Sodium bicarbonate as a single dose antacid in obstetric anaesthesia

Gastric pH and volumes were measured in 84 women who had general anaesthesia for emergency Caesarean section. Forty-eight received only 20 ml 8.4% sodium bicarbonate immediately before induction of anaesthesia and 36 ranitidine 150 mg 6-hourly during labour in combination with NaHCO3. Gastric pH was less than 2.5 in four women who received only bicarbonate. All aspirates from the ranitidine plus bicarbonate group had a pH greater than 2.5. Mean volumes of gastric content aspirated were 87 (SD 87.4) and 60 (SD 46.3) ml for the bicarbonate alone and bicarbonate plus ranitidine series respectively. These differences were not significant. Twenty millilitres of 8.4% NaHCO3 cannot be recommended as a single dose antacid for emergency Caesarean section. Ranitidine plus bicarbonate is considered a reliable antacid regimen to ensure elevation of gastric pH to safe levels.     

RAPID ADMINISTRATION OF CRYSTALLOID PRELOAD DOES NOT DECREASE THE INCIDENCE OF HYPOTENSION AFTER SPINAL ANAESTHESIA FOR ELECTIVE CAESAREAN SECTION

Twenty parturients undergoing elective Caesarean section wereallocated randomly to receive crystalloid preload 20 ml kg^–1over either 20 min or 10 min before spinal anaesthesia. Significanthypotension (systolic arterial pressure <100mm Hg and <80% of baseline value) occurred in six of the 10 patients inthe 20-min preload group and seven of 10 patients in the 10-minpreload group (ns). Both groups had a significant (P < 0.05)increase in central venous pressure during the preload period.The mean central venous pressure in the 10-min group was 11.9mm Hg (range 6–19 mm Hg), which was significantly greater(P < 0.05) than that in the 20-min group (mean 7.3 mm Hg,range 2–13 mm Hg). Three patients in the 10-min grouphad clinically unacceptable increases in central venous pressure.This study has demonstrated that rapid administration of crystalloidpreload before spinal anaesthesia did not decrease the incidenceor severity of hypotension, and questions the role of crystalloidpreload.     

Combination treatment with ranitidine and sodium bicarbonate prior to obstetric anaesthesia

The gastric pH and volume were measured in 175 patients undergoing elective, and 313 undergoing emergency, obstetric procedures. Ranitidine 150 mg was administered orally every 6 hours in labour and at least 2 hours before elective Caesarean section. Patients received 20 ml of 8.4% sodium bicarbonate orally immediately prior to induction of anaesthesia. The combination of ranitidine and sodium bicarbonate produced marked alkalinisation of gastric contents (mean pH 8.9). The administration of sodium bicarbonate pre-operatively in patients who received ranitidine less than 2 hours before operation led to satisfactory elevation of gastric pH. Only four patients had a gastric pH less than 2.5, one patient refused any medication, two received only ranitidine and one patient had a long interval from administration of bicarbonate to aspiration of gastric contents. Gastric volumes were high in labouring patients (mean 84 ml) despite administration of ranitidine. The effectiveness of sodium bicarbonate as a single dose antacid therapy prior to obstetric anaesthesia requires further study.     

Combined treatment with ranitidine and saline antacids prior to obstetric anaesthesia

Ranitidine 150 mg was given to 126 patients requiring elective Caesarean section under general anaesthesia: 43 women had ranitidine alone, 43 had this supplemented by a pre-induction dose of sodium citrate and 40 patients had ranitidine plus sodium bicarbonate. All three sub-groups provided satisfactory gastric pH and volume. Ranitidine 150 mg was given orally every 6 hours to women in labour. Of 221 patients requiring general anaesthesia during labour, 103 women received 30 ml 0.3 M sodium citrate and 118 women, 20 ml of 8.4% sodium bicarbonate 10 minutes before induction of anaesthesia. In the citrate sub-group there was one patient with a gastric pH less than 2.5 (mean pH 6.2, SEM 0.13 range 2.1-8.4). In the bicarbonate sub-group the lowest gastric acidity was 3.8 (mean pH 8.3, SEM 0.11 range 3.8-9.83).     

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.     

Plasma bupivacaine levels associated with extradural anaesthesia for Caesarean section

Plasma bupivacaine levels were measured in 47 women undergoing extradural Caesarean delivery. They were divided into four groups according to the following dose regimens using 0.5% bupivacaine. Group A were given a bolus of 20 ml with increment after 20 minutes. Groups B and C were given 10 ml initially with further increments if required at 10 minutes (group B) and 20 minutes (group C); Group D consisted of patients who had an extradural block extended for emergency Caesarean delivery. In the elective groups the highest and most rapidly achieved values were associated with group A and the lowest levels found in group C. The highest levels of all were found in the emergency group. The investigation indicates that slow controlled induction of extradural anaesthesia for Caesarean section greatly reduces the risk of local anaesthetic toxicity.     

EFFECTS OF KETAMINE ON THE PREGNANT UTERUS

Intra-uterine pressure was recorded by placing a Foley catheterin the extra-amniotic space before the termination of pregnancyin 25 patients, and Caesarean section in 12 patients. The effectsof administration of i.v. ketamine 2 mg/kg body weight, sodiumthiopentone 4 mg/kg body weight and ergometrine 0.5 mg, andintra-cervical 0·5% lignocaine 20 ml were measured inthe first trimester of pregnancy, and i.v. ketamine and sodiumthiopentone in late pregnancy. Ketamine was found to cause uterinecontraction (mean increase 16.1 mm Hg) equal to ergometrine(mean increase 14.8 mm Hg) in early pregnancy, but exert noeffect (mean decrease -1.33 mm Hg) in late pregnancy. Lignocainein early pregnancy given as a paracervical block had no significanteffect on intra-uterine pressure (mean increase 0.33 mm Hg).Sodium thiopentone (mean decrease -4.28 mm Hg first trimesterand -2.22 mm Hg at term) in late pregnancy had no significanteffect on intra-uterine pressure.     

Sciatic nerve palsy following childbirth

Two cases are reported of sciatic nerve palsy after delivery by Caesarean section in primigravidae. One mother was slender and had an emergency Caesarean section for failure to progress with a breech presentation. Epidural analgesia during labour was extended for operative delivery. The other mother was obese, mildly hypertensive, had a large baby with a high head and was delivered by elective Caesarean section under epidural anaesthesia. She experienced severe intrapartum hypotension. Both patients suffered right sided sciatic nerve palsy. The aetiologies of obstetric palsies and those following regional block are reviewed and the importance of careful diagnosis and of avoiding peripheral nerve compression during regional block are emphasised.     

CONTINUOUS SUBARACHNOID INFUSION OF 0.125% BUPIVACAINE FOR ANALGESIA DURING LABOUR

We have studied 20 primiparous women requesting pain relieffor labour, to determine the feasibility of subarachnoid infusionsof bupivacaine for analgesia. A 28-gauge catheter was insertedinto the subarachnoid space through a modified 22-gauge Sprotteneedle. After a bolus dose of up to 7.5 ml of 0.25% bupivacaine,a continuous infusion of 0.725 % bupivacaine was commenced.If analgesia became inadequate, additional 0.5-ml boluses of0.25% bupivacaine were given (mean number of top-ups 2.8; range0–6). Persistent perineal pain occurred in four womenand this was relieved by 0.5% hyperbaric bupivacaine. Analgesiawas good or excellent in 75 of 20 mothers within 70 min andin 79 of 20 within 30 min, and it remained good or excellentthroughout labour and delivery. Motor block was complete inthree of the women who needed hyperbaric 0.5% bupivacaine. Therewere no difficulties with insertion of the catheter, no episodesof significant hypotension (systolic arterial pressure lessthan 700 mm Hg) or postdural puncture headache. Seven mothersdelivered their babies vaginally, eight required assistancewith forceps and five needed a Caesarean section.     

Change in anaesthetic practice for Caesarean section in Germany

BACKGROUND: Initial data from 1996 revealed that in contrast to several other countries general anaesthesia was the preferred anaesthetic technique for Caesarean section in Germany. However, anaesthetic practice for Caesarean section has changed during the last decades world-wide. This investigation was performed to obtain more actual data on anaesthetic procedures in obstetric patients in German hospitals. METHODS: Questionnaires on the practice of anaesthesia for Caesarean section were mailed to 918 German departments of anaesthesiology. Furthermore, the survey evaluated severe perioperative complications in obstetric patients. RESULTS: The 397 completed replies in this survey represent 41.3% of all German deliveries in 2002. Spinal anaesthesia is now the most common technique (50.5%) for elective Caesarean section. In case of urgent and emergency Caesarean, delivery figures decrease to 34.6% and 4.8%, respectively. Epidural anaesthesia is performed in 21.6% of scheduled and 13.2% and 1.0% of non-scheduled urgent or emergency Caesarean sections, respectively. Four maternal deaths and several non-fatal episodes of gastric content aspiration were reported by the respondents. CONCLUSIONS: Compared to data obtained 6 years ago a significant increase in regional anaesthesia for Caesarean section has developed, with spinal anaesthesia being the preferred technique. Surveys can help to initiate discussion and improve current practice of anaesthetic care.     

Randomized trial of bolus phenylephrine or ephedrine for maintenance of arterial pressure during spinal anaesthesia for Caesarean section

Thirty-eight healthy women undergoing elective Caesarean section under spinal anaesthesia at term were allocated randomly to receive boluses of either phenylephrine 100 micrograms or ephedrine 5 mg for maintenance of maternal arterial pressure. The indication for administration of vasopressor was a reduction in systolic pressure to < or = 90% of baseline values. Maternal arterial pressure (BP) and heart rate (HR) were measured every minute by automated oscillometry. Cardiac output (CO) was measured by cross-sectional and Doppler echocardiography before and after preloading with 1500 ml Ringer lactate solution and then every 2 min after administration of bupivacaine. Umbilical artery pulsatility index (PI) was measured using Doppler before and after spinal anaesthesia. The median (range) number of boluses of phenylephrine and ephedrine was similar; 6 (1-10) vs 4 (1- 8) respectively. Maternal systolic BP and CO changes were similar in both groups, but the mean [95% CI] maximum percentage change in maternal HR was larger in the phenylephrine group (-28.5 [-24.2, - 32.9]%) than in the ephedrine group (-14.4 [-10.6, -18.2]%). As a consequence atropine was required in 11/19 women in the phenylephrine group compared with 2/19 in the ephedrine group (P < 0.01). Mean umbilical artery pH [95% CI] was higher in the phenylephrine group (7.29 [7.28-7.30]) than in the ephedrine group (7.27 [7.25-7.28]). The results of the present study support the use of phenylephrine for maintenance of maternal arterial pressure during spinal anaesthesia for elective Caesarean section.      

A prospective observational study of the use of the Proseal laryngeal mask airway for postpartum tubal ligation

BACKGROUND: Though controversial, the risk of pulmonary aspiration during general anaesthesia in the immediate postpartum period appears low. The efficacy of the Proseal laryngeal mask airway was studied prospectively in a group of patients undergoing postpartum tubal ligation. METHODS: The Proseal laryngeal mask airway was employed for airway management in 90 fasted patients undergoing tubal ligation via minilaparotomy at least 8 h after normal vaginal delivery (mean 36.5, range 8-96 h). Gastric volume and pH were measured, using aspiration through a gastric tube. RESULT: Proseal laryngeal mask airway insertion was successful in all patients, requiring one attempt in 75 patients (83%). The median (range) leak pressure was 35 (23-40) cmH2O. Twenty-two patients (25%) had a leak pressure of 40 cmH2O or greater. Gastric tube placement was successful in all patients, described as easy in 79 (87%), and difficult in 11 (13%). The mean initial volume of gastric aspirate was 10.7 (0-64) mL and the final volume 15.6 (0-71) mL. The mean pH of the gastric aspirate was 2.6 (1.2-6.6). There were no incidents of suspected fluid regurgitation or aspiration, but two patients required intubation during surgery. Ten patients (11.1%) complained of sore throat in the recovery room, nine of which were described as mild. All patients reported being satisfied with their anaesthesia. CONCLUSION: The Proseal laryngeal mask airway provides an effective airway for general anaesthesia in fasted patients undergoing tubal ligation from 8 h after normal vaginal delivery. While the safety of an unprotected airway in this population remains uncertain, this study suggested a low risk of regurgitation, especially in the first 24 h post partum.     

Changes in cardiac output during epidural anaesthesia for Caesarean section

Serial haemodynamic investigations were performed in 20 women who had epidural anaesthesia before elective Caesarean section. Cardiac output was measured by Doppler and cross-sectional echocardiography at the aortic valve. Measurements were performed after preloading the circulation with Ringer lactate solution (mean volume 805 ml) and then 10, 20, 30 and 40 minutes after administration of 0.5% bupivacaine. Preloading increased mean stroke volume from 84 to 94 ml and mean cardiac output from 7.01 to 7.70 litres/minute. Relative to basal values, mean arterial pressure decreased in all subjects after administration of bupivacaine (mean - 14%, range - 1 to - 33%). Five subjects were given ephedrine because of hypotension. In three of these subjects hypotension was associated with a marked decrease in cardiac output. No significant changes in arterial blood pressure or cardiac output were demonstrated relative to basal values in the remaining 15 subjects. Ephedrine induced consistent increases in blood pressure and cardiac output.     

Onset of vecuronium neuromuscular block is more rapid in patients undergoing Caesarean section

This investigation was carried out in ten patients undergoing elective Caesarean section and the results were compared with those of a control group of ten nonpregnant females of the same age group. The study investigated the onset of vecuronium neuromuscular block and the conditions of tracheal intubation when ketamine (1.5 mg.kg-1)-vecuronium 100 micrograms.kg-1) sequence was used for rapid-sequence induction of anaesthesia. The ulnar nerve was stimulated supra-maximally at the wrist with train-of-four stimuli every 20 sec, and the electromyographic response of the adductor pollicis muscle was displayed. The onset of 50% neuromuscular block as monitored by electromyography was shorter in the Caesarean group (80 +/- 30 sec) than in the control group (144 +/- 43 sec). The conditions of intubation at 50% block were adequate in both groups. Also, the onset of 90% block was shorter in the Caesarean group. The time of recovery to T1/control ratio of 25% was longer in the Caesarean group (46 +/- 10 min) than in the control patients (28 +/- 10 min). The results show that administration of vecuronium according to body weight results in a more rapid onset and delayed recovery of neuromuscular block in pregnant women undergoing Caesarean section than in the nonpregnant control patients.     

Systemic and pulmonary blood pressure during caesarean section in parturients with gestational hypertension

Twenty severely pre-eclamptic patients requiring caesarean section for delivery were allocated to two groups. One group received epidural anaesthesia consisting of either 20 ml of bupivacaine 0.75 per cent at L3-4 or 12ml at Ll-2. The other group received general anaesthesia consisting of thiopentone, 40 per cent nitrous oxide and halothane 0.5 per cent. Mean arterial pressure (MAP), pulmonary artery pressure (PAP), pulmonary wedge pressure (PWP), and central venous pressure (CVP) were recorded at five-minute intervals for at least 60 minutes before operation and at least every two minutes during anaesthesia. Patients receiving general anaesthesia had pressures recorded every minute during tracheal intubation and extubation. There was a mean increase of MAP of 45 mm Hg, of PAP 20 mm Hg, and PWP 20mm Hg during intubation and extubation. Apart from a slight mean fall in MAP the parturients receiving epidural anaesthesia showed little change in these cardiovascular parameters. It is concluded that tracheal intubation of patients with gestational hypertension produces an increase in MAP, PAP, and PWP which can lead to a significant risk of cerebral haemorrhage and pulmonary oedema. The value and dangers of using short-acting hypotensive agents to prevent these episodes of hypertension has still to be assessed. With epidural anaesthesia there is a danger of hypotension which can be treated with intravenous fluid replacement and ephedrine.     

Flow requirements for the Bain breathing circuit during anaesthesia for caesarean section

We studied the relationship between arterial carbon dioxide tension (PaCO2) and fresh gas flow (FGF) during use of the Bain breathing circuit for Caesarean section anaesthesia. Thirty-one patients undergoing Caesarean section were anaesthetised using the Bain circuit with intermittent positive pressure ventilation. The PaCO2 were measured at FGF of 70 ml X kg-1 X min-1, 80 ml X kg-1 X min-1, and 100 ml X kg-1 X min-1. The FGF requirement to maintain a given PaCO2 during Caesarean section anaesthesia is the same as the requirements for nonpregnant subjects, despite the increase in carbon dioxide production associated with pregnancy. This is probably because the total FGF determined by body weight and given during Caesarean section anaesthesia is 15-20 per cent higher than nonpregnant levels, due to the weight gain associated with pregnancy. A FGF of 100 ml X kg-1 of pregnant weight/min maintains PaCO2 of 4.44 kPa predelivery, which is in the desirable range of PaCO2 during Caesarean section.     

COLLOID (3% DEXTRAN 70) WITH OR WITHOUT EPHEDRINE INFUSION FOR CARDIOVASCULAR STABILITY DURING EXTRADURAL CAESAREAN SECTION

Using a non-invasive cardiac output monitor (Bo-Med NCCOM 3–R7J,we have compared cardiovascular responses, degree of haemodilutionand incidence of nausea during extradural Caesarean sectionin healthy non-labouring mothers given either ephedrine 17.5mgand3% Dextran 70 7.5ml kg^–1 before delivery (group A)or volume loading with Dextran 15 ml kg^–1 without infusionof ephedrine (group B). Smallest systolic arterial pressuresbefore delivery were 114 (SEM 4) mm Hg (group A) and 105 (5)(group B). There were no significant differences between thegroups in mean arterial pressure, heart rate, systemic vascularresistance or central venous pressure, while cardiac outputincreased more with the ephedrine infusion (P < 0.05). Haemodilutionwas 8% in group A and 16% in group B at the time of delivery.Ephedrine infusion was associated with a smaller incidence ofnausea (P < 0.01). Umbilical arterial pH values were notdifferent between the two groups. We conclude that infusionof ephedrine, combined with low volume colloid administration,is a safe alternative to more extensive colloid volume expansionfor control of hypotension and provides effective prophylaxisagainst nausea during extradural Caesarean section in healthynon-labouring mothers.     

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.     

Reversal of neuromuscular blockade by glycopyrrolate and neostigmine

The effect of intravenous glycopyrrolate and neostigmine, a drug combination routinely given to antagonize non-depolarising neuromuscular blockade, on lower oesophageal sphincter tone was studied in twenty patients undergoing Caesarean section. Glycopyrrolate 0.6 mg and neostigmine 2.5 mg i.v. increased LOS pressure insignificantly by a mean of 0.2 kPa (P less than 0.1). In contrast, glycopyrrolate 0.6 mg and neostigmine 5 mg increased LOS pressure by a mean of 1.2 kPa (P less than 0.001). The latter dosage of this drug combination thus appears preferable in patients presenting for emergency surgery, if the integrity of the lower oesophageal sphincter is to be maintained during extubation and recovery from general anaesthesia.     

Transcutaneous electrical nerve stimulation at the PC-5 and PC-6 acupoints reduced the severity of hypotension after spinal anaesthesia in patients undergoing Caesarean section

BACKGROUND: Despite prophylactic measures, hypotension remains a common side-effect of spinal anaesthesia for parturients. Electroacupuncture at the Neiguan (PC-6) and Jianshi (PC-5) points influences haemodynamics. We thus hypothesized that transcutaneous electrical nerve stimulation (TENS) at traditionally used acupuncture points would reduce the severity of hypotension after spinal anaesthesia in patients undergoing Caesarean section. METHODS: After obtaining approval from the local ethics committee and written informed patient consent, 36 singleton parturients undergoing Caesarean section under spinal anaesthesia were randomized into three groups. The control group received no treatment, and the acupoint and non-acupoint groups received TENS at the PC-5 and PC-6 points of both arms and non-acupoints of both shoulders, respectively. RESULTS: The median (range) of the lowest recorded systolic blood pressure was significantly higher in the acupoint group compared with the other groups and that of the non-acupoint group was higher than that of the control group [control, 70 (68-82) mm Hg; acupoint, 94 (84-109) mm Hg; non-acupoint, 81 (70-92) mm Hg: P<0.001]. Significantly more parturients in the control and non-acupoint groups experienced hypotension [control, 10 (83%); acupoint, 4 (33%); non-acupoint, 10 (83%): P=0.013]. More ephedrine was required to maintain arterial blood pressure in the control and non-acupoint groups. CONCLUSIONS: TENS on the traditional acupuncture points reduced the severity and incidence of hypotension after spinal anaesthesia in parturients.