空心螺钉内固定治疗青壮年股骨颈骨折

目的评价空心螺钉内固定治疗青壮年股骨颈骨折的临床疗效。方法2001年1月～2005年12月，采用空心螺钉内固定治疗股骨颈骨折42例。其中男22例，女20例；年龄19～59岁，平均41岁。车祸伤21例，高处坠落伤14例，重物砸伤7例。无移位骨折15例，移位骨折27例。均为新鲜骨折。按照Garden分型：Ⅱ型15例，Ⅲ型16例，Ⅳ型11例。损伤至手术时间7h～15d，平均4．6d。结果42例患者均获随访1～6年，平均2．5年。骨折均愈合，平均愈合时间6．5个月。螺钉无松动及折断。术后2年3例出现股骨头缺血坏死迹象，1例出现股骨头塌陷，建议扶拐不负重活动，观察病情。髋关节功能按Brumbaek评价标准，优18例，良20例，差4例，优良率90．4％。结论空心螺钉内固定是治疗青壮年股骨颈骨折的一种有效方法，能提高骨折愈合率，降低股骨头坏死发生率。     

42例股骨颈骨折经皮空心螺钉内固定术临床观察

自2005年7月～2007年7月采用经皮空心螺钉内固定术治疗股骨颈骨折42例,取得满意疗效. 1 材料与方法 1.1 一般资料 本组42例,男19例,女23例,年龄32～78岁,平均56岁.左侧23例,右侧19例.骨折分型:头下型9例,经颈型18例,基底型15例.无移位型6例,移位型36例.     

生物陶瓷结合可吸收螺钉在胫骨平台骨折中的应用

目的探讨生物陶瓷结合可吸收螺钉在治疗胫骨平台骨折中的应用。方法2001年6月～2004年6月应用生物陶瓷填充替代植骨结合可吸收拉力螺钉内固定治疗SchatzkerⅡ、Ⅲ型胫骨平台骨折61例。结果所有患者随访5～24个月,平均15个月,全部骨折临床愈合。疗效按Rasmussen膝关节功能评价标准,优42例,良14例,中5例,优良率91.8%。结论生物陶瓷结合可吸收螺钉治疗胫骨平台骨折是一种有效的治疗方法。     

空芯螺钉治疗距骨骨折

目的探讨空芯螺钉治疗距骨骨折的疗效。方法对16例距骨骨折患者应用空芯螺钉手术治疗。结果16例均获随访，时间6个月～2年6个月。骨折愈合12例，愈合时间8～42周，为：Ⅰ型3例均愈合，Ⅱ型6例愈合5例，Ⅲ型5例愈合3例，Ⅳ型2例愈合1例。无菌性坏死4例：Ⅱ型1例，Ⅲ型2例，Ⅳ型1例。按Kenwright功能标准：优7例，良5例，可3例，差1例，优良率75％。结论空芯螺钉治疗距骨骨折固定确切，易操作，是一种实用的内固定方法。     

闭合复位经皮空心螺钉内固定选择性治疗踝关节骨折

目的探讨闭合复位经皮空心螺钉内固定选择性治疗踝关节骨折的手术方法、适应证及临床效果。方法回顾性分析2004年3月～2006年4月期间,采用闭合复位经皮空心拉力螺钉内固定治疗32例成人踝关节骨折的临床资料,其中旋后-外旋型19例,旋前-外旋型6例,旋前-外展型4例,旋后-内收型3例。结果平均随访25个月(17～42个月)。骨折愈合时间为8～15周。按美国足踝骨科协会(AOFAS)足踝评分系统评分,平均为92分(78～100分),优30例,可2例,优良率为93.8%。结论闭合复位经皮空心螺钉内固定是一种可用于选择性治疗踝关节骨折的微创术式,具有骨折愈合快,愈合率高,踝关节功能恢复满意的优点。     

螺钉F形固定技术治疗Pauwels Ⅲ型股骨颈骨折北大核心CSCD

目的探讨螺钉F形固定技术治疗PauwelsⅢ型股骨颈骨折的临床疗效。方法 2013年1月—2016年12月,采用螺钉F形固定技术治疗PauwelsⅢ型股骨颈骨折43例。其中男32例,女11例;年龄20～55岁,平均38.9岁。左侧21例,右侧22例。致伤原因:交通事故伤19例,高处坠落伤24例。GardenⅢ型25例、Ⅳ型18例。受伤至手术时间2～3 d,平均2.2 d。记录手术时间、术中透视时间、术后住院时间、骨折复位质量、术后并发症(骨折不愈合、内翻畸形、股骨颈短缩、股骨头缺血性坏死、螺钉退出等)发生情况,采用Harris评分评价髋关节功能。结果手术时间28～45 min,平均37.5 min;术中透视时间13～20 s,平均14.7 s;术后住院时间2～3 d,平均2.7 d。患者切口均Ⅰ期愈合。43例患者均获随访,随访时间18～58个月,平均38.7个月。X线片显示,骨折均获解剖复位;42例骨折愈合,愈合时间3～5个月,平均3.6个月;1例闭合复位者骨折不愈合,行人工全髋关节置换术。末次随访时,髋关节Harris评分为55～100分,平均92.7分。42例骨折愈合患者中发生股骨颈短缩11例、内翻畸形9例、股骨头缺血性坏死3例、螺钉退出8例。GardenⅢ、Ⅳ型患者相关并发症发生情况比较,差异无统计学意义(P>0.05)。结论采用螺钉F形固定技术治疗股骨颈骨折,临床疗效满意,术后并发症发生率较低。     

可吸收螺钉在踝关节骨折中的应用

目的 探讨可吸收螺钉治疗踝关节骨折的疗效. 方法 2004年6月至2010年12月采用可吸收螺钉治疗16例踝关节骨折患者,男9例,女7例;年龄21～62岁,平均35岁;其中三踝骨折4例(AO分型:B型2例,C型2例),内外踝骨折8例(AO分型均为B型),单纯内踝骨折2例,单纯外踝骨折2例(1例为AO分型A型,另1例为外踝Maisonneuve骨折合并下胫腓联合和内侧三角韧带损伤).所有涉及外踝的骨折患者只有AO分型A型骨折采用2枚2.7 mm可吸收螺钉或1枚2.7mm可吸收螺钉辅助1枚1.5 mm可吸收棒固定,其余均采用接骨板螺钉固定.内踝骨折采用2～3枚3.5mm或4.0mm可吸收螺钉固定.1例下胫腓联合损伤采用2枚4.5 mm可吸收螺钉贯穿下胫腓固定.后踝骨折采用l～2枚4.0mm或4.5 mm可吸收螺钉从前向后固定.结果 16例患者术后获1.5～4.0年(平均28个月)随访.骨折愈合时间平均为3.0个月,无骨折延迟愈合及骨折不愈合,未出现伤口并发症.按美国足踝外科协会踝与后足功能标准评分评定疗效:优14例,良2例. 结论 可吸收螺钉内固定治疗踝关节骨折疗效好,无需行二次内固定取出手术,但要慎重选择骨折类型.     

螺钉F形固定技术治疗Pauwels Ⅲ型股骨颈骨折

目的探讨螺钉F形固定技术治疗PauwelsⅢ型股骨颈骨折的临床疗效。方法 2013年1月—2016年12月,采用螺钉F形固定技术治疗PauwelsⅢ型股骨颈骨折43例。其中男32例,女11例;年龄20～55岁,平均38.9岁。左侧21例,右侧22例。致伤原因:交通事故伤19例,高处坠落伤24例。GardenⅢ型25例、Ⅳ型18例。受伤至手术时间2～3 d,平均2.2 d。记录手术时间、术中透视时间、术后住院时间、骨折复位质量、术后并发症(骨折不愈合、内翻畸形、股骨颈短缩、股骨头缺血性坏死、螺钉退出等)发生情况,采用Harris评分评价髋关节功能。结果手术时间28～45 min,平均37.5 min;术中透视时间13～20 s,平均14.7 s;术后住院时间2～3 d,平均2.7 d。患者切口均Ⅰ期愈合。43例患者均获随访,随访时间18～58个月,平均38.7个月。X线片显示,骨折均获解剖复位;42例骨折愈合,愈合时间3～5个月,平均3.6个月;1例闭合复位者骨折不愈合,行人工全髋关节置换术。末次随访时,髋关节Harris评分为55～100分,平均92.7分。42例骨折愈合患者中发生股骨颈短缩11例、内翻畸形9例、股骨头缺血性坏死3例、螺钉退出8例。GardenⅢ、Ⅳ型患者相关并发症发生情况比较,差异无统计学意义(P0.05)。结论采用螺钉F形固定技术治疗股骨颈骨折,临床疗效满意,术后并发症发生率较低。     

颈前路单枚中空加压螺钉内固定治疗齿突骨折

目的初步比较经颈前路单枚单头螺纹中空加压螺钉与双头螺纹中空加压螺钉内固定治疗齿突骨折的效果。方法1997年4月～2003年4月,对20例齿突骨折行经颈前路单枚中空加压螺钉内固定术,其中单头螺纹中空加压螺钉12例,双头螺纹中空加压螺钉8例。Anderson分型:Ⅱ型16例,浅Ⅲ型4例。其中3例伴有单侧椎间关节内撕脱性骨折。观察手术时间、术中出血量、术后骨折愈合以及颈部活动情况。结果手术时间110～150min,平均125min。术中出血20～100ml,平均42ml。术中无一例发生副损伤。术后随访2～72个月,平均14.7个月;19例骨折正常愈合,1例延迟愈合;17例骨折愈合后颈椎活动恢复正常,3例伴单侧椎间关节内骨折者颈部旋转功能较正常减少20%。两种螺钉固定的手术时间、术中出血量、骨折愈合时间和颈椎活动功能无明显差别,差异无显著性(P >0.05)。结论单枚单头螺纹中空加压螺钉与单枚双头螺纹中空加压螺钉固定齿突骨折均可获得良好效果。     

对侧皮质锁定螺钉内固定治疗下肢长骨骨折的疗效评估

目的评估对侧皮质锁定螺钉(Motionloc)在下肢长骨骨折内固定术中的应用效果。方法回顾性分析自2014-05—2016-08诊治的39例下肢长骨骨折,均使用捷迈公司NCB桥接锁定接骨板和Motionloc螺钉进行固定。股骨干及股骨远端骨折29例(AO-32-A型9例,AO-32-B型1例,AO-33-A型9例,AO-33-C型10例),胫骨干及胫骨近端骨折10例(AO-41-A型6例,AO-41-C型1例,AO-42-B型2例,AO-42-C型1例)。结果 39例均获得至少1年的随访。4例骨折不愈合,其中2例Motionloc螺钉断裂(AO-32-A3型骨折1例,AO-42-C3型骨折1例)。35例骨折愈合,骨折愈合时间平均3.8(2~5)个月,完全负重时间平均4.4(3~6)个月。术后1年参照Kolment标准评定患肢膝关节功能:优24例,良10例,可1例,差4例,优良率87.2%。结论与传统锁定螺钉相比,对侧皮质锁定螺钉具有系统刚度低、骨痂形成早、骨痂形成均匀等优点,但螺钉近端强度较低,还未有明确规范的手术适应证及操作指南。     

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.