Proficiency-based progression training: implementing a novel approach to training for epidural analgesia in labour

BACKGROUND

Epidural insertion is a challenging anaesthetic procedural skill to learn and may require up to 75 attempts to achieve competency. Proficiency-based progression (PbP) training based on unambiguously defined metrics was associated with a 53% reduction in epidural failure rate. The aim of this observational study was to examine the feasibility of implementation of innovative PbP training for labour epidural insertion performed by novices in a busy tertiary hospital.

METHODS

All trainees who were scheduled to commence their obstetric anaesthesia training were invited to participate. Novices undertook intensive PbP training with one-to-one supervision by an anaesthetist trained in PbP. Trainees proceeded to the clinical phase only after attaining the pre-defined proficiency benchmark. All subsequent attempts at labour epidural catheter placement were evaluated.

RESULTS

All 12 novice trainees who were scheduled for their initial exposure to obstetric anaesthesia completed PbP training in epidural catheter insertion successfully. The average duration of the training courses was 70 (SD 11) min. Trainee characteristics were broadly similar. They performed a total of 180 labour epidural catheter placements with an overall epidural failure rate of 12.2% (22/180). The proportion of supervisor takeover was 6% (11/179). The incidence of complications was 4% (8/180) and difficulty in epidural catheter insertion due to patient factors was 16% (29/180). Patient satisfaction rates were 80% (satisfied or very satisfied), with 20% unsatisfied with their experience of epidural insertion.

CONCLUSION

In our experience, PbP training in epidural placement is feasible within existing departmental resources in a busy tertiary teaching hospital setting.

Using psychometric ability to improve education in ultrasound-guided regional anaesthesia: a multicentre randomised controlled trial

The learning curve for novices developing regional anaesthesia skills, such as real-time ultrasound-guided needle manipulation, may be affected by innate visuospatial ability, as this influences spatial cognition and motor co-ordination. We conducted a multinational randomised controlled trial to test if novices with low visuospatial ability would perform better at an ultrasound-guided needling task with deliberate practice training than with discovery learning. Visuospatial ability was evaluated using the mental rotations test-A. We recruited 140 medical students and randomly allocated them into low-ability control (discovery learning), low-ability intervention (received deliberate practice), high-ability control, and high-ability intervention groups. Primary outcome was the time taken to complete the needling task, and there was no significant difference between groups: median (IQR [range]) low-ability control 125 s (69-237 [43-600 s]); low-ability intervention 163 s (116-276 [44-600 s]); high-ability control 130 s (80-210 [41-384 s]); and high-ability intervention 177 s (113-285 [43-547 s]), p = 0.06. No difference was found using the global rating scale: mean (95%CI) low-ability control 53% (95%CI 46-60%); low-ability intervention 61% (95%CI 53-68%); high-ability control 63% (95%CI 56-70%); and high-ability intervention 66% (95%CI 60-72%), p = 0.05. For overall procedure pass/fail, the low-ability control group pass rate of 42% (14/33) was significantly less than the other three groups: low-ability intervention 69% (25/36); high-ability control 68% (25/37); and high-ability intervention 85% (29/34) p = 0.003. Further research is required to determine the role of visuospatial ability screening in training for ultrasound-guided needle skills.

Kynurenine pathway metabolism and the neurobiology of treatment-resistant depression: Comparison of multiple ketamine infusions and electroconvulsive therapy

Current first-line antidepressants can take weeks or months to decrease depressive symptoms. Low dose ketamine, an N-methyl-D-aspartate (NMDA) receptor antagonist, shows potential for a more rapid antidepressant effect, with efficacy also evident in previously treatment-resistant populations. However, a greater understanding of the physiological mechanisms underlying such effects is required. We assessed the potential impact of ketamine infusion on neurobiological drivers of kynurenine pathway metabolism in major depression (HPA axis hyperactivity, inflammation) in patients with treatment-resistant depression compared to gender-matched healthy controls. Furthermore, we assessed these biomarkers before and after electroconvulsive therapy (ECT), which is currently the gold standard for management of treatment-resistant depression. As previously demonstrated, treatment with ketamine and ECT was associated with improved depressive symptoms in patients. At baseline, waking cortisol output was greater in the ECT cohort, kynurenine was greater in the ketamine cohort, and kynurenic acid was lower in patients compared to healthy controls, although inflammatory markers (IL-6, IL-8, IL-10 or IFN-γ) were similar in patients and controls. Furthermore, in patients who responded to ECT, the cortisol awakening response was decreased following treatment. Despite a trend towards reduced kynurenine concentrations in those who responded to ketamine, ketamine was not associated with significant alterations in any of the biomarkers assessed.

Serum BDNF as a peripheral biomarker of treatment-resistant depression and the rapid antidepressant response: A comparison of ketamine and ECT

BACKGROUND

Ketamine is associated with rapid antidepressant efficacy but the biological mechanisms underpinning this effect are unclear. Serum brain-derived neurotrophic factor (sBDNF) is a potential circulating biomarker of treatment-resistant depression (TRD) and ketamine response but it is unclear if this is a common target of both ketamine and electroconvulsive therapy (ECT), the current gold standard for TRD. Moreover, the impact of multiple ketamine infusions on sBDNF has not yet been established.

METHODS

Thirty five TRD patients with a current DSM-IV diagnosis of recurrent depressive disorder received up to 12 ECT sessions (N=17) or up to three intravenous infusions of low-dose (0.5mg/kg) ketamine (N=18). Blood samples were taken over the course of the study for assessment of sBDNF. Symptom severity and response were monitored using the 17-item Hamilton Depression Rating Scale (HDRS). sBDNF was assessed in 20 healthy controls to allow comparison with TRD patients.

RESULTS

As expected, sBDNF was lower in TRD patients at baseline compared to healthy controls. Ketamine and ECT treatment were both associated with significant reductions in depressive symptoms. However, sBDNF was significantly elevated only at one week following the first ketamine infusion in those classified as responders one week later. sBDNF was not elevated following subsequent infusions. ECT reduced depressive symptoms, as expected, but was not associated with an enhancement in BDNF.

LIMITATIONS

Patients continued with their psychotropic medications throughout this trial.

CONCLUSIONS

SBDNF normalisation does not appear to be a prerequisite for symptomatic improvement in TRD following ketamine or ECT treatment.

Effect of feedback content on novices' learning ultrasound guided interventional procedures

BACKGROUND

Feedback, of various forms, is effective at improving performance of medical procedures in simulated and clinical settings. Our objectives were to compare the effects of two forms of feedback on i) novice learning of in-plane technique for ultrasound-guided interventional procedures and ii) to evaluate novice retention of skill 24 hours after a standard learning session.

METHODS

Performance data were collected from 30 novices. All participants received training in the form of a standard training video. Participants were randomly allocated to one of three groups: Group C (Control) received no feedback; Group KR (Knowledge of Result) received feedback at the end of each series of tasks in the form of predefined performance intervals; and Group KP (Knowledge of Procedure) received feedback in the form of augmented error feedback. Each participant completed the series of tasks five times, using a standardized phantom model. Participants attempted to perform the same tasks 24 hours later using the same phantom. This performance was videotaped and assessed by two blinded assessors for predefined time and errors.

RESULTS

All groups demonstrated significant learning effect in terms of imaging, needling and performance time. Error reduction was significant over time intervals measured and also in-between groups with significant difference between Control : KP (P<0.001) and KR: KP (P=0.001) but not between Control and KR groups. Marked and similar levels of skill attrition were identified in all three groups 24 hours after the learning phase

CONCLUSION

When feedback was based on KP, novices acquired pre-defined skills more quickly and made fewer errors during the learning phase (compared with controls). When feedback content was based on KR novices acquired pre-defined skills more quickly but made similar numbers of errors during the learning phase (compared with controls). In conclusion, these findings should inform development of training and assessment programs for peripheral nerve blockade.

Automated estimation of sedation depth from the EEG

A method is presented for the automatic determination of a patient's level of sedation from the EEG. Six bipolar channels of EEG recorded from 12 adult patients sedated with low-dose propofol (2, 6-disopropylphenol) were used to develop a linear discriminant based system for depth of sedation monitoring using a number of quantitative EEG measures. A cross fold validation estimate of the performance of the algorithm as a patient independent system yielded a sensitivity of 74.70% and a specificity of 81.67%. It is hoped that the methodology reported here could lead to fully automated systems for depth of sedation monitoring.

Effect of midazolam on in vitro cerebral endothelial ICAM-1 expression induced by astrocyte-conditioned medium

BACKGROUND AND OBJECTIVE

Astrocytes exposed to hypoxia produce pro-inflammatory cytokines and upregulate intercellular adhesion molecule-1 on cerebral endothelium. This study investigated the effects of midazolam on this response.

METHODS

Mouse astrocytes were exposed to 4 h of hypoxia and 24 h of reoxygenation. Astrocyte-conditioned medium were applied to mouse cerebral endothelial cell cultures for 4 h and 24 h in normoxia. Endothelial cells were pre-incubated for 1 h with midazolam (0, 5, 50 microg L-1). Flow cytometry was used to estimate endothelial ICAM-1 expression. IL-1beta concentrations were measured with ELISA. Repeated comparisons were made using ANOVA and post hoc Tukey Test as appropriate. Data are mean (SD).

RESULTS

Mouse cerebral endothelial cell ICAM-1 expression was greater after 24 h exposure to hypoxia-reoxygenation astrocyte-conditioned medium compared to normoxic astrocyte-conditioned medium (mean channel flouresence 112.5 (9.5) vs. 81.5 (7.5), P = 0.01). ICAM-1 expression was decreased by midazolam (5 microg L(-1)) compared to control (mean channel flouresence 81.35 (7.5) vs. 112.5 (9.5), P = 0.01). Supernatant IL-1beta concentrations (pg mL(1)) in astrocytes exposed to hypoxia-reoxygenation were greater than those exposed to normoxia (16.41 (2.35) vs. 10.5 (2.13), P = 0.01).

CONCLUSION

We conclude that decreased cerebral endothelial ICAM-1 expression in response to activated glial cell compartment by midazolam may decrease post ischaemic brain inflammation and secondary brain injury.

The effect of lidocaine on in vitro neutrophil and endothelial adhesion molecule expression induced by plasma obtained during tourniquet-induced ischaemia and reperfusion

BACKGROUND

Changes in neutrophil and endothelial adhesion molecule expression occur during perioperative ischaemia and reperfusion (I/R) injury. We investigated the effects of lidocaine on neutrophil-independent changes in neutrophil and endothelial adhesion molecule expression associated with tourniquet-induced I/R.

METHODS

Plasma was obtained from venous blood samples (tourniquet arm) taken before (baseline), during, 15 min, 2 and 24 h following tourniquet release in seven patients undergoing elective upper limb surgery with tourniquet application. Isolated neutrophils from healthy volunteers (n = 7) were pretreated in the presence or absence of lidocaine (0.005, 0.05 and 0.5 mg mL(-1) for 1 h, and then incubated with I/R plasma for 2 h. Human umbilical vein endothelial cells (HUVECs) were pretreated in the presence or absence of lidocaine (0.005, 0.05 and 0.5 mg mL(-1)) for 1 h, and then incubated with the plasma for 4 h. Adhesion molecule expression was estimated using flow cytometry. Data were analysed using ANOVA and post hoc Student-Newman-Keuls tests.

RESULTS

I/R plasma (withdrawn 15 min following tourniquet release) increased isolated neutrophil CD11b (P = 0.03), CD18 (P = 0.01) and endothelial intercellular adhesion molecule-1 (ICAM-1) (P = 0.008) expression compared to baseline. CD11b, CD18 and ICAM-1 expression on lidocaine (0.005 mg mL(-1)) treated neutrophils was similar to control. CD11b (P < 0.001), CD18 (P = 0.03) and ICAM-1 (P = 0.002) expression on lidocaine (0.05 mg mL(-1)) treated neutrophils and HUVECs was less than that on controls.

CONCLUSION

Increased in vitro neutrophil and endothelial cell adhesion molecule expression on exposure to plasma obtained during the early reperfusion phase is diminished by lidocaine at greater than clinically relevant plasma concentrations.

Effect of atorvastatin and fluvastatin on the metabolism of midazolam by cytochrome P450 in vitro

We have investigated the effects of the statins atorvastatin and fluvastatin on the cytochrome P450 3A4 enzyme (CYP 3A4)-mediated metabolism of midazolam in vitro, using pooled human liver microsomes. Midazolam was metabolised by human hepatic microsomes with a Michaelis-Menten constant (K(m)) of 5.25 (SD 1.2) micromol.l(-1). Atorvastatin was a moderate competitive inhibitor of CYP 3A4 with an inhibitory constant (K(i)) of 12.4 (95% CI 4.65-20.06) micromol.l(-1). Fluvastatin was a weak non-competitive inhibitor of CYP 3A4 with a K(i) of 94.3 (95% CI 55.01-133.5) micromol.l(-1). Both atorvastatin and fluvastatin inhibit the CYP 3A4-mediated metabolism of midazolam in vitro.

The effect of lidocaine on neutrophil CD11b/CD18 and endothelial ICAM-1 expression and IL-1beta concentrations induced by hypoxia-reoxygenation

BACKGROUND

Lidocaine has actions potentially of benefit during ischaemia-reperfusion. Neutrophils and endothelial cells have an important role in ischaemia-reperfusion injury.

METHODS

Isolated human neutrophil CD11b and CD18, and human umbilical vein endothelial cell (HUVEC) ICAM-1 expression and supernatant IL-1beta concentrations in response to hypoxia-reoxygenation were studied in the presence or absence of different concentrations of lidocaine (0.005, 0.05 and 0.5 mg mL(-1)). Adhesion molecule expression was quantified by flow cytometry and IL- 1beta concentrations by ELISA. Differences were assessed with analysis of variance and Student-Newman-Keuls as appropriate. Data are presented as mean+/-SD.

RESULTS

Exposure to hypoxia-reoxygenation increased neutrophil CD11b (94.33+/-40.65 vs. 34.32+/-6.83 mean channel fluorescence (MCF), P = 0.02), CD18 (109.84+/-35.44 vs. 59.05+/-6.71 MCF, P = 0.03) and endothelial ICAM-1 (146.62+/-16.78 vs. 47.29+/-9.85 MCF, P < 0.001) expression compared to normoxia. Neutrophil CD18 expression on exposure to hypoxia-reoxygenation was less in lidocaine (0.005 mg mL(-1)) treated cells compared to control (71.07+/-10.14 vs. 109.84+/-35.44 MCF, P = 0.03). Endothelial ICAM-1 expression on exposure to hypoxia-reoxygenation was less in lidocaine (0.005 mg mL(-1)) treated cells compared to control (133.25+/-16.05 vs. 146.62+/-16.78 MCF, P = 0.03). Hypoxia-reoxygenation increased HUVEC supernatant IL-1beta concentrations compared to normoxia (3.41+/-0.36 vs. 2.65+/-0.21 pg mL(-1), P = 0.02). Endothelial supernatant IL-1beta concentrations in lidocaine-treated HUVECs were similar to controls.

CONCLUSIONS

Lidocaine at clinically relevant concentrations decreased neutrophil CD18 and endothelial ICAM-1 expression but not endothelial IL-1beta concentrations.

The effect of aprotinin on hypoxia-reoxygenation-induced changes in neutrophil and endothelial function

BACKGROUND AND OBJECTIVE

An acute inflammatory response associated with cerebral ischaemia-reperfusion contributes to the development of brain injury. Aprotinin has potential, though unexplained, neuroprotective effects in patients undergoing cardiac surgery.

METHODS

Human neutrophil CD11 b/CD18, endothelial cell intercellular adhesion molecule-1 (ICAM-1) expression and endothelial interleukin (IL)-1beta supernatant concentrations in response to in vitro hypoxia-reoxygenation was studied in the presence or absence of aprotinin (1600 KIU mL(-1)). Adhesion molecule expression was quantified using flow cytometry and IL-1beta concentrations by enzyme-linked immunosorbent assay. Data were analysed using ANOVA and post hoc Student-Newman-Keuls test as appropriate.

RESULTS

Exposure to 60-min hypoxia increased neutrophil CD11b expression compared to normoxia (170+/-46% vs. 91+/-27%, P = 0.001) (percent intensity of fluorescence compared to time 0) (n = 8). Hypoxia (60 min) produced greater upregulation of CD11b expression in controls compared to aprotinin-treated neutrophils [(170+/-46% vs. 129+/-40%) (P = 0.04)] (n = 8). Hypoxia-reoxygenation increased endothelial cell ICAM-1 expression (155+/-3.7 vs. 43+/-21 mean channel fluorescence, P = 0.0003) and IL-1beta supernatant concentrations compared to normoxia (3.4+/-0.4 vs. 2.6+/-0.2, P = 0.02) (n = 3). Hypoxia-reoxygenation produced greater upregulation of ICAM- 1 expression [(155+/-3.3 vs. 116+/-0.7) (P = 0.001)] and IL-1beta supernatant concentrations [(3.4+/-0.3 vs. 2.6+/-0.1) (P = 0.01)] in controls compared to aprotinin-treated endothelial cell preparation (n = 3).

CONCLUSIONS

Hypoxia-reoxygenation-induced upregulation of neutrophil CD11b, endothelial cell ICAM-1 expression and IL-1beta concentrations is decreased by aprotinin at clinically relevant concentrations.

Plasma concentrations of nitric oxide products and cognitive dysfunction following coronary artery bypass surgery

BACKGROUND AND OBJECTIVE

Prospective longitudinal studies now indicate that cognitive dysfunction following coronary artery bypass surgery (CABG) is both common and persistent. This dysfunction is due in part to the inflammatory response and cerebral ischaemia-reperfusion, with nitric oxide (NO) as an important mediator of both. We hypothesized that a clinically significant association exists between plasma concentrations of nitrate/nitrite (NO3-/NO2-) and cognitive dysfunction after CABG.

METHODS

Cognitive assessment was performed on 36 adult patients the day before CABG, on the fourth postoperative day and 3 months postoperatively. Patient spouses (n = 10) were also studied.

RESULTS

A new cognitive deficit was present in 22/36 (62%) 4 days postoperatively and in 16/35 (49%) of patients, 3 months postoperatively. Patients who had cognitive dysfunction 3 months postoperatively were more likely to have cognitive dysfunction and increased plasma NO3-/NO2- concentrations compared to the non-deficit group preoperatively (22.6 (9.2) vs. 27.6 (8.4)) (P = 0.002). Plasma NOx (NO3- plus NO2-) concentrations were greater in patients with cognitive dysfunction 3 months postoperatively, 2 h (24.2 (6.3) vs. 19.1 (5.2)) (P = 0.002), and 12 h postoperatively (24.8 (7.6) vs. 18.8 (5.6)) (P = 0.001). There was, however, a time course similarity in NOx elevations for both deficit and non-deficit groups.

CONCLUSIONS

Perioperative plasma NOx concentrations do not serve as an effective biomarker of cognitive deficit after CABG.

Effect of aprotinin on in vitro cerebral endothelial ICAM-1 expression induced by astrocyte-conditioned medium

BACKGROUND AND OBJECTIVE

Aprotinin administration may decrease the incidence of stroke associated with coronary artery bypass surgery by an unknown mechanism. Astrocytes exposed to hypoxia produce proinflammatory cytokines and upregulate intercellular adhesion molecule (ICAM)-1 on cerebral endothelium. This study investigated the effects of aprotinin on cerebral endothelial activation by hypoxic astrocytes in vitro.

METHODS

Mouse astrocytes were exposed to hypoxia in an anaerobic chamber for 4 h followed by reoxygenation for 24 h. Astrocyte-conditioned medium (ACM) collected from mouse astrocytes subjected to hypoxia/reoxygenation (HR) or normoxia were applied to mouse cerebral endothelial cell (MCEC) cultures for 4 and 24 h in normoxia. Endothelial cells were preincubated for 1 h with aprotinin (1600 KIU mL(-1)) prior to exposure to ACM. Flow cytometry was used to estimate endothelial ICAM-1 expression. Interleukin (IL)-1beta space concentrations in ACM were estimated with enzyme-linked immunosorbent assay (ELISA). Repeated comparisons were made using analysis of variance (ANOVA) and post hoc Tukey test as appropriate. P < 0.05 was considered significant. Data is presented as mean (standard deviation, SD).

RESULTS

MCEC ICAM-1 expression was greater after 24 h exposure to HR-ACM compared to normoxic-ACM (mean channel flouresence (MCF) 107.5 (4.5) vs. 74.3 (4.5), respectively, P < 0.001). ICAM-1 expression was decreased by aprotinin preincubation compared to control (MCF 91.0 (1.1) vs. 107.5 (2.1), P = 0.006). Supernatant IL-1beta concentrations in astrocytes exposed to HR were greater than those exposed to normoxia (7.1 (0.2) vs. 4.1 (0.2), P = 0.01).

CONCLUSIONS

This may be a neuroprotective mechanism associated with aprotinin administration.

Abnormalities of contrast sensitivity and electroretinogram following sevoflurane anaesthesia

BACKGROUND AND OBJECTIVE

We tested the hypothesis that disturbances of the visual pathway following sevoflurane general anaesthesia (a) exist and persist even after clinical discharge criteria have been met and (b) are associated with decreased contrast sensitivity.

METHODS

We performed pattern and full-field flash electroretinograms (ERG) in 10 unpremedicated ASA I patients who underwent nitrous oxide/sevoflurane anaesthesia. ERG and contrast sensitivity were recorded preoperatively, immediately after discharge from the recovery room and 2 h after discontinuation of sevoflurane. The time at which the Post Anaesthesia Discharge Score first exceeded 9 was also noted. Data were analysed using paired, one-tailed t-tests and Pearson's correlation coefficient.

RESULTS

On the full-field photopic ERG, b-wave latency was greater at each postoperative time point (31.6+/-1.1 and 30.8+/-1.1 ms) compared to preoperatively (30.1+/-1.1 ms, P < 0.001 and P = 0.03, respectively). Oscillatory potential latencies were greater on discharge from the recovery room compared with preanaesthetic values (23.1+/-3.1 vs. 22.4+/-3.3 ms, P = 0.01) and returned to baseline by 2 h after emergence from anaesthesia. Also at 2 h after emergence from anaesthesia: (a) P50 latency on the pattern ERG was greater than at baseline (81.5+/-17.9 vs. 51.15+/-22.6ms, P = 0.004); (b) N95 amplitude was less compared to preanaesthetic values (2.6+/-0.5 vs. 3.3+/-0.4 microV, P = 0.003) and (c) contrast sensitivity was less compared to baseline values (349+/-153 vs. 404+/-140, P = 0.048). A positive correlation was demonstrated between contrast sensitivity and both N95 amplitude and b-wave latency (r = 0.99 and r = -0.55 at significance levels of P < 0.005 and P < 0.05, respectively).

CONCLUSIONS

Postoperative ERG abnormalities and associated decreases in contrast sensitivity are consistently present in patients who have undergone nitrous oxide/sevoflurane anaesthesia. These abnormalities persist beyond the time at which standard clinical discharge criteria have been met.

Perioperative Plasma Concentrations of Stable Nitric Oxide Products Are Predictive of Cognitive Dysfunction After Laparoscopic Cholecystectomy

In this study our objectives were to determine the incidence of postoperative cognitive dysfunction (POCD) after laparoscopic cholecystectomy under sevoflurane anesthesia in patients aged >40 and <85 yr and to examine the associations between plasma concentrations of i) S-100beta protein and ii) stable nitric oxide (NO) products and POCD in this clinical setting. Neuropsychological tests were performed on 42 ASA physical status I-II patients the day before, and 4 days and 6 wk after surgery. Patient spouses (n = 13) were studied as controls. Cognitive dysfunction was defined as deficit in one or more cognitive domain(s). Serial measurements of serum concentrations of S-100beta protein and plasma concentrations of stable NO products (nitrate/nitrite, NOx) were performed perioperatively. Four days after surgery, new cognitive deficit was present in 16 (40%) patients and in 1 (7%) control subject (P = 0.01). Six weeks postoperatively, new cognitive deficit was present in 21 (53%) patients and 3 (23%) control subjects (P = 0.03). Compared with the "no deficit" group, patients who demonstrated a new cognitive deficit 4 days postoperatively had larger plasma NOx at each perioperative time point (P < 0.05 for each time point). Serum S-100beta protein concentrations were similar in the 2 groups. In conclusion, preoperative (and postoperative) plasma concentrations of stable NO products (but not S-100beta) are associated with early POCD. The former represents a potential biochemical predictor of POCD.

Postoperative changes in the full-field electroretinogram following sevoflurane anaesthesia

BACKGROUND AND OBJECTIVE

We tested the hypothesis that disturbances of the visual pathway persist following general anaesthesia, even after normal clinical discharge criteria have been met.

METHODS

We performed full-field flash electroretinography in the right eye of 10 unpremedicated ASA I patients who underwent N2O/sevoflurane anaesthesia. Electroretinograms were recorded preoperatively, immediately after discharge from the recovery room and 2 h after discontinuation of sevoflurane. The time at which postanaesthesia discharge score first exceeded 9 was also noted. Data were analysed using paired, one-tailed Student's t-test.

RESULTS

Latency of the b-wave on the photopic electroretinogram was greater at each postoperative time point (30.5 +/- 0.9 and 30 +/- 1.3 ms), compared to preoperative values (29.2 +/- 0.8 ms, P < 0.001 and P = 0.04, respectively). The A-B amplitude of the b-wave was less postoperatively (220.3 +/- 52.7 and 210.3 +/- 42.7 pV) compared to values before operation (248.1 +/- 57.6 microV, P = 0.03 and P = 0.01, respectively). Oscillatory potential latencies were greater at each postoperative time point (21.4 +/- 0.5 and 20.8 +/- 0.6 ms) compared to before operation (20.4 +/- 0.4 ms, P < 0.001 and P = 0.03, respectively). Oscillatory potential amplitudes were less at the first postoperative time point (17.5 +/- 6.1 microV), compared to preoperative values (22 +/- 6.4 microV, P = 0.04).

CONCLUSIONS

Postoperative electroretinogram abnormalities are consistently present in patients who have undergone N2O/sevoflurane anaesthesia. These abnormalities persist beyond the time at which standard clinical discharge criteria have been met.

The effect of clomethiazole on plasma concentrations of interleukin-6, -8, -1beta, tumor necrosis factor-alpha, and neutrophil adhesion molecule expression during experimental extracorporeal circulation

Clomethiazole (CMZ), a neuroprotective drug, has antiinflammatory actions. We investigated the effects of CMZ administration on plasma concentrations of interleukin (IL)-6, IL-8, IL-1beta, tumor necrosis factor-alpha, and neutrophil adhesion molecule expression during experimental extracorporeal circulation. Five healthy volunteers each donated 500 mL of blood, which was subsequently divided into equal portions. Identical extracorporeal circuits were simultaneously primed with donated blood (250 mL) and circulated for 2 h at 37 degrees C. CMZ was added to 1 of the circuits of each pair to achieve a total plasma concentration of 40 micro mol/L. Blood samples were withdrawn at (i) donation, (ii) immediately after addition of CMZ, and at (iii) 30, 60, 90, and 120 min after commencing circulation. Plasma concentrations of IL-6, IL-8, and tumor necrosis factor-alpha were less in the CMZ group compared with control after 60 min of circulation (2.2 [0.3] versus 3.2 [0.4], 14.9 [4.8] versus 21.9 [18.4], 63.3 [43.5] versus 132.2 [118.9] pg/mL, respectively, P < 0.05). After 120 min of circulation, neutrophils from CMZ-treated circuits showed significantly less CD18 expression compared with control (237.5 [97.4] versus 280.5 [111.5], P = 0.03). The addition of CMZ to experimental extracorporeal circuits decreases the inflammatory response. This effect may be of clinical benefit by decreasing inflammatory-mediated neurological injury during cardiopulmonary bypass.

IMPLICATIONS

Enhancement of gamma-aminobutyric acid(A)-mediated effects by clomethiazole (CMZ) and associated neuroprotection has been established in animal models of cerebral ischemia. In an ex vivo study, we demonstrated antiinflammatory activity of CMZ in experimental extracorporeal circulation. This represents a potential neuroprotective mechanism of CMZ in patients undergoing coronary artery bypass surgery.

Effect of sevoflurane on human neutrophil apoptosis

BACKGROUND AND OBJECTIVE

Both chronic occupational exposure to volatile anaesthetic agents and acute in vitro exposure of neutrophils to isoflurane have been shown to inhibit the rate of apoptosis of human neutrophils. It is possible that inhibition of neutrophil apoptosis arises through delaying mitochondrial membrane potential collapse. We assessed mitochondrial depolarization and apoptosis in unexposed neutrophils and neutrophils exposed to sevoflurane in vivo.

METHODS

A total of 20 mL venous blood was withdrawn pre- and postinduction of anaesthesia, the neutrophils isolated and maintained in culture. At 1, 12 and 24 h in culture, the percentage of neutrophil apoptosis was assessed by dual staining with annexin V-FITC and propidium iodide. Mitochondrial depolarization was measured using the dual emission styryl dye JC-1.

RESULTS

Apoptosis was significantly inhibited in neutrophils exposed to sevoflurane in vivo at 24 (exposed: 38 (12)% versus control: 28 (11)%, P = 0.001), but not at 1 or 12 h, in culture. Mitochondrial depolarization was not delayed in neutrophils exposed to sevoflurane.

CONCLUSIONS

The most important findings are that sevoflurane inhibits neutrophil apoptosis in vivo and that inhibition is not mediated primarily by an effect on mitochondrial depolarization.

A dedicated intravenous cannula for postoperative use effect on incidence and severity of phlebitis

A prospective, randomised, controlled clinical study was performed to compare the incidence and severity of postoperative peripheral venous thrombophlebitis associated with a single intravenous cannula used for both intra-operative and postoperative purposes, and two cannulae, one used intra-operatively and the other postoperatively. Sixty American Society of Anaesthesiologists (ASA) physical status I or II patients aged 18-65 years undergoing elective surgery were studied. The technique of cannula insertion was standardised. After surgery, the cannulation sites were examined daily by a blinded investigator for the presence and severity of thrombophlebitis using the Baxter Scale. The two groups were similar in terms of age, gender, weight, type and duration of surgical procedures, and drugs and fluids administered both intra-operatively and postoperatively. The proportion of patients that developed phlebitis was significantly less in the two cannulae group (26.1%) than in the single cannula group (63.3%) (p < 0.0001). The severity of phlebitis was greater in the single cannula group than in the two cannulae group. These results indicate that the use of a dedicated cannula for postoperative use decreases the incidence and severity of postoperative, peripheral, cannula-related phlebitis.

Effects of chronic occupational exposure to anaesthetic gases on the rate of neutrophil apoptosis among anaesthetists

BACKGROUND AND OBJECTIVE

Volatile anaesthetic agents are known to influence neutrophil function. The aim was to determine the effect of chronic occupational exposure to volatile anaesthetic agents on the rate of neutrophil apoptosis among anaesthetists. To test this hypothesis, we compared the rate of neutrophil apoptosis in anaesthetists who had been chronically exposed to volatile anaesthetic agents with that in unexposed volunteers.

METHODS

Venous blood (20 mL) was withdrawn from 24 ASA I-II volunteers, from which neutrophils were isolated, and maintained in culture. At 1, 12 and 24 h in culture, the percentage of neutrophil apoptosis was assessed by dual staining with annexin V-FITC and propidium iodide.

RESULTS

At 1 h (but not at 12 and 24 h) in culture, the rate of neutrophil apoptosis was significantly less in the anaesthetists--13.8 (12.9%) versus 34.4 (12.1%) (P = 0.001).

CONCLUSIONS

Chronic occupational exposure to volatile anaesthetic agents may inhibit neutrophil apoptosis. This may have implications for anaesthetists and similarly exposed healthcare workers in terms of the adequacy of their inflammatory response.

Effect of perioperative administration of dexketoprofen on opioid requirements and inflammatory response following elective hip arthroplasty

BACKGROUND

In this double-blind, randomized, placebo-controlled trial, the safety and analgesic efficacy of perioperative dexketoprofen were evaluated.

METHODS

Thirty ASA I or II patients undergoing elective hip arthroplasty were randomized to one of two groups. One group (D) received dexketoprofen 25 mg tds for 24 h before and 48 h after surgery; the second group (P) received placebo tablets at equivalent times. Hyperbaric 0.5% bupivacaine (17.5 mg if greater than 70 kg and 15 mg if less than 70 kg) and preservative-free morphine (0.6 mg) were administered intrathecally. Postoperatively, PCA was provided (bolus morphine sulphate 1 mg; lockout 5 min; no continuous infusion).

RESULTS

The two groups were similar in terms of age, gender, weight, height, ASA class, duration of operation, and level of sensory block on arrival to the recovery room. Groups were also similar in terms of blood loss, transfusion requirements, ventilatory frequency, and haemodynamic variables. According to visual analogue pain scores patients in group D experienced less pain at 15 h (P=0.02) postoperatively. Cumulative morphine consumption was also less in group D compared with group P at 6 (0.06 (0.2) vs 0.85 (1.4) mg, P=0.04) and 48 h postoperatively (10.1 (8) vs 26.2 (20) mg, P<0.01). Plasma interleukin 6 concentrations increased postoperatively to a significantly lesser extent in group D than in group P (P=0.02). Nausea and vomiting were less (P<0.01) in group D compared with group P at 18 h postoperatively. Sedation scores were less (P=0.03) in group D.

CONCLUSIONS

Perioperative administration of dexketoprofen 25 mg 8 hourly markedly improves analgesia and decreases opioid requirements (and associated adverse effects) following hip arthroplasty. It appears that this regimen decreases the postoperative pro-inflammatory response.

Postoperative changes in visual evoked potentials and cognitive function tests following sevoflurane anaesthesia

We tested the hypothesis that minor disturbance of the visual pathway persists following general anaesthesia even when clinical discharge criteria are met. To test this, we measured visual evoked potentials (VEPs) in 13 ASA I or II patients who did not receive any pre-anaesthetic medication and underwent sevoflurane anaesthesia. VEPs were recorded on four occasions, before anaesthesia and at 30, 60, and 90 min after emergence from anaesthesia. Patients completed visual analogue scales (VAS) for sedation and anxiety, a Trieger Dot Test (TDT) and a Digit Symbol Substitution Test (DSST) immediately before each VEP recording. These results were compared using Student's t-test. P<0.05 was considered significant. VEP latency was prolonged (P<0.001) and amplitude diminished (P<0.05) at 30, 60, and 90 min after emergence from anaesthesia, when VAS scores for sedation and anxiety, TDT, and DSST had returned to pre-anaesthetic levels.

The effects of venous cannulation technique and cardioplegia type on plasma potassium concentration and arterial blood pressure during cardiopulmonary bypass

The cannulation method and cardioplegia solution used during cardiopulmonary bypass (CPB) may both influence plasma potassium concentrations ([K+]) and mean arterial blood pressure (MAP). Bi-caval or right atrial cannulation methods are routinely used in conjunction with crystalloid or blood cardioplegia. We investigated the influence of cannulation method and cardioplegia solutions on plasma [K+] and MAP during cardiopulmonary bypass. Sixty consecutive patients undergoing elective coronary artery bypass grafting (CABG) using CPB were studied. They were randomly divided into three groups of 20 patients. Patients in Group A underwent bi-caval venous cannulation and received crystalloid cardioplegia. Group B patients underwent right atrial cannulation and received crystalloid cardioplegia. Group C patients underwent right atrial cannulation and received blood cardioplegia. In each case. cardioplegia was administered antegrade via the aortic root. Plasma [K+], MAP. and hemoglobin concentration (Hb) were measured over an 8-min period following cardioplegia administration (pilot studies indicated pressure changes occuring post cardioplegia administration up to this time). The combination of bi-caval cannulation and crystalloid cardioplegia (Group A) was associated with the least increase in plasma [K+] and no decrease in MAP. The maximum [K+] for this Group was 4.2 mmol/L (4.6% increase). The minimum mean pressure was 57 mmHg (13.6% increase). Both right atrial cannulation groups (B and C) showed a large rise in plasma [K+] and a decrease in MAP. Group B maximum [K+] was 5.2 mmol/L (27.5% increase). Group C was also 5.2 mmol/L (26.0% increase). Group C showed the largest pressure decrease, the minimum mean pressure was 45 mmHg (21.3% decrease). The Group B minimum mean pressure was 45 mmHg (8.7% decrease). Our results show that patients undergoing CPB operations who are deemed to be at increased risk of suffering adverse effects from hypotensive episodes may benefit from bicaval cannulation and caval snaring, in preference to right atrial cannulation. Crystalloid cardioplegia may be preferable to blood cardioplegia in these cases to maintain the MAP.

The effects of fenoldopam on coronary conduit blood flow after coronary artery bypass graft surgery

OBJECTIVE

To quantify the effects of fenoldopam, 0.1 microg/kg/min, on left internal mammary artery (LIMA) and saphenous vein blood flow after coronary anastomosis.

DESIGN

Prospective, randomized, double-blind, placebo-controlled trial.

SETTING

University teaching hospital, single institution.

PARTICIPANTS

Thirty-one American Society of Anesthesiologists III patients undergoing elective coronary revascularization.

INTERVENTIONS

A perivascular ultrasonic flow probe (Linton Instrumentation, Norfolk, UK) was placed around the LIMA and saphenous vein graft after coronary anastomosis.

MEASUREMENTS AND MAIN RESULTS

Immediately before and at 5-minute intervals for 15 minutes after starting the infusion, blood flow was measured in the LIMA and one saphenous vein graft using a transit time ultrasonic flow probe. Heart rate, blood pressure, and central venous pressure were documented at these time points. Administration of fenoldopam, 0.1 microg/kg/min, did not alter heart rate or blood pressure. A small, nonsignificant increase in LIMA blood flow occurred during the 15-minute study period (30 +/- 12 to 35 +/- 10 mL/min) in patients who received fenoldopam. No significant changes occurred in the placebo group.

CONCLUSIONS

The findings indicate that fenoldopam, 0.1 microg/kg/min, did not influence coronary conduit blood flow to a clinically significant extent. The small increase in LIMA blood flow may be of greater importance in high-risk patients or in the prevention of coronary arterial spasm.

The effects of ropivacaine hydrochloride on platelet function: an assessment using the platelet function analyser (PFA-100)

Amide local anaesthetics impair blood clotting in a concentration-dependent manner by inhibition of platelet function and enhanced fibrinolysis. We hypothesised that the presence of ropivacaine in the epidural space could decrease the efficacy of an epidural blood patch, as this technique requires that the injected blood can clot in order to be effective. Ropivacaine is an aminoamide local anaesthetic used increasingly for epidural analgesia during labour. The concentration of local anaesthetic in blood achieved in the epidural space during the performance of an epidural blood patch is likely to be the greatest which occurs (intentionally) in any clinical setting. This study was undertaken to investigate whether concentrations of ropivacaine in blood, which could occur: (i) clinically in the epidural space and (ii) in plasma during an epidural infusion of ropivacaine, alter platelet function. A platelet function analyser (Dade PFA-100, Miami) was employed to assess the effects of ropivacaine-treated blood on platelet function. The greater concentrations of ropivacaine studied (3.75 and 1.88 mg x ml(-1)), which correspond to those which could occur in the epidural space, produced significant inhibition of platelet aggregation. We conclude that the presence of ropivacaine in the epidural space may decrease the efficacy of an early or prophylactic epidural blood patch.

The effect of the anaesthetic agent isoflurane on the rate of neutrophil apoptosis in vitro

BACKGROUND

Volatile anaesthetic agents influence neutrophil function, and potentially, the inflammatory response to surgery.

AIM

The objective of this study was to determine the effect of isoflurane (1-4%) on human polymorphonuclear neutrophil apoptosis in vitro.

METHODS

Venous blood from 12 healthy volunteers was exposed to 0, 1, and 4% isoflurane delivered via a 14G Wallace flexihub internal jugular cannula, at a fresh gas flow of 0.51/min for 5 minutes. Isolated neutrophils were assessed for apoptosis at 1, 12, and 24 hours in culture using dual staining with annexin V-FITC and propidium iodide (Annexin-V FITC assay). Data were analysed using paired, one-tailed Student's t-tests. p<0.05 was considered significant.

RESULTS

At 1 hour apoptosis was inhibited in the 1% (5.1 [6.8]%; p=0.017) and 4% (4.8 [4.5]%; p=0.008) isoflurane groups compared to control (11.3 [6.9]%). At 12 and 24 hours, a dose-dependent inhibition of apoptosis was demonstrated, i.e. 4% > 1% > 0%.

CONCLUSION

Human neutrophil apoptosis is inhibited in a concentration-dependent manner in vitro by isoflurane in clinical concentrations.

Train of four fade in a child with stiff baby syndrome

A case is described of a child with stiff baby syndrome who underwent open reduction and femoral shortening of congenital dislocated hip under general anaesthesia. Neuromuscular function was measured electromyographically and demonstrated a great degree of train of four fade (57%) after sevoflurane inhalational induction of anaesthesia. The response to suxamethonium (2 mg x kg(-1)) was normal. The neuromuscular response to volatile anaesthetic agents and suxamethonium may be abnormal in these children with stiff baby syndrome and intraoperative neuromuscular monitoring is recommended.

Universal precautions--do Irish anaesthetists comply?

BACKGROUND

Anaesthetists are at high risk from blood-borne pathogens. Universal Precautions (UP) include the routine use of appropriate barrier precautions and techniques to reduce the likelihood of exposure to blood, body fluids and tissues that may contain pathogens. The compliance of Irish anaesthetists with these precautions has not been studied.

AIM

To study the attitudes of Irish anaesthetists to Universal Precautions.

METHOD

A postal questionnaire was sent to 210 anaesthetists currently practising in Ireland. The questionnaire was based on a model used in Australia and New Zealand.

RESULTS

There was a 50% response rate to the survey. Only 15% of respondents had taken a risk history from a patient in the preceding four weeks. Resheathing of needles was commonplace. The effectiveness of hepatitis B immunisation was rarely checked and only 66% of respondents believe implementation of Universal Precautions to be practical.

CONCLUSION

Irish anaesthetists comply poorly with Universal Precautions.

Safety and efficiency of metered dose inhaler delivery of salbutamol in the intubated rabbit

OBJECTIVE

To determine the safety and efficiency of metered dose inhaler salbutamol delivered to the intubated rabbit.

DESIGN

Prospective, comparative, five-group laboratory investigation.

SETTING

Animal laboratory, Department of Nuclear Medicine.

SUBJECTS

A total of 30 adult, anesthetized New Zealand White rabbits.

INTERVENTIONS

Three groups of rabbits underwent tracheal intubation through a tracheostomy and received 5 puffs of 99mTcO4 salbutamol delivered at the elbow connector (group 1) or via a catheter with its distal tip positioned at the midpoint (group 2) or bevel of the endotracheal tube (group 3). No intervention was provided for the rabbits in the fourth group. A fifth group underwent tracheal intubation through the mouth and received salbutamol (5 puffs) delivered at the bevel of the endotracheal tube.

MEASUREMENTS

Delivery efficiency was expressed as the ratio of radioactivity emitted from lungs and trachea to the total radioactivity of the administered dose. Histopathologic injury scores were assigned to each trachea or lung specimen.

MAIN RESULTS

Delivery efficiency was 30 times greater in groups 3 and 5 (full catheter) than in group 1 (elbow). The injury scores were similar in all groups.

CONCLUSION

We conclude that the increased efficiency obtained by administration of metered dose inhaler salbutamol at the distal tip of endotracheal tube is not necessarily associated with increased epithelial injury.

Does chronic occupational exposure to volatile anesthetic agents influence the rate of neutrophil apoptosis?

PURPOSE

The purpose of this preliminary investigation was to determine whether the rate of neutrophil apoptosis in health care workers is influenced by exposure to volatile anesthetic agents.

METHODS

Percentage neutrophil apoptosis (Annexin-V FITC assay) was measured in health care workers (n = 20) and unexposed volunteers (n = 10). For the health care workers, time weighted personal exposure monitoring to N2O, sevoflurane and isoflurane was carried out.

RESULTS

The sevoflurane and isoflurane concentrations to which health care workers were exposed were less than recommended levels in all 20 cases. Percent apoptosis was less at 24 (but not at one and 12) hr culture in health care workers [50.5 (9.7)%; P = 0.008] than in unexposed volunteers [57.3 (5.1)%].

CONCLUSION

Inhibition of neutrophil apoptosis at 24 hr culture was demonstrated in health care workers chronically exposed to volatile anesthetic agents. Exposure was well below recommended levels in the both scavenged and unscavenged work areas in which the study was carried out. Further study is required to assess the effect of greater degrees of chronic exposure to volatile anesthetic agents on neutrophil apoptosis.

Effectiveness of mask ventilation performed by hospital doctors in an Irish tertiary referral teaching hospital

The objective of this study was to assess the effectiveness of mask ventilation performed by 112 doctors with clinical responsibilities at a tertiary referral teaching hospital. Participant doctors were asked to perform mask ventilation for three minutes on a Resusci Anne mannequin using a facemask and a two litre self inflating bag. The tidal volumes generated were quantified using a Laerdal skillmeter computer as grades 0-5, corresponding to 0, 334, 434, 561, 673 and > 800 ml respectively. The effectiveness of mask ventilation (i.e. the proportion of ventilation attempts which achieved a volume delivery of > 434 mls) was greater for anaesthetists [78.0 (29.5)%] than for non anaesthetists [54.6 (40.0)%] (P = 0.012). Doctors who had attended one or more resuscitation courses where no more effective at mask ventilation than their colleagues who had not undertaken such courses. It is likely that first responders to in-hospital cardiac arrests are commonly unable to perform adequate mask ventilation.

Pneumomediastinum, pneumothorax and subcutaneous emphysema complicating MIS herniorrhaphy

PURPOSE

Videoscopic herniorrhaphy is being performed more frequently with advantages claimed over the conventional open approach. This clinical report describes a pneumothorax, pneumomediastinum and subcutaneous emphysema occurring at the end of an extraperitoneal videoscopic herniorrhaphy.

CLINICAL FEATURES

A 25 yr old ASA I man presented for elective extraperitoneal videoscopic hernia repair. Following intravenous induction with fentanyl, midazolam and propofol a balanced anesthetic technique using enflurane in N2O and O2 was used. Apart from a prolonged operating time (195 min), the procedure and anesthetic was uneventful. At the conclusion of the operation, prior to reversal of neuromuscular blockade extensive subcutaneous emphysema was noted on removal of the surgical drapes. Chest radiography revealed a pneumomediastinum and pneumothorax. A 25 FG intercostal tube was inserted and connected to an underwater seal drain. Sedation and positive pressure ventilation was maintained overnight to permit resolution and avoid airway compromise. The clinical and radiological features had resolved by the next morning and the patient's trachea was extubated. His subsequent recovery was uneventful.

CONCLUSION

Pneumothorax and pneumomediastinum are well recognised complications of laparoscopic techniques but have not been described following extraperitoneal herniorrhaphy. In this report we postulate possible mechanisms which may have contributed to their development, including inadvertent breach of the peritoneum and leakage of gas around the diaphragmatic herniae or tracking of gas retroperitoneally. The case alerts us to the possibility of this complication occurring in patients undergoing videoscopic herniorrhaphy.

Cisapride does not alter gastric volume or pH in patients undergoing ambulatory surgery

PURPOSE

To evaluate the efficacy of 20 mg cisapride p.o. in reducing residual gastric volume and pH in adult ambulatory surgical patients.

METHODS

Using a prospective randomised double-blind controlled design, we administered either 20 mg cisapride p.o. or placebo preoperatively to 64 ASA 1-2 ambulatory surgical patients. Following induction of anesthesia we measured volume and pH of residual gastric contents, using blind aspiration through an orogastric tube. Parametric data were analysed using unpaired, one tail Students' t test. Non-parametric data were analysed using Fishers Exact test and Chi square analysis. Statistical significance was accepted at the probability level of < 0.05.

RESULTS

Residual gastric volumes were similar in the two groups (19.5 +/- 23.8, 23.9 +/- 24.4 ml), in the cisapride and placebo groups respectively, P=0.24). Data shown are mean (+/- SD). The proportions of patients with a residual gastric volume exceeding 0.4 ml x kg(-1) were similar in the two groups (4 of 28, and 8 of 23 patients in the cisapride and placebo groups respectively, P=0.09). The pH of the residual gastric contents were similar in the cisapride and placebo groups (1.6 +/- 0.5, 1.4 +/- 0.5, respectively, P=0.26). The proportions of patients with pH < 2.5 was also similar in the cisapride and placebo groups (21 of 25, and 20 of 21 patients respectively, P=0.2).

CONCLUSIONS

Preoperative administration of 20 mg cisapride p.o. to patients scheduled for outpatient surgery does not alter either the volume or the pH of gastric contents. Its use in this setting is of no apparent clinical benefit.

Topical amethocaine (Ametop) is superior to EMLA for intravenous cannulation. Eutectic mixture of local anesthetics

PURPOSE

A eutectic mixture of local anesthetics (EMLA) is commonly used to provide topical anesthesia for intravenous (i.v.) cannulation. One of its side effects is vasoconstriction, which may render cannulation more difficult. A gel formulation of amethocaine (Ametop) is now commercially available. The aim of this study was to compare EMLA and Ametop with regard to the degree of topical anesthesia afforded, the incidence of vasoconstriction and the ease of i.v. cannulation.

METHODS

Thirty two ASA I adult volunteers had a #16 gauge i.v. cannula inserted on two separate occasions using EMLA and Ametop applied in a double blind fashion for topical anesthesia. Parameters that were recorded after each cannulation included visual analogue pain scores (VAPS), the presence of vasoconstriction and the ease of cannulation, graded as: 1 = easy, 2 = moderately difficult, 3 = difficult and 4 = failed.

RESULTS

The mean VAPS +/- SD after cannulation with Ametop M was 12+/-9.9 and with EMLA was 25.3+/-16.6 (P = 0.002). Vasoconstriction occurred after EMLA application on 17 occasions and twice after Ametop (P = 0.001). The grade of difficulty of cannulation was 1.44+/-0.88 following EMLA and 1.06+/-0.25 with Ametop (P = 0.023).

CONCLUSIONS

Intravenous cannulation was less painful following application of Ametop than EMLA. In addition, Ametop caused less vasoconstriction and facilitated easier cannulation. Its use as a topical anesthetic agent is recommended, especially when i.v. access may be problematic.

The effects of EMLA and a topical formulation of 4% amethocaine (Ametop) on pain associated with retrobulbar injection

Retrobulbar block is commonly performed to provide anaesthesia for cataract extraction. This technique can cause significant discomfort. A prospective, randomised, placebo-controlled trial was carried out to investigate the efficacy of a eutectic mixture of local anaesthetics (EMLA) and a 4% amethocaine topical formulation (Ametop) in reducing the pain of retrobulbar injection. Ametop and EMLA proved to be of similar efficacy, both being superior to a placebo in alleviating the discomfort of retrobulbar block. No significant side-effects were observed with the use of either formulation.

Administration of magnesium sulphate before rocuronium: effects on speed of onset and duration of neuromuscular block

The speeds of onset of pancuronium, atracurium and vecuronium are increased by prior administration of magnesium sulphate. A prospective, randomized, double-blind, controlled, clinical study was performed to examine the effects of prior i.v. administration of magnesium sulphate 60 mg kg-1 on the neuromuscular blocking effects of rocuronium 0.6 mg kg-1 during isoflurane anaesthesia. Neuromuscular function was measured electromyographically (Relaxograph) in 30 patients who received either magnesium sulphate 60 mg kg-1 or normal saline, 1-min before rocuronium 0.6 mg kg-1. Mean onset times were similar in the two groups (magnesium sulphate 71 (SD 20) s; normal saline 75 (23) s), but times to initial, 10% and 25% recovery from neuromuscular block were significantly longer in the magnesium sulphate group (42.1 (16.3), 49.0 (12.4) and 56.5 (13.2) min, respectively) than in the saline group (25.1 (9.1), 33.0 (11.1) and 35.6 (13.2) min, respectively) (P < 0.05 in all three cases). Administration of magnesium sulphate was not associated with adverse haemodynamic effects. Prior administration of magnesium sulphate, under the study conditions described, prolonged rocuronium-induced neuromuscular block but did not increase speed of onset.

Pharmacodynamic and hemodynamic effects of mivacurium in infants anesthetized with halothane and nitrous oxide

BACKGROUND

The newly developed neuromuscular blocking agent, mivacurium, has been evaluated in adults and children, but there are no data on its effects in infants. This study was designed to evaluate the neuromuscular effects of mivacurium by dose-response analysis, and its cardiovascular effects in 90 infants 2-11 months of age anesthetized with 1% halothane and nitrous oxide:oxygen.

METHODS

The neuromuscular response was measured by recording the force of contraction of the adductor pollicis during train-of-four stimulation at 0.1 Hz. The infants were divided according to age into two equal groups of 45; group A infants were 2-6 months of age, and group B infants were 7-11 months of age. Each group was further subdivided into five subgroups of nine. Infants in group A received mivacurium at sequential doses of 40, 50, 55, 75, and 150 micrograms/kg, while those in group B received mivacurium at doses 40, 50, 60, 75, and 150 micrograms/kg. The first four doses in each group were used to determine dose-response relationships. The last two doses of 75 and 150 micrograms/kg were based on the observed preceding dose-response data to approximate the ED95 and 2XED95. Heart rate and blood pressure were determined every minute for a minimum of 3 min after mivacurium.

RESULTS

The effective doses for 50% depression of the first twitch response of the train-of-four (ED50) were 44-50 micrograms/kg (confidence limits 29-74 micrograms/kg), without any significant difference between groups A and B. In both groups, a larger dose of mivacurium, 150 micrograms/kg, caused complete ablation of the twitch response in 1.3 +/- 0.2 min (mean +/- SE) with recovery to 5, 25, and 95% of control in 7.6 +/- 0.5, 9.4 +/- 0.6, and 16.2 +/- 0.9 min, respectively. In infants, the 25-75% recovery index was 3.8 +/- 0.4 min, and the 5-95% recovery index was 8.5 +/- 0.8 min. In 28 infants, in whom surgical relaxation was required for more than 20 min, the infusion requirements to maintain 90-99% neuromuscular block in infants 2-6 and 7-11 months of age were 12.1 +/- 1 and 9.9 +/- 1 micrograms.kg-1.min-1, respectively (NS). No significant changes of heart rate of blood pressure occurred in infants, except in the subgroup of infants 7-11 months of age who received 150 micrograms/kg mivacurium. In this group, a 13-mmHg increase in mean systolic blood pressure was seen without any significant change in diastolic pressure or heart rate. In addition, in 7 of 36 patients receiving 75-150 micrograms/kg mivacurium, a greater than 29% change in systolic or diastolic pressure occurred. One infant with cholinesterase deficiency had a prolonged neuromuscular block from mivacurium.

CONCLUSIONS

The ED50 duration of action and infusion requirements of mivacurium in infants 2-6 months of age are comparable with those of infants 7-11 months of age.