Influence of sepsis on minimum alveolar concentration of desflurane in a porcine model

How is depth of anaesthesia assessed in experimental pigs? A scoping review

BACKGROUND

Despite the large number of pigs involved in translational studies, no gold standard depth of anaesthesia indicators are available. We undertook a scoping review to investigate and summarize the evidence that sustains or contradicts the use of depth of anaesthesia indicators in this species.

METHODS

Medline, Embase and CAB abstract were searched up to September 22nd 2022. No limits were set for time, language and study type. Only original articles of in vivo studies using pigs or minipigs undergoing general anaesthesia were included. The depth of anaesthesia indicators reported in the selected papers were divided in two categories: A, indicators purposely investigated as method to assess depth of anaesthesia; B, indicators reported but not investigated as method to assess depth of anaesthesia.

RESULTS

Out of 13792 papers found, 105 were included after the screening process. Category A: 17 depth of anaesthesia indicators were found in 19 papers. Studies were conducted using inhalant anaesthetics as the main anaesthetic agent in the majority of the cases (13/19 = 68.4%), while 3/19 (15.8%) used propofol. The most investigated depth of anaesthesia indicators were bispectral index (8/19 = 42.1%) and spectral edge frequency 95% (5/19 = 26.3%). Contrasting results about the specific usefulness of each depth of anaesthesia indicators were reported. Category B: 23 depth of anaesthesia indicators were found in 92 papers. The most reported depth of anaesthesia indicators were: motor response following a stimulus (37/92 = 40.2%), depth of anaesthesia scores (21/92 = 23.3%), bispectral index (16/92 = 17.8%) and spectral edge frequency 95% (9/92 = 9.8%).

CONCLUSION

Results highlight the lack of scientifically valid and reliable indicators to ensure adequate depth of anaesthesia in pigs.

Anesthetic management of patients with sepsis/septic shock

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection, while septic shock is a subset of sepsis with persistent hypotension requiring vasopressors to maintain a mean arterial pressure (MAP) of ≥65 mmHg and having a serum lactate level of >2 mmol/L, despite adequate volume resuscitation. Sepsis and septic shock are medical emergencies and time-dependent diseases with a high mortality rate for which early identification, early antibiotic therapy, and early source control are paramount for patient outcomes. The patient may require surgical intervention or an invasive procedure aiming to control the source of infection, and the anesthesiologist has a pivotal role in all phases of patient management. During the preoperative assessment, patients should be aware of all possible organ dysfunctions, and the severity of the disease combined with the patient's physiological reserve should be carefully assessed. All possible efforts should be made to optimize conditions before surgery, especially from a hemodynamic point of view. Anesthetic agents may worsen the hemodynamics of shock patients, and the anesthesiologist must know the properties of each anesthetic agent. All possible efforts should be made to maintain organ perfusion supporting hemodynamics with fluids, vasoactive agents, and inotropes if required.

Minimum Alveolar Concentration-Awake of Sevoflurane is Decreased in Patients with Parkinson's Disease: An Up-and-Down Sequential Allocation Trial

Background

An increasing number of patients with Parkinson’s disease (PD) will have surgery under general anesthesia. A previous study demonstrated that propofol requirement for inducing unconsciousness in PD patients was lower than that in non-PD (NPD) patients. However, the requirement of inhaled anesthetics in PD patients has not been clarified. The aim of this study was to investigate the minimum alveolar concentration-awake (MAC_awake) of sevoflurane in patients with PD compared to NPD patients.

Patients and Methods

The current study is an up-and-down sequential allocation trial. The initial end-tidal concentration of sevoflurane (CETsevo) was estimated by the response of the previous patient to verbal command using the Dixon’s up-and-down method. The first patient in each group received CETsevo at 1%, and the step size between patients was 0.2%.

Results

Forty-one patients including 20 PD patients and 21 NPD patients were enrolled. Patients’ characteristics and arterial blood gas parameters (except blood sodium) were comparable between two groups. The MAC_awake of sevoflurane estimated by the Dixon’s up-and-down method in PD patients (0.47% ± 0.08% [Mean ± S.D.]) was significantly lower than that in NDP patients (0.64% ± 0.10%) (P=0.003). The estimated difference in means was 0.17% (95% CI, 0.10–0.24%). Probit analysis showed that the MAC_awake of sevoflurane in PD and NPD patients was 0.49% (95% CI, 0.42–0.57%) and 0.67% (95% CI, 0.59–0.76%), respectively. The relative median potency was 0.73 (95% CI, 0.38–0.94).

Conclusion

Patients with PD exhibit a significantly lower MAC_awake of sevoflurane compared with NPD patients. Clinicians should avoid an overdose of sevoflurane in patients with PD.

Trial Registration

Registered at ChiCTR1900026956.

Emergent airway management of the critically ill patient: current opinion in critical care

PURPOSE OF REVIEW

To describe techniques to facilitate safe intubation in critically ill patients.

RECENT FINDINGS

Despite advances in the treatment of critically ill patients, endotracheal intubation remains a high-risk procedure associated with complications that can lead to appreciable morbidity and mortality. In addition to the usual anatomical factors that can predict a difficult intubation, incorporating pathophysiological considerations and crisis resource management may enhance safety and mitigate risk. Enhancing preoxygenation with high-flow oxygen or noninvasive ventilation, the early use of intravenous fluids and/or vasopressors to prevent hypotension and videolaryngoscopy for first pass success are all promising additions to airway management.Facilitating intubation by either sedation with paralysis or allowing patients to continue to breathe spontaneously are reasonable options for airway management. These approaches have potential advantages and disadvantages.

SUMMARY

Recognizing the unique challenges of endotracheal intubation in critically ill patients is paramount in limiting further deterioration during this high-risk procedure. A safe approach to intubation focuses on recognizing risk factors that predict challenges in achieving an optimal view of the glottis, maintaining optimal oxygenation, and minimizing the risks and benefits of sedation/induction strategies that are meant to facilitate intubation and avoid clinical deterioration.

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.

Experimental animal models of muscle wasting in intensive care unit patients

The muscle wasting and loss of muscle function associated with critical illness and intensive care have significant negative consequences for weaning from the respirator, duration of hospital stay, and quality of life for long periods after hospital discharge. There is, accordingly, a significant demand for focused research aiming at improving our understanding of the mechanisms underlying the impaired neuromuscular function in intensive care unit (ICU) patients. However, the study of generalized muscle weakness in critically ill ICU patients is further complicated by the coexistence of multiple independent factors, such as different primary diseases, large variability in pharmacologic treatment, collection of muscle samples several weeks after admission to the ICU, and exposure to causative agents. This has led to the design of specific animal models mimicking ICU conditions. These models have often been used to study the mechanisms underlying the paralysis and muscle wasting associated with acute quadriplegic myopathy in ICU patients. This short review aims at presenting existing and recently introduced experimental animal models mimicking the conditions in the ICU (i.e., models designed to determine the mechanisms underlying the muscle wasting associated with ICU treatment).

Effects of nitrous oxide on minimum alveolar concentration of desflurane in dogs

Effects of nitrous oxide (N2O) on minimum alveolar concentration (MAC) of desflurane were studied. For that purpose, 30 dogs were randomly allocated into two groups: desflurane group (GD) and N2O and desflurane group (GDN). GD animals received propofol to intubation, and 11.5V% of desflurane diluted in 100% O2. After 30 minutes, they received electric stimulus and if the animal did not react to stimulus, desflurane concentration was reduced by 1.5V%. This protocol was repeated at each 15 minutes, and stimulus was interrupted when voluntary reaction was observed. GDN dogs were submitted to diluent flow 30% O2 and 70% N2O. Desflurane's MAC; heart (HR) and respiratory (RR) rates; systolic, diastolic and mean arterial pressures (SAP, DAP, and MAP, respectively); end tidal carbon dioxide (ETCO2); oxyhemoglobin saturation (SpO2) and body temperature (T) were evaluated. In both groups increase in HR and ETCO2, and decrease in RR and T were associated with administration of the highest dose of desflurane. Blood pressures decreased 30 minutes after desflurane administration in GDN, and after this measurement the values increased. Reduction in desflurane's MAC was observed as well. It is concluded that N2O associated with desflurane reduced desflurane's MAC by 16% with increase in HR and respiratory depression.

A porcine model of acute quadriplegic myopathy: a feasibility study

BACKGROUND

The mechanisms underlying acute quadriplegic myopathy (AQM) are poorly understood, partly as a result of the fact that patients are generally diagnosed at a late stage of the disease. Accordingly, there is a need for relevant experimental animal models aimed at identifying underlying mechanisms.

METHODS

Pigs were mechanically ventilated and exposed to various combinations of agents, i.e. pharmacological neuromuscular blockade, corticosteroids and/or sepsis, for a period of 5 days. Electromyography and myofibrillar protein and mRNA expression were analysed using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), confocal microscopy, histochemistry and real-time polymerase chain reaction (PCR).

RESULTS

A decreased compound muscle action potential, normal motor nerve conduction velocities, and intact sensory nerve function were observed. Messenger RNA expression, determined by real-time PCR, of the myofibrillar proteins myosin and actin decreased in spinal and cranial nerve innervated muscles, suggesting that the loss of myosin observed in AQM patients is not solely the result of myofibrillar protein degradation.

CONCLUSION

The present porcine AQM model demonstrated findings largely in accordance with results previously reported in patients and offers a feasible approach to future mechanistic studies aimed at identifying underlying mechanisms and developing improved diagnostic tests and intervention strategies.