Experimental Determination of Heat Flow Parameters during Induction of General Anesthesia

Background: Alterations in body temperature result from changes in tissue heat content. Heat flow is a complex function of vasomotor status and core, peripheral, and ambient temperatures. Consequently it is difficult to quantify specific mechanisms responsible for observed changes in body heat distribution. Therefore the authors developed two mathematical models that independently express regional tissue heat production and the motion of heat through tissues in terms of measurable quantities.

Methods: The equilibrium model expresses the effective regional heat transfer coefficient in terms of cutaneous heat flux, skin temperature, and temperature at the center of the extremity. It applies at steady states and provides a ratio of the heat transfer coefficients before and after an intervention. In contrast, the heat flow model provides a time-dependent estimate of the heat transfer coefficient in terms of ambient temperature, skin temperature, and temperature at the center of the extremity.

Results: Each model was applied to data acquired in a previous evaluation of heat balance during anesthesia induction. The relation between the ratio of steady state regional heat transfer coefficients calculated using each model was linear. The effective heat transfer coefficient for the forehead (a core site) decreased approximately 20% after induction of anesthesia. In contrast, heat transfer coefficients in the six tested extremity sites more than doubled.     

Optimal Oxygen Concentration during Induction of General Anesthesia

Background: The use of 100% oxygen during induction of anesthesia may produce atelectasis. The authors investigated how different oxygen concentrations affect the formation of atelectasis and the fall in arterial oxygen saturation during apnea.

Methods: Thirty-six healthy, nonsmoking women were randomized to breathe 100, 80, or 60% oxygen for 5 min during the induction of general anesthesia. Ventilation was then withheld until the oxygen saturation, assessed by pulse oximetry, decreased to 90%. Atelectasis formation was studied with computed tomography.

Results: Atelectasis in a transverse scan near the diaphragm after induction of anesthesia and apnea was 9.8 +/- 5.2 cm2 (5.6 +/- 3.4% of the total lung area; mean +/- SD), 1.3 +/- 1.2 cm2 (0.6 +/- 0.7%), and 0.3 +/- 0.3 cm2 (0.2 +/- 0.2%) in the groups breathing 100, 80, and 60% oxygen, respectively (P < 0.01). The corresponding times to reach 90% oxygen saturation were 411 +/- 84, 303 +/- 59, and 213 +/- 69 s, respectively (P < 0.01).     

地佐辛在喉罩置入全麻诱导中的应用

目的：观察不同剂量地佐辛用于妇科腹腔镜手术喉罩置入全麻诱导的安全性与有效性。方法：拟全麻下行择期妇科腹腔镜手术患者80例,随机分为不同剂量地佐辛组（D1、D2、D3组）和芬太尼组（F组）,分别在静脉注射丙泊酚前5分钟给予地佐辛0.1 mg/kg、0.15 mg/kg、0.2 mg/kg和芬太尼3μg/kg,观察诱导前、喉罩置入前、喉罩置入即刻及喉罩置入后1、3、5 min心率（HR）和血压（MAP）的变化。结果：D1组在喉罩置入时及置入后1、3 min的MAP和HR明显高于F组（P＜0.05）,D2组和D3组在各时点MAP和HR与F组比较无明显差异（P＞0.05）。结论：地佐辛用于妇科腹腔镜手术喉罩置入全麻诱导,能够有效维持诱导期间血流动力学稳定,其适宜剂量推荐为0.1 mg/kg。     

全麻诱导期间发生室颤复苏成功一例

患者，女、52岁，体重70千克，因右侧颌下腺肿物拟行肿物切除术。自诉既往无高血压、心脏病史。查体右侧颌下有一2×3cm肿物，与气管无粘连，不影响通气。ECG示：窦性心律，电轴左偏-28度。其他化验检查均呈阴性。术前1日测BP150/90mmHg，术前30分钟肌注鲁米那钠200mg，阿托品0.5mg。入手术室测BP180/95mmHg，     

Redistribution of Microcirculatory Blood Flow within the Intestinal Wall during Sepsis and General Anesthesia

Background: Hypoperfusion of the intestinal mucosa remains an important clinical problem during sepsis. Impairment of the autoregulation of microcirculatory blood flow in the intestinal tract has been suggested to play an important role in the development of multiple organ failure during sepsis and surgery. The authors studied microcirculatory blood flow in the gastrointestinal tract in anesthetized subjects during early septic shock.

Methods: Eighteen pigs were intravenously anesthetized and mechanically ventilated. Regional blood flow in the superior mesenteric artery was measured with ultrasound transit time flowmetry. Microcirculatory blood flow was continuously measured with a six-channel laser Doppler flowmetry system in the mucosa and the muscularis of the stomach, jejunum, and colon. Eleven pigs were assigned to the sepsis group, while seven animal served as sham controls. Sepsis was induced with fecal peritonitis, and intravenous fluids were administered after 240 min of sepsis to alter hypodynamic sepsis to hyperdynamic sepsis.

Results: In the control group, all monitored flow data remained stable throughout the study. During the hypodynamic phase of sepsis, cardiac output, superior mesenteric artery flow, and microcirculatory blood flow in the gastric mucosa decreased by 45%, 51%, and 40%, respectively, compared to baseline (P < 0.01 in all). Microcirculatory blood flow in the muscularis of the stomach, jejunum, and colon decreased by 55%, 64%, and 70%, respectively (P < 0.001 in all). In contrast, flow in the jejunal and colonic mucosa remained virtually unchanged. During the hyperdynamic phase of sepsis, there was a threefold increase in cardiac output and superior mesenteric artery flow. Blood flow in the gastric, jejunal, and colonic mucosa also increased (22%, 24%, and 31% above baseline, respectively). Flow in the muscularis of the stomach returned to baseline, while in the jejunum and colon, flow in the muscularis remained significantly below baseline (55% and 45%, respectively, P < 0.01).     

宫腔镜手术静脉全麻诱导期置入喉罩的最佳血浆靶控浓度

目的探讨宫腔镜手术静脉全麻诱导期置入喉罩时瑞芬太尼复合丙泊酚的最佳血浆靶控浓度(plasma concentration,Cp)。方法2007年1～6月,宫腔镜手术60例,随机分为3组,每组20例。诱导Cp:A组瑞芬太尼2.0ng/ml+丙泊酚2.5μg/ml;B组瑞芬太尼2.5ng/ml+丙泊酚3.0μg/ml;C组瑞芬太尼3.0ng/ml+丙泊酚3.5μg/ml。当效应室浓度与血浆浓度达平衡时置入喉罩维持至扩宫完毕。术中维持Cp瑞芬太尼2.0ng/ml,丙泊酚1.5μg/ml,保留自主呼吸,术毕停药。观察喉罩的总体置入条件:张口度、呛咳、体动及置罩难易条件;记录麻醉前(T0)、瑞芬太尼效应室浓度达设定血浆浓度时(T1)、置喉罩时(T2)、置喉罩后3min(T3)、扩宫时(T4)各时点平均动脉压(MAP)、心率(HR)、氧饱和度(SpO2)、呼气末CO2分压(PETCO2)及脑电双频谱指数(BIS);记录麻醉诱导、手术、呼之睁眼和定向力恢复时间。结果3组诱导时间(C组>A组>B组)、术毕睁眼时间(C组>B组>A组)、定向力恢复时间(C组>B组>A组)均有显著性差异(P<0.05),诱导时丙泊酚和瑞芬太尼用量...     

Motivation and Maternal Presence during Induction of Anesthesia

Background: The authors developed a measure to determine whether maternal motivation to be present during induction (Motivation for Parental Presence during Induction of Anesthesia [MPPIA]) is related to children's anxiety during the induction process.

Methods: Mothers and children (aged 2-12 yr) undergoing outpatient, elective surgery and general anesthesia were enrolled in this study (n = 289 dyads). Items to assess motivation for parental presence during induction were selected by experts in anesthesiology, psychology, and child development; mothers completed the resulting 14-item measure as well as assessments of anxiety and coping style. Children's anxiety and compliance was assessed during induction of anesthesia. Factor analysis was performed, and maternal motivation was then examined against children's anxiety during induction of anesthesia.

Results: Factor analysis resulted in four scales with a total variance of 72.3%: MPPIA-Desire, MPPIA-Hesitancy, MPPIA-Anxiety, and MPPIA-Preparation. Analysis supported the reliability (0.89-0.94) and validity of the MPPIA. The authors found that mothers with high MPPIA-Desire and low MPPIA-Hesitancy had children with significantly higher anxiety (P < 0.0001) during induction of anesthesia, as compared with mothers with low MPPIA-Desire and MPPIA-Hesitancy. The authors also found that highly motivated mothers reported significantly higher levels of anxiety (P = 0.007).     

Distribution of Cerebral Blood Flow during Anesthesia with Isoflurane or Halothane in Humans

Background: Halothane and isoflurane have been shown to induce disparate effects on different brain structures in animals. In humans, various methods for measuring cerebral blood flow (CBF) have produced results compatible with a redistribution of CBF toward deep brain structures during isoflurane anesthesia in humans. This study was undertaken to examine the effects of halothane and isoflurane on the distribution of CBF.

Methods: Twenty ASA physical status patients (four groups, five in each) anesthetized with either isoflurane or halothane (1 MAC) during normo- or hypocapnia (PaCO2 5.6 or 4.2 kPa (42 or 32 mmHg)) were investigated with a two-dimensional CBF measurement (CBFxenon, intravenous133 xenon washout technique) and a three-dimensional method for measurement of the regional CBF (rCBF) distribution with single photon emission computer-aided tomography (SPECT;99m Tc-HMPAO). In the presentation of SPECT data, the mean CBF of the brain was defined as 100%, and all relative flow values are related to this value.

Results: The mean CBFxenon level was significantly influenced by the PaCO2 as well as by the anesthetic used. At normocapnia, patients anesthetized with halothane had a mean CBFxenon of 40 plus/minus 3 (SE) ISI units. With isoflurane, the flow was significantly (P < 0.01, 33 plus/minus 3 ISI units) less than with halothane. Hypocapnia decreased mean CBFxenon (P < 0.0001) during both anesthetics (halothane 24 plus/minus 3, isoflurane 13 plus/minus 2 ISI units). The effects on CBFxenon, between the anesthetics, differed significantly (P < 0.01) also during hypocapnia. There were significant differences in rCBF distribution measured between the two anesthetics (P < 0.05). During isoflurane anesthesia, there was a relative increase in flow values in subcortical regions (thalamus and basal ganglia) to 10-15%, and in pons to 7-10% above average. Halothane, in contrast, induced the highest relative flow levels in the occipital lobes, which increased by approximately 10% above average. The rCBF level was increased approximately 10% in cerebellum with both anesthetics. Changes in PaCO2 did not alter the rCBF distribution significantly.     

Scopolamine Prevents Dreams during General Anesthesia

Background: Dreaming during anesthesia is not a well-understood phenomenon. Anticholinergic drugs are used in anesthesia as premedication, but their use to decrease the incidence of dreams and psychological adverse reactions after anesthesia is not well established. The authors therefore studied the efficacy of intramuscular atropine and scopolamine for the prevention of dreams during general anesthesia with propofol and nitrous oxide.

Methods: Healthy women undergoing minor gynecologic surgery were randomly assigned to receive 2.5 [mu]g/kg scopolamine or 10 [mu]g/kg atropine intramuscularly (n = 50/group). In both groups, anesthesia was induced and maintained with propofol as a 2.5-mg/kg bolus, followed by 12 mg [middle dot] kg-1 [middle dot] h-1 as a continuous infusion and 70% nitrous oxide in oxygen. Two interviews regarding dreaming activity and characteristics were conducted at 20 min and 6 h after surgery.

Results: None of the patients in the scopolamine group and 47% of the patients in the atropine group reported the occurrence of dreams 20 min after recovery. The results were similar at 6 h: 6% of the scopolamine group and 43% of the atropine group reported dream activity. No differences in sedation or anesthetic requirements were found.     

Effects of Sodium Nitroprusside and Phenylephrine on Blood Flow in Free Musculocutaneous Flaps during General Anesthesia

Background: Hypoperfusion and necrosis in free flaps used to correct tissue defects remain important clinical problems. The authors studied the effects of two vasoactive drugs, sodium nitroprusside and phenylephrine, which are used frequently in anesthetic practice, on total blood flow and microcirculatory flow in free musculocutaneous flaps during general anesthesia.

Methods: In a porcine model (n = 9) in which clinical conditions for anesthesia and microvascular surgery were simulated, latissimus dorsi free flaps were transferred to the lower extremity. Total blood flow in the flaps was measured using ultrasound flowmetry and microcirculatory flow was measured using laser Doppler flowmetry. The effects of sodium nitroprusside and phenylephrine were studied during local infusion through the feeding artery of the flap and during systemic administration.

Results: Systemic sodium nitroprusside caused a 30% decrease in mean arterial pressure, but cardiac output did not change. The total flow in the flap decreased by 40% (P < 0.01), and microcirculatory flow decreased by 23% in the skin (P < 0.01) and by 30% in the muscle (P < 0.01) of the flap. Sodium nitroprusside infused locally into the flap artery increased the total flap flow by 20% (P < 0.01). Systemic phenylephrine caused a 30% increase in mean arterial pressure, whereas heart rate, cardiac output, and flap blood flow did not change. Local phenylephrine caused a 30% decrease (P < 0.01) in the total flap flow.     

Wheezing during Induction of General Anesthesia in Patients with and without Asthma: A Randomized, Blinded Trial

Background: Patients with asthma who require general anesthesia and tracheal intubation are at increased risk for the development of bronchospasm during induction. The incidence of wheezing during induction with different intravenously administered agents is unknown. A randomized, double-blinded prospective study was undertaken to evaluate the incidence of wheezing in asymptomatic asthmatic and nonasthmatic patients receiving three commonly used intravenous anesthetic agents for induction of anesthesia.

Methods: Fifty-nine asymptomatic asthmatic and 96 nonasthmatic patients of ASA physical status 1 and 2 were studied. All patients received 1.5 micro gram/kg fentanyl, oxygen, followed by either 5 mg/kg thiopental or thiamylal, 1.75 mg/kg methohexital or 2.5 mg/kg propofol, 1.5 mg/kg succinylcholine, tracheal intubation, and inhalational anesthesia. Wheezing was assessed by an independent blinded observer auscultating the lungs at 2 and 5 min postintubation. Data were analyzed by Pearson's chi-squared, Fisher's exact test, and multiple logistic regression with significance set at P < 0.05.

Results: Both asthmatic and nonasthmatic patients who received a thiobarbiturate for induction had a greater incidence of wheezing than did patients receiving propofol. In asthmatic patients, 45% (23, 67) (mean and 95% confidence interval) who received a thiobarbiturate, 26% (8, 44) who received an oxybarbiturate, and none (0, 17) who received propofol wheezed after intubation. In nonasthmatic patients, 16% (3, 28) who received thiobarbiturate and 3% (0, 9) who received propofol wheezed.     

Nasal Ventilation Is More Effective than Combined Oral-Nasal Ventilation during Induction of General Anesthesia in Adult Subjects

Background: The authors hypothesized that nasal mask ventilation may be more effective than combined oral-nasal mask ventilation during induction of general anesthesia. They tested this hypothesis by comparing the volume of carbon dioxide removed per breath with nasal versus combined oral-nasal mask ventilation in nonparalyzed, apneic, adult subjects during induction of general anesthesia.

Methods: Fifteen adult subjects receiving general anesthesia were ventilated first with a combined oral-nasal mask and then with only a nasal mask. The patient's head was maintained in a neutral position, without head extension or lower jaw thrust. Respiratory parameters were recorded simultaneously from both the nasal and oral masks regardless of ventilation approach.

Results: The volume of carbon dioxide removed per breath during nasal mask ventilation (median, 5.0 ml; interquartile range, 3.4-8.8 ml) was significantly larger than that during combined oral-nasal mask ventilation (median, 0.0 ml; interquartile range, 0.0-0.4 ml; P = 0.001); even the peak inspiratory airway pressure during nasal ventilation (16.7 +/- 2.7 cm H2O) was lower than that during combined oral-nasal ventilation (24.5 +/- 4.7 cm H2O; P = 0.002). The expiratory tidal volume during nasal ventilation (259.8 +/- 134.2 ml) was also larger than that during combined oral-nasal ventilation (98.9 +/- 103.4 ml; P = 0.003).