arterial pressure (mmHg)
92.1 ± 8.9
96.6 ± 11.7
Heart rate start (bpm)
101 ± 12
99 ± 18
Core temperature start (°C)
36.6 ± 0.4
36.5 ± 0.3
Skin temperature start (°C)
18.3 ± 2.1
19.6 ± 3.2
Muscle temperature start (°C)
33.4 ± 0.9
33.1 ± 1.1
Ambient temperature in the car (°C)
19.6 ± 4.2
21.4 ± 5.3
Duration of transport (minutes)
33.2 ± 11.5
34.9 ± 9.5
After transport (T2), tympanic temperature showed no significant difference in either group (36.6 [0.4]°C in group 1 versus 36.5 [0.3]°C in group 2; P= 0.73); the skin temperatures on the lower abdomen were significantly higher in actively warmed women (40.9 [0.7] °C in group 1 versus 18.9 [3.1]°C in group 2; P < 0.01). Similarly, intramuscular temperature along the rectus abdominis muscle differed significantly (38.8 [1.9]°C in group 1 versus 33.7 [0.2]°C in group 2; P < 0.01), which demonstrated the effect of warming.
Women in group 1 felt that their pain reduced by half after treatment (P < 0.01; 72.2 [10.5] mm VAS to 32.4 [18.0] mm VAS) whereas women in group 2 did not (68.8 [13.2] mm VAS to 66.6 [11.2] mm VAS, nonsignificant [n.s.]) (Figure 2). Concordantly, their scores for anxiety in group 1 significantly decreased (P < 0.01) from 59.0 (10.9) mm VAS to 37.5 (24.1) mm VAS during treatment compared with group 2: from 56.7 (18.5) mm VAS to 62.2 (16.7) mm VAS, n.s. A significant (P < 0.01) lessening of nausea (42.7 [6.2] mm VAS to 21.6 [5.0] mm VAS) was recorded in all group 1 women (group 2: from 40.1 [6.1] mm VAS to 41.3 [2.4] mm VAS, n.s.). Upon arrival at the hospital, nausea, pain and anxiety scores consistently showed a significant reduction (P < 0.01) in group 1 as compared with group 2. While all women showed signs of vasoconstriction before treatment, there were significantly (P < 0.01) less women with vasoconstriction in group 1 (2/19 constricted/dilated in group 1 versus 33/0 constricted/dilated in group 2).
We observed a significant (P < 0.01) drop in heart rate in group 1 from 101 (12) bpm to 59 (8) bpm before and after treatment, respectively (group 2: before treatment 99 (18) bpm, afterwards 98 (9) bpm, n.s.), which was reflected in a significant difference (P < 0.01) in heart rate in group 1 and group 2 at the end of transport.
Overall satisfaction with the received care was significantly higher (P < 0.01) in women of the warmed group (25.0 [9.1] mm VAS in group 1 and 47.6 [16.6] mm VAS in group 2). There were no significant changes in blood pressure in either group. The final diagnoses obtained from the hospital covered a wide range of gynaecological diseases (Table 3).
Table 3. Final diagnoses based on hospital findings
Active warming (n= 29)
Passive warming (n= 33)
In the 38 excluded women, the pain VAS was also reduced from 70.1 (15.8) to 65.9 (19.3). This difference was neither statistically significant nor clinically important.
The first of our findings is that pain resulting from gynaecological disorders in an emergency setting is comparable with untreated postoperative pain;5 therefore, there is a need for analgesic treatment in the prehospital phase. The physiological responses to pain include increased heart rate with hypertension, nausea and arteriolar vasoconstriction, all of which further aggravate women on their way to hospital.6
In this study, we used a per-protocol analysis because the final diagnosis of pelvic pain or not could only be made post hoc. Here, an intention-to-treat analysis would have biased the results because all other sources of pain were included in the study.
The central result of this study is that local warming is a safe, rapid and effective analgesic treatment for acute pelvic pain. The ensuing increase in comfort entails a reduction in anxiety, mirrored in the observed changes in VAS for pain and anxiety that were both statistically significant and of clinical importance. A drop in heart rate and increased vasodilation in the active-warming group indicated reduced sympathetic activity. The lessening of nausea could be a result both of a decreased adrenergic reaction and the increased psychological wellbeing due to the effect of warmth and the feeling of being sheltered and cared for.
Our data on women with acute pelvic pain show high sympathetic activity, a reduction of which through active warming seems beneficial. Pertovaara and Kalmari7 demonstrated in rats that visceral nociceptive responses are attenuated after sympathectomy. Our findings are in accordance and underline the role of the sympathetic nervous system in the perception of visceral pain.
Pain relief through heat is achieved by modulating the pathological mechanism that leads to pain. Heat applied to the anterior abdominal wall has been shown to decrease the activity of the gastrointestinal tract, suggesting the possibility of a feedback mechanism affecting visceral smooth muscle. Warming of the skin in the lower thorax also has been reported to increase intestinal blood flow in rats, indicating a possible action via the lessening of pelvic venous congestion.8
Akin et al.9 reported persistent pain relief in dysmenorrhoeic women the day after heat treatment that did not occur in the control group. This supports the hypothesis of an altered visceral pain threshold after heat application. Pain thresholds vary with the normal menstrual cycle, with the highest thresholds during the luteal phase10 and are different in dysmenorrhoeic women.11
Active warming appears ideally suited as an analgesic treatment for women with pelvic pain, to reduce pain in acute care for women with pelvic pain; any physician, nurse, paramedic or emergency medical technician can initiate this treatment at the emergency site without having to rely on drugs with their potential adverse effects or allergenic properties. The electric blanket is easy to handle and the application in different settings requires only minimal training.3 However, a large multicentre trial should follow this study to show further effectiveness of warming in the prehospital setting.