前交叉韧带损伤:3.0TMR影像与关节镜对照分析

目的分析膝关节前交叉韧带损伤的3．0TMRI特征,并与关节镜手术结果对照。方法回顾性分析来我院行3．0T MR膝关节检查的36例前交叉韧带损伤患者的40个膝关节,全部病例经关节镜检查确诊。应用3．0T MR机（Philips Achieva型）,膝关节专用线圈,进行斜矢状位TSE T1WI、TSE T2WI、PD-SPIR和冠状位、轴位TSE T2WI扫描。前交叉韧带损伤分为完全断裂、撕裂（部分断裂）及胫骨端撕脱。将膝关节前交叉韧带损伤的3．0T MR影像特征与关节镜手术结果进行对照分析。结果前交叉韧带完全断裂MRI直接征象表现为韧带连续性中断,断端肿胀（21／25）,间接征象为交叉韧带过度弯曲、T2WI和PD-SPIR股骨髁间窝外侧骨挫伤;MRI与关节镜诊断完全符合率为84．00％。前交叉韧带撕裂（部分断裂）MRI直接征象为ACL矢状T2WI和PD-SPIR显示形态不规则、部分撕裂,ACL局部肿胀增粗,信号增高,仍可见连续存在的纤维低信号;MRI与关节镜诊断完全符合率为66．67％。前交叉韧带胫骨端撕脱MR检查直接征像为胫骨近端可见T1WI、T2WI低信号撕脱骨片（3／3）,ACL水肿、形态不规则,周围可见出血、积液,MRI与关节镜诊断符合率为100％。结论高场强3．0TMR膝关节诊断的多平面、多序列影像相结合可形成ACL立体影像观,结合临床能够有效诊断ACL损伤。     

膝关节骨关节炎软骨下骨病理损伤MRI表现分析

目的探讨膝关节骨关节炎软骨下骨病理损伤磁共振成像(MRI)模式。方法本组共106例,临床均怀疑膝关节骨关节炎。采用GE Signa Profile SYS#0.2TMR Siemens Symphony Maestro class 1.5 T超导型,成像方位为矢状位、冠状位及横断位;序列为自旋回波(SE)T1WI,T2WI,自旋回波质子加权序列。结果膝关节软骨下骨灶状损伤呈多样性改变,包括股骨、胫骨、髌骨软骨下骨灶状损伤。MRI表现:(1)软骨下骨灶状骨髓水肿,本组88个病灶。(2)软骨下骨灶状脂肪样损害,本组79个病灶。(3)软骨下骨灶状血液样损害,本组96个病灶。(4)软骨下骨灶状水样损害,本组99个病灶。(5)软骨下骨灶状纤维样损害,本组87个病灶。结论 MRI膝关节骨关节炎软骨下骨病理损伤MRI模式对明确病理改变、指导临床诊断和治疗有重要意义。     

膝关节的磁共振成像技术与临床应用探讨

目的 探讨膝关节的磁共振成像技术与临床应用价值.方法回顾性分析60例关节镜或骨科手术确诊的膝关节病变MRI影像资料,扫描序列包括矢状位、冠状位、横断位T2WI/SPIR 及矢状位T2WI、T1WI、T2WI/FFE.结果优片率达85%以上.T2WI/FFE序列诊断半月板撕裂或变性30例,关节软骨损伤20例,均优于T2WI/SPIR、T2WI/TSE、T1WI/TSE序列,P值均小于0.01;T2WI/SPIR 诊断膝关节挫伤20例,侧副韧带损伤10例,均优于T2WI/FFE、T2WI/TSE、T1WI/TSE序列,P值均小于0.01;交叉韧带损伤,各序列之间差异性无统计学意义,P值大于0.01.结论膝关节MRI扫描中采用多方位成像、多序列组合,从而准确诊断膝关节损伤的程度、大小、范围,为临床制定正确的治疗方案提供可靠、直观的依据.     

前交叉韧带损伤后膝关节半月板和软骨的MRI定量分析研究进展

膝关节前交叉韧带损伤后多伴有半月板、关节软骨损伤,本文的目的在于探讨在前交叉韧带损伤膝关节的关节软骨、半月板的MRI量化分析研究进展。介绍了d GEMRIC、T1ρ和T2 mapping三种MRI定量分析技术检查关节软骨或半月板损伤的原理,分析这三种MRI定量分析技术的优缺点,介绍国内外关于这些定量分析技术在前交叉韧带损伤并发症的膝关节半月板、软骨损伤的应用情况。希望MRI定量分析技术(d GEMRIC、T1ρ和T2 mapping)越来越多的应用于前交叉韧带损伤后膝关节软骨和半月板损伤的检查,改善患者的术后生活质量。     

膝关节MR检查对100例交叉韧带损伤患者的诊断作用研究分析

目的研究分析核磁共振对膝关节交叉韧带损伤患者的临床诊断价值及特点。方法选取2016年1月至2017年7月本院收治的怀疑为膝关节前交叉韧带损伤患者100例,所有患者均行CT、MRI检查,检查后2~4天以内行关节镜检查,最终CT、MRI诊断结果以关节镜检查结果作为判断准确度的金标准。观察并比较CT、MRI检查前交叉韧带损伤诊断结果及前交叉韧带的损伤在CT及MRI影像学检查的表现。结果本研究100例患者,经关节镜检查结果显示,22例无韧带损伤(22.0%),34例为部分韧带撕裂(34.0%),剩余44例为完全韧带撕裂(44.0%)。CT检查前交叉韧带的诊断为80.0%(80/100),MRI检查前交叉韧带的诊断率为97.0%(97/100),差异具有统计学意义(χ~2=5.0493,P0.05);MRI检查结果显示,完全韧带撕裂的后交叉韧带角度、后交叉韧带弯曲度指数、前交叉韧带与胫骨内侧平舌矢状面夹角均明显小于无韧带损伤及部分韧带撕裂,比较差异具有统计学意义P0.05。结论 MRI在诊断前交叉韧带损伤方面具有明显优势,其对软组织的分辨率及对比度均较高,可以清晰显示关节整体结构及韧带、半月板损伤情况等,可作为交叉韧带损伤诊断的重要检查方法。     

四肢关节专用低场MR在膝关节疾病诊断中的应用

目的　通过对比四肢关节专用低场膝关节核磁共振图象 (MRI)与实体关节镜检查结果 ,探讨四肢关节专用低场核磁共振 (MR)检查在膝关节病变中的诊断价值。方法　自 2 0 0 1年 1 2月～ 2 0 0 3年 5月经四肢专用骨关节核磁共振检查 ,并为膝关节镜证实的 1 33例膝关节病损患者为其研究范围 ,综合对比两种检查结果。结果　四肢关节专用低场MR在膝关节病损中韧带损伤的诊断灵敏度高达 1 0 0 % ,半月板损伤最低仅为 5 5 88% (P <0 0 1 ) ;同样 ,韧带损伤诊断符合率最高 90 5 1 % ,软骨损伤最低为 82 0 9% (P <0 0 1 )。结论　核磁共振检查是临床诊断膝关节病变的一种重要、可靠的检查手段。通过采用MR特殊技术 ,提高病灶区的信号强度 ,使病变易于发现 ,不致发生错误或疏漏     

低场MRI对膝关节交叉韧带损伤诊断的价值

目的探究低场MRI在膝关节交叉韧带损伤诊断中的价值。方法对经手术或临床证实的40例膝关节交叉韧带损伤患者,包括32例前交叉韧带损伤与29例后交叉韧带损伤,进行回顾性MRI对比观察。结果 32例前交叉韧带损伤中可发现直接征象17处,间接征象15处;29例后交叉韧带损伤中可发现直接征象13处,间接征象16处。合并侧副韧带损伤30例、半月板损伤12例、骨挫伤和骨折8例、关节曩积液20例、关节不稳4例。结论低场MRI在对膝关节交叉韧带损伤的诊断中,通过对膝关节交叉韧带损伤的直接和（或）间接征象的认识能较准确的诊断出膝关节交叉韧带损伤的部位、程度以及时间。     

MRI诊断青少年运动员慢性肘关节运动损伤：成像序列的选择

目的探讨MRI诊断青少年运动员慢性肘关节损伤的价值以及成像序列的选择。方法以34名6-16岁运动员的40个肘关节作为研究对象,分别采用矢状位、冠状位及轴位MR扫描,分析图像特点。结果应用轴位T1W、矢状位T1W、T2W、STIR、PDW等序列明确显示肘关节软组织和骨骼解剖及其病变;矢状位T2W、STIR等序列能很好显示关节腔积液、骨膜增厚,PDW序列对骨质损伤、韧带受损及滑膜炎显示较好。结论 MRI可很好地显示青少年运动员慢性肘关节损伤的关节内、外骨骼肌肉组织受损情况;选择适当的成像序列是充分显示病变的基础。     

异常加深的股骨外侧髁压迹是前交叉韧带撕裂的间接证据

目的:探讨股骨外侧髁压迹异常程度与前交叉韧带损伤之间的关系.方法:回顾研究2013年1月至2013年11月治疗的前交叉韧带损伤16例患者的X线片和MRI影像学资料,其中男14例,女2例;左膝关节5例,右膝关节11例;年龄19～52岁,平均28.3岁.膝关节侧位X线或MRI矢状位提示股骨外侧髁压迹有异常,使用影像PACS系统中测量工具测量压迹的深度,并分析患者病历资料、体格检查及关节镜术中影像学资料.结果:4例侧位X线片和MRI矢状位可见股骨外侧髁压迹异常并深度2.0 mm,MRI示前交叉韧带撕裂,前抽屉试验和拉姆征均阳性,关节镜探查手术证实前交叉韧带完全撕裂;2例侧位X线片股骨外侧髁压迹未见异常,但MRI矢状位示股骨外侧髁压迹异常并深度1.0 mm,MRI示前交叉韧带撕裂,前抽屉试验和拉姆征均阳性,MRI示前交叉韧带撕裂,其中1例关节镜探查手术证实前交叉韧带完全撕裂,另1例因未行手术探查而无法证实是否完全断裂.结论:膝关节侧位X线片上股骨外侧髁压迹异常加深与前交叉韧带撕裂有密切相关,异常加深的股骨外侧髁压迹是前交叉韧带撕裂的间接证据.     

不同后交叉韧带指数测量方法对前交叉韧带损伤的诊断价值

目的:比较6种不同测量方法下的后交叉韧带(posterior cruciate ligament,PCL)指数(Index),分析验证其在前交叉韧带(anterior cruciate ligament,ACL)损伤中的临床诊断价值。方法:回顾性分析2018年5月至2022年3月收治的225例患者的膝关节MRI资料,年龄18～60岁,中位数32岁。根据ACL是否损伤,分为ACL正常组和ACL损伤组。在114例ACL损伤和111例ACL完整受试者的膝关节MRI矢状位图像上,测量MRI矢状位PCL在股骨附着点和胫骨附着点之间的直线距离(A)和该直线到矢状位图像上PCL弧形标记点之间的最大垂直距离(B),计算PCL Index并评估其对ACL损伤的诊断价值。结果:ACL正常组和ACL损伤组PCL Index1、2、3、6比较差异无统计学意义(P>0.05);两组PCL Index4、5比较,差异有统计学意义(P<0.001)。ACL正常组的PCL Index2、6与患者年龄呈负相关性(相关系数=-0.213,-0.189;P<0.05),ACL损伤组的PCL Index5与...     

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.     

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.     

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.     

Is the recovery profile of mivacurium independent of the rate of decay of its plasma concentration in patients with normal plasma cholinesterase activity?

Background: The duration of action of muscle relaxants is poorly correlated to the rate of decay of their plasma concentration. The plasma concentration of mivacurium may rapidly decrease below its active concentration because of the extensive hydrolysis of mivacurium. By inflating a tourniquet on one upper limb for 3 min after the administration of atracurium, mivacurium or vecuronium, we studied the influence of the initial decline of their plasma concentration on their effect. Methods: In 50 patients anaesthetised with thiopental, isoflurane and fentanyl, the effect of bolus doses of 0.15 or 0.25 mg . kg^?1 mivacurium (MIV 15, MIV 25), 0.3 or 0.5 mg . kg^?1 atracurium (ATR 30, ATR 50) and 0.06 or 0.1 mg . kg^?1 vecuronium (VEC 06, VEC 10) were measured on both arms (evoked response of the adductor pollicis to train-of-four stimulation every 12 s), a tourniquet being applied on one arm just before and during 3 min after the muscle relaxant bolus. Results: Tourniquet inflation of 3 min almost abolished the neuromuscular effect of mivacurium. In the vecuronium groups and in the ATR 50 group, tourniquet inflation did not modify the maximum degree of depression of the twitch response. Also, the duration of action of vecuronium was unaffected by the tourniquet. In the ATR 30 group, times to return of the twitch response to 25% (duration 25%) and 75% (duration 75%) of control response were significantly shorter in the cuffed arm, 23 min vs 27 min, and 41 min vs 45 min, respectively. In the ATR 50 group, only duration 25% was significantly shorter in the cuffed arm (41 min vs 45 min). Conclusion: The results suggest that the rate of decline of the plasma concentration of mivacurium is so rapid, that a very low and almost clinically ineffective concentration is present as soon as 3 min after its administration. The results also indicate that the recovery from a mivacurium-induced neuromuscular blockade is not influenced by the rate of decay of its plasma concentration in patients with genotypically normal plasma cholinesterase.     

Membranes in Artificial Organs

Abstract: Membrane processes play a pivotal and enabling role in modern replacement therapy for acute and chronic organ failure and in the management of immunologic diseases. In fact, virtually all contemporary extracorporeal blood purification methods employ membrane devices, and the next generation of artificial organs and tissue engineering therapies are almost certain to be similarly grounded in membrane technology. In this short essay, we comment on the similarities and differences among synthetic membranes and their natural counterparts and also provide a critical overview of the demographics and technology of hemodialysis, hemofiltration, apheresis, oxygenation, and emerging membrane technologies and applications.     

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.     

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.