Fernando Altermatt

Estimation of the plasma effect site equilibration rate constant (ke0) of propofol in children using the time to peak effect: comparison with adults.

Background:Targeting the effect site concentration may offer advantages over the traditional forms of administrating intravenous anesthetics. Because the lack of the plasma effect site equilibration rate constant (ke0) for propofol in children precludes the use of this technique in this population, the authors estimated the value of ke0 for propofol in children using the time to peak effect (tpeak) method and two pharmacokinetic models of propofol for children. Methods:The tpeak after a submaximal bolus dose of propofol was measured by means of the Alaris A-Line auditory evoked potential monitor (Danmeter A/S, Odense, Denmark) in 25 children (aged 3–11 yr) and 25 adults (aged 35–48 yr). Using tpeak and two previously validated sets of pharmacokinetic parameters for propofol in children, Kataria’s and that used in the Paedfusor (Graseby Medical Ltd., Hertfordshire, United Kingdom), the ke0 was estimated according to a method recently published. Results:The mean tpeak was 80 ± 20 s in adults and 132 ± 49 s in children (P < 0.001). The median ke0 in children was 0.41 min−1 with the model of Kataria and 0.91 min−1 with the Paedfusor model (P < 0.01). The corresponding t1/2 ke0 values, in minutes, were 1.7 and 0.8, respectively (P < 0.01). Conclusions:Children have a significantly longer tpeak of propofol than adults. The values of ke0 of propofol calculated for children depend on the pharmacokinetic model used and also can only be used with the appropriate set of pharmacokinetic parameters to target effect site in this population.

Remifentanil Requirements during Sevoflurane Administration to Block Somatic and Cardiovascular Responses to Skin Incision in Children and Adults

Background The authors found no studies comparing intraoperative requirements of opioids between children and adults, so they determined the infusion rate of remifentanil to block somatic (IR50) and autonomic response (IRBAR50) to skin incision in children and adults. Methods Forty-one adults (aged 20–60 yr) and 24 children (aged 2–10 yr) undergoing lower abdominal surgery were studied. In adults, anesthesia induction was with sevoflurane during remifentanil infusion, whereas in children remifentanil administration was started after induction with sevoflurane. After intubation, sevoflurane was administered in 100% O2 and was adjusted to an ET% of 1 MAC-awake corrected for age at least 15 min before surgery. Patients were randomized to receive remifentanil at a rate ranging from 0.05 to 0.35 &mgr;g · kg−1 · min−1 for at least 20 min before surgery. At the beginning of surgery, only the skin incision was performed, and the somatic and autonomic responses were observed. The somatic response was defined as positive with any gross movement of extremity, and the autonomic response was deemed positive with any increase in heart rate or mean arterial pressure equal to or more than 10% of preincision values. Using logistic regression, the IR50 and IRBAR50 were determined in both groups of patients and compared with unpaired Student t test. A P value less than 0.05 was considered significant. Results The IR50 ± SD was 0.10 ± 0.02 &mgr;g · kg−1 · min−1 in adults and 0.22 ± 0.03 &mgr;g · kg−1 · min−1 in children (P < 0.001). The IRBAR50 ± SD was 0.11 ± 0.02 &mgr;g · kg−1 · min−1 in adults and 0.27 ± 0.06 &mgr;g · kg−1 · min−1 in children (P < 0.001). Conclusions To block somatic and autonomic responses to surgery, children require a remifentanil infusion rate at least twofold higher than adults.

Remifentanil requirements during propofol administration to block the somatic response to skin incision in children and adults.

BACKGROUND:During sevoflurane administration, children require a remifentanil infusion rate twofold higher than adults to block responses to skin incision. Similar data concerning remifentanil requirements are unavailable during total IV anesthesia. METHODS:We prospectively determined the infusion rate (IR) of remifentanil necessary to block the somatic response to skin incision in 50% (IR50) of adults (n = 20, aged 20–60 yr) and children (n = 20, aged 3–11 yr) during propofol anesthesia. In each patient undergoing lower abdominal surgery, a remifentanil infusion was initiated, followed by target-controlled infusion of propofol set at a plasma concentration of 6 &mgr;g/mL. After tracheal intubation, propofol was reduced to 3 &mgr;g/mL until the end of the study. Remifentanil IR was determined according to Dixons up-and-down method, with the first patient in each group receiving 0.2 &mgr;g · kg−1 · min−1 followed by the consecutive patient receiving 0.02 &mgr;g · kg−1 · min−1 modifications according to the response of the previous patient. The remifentanil IR was kept unchanged for at least 20 min before surgery. At the beginning of surgery, only the skin incision was performed, and the somatic response was observed. If there was any gross movement of extremity the response was considered positive. RESULTS:The IR50 (CI95%) was 0.08 (0.06–0.12) &mgr;g · kg−1 · min−1 in adults and 0.15 (0.13–0.17) &mgr;g · kg−1 · min−1 in children (P < 0.001). CONCLUSION:These results demonstrate that, similar to sevoflurane anesthesia, during total IV anesthesia with propofol, children require a remifentanil IR almost twofold higher than adults to block the somatic response to skin incision.

The Influence of Age on the Dynamic Relationship Between End-Tidal Sevoflurane Concentrations and Bispectral Index

BACKGROUND: Age is an important determinant of the pharmacokinetic profile of inhaled anesthetics. The influence of age on the dynamic profile of sevoflurane’s effect has not been well described. We performed this study to characterize the influence of age and other covariates on the dynamic relationship between sevoflurane end-tidal concentration (CET) and its effect measured by bispectral index (BIS). METHODS: Fifty patients, aged 3–71 yr, scheduled for minor surgery were prospectively studied. The BIS and sevoflurane CET were continuously measured during the study period. During maintenance of anesthesia and after stable BIS values of 60–65 were obtained, the inspired concentration of sevoflurane was increased to 5 vol % for 5 min or until BIS <40 and then decreased. The dynamic relationship between sevoflurane CET and its effect as measured by BIS during this transition period were modeled with an inhibitory Emax model using a population pharmacokinetic–pharmacodynamic approach with NONMEM V. A predictive check method was used to validate the final model. RESULTS: The sensitivity to sevoflurane’s effect as measured by BIS expressed in the C50 [steady-state CET eliciting half of maximum response (Imax)] increased with age. The speed of change of sevoflurane’s effect, expressed as the effect–site equilibration half-life (t1/2 ke0), increased at older ages. The predictive check analysis confirmed the adequacy of the model. CONCLUSIONS: Age significantly affects the dynamic relationship between sevoflurane CET and its effect measured with BIS.

Evaluation of the effect of intravenous lidocaine on propofol requirements during total intravenous anaesthesia as measured by bispectral index

BACKGROUND I.V. lidocaine is increasingly used as an adjuvant during general anaesthesia. The aim of this study was to evaluate the effect of i.v. lidocaine in reducing propofol anaesthetic requirements during total i.v. anaesthesia (TIVA) maintenance and to evaluate its effect on early recovery from anaesthesia. METHODS Forty adult patients undergoing elective laparoscopic cholecystectomy under TIVA were randomly allocated into the lidocaine group (administered 1.5 mg kg(-1) i.v. lidocaine over 5 min followed by 2 mg kg(-1) h(-1)) and the control group (administered an equal volume of saline). Propofol was administered using a target-controlled infusion to maintain the bispectral index values between 40 and 60. After surgery, all infusions were discontinued and the time to extubation was recorded. Serial arterial blood samples were drawn to assess drug plasma levels. RESULTS The maintenance dose of propofol was significantly lower in the lidocaine group [6.00 (0.97) mg kg(-1) h(-1)] vs the control group [7.25 (1.13) mg kg(-1) h(-1); P=0.01]. Propofol plasma levels measured at the end of the infusion were 3.71 (0.89) μg ml(-1) in the lidocaine group and 3.67 (1.28) μg ml(-1) in the control group (P=0.91). The median time to extubation was longer (11.0 min; range: 10.0-21.0) in the lidocaine group vs the control group (8.3 min; range: 5.5-12.5; P=0.02). CONCLUSIONS I.V. lidocaine reduces propofol requirements during the maintenance phase of TIVA, particularly during surgical stimulation. This sparing effect is associated with an increased time to extubation. Owing to its effect on early recovery from anaesthesia, i.v. lidocaine should be taken into account when used as a component of i.v. anaesthesia.

Inserción de la simulación clínica en el currículum de Anestesiología en un hospital universitario. Evaluación de la aceptabilidad de los participantes

INTRODUCTION Clinical simulation is currently an integral part of the curriculum of the Anesthesiology residency programs in other countries. We aimed to describe and evaluate the insertion of simulation in an anesthesia residency training program. METHODS Activities feasible to be used for training in a simulated environment were classified into 2 modules: workshops for technical skills conducted with first year residents, and high fidelity simulation scenarios performed with second and third year residents. After each activity, and using an anonymous questionnaire, residents assessed their satisfaction and objectives accomplished. RESULTS A total of 18 activities: 6 skills workshops and 12 high fidelity scenarios were assessed. A total of 206 questionnaires were analyzed, corresponding to 41 residents. Almost all (96%) of respondents agreed or strongly agreed that workshops met the objectives and should be mandatory in the anesthesia curriculum; however, 11% agreed that the activity caused anxiety and/or nervousness. The high fidelity scenarios were considered realistic and consistent with the objectives by 97% of residents, and 42% felt that workshops caused anxiety and/or nervousness. CONCLUSIONS The inclusion of simulation has been well accepted by the residents. The activities have been described as realistic, and limited to the objectives, essential points in adult education, as according to Kolbs learning model this is associated with profound, useful and long lasting knowledge.

The Sensitivity of Motor Responses for Detecting Catheter-Nerve Contact During Ultrasound-Guided Femoral Nerve Blocks with Stimulating Catheters

BACKGROUND: We determined the sensitivity of motor responses evoked by stimulating catheters in determining catheter-nerve contact using ultrasonography as reference. METHODS: Femoral nerves were contacted using stimulating catheters under ultrasonography scanning in 25 patients. The output current was increased from its minimum until quadriceps muscle contraction occurred. The sensitivity of the motor response in determining catheter-nerve contact was calculated using 0.5 mA as current threshold. RESULTS: The current required for catheter stimulation to evoke a motor response ranged between 0.18 and 2.0 mA. Muscle contraction in response to 0.5 mA occurred in 16 of 25 subjects. The sensitivity of motor response for nerve stimulation was 64% (95% confidence interval: 0.43, 0.82). CONCLUSIONS: The absence of muscle responses at a stimulating current ⩽0.5 mA does not necessarily indicate the absence of catheter-nerve contact.

Adding dexamethasone to peripheral nerve blocks can give better postoperative analgesia

1 James MFM, Michell WL, Joubert IA, Nicol AJ, Navsaria PH, Gillespie RS. Resuscitation with hydroxyethyl starch improves renal function and lactate clearance in penetrating trauma in a randomized controlled study: the FIRST trial (Fluids in Resuscitation of Severe Trauma). Br J Anaesth 2011; 107: 693–702 2 Finfer S, Bellomo R, Boyce N, French J, Myburgh J, Norton R. A comparison of albumin and saline for fluid resuscitation in the intensive care unit. N Engl J Med 2004; 350: 2247–56

Plasma levels of levobupivacaine after combined posterior lumbar plexus and sciatic nerve blocks.

hypoventilation by pulse oximetry. Chest 2004;126:1552–8. 7. Overdyk FJ. PCA presents serious risks. APSF Newsletter 2005;20:33. 8. Downs JB. Has oxygen administration delayed appropriate respiratory care? Fallacies regarding oxygen therapy. Resp Care 2003;48:611–20. 9. Downs JB. Prevention of hypoxemia: the simple, logical, but incorrect solution. J Clin Anesth 1994;6:180–1. 10. Downs JB, Smith RA. Increased inspired oxygen concentration may delay diagnosis and treatment of significant deterioration in pulmonary function. Crit Care Med 1999;12:2844–6.

Which types of peripheral nerve blocks should be included in residency training programs

BackgroundDespite the increasing use of regional anesthesia, specific recommendations regarding the type of procedures to be included in residency training programs are not currently available. We aimed to determine the nerve block techniques that practicing Chilean anesthesiologists perceived as essential to master during residency training.MethodsAfter institutional ethics committee approval, an online survey was sent to 154 anesthesiologists that graduated between 2005–2012, from the two largest university residency programs in Chile. Multiple-choice questions elicited responses concerning the use of regional anesthesia.ResultsA total of 109 questionnaires were completed, which corresponded to a response rate of 70.8%. Almost all (98.2%) of the respondents used regional anesthesia in their clinical practice, 86.7% regularly performed peripheral nerve blocks (PNBs) and 51% used continuous PNB techniques. Residency programs represented their primary source of training. The most common PNB techniques performed were interscalene (100%), femoral (98%), popliteal sciatic (93%), and Bier block (90%). Respondents indicated that they were most confident performing femoral (98%), Bier block (90%), interscalene (90%), and popliteal sciatic (85%) blocks. The PNBs perceived as essential for their actual clinical practice were femoral (81%), interscalene (80%), popliteal sciatic (76%), and Bier blocks (62%).ConclusionsRequesting information from former anesthesiology residents may be a source of information, guiding the specific types of PNBs that should be included in residency training. Other groups can easily replicate this methodology to create their own evidence and clinical practice based guidelines for residency training programs.