Intraoperative fetal oxygen saturation during Caesarean section: general anaesthesia using sevoflurane with either 100% oxygen or 50% nitrous oxide in oxygen

BACKGROUND AND OBJECTIVE: The study was designed to evaluate whether the administration of sevoflurane in 100% oxygen for anaesthesia during Caesarean section would improve fetal and neonatal oxygenation compared with the administration of sevoflurane with 50% nitrous oxide in oxygen. METHODS: The randomized, single-blind controlled study examined 24 mothers, ASA I-II, at term undergoing Caesarean section who were allocated to receive sevoflurane in either 100% oxygen (n = 13) or 50% nitrous oxide in oxygen (n= 11). General anaesthesia was induced in both groups with thiopental 4-5 mg kg(-1) followed by succinylcholine 1.5 mg kg(-1) to facilitate tracheal intubation. Parturients received sevoflurane given either in 100% O2 or in a 50:50 nitrous oxide and oxygen mixture, using 0.5-1.0% progressive incremental dosing up to 1.5-2.0 MAC. Non-invasive fetal oxygen saturation was measured between induction to delivery, and umbilical artery and vein PaO2 were evaluated at birth. RESULTS: Intraoperative fetal oxygen saturation increased in all patients after maternal 100% oxygen administration (P < 0.01). Maternal hyperoxygenation significantly increased the umbilical vein and umbilical artery PaO2 and the umbilical artery SaO2 at birth (P < 0.0001). CONCLUSIONS: Maternal hyperoxygenation significantly improves fetal as well as neonatal oxygenation.     

Supplemental maternal oxygen therapy during caesarean section under epidural anaesthesia: a comparison of nasal prongs and facemask

Forty healthy parturients at term, undergoing elective Caesarean section, were divided into two groups to receive supplemental oxygen by either simple facemask (Group FM, 8 L.min-1) or nasal prongs (Group NP, 4 L.min-1) during the procedure. Anaesthesia was provided by epidural block to equivalent dermatomal levels in all patients. Maternal oxygen saturation was measured continuously with pulse oximetry and supplemental oxygen was provided to the mother after administration of the epidural test dose and continued until the end of the procedure. Following delivery of the infant and concurrent with Apgar scoring, the umbilical cord was double-clamped and arterial and venous samples were drawn. The pH, partial pressures of O2 and CO2 and O2 saturations were measured. There was no difference in the clinical condition of the neonates, as assessed by Apgar scores, or in the acid-base and oxygenation status, as assessed by blood gas analyses between the two groups. Mean umbilical vein oxygen saturation, a measure of fetal oxygen delivery, was 46 +/- 18% (95% confidence interval 39% to 54%) for Group NP and 54 +/- 17% (95% confidence interval 46% to 62%) for Group FM, again not different. We conclude that when the clinical condition, acid-base and oxygenation status of neonates, delivered by elective Caesarean section to healthy, low-risk parturients with normal placental function under epidural anaesthesia, are evaluated, it makes no difference whether the mothers received supplemental oxygen by nasal prongs or simple facemask.     

Supplementary oxygen administration for elective Caesarean section under spinal anaesthesia

We investigated the necessity for administration of supplementary oxygen to mothers undergoing elective Caesarean section under spinal anaesthesia. Sixty-nine women undergoing elective Caesarean section were randomly allocated to one of three groups to be given either oxygen (40%) by facemask, air by facemask or oxygen at 2 l x min(-1) by nasal cannulae. Umbilical arterial and venous blood samples were taken and analysed immediately after delivery. The results showed that there were no significant differences in the umbilical arterial or venous pH, partial pressure of oxygen and partial pressure of carbon dioxide between any of the three groups. We also assessed the patient acceptability of oxygen administered by facemask vs. nasal cannulae should the need for supplementary oxygen arise. It was found that use of the facemask impeded communication.     

Early respiratory depression during Caesarean section following epidural meperidine

A case of respiratory depression which occurred following administration of epidural meperidine during Caesarean section is described. Epidural meperidine, 75 mg (10 mg.ml-1) was given after delivery of the infant to provide postoperative analgesia. Oxygen desaturation (SaO2 90%) and a decrease in respiratory rate (4.min-1) were noted 30 min after epidural meperidine was administered. Naloxone, 0.1 mg, was given iv which resulted in prompt improvement in both respiratory rate and oxygen saturation. Vascular absorption of meperidine from the epidural venous plexus is the most probable explanation for this case of early respiratory depression. We recommend a maximum bolus dose of 50 mg of epidural meperidine for pain management after Caesarean section. It is also important to monitor oxygen saturation continuously during the intraoperative period, and to monitor the patient closely in the recovery room for at least one hour for evidence of respiratory depression.     

Propofol infusion anaesthesia for Caesarean section

Two propofol infusion regimens and a standard general anaesthetic were compared in thirty Chinese women undergoing elective Caesarean section. After induction of anaesthesia with propofol 2 mg.kg-1, ten patients received propofol 6 mg.kg-1.hr-1 and nitrous oxide 50 per cent in oxygen while ten were given propofol 9 mg.kg-1.hr-1 with 100 per cent oxygen. The other ten patients received thiopentone 4 mg.kg-1 and nitrous oxide 50 per cent in oxygen with enflurane one per cent. Maternal recovery times and psychomotor performance were recorded. Neonates were assessed by Apgar scores, neurologic and adapative capacity scores (NACS) and umbilical cord blood gas analysis. Haemodynamic changes were similar immediately following induction but the low propofol infusion group had the best haemodynamic stability subsequently. Recovery times were fastest in the low-infusion group but there were no differences in later postbox testing. Neonatal Apgar scores and umbilical blood gas analysis were similar but NACS at two hours were poorer in the high infusion group. A propofol infusion coupled with nitrous oxide appears to be a satisfactory technique for Caesarean section.     

Concentration of lidocaine hydrochloride in newborn gastric fluid after elective caesarean section and vaginal delivery with epidural analgesia.

Lidocaine concentrations were measured after vaginal delivery or Caesarean section with epidural anaesthesia in samples of maternal and umbilical blood and in newborn gastric contents. The pH of the gastric aspirate was also determined in a number of neonates. Gastric lidocaine concentrations were higher and the pH was lower after vaginal delivery in comparison to Caesarean section. A significant inverse correlation exists between gastric pH and gastric lidocaine concentration, Neonate gastric lidocaine concentration was significantly higher than in maternal or umbilical venous plasma after vaginal delivery, but not after Caesarean section. Due to these differences, gastric lavage for the treatment of neonatal lidocaine intoxication may be more beneficial in reducing foetal systemic local anaesthetic concentration after vaginal than after elective abdominal delivery.     

Halothane 2% for caesarean section.

During the induction-delivery interval for Caesarean section delivery, 2% halothane in pure oxygen was administered. The technique was compared to a 0.5% halothane in 50% oxygen/50% nitrous oxide anaesthesia. When a continuous infusion of oxytocin was administered, no excessive haemorrhage was seen. No maternal reminiscence was seen using 2% halothane, but awareness was recorded using 0.5% halothane in 50% nitrous oxide in 15% of the mothers. When there were no signs of preoperative fetal distress, the neonates were unaffected by the halothane concentration provided the induction-delivery interval was short. In cases of fetal distress, the administration of 2% halothane further aggravated the condition of the neonates, as indicated by lowered 1-min Apgar scores, umbilical oxygen tensions, pH and base excess values.     

MAXIMUM FIO2 DURING CAESAREAN SECTION

Forty patients undergoing elective and emergency Caesarean section(excluding severe fetal distress) were divided into four groupsto receive 50% oxygen, 50% nitrous oxide, and 0.5% halothane(group 1, controls) or 100% oxygen supplemented by 1.5 x MACof halothane, enflurane or isoflurane (groups 2, 3, 4, respectively)reducing to 1.0 x MAC 5 min after induction. The umbilical venousP_O2 in the oxygen-only groups was higher than in the oxygen-nitrousoxide groups, this difference reaching statistical significancewhen the patients in the oxygen-only groups were combined. Bloodloss and uterine contractility were unaffected by the increasedconcentrations of volatile agents, and awareness did not occur.Improved cardiovascular stability was demonstrated in the electivehigh-oxygen groups. The technique is safe and warrants furtherstudy, since there are no important ethical objections.     

A comparison of spinal and general anaesthesia for elective caesarean section: effect on neonatal condition at birth

The condition of 74 neonates delivered by elective caesarean section under general anaesthesia was compared with that of 63 neonates delivered under spinal anaesthesia. When the uterine incision - delivery interval was less than 3 min, neonates in the spinal group exhibited a higher Apgar score at 1 min (P < 0.002) and a higher mean umbilical venous pH (P < 0.05) than the equivalent general anaesthesia group; a significantly greater proportion of the neonates delivered under general anaesthesia had an umbilical venous pH<7.28 at delivery (P < 0.05), a fact which previous work suggests is important. Among anaesthetized mothers inspired oxygen concentration (33% or 50%) before delivery had no significant effect upon neonatal outcome. It is concluded that neonates delivered at elective Caesarean section under spinal anaesthesia are in better condition than those delivered under general anaesthesia.     

EFFECTS OF EXTRADURAL ANAESTHESIA ON HUMAN FETAL BLOOD FLOW IN UTERO: Comparison of Three Local Anaesthetic Solutions

Twenty-seven women, scheduled for elective Caesarean sectionunder extradural anaesthesia were allocated randomly to oneof three groups: group Ea received 1.5% etidocaine with adrenaline,group Bp 0.5% bupivacaine plain, and group Ba 0.5% bupivacainewith adrenaline. There was no difference in the quality anddistribution of sensory blockade between the three groups. Motorblockade was most profound in group Ea. Maternal heart rateand arterial pressure were only slightly affected in the threegroups. Before induction of extradural anaesthesia, and 15 and30 min after, fetal umbilical and aortic blood flows were examinedusing a combination of real-time ultrasono-graphy and the pulsedDoppler technique. Blood flow in the umbilical vein was notaffected in any of the groups, and blood flow in the fetal aortaremained unchanged in groups Ea and Bp, but was increased by12% after 30 min in group Ba. We conclude that, with the threelocal anaesthetic solutions studied during extradural anaesthesiafor elective Caesarean section, fetal circulatory variablesremained stable and within normal limits, when in associationwith normal values of maternal arterial pressure.     

Propofol for induction and maintenance of anaesthesia at Caesarean section A comparison with thiopentone/enflurane

A propofol infusion regimen and a standard general anaesthetic were compared in 40 Chinese women undergoing elective Caesarean section. Twenty patients received propofol 2 mg/kg for induction of anaesthesia followed by propofol 6 mg/kg/hour, while 20 patients received thiopentone 4 mg/kg with enflurane 1% for maintenance of anaesthesia. All patients were given atracurium and their lungs ventilated with nitrous oxide 50% in oxygen until delivery of the neonate. The hypertensive response after intubation was of shorter duration in the propofol group compared with the thiopentone group. Induction to delivery times ranged from 5 to 14 minutes and neonates from both groups had similar and satisfactory Apgar scores. Neurologic and Adaptive Capacity Scores and umbilical cord blood gas analysis. However, a prolonged propofol infusion time before delivery may cause lower Neurologic and Adaptive Capacity Scores. There were no differences in maternal recovery times or psychomotor performance.     

PLACENTAL TRANSMISSION OF ATROPINE AT FULL-TERM PREGNANCY

Measurements of placental transmission of atropine were performedduring Caesarean section. Twenty-five patients received H-atropine0.5 µg. kg^–1 i.v. 1–30 min before delivery.Maternal venous blood was sampled before the induction of anaesthesiaand at the moment of delivery, together with umbilical arterialand venous blood. Total hydrogen-3 activity was determined byliquid scintillation counting. The stability of H-atropine wasconfirmed by paper chromatography. The concentrations in theumbilical vein 1 and 5 min after injection were respectively12% and 93% of the corresponding maternal value. Those in theumbilical artery were approximately 50% of those in the umbilicalvein during the same period.     

Effect of maternal facial oxygen on neonatal behavioural scores during elective Caesarean section with spinal anaesthesia

BACKGROUND AND OBJECTIVE: For many, the administration of additional oxygen to the women receiving regional anaesthesia for Caesarean section is traditional, but for others it is controversial because of doubts about its efficacy. The aim of our study was to determine if beneficial effects of maternal oxygen therapy on the fetus could be revealed using a neonatal behavioural scoring system. METHODS: Sixty women with a normal singleton pregnancy beyond 36 weeks gestation, undergoing elective Caesarean section under spinal anaesthesia were randomized into two groups: Group 1 received air and oxygen mixture through a Hudson style face mask (FiO2 of 0.21-0.25). Group 2 received FiO2 of 0.40-0.60 through an identical Hudson style face mask. Neurologic Adaptive Capacity Score on all the infants within 5 min of birth and between 10 and 24 h after the Caesarean delivery was performed. Apgar score, umbilical venous blood oxygen tension and umbilical artery standardized base excess were recorded. RESULTS: Initial Neurologic Adaptive Capacity Scores at birth in Groups 1 and 2 were 32.6 (SD 4.6) and 31.3 (SD 4.3), respectively. Latter scores were 36.0 (SD 3.0) and 36.5 (SD 1.9), respectively. Neither were statistically significant. There were no significant differences between the groups for any of the recorded variables. CONCLUSIONS: Administering maternal oxygen using a standard commercial Hudson style face mask does not appear to significantly improve oxygen delivery to, nor does it influence acidosis or behavioural effects in, the normal neonate at elective Caesarean delivery with spinal anaesthesia.     

Nitrous oxide concentrations in maternal and fetal blood during caesarean section

BACKGROUND AND OBJECTIVE: There are little data on nitrous oxide (N2O) concentrations in neonatal blood at delivery. We investigated the effects of the time elapsing between the induction of anaesthesia and delivery (the I-D interval) on umbilical blood N2O concentrations. METHODS: Maternal and neonatal blood N2O concentrations were measured in 27 patients undergoing Caesarean section under N2O 67% anaesthesia. The duration of N2O administration (range 2-50 min) was arbitrarily divided into three groups (each n = 9): short (2-9 min), medium (9.1-14 min) and long duration (14.1-50 min). RESULTS: Compared with a rapid increase in the maternal arterial N2O concentration (48.9 +/- 4.7%), the umbilical venous N2O concentration (17.9 +/- 8.3%) rose slowly in the short duration group, whereas the N2O concentrations became more similar (61.6 +/- 4.3 and 43.2 +/- 10.0%, respectively) in the long duration group. The ratio of umbilical vein to maternal artery N2O concentrations correlated with the duration of N2O anaesthesia (r = 0.739), resulting in ratios of 0.37 +/- 0.18, 0.61 +/- 012 and 0.70 +/- 0.13 for the short, medium and long duration groups, respectively. The Apgar score at 1 min correlated inversely with the duration of anaesthesia and with the umbilical vein N2O concentration (r = -0.457 and -0.423, respectively). CONCLUSIONS: The data suggest that placental N2O transfer during Caesarean section is time-dependent and slower compared with maternal N2O uptake. They also suggest that the Apgar score is less affected by N2O administration when the I-D interval is shorter.     

Crystalloid versus colloid for circulatory preload for epidural Caesarean section

Sixty mothers were randomly allocated to receive either 2 litres of crystalloid or 1 litre of colloid solution (hydroxyethyl starch) in order to preload the circulation prior to elective Caesarean section under epidural anaesthesia. There were no differences in the incidence of hypotension, degree of haemodilution, umbilical cord blood gas tensions or umbilical blood osmolalities between the two groups.     

Plasma etomidate levels in mother and fetus

The most commonly used induction agent in anaesthesia for Caesarean section is still thiopentone. The increasing incidence of Caesarean section for delivery of premature babies from a hostile environment may call in question the assumption that the dose of thiopentone received by the neonate will not cause depression in the hours following birth. Previous studies on thiopentone for Caesarean section have shown inconsistency in umbilical vein/maternal vein ratios. We have studied plasma etomidate levels in maternal and umbilical blood at the time of delivery to see whether equilibrium occurs with this agent. We were able to demonstrate an umbilical/maternal vein etomidate ratio of 0.5 (SD 0.18), with no relation to time in the range encountered. Also, the uterine artery/uterine vein etomidate ratio was 0.86 (SD 0.33), suggesting that etomidate uptake into the fetus is effectively complete. Further, in all cases the neonatal plasma etomidate levels were less than half those measured at recovery of consciousness in adults in other studies, despite a larger induction dose than is usually used.     

Intrathecal diamorphine for analgesia after Caesarean sectionA dose finding study and assessment of side-effects

Eighty women undergoing elective Caesarean section under spinal anaesthesia using hyperbaric bupivacaine 0.5% were randomly allocated to receive, in addition, intrathecal diamorphine 0.125, 0.25 or 0.375 mg or saline. Postoperative morphine requirements, measured using a patient-controlled analgesia system, were reduced in a dose-dependent manner by diamorphine. Pain scores were significantly lower at 2 and 6 h following the two larger doses of diamorphine. Less supplemental analgesia was required intra-operatively if intrathecal diamorphine had been given. The incidences of vomiting and pruritus were also dose-related. No respiratory rates of less than 14 breath.min⁻¹ were recorded and the incidence of oxygen saturation readings less than 95% and 90% did not differ between groups. There were no adverse neonatal effects. Intrathecal diamorphine in the present study was found to be safe in doses of up to 0.375 mg following Caesarean section. However, minor side-effects were frequently observed.     

Respiratory effects of spinal anaesthesia for Caesarean section

We report the changes observed in a number of pulmonary function tests performed on 36 patients undergoing Caesarean section under spinal anaesthesia. The tests comprised peak expiratory flow, forced expiratory volume in one second, forced vital capacity, forced expiratory volume in one second to forced vital capacity ratio and the maximal mid-expiratory flow. Significant changes occurred that are consistent with a restrictive ventilatory defect. These changes persisted for four hours after the induction of spinal anaesthesia. Administration of 35% oxygen by facemask failed to change significantly fetal umbilical vein pH or partial pressure of oxygen.     

Randomised trial of intravenous infusion of ephedrine or mephentermine for management of hypotension during spinal anaesthesia for Caesarean section

This study compared the effects of intravenous infusions of ephedrine and mephentermine for maintenance of maternal arterial pressure and neonatal outcome in pregnant women receiving subarachnoid block for lower segment Caesarean section. Sixty patients who developed hypotension following subarachnoid block for Caesarean section were randomly divided into two groups of 30 each to receive an intravenous infusion of ephedrine or mephentermine. Hypotension was defined as a decrease in systolic blood pressure of > or = 20% from the baseline value or an absolute value of <100 mmHg, whichever was higher. The vasopressor infusion was titrated to maintain systolic blood pressure between 'hypotension' and baseline values. Baseline haemodynamic parameters, haemodynamic changes subsequent to the start of vasopressor infusion, duration of hypotension and amount of vasopressor required were statistically similar for both groups. Neonatal APGAR scores and acid-base profiles were also comparable. To conclude, mephentermine can be used as safely and effectively as ephedrine for the management of hypotension during spinal anaesthesia in patients undergoing elective Caesarean section.     

FETAL BLOOD FLOW DURING INTRATHECAL ANAESTHESIA FOR ELECTIVE CAESAREAN SECTION

Fetal aortic and umbilical blood flows were studied in 15 mothersbefore and during spinal (intrathecal) anaesthesia for electiveCaesarean section, using a method combining real-time ultrasonographyand a pulsed Doppler technique. Spinal anaesthesia with 0.5%bupivacaine hydrochloride 2.5ml in 8% glucose monohydrate solutionwas administered after preloading with 2 litre of lactated Ringer'ssolution. Simultaneously with the subarachnoid injection, aninfusion i. v. of ephedrine 50 mg in 500 ml normal saline wasinitiated. Maternal heart rate and systolic arterial pressureremained stable during the spinal anaesthesia, but diastolicarterial pressure decreased (P<0.05). Fetal heart rate increased(P<0.05) 30 min after the introduction of the spinal anaesthesia,but blood flows in the fetal descending aorta and umbilicalvein were unaffected. The pulsatility index of the fetal bloodvelocity decreased (P<0.05) both in the fetal aorta and inthe umbilical artery 30 min after induction of the spinal anaesthesia,indicating a possible decrease in the placental vascular resistance.We conclude that, when normotension is maintained in the motherwith a preload infusion and an infusion of ephedrine, spinalanaesthesia for Caesarean section has no harmful effect on thefetal circulation.