W.D. Ngan Kee

Randomised double‐blinded comparison of phenylephrine vs ephedrine for maintaining blood pressure during spinal anaesthesia for non‐elective Caesarean section*

In a randomised, double‐blinded study, we compared boluses of phenylephrine 100 μg with ephedrine 10 mg for treating hypotension (systolic blood pressure < 100 mmHg) in 204 patients having non‐elective Caesarean section under spinal anaesthesia. Umbilical arterial (UA) and venous (UV) pH and base excess were similar between groups. In the ephedrine group, UA lactate concentration was higher (median 2.6 [interquartile range 2.3–3.3] vs 2.4 [1.9–3.0] mmol.l−1, p = 0.002) and UV lactate concentration was higher (2.5 [2.2–3.2] vs 2.3 [1.9–2.8] mmol.l−1, p = 0.016) and more patients had nausea or vomiting (12.7% vs 3.9%, p = 0.02). Clinical neonatal outcome was similar. Of the protocol‐compliant patients (n = 148), UA Po2 and UV Po2 were lower in the phenylephrine group although oxygen content was similar. We conclude that phenylephrine and ephedrine are both suitable vasopressors for use in non‐elective Caesarean sections.

Ultrasound-guided lumbar plexus block through the acoustic window of the lumbar ultrasound trident

Lumbar plexus block (LPB) is frequently used in combination with an ipsilateral sacral plexus or sciatic nerve block for lower limb surgery. This is traditionally performed using surface anatomical landmarks, and the site for local anaesthetic injection is confirmed by observing quadriceps muscle contraction to peripheral nerve stimulation. In this report, we describe a technique of ultrasound-guided LPB that was successfully used, in conjunction with a sciatic nerve block, for anaesthesia during emergency lower limb surgery. The anatomy, sonographic features, technique of identifying the lumbar plexus, and the potential benefits of using this approach are discussed.

Haemodynamic effects from aortocaval compression at different angles of lateral tilt in non-labouring term pregnant women

BACKGROUND Aortocaval compression (ACC) can result in haemodynamic disturbances and uteroplacental hypoperfusion in parturients. Its detection is difficult because in most patients, sympathetic compensation results in no signs or symptoms. However, profound hypotension may develop after sympathectomy during regional anaesthesia. In this prospective observational study, we aimed to detect ACC by analysing haemodynamic changes in term parturients who were positioned sequentially at different angles of lateral tilt. METHODS We studied haemodynamic changes in 157 non-labouring term parturients who were positioned in random order at 0°, 7.5°, 15°, and full left lateral tilt. Cardiac output (CO), stroke volume, and systemic vascular resistance were derived using suprasternal Doppler. Non-invasive arterial pressure (AP) measured in the upper and lower limbs was analysed to detect aortic compression. RESULTS CO was on average 5% higher when patients were tilted at ≥15° compared with <15°. In a subgroup of patients (n=11), CO decreased by more than 20%, without changes in systolic AP, when they were tilted to <15° which was considered attributable to severe inferior vena caval compression. Only one patient in the supine position had aortic compression with the systolic AP in the upper limb 25 mm Hg higher than the lower limb. CONCLUSIONS Patients with ACC can be identified by the CO changes from serial measurements between supine, 15°, or full lateral tilt. Our findings suggest that in non-labouring parturients, ACC is asymptomatic and can be effectively minimized by the use of a left lateral tilt of 15° or greater.

Closed-loop feedback computer-controlled infusion of phenylephrine for maintaining blood pressure during spinal anaesthesia for caesarean section: a preliminary descriptive study*

We describe the novel use of a closed‐loop feedback computer‐controlled infusion of phenylephrine for maintaining blood pressure in 53 patients having spinal anaesthesia for elective caesarean section. A simple on–off algorithm was used that activated an intravenous phenylephrine infusion at 100 μg.min−1 when systolic blood pressure was less than or equal to baseline and stopped the infusion when systolic blood pressure exceeded baseline. Up to uterine incision, 94.6% of all systolic blood pressure measurements were within the range (baseline ± 20%). Seven patients (13.2%) had one or more episodes of hypotension (systolic blood pressure < 80% of baseline) and 23 patients (37.7%) had one or more episodes of hypertension (systolic blood pressure > 120% of baseline). No patient had nausea or vomiting and in no case was umbilical arterial blood pH < 7.2. Calculated system performance parameters were comparable with those of previously published closed‐loop systems and provide a reference for the potential development and comparison of more advanced algorithms.

Extension of epidural blockade in labour for emergency Caesarean section using 2% lidocaine with epinephrine and fentanyl, with or without alkalinisation.

In a randomised, double‐blind study, we investigated rapid extension of epidural analgesia to surgical anaesthesia for emergency Caesarean section. Parturients receiving epidural analgesia in labour who subsequently required Caesarean section were given a test dose of 3 ml lidocaine 2% with epinephrine 1 : 200 000, followed 3 min later by 12 ml lidocaine 2% with epinephrine 1 : 200 000 and fentanyl 75 µg, to which was added 1.2 ml sodium bicarbonate 8.4% (bicarbonate group; n = 20) or saline (saline group; n = 20). Mean (SD [range]) time to surgical anaesthesia was less in the bicarbonate group (5.2 (1.5) [2–8] min) than the saline group (9.7 (1.6) [6–12] min; mean difference 4.5 min (95% CI 3.5–5.5) min; p < 0.001). Maternal side‐effects and neonatal outcome were similar between groups. We conclude that pH‐adjusted lidocaine 2% with epinephrine and fentanyl is effective for rapidly establishing surgical anaesthesia in patients with a functioning epidural catheter for labour who require emergency Caesarean section.

Supplementary oxygen for emergency Caesarean section under regional anaesthesia

BACKGROUND Controversy still exists if the administration of supplementary oxygen to patients having emergency Caesarean section (CS) under regional anaesthesia is beneficial or potentially harmful. Therefore, in a prospective double-blinded study, we randomized patients having emergency CS under regional anaesthesia to receive either air or 60% oxygen until delivery and compared the effects on fetal oxygenation and lipid-peroxidation in the mother and baby. METHODS We recruited 131 women having emergency CS under regional anaesthesia. Either 21% (air group) or 60% oxygen (oxygen group) was administered using a Venturi-type facemask until delivery. We compared the oxygen exposure duration, umbilical arterial (UA) and venous (UV) blood gases and oxygen content, and plasma concentration of 8-isoprostane. Subanalysis was performed according to whether or not fetal compromise was considered present. RESULTS Data from 125 patients were analysed. For the oxygen group vs the air group, there were greater values for UA PO(2) [mean 2.2 (SD 0.5) vs 1.9 (0.6) kPa, P=0.01], UA O(2) content [6.6 (2.5) vs 4.9 (2.8) ml dl(-1), P=0.006], UV PO(2) [3.8 (0.8) vs 3.2 (0.8) kPa, P<0.0001], and UV O(2) content [12.9 (3.5) vs 10.4 (3.8) ml dl(-1), P=0.001]. There was no difference between the groups in maternal, UA, or UV 8-isoprostane concentration. Apgar scores and UA pH were similar between the groups. Similar changes were observed regardless of whether fetal compromise was considered present (n=37) or not (n=88). CONCLUSIONS Breathing 60% oxygen during emergency CS under regional anaesthesia increased fetal oxygenation with no associated increase in lipid-peroxidation in the mother or fetus.

Randomized comparison of closed-loop feedback computer-controlled with manual-controlled infusion of phenylephrine for maintaining arterial pressure during spinal anaesthesia for Caesarean delivery

BACKGROUND Closed-loop feedback computer-controlled infusion has not been described for administering phenylephrine to maintain arterial pressure (AP) during spinal anaesthesia for caesarean delivery. We aimed to compare AP control using this automated system with a previously described manual infusion system. METHODS We randomly allocated 222 healthy subjects having spinal anaesthesia for scheduled caesarean delivery to have systolic AP maintained near baseline with phenylephrine (100 µg ml(-1)) by computer-controlled infusion utilizing a proportional algorithm or manual-controlled infusion utilizing an on-off algorithm. AP control was assessed by comparing the proportion of systolic AP measurements within ±20% of baseline and by performance error (PE) calculations. RESULTS A total of 212 subjects finished the study. In the computer-control group, 97% of systolic AP recordings fell within ±20% of baseline compared with 95% in the manual-control group (P=0.0004). For computer-control compared with manual-control, wobble was smaller [median 3.5 (inter-quartile range 2.5-4.8)% vs 4.2 (3.3-5.9)%, P=0.003], but there was no difference in the median PE [2.9 (0.3-4.7)% vs 1.9 (0-4.2)%], median absolute PE [4.7 (3.5-5.6)% vs 4.7 (3.8-6.7)%], or divergence [-0.01 (-0.03-0)% vs -0.06 (-0.26-0.08)%]. Fewer interventions per subject for controlling AP were required in the computer-control group [2 (2-2) vs 10 (8-13), P<0.001]. There were no differences in measured clinical outcomes. CONCLUSIONS Within the constraints of the studied algorithms, closed-loop feedback computer-controlled phenylephrine infusion provided better AP control with fewer interventions required compared with manual-controlled infusion.

Effects of different inspired oxygen fractions on lipid peroxidation during general anaesthesia for elective Caesarean section

BACKGROUND During general anaesthesia (GA) for Caesarean section (CS), fetal oxygenation is increased by administering an inspired oxygen fraction (Fi(o(2))) of 1.0. However, it is unclear whether such high Fi(o(2)) will increase oxygen free radical activity. METHODS We randomized 39 ASA I-II parturients undergoing elective CS under GA to receive 30% (Gp 30), 50% (Gp 50), or 100% (Gp 100) oxygen with nitrous oxide and sevoflurane adjusted to provide equivalent minimum alveolar concentration. Baseline maternal arterial blood before preoxygenation and maternal arterial, umbilical arterial and venous blood at delivery were sampled for assays of the by-product of lipid peroxidation, isoprostane, and for measurement of blood gases and oxygen content. RESULTS Maternal and umbilical isoprostane concentrations were similar among the three groups at delivery, despite significantly increased maternal and fetal oxygenation in Gp 100. However, paired comparisons of maternal delivery vs baseline concentration of isoprostane showed an increase at delivery for all groups [Gp 30: mean 342 (sd 210) vs 154 (65) pg ml(-1), P=0.016; Gp 50: 284 (129) vs 156 (79) pg ml(-1), P=0.009; Gp 100: 332 (126) vs 158 (68) pg ml(-1), P<0.001]. The magnitude of increase was similar in all three groups and independent of the Fi(o(2)) or duration after induction. CONCLUSIONS GA for CS is associated with a marked increase in free radical activity in the mother and baby. The mechanism is unclear but it is independent of the inspired oxygen in the anaesthetic mixture. Therefore, when 100% oxygen is administered with sevoflurane for GA, fetal oxygenation can be increased, without inducing an increase in lipid peroxidation.

Randomised double‐blind comparison of morphine vs. a morphine–alfentanil combination for patient‐controlled analgesia

In a randomised, double‐blind study, we compared a combination of morphine and alfentanil with morphine alone for patient‐controlled analgesia (PCA) after Caesarean section under spinal anaesthesia. After surgery, patients were randomly allocated to receive PCA with a bolus dose of either morphine 0.75 mg plus alfentanil 0.125 mg (Group MA, n = 40) or morphine 1.5 mg alone (Group M, n = 37) with a lockout interval of 8 min and no hourly dose limit. Clinical assessments were made in the first 24 h, after which patients completed a written questionnaire. There were no differences between groups in PCA usage or visual analogue scale pain scores measured at 2, 4, 6 and 24 h. There was a low incidence of side‐effects in both groups. In the questionnaire, patients in Group MA scored higher compared with Group M when asked to grade speed of onset and effectiveness of analgesia after a PCA bolus; there were no differences in grading for duration of analgesia or overall patient satisfaction. Addition of alfentanil to morphine may have advantages for PCA.

The effect of the addition of adrenaline to pethidine for patient‐controlled epidural analgesia after Caesarean section

We have investigated the addition of adrenaline to pethidine for patient‐controlled epidural analgesia after elective Caesarean section. In a randomised, double‐blind study, patients received patient‐controlled epidural analgesia for 24 h using pethidine 5 mgml−1 with adrenaline 5 μgml−1 (adrenaline group, n = 40) or pethidine 5 mgml−1 without adrenaline (plain group, n = 38). Visual analogue scale pain scores at rest and on coughing measured 2 h, 6 h and 24 h after surgery were similar between the two groups. There was a trend towards lower mean total consumption of pethidine in the adrenaline group (231.5 mg; SD 140.5 mg) compared with the plain group (289.5 mg; SD 139.5 mg; p = 0.071). Patients in the adrenaline group had higher visual analogue scale scores for nausea at 2 h and 24 h and higher scores for pruritus at 2 h compared with the plain group. Addition of adrenaline to pethidine for patient‐controlled epidural analgesia does not appear to have significant clinical advantages.