光棒在快速诱导经鼻气管内插管中的应用研究

目的探讨快速诱导麻醉下光棒引导经鼻气管内插管临床效果。方法60例全麻患者随机均分为光棒(LW)组和纤维支气管镜(BF)组,比较两组插管时间、置管成功率和导管通过声门顺利率。结果在规定的3min内,LW组插管成功率显著高于BF组(96.7%vs.70.0%,P<0.05);LW组插管时间明显短于BF组[(38.9±16.2)svs.(133.0±37.9)s,P<0.01]。LW组导管通过声门顺利率高于BF组(96.6%vs.66.7%,P<0.05)。结论光棒引导经鼻气管内插管,是口腔颌面部手术全麻快速诱导建立气道安全、有效、快捷的方法之一。     

光棒辅助与普通喉镜气管插管用于颈椎骨折手术患者的比较

目的比较光棒辅助与普通喉镜气管插管用于颈椎骨折全麻患者的插管效果和安全性。方法选择拟行气管插管全麻的颈椎骨折手术患者40例,男28例,女12例,年龄18~65岁,ASAⅡ或Ⅲ级,随机分为两组,每组20例。全麻诱导后,L组采用光棒引导气管插管,C组采用普通喉镜辅助气管插管。记录一次插管成功例数、插管时间,插管前5 min、插管即刻和插管后5 min的MAP和HR,以及插管时不良反应情况。结果 L组的一次性插管成功率明显高于C组(90%vs.60%),插管时间明显短于C组[(31.3±11.1)s vs.(46.6±15.2)s](P0.05)。与C组比较,L组患者插管期间MAP和HR变化更平稳。C组有4例(20%)心律失常,L组无一例心律失常。结论与普通喉镜比较,光棒引导气管插管用于颈椎骨折手术患者插管更容易,安全性更好。     

喉镜辅助光棒在困难气管插管中的临床应用

目的 探讨喉镜辅助下光棒在困难气管插管中的临床应用效果.方法 全麻插管手术患者120例,Yamamoto气道评级Ⅲ～Ⅳ级,随机均分为三组:喉镜组(A组)、单纯光棒组(B组)及喉镜辅助光棒组(C组).记录患者插管前后MAP、HR、去甲肾上腺素(NE)和肾上腺素(E)的变化,及插管成功率、插管时间、插管后并发症的发生情况.结果 与诱导后比较,插管即刻和插管后1min三组患者MAP、NE和E均显著升高,HR明显增快(P＜0.05),且A组高于B、C两组(P＜0.05),B、C两组相比差异无统计学意义.插管成功率A组为82.5％,B组为77.5％,C组为100％,C组显著高于A、B组(P＜0.01).插管时间A组为(43.3±12.5)s,B组为(47.1±15.1)s,C组为(31.1±10.7)s,C组显著短于A、B组(P＜0.05).结论 喉镜辅助下光棒在困难气管插管中成功率高、时间短,对血流动力学影响较轻,术后并发症少.     

肠道准备对经皮横向骶髂关节螺钉固定的影响

[目的]探讨肠道准备对经皮横向骶髂螺钉固定的影响。[方法]2015年8月~2018年12月,30例骶骨骨折行经皮横向S1骶髂关节螺钉置入治疗的患者纳入本研究,采用随机数字表法将患者分为两组,每组15例,准备组患者术前接受肠道准备,无准备组患者术前未接受肠道准备。比较两组手术时间、术中透视次数和曝光时间,以及影像测量的置钉偏差。[结果]准备组的手术时间显著短于无准备组,差异有统计学意义[(32.31±4.92)min vs(40.54±5.83)min,P<0.05)];准备组的术中X线暴露时间显著短于无准备组,差异有统计学意义[(62.59±5.79)s vs(83.19±6.41)s,P<0.05];准备组的术中透视次数显著少于无准备组,差异有统计学意义[(3.71±0.58)次vs(5.21±1.11)次,P<0.05]。术后CT三维重建测量螺钉与术前测量偏移方面,准备组的水平偏移小于无准备组,但差异无统计学意义[(5.53±2.21)°vs(5.63±1.97)°,P>0.05];准备组矢状位偏移小于无准备组,但差异无统计学意义[(4.32±2.08)°vs(4.52±1.91)°,P>0.05]。术后随访6~12个月,所有患者均未发生骶髂关节螺钉松动及断裂等并发症。[结论]肠道准备虽不能提高置钉准确率,但能够缩短手术时间和术中X线暴露时间。     

普通气管导管自然弧度塑型光棒引导对鼻气管插管的影响

<正>光棒(light wand)引导气管插管方便快捷,对口腔黏膜、牙齿等损伤小,血流动力学相对稳定。特别对部分困难气道患者能顺利完成气管插管[1],因此在临床上得到普遍应用。其在经鼻气管内插管中的应用亦有报道[2],适宜的光棒塑型形状对成功实施光棒引导经鼻气管插管至关重要[3],在临床工作中发现光棒传统J形塑型经鼻气管插管并发症较多,本研究旨在比较两种折弯弧度光棒在经鼻气管插管中应用效     

插管型喉罩LMA-Fastrach与I-gel引导盲探气管插管的比较

目的比较插管型喉罩LMA-Fastrach和I-gel喉罩引导盲探气管插管的临床效果。方法择期全麻手术患者60例,随机分为两组,分别采用LMA-Fastrach(L组)和I-gel(I组)行盲探气管插管。记录喉罩和气管导管插入时间、盲探插管总时间,及喉罩和气管导管尝试插入次数。结果I组喉罩插入时间[(20±3)s vs.(27±5)s]、盲探插管总时间[(85±4)s vs.(95±6)s]明显短于L组(P0.05)。两组气管导管插入时间以及喉罩、气管导管插入次数差异无统计学意义。结论LMA-Fastrach和I-gel喉罩均可用于引导盲探气管插管。     

预期困难气道患者喉罩辅助纤维支气管镜引导气管插管的研究

目的 探讨在预期困难气道患者中采用喉罩辅助纤维支气管镜(fiberoptic bronchoscope,FOB)引导气管插管的应用价值. 方法 择期经口气管插管全身麻醉手术预测困难气道患者24例,ASA Ⅰ或Ⅱ级,入选患者达到以下1种或几种条件为预期困难气道:1.5 cm＜张口度＜3 cm,甲颏间距＜6 cm,头颈活动度＜80°,Mallampati分级Ⅲ、Ⅳ级.采用随机数字表法分为喉罩辅助FOB组(F组)和直接喉镜组(L组),每组12例.F组采用喉罩辅助FOB引导下气管插管;L组在直接喉镜暴露下经口气管插管,3次试插未成功者改行F组方法试插.记录两组患者的气道评估情况、气管插管前(基础值)和插管后3 min的MAP和HR、成功插管的次数及术后的并发症的发生情况. 结果 插管前两组气道评估差异无统计学意义(P＞0.05).与插管前相比,L组患者插管后MAP和HR显著增加,差异有统计学意义(P＜0.05).两组插管后的MAP和HR比较,差异有统计学意义(P＜0.05).F组气管插管一次成功率为75％,3次以内插管合计总成功率为100％;L组气管插管一次成功率为25％,3次以内插管合计总成功率为50％;6例L组患者直接喉镜3次插管不成功后改为喉罩辅助FOB插管,2例1次成功,4例2次成功;F组一次插管成功率和3次插管总成功率均显著高于L组,两组比较差异有统计学意义(P＜0.05).与L组插管时间(161±26)s比较,F组插管时间(81±9)s明显缩短,差异有统计学意义(P＜0.05).F组有2例术后轻度咽喉疼痛,L组有6例术后咽喉疼痛明显和轻度声嘶、2例轻度咽痛. 结论 对术前预期为困难气道的患者采用喉罩辅助FOB引导气管插管可显著提高插管的成功率,降低直接喉镜反复试插引起的术后并发症,具有一定的临床应用价值.     

光棒气管插管折弯方法的研究

目的探讨光棒气管插管时其前端折弯的最佳方法。方法72例患者随机均分为三组,A组:采用下颌骨颏角至舌骨的长度作为光棒折弯部分的长度;B组:以“门甲垂线距离”作为光棒折弯长度[测算方法,分别从上门齿和甲状软骨最高点(喉结)向侧面作两条与手术床垂直的线,两条垂线的水平距离即为光棒折弯长度];C组:“门甲垂线距离” 1cm作为光棒折弯长度。分别观察和记录插管时间、插管次数、插管成功率、血液动力学变化及不良反应。结果三组患者插管均成功,其中B组的插管时间和一次插管成功率与A、C两组相比差异有显著意义(P<0.05);三组患者的血液动力学差异无显著意义。结论以“门甲垂线距离”作为光棒气管插管时其前端折弯长度的标准,方法简便,容易定位、一次插管成功率高。     

Airtraq喉镜联合弹性插管探条在预计困难气道支气管插管中的应用

目的 比较Airtraq喉镜联合弹性插管探条(gum elastic bougie,GEB)和纤维支气管镜(fiberoptic bronchoscope,FOB)在预计困难气道患者支气管插管中的效果.方法 择期行右侧单肺通气的胸外科手术患者48例,张口度大于3 cm,Mallampati分级Ⅲ或Ⅳ级,随机数字表法分为两组(每组24例):Airtraq喉镜联合GEB组(A组)和FOB组(F组).记录插管首次成功率、置管时间、支气管对位用时和气道损伤情况,记录麻醉诱导前和支气管对位成功后2 min时点的SBP、DBP、HR和血浆去甲肾上腺素(norepinephrine,NE)浓度.结果 插管首次成功率A组与F组差异无统计学意义(91.7％比95.8％,P＞0.05);A组置管时间[(91±17)s]短于F组[(105±19) s](P＜0.05);A组支气管对位用时[(132±34)s]长于F组[(55±12)s](P＜0.05);气道损伤并发症两组之间差异无统计学意义(P＞0.05).两组SBP、DBP、HR和血浆NE浓度在插管完成后2 min均较麻醉诱导前明显升高(P＜0.05),且A组高于F组(P＜0.05).结论 Aiaraq喉镜联合GEB用于预计困难气道支气管插管与FOB一样安全有效,但支气管对位较慢,心血管应激反应较大.     

光棒与纤维支气管镜用于强直性脊柱炎困难气道气管插管的比较

目的 比较光棒(light wand,LW)与纤维支气管镜(fiberoptic bronchoscope,FOB)用于强直性脊柱炎患者的困难气道行气管插管的应用效果.方法 选择62例行择期手术的强直性脊柱炎患者,随机分为LW引导气管插管组(LW组,n=32)和FOB引导气管插管组(FOB组,n=30),经口行气管插管,记录插管时间、成功率,评估血流动力学及插管相关并发症.结果 LW组患者气管插管时间明显短于FOB组(P＜0.01),在插管成功率、气管插管相关并发症及血流动力学变化等方面,两组之间差异无统计学意义(P＞0.05).结论 LW和FOB均可用于强直性脊柱炎患者困难气道的气管插管,成功率高,并发症少,对血流动力学影响轻微,而LW操作更为简单,并能缩短气管插管时间.     

Vasopressor hormone response following mesenteric traction during major abdominal surgery

Background : We investigated the vasopressor hormone response following mesenteric traction (MT) with hypotension due to prostacyclin (PGI₂) release in patients undergoing abdominal surgery with a combined general and epidural anesthesia. Methods : In a prospective, randomized, placebo-controlled study we administered 400 mg ibuprofen (i.v.) in 42 patients scheduled for abdominal surgery. General anesthesia was combined with epidural anesthesia (T4-L1). Before as well as 5, 15, 30, 45, and 90 min after MT we recorded plasma osmolality, hemodynamics and measured 6-keto-PGFlα (stabile metabolite of PGI₂), TXB₂ (stabile metabolite of thromboxane A₂) active renin, and arginine vasopressin (AVP) plasma concentrations by radioimmunoassay. Catecholamine levels were assessed by high-pressure liquid chromatography (HPLC) with electrochemical detection. Results : Following MT, arterial hypotension occurred along with a substantial PGI₂ release. This was completely abolished by ibuprofen administration. Although plasma levels of 6-keto-PGF_1α (1133 (708) vs. 60 (3) ng/L, median (median absolute deviation), P=0.0001, placebo vs. ibuprofen) remained significantly elevated, blood pressure was restored within 30 min after MT in the placebo group. At the same point in time plasma concentrations of TXB² (164 (87) vs. 58 (1) ng/L, P=0.0001), epinephrine (46 (33) vs. 14 (6) ng/L, P=0.001), AVP (41 ± (18) vs. 12 (7) ng/L, P=0.0004), and active renin (27 (12) vs. 12 (4) ng/L, P = 0.001) were significantly higher in placebo-treated patients. Conclusion : Under combined general and epidural anesthesia arterial hypotension following MT due to endogenous PGI₂ release is associated with enhanced release of AVP, active renin, epinephrine and thromboxane A₂, presumably contributing to hemodynamic stability within 30 min after MT.     

A Teaspoon Pump for Pumping Blood with High Hydraulic Efficiency and Low Hemolysis Potential

Abstract: Virtually all blood pumps contain some kind of rubbing, sliding, closely moving machinery surfaces that are exposed to the blood being pumped. These valves, internal bearings, magnetic bearing position sensors, and shaft seals cause most of the problems with blood pumps. The original teaspoon pump design prevented the rubbing, sliding machinery surfaces from contacting the blood. However, the hydraulic efficiency was low because the blood was able to "slip around" the rotating impeller so that the blood itself never rotated fast enough to develop adequate pressure. An improved teaspoon blood pump has been designed and tested and has shown acceptable hydraulic performance and low hemolysis potential. The new pump uses a nonrotating "swinging" hose as the pump impeller. The fluid enters the pump through the center of the swinging hose; therefore, there can be no fluid slip between the revolving blood and the revolving impeller. The new pump uses an impeller that is comparable to a flexible garden hose. If the free end of the hose were swung around in a circle like half of a jump rope, the fluid inside the hose would rotate and develop pressure even though the hose impeller itself did not "rotate"; therefore, no rotating shaft seal or internal bearings are required.     

Microspheres Based Detoxification System: A New Method in Convective Blood Purification

Abstract: A variety of protein-bound or hydrophobic substances, accumulating as a result of pathologic conditions such as exogenous or endogenous intoxications, are removed poorly by conventional detoxification methods because of low accessibility (hemodialysis), insufficient adsorption capabilities (hemosorption), low efficiency (peritoneal dialysis), or economic limitations (high-volume plasmapheresis). Combining advantages of existing methods with microspheric technology, a module-based system was designed. Major operating parameters of the latter can be modified to allow for adjustment to individual clinical situations. An extracorporeal blood circuit including a plasmafilter is combined with a secondary high-velocity plasma circuit driven by a centrifugal pump. Different microspheric adsorbers can be combined in one circuit or applied in sequence. Thus, a prolonged treatment can be tailored using specially designed selective adsorber materials. Comparing this system with existing methods (high-flux hemodialysis, molecular adsorbent recycling system), results from our in vitro studies and animal experiments demonstrate the superior efficiency of substance removal.     

Tissue perfusion in relation to cardiac output during continuous positive-pressure ventilation and administration of propranolol or verapamil

Background : Our objective was to determine whether administration of propranolol or verapamil modifies the hemodynamic adaptation to continuous positive-pressure ventilation (CPPV), in particular the regional distribution of cardiac output (CO).
Methods : General hemodynamics and regional blood flows assessed by microsphere technique (15 (μm) were recorded in 16 anesthetized pigs during spontaneous breathing (SB) and CPPV with 8 cm H₂O end-expiratory pressure (CPPV8) before and after intravenous administration of propranolol (0.3 mg · kg⁻¹ followed by 0.15 mg · kg⁻¹ · h⁻¹, n=8) or verapamil (0.1 mg · kg⁻¹ followed by 0.3 mg · kg⁻¹ · h⁻¹, n=8).
Results : CPPV8 depressed CO by 25% without shifts in its relative distribution with the exception of a noteworthy increase in adrenal perfusion. Propranolol increased arterial blood pressure, and due to a fall in heart rate, CO dropped by 25%. The kidneys and, to a lesser extent, the splanchic region and central nervous system received increased fractions of the remaining CO at the expense of skeletal muscle flow. Similar patterns were seen during SB and CPPV8 such that the combination of propranolol and CPPV8 depressed CO by 50%. The circulatory effects of verapamil were less evident but myocardial perfusion tended to increase.
Conclusions : The combination of propranolol or verapamil with CPPV does not result in any specific hemodynamic interaction in anesthetized pigs, except that the combined effect of propranolol and CPPV may severely reduce CO.     

Bariatric Surgery in Some "Central and East-European (former Eastern bloc)"Countries - Current Status and Prediction for the Next Millennium

Background: Obesity is increasing globallly, including in the formerly "Eastern Bloc" countries. Methods: A survey was made of obesity and bariatric surgery. Results: In the 8 East and Central European countries studied, with total population 300 million, roughly 43% of the population was overweight (BMI 25-30), 23% obese (BMI > 30), with about 15 million people morbidly obese (BMI > 40). From 0-10 morbidly obese individuals/100,000/year undergo bariatric surgery. Conclusion: Most countries were found to provide inadequate treatment for obesity.The majority of the morbidly obese are not treated effectively. However, health-care awareness of obesity and bariatric surgeons are slowly increasing.     

Volatile anaesthetics reduce adhesion of blood platelets under low-flow conditions in the coronary system of isolated guinea pig hearts

Background : Inhibitory effects of volatile anaesthetics on platelet aggregation have been demonstrated in several studies. However, the influence of volatile anaesthetics on intracoronary platelet adhesion has not been elucidated so far.
Methods : Isolated hearts of guinea pigs were perfused with buffer in the absence or presence of volatile anaesthetics (0.5 and 1 MAC) at constant coronary flow rates of 5 ml/min for 25 min, then 1 ml/min for 30 min and again 5 ml/min for 10 min. Before, during and after low-flow perfusion, a bolus of human platelets was applied into the coronary system. To simulate thrombogenic conditions, 0.3 U/ml human thrombin was infused during low-flow perfusion and reperfusion. The number of platelets sequestered to the endothelium was calculated from the difference between coronary in- and output of platelets. The myocardial production of lactate and consumption of pyruvate and coronary perfusion pressure were also determined.
Results : At a flow rate of 5 ml/min only about 3% of the applied platelets did not emerge from the coronary system, in any group. In contrast, 13.1±1.2% (mean±SEM) of infused platelets became adherent in low-flow perfusion in the control group without anaesthetic. The adherence was reduced with each 1 MAC isoflurane (to 6.2±1.2%), sevoflurane (to 4.4±0.9%) or halothane (to 3.2±1.5%) (each P <0.05 vs. control). Volatile anaesthetic, 0.5 MAC, did not inhibit platelet adhesion to a statistically significant extent in any case. Perfusion pressure and metabolic parameters were not statistically different between the control and the hearts exposed to anaesthetics.
Conclusion : Volatile anaesthetics in a concentration of 1 MAC can reduce the adhesion of platelets in the coronary system under reduced flow conditions. This action does not arise from vasodilation or inhibition of ischaemic stress.     

Synergistic interaction between the effects of propofol and midazolam with fentanyl on phrenic nerve activity in rabbits

Background: It has been shown that the depressive effects of both propofol and midazolam on consciousness are synergistic with opioids, but the nature of their interactions on other physiological systems, e. g. respiration, has not been fully investigated. The present study examined the effect of propofol and midazolam alone and in combination with fentanyl on phrenic nerve activity (PNA) and whether such interactions are additive or synergistic. Methods: PNA was recorded in 27 anaesthetised and artificially ventilated rabbits. In three groups, propofol, fentanyl and midazolam were administered intravenously in incremental doses to construct dose-response curves for the depressant effects of each one on PNA. In another two groups, the effect of pretreatment with either fentanyl 1 μg · kg^?1 i. v. or midazolam 0.05 mg · kg^?1 i. v. on the effects of propofol and fentanyl respectively on PNA were studied. Results: Propofol and fentanyl caused a dose-dependent depression of PNA with complete abolition at the highest total doses of 16 mg · kg^?1 i. v. and 32 μg · kg^?1 i. v., respectively. In contrast, midazolam in incremental doses to a total of 0.8 mg · kg^?1 reduced mean PNA by 63%, but approximately 12% of PNA remained at a total dose as high as 6.4 mg · kg^?1. The mean ED₅₀s, calculated from dose-response curves, were 5.4 mg · kg^?1, 3.9 μg · kg^?1 and 0.4 mg · kg^?1 for propofol, fentanyl and midazolam, respectively. Initial doses of either fentanyl 1 μg · kg^?1 i. v. or midazolam 0.05 mg · kg^?1 i. v. acted synergistically with subsequent doses of either propofol or fentanyl to abolish PNA at total doses of 8 mg · kg^?1 and 8 μg · kg^?1, respectively. Conclusion: Fentanyl has a synergistic interaction with both propofol and midazolam on PNA and hence potentially on respiration.     

Influence of dopexamine hydrochloride on haemodynamics and regulators of circulation in patients undergoing major abdominal surgery

Background: Catecholaminergic support is often used to improve haemodynamics in patients undergoing major abdominal surgery. Dopexamine is a synthetic vasoactive catecholamine with beneficial microcirculatory properties. Methods: The influence of perioperative administration of dopexamine on cardiorespiratory data and important regulators of macro- and microcirculation were studied in 30 patients undergoing Whipple pancreaticduodenectomy. The patients received randomized and blinded either 2 μg · kg^?1 · min^?1 of dopexamine (n=15) or placebo (n=15, control group). The infusion was started after induction of anaesthesia and continued until the morning of the first postoperative day. Endothelin-1 (ET-1), vasopressin, atrial natriuretic peptide (ANP), and catecholamine plasma levels were measured from arterial blood samples. Measurements were carried out after induction of anaesthesia, 2 h after onset of surgery, at the end of surgery, 2 h after surgery, and on the morning of the first postoperative day. Results: Cardiac index (CI) increased significantly in the dopexamine group (from 2.61±0.41 to 4.57±0.78 1 · min^?1 · m^?2) and remained elevated until the morning of the first postoperative day. Oxygen delivery index (DO₂I) and oxygen consumption index (VO₂I) were also significantly increased in the dopexamine group (DO₂I: from 416±91 to 717±110 ml/m² · m²; VO₂I: from 98±25 to 157±22 ml/m² · m²), being significantly higher than in the control group. pHi remained stable only in the dopexamine patients, indicating adequate splanchnic perfusion. Vasopressive regulators of circulation increased significantly only in the untreated control patients (vasopressin: from 4.37±1.1 to 35.9±12.1 pg/ml; ET-1: from 2.88±0.91 to 6.91±1.20 pg/ml). Conclusion: Patients undergoing major abdominal surgery may profit from prophylactic perioperative administration of dopexamine hydrochloride in the form of improved haemodynamics and oxygenation as well as beneficial influence on important regulators of organ blood flow.     

Systemic analgesia adapted to the children's condition

A concept of balanced analgesia using nonsteroidal anti-inflammatory drugs (NSAIDs), paracetamol (acetaminophen), opioids, and corticosteroids can also be used in patients with pre-existing illnesses. NSAIDs are the most effective treatment for acute pain of moderate intensity in children; however, these drugs should be avoided in patients at increased risk for serious side effects, e.g. patients with renal impairment, bleeding tendency, or extreme prematurity. NSAIDs can be given with minimal risks to the younger child with mild to moderate asthma, and, in these patients, the use of steroids can be encouraged; in addition to their antiemetic and analgesic action, a beneficial effect on asthma symptoms can be expected. In the non-intubated child with cerebral trauma, exaggerated sedation caused by opioids and increased bleeding tendency caused by NSAIDs must be avoided. In neonates and small infants, the oral administration of sucrose or glucose is helpful to minimize pain reaction during short uncomfortable interventions.     

A comparison of the inhibitory effects of four volatile anaesthetics on the metabolism of chlorzoxazone, a substrate for CYP2E1, in rabbits

Background: Halothane inhibits in vitro and in vivo activity of cytochrome P-450 (CYP) 2E1. There are several fluorinated volatile anaesthetics besides halothane, and most of them are defluorinated by CYP2E1. It is unclear whether other fluorinated anaesthetics inhibit the in vivo activity of CYP2E1.
Methods: We compared the inhibitory effects of therapeutic concentrations of four inhalational anaesthetics, halothane, enflurane, isoflurane, and sevoflurane, on chlorzoxazone metabolism in rabbits receiving artificial ventilation.
Results: All four inhalational anaesthetics decreased arterial blood pressure and increased plasma chlorzoxazone concentration. However, no significant differences in the plasma chlorzoxazone concentration were found between the four anaesthetics. The estimated chlorzoxazone clearance increased after beginning inhalation with all four agents, but no significant difference in clearance was noted between agents.
Conclusions: At therapeutic concentrations, the in vivo inhibitory effect on chlorzoxazone metabolism was similar for all four inhalational anaesthetics examined, even though their chemical characteristics and extent of hepatic metabolism differ considerably.