肌松监测指导老年患者全麻后气管拔管与传统拔管的比较

目的:观察肌松监测下指导老年患者全麻后气管拔管的血液动力学变化及术后肌松残余的发生率.方法:选择老年患者100例,年龄65-75岁,ASAⅠ～Ⅱ级,实施全凭静脉麻醉.随机分为肌松监测下气管拔管组(A组)和传统气管拔管组(B组)各50例.记录各时间点(术前、拔管时、拔管后30min、拔管后1h)的MAP,HR,脑电双频指数(B1S),四个成串刺激(TOF),TOF＜0.9为肌松残余.结果:肌松监测组MAP,HR指标稳定(P＞0.05),拔管后1h的肌松残余(PORC)发生率为0%;传统组MAP,HR均有显著变化(P＜0.01),拔管后1h的PORC发生率28%.结论:老年患者在肌松监测下气管拔管,其血流动力学稳定,术后肌松残余发生率低,具有临床应用价值.     

残余肌松对全麻患者术后拔管早期呼吸功能的影响

目的 观察术后残余肌松发生率及其对全麻患者术后拔管早期呼吸功能的影响.方法 选择择期全麻手术患者124例,术前测定肺功能,术毕保留气管内导管转入麻醉后恢复室(PACU).根据临床征象判断拔管,测定拔管后患者拇内收肌TOFr及拔管后10、40 min的肺功能.根据TOFr,将患者分为无残余肌松组(NR组,TOF≥0.9)和残余肌松组(R组,TOF<0.9),对两组患者肺功能指标进行比较.结果 124例患者中,NR组78例,R组46例,术后残余肌松发生率为37.1%.NR组和R组患者术前肺功能差异无统计学意义.拔管后10 min,NR组的用力肺活量(FVC)、一秒钟用力呼气容积(FEV1)、最大通气量(MVV)分别可恢复至术前的(65.6±17.7)%、(63.3±18.4)%和(62.2±17.4)%,R组可恢复至术前的(56.1±17.6)%、(52.2±16.4)%和(53.3±15.9)%,NR组恢复程度显著优于R组(P<0.05).拔管后40 min,NR组患者的FVC、FEV1、MVV可恢复至术前的(73.3±16.0)%、(72.3±18.9)%和(72.2±17.2)%,R组可恢复至术前的(66.1±17.9)%、(61.3±17.1)%和(61.8±17.4)%,NR组恢复程度显著优于R组(P<0.05).结论 依据临床征象判断拔管的患者,拔管后残余肌松发生率较高,且拔管后早期呼吸功能明显受损.     

术后残余肌松的危险因素分析

目的 探讨术后麻醉恢复室(PACU)中患者残余肌松的主要危险因素.方法 全麻下择期手术患者208例,常规麻醉诱导和维持.术毕在PACU根据临床拔管指征拔除气管导管.拔管后即刻测定肌力恢复情况.根据四个成串刺激比值(TOF-R)将患者分为非残余肌松组(TOF-R≥0.9,n=147)以及残余肌松组(TOF-R<0.9,n=61).分别对两组患者24个术前变量、15个术中变量和10个术毕变量进行比较.结果 各临床指标的统计分析显示患者的肾病病史、血肌酐(Cr)、血尿素氮(BUN),失血量、术中低温、应用肌松拮抗药等6种指标与术后残余肌松密切相关.结论 肾病病史、Cr、BUN、失血量、术中低温、应用肌松拮抗药是术后发生残余肌松的主要危险因素.     

腹腔镜手术中持续输注与间断静注顺式阿曲库铵维持深度肌松的药效学比较

目的探讨持续输注顺式阿曲库铵维持深度肌松在腹腔镜手术中的有效性和安全性。方法择期行腹腔镜辅助胃肠道肿瘤根治术患者60例,年龄18~65岁,随机分为A、B两组,每组30例。A组使用顺式阿曲库铵0.15 mg/kg诱导插管,并在强直刺激后计数(post tetanic count,PTC)恢复至≥3时以初始速率0.2mg·kg-1·h-1开始泵注,术中维持肌松深度在PTC≤2。B组使用顺式阿曲库铵0.15mg/kg诱导插管,并在每次PTC恢复至≥3时间断追加0.05mg/kg,术中维持肌松深度在PTC≤2。记录肌松药使用总量,肌松药使用时间(A组:诱导至泵注结束时间;B组:诱导到最后一次加药时间),手术时间,手术开始0、1、2h及关腹时肌松满意度(0~10分),恢复指数(T1从25%恢复至75%的时间),TOFr比值恢复至0.7、0.9的时间,以及压舌板试验完成情况,低氧血症、肺不张、肺炎等情况。结果与B组比较,A组平均肌松药使用量明显增加(P0.05);在手术开始0、1、2h时手术医师对肌松满意度A组明显高于B组(P0.05);恢复指数、TOFr比值恢复至0.7的时间和TOFr比值恢复至0.9的时间两组差异无统计学意义。拔管后A组出现低氧血症2例(7.1%),B组出现低氧血症1例(4.2%);不能完成压舌板试验A组3例(10.7%),B组4例(16.7%),两组差异均无统计学意义。术后均未出现肺不张、肺炎。结论持续输注顺式阿曲库铵用于腹腔镜手术维持深度肌松安全有效。相较于间断静注给药,持续输注肌松药使用量较大,肌松满意度高,虽然停药后恢复时间稍长,但对术后肌松残余无明显影响。     

老年患者全麻术后罗库溴铵的残余作用

目的观察老年患者全麻术后罗库溴铵的残余效应(PORC)。方法择期全麻手术患者40例,根据年龄分为中青年组和老年组,每组20例。采用静脉复合全麻,罗库溴铵用量为0.9mg/kg。术中用四个成串刺激(TOF)监测肌松,直至拔管后TOF值(TOFr)≥90%。记录各组TOFr从0恢复到25%(临床时效)、从25%恢复到90%的时间,以及拔管时TOFr<90%(PORC)患者TOFr恢复到90%的时间。监测拔管后及TOFr达90%时的动脉血气。结果老年组罗库溴铵作用时效[(60.70±14.27)minvs.(45.51±7.80)min]及TOFr从25%恢复至90%时间[(46.50±11.56)minvs(34.50±9.56)min]均长于中青年组(P<0.05);老年组PORC发生率高于中青年组(15/20vs12/20),PORC持续时间长于中青年组[(26.00±8.43)minvs(17.20±8.00)min](P<0.05);老年组拔管后CO2蓄积例数多于中青年组(13例vs.6例)(P<0.05)。结论老年患者罗库溴铵的PORC发生率高于中青年患者,应加强围手术期肌松监测,掌握恰当的拔管时机。     

舒更葡糖钠对胸腹腔镜食管癌根治术患者术后肌松恢复的影响

目的探讨舒更葡糖钠对全麻下胸腹腔镜食管癌根治术患者术后肌松恢复的影响。方法选择全麻下行胸腹腔镜食管癌根治术患者96例,男61例,女35例,年龄18~65岁,ASAⅠ或Ⅱ级。采用随机数字表法将患者分为两组:新斯的明联合阿托品组(C组)和舒更葡糖钠组(S组),每组48例。两组麻醉诱导和术中全麻维持方案相同,使用四个成串刺激(TOF)监测肌松。手术结束后,待肌松监测T2出现时,C组静脉注射新斯的明0.05 mg/kg联合阿托品0.02 mg/kg,S组静脉注射舒更葡糖钠2 mg/kg。记录从给予肌松拮抗药到TOF比值(TOFr)恢复至0.9的时间,从给予肌松拮抗药到拔除气管导管的时间(拔管时间)。计算给予肌松拮抗药后5、15、30 min时肌松残余率。记录术后首次排气、排便时间,记录术后恶心呕吐(PONV)等并发症的发生情况。结果与C组比较,S组TOFr恢复至0.9的时间明显缩短[(2.2±0.9)min vs(16.2±3.4)min,P<0.01],拔管时间明显缩短[(12.3±2.0)min vs(33.0±5.1)min,P<0.01],给予肌松拮抗药后5、15 min时S组肌松残余率明显降低(12%vs 100%、0%vs 65%,P<0.01),S组术后首次排气时间明显缩短[(23.4±2.1)h vs(30.5±3.1)h,P<0.01],PONV发生率明显降低[7例(15%)vs 19例(40%),P<0.05]。两组术后首次排便时间差异无统计学意义。结论舒更葡糖钠用于胸腹腔镜食管癌根治术患者,能更快地逆转罗库溴铵作用下的肌松作用,降低肌松残余发生率,促进患者术后胃肠运动的恢复,减少术后并发症的发生,改善术后肌松恢复质量。     

儿童右美托咪定术前滴鼻用药对舒更葡糖钠拮抗罗库溴铵残余肌松的影响

目的探讨儿童右美托咪定术前滴鼻对舒更葡糖钠拮抗罗库溴铵残余肌松的影响。方法选取2020年4月至2020年11月择期行下腹部手术的患儿64例, 美国麻醉医师协会分级Ⅰ、Ⅱ级, 年龄1～12岁。采用随机数字表法将患儿分为实验组和对照组(每组32例), 分别在麻醉诱导前给予右美托咪定1.0 μg/kg或等容量生理盐水滴鼻。术中应用肌松监测仪四个成串刺激(TOF)模式监测肌松。术毕当肌松监测TOF T2再现时, 两组患儿均静脉注射舒更葡糖钠2 mg/kg。记录患儿TOF比值(TOFR)恢复到0.9的时间;记录患儿一般情况、手术时间、术毕体温、拔管时间及麻醉后监测治疗室(PACU)滞留时间;记录肌松拮抗前即刻、拮抗后2 min、拮抗后5 min的脑电双频指数(BIS)、心率、收缩压、舒张压以及苏醒期皮疹、恶心、呕吐、躁动的发生情况。结果两组患儿一般情况、TOFR恢复至0.9的时间、手术时间、术毕体温差异无统计学意义(均P>0.05), 实验组患儿拔管时间和PACU滞留时间较对照组明显较长(均P<0.05)。与对照组比较, 实验组患儿肌松拮抗前即刻、拮抗后2 min BIS较低(均P&...     

老年人术后肌松作用消退与呼吸力学恢复的关系

Kopman等建议以TOF≥90％替代过去的TOF≥70％作为肌松残余作用和呼吸功能恢复的标准。本研究拟观察老年患者术后肌松作用自然消退过程中，肌松监测TOF比值与呼吸力学恢复之间的关系，为老年患者肌松药的合理应用和避免肌松药残余作用提供参考。     

肌松药的术后残余箭毒化作用

新的神经肌肉传递功能完全恢复的全标准是TOF比值≥0.9,TOF值〈0.9可视为有术后残余肌松箭毒化作用（PORC）,在临床工作中,全麻恢复期能观察到有残余肌松阻滞,为了降低PORC的发生率,使患者完全恢复骨骼肌收缩功能和反射活动,以抗胆碱酯酶药作为拮抗剂拮抗残余肌松。但抗胆碱酯酶药有术后恶心,呕吐,心动过缓等副作用,衡量肌松拮抗的利弊,并做出合理的决定,对麻醉医师来说尤为重要。本篇就术后肌松残余阻滞作用及肌松拮抗应用方面的争议作一综述。     

布比卡因硬膜外麻醉对泮库溴铵肌松时效的影响

目的;观察布比卡因硬膜外麻醉对泮库溴铵肌松时效的影响,为临床减少复合全麻用药提供理论依据。方法:40例行上腹部手术患者,随机分为两组。A组选用泮库溴铵肌松全麻。B组选用泮库溴铵肌松全麻加用布比卡因硬膜外麻醉。分别观察两组泮库溴铵肌松时效。结果:A组和B组泮库溴铵肌松起效时间分别为3.7±0.5分和3.5±0.7分(P>0.05)。无反应期分别为35±4.1分和38±2.3分(P<0.01)。25％NMB恢复时间分别为41±6.7分和48±5.6分(P<0.01)。75％NMB恢复时间分别为71±8.1分和89±6.7分(P<0.01)。恢复指数分别为30.1±1.7和31.1±1.6(P>0.05)。结论:布比卡因硬膜外麻醉可使泮库溴铵肌松时效增强。     

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.