急性等容血液稀释在外伤性颅内血肿患者的应用

目的探讨对外伤性颅内血肿患者实施急性等容血液稀释的操作方法及有效性。方法56例外伤性颅内血肿患者随机分为两组，对照组（C组，n=28）、血液稀释组（H组，n=28）。H组于术前即刻行等容血液稀释，目标红细胞压积（Hct）为30％。于术前（To）、手术开始后2小时（T1）分别抽取静脉血测血液流变学指标。结果To时，两组血液流变学指标相似，差异无统计学意义。T-时C组明显升高，两组间相比差异有统计学意义（P〈0．05）。结论颅脑外伤后，血液流变学指标升高，急性等容血液稀释（Hct=30％）可以降低血液黏度，改善脑挫伤后脑组织氧代谢紊乱，发挥一定的脑保护作用。     

急性中度等容血液稀释对小肠氧输送和氧耗的影响

目的 探讨术中急性中度等容血液稀释对小肠血流灌注和氧输送,氧耗的影响。方法 １５只雄性家猫,用多聚明胶将血红蛋白稀释至８４ｇ／Ｌ在血液稀释前后分别测定肠系膜上动脉血流量,肠系膜上静脉血乳酸量,作肠系膜上动脉,静脉血气分析,分析计算血液稀释前后的小肠氧输送量,氧耗量和氧摄取率。结果 血液稀释后肠系膜上动脉血流量及小肠氧耗量较称释前有显著意义的升高（Ｐ〈０．０５）,小肠氧输送量和小肠氧摄取率无显著性变     

非体外循环冠脉搭桥术中的血液动力学和氧代谢的变化

目的 观察非体外循环冠脉搭桥术（OPCABG）中的血液动力学及氧代谢参数的变化,并分析其麻醉处理特点。方法 择期行OPCABG手术患者87例。均采用芬太尼、异氟醚、笑气、异丙酚行静吸复合全麻。采用肺动脉漂浮导管和连续心排血量方法测定血液动力学,分别在手术前（T1）、锯胸骨后（T2）、吻合血管桥前（T3）、吻合前降支时（T4）、吻合后降支或右冠状动脉时（T5）、吻合左回旋支或对角支时（T6）、血管吻合完成并恢复心脏自然位置（T7）、闭合胸骨前（T8）及手术结束时（T9）等时间点测定及计算血液动力学参数;分别在上述的T1、T2、T3、吻合开始后1.5h（T4-）、及T9的5个时间点检测动脉、混合静脉血气,并进一步计算氧代谢参数包括氧供8指数（DO2I）、氧耗指数（VO2I）、氧摄取率（ERO2）等。记录术后拔气管导管时间及ICU停留时间。结果 与T1相比,T2与T3的HR、CO、CI、PAWP、MPAP、LVWI、RVWI、RVSWI、DO2I、SO2、PO2均显著增加（P〈0.05或0.01）,而VO2I与ERO2明显降低（P〈0.05或0.01）,但SI、LVSWI和PVRI无显著性改变（P〉0.05）。在吻合靶血管过程中（T4、T5、T6）,CI、SI、MAP、LVWI、LVSWI、RVWI、RVSWI、DO2I、SO2、PO2、VO2I等不同程度地降低（P〈0.05或0.01）,而HR、RAP、MPAP、PAWP和ERO2则显著增高（P〈0.05或0.01）。血管吻合完毕后至术毕（T7、T8、T9）各项参数均逐渐恢复至T1水平或明显改善。术后平均6.5±2.3h拔除气管导管,ICU停留时间为2.6±1.4d。结论 在可靠的血液动力学监测和合理使用血管活性药物情况下,OPCABG病人可安全地渡过吻合靶血管时的循环波动期,恢复机体的氧供需平衡。     

丙泊酚对血液稀释时组织氧代谢的影响

目的　观察丙泊酚对急性等容血液稀释 (ANH)时组织氧代谢的影响。方法　择期手术病人 2 4例 ,随机分为三组 ,每组 8例 :A组为ANH组 ,P4组为ANH +丙泊酚 4mg组 ,P8组为ANH +丙泊酚 8mg组 ,三组病人ANH后Hct降至 2 7 1 %。漂浮导管放置完成后稳定 2 0min(T1 ) ,P4和P8组给予丙泊酚负荷剂量 2mg/kg后 ,分别给与丙泊酚维持剂量 (P4组 :4mg·kg-1 ·h-1 ;P8组 :8mg·kg-1 ·h-1 )。稳定 1 0min后 (T2 ) ,开始进行血液稀释。同时于T1 、T2 、T3 (血液稀释完成后1 5min)分别监测血液动力学指标和混合静脉血氧饱和度 (S vO2 ) ,血乳酸值 (T1 、T3 )。结果　三组病人ANH后均可见心排血量 (CO) ,每搏量 (SV)升高非常显著 ,外周血管阻力 (SVR)和动脉血氧含量(CaO2 )下降非常显著 ,氧供给 ( DO2 )、S vO2 及血乳酸改变不明显 ;P4和P8组SVR下降显著 ,MAP下降非常显著 ,组间比较无差异。结论　本实验剂量范围内 ,丙泊酚与ANH合用时 ,组织氧代谢水平未受明显影响     

急性等容血液稀释对心脏手术病人血液动力学,氧供,氧耗和脑 …

目的：了解急性等容血液稀释对心脏直视手术病人可能产生的影响，以指导其在体外循环中的应用。方法：观察１６例ＡＳＡⅡ－Ⅲ级择期心脏直视手术病人，接受体外循环前实施２急性等容血稀释，监测病人血液动力学、氧供、氧耗、乳酸浓度等及颈内静脑海氧饱和度等指标的变化。结果：血液稀释后病人的心指数增加了１５．５％，氧供和氧耗无显著变化，氧摄取经无显著变化。颈内静脉血氧饱和度，动脉血乳酸浓度及颈内静脉血乳酸浓度无明显     

6%羟乙基淀粉急性高容性血液稀释在儿科病人的应用

目的研究6%羟乙基淀粉用于婴幼儿和儿童对于血液流变学、血小板功能和凝血功能等的影响.方法20例手术病人按年龄分为婴幼儿组（Ⅰ组,〈3岁,n=9）和儿童组（C组,3～12岁,n=11）,术前用6%羟乙基淀粉10 ml/kg行高容性血液稀释,输液前后分别抽取颈静脉血测定血液流变学、血小板功能和凝血功能,比较各组输液前后以及两组之间的变化.结果两组病人输液后全血低切、中切和高切粘度均显著下降（P〈0.01）,但血浆粘度无显著改变;两组病人血细胞比容、纤维蛋白原在输液后均显著下降（P〈0.01）;红细胞聚集指数、刚性指数、变形指数在输液前后无显著变化;与输液前比较,输液后红细胞电泳指数显著增加（P〈0.05）;两组病人血沉、血小板计数和血小板聚集率、部分凝血活酶时间在输液后无显著变化;C组病人输液后凝血酶原时间显著延长.两组间各项指标相同时点比较虽有一定变化,但无显著性差异（P＞0.05）.结论6%羟乙基淀粉用于1～12岁儿科病人进行术前急性高容性血液稀释,能改善血液流变性,稳定血液动力学,但对凝血功能无影响,不增加出血倾向.     

急性高容量血液稀释联合控制性降压对血液动力学及氧代谢的影响

目的 观察术中急性高容量血液稀释(AHH)联合硝普钠或尼卡地平控制性降压(CH)时血液动力学、氧代谢的变化,评价其可行性。方法 全麻手术病人30例,随机分为两组,每组15例。组Ⅰ AHH联合硝普钠CH;组ⅡAHH联合尼卡地平CH。手术开始后在30 min内输入15 ml·kg-1中分子羟乙基淀粉溶液。同时,以MAP基础值的70％为目标,行CH。分别于麻醉诱导后即AHH联合CH前(基础值,T0)、AHH联合CH后30min(T1)、60min(T2)记录血液动力学指标,同时采集中心静脉血、股动脉血测定血气及动脉血乳酸浓度(LAC),计算氧供(DO2)、氧耗(VO2)和氧摄取率(ERO2)。结果 与T0比较:两组Hb、Hct、MAP、SVR下降,HR增快(P<0.01),VO2、LAC无明显变化(P>0.05);组Ⅰ CO、CI、CVP均无明显变化(P>0.05),组Ⅱ上升(P<0.01);组Ⅰ ScvO2、DO2,显著性降低(P<0.01),组Ⅱ无明显变化(P>0.05);组Ⅰ ERO2增加(P<0.01),组Ⅱ无明显变化(P>0.05)。与组Ⅰ比较,组ⅡT0时各指标差异无显著性(P>0.05),T1、T2时CO、CI、CVP、ScvO2、DO2升高,而HR、SvR、ERO2降低(P<0.01)。结论 急性高容量血液稀释联合硝普钠或尼卡地平CH,能维持机体血液动力学和氧代谢的相对稳定,硝普钠减低容量负荷作用强于尼卡地平,而尼卡地平对机体氧代谢影响更小。     

脊柱内固定术患者自体血液回收-回输后氧代谢的变化

目的评价自体血液回收-回输对脊柱内固定术患者氧代谢的影响。方法40例行脊柱内固定手术病人随机分为两组:自体血液回收-回输组(A组,n=20);等量异体血液输入组(B组,n=20)。分别在麻醉前、输入自体血或等量异体血后、术毕时及术后1d,采集血液动力学和血气分析数据,计算心脏指数(CI)、氧供(DO2)、氧耗(VO2)、氧摄取率(ERO2),并测定血液乳酸(LA)浓度。结果与麻醉前相比,两组输血后、术毕时DO2升高(P<0.05),其他指标各时点差异无统计学意义(P>0.05)。与B组比较,术毕时A组ERO2降低(P<0.05),在各时点DO2、VO2差异无统计学意义,LA差异也无统计学意义,且数值均在正常范围内。结论自体血液回收技术在一定的出血范围之内,可以满足脊柱内固定术患者机体氧代谢的需求。     

急性等容血液稀释对靶控输注异丙酚血药浓度及系统性能的影响

目的探讨急性等容血液稀释对靶控输注（TCI）异丙酚血药浓度及系统性能的影响。方法择期骨科手术患者35例,ASAⅠ级或Ⅱ级,随机分为稀释组（n=17）和对照组（n=18）。稀释组在麻醉诱导插管后,实施急性等容血液稀释,达稀释目标（Hct 0．25～0．27）10 min后,TCI异丙酚;对照组不行血液稀释,直接TCI异丙酚。设定血浆靶浓度3μg/ml,TCI异丙酚60 min,间断采血180 min,用气相色谱-质谱法测定异丙酚血药浓度并评价TCI系统的性能。结果稀释组的实测血药浓度低于对照组40．8％～73．1％（P＜0．05）。稀释组TCI系统偏离度、精确度和摆动度分别为-8．83％、22．98％和22．12％。结论急性等容血液稀释降低了异丙酚TCI的实测血药浓度,优化了TCI的系统性能。     

适度急性等容血液稀释改变冠状动脉疾病患者的心肌功能

背景通常冠状动脉手术患者都能较好地耐受中度血液稀释,但这一情况并不适用于心肌氧需增加的患者。我们假设,在此类心率增快的患者中,血液稀释将导致心肌功能损害。方法根据房室起搏率将40例冠状动脉手术患者随机分为2组（n=20）,房室起搏率70bpm（组70）和90bpm（组90）。按固定心率起搏下,在心肺转流术前实施血液稀释。通过肺动脉、PiCCO管和左室压力导管采集数据。所有的数据均取自等容稀释前后血流动力学稳定阶段。结果组70的血液稀释将血球压积从40％±2％降至30％±1％,组90的血液稀释将血球压积从39％±4％降到30％±2％,结果2组患者的体循环血管阻力均下降,而舒张末容积增加。组70患者伴有每搏量的增加,组90没有。组90在血液稀释后,最大压力上升速率下降[从856±93mmHg／s下降到716±80mmHg／s（P〈0．01）],而组70的值保持不变（血液稀释前843±86mmHg／s,稀释后832±79mmHg／s）。结论本研究结果显示,中度血液稀释的患者,心率增加可能导致心肌功能的抑制。     

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.