Optimal volume of local anaesthetic for adductor canal block: using the continual reassessment method to estimate ED95.

BACKGROUND: Theoretically, the ideal volume of local anaesthetic for adductor canal block (ACB) would ensure sufficient filling of the canal and avoid proximal spread to the femoral triangle. In this dose-finding study, we aimed to investigate the minimal effective volume for an ACB needed to fill the adductor canal distally in at least 95% of patients (ED95). METHODS: We performed a blinded trial, enrolling 40 healthy men. All subjects received an ACB with lidocaine 1%. Volumes were assigned sequentially to the subjects using the continual reassessment method followed by Bayesian analysis to determine the ED95. Distal filling of the adductor canal was assessed by magnetic resonance imaging (primary outcome). Secondary outcomes were the effect of volume on proximal spread to the femoral triangle (also assessed by magnetic resonance imaging), quadriceps muscle weakness (decrease by ≥25% from baseline) and sensory block. RESULTS: The ED95 was 20 ml, with an estimated probability of sufficiently filling the canal of 95.1% (95% credibility interval: 0.91-0.98). Proximal spread to the femoral triangle was seen in 0/4 (0%), 7/12 (58%), 4/8 (50%), and 8/16 (50%) subjects with the 5, 10, 15, and 20 ml doses, respectively (P=0.25). Seven subjects had a reduction in muscle strength, but there was no difference between groups (P=0.85). CONCLUSIONS: For an ACB, the dose closest to the ED95 needed to fill the adductor canal distally was 20 ml. There was no significant correlation between volume and proximal spread or muscle strength. CLINICAL TRIAL REGISTRATION: NCT02033356.

Ultrasound-guided block of the suprascapular nerve - a volunteer study of a new proximal approach.

BACKGROUND: The standard approach for the suprascapular nerve block is deep in the supraspinous fossa. However, with this approach, the suprascapular nerve is difficult to visualize by ultrasound. The aim of this study was to describe a new method to visualize and selectively block the suprascapular nerve in a more superficial and proximal location. METHODS: Twelve healthy volunteers were included. We located the brachial plexus in transverse section with ultrasound, and by longitudinal slide, we identified the departure of the suprascapular nerve from the superior trunk. The suprascapular nerve was followed under ultrasound visualization into the subclavian triangle under the inferior belly of the omohyoid muscle. We performed in-plane ultrasound-guided selective suprascapular nerve block by injecting 1 ml of lidocaine, 20 mg/ml close to the nerve. Nerve identification was aided by nerve stimulation. We assessed sensory and motor block of the suprascapular, axillary, radial, median, and ulnar nerves before, 15 and 30 min after performing the block. RESULTS: Eight volunteers demonstrated a selective suprascapular nerve block. Three had block failure and one volunteer did not receive the intervention. CONCLUSIONS: We describe a new ultrasound-guided low-volume local anaesthetic technique to selectively block the suprascapular nerve. The potential clinical role of this new approach remains to be determined.

Ultrasound-guided block of the axillary nerve: a case series of potential clinical applications.

The specific blocking of the axillary nerve has never been investigated clinically. We present four cases illustrating potential applications of the axillary nerve block in the perioperative setting and discuss possible directions for future research in this area. The axillary nerve blocks were all performed using a newly developed in-plane ultrasound-guided technique. In one patient undergoing arthroscopic shoulder surgery, we used the axillary nerve block as the only analgesic combined with propofol sedation and spontaneous breathing. Chronic shoulder pain was eliminated after the axillary nerve block in two patients. The pain score after arthroscopic shoulder surgery in these two patients remained low until termination of the nerve block. In a fourth patient, severe post-operative pain after osteosynthesis of a displaced proximal humerus fracture was almost eliminated after performing an axillary nerve block. These findings warrant larger clinical trials that investigate the pain-mediating role of the axillary nerve in the perioperative setting.

Effects of adductor-canal-blockade on pain and ambulation after total knee arthroplasty: a randomized study.

BACKGROUND: Total knee arthroplasty (TKA) is associated with intense post-operative pain. Besides providing optimal analgesia, reduction in side effects and enhanced mobilization are important in this elderly population. The adductor-canal-blockade is theoretically an almost pure sensory blockade. We hypothesized that the adductor-canal-blockade may reduce morphine consumption (primary endpoint), improve pain relief, enhance early ambulation ability, and reduce side effects (secondary endpoints) after TKA compared with placebo. METHODS: Patients aged 50-85 years scheduled for TKA were included in this parallel double-blind, placebo-controlled randomized trial. The patients were allocated to receive a continuous adductor-canal-blockade with intermittent boluses via a catheter with either ropivacaine 0.75% (n = 34) or placebo (n = 37) (http://www.clinicaltrials.gov Identifier: NCT01104883). RESULTS: Seventy-five patients were randomized in a 1 : 1 ratio and 71 patients were analyzed. Morphine consumption from 0 to 24 h was significantly reduced in the ropivacaine group compared with the placebo group (40 ± 21 vs. 56 ± 26 mg, P = 0.006). Pain was significantly reduced in the ropivacaine group during 45 degrees flexion of the knee (P = 0.01), but not at rest (P = 0.06). Patients in the ropivacaine group performed the ambulation test, the Timed-Up-and-Go (TUG) test, at 24 h significantly faster than patients in the placebo group (36 ± 17 vs. 50 ± 29 s, P = 0.03). CONCLUSION: The adductor-canal-blockade significantly reduced morphine consumption and pain during 45 degrees flexion of the knee compared with placebo. In addition, the adductor-canal-blockade significantly enhanced ambulation ability assessed by the TUG test.

Continuous adductor-canal-blockade for adjuvant post-operative analgesia after major knee surgery: preliminary results.

Because both the saphenous nerve and in part the obturator nerve are traversing the adductor canal of the thigh, we hypothesised that repeated administration of a local anaesthetic (LA) into this aponeurotic space could be a useful option for post-operative analgesia after knee replacement surgery. A systematic search of the literature pertinent to the blockade of the saphenous and/or obturator nerves for pain relief after knee surgery was conducted. Further, pain and opioid requirements were evaluated in eight patients receiving a continuous blockade of the saphenous and obturator nerve (adductor-canal-blockade) after total knee arthroplasty (TKA). Finally, we performed cross-sectional MR scans of the adductor canal after injection of ropivacaine 30ml in one patient. The systematic literature search revealed only one controlled study, where selective blockade of the saphenous nerve was investigated for the purpose of clinical pain relief after knee arthroscopy. We located no studies reporting on saphenous and/or obturator nerve block for pain relief after TKA. Preliminary findings in eight patients demonstrated that a continuous adductor-canal-blockade for 48h after TKA was associated with low mean pain scores at rest and low mean requirements for supplemental morphine. MR scans in one patient demonstrated that 30ml of LA filled the adductor canal, including the distal part, where the posterior branch of the obturator nerve joins the vessels and the saphenous nerve. Continuous adductor-canal-blockade may be a valuable adjunct for post-operative analgesia after major knee surgery. These preliminary results should be confirmed in randomised, controlled trials.

Stroke volume of the heart and thoracic fluid content during head-up and head-down tilt in humans.

BACKGROUND: The stroke volume (SV) of the heart depends on the diastolic volume but, for the intact organism, central pressures are applied widely to express the filling of the heart. METHODS: This study evaluates the interdependence of SV and thoracic electrical admittance of thoracic fluid content (TA) vs. the central venous (CVP), mean pulmonary artery (MPAP) and pulmonary artery wedge (PAWP) pressures during head-up (HUT) and head-down (HDT) tilt in nine healthy humans. RESULTS: From the supine position to 20 degrees HDT, SV [112 +/- 18 ml; mean +/- standard deviation (SD)], TA (30.8 +/- 7.1 mS) and CVP (3.6 +/- 0.9 mmHg) did not change significantly, whereas MPAP (from 13.9 +/- 2.7 to 16.1 +/- 2.5 mmHg) and PAWP (from 8.8 +/- 3.4 to 11.3 +/- 2.5 mmHg; P < 0.05) increased. Conversely, during 70 degrees HUT, SV (to 65 +/- 24 ml) decreased, together with CVP (to 0.9 +/- 1.4 mmHg; P < 0.001), MPAP (to 9.3 +/- 3.8 mmHg; P < 0.01), PAWP (to 0.7 +/- 3.3 mmHg; P < 0.001) and TA (to 26.7 +/- 6.8 mS; P < 0.01). However, from 20 to 50 min of HUT, SV decreased further (to 48 +/- 21 ml; P < 0.001), whereas the central pressures did not change significantly. CONCLUSIONS: During both HUT and HDT, SV of the heart changed with the thoracic fluid content rather than with the central vascular pressures. These findings confirm that the function of the heart relates to its volume rather than to its so-called filling pressures.

Electrical admittance for filling of the heart during lower body negative pressure in humans.

To evaluate whether electrical admittance of intracellular water is applicable for monitoring filling of the heart, we determined the difference in intracellular water in the thorax (Thorax(ICW)), measured as the reciprocal value of the electrical impedance for the thorax at 1.5 and 100 kHz during lower body negative pressure (LBNP) in humans. Changes in Thorax(ICW) were compared with positron emission tomography-determined C(15)O-labeled erythrocytes over the heart. During -40 mmHg LBNP, the blood volume of the heart decreased by 21 +/- 3% as the erythrocyte volume was reduced by 20 +/- 2% and the plasma volume declined by 26 +/- 2% (P < 0.01; n = 8). Over the heart region, LBNP was also associated with a decrease in the technetium-labeled erythrocyte activity by 26 +/- 4% and, conversely, an increase over the lower leg by 92 +/- 5% (P < 0.01; n = 6). For 15 subjects, LBNP increased thoracic impedance by 3.3 +/- 0.3 Omega (1.5 kHz) and 3.0 +/- 0.4 Omega (100 kHz), whereas leg impedance decreased by 9.0 +/- 3.3 Omega (1.5 kHz) and 6.1 +/- 3 Omega (100 kHz; P < 0.01). Thorax(ICW) was reduced by 7.1 +/- 1.9 S. 10(-4) (P < 0.01) and intracellular water in the leg tended to increase (from 37.8 +/- 4.6 to 40.9 +/- 5.0 S. 10(-4); P = 0.08). The correlation between Thorax(ICW) and heart erythrocyte volume was 0.84 (P < 0.05). The results suggest that thoracic electrical admittance of intracellular water can be applied to evaluate changes in blood volume of the heart during LBNP in humans.

Influence of temperature on the distribution of blood in humans as assessed by electrical impedance.

This study investigated whether ambient temperature influences the distribution of blood as indicated by electrical impedance. In ten supine humans, the room temperature was raised from 14 to 35 degrees C. Skin temperature and blood flow on the thorax increased by 3.6 (SD 0.3) degrees C and 84 (SD 40)%, respectively, and by 9.8 (SD 1) degrees C and 115 (SD 45)%, respectively, on the extremities (P < 0.05). Cardiac output remained unchanged, ear temperature and heart rate became elevated, and the oesophageal temperature and mean arterial pressure decreased (P < 0.05). At five discrete frequencies (1.5. 5, 50, 100, 200 kHz) thoracic impedance was increased by 1.2 (SD 1) to 1.5 (SD 1) omega (P < 0.05). In contrast, total body impedance was reduced by 16.4 (SD 5) omega and leg impedance was reduced by 4.0 (SD 2) omega, while an index of intracellular water within the thorax (the difference between the admittances at 100 kHz and 1.5 kHz) was decreased by 10 (SD 1) x 10(-4)S (P < 0.05). The results would suggest that total body impedance is dominated by the impedance of the extremities. The increase in thoracic impedance and a decrease in leg impedance (as in total body impedance) could be explained by a redistribution of blood from the thorax to the extremities during heating. Such a translocation of blood was confirmed by a reduced impedance based index of intracellular water within the thorax.

Continuous stroke volume monitoring by modelling flow from non-invasive measurement of arterial pressure in humans under orthostatic stress.

The relationship between aortic flow and pressure is described by a three-element model of the arterial input impedance, including continuous correction for variations in the diameter and the compliance of the aorta (Modelflow). We computed the aortic flow from arterial pressure by this model, and evaluated whether, under orthostatic stress, flow may be derived from both an invasive and a non-invasive determination of arterial pressure. In 10 young adults, Modelflow stroke volume (MFSV) was computed from both intra-brachial arterial pressure (IAP) and non-invasive finger pressure (FINAP) measurements. For comparison, a computer-controlled series of four thermodilution estimates (thermodilution-determined stroke volume; TDSV) were averaged for the following positions: supine, standing, head-down tilt at 20 degrees (HDT20) and head-up tilt at 30 degrees and 70 degrees (HUT30 and HUT70 respectively). Data from one subject were discarded due to malfunctioning thermodilution injections. A total of 155 recordings from 160 series were available for comparison. The supine TDSV of 113+/-13 ml (mean+/-S.D.) dropped by 40% to 68+/-14 ml during standing, by 24% to 86+/-12 ml during HUT30, and by 51% to 55+/-15 ml during HUT70. During HDT20, TDSV was 114+/-13 ml. MFSV for IAP underestimated TDSV during HDT20 (-6+/-6 ml; P<0.05), but that for FINAP did not (-4+/-7 ml; not significant). For HUT70 and standing, MFSV for IAP overestimated TDSV by 11+/-10 ml (HUT70; P<0.01) and 12+/-9 ml (standing; P<0.01). However, the offset of MFSV for FINAP was not significant for either HUT70 (3+/-8 ml) or standing (3+/-9 ml). In conclusion, due to orthostasis, changes in the aortic transmural pressure may lead to an offset in MFSV from IAP. However, Modelflow correctly calculated aortic flow from non-invasively determined finger pressure during orthostasis.

Pollution with nitrous oxide using laryngeal mask or face mask.

BACKGROUND: As environmental pollution by nitrous oxide may influence the health of the personnel working in operating theatres, the incidence and magnitude of nitrous oxide (N2O) leakage, when using a face mask or a laryngeal mask airway (LMA) for controlled ventilation, were studied in 34 patients scheduled for elective cystoscopy. METHODS: A semi-closed gas delivery ventilation system with active scavenging was used. The N2O concentrations were measured every 8 s at a position 30 cm above the patient's mouth with a N2O gas monitor (GD 200, Simrad Optronics). RESULTS: When using a face mask, the leakage of N2O resulted in a N2O concentration of 157 (85-332) p.p.m. (parts per million) (median concentration and 25% and 75% percentiles). With the LMA, a lower median concentration of N2O of 60 (28-126) p.p.m. was found (P=0.04). With the face mask, a concentration above 100 p.p.m. was found during 51% of the exposure time compared to 24% of the time in the LMA group. CONCLUSION: Environmental pollution was less with the LMA than the face mask, but under the conditions of the study both modes of airway management were associated with levels of N2O peak concentrations in the breathing zone of anaesthetists that are deemed to be excessively high by the Danish National Institute for Occupational Safety.

A maximal central venous oxygen saturation (SvO2max) for the surgical patient.

Before induction of anaesthesia, 23 patients scheduled for major abdominal surgery had blood samples drawn from a central venous catheter for oxygen saturation (SvO2) after graded infusion of isotonic saline. The infusion of saline was continued until further administration resulted in a stable SvO2 (SvO2max). The SvO2 increased from 69 (53-83) to 72 (66-83) % (median and range; P < 0.0001), when the patients received 10 (0-26) mL.kg-1, average 500 mL, of saline. At the same time central venous haematocrit decreased from 38 (32-47) to 36 (23-47) % which suggests that the intravascular volume was expanded by 420 (180-3070) mL or by 72 (18-174) % of the administered volume. The results demonstrate that volume expansion by saline can establish a maximal venous oxygen saturation in the surgical patient.

Alfentanil infusion in total intravenous anaesthesia (TIVA). Population pharmacokinetics fails to predict plasma concentration of alfentanil.

In order to evaluate the ability to predict plasma concentrations from population-corrected pharmacokinetics, a prospective study comprising 14 women admitted for elective hysterectomy was done. Alfentanil was given in combination with propofol in a total intravenous anaesthesia technique. The predicted median alfentanil concentration (289(256-363) ng ml-1) was significantly lower than the measured median plasma concentration of 368(168-666) ng ml-1). In conclusion, population-based pharmacokinetics were found not to be accurate as they underestimate plasma concentrations of alfentanil.

Total intravenous anaesthesia with propofol or etomidate.

In combination with fentanyl, propofol was compared with etomidate for total intravenous anaesthesia in 21 women (ASA Grades I-II) admitted for elective hysterectomy. They received either propofol (bolus 1.5 mg kg-1, infusion 9 mg kg-1 h-1 for 10 min thereafter 6 mg kg-1 h-1) or etomidate (bolus 0.10 mg kg-1, infusion 3 mg kg-1 h-1 reduced to 0.6 mg kg-1 h-1). Fentanyl 10 micrograms kg-1 was given for induction followed by an infusion of 30 micrograms kg-1 h-1 for 10 min reduced to 6 micrograms kg-1 h-1 for the first hour and successively reduced over time. Induction was smooth and maintenance easy to manage in both groups. There was no difference in time from end of infusion until extubation, but the time until the patients could report their date of birth was significantly shorter in the propofol group. Nausea and vomiting were more pronounced in the etomidate group, and mental side-effects were only seen after etomidate. After 3 months, more patients in the etomidate group complained of reduced power of concentration. We conclude that total intravenous anaesthesia with either propofol or etomidate is equally easy to manage, but in the recovery situation propofol was advantageous in time and quality.

[The laryngeal mask: a new alternative to the facial mask and the endotracheal tube]. / Larynxmasken: Et nyt alternativ til ansigtsmasken og endotrakealtuben.

The laryngeal mask is a new airway system for use under anaesthesia which assumes a position between the face mask and the endotracheal tube. Employment of this system achieves several of the advantages of intubation while the disadvantages are avoided. The possibilities which this system offers in cases of difficult intubation are particularly interesting, especially in unexpected.

Awakening and recovery of simple cognitive and psychomotor functions 2 h after anaesthesia for day-case surgery--total intravenous anaesthesia with propofol-alfentanil versus thiopentone-alfentanil.

Fifty-seven patients undergoing minor out-patient gynaecological procedures were allocated to one of two total intravenous anaesthesia regimes: propofol and alfentanil or thiopentone and alfentanil. Diazepam was given orally as premedication. To assess objectively the quality of recovery, the patients underwent a number of tests pre-operatively and two hours post-operatively. The time to opening of eyes and orientation was equal in both groups, as was the recovery of the tested cognitive and psychomotor functions after 2 h, when the score in both groups had returned to baseline. We conclude that the use of propofol instead of thiopentone for shorter surgical procedures gives no advantage as regards length of stay in hospital.

Total i.v. anaesthesia with propofol-alfentanil or propofol-fentanyl.

In combination with propofol, alfentanil was compared with fentanyl for total i.v. anaesthesia in 29 women (ASA classes I, II) admitted for elective hysterectomy. Infusion rates of propofol and fentanyl were determined from the literature and from pilot studies, while alfentanil was given according to a computer program. Dosage was: propofol, bolus 1.5 mg kg-1, infusion 9 mg kg-1 h-1 for 10 min and thereafter 6 mg kg-1 h-1; fentanyl, bolus 7.5 micrograms kg-1, infusion 15 micrograms kg-1 h-1 reduced successively to 1.8 micrograms kg-1 h-1; alfentanil, bolus 60 micrograms kg-1, infusion 240 micrograms kg-1 h-1 reduced successively to 100 micrograms min-1. Induction was smooth and maintenance easy to manage in both groups. Plasma concentrations were stable with a ratio of alfentanil to fentanyl of 100:1. Recovery times were equal and short, but recovery tests performed 3 h after operation showed that alfentanil produced a greater effect on ability to concentrate and fine co-ordination.