Pathophysiological Basis of Acute Respiratory Failure on Non-Invasive Mechanical Ventilation.

Noninvasive mechanical ventilation (NIMV) was created for patients who needed noninvasive ventilator support, this procedure decreases the complications associated with the use of endotracheal intubation (ETT). The application of NIMV has acquired major relevance in the last few years in the management of acute respiratory failure (ARF), in patients with hypoxemic and hypercapnic failure. The main advantage of NIMV as compared to invasive mechanical ventilation (IMV) is that it can be used earlier outside intensive care units (ICUs). The evidence strongly supports its use in patients with COPD exacerbation, support in weaning process in chronic obstructive pulmonary disease (COPD) patients, patients with acute cardiogenic pulmonary edema (ACPE), and Immunosuppressed patients. On the other hand, there is poor evidence that supports the use of NIMV in other pathologies such as pneumonia, acute respiratory distress syndrome (ARDS), and during procedures as bronchoscopy, where its use is still controversial because the results of these studies are inconclusive against the decrease in the rate of intubation or mortality.

Humidification on Ventilated Patients: Heated Humidifications or Heat and Moisture Exchangers?

The normal physiology of conditioning of inspired gases is altered when the patient requires an artificial airway access and an invasive mechanical ventilation (IMV). The endotracheal tube (ETT) removes the natural mechanisms of filtration, humidification and warming of inspired air. Despite the noninvasive ventilation (NIMV) in the upper airways, humidification of inspired gas may not be optimal mainly due to the high flow that is being created by the leakage compensation, among other aspects. Any moisture and heating deficit is compensated by the large airways of the tracheobronchial tree, these are poorly suited for this task, which alters mucociliary function, quality of secretions, and homeostasis gas exchange system. To avoid the occurrence of these events, external devices that provide humidification, heating and filtration have been developed, with different degrees of evidence that support their use.

Noninvasive Mechanical Ventilation in Acute Respiratory Failure Patients: A Respiratory Therapist Perspective.

Physiotherapist in Chile and Respiratory Therapist worldwide are the professionals who are experts in respiratory care, in mechanical ventilation (MV), pathophysiology and connection and disconnection criteria. They should be experts in every aspect of the acute respiratory failure and its management, they and are the ones who in medical units are able to resolve doubts about ventilation and the setting of the ventilator. Noninvasive mechanical ventilation should be the first-line of treatment in acute respiratory failure, and the standard of care in severe exacerbations of chronic obstructive pulmonary disease, acute cardiogenic pulmonary edema, and in immunosuppressed patients with high levels of evidence that support the work of physiotherapist. Exist other considerations where most of the time, physicians and other professionals in the critical units do not take into account when checking the patient ventilator synchrony, such as the appropriate patient selection, ventilator selection, mask selection, mode selection, and the selection of a trained team in NIMV. The physiotherapist needs to evaluate bedside; if patients are properly connected to the ventilator and in a synchronously manner. In Chile, since 2004, the physioterapist are included in the guidelines as a professional resource in the ICU organization, with the same skills and obligations as those described in the literature for respiratory therapists.

Acetylcholinesterase and inhibitors: effects upon normal and regenerating nerves of the rat.

In peripheral nerves, the function of acetylcholinesterase (AChE) is not related to hydrolysis of acetylcholine. To test for a trophic role, AChE or its inhibitors were administered locally to normal and regenerating nerves of rats. In the normal nerve, neither AChE nor serum albumin affected the cytological pattern of the nerve. BW284c51, a specific inhibitor of AChE, resulted in demyelination, proliferation of Schwann cells and sprouting of axons after 5-7 days. Edrophonium or propidium, other specific inhibitors of AChE, did so to a much lesser extent. Vehicle, and iso-OMPA (inhibitor of pseudocholinesterases) did not affect the cytology of the nerve. Elongation of regenerating axons was evaluated at day 3 post-crush. Native AChE applied distal to the crush reduced the elongation of regenerating axons (- 36%), while serum albumin, heated AChE and filtered AChE did not. BW284c51, edrophonium or propidium enhanced the axonal elongation (33%) when they were administered for 2 days before, but not after, the crush. Iso-OMPA or vehicle administered before or after the crush were not effective. Thus, AChE reduces elongation of regenerating axons, while inhibition of AChE enhances elongation and affects the cytology of the normal nerve as well. We propose that AChE has a trophic role in mammalian peripheral nerves.

Pattern formation in a patch occupancy metapopulation model: a cellular automata approach.

The explicit consideration of space in ecological research is of paramount importance to understand the structure and functioning of ecological systems. In this paper we develop a simple spatially explicit metapopulation model in which colonization is constant and independent of the number of occupied patches (i.e. propagule-rain effect, Gotelli, 1991). Extinction, on the other hand, is modelled as a stochastic process whose intensity depends on the number of occupied patches in the neighborhood of each focal patch. Our model is the CA counterpart of two classical patch occupancy metapopulation models. We analytically prove this by showing that our CA converges to the differential equation in the mean-field approximation. The asymptotic behaviour of the system, expressed as the proportion of occupied patches, agrees with the equilibrium proportion of patches derived by using ODEs. In both models, the existence of a rescue-effect increases the range of extinction and colonization parameters over which the system attains complete occupancy of patches. However, in our model this result is strongly influenced by the degree of coupling among patches and is apparent only for local interactions. With local interactions and particular parameter values of colonization and extinction, self-organized spatio-temporal patterns emerge with a fractal-like clustering, even though the environment is spatially homogeneous. Our results point out that the importance of being spatial and discrete (Durrett & Levin, 1994a) in our model is a result of local interactions.