Seasonal and diurnal variations of Kelvin-Helmholtz Instability at terrestrial magnetopause

Kelvin-Helmholtz Instability is ubiquitous at Earth's magnetopause and plays an important role in plasma entry into the magnetosphere during northward interplanetary magnetic fields. Here, using one solar cycle of data from NASA THEMIS (Time History of Events and Macro scale Interactions during Substorms) and MMS (Magnetospheric Multiscale) missions, we found that KHI occurrence rates show seasonal and diurnal variations with the rate being high near the equinoxes and low near the solstices. The instability depends directly on the Earth's dipole tilt angle. The tilt toward or away from the Sun explains most of the seasonal and diurnal variations, while the tilt in the plane perpendicular to the Earth-Sun line explains the difference between the equinoxes. The results reveal the critical role of dipole tilt in modulating KHI across the magnetopause as a function of time, highlighting the importance of Sun-Earth geometry for solar wind-magnetosphere interaction and for space weather.

PROSPECT guideline for total hip arthroplasty: a systematic review and procedure-specific postoperative pain management recommendations

The aim of this systematic review was to develop recommendations for the management of postoperative pain after primary elective total hip arthroplasty, updating the previous procedure-specific postoperative pain management (PROSPECT) guidelines published in 2005 and updated in July 2010. Randomised controlled trials and meta-analyses published between July 2010 and December 2019 assessing postoperative pain using analgesic, anaesthetic, surgical or other interventions were identified from MEDLINE, Embase and Cochrane databases. Five hundred and twenty studies were initially identified, of which 108 randomised trials and 21 meta-analyses met the inclusion criteria. Peri-operative interventions that improved postoperative pain include: paracetamol; cyclo-oxygenase-2-selective inhibitors; non-steroidal anti-inflammatory drugs; and intravenous dexamethasone. In addition, peripheral nerve blocks (femoral nerve block; lumbar plexus block; fascia iliaca block), single-shot local infiltration analgesia, intrathecal morphine and epidural analgesia also improved pain. Limited or inconsistent evidence was found for all other approaches evaluated. Surgical and anaesthetic techniques appear to have a minor impact on postoperative pain, and thus their choice should be based on criteria other than pain. In summary, the analgesic regimen for total hip arthroplasty should include pre-operative or intra-operative paracetamol and cyclo-oxygenase-2-selective inhibitors or non-steroidal anti-inflammatory drugs, continued postoperatively with opioids used as rescue analgesics. In addition, intra-operative intravenous dexamethasone 8-10 mg is recommended. Regional analgesic techniques such as fascia iliaca block or local infiltration analgesia are recommended, especially if there are contra-indications to basic analgesics and/or in patients with high expected postoperative pain. Epidural analgesia, femoral nerve block, lumbar plexus block and gabapentinoid administration are not recommended as the adverse effects outweigh the benefits. Although intrathecal morphine 0.1 mg can be used, the PROSPECT group emphasises the risks and side-effects associated with its use and provides evidence that adequate analgesia may be achieved with basic analgesics and regional techniques without intrathecal morphine.

PROSPECT guideline for tonsillectomy: systematic review and procedure-specific postoperative pain management recommendations

Tonsillectomy is one of the most frequently performed surgical procedures; however, pain management remains challenging. Procedure‐specific efficacy as well as specific risks of treatment options should guide selection of pain management protocols based on evidence and should optimise analgesia without harm. The aims of this systematic review were to evaluate the available literature and develop recommendations for optimal pain management after tonsillectomy. A systematic review utilising preferred reporting items for systematic reviews and meta‐analysis guidelines with procedure‐specific postoperative pain management (PROSPECT) methodology was undertaken. Randomised controlled trials published in the English language up to November 2019 assessing postoperative pain using analgesic, anaesthetic or surgical interventions were identified. Out of the 719 potentially eligible studies identified, 226 randomised controlled trials met the inclusion criteria, excluding the studies examining surgical techniques. Pre‐operative and intra‐operative interventions that improved postoperative pain were paracetamol; non‐steroidal anti‐inflammatory drugs; intravenous dexamethasone; ketamine (only assessed in children); gabapentinoids; dexmedetomidine; honey; and acupuncture. Inconsistent evidence was found for local anaesthetic infiltration; antibiotics; and magnesium sulphate. Limited evidence was found for clonidine. The analgesic regimen for tonsillectomy should include paracetamol; non‐steroidal anti‐inflammatory drugs; and intravenous dexamethasone, with opioids as rescue analgesics. Analgesic adjuncts such as intra‐operative and postoperative acupuncture as well as postoperative honey are also recommended. Ketamine (only for children); dexmedetomidine; or gabapentinoids may be considered when some of the first‐line analgesics are contra‐indicated. Further randomised controlled trials are required to define risk and combination of drugs most effective for postoperative pain relief after tonsillectomy.

Gradual withdrawal of remifentanil infusion may prevent opioid-induced hyperalgesia

BACKGROUND

The aim of this study was to examine if gradual withdrawal of remifentanil infusion prevented opioid-induced hyperalgesia (OIH) as opposed to abrupt withdrawal. OIH duration was also evaluated.

METHODS

Nineteen volunteers were enrolled in this randomized, double-blinded, placebo-controlled, crossover study. All went through three sessions: abrupt or gradual withdrawal of remifentanil infusion and placebo. Remifentanil was administered at 2.5 ng ml(-1) for 30 min before abrupt withdrawal or gradual withdrawal by 0.6 ng ml(-1) every five min. Pain was assessed at baseline, during infusion, 45-50 min and 105-110 min after end of infusions using the heat pain test (HPT) and the cold pressor test (CPT).

RESULTS

The HPT 45 min after infusion indicated OIH development in the abrupt withdrawal session with higher pain scores compared with the gradual withdrawal and placebo sessions (both P<0.01. Marginal mean scores: placebo 2.90; abrupt 3.39; gradual 2.88), but no OIH after gradual withdrawal compared with placebo (P=0.93). In the CPT 50 min after end of infusion there was OIH in both remifentanil sessions compared with placebo (gradual P=0.01, abrupt P<0.01. Marginal mean scores: placebo 4.56; abrupt 5.25; gradual 5.04). There were no differences between the three sessions 105-110 min after infusion.

CONCLUSIONS

We found no development of OIH after gradual withdrawal of remifentanil infusion in the HPT. After abrupt withdrawal OIH was present in the HPT. In the CPT there was OIH after both gradual and abrupt withdrawal of infusion. The duration of OIH was less than 105 min for both pain modalities.

CLINICAL TRIAL REGISTRATION

NCT 01702389. EudraCT number 2011-002734-39.

The discriminatory value of cardiorespiratory interactions in distinguishing awake from anaesthetised states: a randomised observational study

Depth of anaesthesia monitors usually analyse cerebral function with or without other physiological signals; non‐invasive monitoring of the measured cardiorespiratory signals alone would offer a simple, practical alternative. We aimed to investigate whether such signals, analysed with novel, non‐linear dynamic methods, would distinguish between the awake and anaesthetised states. We recorded ECG, respiration, skin temperature, pulse and skin conductivity before and during general anaesthesia in 27 subjects in good cardiovascular health, randomly allocated to receive propofol or sevoflurane. Mean values, variability and dynamic interactions were determined. Respiratory rate (p = 0.0002), skin conductivity (p = 0.03) and skin temperature (p = 0.00006) changed with sevoflurane, and skin temperature (p = 0.0005) with propofol. Pulse transit time increased by 17% with sevoflurane (p = 0.02) and 11% with propofol (p = 0.007). Sevoflurane reduced the wavelet energy of heart (p = 0.0004) and respiratory (p = 0.02) rate variability at all frequencies, whereas propofol decreased only the heart rate variability below 0.021 Hz (p < 0.05). The phase coherence was reduced by both agents at frequencies below 0.145 Hz (p < 0.05), whereas the cardiorespiratory synchronisation time was increased (p < 0.05). A classification analysis based on an optimal set of discriminatory parameters distinguished with 95% success between the awake and anaesthetised states. We suggest that these results can contribute to the design of new monitors of anaesthetic depth based on cardiovascular signals alone.

Plasmoid formation in current sheet with finite normal magnetic component

Current sheet configurations in natural and laboratory plasmas are often accompanied by a finite normal magnetic component that is known to stabilize the two-dimensional resistive tearing instability in the high Lundquist number regime. Recent magnetohydrodynamic simulations indicate that the nonlinear development of ballooning instability is able to induce the formation of X lines and plasmoids in a generalized Harris sheet with a finite normal magnetic component in the high Lundquist number regime where the linear two-dimensional resistive tearing mode is stable.

Effect of a single dose of pregabalin on post-operative pain and pre-operative anxiety in patients undergoing discectomy

BACKGROUND

Pregabalin acts as a membrane stabilizer and has both analgesic and anxiolytic effects. We hypothesized that one pre-operative dose of pregabalin would reduce pre-operative anxiety and post-operative pain in patients undergoing discectomy.

METHODS

We performed a randomized, placebo-controlled study of 150 mg pregabalin administered before lumbar discectomy in general anaesthesia. The primary endpoint was pain at rest [visual analogue scale (VAS)] 120 min after surgery. The secondary outcomes were morphine consumption, pre-operative anxiety (VAS) and the occurrence of side effects.

RESULTS

The VAS scores for pain at rest and morphine consumption were higher in the placebo group during the 4-h stay in the post-anaesthetic care unit (PACU), but did not differ significantly 24 h after surgery. Pain scores at 7 days were similar and there was no difference in the occurrence of side effects. Pre-operative anxiety was significantly lower in the pregabalin group (2.23±1.11 vs. 4.17±2.37, 95% confidence interval: 0.82-3.05, P=0.001) and there was a significant positive correlation between the pre-operative anxiety score and post-operative pain at 120 min in the pregabalin group.

CONCLUSIONS

A single dose of pregabalin (150 mg) reduced post-operative pain at rest and morphine consumption during the PACU period after lumbar discectomy. Pre-operative anxiety was lower, without increased incidence of side effects.

Safety of laryngeal mask airway and short-stay practice in office-based adenotonsillectomy

BACKGROUND

It is still disputed whether laryngeal mask airway (LMA) is safe and convenient for adenotonsillectomy, and whether these procedures can be safely undertaken in an office-based short-stay ambulatory setting. We report the result of this practice in 1126 consecutive children < 16 years of age.

METHODS

The patients received general anaesthesia with propofol and remifentanil. For analgesic prophylaxis, they received paracetamol, fentanyl and local anaesthetic administration. NSAIDs were given to patients weighing above 15 kg. A surgical technique with elevation, scissors and electrocoagulation was used. Post-operatively, the tonsillectomies were observed in the unit for at least 1.5 h and the adenoidectomies for at least 15-20 min.

RESULTS

Conversion from LMA to an endotracheal tube was carried out in six patients (0.5%), mostly due to airway leakage during ventilation. One patient had a pulmonary atelectasis and was re-intubated. No re-operation was needed in the clinic after surgery, and all patients, except for the one with atelectasis (0.1%), were discharged home as planned. In 122 patients answering a questionnaire, after discharge, two patients (1.6%) were admitted to hospital and re-operated due to bleeding; a further six patients (4.9%) were admitted for observation. In 25% of the patients, nausea and vomiting occurred after discharge, including 21% vomiting of swallowed blood during home travel. Only 5.6% reported significant post-discharge pain.

CONCLUSION

With a well-trained team, adenotonsillectomy on children can be carried out safely in an office-based setting with LMA and a short post-operative stay.

Fast-track surgery for bariatric laparoscopic gastric bypass with focus on anaesthesia and peri-operative care. Experience with 500 cases

BACKGROUND

Bariatric surgery for morbid obesity implies challenges in anaesthesiological handling. We report our experience from 500 consecutive patients during 3 years.

METHODS

The patients were due for laparoscopic Roux-en-Y gastric bypass and enteral bypass. Sleep was induced after pre-oxygenation with target control infusions (TCI) of remifentanil and propofol; vecuronium was supplied for facilitating endotracheal intubation. The propofol infusion was stopped and desflurane 3-6% was given for BIS-titrated anaesthetic maintenance together with remifentanil TCI. Antiemetic prophylaxis was supplied with intravenous (IV) droperidol, ondansetron and dexamethasone; post-operative pain prophylaxis was IV paracetamol, parecoxib and bupivacaine infiltration. The patients were extubated in the operating room and kept in the post-operative care unit for 3-4 h, being tested for a 20 m walk before discharge to the ward.

RESULTS

The procedure was uncomplicated peri-operatively in all 500 cases and in 497 patients (99.4%) post-operatively. Three patients had one complication, which resolved without sequelae: oesophageal rupture from gastric tubing, reoperation for anastomosis leakage and pneumonia. The mean duration of surgery was 57 min (range 37-91). The mean time from the start of anaesthesia until the start of surgery and time from the end of surgery until the end of anaesthesia were both significantly reduced throughout the study period, from 23 to 7.8 and 5.8 to 1.9 min, respectively (P<0.001). The mean total hospital stay was reduced from 3 days at start to 2 days in the end of the series (P<0.05).

CONCLUSION

Safe bariatric short-stay surgery is feasible with a dedicated anaesthesiological concept in an expert surgical team.

Comparison of etoricoxib vs. ketorolac in postoperative pain relief

BACKGROUND

COX-2 inhibitors have been claimed to have equal analgesic efficacy as non-selective nonsteroidal anti-inflammatory drugs, but this has been disputed in animal experiments.

METHODS

One hundred thirty-three women scheduled for ambulatory, laparoscopic gynaecological surgery were included in this randomised, double-blind study. Group E received 120 mg etoricoxib orally as premedication. Group K received 30 mg ketorolac i.v. after induction of anaesthesia. General anaesthesia was induced and maintained with propofol and remifentanil. Fentanyl 0.5 microg/kg i.v. and local wound anaesthesia was administered at the end of surgery. Postoperatively, the patients received fentanyl 0.5 microg/kg i.v. if visual analogue scale (VAS) >or=30 mm. Before discharge, Group K received 30 mg ketorolac i.v. Twenty-four hours postoperatively, Group E received 120 mg etoricoxib.

RESULTS

The first 4 h postoperatively, Group K required 83+/-65 microg and Group E required 123+/-91 microg fentanyl [mean (SD), P=0.004]. After 30 min VAS in Group K was 31.3+/-19.7 mm and 43.8+/-16.9 mm in Group E [mean (SD), P<0.001]. Discharge readiness was significantly shorter in Group K (222+/-40 min) compared with Group E (244+/-47 min) [mean (SD), P=0.004]. There were no differences in pain scores or rescue pain medication at 24 or 48 h postoperatively. Less nausea was observed in the 4-24-h period in Group E.

CONCLUSIONS

Thirty milligram ketorolac i.v. after induction of anaesthesia resulted in significantly less immediate pain and opioid consumption during the first 4 h postoperatively compared with 120 mg etoricoxib preoperatively.

Administration of fentanyl before remifentanil-based anaesthesia has no influence on post-operative pain or analgesic consumption

BACKGROUND

Remifentanil's short-acting analgesic effect and the potential of producing hyperalgesia is a challenge to post-operative pain control. This study investigated whether pre-treating the patients with fentanyl before remifentanil-based anaesthesia could reduce post-operative pain or analgesic consumption.

METHODS

One-hundred patients admitted for anterior cruciate ligament repair were included in a double-blind study. Propofol and remifentanil were used for general anaesthesia. Group Pre received fentanyl 1.5 microg/kg intravenously (IV) and Group Post placebo before the remifentanil infusion. At the end of surgery, Group Pre received 1.5 microg/kg and Group Post received 3.0 microg/kg. Patient-controlled analgesia with fentanyl was used as analgesic rescue medication during the first 4 h post-operatively. Oxycodone 5 mg orally was taken as needed during the subsequent 4-24-h period.

RESULTS

A mean dose of remifentanil 0.43 microg/kg/min was used for 90 min during surgery in both groups. There were no differences in the verbal rate scale (VRS) score or need of rescue analgesic medication between the groups during the first 4 h. Group Post had significantly less pain in the 4-24-h period after surgery, with a median VRS score of 'slight pain' vs. 'moderate pain' in Group Pre (P<0.05). The oxycodone consumption was similar in both groups.

CONCLUSION

Pre-treatment with fentanyl 1.5 microg/kg IV yielded no reduction in post-operative pain or analgesic consumption after 90 min of remifentanil-based anaesthesia with 0.43 microg/kg/min of remifentanil.

Analgesic and antiemetic effect of ketorolac vs. betamethasone or dexamethasone after ambulatory surgery

BACKGROUND

Glucocorticoids are known to provide slower onset and more prolonged duration of analgesic effect than ketorolac. In the present study, we wanted to evaluate the effect over time from a single dose of either intravenous (i.v.) dexamethasone or an intramuscular (i.m.) depot formulation of betamethasone compared with i.v. ketorolac.

MATERIALS AND METHODS

One hundred and seventy-nine patients admitted for mixed ambulatory surgery were included in the study. After induction of general i.v. anaesthesia, the patients were randomized to receive double-blindly either dexamethasone 4 mg i.v. (Group D) or betamethasone depot formulation 12 mg i.m. (Group B) or ketorolac 30 mg i.v. (Group K). Fentanyl was used for rescue analgesic medication in the post-operative care unit (PACU) and codeine with paracetamol after discharge, for a study period of 3 days.

RESULTS

There was significantly less post-operative pain in the ketorolac group during the stay in the unit (88% with minor or less pain in Group K vs. 74% and 67% in Groups D and B, respectively, P < 0.05), significantly less need for rescue medication (P < 0.05) and significantly less nausea or vomiting (12% in Group K vs. 30% in the other groups pooled, P < 0.05). The ketorolac patients were significantly faster for ready discharge, median 165 min vs. 192 min and 203 min in Groups D and B, respectively (P < 0.01). There were no differences between the groups in perceived pain, nausea, vomiting or rescue analgesic consumption in the 4- to 72-h period.

CONCLUSION

Dexamethasone 4 mg or bethamethasone 12 mg did not provide prolonged post-operative analgesic effect compared with ketorolac 30 mg, which was superior for analgesia and antiemesis in the PACU.

Can the cerebral state monitor replace the bispectral index in monitoring hypnotic effect during propofol/remifentanil anaesthesia?

BACKGROUND

In 2004, the cerebral state monitor, CSM, was launched as a low-cost alternative to the bispectral index, BIS, for monitoring depth of sleep during anaesthesia. We tested whether the two monitors would reflect hypnosis equally during propofol/remifentanil anaesthesia.

METHODS

During laparoscopy or breast/surface surgery, 55 non-paralyzed patients were monitored simultaneously with the BIS and the CSM. Trend curves for the indexes [BIS and cerebral state index (CSI)] were compared for congruence. The difference between the two indexes for the entire course was quantified, and the ability of the two monitors to separate awake from asleep during induction was described.

RESULTS

In the majority of the patients, 87%, there was a good fit between the indexes. There were major deviations in seven patients, in whom CSI indicated that the patients were awake during parts of the course despite clinical sleep, correctly identified with the BIS. Both indexes separated awake from asleep during induction in the individual patient, but the overlap in values between patients was more pronounced for CSI.

CONCLUSION

CSM and BIS show some important differences in measuring hypnotic state during clinical propofol/remifentanil anaesthesia.

Does esomeprazole prevent post-operative nausea and vomiting?

BACKGROUND

Esomeprazole is a potent proton pump inhibitor (PPI), reducing acid production as well as gastric juice volume. This study evaluated the possible beneficial effect of esomeprazole on reducing post-operative nausea and vomiting (PONV).

METHODS

Patients undergoing laparoscopic or open gynaecological surgery, or laparoscopic cholecystectomy were randomized to receive three peri-operative doses double blindly of either esomeprazole 40 mg or placebo, given intravenously or orally. All patients were given a standardized anaesthesia regimen including fentanyl and sevoflurane/nitrous oxide.

RESULTS

The study population consisted of 284 patients. Demographic data and known PONV risk factors were similar for the two treatment groups. PONV was observed in 77% of patients on esomeprazole vs. 81% on placebo (NS) and rescue antiemetic medication was needed in 56% vs. 53%, respectively (NS). The proportion of patients that vomited during 0-24 h was lower on esomeprazole than placebo (38% vs. 49%; NS), and the mean amount of vomit was significantly lower (52 vs. 86 g; P < 0.05). The use of neostigmine, use of opioids and type of surgery were significant risk factors for PONV (P < 0.05). The 24-h incidence of PONV was 63% after laparoscopic gynaecology, 80% after laparoscopic cholecystectomy and 88% after open gynaecological laparotomy, whereas laparoscopic cholecystectomy had the lowest risk when corrected for other risk factors of PONV.

CONCLUSION

Esomeprazole had no clinically relevant effect on the overall 24-h incidence of PONV. However, esomeprazole significantly reduced the total amount of vomit during 24-h post-operatively. This may be of value in patients with an increased risk of pulmonary aspiration.

Skin conductance or entropy for detection of non-noxious stimulation during different clinical levels of sedation

BACKGROUND

State entropy (SE) measures electroencephalographic signals, whereas response entropy (RE) also includes frontal electromyographic activity. In the presence of electromyographic activity, the RE index is larger than the SE index, the difference being denoted as RE-Delta (RE-Delta= RE - SE). Skin conductance (SC) may be expressed by a slow reacting variable, the mean SC level, the derivate of the mean SC level (D-SC), the number of SC fluctuations (NSCF) or the amplitude of the SC fluctuations (ASCF), which directly shows skin sympathetic nerve activity. The goal of this study was to evaluate whether these SC and entropy variables could differentiate between the responses obtained to load sound stimuli at different sedation levels before the induction of general anaesthesia.

METHODS

Twenty women scheduled for gynaecological laparotomy were studied. The modified observer's assessment of alertness sedation (OAAS) was used to classify the patients' hypnotic levels. White sounds (98 dB) were given at OAAS level 5 without propofol, at OAAS levels 4-3 and 3-2 with propofol and at OAAS levels 3-2 and < 2 with propofol and remifentanil.

RESULTS

RE and SE showed a steady decline from OAAS level 5 to level < 2 (P < 0.01). RE-Delta did not discriminate between any of the OAAS levels (P= NS). The mean SC level discriminated between OAAS levels 4-3 to < 2 (P < 0.01). D-SC discriminated between all the different OAAS levels (P < 0.01). NSCF discriminated between OAAS levels 5 to 3-2 (P < 0.05), but did not discriminate at OAAS level 3-2 between propofol alone or combined with remifentanil, or between OAAS level 3-2 and < 2. ASCF differentiated between OAAS levels 5 and 4 (P < 0.001) and OAAS levels 3-2 and < 2 (P < 0.05) only.

CONCLUSION

RE, SE and D-SC showed a similar discrimination between sound responses at the different sedation levels.

Comparison of skin conductance with entropy during intubation, tetanic stimulation and emergence from general anaesthesia

BACKGROUND

The number of skin conductance fluctuations (NSCF) expresses sympathetic skin nerve activity. The response entropy (RE) measures electromyographic and electroencephalographic activity in the forehead. The state entropy (SE) measures mainly electroencephalographic activity. When the suppression of frontal muscular activity is complete, RE is equal to SE. RE-Delta is defined as SE minus RE. The purposes of this study were to examine whether NSCF and RE-Delta correlate with signs of clinical stress during intubation and tetanic noxious stimulation and to elucidate how rapidly and accurately entropy and NSCF react during emergence from general anaesthesia.

METHODS

Twenty women scheduled for gynaecological laparotomy were studied. During intubation in remifentanil and propofol general anaesthesia, NSCF and RE-Delta were correlated with the clinical stress score. After a wash-out period, two series of tetanic stimuli were given, the first with (R+) and the second without (R-) remifentanil infusion. The tetanic pre-stimuli periods were compared with the tetanic post-stimuli periods, and R+ was compared with R-. During emergence, the responses of entropy and skin conductance were related to the time of extubation.

RESULTS

NSCF correlated well with the clinical stress score during intubation (r(2)= 0.73, P < 0.0005). RE-Delta showed a weaker correlation (r(2)= 0.33, P= 0.007). During tetanic stimuli, the NSCF pre-stimuli level was lower than the post-stimuli level (P < 0.001), and the NSCF R+ response was lower than the NSCF R- response (P= 0.002). RE-Delta did not show similar differences. During emergence, RE reacted before NSCF and SE (P= 0.003).

CONCLUSION

NSCF was better than RE-Delta for the measurement of clinical stress during intubation, and was sensitive to tetanic stimuli at different opioid analgesic levels, by contrast with RE-Delta. Both modalities were able to predict emergence at the end of anaesthesia, but RE was more rapid.

Similar onset time of 2-chloroprocaine and lidocaine + epinephrine for epidural anesthesia for elective Cesarean section

BACKGROUND

The use of regional anesthesia for elective Cesarean section has been demonstrated to be safe for both the mother and new-born. In parturients with an epidural catheter placed previously for labor analgesia, extension of the epidural block may be the preferred option, provided that adequate speed of onset and adequate surgical anesthesia are obtained. We therefore performed a prospective, randomized, double-blind trial to examine the speed of onset and anesthetic quality of 2-chloroprocaine vs. a solution of lidocaine with one additive, epinephrine 5 microg/ml.

METHODS

Forty ASA I patients, scheduled for elective Cesarean section, were randomly assigned to two groups: the 2-chloroprocaine group received 2-chloroprocaine 30 mg/ml and the lidocaine group received the same amount (ml) of lidocaine 20 mg/ml with 5 microg/ml epinephrine. The speed of onset was defined as the time taken to loss of cold sensation from 70% ethanol application at thoracic dermatome level 5 (Th5).

RESULTS

The time to achieve loss of cold sensation at Th5 was similar in both groups: median of 8 min (range, 4-13 min) in the 2-chloroprocaine group vs. 5 min (range, 2-22 min) in the lidocaine group (NS). Epidural anesthesia was successful for surgery in all but one patient (lidocaine group). There was no significant difference in the need for supplemental intravenous alfentanil between the two groups: 30% vs. 20% of patients in the 2-chloroprocaine and lidocaine groups, respectively; the pain scores (visual analog scale) were also similar. Intra-operative complications occurred with similar frequency, and none was serious. In the patients in the 2-chloroprocaine group, 11 (55%) had episodes of systolic blood pressure less than 90 mmHg vs. 15 (75%) in the lidocaine group (NS).

CONCLUSION

Both 2-chloroprocaine and lidocaine have a rapid onset of effect and are suitable local anesthetic agents for Cesarean section. In view of the time taken for preparation and the potential for logistic problems when an additive is used, a pre-prepared solution, such as 2-chloroprocaine, may be preferred.

Why do women wake up faster than men from propofol anaesthesia?

BACKGROUND

It has repeatedly been shown that female patients wake up faster from propofol anaesthesia than male patients. The reason for this is not clear. It is possible that female patients have a more rapid decline in plasma propofol concentration after termination of an infusion, or there could be gender differences in the sensitivity to propofol, making women wake up at higher concentrations. We tested the hypothesis that women wake up faster because of a more rapid decline in plasma propofol.

METHODS

Sixty adult patients (30 female and 30 male; ASA I or II) undergoing lower limb surgery under regional anaesthesia, were enrolled in an open study. Propofol was given as the only hypnotic drug, administered by the plasma target control system (TCI) Diprifusor, titrated to bispectral index (BIS) values of 40-60. Blood samples for propofol measurements were taken just before the propofol infusion was stopped and when the patients woke up.

RESULTS

The female patients woke up faster than the male patients (5.6 vs 8.2 min, P=0.003). The plasma propofol concentration declined more rapidly in the women (P=0.02). An additional significant finding was that the TCI algorithm had a better fit for the women than for the men, with a median prediction error (MDPE) of 2% in the female patients compared with 40% in the male patients (P<0.001). At emergence the men had a significantly higher measured propofol concentration than the women (P=0.05).

CONCLUSION

The female patients had a more rapid decline in plasma propofol at the end of infusion. Gender differences in pharmacokinetics could explain the faster emergence for female patients after propofol anaesthesia, and gender differences in propofol sensitivity may also be present.

Is peri-operative cortisol secretion related to post-operative cognitive dysfunction?

BACKGROUND

The pattern of cortisol secretion is influenced by surgery. As cortisol can adversely affect neuronal function, this may be an important factor in the development of post-operative cognitive dysfunction (POCD). We hypothesized that the incidence of POCD would be related to changes in cortisol level.

METHODS

We studied 187 patients aged over 60 years undergoing major non-cardiac surgery with general or regional anaesthesia. Saliva cortisol levels were measured pre-operatively and at 1 day, 7 days and 3 months post-operatively in the morning (08.00 h) and in the afternoon (16.00 h) using salivettes. Cognitive function was assessed pre-operatively, on day 7 and at 3 months using four neuropsychological tests. POCD was defined as a combined Z score of greater than 1.96.

RESULTS

After surgery, salivary cortisol concentrations increased significantly. POCD was detected in 18.8% of subjects at 1 week and in 15.2% after 3 months. The pre-operative ratios between the morning and afternoon cortisol concentrations (am/pm ratios) were 2.8 and 2.7 in patients with POCD at 1 week vs. those without POCD at 1 week, respectively. The am/pm ratios decreased significantly post-operatively to 1.9 and 1.6 at 1 week, respectively (P = 0.02 for both). In an analysis considering all am/pm ratios, it was found that the persistent flattening in am/pm ratio was significantly related to POCD at 1 week.

CONCLUSION

The pattern of diurnal variation in cortisol level was significantly related to POCD. Thus, circadian rhythm disturbance or metabolic endocrine stress could be an important mechanism in the development of cognitive dysfunction after major surgery.

Pre-operative fasting guidelines: an update

Liberal pre-operative fasting routines have been implemented in most countries. In general, clear fluids are allowed up to 2 h before anaesthesia, and light meals up to 6 h. The same recommendations apply for children and pregnant women not in labour. In children <6 months, most recommendations now allow breast- or formula milk feeding up to 4 h before anaesthesia. Recently, the concept of pre-operative oral nutrition using a special carbohydrate-rich beverage has also gained support and been shown not to increase gastric fluid volume or acidity. Based on the available literature, our Task Force has produced new consensus-based Scandinavian guidelines for pre-operative fasting. What is still not clear is to what extent the new liberal fasting routines should apply to patients with functional dyspepsia or systematic diseases such as diabetes mellitus. Other still controversial areas include the need for and effect of fasting in emergency patients, women in labour and in association with procedures done under 'deep sedation'. We think more research on the effect of various fasting regimes in subpopulations of patients is needed before we can move one step further towards completely evidence-based pre-operative fasting guidelines.

McArdle's disease and anaesthesia: case reports. Review of potential problems and association with malignant hyperthermia

BACKGROUND

McArdle's disease of isolated deficiency in glycogen degradation in skeletal muscles has the potential of creating perioperative anaesthesiological problems; such as hypoglycaemia, rhabdomyolysis, myoglobinuria, acute renal failure and possibly malignant hyperthermia.

METHODS

Eight patients with McArdle's disease were asked about previous surgery, anaesthesia and perioperative problems, and available hospital records were reviewed. Existing literature was reviewed for reports on McArdle's disease and anaesthesia.

RESULTS

The eight patients had 35 anaesthesias (23 general anaesthesias, three regional anaesthesias and nine local anaesthesias). Perioperative problems of a non-specific nature were mentioned in three cases of general anaesthesia: two with postoperative nausea/vomiting, and one with an episode of tachycardia and low blood pressure. Three patients were tested for malignant hyperthermia (MH) using the in vitro contracture test (IVCT); two of them with a positive result. The literature search revealed seven case reports of McArdle's disease and anaesthesia. Apart from one report of hyperthermia, pulmonary oedema and rhabdomyolysis; probably not associated with MH, no problems were encountered from the literature search.

CONCLUSION

McArdle's disease does not seem to cause severe perioperative problems in routine anaesthetic care. However, measures for preventing muscle ischaemia and rhabdomyolysis should be kept in mind, as well as the potential for these patients to develop postoperative fatigue, myoglobinuria and renal failure. Although no clinical association with malignant hyperthermia has been established, many of these patients can have a positive in vitro contracture test, and simple prophylactic measures, as with malignant hyperthermia, may be recommended if otherwise not contraindicated.

Palmar skin conductance compared to a developed stress score and to noxious and awakening stimuli on patients in anaesthesia

BACKGROUND

The number of fluctuations in the skin conductance per s (NFSC) as a measure of the sympathetic nervous system may be a tool for monitoring physiological stress during surgery and general anaesthesia. The purpose of this study was to find the sensitivity and specificity of the NFSC when compared to a peroperative clinical stress score. Moreover, different patterns of skin conductance responses were compared with the BIS score to find out if the mean level of skin conductance (SC) and NFSC monitoring could differentiate between awakening and noxious stimuli.

METHODS

Fourteen patients were studied during stressful or non-stressful registration periods. During each registration period, the NFSC was compared to a five-point clinical stress score (CSS) (systolic blood pressure >130 mmHg, cough, tears, EMG in the forehead >50 or movements) and BIS score.

RESULTS

The NFSC and the CSS both indicated physiological stress at 12 registrations and no stress at 186 registrations. The NFSC indicated physiological stress without signs of clinical stress (CSS = 0) in 28 registrations, whereas signs of clinical stress (CSS > 0) were indicated on two occasions without signs of stress in the NFSC. The sensitivity of the NFSC when compared to the CSS was 86% and the specificity was 86%. Moreover, in all situations (n = 16) where NFSC indicated stress and the BIS score >50, the SC increased. This was different from situations (n = 13) where NFSC indicated stress and the BIS score <50, then the SC did not increase (P < 0.001).

CONCLUSION

The NFSC is sensitive to clinical stress during surgical stimulation. Moreover, the combined use of SC and NFSC may have a potential to differentiate between situations of stress due to inadequate hypnotic effect vs. inadequate analgesic effect.

The impact of increasing the use of regional anaesthesia for emergency caesarean section

BACKGROUND AND OBJECTIVE

In 1991 general anaesthesia was used extensively for emergency Caesarean section at Haukeland University Hospital even in patients with an ongoing epidural infusion. With increased knowledge of the potential safety benefits of regional anaesthesia and increased experience with the technique, we decided to use indwelling epidural catheters for emergency Caesarean section.

METHODS

We conducted a retrospective analysis of a full annual data set on emergency Caesarean section in parturients with ongoing epidural analgesia in 1997 and compared it with a similar data set from 1991.

RESULTS

Epidural anaesthesia was used significantly more often in 1997 with 115 (78%) cases than in 1991 with five (12%) cases (P < 0.001). Elapsed time before adequate anaesthesia and the start of surgery was significantly shorter in 1991 (mean 8.3 min) compared to 1997 (mean 13 min) (P < 0.001). No deaths or major complications were observed in either group. Intraoperative minor complications were observed more frequently in 1997 with 70 cases (47%) than in 1991 with two cases (6%) (P < 0.001). The principal complications were hypotension and nausea. Postoperative complications in mother and neonate were similar in both groups. There was a significantly shorter mean hospital stay in 1997 (6 days), compared with 1991 (8 days) (P < 0.001).

CONCLUSION

The increase in the use of indwelling epidural catheters for emergency Caesarean section has resulted in a significant increase in the use of regional anaesthesia. A modest increase in time elapsed before start of surgery was observed although there were no significant differences in the number of neonates with low Apgar scores. No major complications were observed, but there was an increased frequency of minor complications in 1997.

Increased spillover of norepinephrine to the portal vein during CO-pneumoperitoneum in pigs

BACKGROUND

Elevated intra abdominal pressure (IAP) during CO2-insufflation has been associated with increased catecholamine concentrations in plasma. We have previously indicated that this may be due to a regional increased spillover from the abdominal region. In this experimental study we investigated catecholamine spillover from the drainage area of the portal vein during CO2-pneumoperitoneum.

METHODS

Eight pigs under general anesthesia were investigated before and after CO2-pneumoperitoneum with an IAP of 15 mmHg. Regional spillover of catecholamines was determined by measuring plasma catecholamine concentrations and flow simultaneously. Plasma concentrations of catecholamines were measured from the portal and femoral veins, the pulmonary and carotid arteries. Flow data were collected with laser-Doppler transit time flow probes around the portal and femoral veins. Cardiac output was measured by the thermo-dilution technique. Estimated spillover was calculated by the veno-arterial difference multiplied by flow.

RESULTS

We found a significant increase in estimated spillover of norepinephrine from the drainage area of the portal vein from 10 (-1.2, 78) ng x min(-1) to 27 (1.8, 475) ng x min(-1)[median (range)] (P = 0.05), but no change in estimated spillover of norepinephrine from the drainage area of the femoral vein. Plasma concentrations of norepinephrine increased in central venous and arterial blood. There was no significant change in epinephrine concentrations in arterial blood.

CONCLUSION

Estimated norepinephrine spillover from the drainage area of the portal vein increased during CO2-pneumoperitoneum in pigs. This may indicate that the increased norepinephrine concentrations found in arterial plasma reflects a local activation of sympathetic nerves in the region of the portal drainage area.

Bispectral index, serum drug concentrations and emergence associated with individually adjusted target-controlled infusions of remifentanil and propofol for laparoscopic surgery

BACKGROUND

Target-controlled infusions (TCI) are used to simplify administration and increase precision of i.v. drugs during general anaesthesia. However, there is a limited relationship between preset targets and measured concentrations of drugs and between measured concentrations and measures of brain function, such as the bispectral index (BIS).

METHODS

We set out to evaluate the performance of TCI devices for propofol (Diprifusor) and remifentanil (Remifusor, prototype), during laparoscopic cholecystectomy in 21 patients. We also checked if there was any correlation between serum concentrations of propofol and BIS during individually adjusted anaesthesia.

RESULTS

The Diprifusor and Remifusor had a median absolute performance error of 60% and 25% respectively. Propofol concentrations were underpredicted by a median of 60%, and remifentanil concentrations were slightly overpredicted by a median of 7%. When anaesthesia was adjusted to keep BIS values between 45 and 60, no correlation existed between measured concentrations of propofol and the corresponding BIS values, although both BIS and serum propofol concentration discriminated well between the awake and asleep states. Emergence was rapid and uneventful in all patients. Female patients had a more rapid emergence than male patients (6.6 and 11.6 min respectively).

CONCLUSIONS

TCI devices for remifentanil and propofol result in large variation in measured serum concentrations. The lack of correlation between BIS and serum concentrations of propofol adds to the debate about whether BIS measures hypnosis as a graded state during surgery. This study confirms that women wake up faster than men, but provides no explanation for this repeatedly shown difference.

Cognitive dysfunction after minor surgery in the elderly

BACKGROUND

Major surgery is frequently associated with postoperative cognitive dysfunction (POCD) in elderly patients. Type of surgery and hospitalization may be important prognostic factors. The aims of the study were to find the incidence and risk factors for POCD in elderly patients undergoing minor surgery.

METHODS

We enrolled 372 patients aged greater than 60 years scheduled for minor surgery under general anesthesia. According to local practice, patients were allocated to either in- (199) or out-patient (173) care. Cognitive function was assessed using neuropsychological testing preoperatively and 7 days and 3 months postoperatively. Postoperative cognitive dysfunction was defined using Z-score analysis.

RESULTS

At 7 days, the incidence (confidence interval) of POCD in patients undergoing minor surgery was 6.8% (4.3-10.1). At 3 months the incidence of POCD was 6.6% (4.1-10.0). Logistic regression analysis identified the following significant risk factors: age greater than 70 years (odds ratio [OR]: 3.8 [1.7-8.7], P = 0.01) and in- vs. out-patient surgery (OR: 2.8 [1.2-6.3], P = 0.04).

CONCLUSIONS

Our finding of less cognitive dysfunction in the first postoperative week in elderly patients undergoing minor surgery on an out-patient basis supports a strategy of avoiding hospitalization of older patients when possible.

Does anaesthesia cause postoperative cognitive dysfunction? A randomised study of regional versus general anaesthesia in 438 elderly patients

BACKGROUND

Postoperative cognitive dysfunction (POCD) is a common complication after cardiac and major non-cardiac surgery with general anaesthesia in the elderly. We hypothesized that the incidence of POCD would be less with regional anaesthesia rather than general.

METHODS

We included patients aged over 60 years undergoing major non-cardiac surgery. After giving written informed consent, patients were randomly allocated to general or regional anaesthesia. Cognitive function was assessed using four neuropsychological tests undertaken preoperatively and at 7 days and 3 months postoperatively. POCD was defined as a combined Z score >1.96 or a Z score >1.96 in two or more test parameters.

RESULTS

At 7 days, POCD was found in 37/188 patients (19.7%, [14.3-26.1%]) after general anaesthesia and in 22/176 (12.5%, [8.0-18.3%]) after regional anaesthesia, P = 0.06. After 3 months, POCD was present in 25/175 patients (14.3%, [9.5-20.4%]) after general anaesthesia vs. 23/165 (13.9%, [9.0-20.2%]) after regional anaesthesia, P = 0.93. The incidence of POCD after 1 week was significantly greater after general anaesthesia when we excluded patients who did not receive the allocated anaesthetic: 33/156 (21.2%[15.0-28.4%]) vs. 20/158 (12.7%[7.9-18.9%]) (P = 0.04). Mortality was significantly greater after general anaesthesia (4/217 vs. 0/211 (P < 0.05)).

CONCLUSION

No significant difference was found in the incidence of cognitive dysfunction 3 months after either general or regional anaesthesia in elderly patients. Thus, there seems to be no causative relationship between general anaesthesia and long-term POCD. Regional anaesthesia may decrease mortality and the incidence of POCD early after surgery.

Catecholamine release during laparoscopic fundoplication with high and low doses of remifentanil

BACKGROUND

Reports on stress responses to laparoscopic surgery have been conflicting. Depth of anesthesia may influence the neuro-hormonal release, including catecholamines. Opioids depress general sympathetic activation in a dose-dependent manner. We investigated the hypothesis that remifentanil would depress the catecholamine response to pneumoperitoneum and laparoscopic surgery differently with a high dose (HD) compared with a low dose (LD).

METHODS

In a randomized, prospective study we investigated 18 ASA I-II patients undergoing laparoscopic fundoplication with an intra-abdominal pressure of 12 mmHg. The patients were randomized to receive either a LD (0.13 microg kg-1x min-1) or HD (0.39 microg kg-1 x min-1) of remifentanil with a target-controlled infusion (TCI) technique. Bispectral index of EEG (BIS) was maintained at 40-55 by propofol delivered by a TCI system. Arterial catecholamines were analyzed at different times during the procedure.

RESULTS

Norepinephrine increased equally in both groups during pneumoperitoneum and surgical intervention. Epinephrine stayed low in the HD-group, while increasing during surgery in the LD-group.

CONCLUSION

High dose of remifentanil depressed the epinephrine response to pneumoperitoneum and surgery, indicating no general activation of the sympathetic nervous system. Neither a LD nor HD of remifentanil depressed the norepinephrine response during pneumoperitoneum. This suggests a centrally independent release of norepinephrine.

Ondansetron disintegrating tablets of 8 mg twice a day for 3 days did not reduce the incidence of nausea or vomiting after laparoscopic surgery

BACKGROUND AND OBJECTIVE

Although many antiemetic drugs are available for intravenous use in the hospital setting, few are available after patient discharge. Consequently, nausea and vomiting are frequent complaints from patients at home after ambulatory surgery. We tested the hypothesis that the new 8 mg ondansetron disintegrating tablets will decrease the rate of nausea and vomiting at home after laparoscopic surgery.

METHODS

Ninety-six patients were studied in a randomized double-blind study. Starting the first evening after operation and continuing every 12 h for 3 days, patients received either placebo or ondansetron 8 mg disintegrating tablets orally. The patients returned a questionnaire about postoperative nausea and vomiting, other side-effects, e.g. dizziness, headache, nightmare, anxiety and pain, as well as their overall satisfaction at 24 and 72 h after completion of surgery.

RESULTS

The rates of nausea and vomiting were similar in the two groups, both during the first 24 h (28 versus 48%, placebo and ondansetron, respectively (ns) and during the 24-72 h (21 versus 35% (ns)). The incidence rate of vomiting was 8% (placebo) versus 12% (ondansetron) during the first 24 h (ns) and 9 versus 13% respectively in the 24-72 h (ns). No difference between groups was observed in overall satisfaction, incidence of postoperative pain or other side-effects.

CONCLUSIONS

The use of ondansetron disintegrating tablets of 8 mg twice a day for 3 days did not reduce the incidence of nausea and vomiting in patients undergoing outpatient laparoscopic surgery.

Guidelines for the practice of anesthesia in Norway

Since the first version saw the light of day in 1991 the Guidelines have occupied a central position in the Norwegian practice of anesthesia. This document comprises part of the quality management documents held in the departments of anesthesia in Norwegian hospitals. If departments of anesthesia are unable to adhere to certain specific points in the Guidelines, it is recommended that this should be documented in writing. It has been stated by central governmental bodies and patients' insurance organizations that the Guidelines will be an important factor in medico legal cases, although it is not an obligatory legal document for hospital owners. It is our objective that the document will form the foundation for quality assurance work in the departments of anesthesia in Norway. The purpose of this document is to ensure a satisfactory standard for the practice of anesthesia in Norway. 'The Guidelines for the Practice of Anesthesia in Norway' (the Guidelines) is a series of recommended guidelines. The practice of anesthesia in this context includes general anesthesia, regional anesthesia, controlled sedation, postoperative monitoring, and other observations where anesthesia personnel are required. The Guidelines apply to all doctors, nurses, and other personnel undertaking the delegated practice of anesthesia. Deviations from the Guidelines should be explained and documented in every case. The Guidelines should be adhered to in medical emergencies as far as possible. The Guidelines must not be allowed to prevent the execution of immediate and lifesaving measures. The Guidelines should be revised at regular intervals so that it is up-to-date with current legislation and medical and technological developments and practice.

Improved long-lasting postoperative analgesia, recovery function and patient satisfaction after inguinal hernia repair with inguinal field block compared with general anesthesia

BACKGROUND

Inguinal hernia repair is a common surgical procedure, and different types of anesthetic techniques are in use. We wanted to test if preoperative inguinal field block (IFB) with ropivacaine would provide benefits in the postoperative period compared with general anesthesia and wound infiltration.

METHODS

Sixty patients scheduled for inguinal hernia repair were randomized to receive general anesthesia with wound infiltration postoperatively, or inguinal field block (IFB) before surgery, with no or only light sedation intraoperatively. General anesthesia was induced with midazolam, fentanyl and propofol, maintained with propofol and alfentanil, and supplemented with nitrous oxide in oxygen through a laryngeal mask. The IFB was performed by an anesthesiologist, with 50-60 ml ropivacaine and 5 mg/ml with a dedicated technique.

RESULTS

All significant differences were in favor of the IFB group: less pain (visual analog scale, verbal pain score) postoperatively and until day 7, faster mobilization with less pain, lower analgesic consumption, and higher patient satisfaction.

CONCLUSION

Preoperative inguinal field block for hernia repair provides benefits for patients in terms of faster recovery, less pain, better mobilization and higher satisfaction throughout the whole first postoperative week.

Wound infection in day-surgery

To determine the surgical wound infection rate associated with day-surgery and to assess whether infection was related to patient factors, a prospective study of all electively operated adult day-cases was carried out during a 6 month period between January and June 1996. The study included gastroenterological orthopaedic, vascular, plastic and urological surgery. No operations involving obviously infected patients were performed in the unit. Strict criteria for diagnosis of infection were used. All patients were examined on the 7th and 30th post-operative day. A total of 642 (98.8%) patients were included (316 females 334 males). Infection developed in 22 of the 642 patients (3.5%), only three were diagnosed before the 7th day visit. Orthopaedic procedures accounted for more than 40% of the surgery, but only 22.7% of the wound infections. Gastroenterology made up nearly 36% of the procedures and accounted for 36.4% of the infections. Vascular procedures were 5.7% of the total but accounted for 18% of the infections. No correlation was found between age, gender, operation time or ASA-group and the infection rate. The study is to small to quantify with statistical significance risk-factors associated with wound infection in ambulatory surgery. Our data may suggest that the type of surgery as well as individual factors associated with surgeons may influence the wound infection rate.

Day-case laparoscopic fundoplication for gastro-oesophageal reflux disease

BACKGROUND

Based on a series of successful outpatient laparoscopic cholecystectomies, day-case laparoscopic fundoplication for gastro-oesophageal reflux disease was introduced in January 1997. The initial results are reported.

METHODS

Inclusion criteria were American Society of Anesthesiologists grade I-II, living within 30 min travel from the hospital, and adult company at home. Initially only selected patients were offered day-case treatment, but later it was adopted as routine. The patients underwent general intravenous anaesthesia with propofol and remifentanil, and were given ketorolac, propacetamol, droperidol and ondansetron as prophylaxis against postoperative pain and nausea. The surgical procedure was Nissen-Rosetti fundoplication or semifundoplication depending on oesophageal manometric results.

RESULTS

Forty-five patients were included. Four patients were admitted; 41 were discharged as planned 3-8 h after operation, and five of these patients were readmitted. One underwent reoperation for necrosis of the gastric fundus. A further five patients visited the outpatient department without need for admission. At follow-up 31 patients were satisfied with the day-case treatment, five were indifferent, and five were dissatisfied because of pain. If offered a similar operation in the future, 26 patients would have preferred and seven would have accepted day-case treatment, and eight would not.

CONCLUSION

Outpatient laparoscopic fundoplication is safe and well tolerated by the majority of patients.