Usefulness and limits of near infrared spectroscopy monitoring during endovascular neuroradiologic procedures.

BACKGROUND: Transcranial cerebral oximetry (TCCO) with near-infrared spectroscopy (NIRS) is a non-invasive, bedside technique, which allows the continuous measurement of regional cerebral oxygenation. The aim of this study was to evaluate TCCO monitoring during endovascular neuroradiologic procedures. METHODS: Adult patients undergoing elective endovascular embolization of cerebral aneurysms, arteriovenous malformations, dural arteriovenous fistulas and meningiomas under general anesthesia were included in the study, over a period of 12 months. Twenty-eight procedures in 25 patients were analyzed. RESULTS: Regional cerebral oxygenation rSO(2) readings were significantly different according to the different phases of the neuroendovascular procedure. An effect of the underlying cerebral pathology on regional cerebral oxygenation rSO(2) recording, in relation to the different stage of the interventional procedure, was also evident, the more invasive the procedure the greater the impact on rSO(2) reading. NIRS monitoring contributed to a prompt diagnosis and management of two adverse intraoperative events and helped in early evaluation of prognosis. CONCLUSION: TCCO with NIRS is a promising monitoring tool to assess the balance between oxygen supply and demand during neuroradiologic procedures. Nevertheless, some limits should be acknowledged, such as the study of the posterior circulation and artefacts related to contrast agent injection. A careful understanding of the undergoing step of the procedure as well of the possible influence of intrinsic and extrinsic factors affecting recording is important for interpretation of data.

Heart rate variability: a diagnostic and prognostic tool in anesthesia and intensive care.

The autonomic nervous system (ANS) plays an important role in the human response to various internal and external stimuli, which can modify homeostasis, and exerts a tight control on essential functions such as circulation, respiration, thermoregulation and hormonal secretion. ANS dysfunction may complicate the perioperative course in the surgical patient undergoing anesthesia, increasing morbidity and mortality, and, therefore, it should be considered as an additional risk factor during pre-operative evaluation. Furthermore, ANS dysfunction may complicate the clinical course of critically ill patients admitted to intensive care units, in the case of trauma, sepsis, neurologic disorders and cardiovascular diseases, and its occurrence adversely affects the outcome. In the care of these patients, the assessment of autonomic function may provide useful information concerning pathophysiology, risk stratification, early prognosis prediction and treatment strategies. Given the role of ANS in the maintenance of systemic homeostasis, anesthesiologists and intensivists should recognize as critical the evaluation of ANS function. Measurement of heart rate variability (HRV) is an easily accessible window into autonomic activity. It is a low-cost, non-invasive and simple to perform method reflecting the balance of the ANS regulation of the heart rate and offers the opportunity to detect the presence of autonomic neuropathy complicating several illnesses. The present review provides anesthesiologists and intensivists with a comprehensive summary of the possible clinical implications of HRV measurements, suggesting that autonomic dysfunction testing could potentially represent a diagnostic and prognostic tool in the care of patients both in the perioperative setting as well as in the critical care arena.

Anaesthetics and postoperative cognitive dysfunction: a pathological mechanism mimicking Alzheimer's disease.

With longevity, postoperative cognitive decline in the elderly has emerged as a major health concern for which several factors have been implicated, one of the most recent being the role of anaesthetics. Interactions of anaesthetic agents and different targets have been studied at the molecular, cellular and structural anatomical levels. Recent in vitro nuclear magnetic resonance spectroscopy studies have shown that several anaesthetics act on the oligomerisation of amyloid beta peptide. Uncontrolled production, oligomerisation and deposition of amyloid beta peptide, with subsequent development of amyloid plaques, are fundamental steps in the generation of Alzheimer's disease. Amyloid beta peptide is naturally present in the central nervous system, and is found at higher tissue concentrations in the elderly. We argue that administering certain general anaesthetics to elderly patients may worsen amyloid beta peptide oligomerisation and deposition and thus increase the risk of developing postoperative cognitive dysfunction. The aim of this review is to highlight the clinical aspects of postoperative cognitive dysfunction and to find plausible links between possible anaesthetic effects and the molecular pathological mechanism of Alzheimer's disease. It is hoped that our hypothesis will stimulate further enquiry, especially triggering research into elucidating those anaesthetics that may be more suitable when cognitive dysfunction is a particular concern.

Remifentanil and the brain.

BACKGROUND AND AIM: Remifentanil is an ultra-short-acting opioid, increasingly used today in neuroanesthesia and neurointensive care. Its characteristics make remifentanil a potentially ideal agent, but previous data have cast a shadow on this opioid, supporting potentially toxic effects on the ischemic brain. The aim of the present concise review is to survey available up-to-date information on the effects of remifentanil on the central nervous system. METHOD: A MEDLINE search within the past seven years for available up-to-date information on remifentanil and brain was performed. RESULTS: Concise up-to-date information on the effects of remifentanil on the central nervous system was reported, with a particular emphasis on the following topics: cerebral metabolism, electroencephalogram, electrocorticography, motor-evoked potentials, regional cerebral blood flow, cerebral blood flow velocity, arterial hypotension and hypertension, intracranial pressure, cerebral perfusion pressure, cerebral autoregulation, cerebrovascular CO(2) reactivity, cerebrospinal fluid, painful stimulation, analgesia and hyperalgesia, neuroprotection, neurotoxicity and hypothermia. CONCLUSION: The knowledge of the influence of remifentanil on brain functions is crucial before routine use in neuroanesthesia to improve anesthesia performance and patient safety as well as outcome.

Transcranial Doppler and anesthetics.

Transcranial Doppler (TCD) is widely used to investigate the effects of anesthetic drugs on cerebral blood flow. Its repeatability and non-invasivity makes it an ideal, first choice method. Anesthesia providers are required to be conscious of the cerebral hemodynamic effects of drugs given in their practice, especially in neurosurgery and in subjects with impaired brain functions. The purpose of this review is to present the basic concepts of the TCD technique and the effects on cerebral hemodynamics of the most popular anesthetic drugs evaluated using TCD ultrasonography.

Alzheimer's disease and anaesthesia: implications for the central cholinergic system.

Alzheimer's disease (AD) is associated with a loss of cholinergic neurons resulting in profound memory disturbances and irreversible impairment of cognitive function. The central cholinergic system is involved in the action of general anaesthetic agents. Anaesthetic modulation of cholinergic transmission has profound effects on brain function via a cascade of synaptic and postsynaptic events by binding both nicotinic and muscarinic receptors. During general anaesthesia, decrease in acetylcholine release and depression of cholinergic transmission facilitates the desirable effects of general anaesthetics, such as loss of consciousness, pain, voluntary movements and memory. From this point of view, patients with AD, characterized by a compromised neuronal transmission, represent particular cases in which the choice of anaesthesia drugs may have a negative effect on the postoperative outcome. A future challenge may be the identification of brain targets of general anaesthetics which do not expose patients to postoperative cognitive dysfunction, nor interfere with prognosis of brain degenerative disease.

Cerebral haemodynamic changes during propofol-remifentanil or sevoflurane anaesthesia: transcranial Doppler study under bispectral index monitoring.

BACKGROUND: Sevoflurane or propofol-remifentanil-based anaesthetic regimens represent modern techniques for neurosurgical anaesthesia. Nevertheless, there are potential differences related to their activity on the cerebrovascular system. The magnitude of such difference is not completely known. METHODS: In total 40 patients, treated for spinal or maxillo-facial disorders, were randomly allocated to either i.v. propofol-remifentanil or inhalational sevoflurane anaesthesia. Transcranial Doppler was used to assess changes in cerebral blood flow velocity, carbon dioxide reactivity, cerebral autoregulation and the bispectral index to assess the depth of anaesthesia. RESULTS: Time-averaged mean flow velocity (MFV) was significantly reduced after induction of anaesthesia in both sevoflurane and propofol-remifentanil groups (P<0.001). At deeper levels of anaesthesia, MFV increased in the sevoflurane group, suggesting an uncoupling flow/metabolism, whereas it was further reduced in the propofol-remifentanil group (P<0.001). Indices of cerebral autoregulation were reduced in patients with high-dose sevoflurane whereas autoregulation was preserved in patients anaesthetized with propofol-remifentanil (P<0.001). Higher CO(2) concentrations impaired cerebral autoregulation in the sevoflurane group but not in patients anaesthetized with propofol-remifentanil. CONCLUSIONS: Propofol-remifentanil anaesthesia induced a dose-dependent low-flow state with preserved cerebral autoregulation, whereas sevoflurane at high doses provided a certain degree of luxury perfusion.

Significance of hypoxemia screening in candidates for liver transplantation: our experience.

Hepatopulmonary syndrome (HPS) is recognized as one of the causes of hypoxemia in patients with chronic liver disease. This complication is responsible for increased mortality and increased perioperative risk in liver transplantation candidates. Recent data from the literature suggest extending the screening for HPS to all candidates for liver transplantation. The aim of this retrospective study was to evaluate the incidence of hypoxemia among a population of patients awaiting liver transplantation. Using pulse oximetry as a screening tool for hypoxemia, 39 of 198 patients (20%) were hypoxemic. The results of this study confirmed the importance of screening for hypoxemia among patients awaiting liver transplantation. In these patients, a more accurate evaluation of respiratory function should be performed to confirm or exclude the diagnosis of HPS.

The importance of predicting the prognosis in patients with hepatopulmonary syndrome: a simple scoring system.

Hepatopulmonary syndrome (HPS) is a pulmonary vascular disorder, complicating hepatic diseases, and is responsible for an increased morbidity and mortality among patients awaiting liver transplantation. Nowadays, it is recognized as an independent risk factor for death in this patient population. The severity of hypoxemia and the advanced stage of the liver dysfunction are determinants for the prognosis. Therefore, the possibility to be successful, thus improving survival, consists of addressing HPS at an earlier stage, giving more attention to moderate evidences of this pathology instead of the severe ones. On the basis of scientific evidence, we suggest a simple scoring system to predict prognosis among patients with HPS, founded on the integration of two main factors: the severity of hepatic disease, expressed as class of Child-Pugh, and the severity of the hypoxemia. This model of prognostic evaluation has the objective of estimating the additional risk of these patients, thereby avoiding a deleterious underestimate of risk and an arbitrariness of management.

Effect of tramadol on Bispectral Index during intravenous anaesthesia with propofol and remifentanil.

The aim of this study was to investigate the effects of tramadol on the Bispectral Index (BIS) during total intravenous propofol-remifentanil anaesthesia. Forty-four adult ASA Physical status I-II patients, scheduled for elective general surgical procedures were included in a prospective observational randomized study. Doses for anaesthetics and opioids were adjusted to keep the BIS value at 50 +/- 5. After 20 minutes of stable anaesthesia, the subjects were randomly allocated to receive intravenous saline (control group) or tramadol 1.5 mg/kg (tramadol group). BIS values, mean arterial pressure, and heart rate were recorded every five minutes for 20 minutes. Mean BIS values after tramadol administration were not significantly different from those following saline, throughout the observation period (P > 0.05). There were no patients in whom BIS values were more than 60 or who presented explicit recall of events under anaesthesia. There were no significant changes in mean arterial pressure, SpO2, or heart rate (P > 0.05). The results indicate that the administration of tramadol during stable total intravenous anaesthesia with propofol-remifentanil does not affect BIS values. The clinical relevance is that tramadol can be safely administered pre- and intraoperatively as pre-emptive or preventive analgesia without modification of the depth of anaesthesia.

Fatal exacerbation of peripheral neuropathy during lamivudine therapy: evidence for iatrogenic mitochondrial damage.

A 57-year-old man with mild neuropathy who was positive for hepatitis B and C viruses was treated with lamivudine 300 mg.day(-1). After 3 months he presented with dysphonia and progressive muscle weakness. Subsequently, he developed tetraparesis followed by acute respiratory failure requiring mechanical ventilation, which was complicated by sudden cardiac arrest. After lamivudine was stopped, the neuropathy improved and respiratory capacity improved. Unfortunately, the patient died suddenly in spite of haemodynamic, ventilatory and metabolic support. Electrophysiological studies showed evidence of a sensory-motor axonal neuropathy. Nerve biopsy, muscle biopsy, biochemistry and mitochondrial DNA molecular genetics suggested possible widespread iatrogenic mitochondrial damage. Mitochondrial DNA dysfunction could be a potential cause of the sudden cardiac arrest. Stopping lamivudine treatment sooner after the onset of peripheral neuropathy or its exacerbation is important as continued therapy could lead to acute respiratory failure requiring mechanical ventilation and intensive care unit admission.

Tramadol does not modify the Bispectral Index during anaesthesia with sevoflurane and remifentanil.

BACKGROUND: The aim of this study was to investigate the effects of tramadol administered with ketorolac on the Bispectral Index (BIS) during anaesthesia with sevoflurane and remifentanil. METHODS: Forty-six adult patients, ASA I-III, scheduled for elective minor surgical procedures were studied. Patients were premedicated with remifentanil infusion 0.4 microg kg(-1) min(-1) and anaesthesia was induced 4-5 min later with propofol 1.5 mg kg(-1) and maintained with air-oxygen (FI(O(2)) 0.4), remifentanil 0.1-0.15 microg kg(-1) min(-1) and sevoflurane, adjusted to keep the BIS between 40 and 50. After 20 min of stable anaesthesia, the subjects were allocated randomly to receive i.v. tramadol 1.5 mg kg(-1) and i.v. ketorolac 0.3 mg kg(-1) (tramadol group) or saline (control group). BIS values, mean arterial pressure, heart rate and end-tidal carbon dioxide were recorded every 5 min for 20 min. RESULTS: Mean BIS values after tramadol administration were not significantly different from those recorded in patients receiving saline throughout the period of observation. There were no patients who presented explicit recall of events under anaesthesia. No significant changes in mean arterial pressure, heart rate and end-tidal carbon dioxide were noted after tramadol injection. CONCLUSION: Tramadol, given with ketorolac to prevent postoperative pain, during anaesthesia maintained with sevoflurane and remifentanil at BIS between 40 and 50, does not modify the BIS value.

Hepatopulmonary syndrome: a concern for the anesthetist? Pre-operative evaluation of hypoxemic patients with liver disease.

Liver cirrhosis and other chronic hepatic diseases are followed in a subset of affected patients by gas exchange abnormalities resulting from a syndrome called hepatopulmonary syndrome (HPS). The structural basis of this clinical entity is an alteration of pulmonary vasculature resulting in abnormal vasodilatation and mismatching of ventilation and perfusion of the lung. Dilatation of the capillary bed near the gas exchange area is the most important factor implicated; it precludes O2 molecules diffusing to the centrum of the dilated vessels to oxygenate venous blood. Contrast (microbubbles) echocardiography and lung perfusion scan are, respectively, the screening tests with the highest sensitivity and specificity for HPS diagnosis. Because of the high morbidity and mortality of HPS, clinicians have been trying to understand the pathophysiology of pulmonary vasodilatation in the hope that the process can be reversed pharmacologically or surgically. An imbalance between production and clearance of vasoactive circulating substances has been implicated in the pathogenesis of HPS with glucagon and nitric oxide among the principal responsible factors. To date various molecules have been implicated for therapy but without definitive positive results. Liver transplantation remains the only real therapy for HPS, and resolution of gas exchange defects outlines the possible functional reversible nature of vascular abnormalities of this syndrome. The need to perform surgery under general anesthesia for hepatic and extrahepatic procedures in patients with HPS is followed by an increased peri-operative risk. The authors emphasize the role of pre-operative clinical evaluation for proper patient management during the peri-operative period.

Acute motor axonal polyneuropathy after a cisatracurium infusion and concomitant corticosteroid therapy.

A 40-yr-old male was admitted to the intensive care unit following blunt chest trauma. He had multiple rib fractures, bilateral pneumothoraces, and acute respiratory failure requiring mechanical ventilation. Sedation was achieved with midazolam and morphine, and later with propofol. The patient was paralysed with a continuous infusion of cisatracurium 1.42-5.75 micro g kg(-1) min(-1). Methylprednisolone 125 mg i.v. every 12 h was also started. After discontinuation of the cisatracurium infusion 7 days later, the patient manifested a flaccid quadriplegia with absence of deep-tendon reflexes. No sensory deficits were observed. Electromyography (EMG), repetitive nerve stimulation testing, and single fibre EMG (SFEMG) were performed at regular intervals after stopping cisatracurium. Clinical symptoms and electrophysiological examinations supported the diagnosis of acute motor axonal polyneuropathy related to concomitant administration of cisatracurium and corticosteroid therapy.