Hiromasa Kawakami

Minimum alveolar concentration (MAC) of xenon with sevoflurane in humans

BackgroundAlthough more than 30 yr ago the minimum alveolar concentration (MAC) of xenon was determined to be 71%, that previous study had technological limitations, and no other studies have confirmed the MAC value of xenon since. The current study was designed to confirm the MAC value of xenon in adult surgical patients using more modern techniques. MethodsSixty patients were anesthetized with sevoflurane with or without xenon. They were randomly allocated to one of four groups; patients in group 1 received no xenon, whereas those in groups 2, 3, and 4 received end-tidal concentrations of 20, 40, and 60%, respectively (n = 15 each group). Target end-tidal sevoflurane concentrations were chosen using the “up-and-down” method in each group. After steady state sevoflurane and xenon concentrations were maintained for at least 15 min, each patient was monitored for a somatic response at surgical incision. Somatic response was defined as any purposeful bodily movement. The MAC of sevoflurane and its reduction by xenon was evaluated using the multiple independent variable logistic regression model. ResultsThe interaction coefficient of the multiple variable logistic regression was not significantly different from zero (P = 0.143). The MAC of xenon calculated as xenon concentration that would reduce MAC of sevoflurane to 0% was 63.1%. ConclusionsThe authors could not determine whether interaction in blocking somatic responses in 50% of patients is additive. The MAC of xenon is in the range of the values that were predicted in a previous study.

Plasma concentration of fentanyl with xenon to block somatic and hemodynamic responses to surgical incision.

BACKGROUND Although anesthesia with xenon has been supplemented with fentanyl, its requirement has not been established. This study was conducted to determine the plasma concentrations of fentanyl necessary to suppress somatic and hemodynamic responses to surgical incision in 50% patients in the presence of 0.7 minimum alveolar concentration (MAC) xenon. METHODS Twenty-five patients were allocated randomly to predetermined fentanyl concentration between 0.5 and 4.0 ng/ml during 0.7 MAC xenon anesthesia. Fentanyl was administered using a pharmacokinetic model-driven computer-assisted continuous infusion device. At surgical incision each patient was monitored for somatic and hemodynamic responses. A somatic response was defined as any purposeful bodily movement. A positive hemodynamic response was defined as a more than 15% increase in heart rate or mean arterial pressure more than the preincision value. The concentrations of fentanyl to prevent somatic and hemodynamic responses in 50% of patients were calculated using logistic regression. RESULTS The concentration of fentanyl to prevent a somatic response to skin incision in 50% of patients in the presence of 0.7 MAC xenon was 0.72 +/- 0.07 ng/ml and to prevent a hemodynamic response was 0.94 +/- 0.06 ng/ml. CONCLUSIONS Comparing these results with previously published results in the presence of 70% nitrous oxide, the fentanyl requirement in xenon anesthesia is smaller than that in the equianesthetic nitrous oxide anesthesia.

Hypertension and anesthesia.

Purpose of review There are still many controversies about perioperative management of hypertensive patients. This review aims to provide relevant instruction based on evidence regarding the treatment of those patients. Recent findings Mild to moderate hypertension is not independently responsible for perioperative cardiac complications. The position is less clear for severely hypertensive patients. A randomized study shows no benefit of the traditional practice of delaying elective surgery in severely hypertensive patients until better control of blood pressure is achieved. Perioperative use of β-blockers or α-2 agonists has been shown to maintain perioperative hemodynamic stability and thereby to prevent major cardiac complications. Summary Delaying surgery only for the purpose of blood pressure control may not be necessary, especially in the case of mild to moderate hypertension. Strict care, however, should be taken to ensure perioperative hemodynamic stability because labile hemodynamics, rather than preoperative hypertension per se, appears to be more closely associated with adverse cardiovascular complications. Delaying surgery in hypertensive patients may be justified if target organ damage exists that can be improved by such a delay or if (suspected) target organ damage should be evaluated further before the operation.

Role of VPAC2 receptor in monocrotaline-induced pulmonary hypertension in rats.

Pulmonary hypertension (PH) is associated with significant morbidity and mortality. Vasoactive intestinal peptide (VIP) and pituitary adenylyl cyclase activating peptide (PACAP) have pulmonary vasodilatory and positive inotropic effects via receptors VPAC1 and VPAC2, which possess a similar affinity for both peptides, and PAC1, a PACAP-preferring receptor. VIP is a promising option for PH treatment; however, various physiological effects of VIP have limited its clinical use. We investigated the effects of VPAC1 and VPAC2 selective agonists VIP and PACAP to explore more appropriate means of treatment for PH. We examined hemodynamic changes in right ventricular systolic pressure (RVSP), systemic blood pressure (SBP), total pulmonary resistance index (TPRI), total systemic resistance index, and cardiac index (CI) in response to their agonists with monocrotaline (MCT)-induced PH and explored involvement of VIP/PACAP expression and receptors in PH. Sprague-Dawley rats were divided into the MCT group (administered MCT 60 mg/kg) and control group. In MCT-induced PH, decreased VIP and PACAP were associated with upregulation of VPAC1, VPAC2, and PAC1 in lung tissues. Intravenous injection of VPAC2-selective agonist BAY 55-9837 and VIP, but not [Ala(11,22,28)]VIP, improved the CI. The decrease in SBP with VPAC2 agonist was significantly less than that in the control. Although they decreased SBP, these agonists hardly affected RVSP in the control. Activation of VPAC2 receptor with BAY 55-9837 effectively improved RVSP, TPRI, and CI in MCT-induced PH, suggesting a VPAC2 agonist as a possible promising treatment for PH.

Influence of Mental Workload on the Performance of Anesthesiologists during Induction of General Anesthesia: A Patient Simulator Study

The aim of this study was to reveal the effect of anesthesiologists mental workload during induction of general anesthesia. Twenty-two participants were categorized into anesthesiology residents (RA group, n = 13) and board certified anesthesiologists (CA group, n = 9). Subjects participated in three simulated scenarios (scenario A: baseline, scenario B: simple addition tasks, and scenario C: combination of simple addition tasks and treatment of unexpected arrhythmia). We used simple two-digit integer additions every 5 seconds as a secondary task. Four kinds of key actions were also evaluated in each scenario. In scenario C, the correct answer rate was significantly higher in the CA versus the RA group (RA: 0.370 ± 0.050 versus CA: 0.736 ± 0.051, p < 0.01, 95% CI −0.518 to −0.215) as was the score of key actions (RA: 2.7 ± 1.3 versus CA: 4.0 ± 0.00, p = 0.005). In a serious clinical situation, anesthesiologists might not be able to adequately perform both the primary and secondary tasks. This tendency is more apparent in young anesthesiologists.

Amount of accidental flush by syringe pump due to inappropriate release of occluded intravenous line

BACKGROUND An unintended bolus is delivered by the syringe pump if intravenous line occlusion is released in an inappropriate manner. OBJECTIVE The aim of this study was to measure the amount of flushed fluid when an occlusion is inappropriately released and to assess the effect of different syringe pump settings (flow rate, alarm setting, size of syringe and syringe pump model) on the flushed amount. METHODS After the stopcock was closed, infusions were started with different model syringe pumps (Terufusion® TE312 and TE332S), different syringe sizes or at different alarm settings. After the occlusion alarm sounded, the occlusion was released and the amount of fluid emerging from the stopcock was measured. RESULTS The bolus was significantly lower when the alarm was set at a low-pressure setting. The bolus was significantly lower with a 10-ml than a 50-ml syringe. A significant difference was seen only when a 50-ml syringe was used (TE312: 1.99 ± 0.16 ml vs. TE332S: 0.674 ± 0.116 ml, alarm High, p < 0.001). CONCLUSION To minimize the amount of accidentally injected medication, a smaller syringe size and a low alarm setting are important. Using a syringe pump capable of reducing the inadvertently administered bolus may be helpful.

Effect of magnesium added to local anesthetics for caudal anesthesia on postoperative pain in pediatric surgical patients: A systematic review and meta-analysis with Trial Sequential Analysis

Background Magnesium has been investigated as an adjuvant for neuraxial anesthesia, but the effect of caudal magnesium on postoperative pain is inconsistent. The aim of this systematic review and meta-analysis was to evaluate the analgesic effect of caudal magnesium. Methods We searched six databases, including trial registration sites. Randomized clinical trials reporting the effect of caudal magnesium on postoperative pain after general anesthesia were eligible. The risk ratio for use of rescue analgesics after surgery was combined using a random-effects model. We also assessed adverse events. The I2 statistic was used to assess heterogeneity. We assessed risk of bias with Cochrane domains. We controlled type I and II errors due to sparse data and repetitive testing with Trial Sequential Analysis. We assessed the quality of evidence with GRADE. Results Four randomized controlled trials (247 patients) evaluated the need for rescue analgesics. In all four trials, 50 mg of magnesium was administered with caudal ropivacaine. The results suggested that the need for rescue analgesia was reduced significantly by caudal magnesium administration (risk ratio 0.45; 95% confidence interval 0.24–0.86). There was considerable heterogeneity as indicated by an I2 value of 62.5%. The Trial Sequential Analysis-adjusted confidence interval was 0.04–5.55, indicating that further trials are required. The quality of evidence was very low. The rate of adverse events was comparable between treatment groups. Conclusion Caudal magnesium may reduce the need for rescue analgesia after surgery, but further randomized clinical trials with a low risk of bias and a low risk of random errors are necessary to assess the effect of caudal magnesium on postoperative pain and adverse events. Trial registration University Hospital Medical Information Network Clinical Trials Registry UMIN000025344.

Consequences of not relieving negative internal pressure of a medication vial: A survey and simulation study

STUDY OBJECTIVE The glass vial of acetaminophen as an intravenous preparation (Acelio®, Terumo, Japan) has a strong internal negative pressure. The aim of our study was to determine if this negative pressure could result in medication administration errors if not released prior to connecting to the IV set. DESIGN Questionnaire survey and simulation study. SETTING University hospital and its affiliated hospitals. SUBJECTS Fifty-two anesthesiologists in 6 different hospitals in Yokohama. MEASUREMENTS A questionnaire on current practice was sent to the subjects. The authors then first calculated the internal pressure of the Acelio® vial followed by a simulation set-up. This set-up measured the amount of saline that could be aspirated from a syringe loaded on a syringe pump connected via a secondary IV line when the Acelio® vial was attached to the primary line without prior release of the internal pressure. The volume of aspiration was tested with two syringe sizes and with a fully open IV clamp vs partially closed. MAIN RESULTS Twenty-nine (56.9%) of 51 anesthesiologists who responded to the survey had connected the Acelio® vial at least once without releasing the internal negative pressure, and 21 experienced consequences such as backflow of the venous blood. The pressure inside the Acelio® vial was 81.8±19.6Torr. With the clamp of the simulated IV line fully open, the amount of saline aspirated before the alarm of the syringe pump went off was 1.5±0.1ml and 3.2±0.3ml when 20ml and 50ml syringes were used, respectively. When the clamp was partially closed to allow 2 drops per second, this value was 1.3±0.1ml and 2.3±0.1ml, respectively. After removing the plunger from the holder of the syringe pump, an additional 7ml (clamp partially closed) or 15-18ml (clamp fully open) was aspirated in the subsequent 1min. CONCLUSIONS A considerable number of anesthesiologists experienced consequences caused by the negative pressure inside the Acelio® vial. This can also cause aspiration of the contents of the syringe pump.