An intravenous fluid bolus is not necessary before administration of intrathecal fentanyl for labor analgesia

A randomized controlled trial of the effect of intrapartum intravenous fluid management on breastfed newborn weight loss

OBJECTIVE

To determine the effect of conservative versus usual intrapartum intravenous (IV) fluid management for low-risk women receiving epidural analgesia on weight loss in breastfed newborns.

DESIGN

A randomized controlled trial.

SETTING

A tertiary perinatal center in a large urban setting.

SAMPLE

Women experiencing uncomplicated pregnancies who planned to have epidural analgesia and to breastfeed.

METHODS

Healthy pregnant women were randomized to receive an IV epidural preload volume of <500 mLs continuing at an hourly rate of 75-100 mL/h (conservative care) or an epidural preload volume of ≥500 mLs and an hourly rate >125 mL/h (usual care). The primary study outcome was breastfed newborn weight loss >7% prior to hospital discharge. Secondary study outcomes included breastfeeding exclusivity, referral to outpatient breastfeeding clinic support, and delayed discharge. Other outcomes were admission to the neonatal intensive care unit and cord blood pH <7.25.

RESULTS

Two hundred women participated (100 in the conservative care and 100 in the usual care groups). Forty-eight of 100 infants in the usual care group and 44 of the 100 infants in the conservative care group lost >7% of their birth weight prior to discharge, p < 0.52 RR 0.92 [0.68-1.24].

CONCLUSION

A policy of restricted IV fluids did not affect newborn weight loss. Women and their care providers should be reassured that the volumes of IV fluid <2500 mLs are unlikely to have a clinically meaningful effect on breastfed newborn weight loss >7%. Exploratory analyses suggest that breastfed newborn weight loss increases when intrapartum volumes infused are >2500 mLs. Care providers are encouraged to consider volumes of IV fluid infused intrapartum as a factor that may have contributed to early newborn weight loss in the first 48 h of life.

Spinal opioid receptor-sensitive muscle afferents contribute to the fatigue-induced increase in intracortical inhibition in healthy humans

We investigated the influence of spinal opioid receptor-sensitive muscle afferents on cortical changes following fatiguing unilateral knee-extensor exercise. On separate days, seven subjects performed an identical five sets of intermittent isometric right-quadriceps contractions, each consisting of eight submaximal contractions [63 ± 7% maximal voluntary contraction (MVC)] and one MVC. The exercise was performed following either lumbar interspinous saline injection or lumbar intrathecal fentanyl injection blocking the central projection of spinal opioid receptor-sensitive lower limb muscle afferents. To quantify exercise-induced peripheral fatigue, quadriceps twitch force (Q(tw,pot)) was assessed via supramaximal magnetic femoral nerve stimulation before and after exercise. Motor evoked potentials and cortical silent periods (CSPs) were evaluated via transcranial magnetic stimulation of the motor cortex during a 3% MVC pre-activation period immediately following exercise. End-exercise quadriceps fatigue was significant and similar in both conditions (Q(tw,pot) -35 and -39% for placebo and fentanyl, respectively; P = 0.38). Immediately following exercise on both days, motor evoked potentials were similar to those obtained prior to exercise. Compared with pre-exercise baseline, CSP in the placebo trial was 21 ± 5% longer postexercise (P < 0.01). In contrast, CSP following the fentanyl trial was not significantly prolonged compared with the pre-exercise baseline (6 ± 4%). Our findings suggest that the central effects of spinal opioid receptor-sensitive muscle afferents might facilitate the fatigue-induced increase in CSP. Furthermore, since the CSP is thought to reflect inhibitory intracortical interneuron activity, which may contribute to central fatigue, our findings imply that spinal opioid receptor-sensitive muscle afferents might influence central fatigue by facilitating intracortical inhibition.

Group III and IV muscle afferents contribute to ventilatory and cardiovascular response to rhythmic exercise in humans

We investigated the role of somatosensory feedback on cardioventilatory responses to rhythmic exercise in five men. In a double-blind, placebo-controlled design, subjects performed the same leg cycling exercise (50/100/150/325 ± 19 W, 3 min each) under placebo conditions (interspinous saline, L(3)-L(4)) and with lumbar intrathecal fentanyl impairing central projection of spinal opioid receptor-sensitive muscle afferents. Quadriceps strength was similar before and after fentanyl administration. To evaluate whether a cephalad migration of fentanyl affected cardioventilatory control centers in the brain stem, we compared resting ventilatory responses to hypercapnia (HCVR) and cardioventilatory responses to arm vs. leg cycling exercise after each injection. Similar HCVR and minor effects of fentanyl on cardioventilatory responses to arm exercise excluded direct medullary effects of fentanyl. Central command during leg exercise was estimated via quadriceps electromyogram. No differences between conditions were found in resting heart rate (HR), ventilation [minute ventilation (VE)], or mean arterial pressure (MAP). Quadriceps electromyogram, O(2) consumption (VO(2)), and plasma lactate were similar in both conditions at the four steady-state workloads. Compared with placebo, a substantial hypoventilation during fentanyl exercise was indicated by the 8-17% reduction in VE/CO(2) production (VCO(2)) secondary to a reduced breathing frequency, leading to average increases of 4-7 Torr in end-tidal PCO(2) (P < 0.001) and a reduced hemoglobin saturation (-3 ± 1%; P < 0.05) at the heaviest workload (∼90% maximal VO(2)) with fentanyl. HR was reduced 2-8%, MAP 8-13%, and ratings of perceived exertion by 13% during fentanyl vs. placebo exercise (P < 0.05). These findings demonstrate the essential contribution of muscle afferent feedback to the ventilatory, cardiovascular, and perceptual responses to rhythmic exercise in humans, even in the presence of unaltered contributions from other major inputs to cardioventilatory control.

Opioid-mediated muscle afferents inhibit central motor drive and limit peripheral muscle fatigue development in humans

We investigated the role of somatosensory feedback from locomotor muscles on central motor drive (CMD) and the development of peripheral fatigue during high-intensity endurance exercise. In a double-blind, placebo-controlled design, eight cyclists randomly performed three 5 km time trials: control, interspinous ligament injection of saline (5K(Plac), L3-L4) or intrathecal fentanyl (5K(Fent), L3-L4) to impair cortical projection of opioid-mediated muscle afferents. Peripheral quadriceps fatigue was assessed via changes in force output pre- versus postexercise in response to supramaximal magnetic femoral nerve stimulation (DeltaQ(tw)). The CMD during the time trials was estimated via quadriceps electromyogram (iEMG). Fentanyl had no effect on quadriceps strength. Impairment of neural feedback from the locomotor muscles increased iEMG during the first 2.5 km of 5K(Fent) versus 5K(Plac) by 12 +/- 3% (P < 0.05); during the second 2.5 km, iEMG was similar between trials. Power output was also 6 +/- 2% higher during the first and 11 +/- 2% lower during the second 2.5 km of 5K(Fent) versus 5K(Plac) (both P < 0.05). Capillary blood lactate was higher (16.3 +/- 0.5 versus 12.6 +/- 1.0%) and arterial haemoglobin O(2) saturation was lower (89 +/- 1 versus 94 +/- 1%) during 5K(Fent) versus 5K(Plac). Exercise-induced DeltaQ(tw) was greater following 5K(Fent) versus 5K(Plac) (-46 +/- 2 versus -33 +/- 2%, P < 0.001). Our results emphasize the critical role of somatosensory feedback from working muscles on the centrally mediated determination of CMD. Attenuated afferent feedback from exercising locomotor muscles results in an overshoot in CMD and power output normally chosen by the athlete, thereby causing a greater rate of accumulation of muscle metabolites and excessive development of peripheral muscle fatigue.

Prophylactic intravenous preloading for regional analgesia in labour

BACKGROUND

Reduced uterine blood flow from maternal hypotension may contribute to fetal heart rate changes which are common following regional analgesia (epidural or spinal or combined spinal-epidural (CSE)) during labour. Intravenous fluid preloading may help to reduce maternal hypotension but using lower doses of local anaesthetic, and opioid only blocks, may reduce the need for preloading.

OBJECTIVES

To assess the effects of prophylactic intravenous fluid preloading before regional analgesia during labour on maternal and fetal well-being.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group trials register (19 February 2004).

SELECTION CRITERIA

Randomised and quasi-randomised trials comparing prophylactic intravenous preloading before regional analgesia during labour with a control group (dummy or no preloading).

DATA COLLECTION AND ANALYSIS

Two reviewers independently applied eligibility criteria, assessed trial quality and extracted data.

MAIN RESULTS

Six studies are included (473 participants). In one epidural trial using high-dose local anaesthetic, preloading with intravenous fluids was shown to counteract the hypotension which frequently follows traditional epidural analgesia (relative risk (RR) 0.07, 95% confidence interval (CI) 0.01 to 0.53; 102 women). This trial was also associated with a reduction in fetal heart rate abnormalities (RR 0.36, 95% CI 0.16 to 0.83; 102 women); no differences were detected in other perinatal and maternal outcomes for this trial and another high-dose epidural trial. In the two epidural low-dose anaesthetic trials, no significant difference in maternal hypotension was found (RR 0.73, 95% CI 0.36 to 1.48; 260 women), although they were underpowered to detect less than a very large effect. No significant differences were seen between groups in these trials for fetal heart rate abnormalities (RR 0.64, 95% CI 0.39 to 1.05; 233 women). In the two CSE trials, no differences were reported between preloading and no preloading groups. In the spinal/opioid trial, the RR for hypotension was 0.89, 95% CI 0.43 to 1.83 (40 women) and 0.70, 95% CI 0.36 to 1.37 for fetal heart rate abnormalities (32 women). In the opioid only study (30 women), there were no instances of hypotension or fetal heart rate abnormalities in either group.

REVIEWERS' CONCLUSIONS

Preloading prior to traditional high-dose local anaesthetic blocks may have some beneficial fetal and maternal effects in healthy women. Low-dose epidural and CSE analgesia techniques may reduce the need for preloading. The studies reviewed were too small to show whether preloading is beneficial for women having regional analgesia during labour using the lower-dose local anaesthetics or opioids. Further investigation of low-dose epidural or CSE (including opioid only) blocks, and the risks and benefits of intravenous preloading for women with pregnancy complications, is required.

Prophylactic intravenous preloading for regional analgesia in labour

BACKGROUND

Fetal heart rate changes are common following regional analgesia (epidural or spinal) during labour. Reduced uterine blood flow from maternal hypotension (low blood pressure) may contribute to this. Intravenous fluid preloading (volume expansion) may help to reduce maternal hypotension. Newer protocols using weaker solutions of local anaesthetic, and opioid only blocks, may reduce the need for preloading.

OBJECTIVES

The objective of this review was to assess the effects of prophylactic intravenous fluid preloading prior to epidural analgesia during labour on maternal and fetal well-being.

SEARCH STRATEGY

The Cochrane Pregnancy and Childbirth Group trials register (November 2001) and the Cochrane Controlled Trials Register (The Cochrane Library, Issue 3, 2001) were searched.

SELECTION CRITERIA

Randomised and quasi-randomised trials comparing prophylactic intravenous preloading before epidural analgesia during labour with a control group (dummy or no preloading).

DATA COLLECTION AND ANALYSIS

The reviewer assessed trial quality and extracted data.

MAIN RESULTS

For high dose local anaesthetic blocks, one study involving 102 women was included. There was potential for considerable bias in this trial. Preloading with intravenous fluids was associated with a reduction in hypotension (relative risk 0.07, 95% confidence interval 0.01 to 0.53). It was also associated with a reduction in fetal heart rate abnormalities (relative risk 0.36, 95% confidence interval 0.16 to 0.83). No differences were detected in other perinatal and maternal outcomes. The trials in women receiving low-dose local anaesthetic (95 women) or opioid only blocks (30 women) demonstrated no statistically significant differences in maternal hypotension or fetal heart rate abnormality, but were too small to exclude the possibility of moderate effects with certainty.

REVIEWER'S CONCLUSIONS

There are methodological limitations in the trials studied. However, preloading prior to high-dose local anaesthetic blocks may have beneficial fetal and maternal effects in healthy women. Further investigation of the effects in women receiving low-dose local anaesthetic or opioid only blocks, and the risks and benefits of intravenous preloading for women with pregnancy complications, is required.