J.P.H. Fee

Patient controlled analgesia for labour: a comparison of remifentanil with pethidine*

We compared the analgesic efficacy and safety of remifentanil and pethidine via patient controlled analgesia for women in established uncomplicated labour. Women received either remifentanil 40 μg with a 2‐min lockout (n = 20) or pethidine 15 mg with a 10‐min lockout (n = 19). Visual analogue scores for pain during the study and for overall pain were similar for both groups (mean (SD) 6.4 (1.5) cm for remifentanil and 6.9 (1.7) cm for pethidine). The area under the curve for visual analogue scores of satisfaction with analgesia was higher for remifentanil than for pethidine (p = 0.001). Maternal arterial oxygen saturation was similar in both groups. Neurologic and Adaptive Capacity Scores at 30 min were higher for remifentanil than for pethidine (median (interquartile range [range]) 36 (34.5–37 [32–39]) vs 34 (33–35 [30–35]), respectively; p = 0.003).

Changes in serum enzyme levels following ketamine infusions

The levels of four serum enzymes, known to be elevated in toxic hepatitis, were measured preoperatively and on the 3–4th and 13–15th postoperative days in patients anaesthetised with ketamine infusions (54) or with a standard technique (64). Significant elevations in enzyme levels were considered to have occurred when the postoperative levels were outside the accepted normal range and had increased by more than 3 × SD from controls. About half the patients in each group had minor gynaecological operations and 2120 in the ketamine series had postoperative elevation of enzyme levels, with no changes in the non‐ketamine group. Following intermediate operations 14134 anaesthetised with ketamine showed abnormal enzyme levels compared with 7/34 who had standard operations. None, of the latter had more than one abnormal test as compared with six in the ketamine series. The causes and significance of these findings are not known.

The effect of high altitude commercial air travel on oxygen saturation

The recent paper on the effect of high altitude commercial air travel on oxygen saturation [1] presentedobservational findings from a group of subjects undertaking commercial air travel. Unfortunately, it contained a number of errors and omissions which we feel should be corrected. The repeated statement that the fractional inspired oxygen concentration is reduced at altitude is erroneous. If air is breathed, the FiO2 will not change with alterations in ambient pressure, as air is defined as containing 20.9% oxygen. The physiological effects that are associated with ascent to altitude breathing air arise from a reduction in the inspired, alveolar and arterial partial pressures of oxygen as a consequence of the decrease in ambient barometric pressure (Dalton’s Law). The effects on peripheral haemoglobin saturation of exposure to the modest reduction in ambient pressure in an intact commercial aircraft pressure cabin during flight have been known for a long time, as a review of the standard textbooks of aviation medicine would have revealed [2, 3]. The effects of a modest degree of hypoxia on passengers, in health and sickness, were extensively reviewed by the British Thoracic Society in the preparation of its guidelines on managing patients with respiratory disease planning air travel [4]. These guidelines confirm that at maximum cabin altitudes the SpO2 will be expected to fall to 85– 91% ofnormal, but that healthypassengers do not generally experience symptoms or require supplemental oxygen. The subject of cabin air quality has also been extensively reviewed, most recently by the European Community CabinAir study [5]. The results of that study do not support the claim that there is a paucity of data available on this aspect of air travel. In the paper’s discussion, reference is made to a putative association between modest hypoxia and an increase in coagulability. The results of Bendz et al. referenced in the paper [6] have not been supported by the findings of other workers [7,8] and further data from larger controlled studies will be reported from the WHO research programme (the WRIGHT project) investigating the presence or absence of a link between air travel and venous thromboembolism. Air travel is now very common, with well over 1 billion people worldwide taking commercial flights each year. Considerations for their health and welfare are clearly important. It is therefore disappointing to see a paper containing statements so much at variance with well documented information.

The effect of high altitude commercial air travel on oxygen saturation: High altitude air travel on oxygen saturation

Air travel has increased steadily over the last decade, and its effect on the health of passengers has been the subject of much debate. There is a paucity of evidence on the effects of air travel on oxygen saturation in general populations. The peripheral oxygen saturation and pulse rate of 84 passengers, aged 1–78 years, were measured by pulse oximetry at round level and altitude during air travel. There was a statistically significant reduction in oxygen saturation in all passengers travelling long haul and short haul flights (p < 0.05). The mean [range] (SD) SpO2 for all flights at ground level was 97% [93–100] (1.33) and at cruising altitude 93% [85–98] (2.33). Fifty‐four per cent of passengers had SpO2 values of 94% or less at cruising altitude. This is a value which may prompt physicians to administer supplemental oxygen in hospital patients.

Assessment of tracheal intubation in children after induction with propofol and different doses of remifentanil

Tracheal intubating conditions were assessed in 112 children after induction of anaesthesia with propofol and remifentanil 1.0, 2.0 or 3.0 µg.kg−1. Subjects in a control group were given propofol and mivacurium 0.2 mg.kg−1. Haemodynamic and respiratory parameters were recorded. Plasma catecholamine levels were measured in a subgroup of 40 children. Intubating conditions were acceptable in 14/28 (50%), 18/26 (69%) and 22/27 (82%) in those subjects given remifentanil 1.0, 2.0 or 3.0 µg.kg−1, respectively, and in 27/28 (96%) of the control group. Intubating conditions in subjects given remifentanil 3.0 µg.kg−1 were better than in those given remifentanil 1.0 µg.kg−1 (p < 0.05). There were no significant differences in intubating conditions between those given remifentanil 3.0 µg.kg−1 and the control group. Systolic blood pressure and heart rate increased in response to tracheal intubation in subjects given remifentanil 1.0 µg.kg−1 and in the control group (p < 0.05). Time to resumption of spontaneous respiration was prolonged in subjects given remifentanil 3.0 µg.kg−1 (p < 0.001). In conclusion, remifentanil 2 µg.kg−1 provides acceptable intubating conditions and haemodynamic stability without prolonging the return of spontaneous respiration.

Tracheal intubating conditions after induction with sevoflurane 8% in children. A comparison with two intravenous techniques.

We studied tracheal intubating conditions in 120 healthy children, aged 3–12 years, in a blinded, randomised clinical trial. Children were randomly allocated to one of three groups: group PS, propofol 3 mg.kg−1 and succinylcholine 1 mg.kg−1 (n = 40); group PA, propofol 3 mg.kg−1 and alfentanil 10 µg.kg−1 (n = 40); group SF, sevoflurane 8% in 60% nitrous oxide in oxygen for 3 min (n = 40). Tracheal intubating conditions were graded according to ease of laryngoscopy, position of vocal cords, coughing, jaw relaxation and movement of limbs. Overall intubating conditions were acceptable in 39 of 40 children in the propofol/succinylcholine group, 21 of 40 children in the propofol/alfentanil group and 35 of 40 children in the sevoflurane group. Children receiving propofol and succinylcholine or sevoflurane had better intubating conditions overall than those given propofol and alfentanil (p < 0.01). In conclusion, anaesthetic induction and tracheal intubation using sevoflurane 8% for 3 min is a satisfactory alternative to propofol with succinylcholine in children.

An investigation of the potential morphine sparing effect of midazolam

The effect of a bolus and continuous infusion of midazolam on postoperative morphine consumption was assed in a placebo‐controlled, double‐blind, randomly allocated trial of 50 patients undergoing elective abdominal hysterectomy. Patients in the trial group received a bolus dose of midazolam 5 mg.70 kg‐1 at induction followed by an infusion at a rate of 1 mg.70 kg h‐1 over the next 48h. Morphine consumption in the midazolam group was scientifically lower in the first 12 h postoperatively. (p < 0.02) but there was no significant difference between the two groups thereafter. Patients in the midazolam treated group had lower pain scores over the first 24 h. Also, a significantly greater number of patients in the midazolam group required no antiemetic medication over the 48 h study period (p < 0.05). Assessment of sedation revealed no significant difference between groups. We conclude that low dose midazolam has a significant, but short‐lived, morphine sparing effect.

The effects of subanaesthetic concentrations of xenon in volunteers.

This study reports the subjective, psychomotor and physiological properties of subanaesthetic concentrations of xenon. Ten healthy male volunteers received either xenon or nitrous oxide in a randomised crossover study design. The subjects breathed either xenon (Xe) or nitrous oxide (N2O) from a closed circuit breathing system, according to a randomised, double‐blind protocol. The concentration of xenon required to produce sedation, ranged between 27 and 45%(median 35%). All subjects completed the xenon protocol. Subjects were tested using the Critical Flicker Fusion test and derived electroencephalogram parameters, however, neither test was found to reliably predict sedation. The respiratory rate decreased markedly during sedation with xenon. The subjects did not experience any airway irritability (coughing, breath‐holding or laryngospasm) during administration of either gas. One subject required anti‐emetic treatment in the N2O group compared to none in the Xe group. Eight subjects reported that they found sedation with xenon pleasant and preferable to nitrous oxide. Xenon sedation was well tolerated and was not associated with any adverse physiological effects, however, it was reported to be subjectively dissimilar to nitrous oxide.

Molecular sieves: an alternative method of carbon dioxide removal which does not generate compound A during simulated low‐flow sevoflurane anaesthesia

Molecular sieves are used in industry to scrub’ industrial gases. We examined, during simulated low‐flow closed system anaesthesia, (1) the carbon dioxide adsorbing potential of molecular sieves and (2) the reactivity of the sieves compared to soda lime using sevoflurane as an indicator. A low‐flow anaesthetic system containing 13X molecular sieves was connected to a model lung. End‐tidal concentrations of CO2 were measured continuously at an O‐2 flow of 800 ml.min‐1 and a CO2 flow of 200 ml.min‐1. In the second study, sevoflurane (FEsevo 1.7%) was added to the system after which samples were taken from the inspiratory limb of the anaesthetic system. This experiment was performed both during carbon dioxide removal with soda lime and with the molecular sieves. The samples were stored in gas‐tight syringes and analysed by gas chromatography. The temperature of both absorbents was measured throughout the study. The molecular sieves adsorbed carbon dioxide (20 %) efficiently for a period of 5h. There was a gradual increase from the baseline of 4.4% to 4.5, 5.4, and 6.0% at 90, 180, and 300 min, respectively. When sevoflurane was added to the system, compound A was detected at the start of both experiments. However, when soda lime was used the concentrations of compound A increased 10‐fold after 2.5 h compared with baseline values. No increase in compound A was observed when molecular sieves were used for carbon dioxide removal. The highest mean (SD) temperature of the molecular sieves was 41.5 (3.2)° C. Molecular sieves are effective adsorbents of carbon dioxide when used in a simulated low‐flow, closed anaesthetic system. Compound A is not formed when sevoflurane is added to the system.

Ineffective analgesia after extradural tramadol hydrochloride in patients undergoing total knee replacement

Postoperative analgesia after two extradural tramadol regimens was compared with that obtained using a standard extradural morphine regimen in patients undergoing total knee replacement. Extradural anaesthesia with light general anaesthesia was used. Patients received extradurally either: tramadol 50mg by bolus injection followed by infusion (5mg.h‐1 for 12 h and 2.5mg.h‐1 for a further 12 h) (group T50), tramadol 100 mg by bolus injection followed by infusion (10 mg.h‐1 for 12 h and 5mg.h‐1 for a further 12 h) (group T100) or morphine sulphate 2 mg by bolus injection followed by infusion (0.2 mg.h‐1 for 12 h and at 0.1 mg.h‐1 for a further 12 h) (group M). Analgesia was allocated according to a controlled double‐blind design. Visual analogue pain scores were markedly poorer (p < 0.05) and patient‐controlled analgesic consumption was significantly greater (p < 0.01) in the two tramadol groups when compared with the morphine group. The study was discontinued after recruitment of 12 patients, as analgesia was deemed inadequate in those receiving tramadol extradurally. However, further study of this drug may be warranted to examine its effectiveness where postoperative pain is expected to be less severe, and to assess the effect of larger extradural doses and of co‐administration of tramadol and morphine by this route.