Lactated Ringer's solution versus hydroxyethyl starch for volume replacement in autologous blood donors with cardiovascular disease: a controlled, randomized trial

BACKGROUND AND OBJECTIVES

The study was designed to evaluate whether volume replacement following blood donation can prevent arterial hypotension in autologous blood donors with cardiovascular disease.

MATERIALS AND METHODS

One hundred nineteen autologous blood donors with known cardiovascular disease were randomly allocated to receive, following withdrawal of 500 ml of blood, either no infusion (control group) or a 25 ml/min intravenous infusion of either 1,500 ml of lactated Ringer's solution (LRS) or 500 ml of 6% hydroxyethyl starch (HES). Starting before phlebotomy, arterial blood pressure was measured oscillometrically every 5 min until 90 min after donation.

RESULTS

Group means showed little difference between the groups in blood pressure throughout the monitoring period. The proportion of patients who at least once had a > or = 20% decrease from baseline in systolic blood pressure was 3-5 times greater in the control group than in the LRS and the HES group (50 vs. 10 and 15%, respectively; p < 0.001 on chi 2 analysis for a 2 x 3 table). Systolic hypertensive episodes (> or = 20% increase over baseline) were observed more frequently in the LRS group than in the control and the HES group (41 vs. 10 and 18%, respectively; p = 0.003).

CONCLUSION

Both LRS and HES, administered at a volume ratio to blood loss of 3:1 and 1:1, respectively, significantly reduced the incidence of systolic hypotensive episodes in autologous blood donors with cardiovascular disease. LRS at a 3:1 volume ratio to blood loss was associated with a high rate of systolic hypertension.

Comparison of intubating conditions after rapacuronium (Org 9487) and succinylcholine following rapid sequence induction in adult patients

We have assessed intubating conditions provided by rapacuronium (Org 9487) and succinylcholine after rapid sequence induction of anaesthesia in adult patients undergoing elective surgery. We studied 335 patients, ASA I and II, in five centres. Two hundred and thirty-four subjects with normal body weight and 101 obese subjects were allocated randomly to one of four treatment groups differing in the neuromuscular blocking drug administered (rapacuronium 1.5 mg kg-1 or succinylcholine 1 mg kg-1) and in the technique used for induction of anaesthesia (fentanyl 2-3 micrograms kg-1 with thiopental 3-6 mg kg-1 or alfentanil 20 micrograms kg-1 with propofol 1.5-2 mg kg-1). Intubation was started at 50 s by an anaesthetist blinded to the drugs used. Intubating conditions were clinically acceptable (excellent or good) in 89.4% of patients after rapacuronium and in 97.4% after succinylcholine (P = 0.004), the estimated difference being 8.1% (95% confidence interval (CI) 2.0-14.1%). Neither anaesthetic technique nor subject group had an influence on intubating conditions. After intubation, the maximum increase in heart rate averaged 23.1 (SD 25.4%) and 9.4 (26.1%) after rapacuronium and succinylcholine, respectively (P < 0.001). Pulmonary side effects (bronchospasm and increased airway pressure) were observed in 10.7% (95% CI 5.8-17%) and 4.1% (95% CI 1.3-8.8%) of patients given rapacuronium and succinylcholine, respectively (P = 0.021). We conclude that after rapid sequence induction of anaesthesia in adults, clinically acceptable intubating conditions were achieved less frequently after rapacuronium 1.5 mg kg-1 than after succinylcholine.

[The clinical pharmacology of cisatracurium]

Cisatracurium (51W89) is one of the ten stereoisomers of atracurium, accounting for about 15% of the racemate. The ED95 of cisatracurium was determined to be about 50 micrograms/kg (cation, molecular weight 929), while the ED95 of atracurium (besylate salt, molecular weight 1245) was 250 micrograms/kg. Thus, on a molar basis in adult patients, cisatracurium is about 3.5 times as potent as the racemic atracurium mixture. We compared atracurium with cisatracurium in healthy adult patients and found an almost identical pharmacodynamic profile. In children, an ED95 of about 40 micrograms/kg was determined, while a 1-min-longer onset of cisatracurium was found in geriatric than in young adult patients. The presence of chronic renal failure did not prolong the duration of action of cisatracurium. The recovery of neuromuscular transmission from a cisatracurium infusion of up to 145 h was investigated in intensive care unit patients. Their time from the end of infusion to a train-of-four ratio > 0.7 (68 +/- 18 min) was on average only some 70% longer than after an infusion of cisatracurium for 2 h in normal surgical patients. In another study, no signs of histamine release nor any clinically relevant cardiovascular effects of cisatracurium were found in doses up to eight times ED95.

[The clinical pharmacology of mivacurium]

Mivacurium is a short-acting, nondepolarising muscle relaxant of the benzylisoquinoline type that undergoes rapid breakdown by plasma cholinesterase. After 2.5 times the ED95 (0.2 mg/kg), tracheal intubation can be accomplished within 2-3 min following injection. The ensuing DUR 25% (i.e., time from injection to 25% recovery of control twitch tension) is three times as long as with succinylcholine. The principal side effects of mivacurium are facial flushing and a transient fall in blood pressure due to moderate histamine release following doses 3-4 times the ED95. In patients with end-stage liver or renal disease as well as those with atypical plasma cholinesterase, the duration of action of mivacurium is prolonged.

[Esters and stereoisomers]

This review discusses concepts of isomers, stereoisomers, chirality, and enantiomers as applied to drugs used in anaesthesia. The inhalational anaesthetics enflurane and isoflurane are examples of stereoisomers. A chiral centre is formed when a carbon or quaternary nitrogen atom is connected to four different atoms. A molecule with one chiral centre is then present in one of two possible configurations termed enantiomers. A racemate is a mixture of both enantiomers in equal proportions. Many of the drugs used in anaesthesia are racemic mixtures (the inhalation anaesthetics, local anaesthetics, ketamine, and others). The shape of the atracurium molecule is comparable to that of a dumb-bell:the two isoquinoline groups representing the two bulky ends connected by an aliphatic chain. In each isoquinoline group there are two chiral centres, one formed by a carbon and the other by a quaternary nitrogen atom. From a geometric point of view, the connections from the carbon atom to a substituted benzene ring and from the quaternary nitrogen to the aliphatic chain may point in the same direction (cis configuration) or in opposite directions (trans configuration). The two isoquinoline groups in atracurium are paired in three geometric configurations: cis-cis, trans-trans, or cis-trans. However, the two chiral centres allow each isoquinoline group to exist in one of four stereoisometric configurations. In the symmetrical atracurium molecule, the number of possible stereoisomers is limited to ten. Among these, 1 R-cis, 1'R-cis atracurium was isolated and its pharmacologic properties studied. This isomer, named cis-atracurium, offers clinical advantages over the atracurium mixture, principally due to the lack of histamine-releasing propensity and the higher neuromuscular blocking potency. The ester groups appear in one of two steric configurations true and reverse esters. In the true esters, oxygen is positioned between the nitrogen atom and the carbonyl group, while in the reverse esters in its positioned on the other side of the carbonyl group. True esters, suxamethonium and mivacurium, are hydrolysed by the enzyme plasma cholinesterase (butyrylcholinesterase), albeit at different rates. The more rapid degradation of suxamethonium is responsible for its fast onset and short duration of action in comparison with mivacurium. The reverse esters, atracurium, cisatracurium, and remifentanil, are hydrolysed by nonspecific esterases in plasma (carboxyesterases). Remifentanil is hydrolysed rapidly; the degradation leads to its inactivation and short duration of action. Cis-atracurium is preferentially degraded and inactivated by a process known as Hofmann elimination. In a second step, one of the degradation products, the monoester acrylate, is hydrolysed by a nonspecific esterase.

Onset of the neuromuscular block simulated in an anatomical model

AIMS

The aim of this study was to develop a pharmacodynamic model for nondepolarizing muscle relaxants (neuromuscular blocking agents, NMBAs) based on anatomical, physiological, and pharmacological considerations and analyse whether the time to onset of the submaximal neuromuscular block (NMB) depends on the affinities of the NMBAs for the postsynaptic receptors or on the pharmacokinetic properties of the NMBAs.

METHODS

A quantitative description of the development of neuromuscular block was achieved by formulating a pharmacodynamic model based on anatomical, physiological and pharmacological considerations. The principal characteristics of the model are: (1) Diffusion of the NMBAs out of the capillaries into the interstitial space of muscle and from there into the synaptic space of the motor end plates (2) Receptor concentration in the synaptic space of 300 microM and the total amount of receptors in 100 g muscle of between 1.43 x (10(-11) to 10(-10) mol. (3) Interaction of NMBAs with the receptors defined by the association (k(assoc) = 4 x 10(8) min-1 x M-1) and dissociation (k(dissoc) one of 4, 40, or 400 min-1) rate constants.

RESULTS

The simulations demonstrated that different affinities of the NMBAs for the postsynaptic receptors (defined by k(assoc)/k(dissoc)) do not influence the onset of the submaximal NMB. On the other hand, the time to the peak submaximal NMB is dependent on the pharmacokinetic properties of the drugs: Those NMBAs that leave plasma rapidly produce the block faster but the fraction of the dose that contributes to the block is small. This fraction is larger for those NMBAs that produce NMB later and, hence, these NMBAs require smaller equieffective doses.

CONCLUSIONS

We conclude that those muscle relaxants that produce neuromuscular block rapidly require larger equieffective doses due to their more rapid initial disappearance from plasma.

[Muscle relaxants. New substances and neuromuscular monitoring]

INTRODUCTION

Recent developments in both the quantitative evaluation of neuromuscular blockade and new muscle relaxants are reviewed. With respect to nerve stimulation, neuromuscular recording, and definition of parameters, the results of the 1994 Copenhagen International Consensus Conference are highlighted. Future clinical studies should adhere to these standards.

MUSCLE RELAXANTS

Rocuronium, cisatracurium, and mivacurium are new muscle relaxants that were released for clinical use in 1995/1996. Of these, rocuronium has the shortest time of onset, whereas its recovery characteristics closely resemble those of vecuronium. Rocuronium is five times less potent than vecuronium. Twice the ED95 of rocuronium provides good or excellent intubating conditions within 60 to 90 s. Slight vagolytic effects were reported following injection of 0.6 mg/kg rocuronium, while histamine release was not observed. Cisatracurium is one of the ten steroisomers of atracurium. It is five times as potent as the chiral mixture while having a similar pharmacodynamic and -kinetic profile. Up to eight times the ED95 did not cause significant histamine release or clinically relevant cardiovascular effects. Mivacurium is a short-acting nondepolarizing benzylisoquinoline muscle relaxant that undergoes rapid break-down by plasma cholinesterase (PChE). Its duration of action is about one-half as long as that of equipotent doses of atracurium and vecuronium and three times as long as succinylcholine. Mivacurium has a moderate histamine-releasing potential. In patients with atypical or reduced PChE activity, the duration of action of mivacurium is prolonged.

A comparison of cisatracurium and atracurium: onset of neuromuscular block after bolus injection and recovery after subsequent infusion

Cisatracurium is a new nondepolarizing muscle relaxant. In patients randomized to receive either cisatracurium (n = 40) or atracurium (n = 20) we compared the time course of neuromuscular block. The initial bolus dose of cisatracurium was 0.1 mg/kg, that of atracurium 0.5 mg/kg. Neuromuscular block, maintained with an infusion of either drug, was reversed with neostigmine 45 micrograms/kg and atropine 20 micrograms/kg in one half of the patients. Neuromuscular transmission was assessed by recording the mechanical twitch response to train-of-four nerve stimulation. Onset times were 3.1 +/- 1.0 min with cisatracurium and 2.3 +/- 1.1 min with atracurium (P = 0.008). The infusion rates for a 95% +/- 4% neuromuscular block were 1.5 +/- 0.4 micrograms.kg-1.min-1 for cisatracurium and 6.6 +/- 1.7 micrograms.kg-1.min-1 for atracurium, 3.3 times those of cisatracurium when referenced to the active cations. After the infusion, the spontaneous recovery intervals 25%-75% of 18 +/- 11 min and 18 +/- 8 min for cisatracurium and atracurium (P = 0.896) were shortened to 5 +/- 2 min and 4 +/- 3 min (P = 0.921) after neostigmine. While attributing different onset times also to differences in the initial doses, we conclude that time profiles for neuromuscular block of both muscle relaxants, when given in equipotent doses, are not different.

Mivacurium chloride--a comparative profile

Mivacurium is a new nondepolarizing muscle relaxant of the benzylisoquinoline type. Its short duration of action is due to rapid breakdown by plasma cholinesterase. The dose of mivacurium which produces 95% inhibition of twitch response (ED95) is between 60 and 80 micrograms/kg. Thus, mivacurium is 0.8 times and four times as potent as vecuronium and atracurium, respectively. With 2-3 x ED95, tracheal intubation can be accomplished within 2.5 min of intravenous injection. The ensuing DUR25% (time from injection to 25% recovery of control twitch tension) is twice as long as with suxamethonium and about half as long as with equipotent doses of atracurium or vecuronium. For muscle relaxation during long surgical procedures, mivacurium has been used as a continuous infusion. The average 6-min recovery index after infusion of mivacurium is particularly favourable for flexible control of muscle paralysis, whereas the recovery indices after infusion of atracurium or vecuronium are 15-30 min. In conclusion, mivacurium will close the pharmacodynamic gap between suxamethonium and the nondepolarizing muscle relaxants of intermediate duration of action. It will probably also be a suitable alternative to suxamethonium in elective cases.

[Modern muscle relaxants and their clinical application]

Various new muscle relaxants are available: atracurium, rocuronium and vecuronium all have an intermediate duration of action, whereas doxacurium and pipecuronium are long-acting and mivacurium is a short-acting nondepolarizing muscle relaxant. The duration of action of atracurium and mivacurium is determined by their degradation, which makes them unique among the nondepolarizing muscle relaxants in this respect. The time of onset is shortest with rocuronium, while vecuronium is probably the muscle relaxant with the fewest undesirable side-effects. In clinical practice, muscle relaxants of short and intermediate duration of action should be preferred, since such agents carry the least risk of residual neuromuscular block postoperatively. Because recovery from them is slow, long-acting agents should preferentially be used only when postoperative mechanical ventilation is intended. The use of a peripheral nerve stimulator is the only reliable guide to appropriate administration of muscle relaxants.

Dose-response relationship of rocuronium bromide during intravenous anaesthesia

The dose-response relationship and time course of neuromuscular block following bolus injections of rocuronium was determined in four groups of nine patients each under nitrous oxide-narcotic anaesthesia. Each patient received a total of 800 micrograms kg-1 rocuronium in two divided doses, i.e. 120 and 680, 200 and 600, 250 and 550, or 300 and 500 micrograms kg-1. The respective second dose was injected when, following the first dose, the evoked twitch tension had recovered to 95% of its control value. The mean ED50 and ED95 values, calculated from the first doses, were 103 and 271 micrograms kg-1, respectively. The DUR25 ranged between 11 +/- 4 (200 micrograms kg-1) to 14 +/- 3 min (300 micrograms kg-1) following the first and from 30 +/- 6 (500 micrograms kg-1) to 43 +/- 11 min (680 micrograms kg-1) following the second doses. The recovery index following the second doses varied between 14 +/- 5 (500 micrograms kg-1) and 24 +/- 20 min (600 micrograms kg-1), more than twice as long as following the first doses. We conclude that rocuronium is a muscle relaxant of low potency with an intermediate duration of action.

Variability of pipecuronium neuromuscular blockade

The dose-response relationship and the variability of the time variables in pipercuronium neuromuscular blockade were studied in 29 patients (ASA physical status 3) during halothane anaesthesia. The ED95 (twitch tension) was determined in 9 patients using the cumulative dose response technique. Another 20 patients received the resulting ED95 as a single bolus. The mean ED95 was 35 micrograms.kg-1 (95% confidence interval: 29-41 micrograms.kg-1). Following bolus injection of 1.ED95, an 80-100% twitch depression was achieved within 4.6 +/- 1.3 min (mean +/- s.d.). The duration from end of injection of pipecuronium to 25% twitch recovery, the time from 25% to 75% twitch recovery, and the time from 25% twitch recovery to the train-of-four ratio (TOF) returning to 0.7 was 35 +/- 14, 37 +/- 26, and 63 +/- 27 min, respectively. The time from end of injection to TOF = 0.7 varied within a 2-h range (54-160 min). Thus, the time variables in pipecuronium neuromuscular blockade were as poorly predictable as those reported in the literature on pancuronium, alcuronium and doxacurium.

Atracurium and Vecuronium

The purpose of this study was to compare the characteristics of recovery from neuromuscular blockade after either atracurium or vecuronium given by intravenous infusion or by repeated injection. Four groups of 10 patients each were studied during nitrous oxide narcotic anesthesia. An initial intravenous dose of 2 x ED95 of either muscle relaxant was followed by an intravenous infusion started at 5% recovery of control twitch tension and adjusted for 95% block or by repeated injection of 0.6 x ED95 administered whenever twitch tension had returned to 25% of control. There were no significant differences between the maintenance doses required based on method of administration: atracurium repeated injection, 1.6 +/- 0.3 x ED95 h-1; atracurium infusion, 1.7 +/- 0.3 x ED95 h-1; vecuronium repeated injection, 1.8 +/- 0.5 x ED95 h-1; and vecuronium infusion, 1.6 +/- 0.4 x ED95 h-1. Nevertheless, differences of up to 20 min were noted in the recovery indices in the following order: atracurium repeated injection = atracurium infusion less than vecuronium repeated injection less than vecuronium infusion. A single dose of neostigmine (7 micrograms/kg) significantly reduced the recovery indices, thereby eliminating their differences.

Mivacurium: dose-response relationship and administration by repeated injection or infusion

The dose-response relationship and neuromuscular blockade after infusion or repeated injection of mivacurium were studied in 65 patients in nitrous oxide-narcotic anesthesia. The ED95 (twitch tension) was determined in 45 patients by intravenous injection of a single bolus of 30, 39, 47, 54, or 60 micrograms/kg (9 patients per dose). Another 20 patients received an initial bolus of 2 x ED95 followed either by an infusion started at 5% twitch recovery (i.e., 95% depression) and adjusted to sustain 95% twitch depression (n = 10) or by repeated injection of 0.6 x ED95 whenever twitch tension had recovered to 25% of control (n = 10). Five patients in each of these two groups received 7 micrograms/kg of neostigmine at 25% twitch recovery, and the others recovered twitch tension spontaneously. The mean ED95 was 73 micrograms/kg. A 2 x ED95 bolus was followed by complete twitch depression within 2.2 +/- 0.7 min. The mean infusion rate resulted in 6 +/- 2 micrograms.kg-1.min-1. The ensuing recovery index was 6 +/- 3 min. A 6 +/- 2 min recovery index was found after up to 10 repeat injections given every 9 +/- 3 min. There was no significant effect of neostigmine in both groups. In conclusion, the recovery indices after the infusion or repeat injection of near-equal doses of mivacurium were identical.

[Mechanomyography and electromyography--2 competing methods of relaxometry using vecuronium]

The recording of the evoked twitch tension has been the established reference method to quantitate neuromuscular blockade. The evoked compound electromyogram has been introduced later as a clinically more convenient alternative. We compared both methods in 20 patients in whom cumulative dose response curves of vecuronium and the time constants of weaning neuromuscular blockade were determined. The evoked twitch tension was slightly more sensitive in detecting residual neuromuscular blockade than the EMG. No significant differences between the two methods were found in the cumulative 90% blocking dose, the duration of block and the recovery time (25%-75%). These results are in agreement with communications of previous authors using different nondepolarizing muscle relaxants. In the absence of abnormal conditions such as neuromuscular disorders and hypothermia, recording of evoked electromyography is a clinically satisfactory method to quantitate neuromuscular blockade.