Chronic intraperitoneal endotoxin treatment in rats induces resistance to d-tubocurarine, but does not produce up-regulation of acetylcholine receptors

The Sick and the Weak: Neuropathies/Myopathies in the Critically Ill

Critical illness polyneuropathies (CIP) and myopathies (CIM) are common complications of critical illness. Several weakness syndromes are summarized under the term intensive care unit-acquired weakness (ICUAW). We propose a classification of different ICUAW forms (CIM, CIP, sepsis-induced, steroid-denervation myopathy) and pathophysiological mechanisms from clinical and animal model data. Triggers include sepsis, mechanical ventilation, muscle unloading, steroid treatment, or denervation. Some ICUAW forms require stringent diagnostic features; CIM is marked by membrane hypoexcitability, severe atrophy, preferential myosin loss, ultrastructural alterations, and inadequate autophagy activation while myopathies in pure sepsis do not reproduce marked myosin loss. Reduced membrane excitability results from depolarization and ion channel dysfunction. Mitochondrial dysfunction contributes to energy-dependent processes. Ubiquitin proteasome and calpain activation trigger muscle proteolysis and atrophy while protein synthesis is impaired. Myosin loss is more pronounced than actin loss in CIM. Protein quality control is altered by inadequate autophagy. Ca(2+) dysregulation is present through altered Ca(2+) homeostasis. We highlight clinical hallmarks, trigger factors, and potential mechanisms from human studies and animal models that allow separation of risk factors that may trigger distinct mechanisms contributing to weakness. During critical illness, altered inflammatory (cytokines) and metabolic pathways deteriorate muscle function. ICUAW prevention/treatment is limited, e.g., tight glycemic control, delaying nutrition, and early mobilization. Future challenges include identification of primary/secondary events during the time course of critical illness, the interplay between membrane excitability, bioenergetic failure and differential proteolysis, and finding new therapeutic targets by help of tailored animal models.

Pharmacodynamic changes with vecuronium in sepsis are associated with expression of α7- and γ-nicotinic acetylcholine receptor in an experimental rat model of neuromyopathy

BACKGROUND

Resistance to non-depolarizing neuromuscular blocking agents induced by sepsis is associated with the qualitative change in the nicotinic acetylcholine receptor (nAChR). This study aims to investigate the effects of sepsis on the neuromuscular block properties of vecuronium in relation to the expression of fetal and neuronal α7 type nAChR.

METHODS

Male Sprague-Dawley rats were randomly divided into sham and sepsis groups. Sepsis was induced by caecal ligation and puncture (CLP). The rats were injected i.v. with ulinastatin or normal saline on Day 10. Neuromuscular block properties of vecuronium were evaluated and neuromuscular function was assessed by electromyography on Days 1, 3, 7, and 14 after CLP. Expression of fetal and neuronal type α7-nAChR on the tibialis anterior muscle was assessed using immunohistochemistry and western blot. The mRNA encoding for γ- and α7 subunits was evaluated by real-time polymerase chain reaction.

RESULTS

The half maximal inhibitory response of vecuronium in the sepsis group significantly increased, peaked on Day 7, and then declined on Day 14 (P<0.05). The neuromuscular function decreased with increasing postoperation time in the sepsis group (P<0.05). Sepsis significantly increased the expression of γ- and α7-nAchR along with expression of γ- and α7 subunits mRNA, peaked on Day 7, and declined on Day 14 (P<0.05). Ulinastatin suppressed the expression of receptor protein and mRNA encoding for γ- and α7 subunits (P<0.05).

CONCLUSIONS

Pharmacodynamic changes with vecuronium seem to be associated with the expression of γ- and α7-nAChR in the skeletal muscle. Ulinastatin can improve this effect by inhibiting the expression of these receptors.

The limits of succinylcholine for critically ill patients

BACKGROUND

Urgent tracheal intubations are common in intensive care units (ICU), and succinylcholine is one of the first-line neuromuscular blocking drugs used in these situations. Critically ill patients could be at high risk of hyperkalemia after receiving succinylcholine because one or more etiologic factors of nicotinic receptor upregulation can be present, but there are few data on its real risk. Our objectives in this study were to determine the factors associated with arterial potassium increase (ΔK) and to assess the occurrence of acute hyperkalemia ≥6.5 mmol/L after succinylcholine injection for intubation in the ICU.

METHODS

In a prospective, observational study, all critically ill patients intubated with succinylcholine in an ICU were screened. Only intubations with arterial blood gases and potassium measurements before and after (K(after)) a succinylcholine injection were studied.

RESULTS

During 18 months, 131 critically ill patients were intubated after receiving succinylcholine with arterial potassium before and after intubation (K(after)) for a total of 153 intubations. After multivariate analysis, the only factor associated with ΔK was the length of ICU stay before intubation (ρ = 0.561, P < 0.001). The factors associated with K(after) ≥6.5 mmol/L (n = 11) were the length of ICU stay (P < 0.001) and the presence of acute cerebral pathology (P = 0.047). The threshold of 16 days was found highly predictive of acute hyperkalemia ≥6.5 with 37% (95% confidence interval: 19%-58%) of K(after) ≥6.5 after the 16th day compared with only 1% (95% confidence interval: 0%-4%) of K(after) ≥6.5 when succinylcholine was injected during the first 16 days.

CONCLUSIONS

This study shows that the risk of ΔK after succinylcholine injection is strongly associated with the length of ICU stay. The risk of acute hyperkalemia ≥6.5 mmol/L is highly significant after 16 days.

Chronic exercise and the pro-inflammatory response to endotoxin in the serum and heart

PURPOSE

To examine the effects of moderate intensity chronic exercise on tumor necrosis factor-alpha (TNFalpha) and inducible nitric oxide synthase (iNOS) responses to endotoxin in female Sprague-Dawley rats.

METHODS

Rats were divided into two groups, exercise (n=17) and sedentary (n=24). Exercise (Ex) rats completed 12 weeks of motorized treadmill running 3 days/week for 15-25 min at 22-25 m/min, while sedentary (Sed) rats remained in their cages. Twenty-four hrs after the last exercise session, animals were subdivided into three groups. One subgroup served as baseline controls. These rats received an injection of saline (s) and were killed immediately (Sed-s and Ex-s), while the other groups received an injection of lipopolysaccharide (LPS). LPS animals were killed 2 h (Sed-L2 and Ex-L2) or 4 h after the LPS injection (Sed-L4 and Ex-L4).

RESULTS

Serum TNFalpha was elevated 2 h after LPS injection in both Sed and Ex groups, but was significantly higher in the chronic exercise group (Ex-L2 versus. Sed-L2). Similarly, serum beta glucuronidase activity, an indicator of tissue damage, was elevated 2 and 4 h after LPS injection, and was significantly higher in the exercise groups. Post-treatment left ventricular TNFalpha and iNOS activity, as well as stable nitric oxide derivatives in the serum (NOx), were significantly higher in LPS-injected groups compared to saline groups, but no difference in LPS effect was observed between sedentary and exercise groups.

CONCLUSIONS

Moderate intensity chronic exercise stress caused an exaggerated serum TNFalpha response to endotoxin and an elevation in a serum marker of LPS-induced tissue damage.