右美托咪定预防七氟醚麻醉患儿苏醒期躁动的效果

目的观察右美托咪定预防七氟醚麻醉患儿苏醒期躁动的效果。方法随机将86例行七氟醚麻醉的患儿分为2组,各43例。观察组在麻醉诱导后行右美托咪定液0.5μg/kg静脉泵注,15 min注完。对照组在麻醉诱导后静脉泵注等容量的生理盐水。比较2组注射后5 min(T_1)、苏醒睁眼时(T_2)及拔管后5 min(T_3)患儿的心率(HR)、平均动脉血压(MAP)变化。根据麻醉苏醒期躁动量化评分量表(PAED)比较2组麻醉苏醒期的躁动情况。结果 2组患儿各时点的MAP和HR比较,差异无统计学意义(P0.05);观察组患儿苏醒期躁动发生率及PAED评分均低于对照组,差异有统计学意义(P0.05)。结论麻醉诱导后静脉泵注右美托咪定,可有效预防七氟醚麻醉患儿苏醒期躁动发生情况,而且能维持血流动力学平稳。     

右美托咪定对七氟醚麻醉扁桃体切除术患儿苏醒期躁动的影响

目的观察右美托咪定对七氟醚麻醉扁桃体切除术患儿苏醒期躁动的影响。方法选取2017-01-2018-09间在郑大二附院行七氟醚麻醉扁桃体切除术的40例患儿,随机分为2组,各20例。A组采用七氟醚复合芬太尼全麻。B组在A组基础上采用右美托咪定0.5μg/kg预处理,术中0.2~0.4μg/(kg·h)维持。记录患儿入室后(T0)、气管插管后(T1)、手术开始时(T2)、切扁桃体时(T3)、拔管后(T4)的MAP(平均动脉压)、HR(心率),以及手术时间、麻醉时间、苏醒时间、术后躁动评分。结果 A组T3时的MAP、HR与T0、T1、T2时相比,差异有统计学意义(P<0.05);B组T3时的MAP、HR与T1、T2时刻比较,差异无统计学意义(P>0.05)。2组手术时间、麻醉时间、苏醒时间,差异无统计学意义(P>0.05)。2组苏醒期躁动发生率,差异有统计学意义(P<0.05)。结论右美托咪定预处理可降低七氟醚麻醉扁桃体切除术患儿苏醒期躁动的发生率。     

右美托咪定对预防老年手术患者七氟醚麻醉苏醒期躁动的效果

目的观察右美托咪定对预防老年手术患者七氟醚麻醉苏醒期躁动的效果。方法随机将接受七氟醚麻醉下行择期手术的96老年患者分为2组,各48例。手术结束前10 min,观察组静脉输注右美托咪定1.0μg/kg,对照组静脉输注等容量的生理盐水。输注时间均为10 min。比较2组苏醒期躁动发生率,及拔管时(T_0)和拔管后5 min(T_1)、10 min(T_2)、20 min(T_3)的Ramsay镇静评分。结果观察组患者苏醒期躁动发生低于对照组;各时点镇静评分优于对照组,差异均有统计学意义(P0.05)。结论在老年患者七氟醚麻醉手术结束前静脉输注右美托咪定,可有效降低苏醒期患者的躁动发生率,并可显著改善镇静评分。     

右美托咪啶预防儿童七氟醚麻醉苏醒期躁动效果的观察

目的观察应用右美托咪啶预防儿童七氟醚麻醉苏醒期躁动的效果。方法将56例接受七氟醚麻醉手术的患儿随机分为2组,每组28例。观察组:麻醉诱导后静脉泵注右美托咪定注射液0.5μg/kg(稀释到15 m L),10~20 min注完后开始手术。对照组:麻醉诱导后手术开始前泵注15 m L生理盐水。比较2组患儿右美托咪啶或生理盐水注射前(T0)、注射5 min后(T1)、患儿苏醒睁眼时间点(T2)及拔管5 min后(T3)心率、血压变化和麻醉后的苏醒时间、躁动情况等。结果对照组T2和T3时点的NAP和HR较T0明显升高,差异有统计学意义(P0.05);与对照组比较,观察组T2和T3时间点MAP明显降低,同时T1、T2和T3时间点HR明显降低,差异均有统计学意义(P0.05)。观察组患儿苏醒期躁动发生率低于对照组,苏醒时间长于于对照组,2组比较差异具有统计学意义(P0.05)。结论麻醉诱导后手术开始前应用右美托咪啶,在儿童七氟醚麻醉时能较好维持血流动力学的平稳,降低苏醒期的躁动发生率。     

不同剂量右美托咪啶对腹腔镜卵巢囊肿剥除术患者七氟醚用量的影响

目的 评价不同剂量右美托咪啶对腹腔镜卵巢囊肿剥除术患者七氟醚用量的影响.方法 择期全麻下行腹腔镜卵巢囊肿剥除术患者80例,ASA分级Ⅰ或Ⅱ级,年龄25～50岁,体重指数18～ 25 kg/m2,采用随机数字表法,将患者随机分为4组(n=20):对照组(C组)于切皮前10 min静脉输注生理盐水20 ml;低、中和高剂量右美托咪啶组(DL组、DM组和DH组)于切皮前10 min分别静脉输注右美托咪啶0.3、0.6、0.9 μg/kg,输注时间10 min.吸入七氟醚维持麻醉,术中维持Narcotrend值40～50.于给予右美托咪啶前即刻(T1)、切皮(T2)、气腹即刻(T3)、气腹后10 min(T4)和术毕(T5)时测定呼气末七氟醚浓度(ETsev),记录单位时间七氟醚用量、苏醒时间和拔除气管导管时间,拔除气管导管后10 min观察躁动发生情况,于入室静卧10 min(T0)、T3～5时采集外周静脉血样,用快速血糖分析仪测定血糖,用放射免疫法测定血清皮质醇浓度.结果 C组、DL组、DM组和DH组单位时间七氟醚用量、T2～5时ETsev、T3～5时血糖和皮质醇浓度依次降低(P＜0.05);与C组比较,DL组、DM组和DH组拔除气管导管时间、苏醒时间缩短,躁动发生率降低(P＜0.05).结论 右美托咪啶可呈剂量依赖性地减少腹腔镜卵巢囊肿剥除术患者七氟醚用量.     

右美托咪定复合氟哌利多对七氟醚全麻胸科手术老年患者苏醒期躁动的影响

目的评价右美托咪定复合氟哌利多治疗七氟醚全麻胸科手术老年患者苏醒期躁动的有效性及安全性。方法选取七氟醚全麻下普胸外科术后严重躁动老年患者60例,男48例,女12例,年龄66～75岁,ASAⅡ或Ⅲ级,按照随机数字表分为三组:氟哌利多组(F组)、右美托咪定组(D组)和右美托咪定复合氟哌利多组(DF组)。被诊断为苏醒期严重躁动后,F组静脉推注氟哌利多0.06 mg/kg;D组右美托咪定1μg/kg泵注10 min,继以0.2μg·kg~(-1)·h~(-1)维持泵注1 h;DF组静脉推注氟哌利多0.03 mg/kg,同时给予右美托咪定0.5μg/kg泵注10 min,继以0.2μg·kg~(-1)·h~(-1)维持泵注1 h。观察并记录躁动评分、Ramsay镇静评分、PaCO_2变化以及恶心、呕吐等不良反应的发生情况。结果给药后5、10、15、20 min DF组躁动评分明显低于D组(P0.05);给药后60、90、120 min DF组躁动评分明显低于F组(P0.05)。给药后60、120 min三组PaCO_2差异无统计学意义。DF组和D组过度镇静比例明显低于F组(P0.05)。三组恶心、呕吐、心动过缓、高血压、低血压发生率差异无统计学意义。结论右美托咪定复合氟哌利多用于老年患者七氟醚全身麻醉苏醒期躁动的治疗效果确切,安全性好,可以规避右美托咪定不能快速推注同时避免氟哌利多导致过度镇静的缺点。     

右美托咪定预防小儿唇腭裂手术术后苏醒期躁动的临床研究

目的评价右美托咪定对唇腭裂修复术患儿苏醒期躁动的影响。方法选取本院2015年6月至2018年6月于全身麻醉下行唇腭裂修复术的患儿共计220例。纳入患儿采用计算机随机软件随机分为右美托咪定组(Dexmedetomidine group,D组)和生理盐水组(Control group,C组),每组患者各110例。D组患者于麻醉诱导后泵注右美托咪定0.5μg/kg/h。C组患者泵注等量生理盐水。记录两组患儿麻醉诱导前(T0)、麻醉诱导后即刻(T1)、手术开始后15分钟(T2)、手术结束即刻(T3)的平均动脉压(MAP)和心率(HR)。记录患儿术中低血压、心动过缓发生人数及拔管时间。使用PAED评分评价患儿苏醒期躁动情况。结果两组患者各时点MAP、HR差异均无统计学意义(P0.05)。两组患者术中低血压、心动过缓发生率差异均无统计学意义(P0.05)。C组患者苏醒期躁动发生率显著高于D组患者,差异有统计学意义(P0.05);C组患者苏醒期躁动评分亦显著高于D组患者,差异有统计学意义(P0.05)。D组患者拔管时间显著低于C组患者,差异有统计学意义(P0.05);D组患者切口出血发生率显著低于C组患者,差异有统计学意义(P0.05)。结论术中泵注右美托咪定显著降低小儿唇腭裂手术患儿苏醒期躁动发生率,并且对术中血流动力学无明显影响,值得在临床中推广使用。     

右美托咪定对七氟醚麻醉诱导时患者躁动及应激反应的影响

近年来七氟醚在临床应用逐渐增多,但麻醉诱导期间多数患者会出现兴奋,表现为躁动,影响麻醉诱导质量.右美托咪定是选择性的α2受体激动药,具有镇静、镇痛作用,对呼吸抑制轻.研究证实右美托咪定可以减少小儿七氟醚麻醉气管拔管期间的躁动[1].但右美托咪定能否减少七氟醚麻醉诱导期间的躁动及提高七氟醚吸入麻醉诱导的质量尚无定论.本研究拟观察预先输注右美托咪定对七氟醚麻醉诱导期间患者躁动及应激反应的影响.     

不同药物预防七氟醚术后躁动的研究

目的观察右美托咪定、芬太尼和氯胺酮预防七氟醚术后躁动的效果。方法斜视矫正术患儿120例,年龄3～10岁,均采用七氟醚麻醉诱导和维持。患儿随机均分为四组,在手术结束前10min分别给予右美托咪定0.3μg/kg(D组)、芬太尼1μg/kg(F组)、氯胺酮0.5mg/kg(K组)或生理盐水(C组)。观察并记录给药即刻、5min、10min的呼吸循环变化。观察术后躁动发生率、手术时间、苏醒时间以及离开麻醉后恢复室时间。结果四组患儿呼吸循环变化差异无统计学意义。D组和F组苏醒时间明显长于C组(P<0.05),但明显短于K组(P<0.05)。C组术后躁动发生率明显高于其他三组(P<0.01),而D、F和K组组间差异无统计学意义。K组离开麻醉后恢复室时间明显长于其他三组(P<0.05)。结论右美托咪定、芬太尼、氯胺酮均能明显降低七氟醚术后躁动的发生率。     

右美托咪定用于小儿唇腭裂手术麻醉的临床观察

目的 探讨右美托咪定用于小儿唇腭裂手术麻醉中的临床效果,为小儿唇腭裂手术麻醉安全用药提供依据.方法 先天性唇腭裂修复术患儿40例,随机分为右美托咪定组(D组)和对照组(C组).两组患儿均采用紧闭面罩8％七氟烷吸入麻醉诱导,D组同时静脉泵注右美托咪定1 μg/kg,C组给予同等容量生理盐水,均于10 min给完.两组患儿均采用气管插管静吸复合全身麻醉方法,术中维持C组采用异丙酚-七氟烷复合麻醉;D组采用右美托咪定-异丙酚-七氟烷复合麻醉,观察并记录不同时点患儿心率、平均动脉压、脉搏血氧饱和度、呼气末二氧化碳分压并进行躁动评分,记录两组呼吸抑制及躁动发生率.结果 两组患儿的手术时间、麻醉时间及苏醒时间差异无统计学意义(P＞0.05).D组患儿在气管插管即刻(T2)、术中20 min(T3)、术毕(T4)及拔管(T5)时平均动脉压和心率均明显低于C组(P＜0.05).D组躁动发生率为11.1％,明显低于C组36.4％(P＜0.05).D组无一例发生呼吸抑制.结论 右美托咪定用于小儿唇腭裂修复术安全有效,术中血流动力学平稳,术后恢复期安静、舒适,能够减少围术期并发症的发生.     

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 comparison of the inhibitory effects of four volatile anaesthetics on the metabolism of chlorzoxazone, a substrate for CYP2E1, in rabbits

Background: Halothane inhibits in vitro and in vivo activity of cytochrome P-450 (CYP) 2E1. There are several fluorinated volatile anaesthetics besides halothane, and most of them are defluorinated by CYP2E1. It is unclear whether other fluorinated anaesthetics inhibit the in vivo activity of CYP2E1.
Methods: We compared the inhibitory effects of therapeutic concentrations of four inhalational anaesthetics, halothane, enflurane, isoflurane, and sevoflurane, on chlorzoxazone metabolism in rabbits receiving artificial ventilation.
Results: All four inhalational anaesthetics decreased arterial blood pressure and increased plasma chlorzoxazone concentration. However, no significant differences in the plasma chlorzoxazone concentration were found between the four anaesthetics. The estimated chlorzoxazone clearance increased after beginning inhalation with all four agents, but no significant difference in clearance was noted between agents.
Conclusions: At therapeutic concentrations, the in vivo inhibitory effect on chlorzoxazone metabolism was similar for all four inhalational anaesthetics examined, even though their chemical characteristics and extent of hepatic metabolism differ considerably.     

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.     

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.