一期前路病灶清除植骨内固定治疗脊柱结核

目的探讨经前路病灶清除植骨一期前路内固定术治疗脊柱结核的临床效果。方法对43例脊柱结核患者,行前路病灶彻底清除、椎间植骨、一期前路内固定术。结果脊柱结核复发2例（4.7%）,植骨不融合3例（7.0%）。植骨融合时间3～8个月。脊柱后凸畸形平均矫正70.2%±11.4%。11例截瘫患者神经功能Frankel分级术后恢复情况：术前A级3例术后恢复至B级1例、2例无恢复;B级5例恢复至C级1例、D级2例、E级1例、1例无恢复;C级3例恢复至D级1例、E级2例。结论经前路病灶清除植骨一期前路内固定术治疗脊柱结核能彻底清除结核病灶,充分减压,矫正脊柱后凸畸形,提高脊柱结核的治愈率。     

胸腔镜辅助下小切口在胸椎前路手术的临床应用

目的探讨胸腔镜辅助下小切口行胸椎前路手术的可行性. 方法 2001年10月～2002年10月,我院在胸腔镜辅助下小切口行胸椎前路手术14例.其中6例胸椎转移瘤行病变椎体切除、钢板骨水泥椎体重建及前路针棒内固定;4例胸椎结核行病灶清除、植骨及前路钉棒内固定;2例胸椎间盘突出症行髓核摘除、椎间植骨融合;2例胸椎椎体骨折合并脱位行脱位椎体复位、椎管减压、椎体间植骨及前路钉棒内固定. 结果术后影像学显示病灶清除彻底,内固定效果确切.14例术后随访 4～12个月,14例胸背痛完全消失,13例脊髓压迫症中除1例转移瘤无改善外,其余12例肌力术前A～D级,术后恢复至C～E级. 结论胸腔镜辅助下小切口行胸椎前路手术方法可行,近期疗效满意.     

前路减压与植骨内固定治疗胸腰椎骨折伴截瘫

目的探讨胸腰段脊柱骨折伴脊髓损伤前路伤椎大部切除减压、植骨融合、钢板内固定的手术方式与效果。方法41例胸腰段骨折伴脊髓损伤患者均行前路椎管减压、植骨融合及钢板内固定。对神经功能恢复情况、局部脊柱的稳定性进行分析。结果41例均获随访,时间6个月～4.5年,平均（30±7.8）个月,椎体间均获骨性融合,时间4～8个月。神经功能Frankel分级：A级7例恢复至B级5例,2例无恢复;B级15例恢复至C级10例、D级4例,1例无恢复;C级10例恢复至D级9例,1例无恢复;D级7例恢复至E级;E级2例无变化,无并发症发生。结论胸腰段脊柱骨折伴神经损伤,前入路手术直视下减压彻底,神经功能恢复好,Ⅰ期植骨融合内固定前路重建脊柱稳定性好,疗效满意。     

颈椎前路单节段减压四种不同融合方式的疗效比较

目的比较颈椎前路单节段减压并不同融合方法治疗脊髓型颈椎病（cervical spondylotic myelopathy，CSM）的临床疗效。方法对168例单节段病变的CSM患者采用前路减压并植骨融合治疗，其中单纯植骨融合42例（A组）、颈椎前路减压界面固定术（cervical interbody fusioncage，CIFC）54例（B组）、植骨融合并颈椎前路钢板内固定40例（C组）、CIFC并前路钢板内固定32例（D组）。术后定期随访并摄X线片，观察疗效、椎间高度、颈椎前弯曲度和融合情况。结果经过随访，A组融合率为83．3％，B组融合率为96．3％，C组融合率为95．0％，D组融合率为96.9％。终访时，A组平均椎间高度和颈椎前弯曲度较术后早期显著降低（P〈0．05），B组、C组和D组则无显著差异（P〉0．05）。结论脊髓型颈椎病的治疗关键不仅在于充分减压及有效植骨融合，而且不同融合技术对疗效有明显影响。     

经胸一期病灶清除植骨融合内固定术治疗胸椎结核

目的评价经胸入路一期病灶清除植骨融合内固定治疗胸椎结核的疗效。方法对28例胸椎结核患者[10例伴有后凸畸形,Cobb角为13～30(22±3)°;16例伴有神经功能障碍]采用经胸入路一期病灶清除植骨融合内固定术治疗,随访观察治疗效果。结果术后Cobb角为2～10(5±3)°,后凸矫正角度无明显丢失,无手术并发症。28例均获随访,时间12～24个月。患者均临床治愈无复发。术后3～8(4.2±1)个月植骨全部融合,内固定无松动、断裂。16例脊髓损害者神经功能Frankel分级:A级1例恢复至C级;B级3例恢复至D级1例、E级2例;C级4例、D级8例均恢复至E级。结论经胸一期病灶清除植骨融合内固定治疗胸椎结核暴露充分,有利于病灶清除、前方脊髓减压、重建脊柱稳定性,植骨融合率高。     

前路手术治疗陈旧性下颈椎骨折脱位

目的：探讨陈旧性下颈椎骨折脱位的手术入路选择以及前路手术治疗的治疗效果。方法：2003年1月至2010年5月,17例下颈椎骨折脱位患者因不同原因于伤后4周以上行持续颅骨牵引和前路减压植骨钢板内固定术。其中男11例,女6例;年龄24～56岁,平均41岁;受伤至手术时间4周～3个月。Frankel分级：A级7例,B级4例,C级2例,D级2例,E级2例。评价治疗前后的神经功能,观察术后植骨融合情况、椎间高度和颈椎椎体序列。结果：17例患者切口均Ⅰ期愈合。1例出现声音嘶哑,1个月后症状消失。平均随访23个月（4～47个月）,术后X线示椎间隙高度和颈椎序列恢复满意,内固定物和植骨稳定无松动,融合满意。术后Frankel分级明显改善,A级5例,B级5例,C级1例,D级3例,E级3例。结论：单纯前路手术可以使屈曲牵引型（DF）Ⅰ、Ⅱ型和部分Ⅲ型复位,对陈旧性下颈椎骨折脱位的患者采用前路减压植骨钢板内固定术是一种有效、简便、安全的方法。     

一期前路病灶清除联合自体肋骨植骨融合内固定治疗胸椎结核

目的：分析一期前路病灶清除、自体肋骨椎间植骨融合前路内固定术治疗胸椎结核的临床效果。方法2003年6月～2008年5月手术治疗胸椎脊柱结核42例,男25例,女17例,均采用一期前路病灶清除、自体肋骨椎间植骨融合前路内固定术。根据术前、术后随访的X线片,分析植骨融合及脊柱后凸畸形矫正效果;采用Frankel分级、红细胞沉降率（ erythrocyte sedimentation rate, ESR）、C反应蛋白（ C-reactionprotein, CRP ）及视觉模拟量表（ visual analog scale, VAS）评分评估临床治疗效果。结果随访1～7年,平均50．8个月,42例患者均获骨性愈合,愈合时间3～7个月,平均4．5个月,无内固定松动、脱出及断裂;术前Cobb角平均19．8°,术后1周为3．7°,末次随访时为4．6°;Frankel分级,术前B级为3例,C级9例,D级20例,E级10例,末次随访时为D级6例,E级36例;VAS评分术前平均为8．2,术后1周为1．8,末次随访时为1．2。除2例患者术后出现疼痛,持续2个月后自行缓解外,无其他并发症。无复发结核感染出现。结论一期行前路病灶清除、自体肋骨椎间融合前路内固定术治疗胸椎结核,可有效矫正脊柱后凸畸形,重建脊柱稳定性,获得较好的临床效果。     

犬椎间隙感染治疗的实验研究

目的探讨椎间隙感染前路病灶清除一期植骨内固定的可行性、安全性及疗效和病理转归。方法犬腰椎间隙内注射金黄色葡萄球菌建立椎间隙感染模型。监测肛温、ESR、CRP;术后2周摄腰椎正侧位X线片和MRI,证实椎间隙感染模型成功建立。32只建模成功的犬随机均分为4组。A组：抗生素治疗;B组：抗生素治疗＋前路病灶清除;C组：抗生素治疗＋前路病灶清除＋椎间植骨;D组：抗生素治疗＋前路病灶清除＋前路椎间植骨＋钢板内固定。治疗后3d及1、2、3周测肛温、ESR、CRP;12周摄X线片后处死,取椎间隙组织病理学检查和培养。结果A组：治疗3周后肛温、ESR及CRP下降缓慢,12周内死亡3只,存活5只未发现椎体间融合。B、C、D3组与A组比较：3周后肛温、ESR、CRP均下降迅速,差异有显著性（P〈0．05）。观察12周感染无复发,但B、C组出现脊柱后凸畸形各1只。12周后D组椎体间融合6只,与A、B、C组相比融合率升高（P〈0．05）,无脊柱畸形发生和感染复发。结论前路手术可彻底清除犬椎间隙感染病灶,一期植骨内固定无感染复发,融合率高,病理转归佳。     

经胸一期病灶清除植骨融合内固定术治疗胸椎结核合并截瘫

目的探讨经右侧胸腔一期植骨融合内固定治疗胸椎结核合并截瘫的疗效。方法对10例胸椎结核合并截瘫患者采用经右侧胸腔一期植骨融合内固定术(单钉棒固定6例,钉板固定4例)治疗,随访观察治疗效果。结果 10例患者均获随访,时间1～5年。神经功能恢复情况按ASIA分级:C级8例中6例术后4周内恢复至E级,2例术后3个月内恢复至E级;D级2例术后4周内均恢复至E级。患者血沉均恢复正常,未见结核复发,胸背痛消失。植骨全部融合,融合时间为3～8个月。结论采用经右胸腔前路一期植骨内固定治疗上胸椎结核合并截瘫是安全、有效的方法,且并发症少。     

前路融合内固定方式对颈椎曲度的影响

目的分析颈椎前路减压融合术中,不同植骨融合内固定方式对恢复颈椎生理曲度的影响。方法2000年1月～2002年12月施行颈椎前路减压内固定手术治疗颈椎伤病患者67例,将26例单节段减压内固定病例分为前路钢板 髂骨植骨融合组(A组,11例)及Cage植骨融合组(B组,15例);将41例多节段(双或三节段)椎体次全切除减压内固定病例分为钢板 髂骨植骨融合组(C组,19例)及钢板 钛网植骨融合组(D组,22例)。以D值法(颈椎侧位X线片上,C4椎体后下缘到齿突后缘与C7椎体后下缘连线的垂直距离)分别比较A、B两组及C、D两组在恢复颈椎生理曲度方面的疗效。结果术后即刻A、B两组及C、D两组之间D值的增值差异无显著性(P >0.05)。全部病例随访10～36个月(平均21.5个月),均获骨性融合。A、B两组及C、D两组之间末次随访时D值增值差异无显著性(P >0.05),各组内术后即刻与末次随访时D值增值的差异无显著性(P >0.05),多节段减压组(C D组)与单节段减压组(A B组)D值增值在术后即刻与随访时差异均有显著性(P< 0.01)。结论在均行单节段或多节段减压融合的病例中,采用不同的前路融合内固定方式对恢复颈椎曲度无明显影响,由此推断正确掌握前路手术适应证是有效恢复颈椎生理曲度的首要因素,恢复颈椎生理曲度的关键步骤在术中而非术后。     

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.