Department of Anaesthesiology, Aretaieion Hospital, Medical School, University of Athens, 76 Vassilissis Sofias Avenue, Athens 11528, Greece
* Corresponding author. E-mail: afassou1{at}otenet.gr and fassoula{at}aretaieio.uoa.gr
Accepted for publication May 10, 2004.
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Abstract |
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Methods. We assessed the level of subarachnoid anaesthesia after 1.8 ml of hyperbaric lidocaine 5% and the postoperative analgesic requirements in women undergoing Caesarean section and undergoing abdominal hysterectomy (30 each group). Intraoperatively epidural ropivacaine was given as required. All patients received 10 ml of ropivacaine 0.2% epidurally 2, 10, and 24 h after operation and the VAS pain score was assessed. They also had access to patient controlled analgesia i.v. morphine.
Results. Duration of surgery was 64 (13.7) vs 127 (33.8) min (P<0.0001) in the pregnant and non-pregnant groups. Ten minutes after subarachnoid injection, sensory block was higher by three dermatomes in the pregnant group (P<0.0001). Time to first ropivacaine dose was 37 (19.7) vs 19 (12.2) min (P<0.001) and the ropivacaine normalized for the duration of anaesthesia was 0.8 (0.6) vs 1.3 (0.5) mg1 (P=0.001) in the pregnant and non-pregnant groups, respectively. The time between the first and second ropivacaine dose was similar in the two groups (P=0.070). Fewer pregnant women (81 vs 100%) required ropivacaine intraoperatively (P=0.017). The VAS scores were similar but parturients consumed more i.v. morphine (33 (14) vs 24 (12) mg, P=0.016) during the first 24 h after operation.
Conclusions. Pregnant patients exhibited a higher level of subarachnoid sensory block and required more i.v. morphine after operation.
Keywords: anaesthesia, obstetric, Caesarean section ; anaesthetic techniques, subarachnoid ; analgesia, patient-controlled ; analgesics opioid, morphine ; pain, postoperative
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Introduction |
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Other factors related to physiological and endocrine changes during pregnancy may be important. Pregnant women exhibit increased susceptibility to local anaesthetics, when these are administered to produce peripheral nerve blocks.5 In pregnant rats the antinociceptive effects of epidural lidocaine is enhanced6 and the levels of nociceptive responses to noxious stimuli are increased. This antinociception may be mediated by the - and
-opioid receptors in the spinal cord, which are activated by the increased estrogen and progesterone levels.78 However, the underlying mechanisms of reduced local anaesthetic requirements and increased pain threshold during pregnancy are not clear, and there is very few hard human data on the topic.
The aim of the present study was to compare in groups of pregnant and non-pregnant patients: (i) the spread of subarachnoid anaesthesia, (ii) the doses of the local anaesthetic administered epidurally until surgery was completed, and (iii) the postoperative morphine analgesic requirements during the first 24 h after operation.
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Methods |
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The assessment of the level of the sensory and motor block was explained in all patients during the preoperative visit as well as the VAS score and the use of patient controlled analgesia (PCA) after operation. The directions to the patient regarding the PCA were standardized.
Anaesthetic technique
Pre-medication was omitted. In the operating room standard monitoring (ECG, , and non-invasive arterial pressure) was used. Before regional anaesthesia, patients in each group received 500 ml of colloid (Hydroxyethyl starch 6% HAES-steril® 6%). Each patient was placed on her left side. After disinfecting the skin and infiltration with local anaesthetic (lidocaine 2%) a 16-G (8 cm long) epidural needle (Portex®) was inserted in the L2L3 intervertebral space. When the epidural space was identified a 27-G spinal needle was inserted through the epidural needle and when cerebrospinal fluid was seen 1.8 ml of 5% hyperbaric lidocaine was injected slowly within 15 s and without barbotage. At this point 2.5 mg of ephedrine was given i.v.. Then, the spinal needle was removed, an epidural catheter threaded through the Tuohy needle, the Tuohy needle removed and the catheter fixed in place. Intraoperatively, left lateral tilt was applied to both pregnant and non-pregnant women.
Measurements
Sensory block was assessed 10 min after the subarachnoid injection. Four points lying on the posterior, middle and anterior axillary lines of the left abdominal wall and on a line 5-cm medial to the anterior axillary line were drawn as described previously.911 The level of sensory block was determined unilaterally (left side) by moving a pressure palpator (Pressure feeler 650-g Dedatelec; Chemin de Muriers, Irigny, France) along each longitudinal line in a caudad to cephalad direction as described previously.911 The four points, each representing the level of the block, were joined by a line, which determined the dermatome at which sensory block had occurred.
Motor block was also assessed for each lower limb 10 min after subarachnoid injection, using the modified Bromage scale (patient could move nothing, 3; move the hip, 2; flex and extend the knee, 1; flex and extend the foot, 0). Sensory and motor block were also assessed at the end of surgery.
Conduct of anaesthesia
All patients received a Pfannenstiel incision. Intraoperatively 6 ml of ropivacaine 0.75% was administered epidurally each time the patient complained of starting to feel something pulling at the level of the epigastrium. To enhance the spread of sensory block after epidural injection, 50% of nitrous oxide in oxygen9 was given as long as required for the patient to feel comfortable. The time to the first dose of ropivacaine, the number of ropivacaine doses required intraoperatively, the time elapsed between the first and second epidural dose of ropivacaine, and the duration of nitrous oxide administration were recorded. To compare the epidural ropivacaine requirements intraoperatively between the two groups, the ropivacaine doses given in each patient intraoperatively were normalized for the duration of anaesthesia by dividing the intraoperative doses of ropivacaine in milligrams by the duration of anaesthesia in minutes. We defined as duration of anaesthesia the time from subarachnoid injection to the end of surgery (skin closure), and duration of surgery from the skin incision to skin closure. Ephedrine administration was repeated when systolic arterial pressure was more than 20% of the baseline recorded in the operating room before any intervention. The doses of ephedrine given in each group were also recorded.
Postoperative care and analgesia
All patients received 10 ml of ropivacaine 0.2% epidurally 2, 10, and 24 h after surgery. At these time intervals pain was assessed at rest and after cough using the VAS score. Assessment was done before ropivacaine injection. Patients also had access to i.v. morphine via a PCA device (Freedom5®, VYGON, B.P. 7, 95440 Ecouen, France). This device allows delivery of 1 ml solution, containing 1 mg of morphine with lockout interval of 7 min. During the first 24 h after surgery patients did not receive other analgesics such as paracetamol or NSAIDs, except those predetermined by the study protocol, such as epidural ropivacaine and PCA i.v. morphine. Patients were examined 24 and 48 h after the operation for transient neurological symptoms defined as: back pain and/or dysesthesia radiating to the buttocks, thighs, hips, or calves and began within the first 24 h after surgery.
Statistical analysis
Initial sample size estimation (eight patients in each group) showed that approximately 30 subjects should be included in each group in order to ensure power of 0.80 for detecting a clinically meaningful difference of 25% difference in morphine dose (expressed in milligrams) as well as a difference of one dermatome between the two groups. Standard deviations (SD), estimated from initial pilot observations, were 11 and 1.9 for morphine dose and dermatomal spread, respectively. The error was assumed to be 0.05. Levene's test was used to compare the equality of variances.
Patient characteristics, duration of surgery and anaesthesia, the time until the first ropivacaine dose was given, the total number of ropivacaine doses, cumulative ropivacaine doses, the dose of ephedrine required, the duration (minutes) of nitrous oxide administration, and the postoperative morphine requirements were compared between the groups using independent sample t-tests. The time interval between the first and second dose of epidural ropivacaine was compared between the groups with the MannWhitney test. To compare the level of sensory block between the pregnant and non-pregnant groups 10 min after subarachnoid anaesthesia and at the end of surgery, the dermatomes L5T1 were coded from lowest to highest as 117 and the MannWhitney test was used. Motor block 10 min after subarachnoid injection and at the end of surgery, the number of subjects that required ropivacaine doses in each group and postoperative neurological complications were compared between the groups using the Pearson 2. ANOVA with repeated measures was used to compare the VAS scores recorded 2, 10, and 24 h after the operation between the groups, when at rest as well as after cough. We considered values P<0.05 as statistically significant.
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Results |
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The pregnant and non-pregnant groups did not differ regarding body weight (71 (7.9) vs 66 (9.9) kg, respectively) and height (164 (0.05) vs 165 (0.05) cm, respectively). A difference was found in age between the pregnant and non-pregnant group (32 (4.52) (2443) vs 40 (7.6) (2350) yr, respectively, P<0.0001). Duration of surgery was shorter in the pregnant group (64 (13.7) vs 127 (33.8) min, respectively, P<0.0001) as well as duration of anaesthesia (81 (15.4) vs 146 (33.9) min, respectively, P<0.001).
Ten minutes after subarachnoid injection the two groups did not differ regarding the motor block of the right or the left leg. Sensory block assessed 10 min after the subarachnoid injection was higher in the pregnant group by three dermatomes (T5) when compared with the non-pregnant group (T8) (P<0.001). At the end of surgery the two groups did not differ in sensory or motor block (Table 1).
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Discussion |
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Changes in curvature of the spinal column in the later stages of pregnancy, such as the apex of lumbar lordosis to be caudad and thoracic kyphosis to be reduced in the supine position may enhance the cephalad spread of local anaesthetic.3 Another reason for the wider spread of subarachnoid local anaesthetic may be the enlargement of the epidural veins as a result of obstruction of the inferior vena cava by the gravid uterus and therefore a decrease in the volume of cerebrospinal fluid.4 Finally, high progesterone levels in CSF and/or blood may be the cause of the different response to subarachnoid injection of local anaesthetic during late pregnancy.12 However, the increased levels of progesterone during the second but not during the first trimester were associated with higher levels of sensory subarachnoid block.13
Though we found a difference regarding the sensory block between the groups, the motor block did not differ between the pregnant and non-pregnant subjects. However, after hyperbaric lidocaine most of the patients had a dense motor block, which when above the level of T10 is difficult to establish clinically. Therefore, it is impossible to demonstrate a difference in motor block between the groups.
We used the lidocaine 5%, as local anaesthetic for subarachnoid injection as no other licensed local anaesthetic was available for subarachnoid anaesthesia in Greece at the time of the study. The transient neurological symptoms in the two patients occurred within 24 h and resolved without any treatment. Aouad and colleagues reported a 3% incidence of transient neurological symptoms after subarachnoid lidocaine for Caesarean section, and a height of sensory block at T4.14
Measurements of sensory block were made only 10 min after subarachnoid injection, as delaying surgery was undesirable for patients, particularly if pregnant. The non-pregnant subjects consumed more epidural ropivacaine intraoperatively, the total dose of ropivacaine being normalized for the duration of anaesthesia. However, the doses of ropivacaine used are not a satisfactory guide of the epidural requirements because the duration of surgery was longer in the non-pregnant patients. To assess the height of first epidural dose was technically impossible, as we could not interfere with the sterile drapes intraoperatively. So we limited our investigation to determination of the interval elapsing between the first and second dose of epidural ropivacaine, which did not differ between the two groups.
An increased susceptibility to lidocaine neural block has been reported in pregnant rats,15 although spinal root axons of pregnant rats did not exhibit increased susceptibility to bupivacaine.16 Further discussion of these reports is beyond the scope of this article.
Besides, these results cannot be extrapolated to the results of the present study because of species difference, neuraxial vs peripheral anaesthesia, and different physicochemical properties of the local anaesthetics.
The interval elapsed between the first and second dose of ropivacaine intraoperatively between the groups did not differ and the pregnant patients consumed a higher dose of morphine by 35%. These results are not consistent with an assumed increased pain threshold during pregnancy, an increase in sensory perception threshold or an enhanced effect of local anaesthetics as a result of changes at central locations of the CNS.
As patients had an epidural catheter in place, additionally to the i.v. morphine administered by a PCA device, they received a low concentration of ropivacaine at fixed time intervals. We routinely administer multimodal analgesia to improve quality of pain relief with fewer side effects.
A limitation of the study may be the different operations. Nevertheless, to compare postoperative pain and analgesic requirements in pregnant vs non-pregnant patients, the choice of total abdominal hysterectomy is reasonable. Both operations concern the lower abdomen. Caesarean section is an operation of shorter duration and probably equally or less painful surgery than total abdominal hysterectomy. Total abdominal hysterectomy is associated with greater surgical manipulation of deep lower abdominal structures and more severe tissue damage because of removal of the uterus and relevant tissues. These differences apply to the postoperative period as well with an impact on postoperative pain. The difference in age between the groups, though significant, is not of magnitude to explain increased analgesic requirements after surgery in the pregnant patients. Another explanation for the higher i.v. morphine use in the parturients may be the more epidural ropivacaine consumed intraoperatively by the non-pregnant group, which might have produced a prolonged analgesic effect after surgery. However, at the end of surgery the level of sensory block was similar in the pregnant and non-pregnant groups. Greater morphine requirements in the pregnant group could represent a difference in severity of pain or sensitivity to morphine.
We conclude that pregnant women at term, after subarachnoid anaesthesia for Caesarean section, exhibit higher levels of sensory block, similar time intervals between the supplementary doses of epidural ropivacaine intraoperatively, and increased requirements of i.v. morphine postoperatively vs non-pregnant women having total abdominal hysterectomy. Additional studies assessing analgesic requirements in pregnant women at term vs non-pregnant women are needed to enlighten these differences.
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References |
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2 Fagraeus L, Urban BJ, Bromage PR. Spread of epidural analgesia in early pregnancy. Anesthesiology 1983; 58: 1847[ISI][Medline]
3 Hirabayashi Y, Shimizu R, Fukuda H, Saitoh K, Furuse M. Anatomical configuration of the spinal column in the supine position. II. Comparison of pregnant and non-pregnant women. Br J Anaesth 1995; 75: 68
4 Barclay DL, Renegar OJ, Nelson EW. The influence of inferior vena cava compression on the level of spinal anesthesia. Am J Obst Gyn 1968; 101: 792800[ISI][Medline]
5 Butterworth JF, Walker FO, Lysak SZ. Pregnancy increases median nerve susceptibility to lidocaine. Anesthesiology 1990; 72: 9625[ISI][Medline]
6 Kaneko M, Saito Y, Kirihara Y, Kosaka Y. Pregnancy enhances the antinociceptive effects of extradural lidocaine in the rat. Br J Anaesth 1994; 72: 65761[Abstract]
7 Dawson-Basoa ME, Gintzler AR. Estrogen and progesterone activate spinal kappa-opiate receptor analgesic mechanisms. Pain 1996; 64: 60715[CrossRef][ISI]
8 Dawson-Basoa ME, Gintzler AR. 17-ß-Estradiol and progesterone modulate an intrinsic opioid analgesic system. Brain Res 1993; 601: 2415[CrossRef][ISI][Medline]
9 Fassoulaki A, Sarantopoulos C, Zotou M. Nitrous oxide enhances the level of sensory block produced by intrathecal lidocaine. Anesth Analg 1997; 85: 110811[Abstract]
10 Fassoulaki A, Zotou M, Sarantopoulos C. Effect of nimodipine on regression of spinal analgesia. Br J Anaesth 1998; 81: 35860[CrossRef][ISI][Medline]
11 Fassoulaki A, Sarantopoulos C, Zotou M, Karabinis G. Assessment of sensory block after subarachnoid anesthesia using a pressure palpator. Anesth Analg 1999; 88: 398401
12 Datta S, Hurley RJ, Naulty JS, et al. Plasma and cerebrospinal fluid progesterone concentrations in pregnant and nonpregnant women. Anesth Analg 1986; 65: 9504[Abstract]
13 Hirabayashi Y, Shimizu R, Saitoh K, Fukuda H. Cerebrospinal fluid progesterone in pregnant women. Br J Anaesth 1995; 75: 6837
14 Aouad MT, Siddik SS, Jalbout MI, Baraka AS. Does pregnancy protect against intrathecal lidocaine-induced transient neurologic symptoms? Anesth Analg 2001; 92: 4014
15 Popitz-Berger FA, Leeson S, Thalhamer JG, Strichartz G. Intraneural lidocaine uptake compared with analgesic differences between pregnant and nonpregnant rats. Reg Anesth 1997; 22: 36371[ISI][Medline]
16 Dietz FB, Jaffe RA. Pregnancy does not increase susceptibility to bupivacaine in spinal root axons. Anesthesiology 1997; 87: 6106[ISI][Medline]
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