Neuromuscular interactions between suxamethonium and magnesium sulphate in the cat

The effect of magnesium on the reversal of rocuronium-induced neuromuscular block with sugammadex: an ex vivo laboratory study

BACKGROUND

Magnesium dose-dependently potentiates the effect of non-depolarizing neuromuscular blocking agents. We investigated whether the potentiation of rocuronium-induced blockade by magnesium reduces the effect of sugammadex in an ex-vivo environment and how this influences the safety margin of reversal.

METHODS

Phrenic nerve - hemidiaphragm tissue preparations were isolated from male Wistar rats. The specimens were suspended in a tissue holder that allowed registering muscle contraction amplitude following electrical stimulation of the nerve. Concentration-response relationships were elucidated for magnesium, as well as for rocuronium and sugammadex.

RESULTS

The mean (95% confidence interval [CI]) half effective concentrations (EC₅₀) of rocuronium in the presence of magnesium 1 mM or 1.5 mM were 7.50 μM (6.97-8.07 μM) and 4.25 μM (4.09-4.41 μM), respectively (p < 0.0001). Increasing magnesium from 1 mM to 1.5 mM during reversal of rocuronium-induced block increased the mean (95% CI) EC₅₀ of sugammadex from 3.67 μM (3.43-3.92 μM) to 5.36 μM (5.18-5.53 μM), whereas mean (95% CI) effective concentrations for 95% effect (EC₉₅) were not significantly different at 7.22 μM (6.09-8.54 μM) and 7.61 μM (7.05-8.20 μM), respectively (p = 0.542). When rocuronium-induced block was reversed to a train-of-four (TOF) ratio > 0.9, but with still visible fade, increasing magnesium from 1 mM to 2 mM decreased the TOF ratio to below 0.9. If there was no visible fade after reversal, increasing magnesium concentration did not reduce the TOF ratio.

CONCLUSIONS

Magnesium potentiates the neuromuscular effect of rocuronium and shifts the concentration-response curve to the left. Magnesium decreases the safety margin of reversal of rocuronium-induced neuromuscular block with sugammadex.

Is magnesium sulfate by the intrathecal route efficient and safe?

The polypharmacological approach to the treatment of postoperative pain has become routine in an attempt to minimize the adverse side effects of opioids. Magnesium sulphate is a noncompetitive antagonist of the N-methyl-d-aspartate (NMDA) receptor and thus can modify nociceptive modulation. Intravenous administration of magnesium sulphate can improve postoperative analgesia and decrease the requirement for postoperative opiates, but the effects are inconsistent and have not been reliably accompanied by a reduction in the incidence of morphine-related adverse events. Several studies have shown that the administration of magnesium by the intrathecal route is safe and, in combination with opiates, extends the effect of spinal anaesthesia in both animal and human studies. The analysis of these studies justifies further investigation of the use of magnesium sulphate by the intrathecal route.

The role of the anaesthetist in the management of the pre-eclamptic patient

PURPOSE OF REVIEW

Recent literature on the anaesthetist's role in the management of the patient with severe pre-eclampsia is reviewed, with particular emphasis on the role of regional anaesthesia.

RECENT FINDINGS

Laboratory findings in pre-eclamptic women include increased levels of markers of oxidative stress and circulating tyrosine kinase 1, and inflammatory activation of leucocytes. Magnesium sulphate is the most effective agent for seizure prophylaxis. The optimal pharmacological agents for acute control of blood pressure remain controversial. The benefits of epidural analgesia in labour are well established. Single-shot spinal anaesthesia for caesarean section is safe in the absence of contraindications. Successful use of combined spinal-epidural anaesthesia has been described. Most studies on maternal haemodynamics have employed heart rate and blood pressure data as surrogate measures of cardiac output. Noninvasive cardiac output studies provide further insight into the haemodynamic response during neuraxial techniques for caesarean section.

SUMMARY

The value of regional anaesthesia cannot be over-emphasized. Recent research into spinal anaesthesia for caesarean section suggests a lower susceptibility to hypotension and probably less impairment of cardiac output than in healthy parturients. Noninvasive cardiac output measurement may also have advantages in critical care management.

The Comparative Effects of Remifentanil or Magnesium Sulfate Versus Placebo on Attenuating the Hemodynamic Responses After Electroconvulsive Therapy

In this prospective, randomized, double-blind, placebo-controlled, crossover study we compared the effects of remifentanil or magnesium sulfate (MgSO4) versus placebo in attenuating the sympathetic response to electroconvulsive therapy. Twenty adults underwent a total of 115 anesthetics for therapeutic electroconvulsive therapy. Patients were randomly allocated twice into each of the three test groups: placebo control, MgSO4 30 mg/kg, or remifentanil 1.0 microg/kg. Systolic and diastolic arterial blood pressures, heart rate, and oxygen saturations were recorded before IV access was established. Anesthesia was induced with thiopental 4 mg/kg. The trial drug was then administered and neuromuscular blockade was followed with succinylcholine 0.5 mg/kg before electroconvulsive therapy was performed. All measurements were repeated at 0, 1, 3 and 10 min after the seizure ended. Remifentanil and MgSO4 produced a statistically significant attenuation of the increase in systolic arterial blood pressure at 0, 1, and 3 min (P < 0.05). Remifentanil, but not MgSO4 or placebo, attenuated the increase in heart rate at 1 and 3 min but not the peak rate. Remifentanil increased the duration of apnea (mean 90 s), with no other adverse respiratory effects. Mean seizure duration time was 33 (+/- 14) s, with no difference among the groups. In conclusion, remifentanil 1.0 microg/kg and MgSO4 30 mg/kg attenuated the systolic arterial blood pressure response to electroconvulsive therapy without reducing the duration of seizure activity. Because MgSO4 has less effect on HR, it might offer advantages over remifentanil in patients at risk for post-electroconvulsive therapy bradycardia.

Anesthetic management of preeclampsia/eclampsia

Preeclampsia/eclampsia affects only a small proportion of all pregnancies, yet accounts for much of the obstetric morbidity and mortality seen in the USA and UK. A full understanding of preeclampsia/eclampsia, its variable presentation and complex pathophysiology allows the consulting anesthesiologist to optimize a plan for anesthetic management of the afflicted patient.