Summary

In this review paper, the authors critically analyse the use of a number of depth of anaesthesia monitors in light of the most recent literature and their own clinical experience. There appears to be increasing evidence that anaesthesia depth monitors reduce the incidence of unexpected intraoperative awareness and also that they improve the quality of anaesthesia. Proper use of these monitors necessitates background knowledge about the physiology of the loss of consciousness, the type of variable recorded and processed by the monitoring devices, the factors that might interfere with recording and the limits of use. The information provided by anaesthesia depth monitors is detailed and relationships with clinical practice are established to provide the reader with key features for optimal use of those monitors and correct interpretation of data. Practitioners and patient's knowledge and expectations regarding this matter, as well as the cost–benefit relationship are also discussed.

Summary

Background and objective: Former studies revealed conflicting information on the usefulness of intraoperative monitoring of visual evoked potentials. This study was designed to evaluate the characteristics of visual evoked potential recording in surgically anaesthetized patients using the modality of steady-state visual evoked potentials.

Methods: In 30 cases with non-cranial surgery steady-state visual evoked potentials were recorded in the awake and surgically anaesthetized patient using total intravenous anaesthesia. For stimulation, goggles with red light-emitting diodes at a frequency of 8.5 Hz were used. A two-channel recording with silver cup electrodes at Oz to Fz and Oz to earlobe was used. All traces were analysed for the presence of the characteristically sinusoidal waveform and amplitudes and latencies of the main peaks were measured.

Results: Recordings during surgery demonstrated a minor latency prolongation of 16% and a more pronounced amplitude attenuation of 67% compared to the recordings in the awake patients. These differences were statistically significant (paired t-test, P < 0.001). In surgically anaesthetized patients steady-state visual evoked potentials showed a relatively high intra- and interindividual variability. In four of 30 patients completely stable recordings were obtained, whereas in 14 patients identifiable waves were recordable in only less than 50% of the intraoperative traces. Of the total 1360 traces recorded intraoperatively clearly identifiable steady-state visual evoked potentials patterns were present in 56% of the traces. There was no correlation between the magnitude of the evoked potential amplitude and its stability in intraoperative recordings.

Conclusions: We conclude from this study, that steady-state visual evoked potential recordings in the surgically anaesthetized patient appeared to be more stable compared to our earlier findings using transient visual evoked potentials. However, further efforts are necessary to improve the stability of the recordings during surgery and thus allow for a more reliable intraoperative monitoring of visual pathways in routine clinical practice.

Summary

Background and objective: The anaesthesiologist's preoperative interview with the patient is important in preparing the patient for surgery. Its potential protective influence on adverse side-effects from anaesthesia and convalescence is rarely investigated within the context of other perioperative factors. Structural equation modelling allows detection and quantification of all causal relationships and mediator effects in multivariate models. Therefore, this method is presented as a tool and applied to discover the influence of the preoperative interview within socio-demographic variables and duration of surgery on complaints and recovery after anaesthesia.

Methods: The influence of individual satisfaction with the anaesthesiologist's preoperative interview on postoperative events such as nausea/vomiting, difficulties in recovering from anaesthesia, experience of postoperative pain, physical discomfort and satisfaction with convalescence expressed by the patient was analysed by means of structural equation modelling. The variables gender, age and duration of surgery were also included as predictors in the analyses. The model in the total sample of 710 patients was then analysed for structural differences between groups treated either with propofol (n = 204) or with isoflurane + nitrous oxide (n = 267) for maintenance of anaesthesia.

Results: The model revealed that the anaesthesiologist's preoperative interview in combination with associated mediating side-effects explains 45% of the variance of ‘feeling physical discomfort’ and 18% of the variance of ‘satisfaction with convalescence’. The same model could be fitted in the propofol and the isoflurane + nitrous oxide group. Moreover, the structure and the strength of causal relations between variables were identical in the two groups.

Conclusions: The anaesthesiologist's efforts to improve the interview with the patient by more reassuring and proper information will result in less side-effects from anaesthesia and better recovery from surgery. It could be demonstrated that structural equation modelling is a powerful tool for detection of causal relationships and mediator effects in perioperative medicine.

Summary

Background and objective:Only regular training of anaesthetic personnel ensures safe and reliable application of cricoid pressure during rapid sequence induction of anaesthesia. Previously described training devices are either complicated, too expensive and usually unavailable, or they are very simple and do not correctly simulate the process of applying cricoid force. We designed and tested a cricoid pressure trainer with real-time display of applied force. The device is easy to assemble at relatively little cost with material widely available. It allows effective biofeedback training of the force required during the Sellick manoeuvre and can be used for routine staff assessment.

Methods:Thirty-six anaesthesia assistants were assessed for their correct application of cricoid pressure. Previous training in, and knowledge of, applying cricoid pressure was first evaluated by a questionnaire. We designed a model for testing the application of cricoid force. Pre-training cricoid forces were obtained by asking the subjects to apply ‘awake’ (10 N = 1.020 kg) and ‘asleep’ (30 N = 3.060 kg) cricoid pressure on our model while blinded to the actual pressure produced. The volunteer was then trained to apply correct pressure employing real-time biofeedback. Post-training values were later determined with the subject again blinded to the actual applied pressure.

Results:Post-training performance showed significant improvement in the application of the correct cricoid force (P<0.0005). Only 8% (3/36) of subjects applied incorrect ‘awake’ cricoid pressure after training vs. 56% (20/36) before training. All participants applied correct ‘asleep’ cricoid pressure after training vs. 72% (26/36) failing before training.

Conclusions:Our biofeedback cricoid pressure trainer is effective in the assessment and training of correct cricoid pressure application by anaesthetic personnel.

Summary

Background and objective: To compare the recently introduced Microcuff® endotracheal tube with conventional tubes in respect of the cuff pressures required to prevent air leakage.

Methods: The following tubes (ID 7.0 mm) were compared: Microcuff® HVLP ICU, Mallinckrodt HiLo®, Portex Profile Soft Seal®, Rüsch Super Safety Clear® and Sheridan CF®. Fifty patients undergoing endotracheal intubation with a cuffed tube of internal diameter 7.0 mm were studied. Tracheas were intubated using one of the endotracheal tubes in random order. Cuff pressure to prevent air leakage at standardized ventilator setting (peak inspiratory pressure 20 cmH2O/PEEP 5 cmH2O/respiratory rate 15 breaths min−1) was assessed by auscultation of audible sounds at the mouth. Patients characteristics and cuff pressures from each brand were compared to the Microcuff® group using the Mann-Whitney U-test (P < 0.05 was chosen as the level of statistical significance).

Results: Patients' median age (range) was 14.2 (12.0–17.1) yr, body weight 57.5 (40.0–81.9) kg and length 164.9 (146.5–190.0) cm. No significant differences in patients' characteristics were found between groups. Mean cuff pressure (all tubes) required for air sealing was 19.1 (8–42) cmH2O. The Microcuff® tube required significantly lower sealing pressures (9.5 (8–12) cmH2O) compared to the other brands of endotracheal tube (P < 0.05, Mann-Whitney U-test).

Conclusion: The Microcuff® endotracheal tube with its ultra-thin polyurethane cuff membrane required the lowest sealing pressure to prevent air leakage. These features are potentially of interest for long-term intubated patients and for cuffed endotracheal tubes in children, allowing tracheal sealing at lower cuff pressures implying less damage to the trachea.

Summary

Background and objective: Epidural anaesthesia is the preferred technique of anaesthesia for Caesarean section in pre-eclampsia. Spinal anaesthesia is considered by some as a safe and effective alternative, which is especially useful in emergency situations. Combined spinal–epidural anaesthesia, using low doses of local anaesthetics with opioids, is effective and reduces the incidence of hypotension in normal pregnancy. We performed a retrospective chart analysis to evaluate the effects of combined spinal–epidural anaesthesia on maternal haemodynamics and fetal outcome compared to conventional epidural anaesthesia.

Methods: A retrospective anaesthesia chart analysis of all pre-eclamptic patients who underwent Caesarean section over a 4 yr period was performed. Patient characteristic, obstetric, haemodynamic, fetal and neonatal data were gathered and analysed according to the anaesthetic technique used.

Results: Seventy-seven pre-eclamptic parturients undergoing Caesarean section were identified (26 women were severely pre-eclamptic and 51 demonstrated mild pre-eclampsia). Epidural anaesthesia was performed in 62 patients and combined spinal–epidural anaesthesia was performed in 15. No differences in patient characteristic and obstetric data were noted. Highest mean arterial pressure prior to anaesthesia was comparable between the groups (epidural: 106 ± 12 vs. combined spinal–epidural anaesthesia: 109 ± 18 mmHg) as well as the lowest recorded mean arterial pressure following anaesthesia (epidural: 93 ± 13 vs. combined spinal–epidural anaesthesia: 98 ± 17 mmHg). In the combined spinal–epidural anaesthesia group more ephedrine was used compared to the epidural group (14.6 ± 4.4 vs. 3.6 ± 4.6 mg, P<0.05). However, more lactated Ringer's was used in the epidural group. Umbilical artery pH was lower in the epidural group (7.26 ± 0.01 vs. 7.29 ± 0.02, P<0.05). Similar results were noted in 26 severely pre-eclamptic patients. Seven women underwent combined spinal– epidural anaesthesia and 19 underwent epidural anaesthesia in the severely pre-eclamptic group. Also more ephedrine was used in the combined spinal–epidural anaesthesia group. A tendency towards a lower umbilical artery pH was observed in the epidural group but this difference did not reach statistical significance.

Conclusions: Combined spinal–epidural anaesthesia appears to be safe as anaesthetic technique for pre-eclampsia and severe pre-eclampsia. However, it is important to consider the retrospective design of the study and the large number of epidural anaesthetics performed.

Summary

Background and objective: Absorption and disposition kinetics can be studied with a stable-isotope method. The aim of this study was to validate a stable-isotope method for levobupivacaine and to derive the relevant pharmacokinetics after epidural administration.

Methods: Eight volunteers (18–32 yr) received approximately 23 mg of both levobupivacaine and deuterium-labelled levobupivacaine simultaneously by intravenous infusion. Venous blood samples were taken for 8 h. Fifteen patients (23–85 yr) received 19 mL levobupivacaine 0.5% (including a 3 mL test dose) epidurally and, 25 min later, approximately 25 mg deuterium-labelled levobupivacaine (D3-levobupivacaine) intravenously. Arterial blood samples were collected for 24 h. Plasma concentrations were determined using liquid chromatography-mass spectrometry. Plasma concentration–time data were analysed by compartmental and non-compartmental analysis.

Results: Based on the ratio of the normalized areas under the curve of unlabelled and deuterium-labelled levobupivacaine in volunteers, as determined by both compartmental (mean ratio: 1.02, 90% CI: 1.00–1.04) and non-compartmental analysis (mean ratio: 1.02, 90% CI: 1.00–1.03) the two formulations were considered equivalent. In surgical patients the elimination half-life (mean ± SD: 196 ± 65 min), total body clearance (349 ± 114 mL min−1) and volume of distribution at steady state (56 ± 14 L), derived by compartmental analysis, were similar to those obtained by non-compartmental analysis. The absorption was bi-phasic. The fraction absorbed and half-life of the fast absorption process were 0.22 ± 0.06 and 5.2 ± 2.7 min, respectively. The values for the slow absorption process were 0.84 ± 0.14 and 386 ± 91 min, respectively.

Conclusions: D3-levobupivacaine is pharmacokinetically equivalent to unlabelled levobupivacaine and can be used to study the absorption and disposition kinetics after perineural administration of levobupivacaine in a single experiment.

Summary

Background and objective: The analgesic potency of non-steroidal anti-inflammatory drugs and acetaminophen are still being debated. We have assessed the relative analgesic effect of ibuprofen, acetaminophen or the combination of both after orthopaedic surgery.

Methods: Sixty-one ASA I patients, scheduled for an elective anterior cruciate ligament reconstruction under general anaesthesia were randomized, in a double blind fashion, into one of three groups. The ibuprofen group (n = 17) received ibuprofen 800 mg orally 1 h before operation and again at 6 and 12 h after the initial dose. The acetaminophen group (n = 20) received of acetaminophen 1 g orally at the same time intervals. The combination group (n = 24) received both ibuprofen 800 mg and acetaminophen 1 g. Surgery was performed under general anaesthesia with propofol and fentanyl for induction and maintenance with propofol and nitrous oxide in oxygen. The patients were monitored for 24 h thereafter, and the following variables were assessed: pain by visual analogue and verbal scales, need for rescue intravenous opioid analgesia (i.e. ketobemidone) and adverse events.

Results: The ibuprofen group and the combination group experienced significantly less pain during the first 6 h after surgery than the acetaminophen group using the visual analogue and the verbal scales. The acetaminophen group also had a significantly higher average consumption of opioids during the first 6 and 24 h. There were no significant differences between the ibuprofen group and the combination group in respect of experienced pain or consumption of rescue analgesia. The incidence of side-effects, postoperative haemoglobin concentration and renal function, judged by creatinine clearance, were identical between the groups.

Conclusion: Ibuprofen 800 mg thrice daily reduced pain to a greater degree than acetaminophen 1 g thrice daily, after anterior cruciate ligament reconstruction under general anaesthesia. The combination of acetaminophen and ibuprofen did not provide any superior analgesic effect.

Summary

Background and objective: This randomized, double-blinded, prospective study compared the effects of clonidine, esmolol or alfentanil on the level of hypnosis and haemodynamic responses to intravenous induction of anaesthesia and endotracheal intubation.

Methods: Forty-five patients scheduled for elective surgery were allotted to one of three groups. They were given either alfentanil 3 μg kg−1min−1 (n = 15); esmolol 1 mg kg−1min−1 (n = 16) or clonidine 3 μg kg−1 (n = 14) as a 10 min infusion. The infusions of alfentanil and esmolol, but not of clonidine, were maintained during endotracheal intubation. Anaesthesia was induced with midazolam (2 mg) and thiopental as required to suppress the eyelash reflex. Atracurium (0.5 mg kg−1) was given to produce neuromuscular block. Mean arterial pressure, heart rate, and bispectral index were recorded on arrival (baseline), after study drug infusion, after injecting midazolam and thiopental, as well as after endotracheal intubation. ANOVA and χ2-test were used for analysis.

Results: Blood pressure, heart rate and the bispectral index were unaltered by the study drugs, but thiopental requirements were reduced by alfentanil and clonidine (P < 0.014). Mean arterial pressure values (mean ± standard error of mean) in the alfentanil, esmolol and clonidine groups were: baseline: 107.8 ± 3.8; 106.6 ± 3.9; 103.4 ± 3.7 mmHg; after thiopental: 74.0 ± 4.2; 85.6 ± 4.3; 94.2 ± 4.1 mmHg and after endotracheal intubation: 91.7 ± 5.3; 114.1 ± 6.9; 123.6 ± 5.6 mmHg, respectively (two-way ANOVA, P < 0.001). Mean arterial pressure changed significantly after intubation from baseline (P < 0.001) after alfentanil (− 15%) and clonidine (+ 20%) but not after esmolol (+ 7%), while the changes between pre- and postintubation values were similar in all groups (24–33% increase). The bispectral index indicated that all patients had an adequate level of hypnosis, but the variability was higher in the esmolol group (P < 0.002).

Conclusions: None of the study drugs blocked the increase in mean arterial pressure induced by endotracheal intubation, but esmolol provided better overall haemodynamic stability. All groups had an adequate level of hypnosis.

Summary

Background and objective: One of the complications of laparoscopic surgery is carbon monoxide production during electrocautery. The aim of our study was to ascertain the relationship between intraperitoneal and alveolar concentrations of carbon monoxide and systemic carboxyhaemoglobin in patients undergoing laparoscopic cholecystectomy and anaesthetized with a closed system, where the carbon monoxide excreted through the lungs is accumulated in the circuit and thus re-inhaled.

Methods: Nine consecutive patients undergoing laparoscopic cholecystectomy were studied. Patients' lungs were ventilated with a closed anaesthesia breathing system (Physioflex®). Measurements were taken after establishing pneumoperitoneum (baseline) and at 5, 15 and 30 min after starting electrocautery.

Results: Mean duration of pneumoperitoneum was 42 ± 13 min with cumulative electrocautery time of 2.4 ± 1.8 min. Intraperitoneal carbon monoxide concentrations increased significantly at 5, 15 and 30 min reaching peak values of 481 ± 151 ppm at 15 min. No significant differences were found in alveolar carbon monoxide and carboxyhaemoglobin concentrations with respect to baseline.

Conclusions: No significant increase in carboxyhaemoglobin is produced during laparoscopic surgery, even under closed-system anaesthesia without pulmonary carbon monoxide elimination. This is most likely due to a low peritoneal absorption of carbon monoxide. We conclude that in adult patients, no carbon monoxide intoxication is caused if reasonable periods of electrocautery are used and the intraperitoneal gas is regularly renewed.

Summary

Background and objective: The efficiency of bilateral paravertebral blockade combined with general anaesthesia (active) vs. general anaesthesia alone (control) in reducing postoperative pain following laparoscopic cholecystectomy was evaluated using a prospective randomized study design.

Methods: Patients were randomly assigned to either group. Nerve-stimulator guided paravertebral blockade at the T5–6 level was performed with a local anaesthetic mixture (0.30 mL kg−1). Twenty millilitres of the mixture contained lidocaine 2% 6 mL; lidocaine 2% 6 mL with epinephrine 1/200 000; bupivacaine 0.5% 5 mL; fentanyl 1 mL (50 μg mL−1) and clonidine 2 mL (150 μg mL−1). Postoperative pain and consumption of opioids were assessed during the first 72 h.

Results: Two-times 30 patients were analysed. Patient characteristics data, and pre- and peroperative variables were similar in both groups. Mean pain scores visual analogue scale were significantly less with active compared with control (P < 0.05) at 6 h (1.56 ± 1.58 vs. 4.78 ± 1.67), at 12 h (1.52 ± 1.58 vs. 3.81 ± 1.63), at 24 h (1.16 ± 1.34 vs. 2.71 ± 1.50), at 36 h (0.68 ± 1.02 vs. 2.29 ± 1.41), at 48 h (0.60 ± 1.04 vs. 1.61 ± 1.33) and at 72 h (0.40 ± 0.86 vs. 1.19 ± 1.16). The number of patients consuming supplemental analgesics was significantly less (P < 0.05) with active compared with control, at 6 h (6 vs. 29), at 12 h (2 vs. 26), at 24 h (1 vs. 23) and at 36 h (2 vs. 15). More patients were free from nausea (P < 0.05) with active compared with control at 6 h (23 vs. 9) and at 12 h (29 vs. 19).

Conclusion: When used as a complement to general anaesthesia, bilateral nerve-stimulator guided paravertebral blockade with lidocaine, bupivacaine, fentanyl and clonidine may improve postoperative pain relief.