关节镜下采用腘绳肌肌腱和微型钢板纽扣同时重建前、后十字韧带

目的关节镜下采用绳肌肌腱和微型钢板纽扣同时重建前、后十字韧带,并对重建效果进行评估。方法对12例前、后十字韧带损伤患者,在关节镜下采用同侧半腱肌肌腱和微型钢板纽扣重建前十字韧带,采用对侧半腱肌肌腱、股薄肌肌腱和微型钢板纽扣重建后十字韧带。其中2例还同时行后外侧韧带结构重建,1例同时行后内侧韧带结构重建。术后随访12～24个月,采用IKDC和Lysholm膝关节功能评分表对患膝功能进行评估,通过KT-1000检查了解膝关节的前后松弛度。结果术后无伸膝受限,屈膝活动度120°～140°,平均128°。终末随访时IKDC评分为A4例(33.3%),B7例(58.3%),C1例(8.3%)。屈膝25°位KT-1000检查,双侧膝关节前向松弛度差异小于2mm者8例,3～5mm者3例,7mm者1例;屈膝70°位检查,双侧胫骨结节后坠差异为0～2mm者9例,2～4mm者3例。陈旧性损伤患者术前Lysholm膝关节功能评分为(66.5±3.1)分,终末随访时为(93.8±3.5)分,差异具有非常显著性(t=5.376,P<0.01)。10例患者(83.3%)恢复了原来的运动水平,2例患者(16.7%)运动水平较前有所降低。结论在关节镜下采用双侧绳肌肌腱和微型钢板纽扣同时重建前、后十字韧带,能够较满意地恢复膝关节功能。     

采用四股半腱肌肌腱和缝线钢板重建前十字韧带后的康复训练

目的介绍采用四股半腱肌肌腱和缝线钢板重建前十字韧带后的康复训练方法,总结其近期效果。方法对51例陈旧性前十字韧带损伤的患者采用四股半腱肌肌腱和缝线钢板进行重建,术后进行1年以上系统的康复指导。按照Lysholm膝关节功能评分标准,术前膝关节功能评分为(56.7±7.4)分。康复内容包括支具制动及负重计划、肌力、活动度、本体感受器训练和肌肉牵张训练等方面。通过膝关节稳定性、肌力、活动度、步态分析,以及膝关节功能评分,总结这种训练方法的可行性和效果。结果术后3个月,膝关节的活动度均恢复正常。术后1年,患肢的股四头肌-绳肌峰力矩比值超过正常侧的80%。KT-1000检查结果显示,术后6、12个月,患侧膝关节前向松弛度大于健侧的比例分别为11.76%(6/51)和10.41%(5/48),但松弛度差异均在4mm以内,其余患者患侧膝关节前向松弛度与健侧相同或者小于健侧。术后1年,95.83%的患者都能够恢复正常步态,膝关节功能评分为(97.8±1.2)分。统计学分析显示,术后与术前评分相比差异有显著性意义。结论对于不合并严重内、外侧韧带复合结构损伤的陈旧性前十字韧带损伤,在采用四股半腱肌肌腱和缝线钢板进行重建后,采用该方法进行康复训练是切实可行且有效的。     

关节镜下采用半腱肌和股薄肌肌腱重建后交叉韧带

目的评价四股半腱肌肌腱、两股股薄肌肌腱重建后交叉韧带的临床疗效。方法对12例后交叉韧带断裂患者,在关节镜下采用四股半腱肌肌腱和两股股薄肌肌腱进行重建。结果所有患者随访12～24个月,所有患者术后膝关节不稳定症状消失,胫骨后坠征阴性,后抽屉试验阴性。术后1年,根据Lysholm膝关节功能评分,优10例,良2例,平均积分85±4.1。结论关节镜下采用四股半腱肌肌腱、两股股薄肌肌腱和微型纽扣钢板重建后交叉韧带,手术创伤小,重建韧带强度大,临床效果满意。     

关节镜下LARS人工韧带及4股半腱肌肌腱重建前交叉韧带

目的评价LARS人工韧带和自体4股半腱肌肌腱关节镜下重建膝前交叉韧带（ACL）的临床疗效。方法对28例膝ACL断裂患者行关节镜下ACL重建术,根据重建材料的来源分为LARS人工韧带组（13例）和自体4股半腱肌肌腱组（15例）。采用ACL解剖等长重建技术建立胫骨、股骨骨道。并对两组的关节稳定性和Lysholm膝关节功能评分进行对比研究。结果术后膝关节稳定性LARS人工韧带组优于4股半腱肌肌腱组（P〈0.05）。移植后两组Lyshrolm膝关节功能评分较移植前提高（P〈0.05）。术后6个月LARS人工韧带组Lysholm评分（90.4分±5.3分）高于4股半腱肌肌腱组（81.2分±4.7分）（P〈0.05）。结论在关节镜下重建ACL术中,LARS人工韧带可作为自体材料的良好替代物。     

关节镜下四股半腱肌股薄肌肌腱重建交叉韧带

目的 探讨关节镜下采用可吸收界面螺钉固定四股半腱肌股薄肌肌腱重建交叉韧带的临床疗效.方法 关节镜下采用四股自体半腱肌股薄肌肌腱移植加可吸收螺钉固定法治疗6例交叉韧带损伤患者.结果 6例患者随访10个月,按Lysholm膝关节功能评分标准,术前膝关节功能评分平均为56.7分,术后10个月时为76～96分(平均82.2分).结论 自体四股半腱肌股薄肌肌腱弹性模量与交叉韧带相似,强度大于交叉韧带.植入物为四股,可吸收螺钉固定,固定牢固,生物相容性好.     

关节镜下采用腘绳肌肌腱和微型钢板纽扣重建后十字韧带

目的介绍在关节镜下利用绳肌肌腱和微型钢板纽扣重建后十字韧带(PCL)的方法,探讨其临床效果。方法对21例单纯PCL断裂的患者,在关节镜下利用绳肌肌腱和微型钢板纽扣进行重建,术后进行1年以上的随访,了解膝关节功能。结果术后3个月,所有患者均无伸膝受限,膝关节屈膝活动度均大于120°。术后1年,患肢的股四头肌-绳肌峰力矩比超过正常侧的90%;屈膝70°时后抽屉试验Ⅰ度阳性2例,其余均为阴性;屈膝30°时后抽屉试验Ⅰ度阳性6例,其余为阴性;膝关节功能Lysholm评分为90.7±2.3。结论在关节镜下利用绳肌肌腱和微型钢板纽扣重建PCL方法简单,能够可靠恢复膝关节功能。     

关节镜辅助下修复重建膝关节多韧带损伤

目的 探讨关节镜辅助下修复重建膝关节多韧带损伤的手术效果.方法 对15例患者在关节镜监控下采用自体肌腱(腓骨长肌腱或健侧肢体半腱肌、股薄肌腱)、同种异体肌腱重建关节内的前、后交叉韧带,关节外的侧副韧带采用带线锚钉原位直接缝合或加强缝合.结果 15例均获得随访,时间10～24个月.按Lysholm功能评分标准:术前为25～42 (30.2±3.5)分,末次随访时为75～96(87.0±6.0)分;主动关节活动范围由术前40～100(65.0±12.5)°提高到术后100～140(120.0±15.0)°;术前、术后比较差异有统计学意义(P<0.05).无感染或血管神经损伤等并发症发生.结论 关节镜辅助下联合使用自体和同种异体肌腱修复膝关节前、后交叉韧带损伤,可重建膝关节稳定性,是治疗膝关节多韧带损伤的有效方法.     

关节镜下采用四股和八股腘绳肌肌腱双束重建前十字韧带的比较研究

目的比较关节镜下采用四股和八股腘绳肌肌腱双束重建前十字韧带的临床效果。方法2001年9月至2002年8月,将76例陈旧性前十字韧带损伤患者随机分为两组进行双束重建。一组采用四股腘绳肌肌腱移植物:取同侧半腱肌肌腱,做成两个两股肌腱移植物,分别重建前十字韧带前、后束;一组采用八股腘绳肌肌腱移植物:取同侧半腱肌肌腱做成一个四股肌腱移植物重建前束,取同侧股薄肌肌腱做成另一个四股肌腱移植物重建后束。按照IKDC、Lysholm和Tegner膝关节评分标准评价疗效。结果四股肌腱移植物组有33例、八股肌腱移植物组有35例获得随访,随访时间1～3年,平均16个月。四股肌腱移植物组KT-1000检查示,双侧膝关节前向松弛度差异<3mm者25例(75.8%,25/33),3～5mm者5例(15.2%,5/33),6～10mm者3例(9.1%,3/33);轴移试验阴性28例(84.8%),阳性5例(15.2%)。八股肌腱移植物组KT-1000检查示,双侧膝关节前向松弛度差异<3mm者33例(94.3%,33/35),3～5mm者2例(5.7%,2/35);轴移试验阴性34例(97.1%),阳性1例(2.9%)。根据IKDC检查标准,四股肌腱移植物组有29例(87.9%,29/33)、八股肌腱移植物组有34例(97.1%,34/35)为正常或者接近正常,Lysholm评分分别为(90.2±2.9)分和(97.3±1.7)分,两组比较差异有统计学意义(P<0.05)。结论关节镜下采用八股腘绳肌肌腱较采用四股腘绳肌肌腱双束重建前十字韧带能够明显提高膝关节稳定性。     

关节镜下半腱肌腱和股薄肌腱双隧道重建前十字韧带

目的探讨关节镜下联合应用半腱肌腱和股薄肌腱重建前十字韧带(anteriorcruciateligament,ACL)的方法及疗效。方法回顾自1998年4月～2000年5月在关节镜下联合应用半腱肌腱和股薄肌腱重建ACL的患者12例。于ACL前内侧束和后外侧束的附着部分别钻直径4.5mm的隧道,用半腱肌腱重建前内侧束,股薄肌腱重建后外侧束,保留半腱肌腱和股薄肌腱的附着点,在股骨隧道外口将半腱肌腱和股薄肌腱打结固定,不行内固定。所有患者术前及术后18个月行膝关节屈曲30°、60°、90°前抽屉试验,Lysholm评分方法评定膝关节功能。结果术后随访18～43个月,平均26个月。术前所有患者前抽屉试验均为阳性,术后9例阴性,2例屈膝30°位阳性,1例屈膝30°、60°位阳性。术前Lysholm评分为40～58分,平均50.5分,手术后18个月为62～92分,平均85分,总优良率为91.7%。结论应用半腱肌腱和股薄肌腱联合重建ACL,术后膝关节动态稳定性好,疗效满意。     

关节镜下解剖等长重建技术在重建前交叉韧带中的应用

[目的]探讨前交叉韧带(ACL)解剖等长重建技术在关节镜下应用的可行性及近期疗效.[方法]对20例前交叉韧带损伤行关节镜下ACL重建木.采用前交叉韧带解剖等长重建技术钻胫骨、股骨骨道.移植物用LARS人工韧带11例,用四股半腱肌股薄肌腱9例.LARS人工韧带用2枚界面螺钉固定韧带,四股半腱肌股薄肌腱股骨端用Endobutton固定、胫骨端用可吸收界面螺钉固定.[结果]手术时间LARS人工韧带组30～80 min,平均56 min.四股半腱肌股薄肌腱组80～120 min,平均100 min.20例均随访6～12个月,平均9个月.根据Lysholm膝关节功能评分,LARS人工韧带组术前评分22～65分(36.72±15.54)分;术后6个月评分80～98分(90.45±4.68)分(t=10.535,P＜0.01).四股半腱肌股薄肌腱组术前评分20～60分(37.11±12.26)分;术后6个月评分75～87分(80.44±4.16)分(t=9.615,P＜0.01).术后6个月LARS人工韧带组与四股半腱肌股薄肌腱组评分在统计学上有显著差异(t=10.569,P＜0.01).[结论]前交叉韧带解剖等长重建技术在关节镜下重建前交叉韧带术中操作简便,效果可靠,值得推广.LARS人工韧带组近期疗效明显优于四股半腱肌股薄肌腱组.     

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.