Influence of acute normovolaemic haemodilution on the dose-response and time-course of action of atracurium

Onset and duration of cis-atracurium neuromuscular block during fentanyl and lidocaine infusions in isoflurane-anaesthetised dogs

BACKGROUND

This retrospective study assessed the onset and duration of the neuromuscular block (NMB) induced by cis-atracurium 0.15 mg/kg intravenously with and without fentanyl or lidocaine infusions in 45 isoflurane-anaesthetised dogs.

METHODS

Dogs with neuromuscular function assessed by a calibrated train-of-four (TOF) monitor with stimulation (every 13 s) of the peroneal nerve were included. The onset and duration of the NMB were defined as the time from cis-atracurium administration until TOF=0 and the time during TOF=0 display, respectively.

RESULTS

The NMB onset was shorter during fentanyl (mean±sd) (1.9±0.7 minutes; P=0.0042) and lidocaine (2.0±0.7 minutes; P=0.0154) compared with control (2.9±0.8 minutes). The NMB duration was shorter in the fentanyl (27.5±7.3 minutes; P=0.0491), but not in the lidocaine group (32.3±6.9 minutes; P=0.0790), compared with control (33.7±9.1 minutes). The NMB onset was poorly but significantly correlated with the dose of fentanyl and lidocaine administered before cis-atracurium (r=-0.3396; P=0.0225). The fentanyl and lidocaine groups received more crystalloid and colloid boluses than the control.

CONCLUSIONS

Fentanyl and lidocaine shortened the NMB onset and the former decreased the NMB duration. Further prospective studies are required to clarify whether this was associated with an indirect decrease in blood pressure or a direct interaction between cis-atracurium and fentanyl and lidocaine.

Factors that affect the onset of action of non-depolarizing neuromuscular blocking agents

Neuromuscular blockade plays an important role in the safe management of patient airways, surgical field improvement, and respiratory care. Rapid-sequence induction of anesthesia is indispensable to emergency surgery and obstetric anesthesia, and its purpose is to obtain a stable airway, adequate depth of anesthesia, and appropriate respiration within a short period of time without causing irritation or damage to the patient. There has been a continued search for new neuromuscular blocking drugs (NMBDs) with a rapid onset of action. Factors that affect the onset time include the potency of the NMBDs, the rate of NMBDs reaching the effect site, the onset time by dose control, metabolism and elimination of NMBDs, buffered diffusion to the effect site, nicotinic acetylcholine receptor subunit affinity, drugs that affect acetylcholine (ACh) production and release at the neuromuscular junction, drugs that inhibit plasma cholinesterase, presynaptic receptors responsible for ACh release at the neuromuscular junction, anesthetics or drugs that affect muscle contractility, site and methods for monitoring neuromuscular function, individual variability, and coexisting disease. NMBDs with rapid onset without major adverse events are expected in the next few years, and the development of lower potency NMBDs will continue. Anesthesiologists should be aware of the use of NMBDs in the management of anesthesia. The choice of NMBD and determination of the appropriate dosage to modulate neuromuscular blockade characteristics such as onset time and duration of neuromuscular blockade should be considered along with factors that affect the effects of the NMBDs. In this review, we discuss the factors that affect the onset time of NMBDs.

[Effects of changes in ion concentrations, osmolarity, and pH on recovery from atracurium- or vecuronium-induced neuromuscular blockade]

OBJECTIVES

To determine changes in sodium, potassium, calcium, magnesium and chloride ion concentrations in blood, osmolarity, and pH during surgery, and to assess the influence of such changes on atracurium- or vecuronium-induced neuromuscular blockade under inhaled or intravenous anesthesia.

MATERIAL AND METHODS

Prospective study randomizing 119 ASA 1-2 patients; 52.1% of the patients received atracurium (26.8%, with isoflurane; 25.2%, with propofol) and 47.9% received vecuronium (23.5%, with isoflurane; 24.3%, with propofol). The neuromuscular blockade was confirmed by electromyography of the adductor pollicis muscle (stimuli delivered to the cubital nerve). Two venous blood samples were extracted to measure ureic nitrogen, creatinine, glucose, ion concentrations (sodium, chloride, potassium, calcium, and magnesium), and osmolarity. Arterial blood gases and pH were also assessed. The first blood sample was extracted on inserting the venous catheter and the second on recovery of 25% of the first train-of-four twitch.

RESULTS

The onset and duration of action for equipotent doses of atracurium and vecuronium were similar. Likewise, recovery was also similar. Plasma chloride ion and glucose levels tended to rise during surgery, while sodium, potassium and magnesium ion concentrations fell. Both total and effective plasma osmolarities also decreased. Fluid replacement therapy during surgery was at least partly responsible for these changes. Low calcium and magnesium concentrations and alkalosis prolonged some phases of atracurium recovery, while low sodium levels shortened the duration of some atracurium-induced blockade recovery phases. The effect of changes in chloride ion concentrations on recovery was variable. High chloride, low calcium, and especially low sodium ion concentrations shortened some phases of the vecuronium-induced blockade, while alkalosis prolonged its duration.

CONCLUSIONS

Changes in electrolyte concentrations and pH as a result of standard fluid replacement therapy are moderate, well tolerated, and do not exercise a strong effect on the behavior of the neuromuscular blockade.

The effect of hemodilution during normothermic cardiac surgery on renal physiology and function: a review

Although the definitions of renal dysfunction vary, loss of renal function is a common complication following cardiac surgery using cardiopulmonary bypass (CPB). When postoperative dialysis is required, mortality is approximately 50%. CPB-accompanied hemodilution is a major contributing factor to renal damage as it notably reduces oxygen delivery by reducing the oxygen transport capacity of the blood as well as disturbing the microcirculation. To minimize hypoxemic damage during CPB, lowering of body temperature is applied to reduce the patient’s metabolic rate. At present, however, temperature management during elective adult cardiac surgery is shifting from moderate hypothermia to normothermia. To determine whether the currently accepted levels of hemodilution during CPB can suffice the normothermic patient’s high oxygen demand, we focused this study on renal physiology and postoperative renal function. Hemodilution reduces the capillary density through a diminished capillary viscosity, thereby, redistributing blood from the renal medulla to the renal cortex. As the physiology of the renal medulla makes it a hypoxic environment, this part of the kidney appears to be especially at risk for hypoxic damage caused by a hemodilution-induced lowered oxygen transport and oxygen delivery. In addition, hemodilution is also likely to disturb the hormonal systems regulating renal blood distribution. Clinical studies, mostly of retrospective or observational nature, show that perioperative nadir hematocrit levels lower than approximately 24% are associated with an increased risk to develop postoperative renal failure. A better comprehension of the cause-and-effect relation between low perioperative hematocrits and loss of postoperative renal function may enable more effective renal protective strategies.

Influence of acute normovolaemic haemodilution on the dose-response relationship and time course of action of cisatracurium besylate

BACKGROUND

Acute normovolaemic haemodilution (ANH) is an efficacious blood conservation strategy aiming at avoiding allogeneic blood transfusion. ANH was shown to increase the potency of vecuronium, atracurium, and rocuronium. The aim of our study was to investigate whether cisatracurium potency is altered with ANH.

METHODS

Using the Relaxometer mechanomyograph, we compared cisatracurium dose-response relationship and time course of action in 60 patients randomly allocated to the ANH or control groups. Patients in each group were randomly allocated to receive one of three cisatracurium doses (30, 40, 50 microg kg(-1)) followed by a second supplemental dose to reach a total of 100 microg kg(-1).

RESULTS

ANH did not result in a significant shift in cisatracurium log dose-probit dose-response curve. There was no significant difference in mean (95% confidence intervals) ED(50), ED(90), and ED(95) (effective doses required for 50, 90, and 95% first twitch depression) between the ANH group [29.5 (27-32), 50.4 (47.4-53.4), 58.7 (55.3-62) microg kg(-1)] and the control group [28.2 (25.3-31), 47.6 (44.9-50.3), 55.3 (52.5-58.1) microg kg(-1)], whereas there was no difference in mean (SD) Dur(25) and Dur(0.8) (time until 25% first twitch and 0.8 train-of-four ratio recoveries) between the ANH group [40.8 (5.9), 64.7 (8.4) min] and the control group [42.2 (7.6), 66.5 (10.7) min].

CONCLUSIONS

Our results demonstrated that unlike other previously reported neuromuscular blocking drugs, ANH did not alter cisatracurium potency. Thus, cisatracurium would be the neuromuscular blocking drug of choice in patients who undergo surgery with ANH, as no dose adjustments are required.

Influence of acute normovolaemic haemodilution on the dose-response relationship, time-course of action and pharmacokinetics of rocuronium bromide

BACKGROUND

Acute normovolaemic haemodilution (ANH) is an effective strategy for avoiding or reducing allogeneic blood transfusion. We aimed to study its effect on the pharmacological profile of rocuronium.

METHODS

In two study centres, 28 patients undergoing major surgery with ANH were matched with 28 control patients. In the dose-response groups, using the mechanomyograph, neuromuscular block of six consecutive incremental doses of rocuronium 50 microg kg(-1), followed by 300 microg kg(-1), was evaluated. In the pharmacokinetics groups, serial arterial blood samples were withdrawn for rocuronium assay after a single dose of rocuronium 600 microg kg(-1).

RESULTS

ANH resulted in a shift to the left of rocuronium dose-response curve. Rocuronium effective dose(95) (ED(95)) was 26% lower (P<0.05) in the ANH group [283.4 (92.0) microg kg(-1)] compared with the control group [383.5 (127.3) microg kg(-1)]. Times from administration of last incremental dose until 25% of first response of train-of-four (TOF) recovery (Dur(25)) and 0.8 TOF ratio recovery (Dur(0.8)) were 28% longer in the ANH group [39.9 (8.4), 66.7 (14.2) min] compared with the control group [31.1 (6.6), 52.1 (15.8) min] (P<0.01, P<0.05), respectively. Volume of distribution was higher (P<0.01), central clearance was lower (P<0.05) and terminal elimination half-life was longer (P<0.0001) in the ANH group [234.97 (47.11) ml kg(-1), 4.70 (0.94) ml kg(-1) min(-1), 77.29 (12.25) min] compared with the control group [181.22 (35.73) ml kg(-1), 5.71 (1.29) ml kg(-1) min(-1), 56.86 (10.05) min, respectively].

CONCLUSION

ANH resulted in prolongation of rocuronium time-course of action, thus careful monitoring of neuromuscular block is recommended in patients who undergo ANH.