Mechanical Ventilation At A Glance

Mechanical ventilation may be either non-invasive and include various types of face masks, or else, by means of invasive endotracheal intubation (Restoring and Backing up the airways: endotracheal tube). The choice of the appropriate method requires a basic understanding of the mechanics of breathing. Indications There are numerous indications for endotracheal intubation and mechanical ventilation (see table: situations that require you to secure the airways), but in general mechanical ventilation should be considered if there is clinical or laboratory evidence that the patient does not has control over his breathing or does not have adequate oxygenation and ventilation. Among the findings, respiratory rate> 30 / min, the inability arterial O2 saturation is one of> 90% with fractional inspired O2 (FiO2) maintain> 0.60 and PaCO2> 50 mmHg at a pH <7.25. The decision to initiate a mechanical ventilation should after a clinical assessment that takes into account the entire clinical situation are taken, and should not be delayed until the patient is critical. Mechanical aspects of ventilation The normal inspiration leads to a negative intrapleural pressure, so that a pressure gradient between atmosphere and the Lungenalveoli results, from which the resulting inhalation. In case of mechanical ventilation this pressure gradient from the (positive) pressure, which emanates from the ventilation source is produced. The airway peak pressure is measured at the time of opening of the airway (Pao) and routinely displayed by a ventilator. This pressure represents the total pressure required to push a volume of gas in the lungs. It is composed of the press together, which results from the inspiratory flow resistance (resistive pressure), the elastic recoil of the lungs and chest wall (elastic pressure), as well as the alveolar pressure at the beginning of the breath (positive end-expiratory pressure [PEEP]) (under components of the airway pressure during mechanical ventilation; shown for a breath with inspiratory plateau (inspiratory hold)).. This results in resistive pressure from the resistance in the ventilation system and the air flow. When mechanically ventilated patients develop a resistance to the flow of gas that occurs in the circuit system of ventilation unit, the endotracheal tube and particularly in the respiratory tract of the patient. Note: Even if these factors are held constant, an increased flow components leads to an increase of the resistive pressure of the airway pressure during mechanical ventilation;. shown for a breath with inspiratory plateau (inspiratory hold). PEEP = positive end-expiratory pressure. The elastic pressure is the product of the elastic restoring force of the lungs and chest wall (elastance) and the volume of the administered gas. For a given volume of the elastic pressure rises (as in pulmonary fibrosis) or by the restricted ability of excursion chest wall or diaphragm (z. B. even with massive ascites or massive obesity) to increase by the lung stiffness. Because elastance and compliance behave inversely, resulting in high elastance low compliance. The end-expiratory pressure in the range of alveoli usually corresponds to the atmospheric pressure. However, when the alveoli are not completely emptied as a result of airway obstruction or the duration of expiration is shortened, the end-expiratory pressure compared with atmospheric pressure can be positive. This pressure is referred to as intrinsic PEEP or auto-PEEP. This expresses that it is different from an externally supplied (therapeutic) PEEP, which creates a positive pressure in the region of the airway by the respective setting of a ventilator or the application of a tight-fitting mask. Each increase in the respiratory peak pressure (z. B.> 25 cm H2O) should directly from a measurement of the end-inspiratory pressure (plateau pressure) may be followed. This is done with an end-inspiratory breath hold ( “end-inspiratory hold maneuver”) so as to determine the relative proportions of the resistive and elastic pressure. In this maneuver, the exhalation valve for about 0.3-0.5 seconds after the inspiration is kept closed. During this time the airway pressure drops as a function of the decrease in respiratory flow of the maximum value. The resulting end-inspiratory pressure is, after deduction of the PEEP pressure represents the elastic (assuming the patient makes no inspiratory or expiratory active contractions of the muscles at the measurement time). The difference between peak and plateau pressure is then the resistive pressure. Increased resistive pressure (eg. As> 10 cm H2O) suggests a blockage of the endotracheal tube with secretion, intraluminal obstacles and accumulations of secretions or bronchospasm. An increase in the elastic pressure (z. B.> 10 cm H2O) indicates a decreased lung compliance by edema, fibrosis or lobar atelectasis, or on large pleural effusions, pneumothorax or fibrothorax. Extrapulmonary restriction resulting from orbiting burns or other chest wall, ascites, pregnancy or massive obesity, may also cause, or a tidal volume which is too large for the lung (eg. B. when a normal tidal volume of a single lung supplied is because the endotracheal tube is positioned incorrectly). The intrinsic PEEP can be found in passive patient with the aid of end-expiratory breath stop ( “end-expiratory hold”). Immediately before a breath, the exhalation valve is closed for 2 seconds. The respiratory rate decreases, the resistive pressure is eliminated. Then the resulting pressure reflects the intra-alveolar pressure at the end of expiration (intrinsic PEEP). Although a precise measurement depends on that the patient is completely passive ventilator, the use of a neuromuscular blockade solely for measuring the intrinsic PEEP is unjustified. A non-quantitative method for the determination of the intrinsic PEEP is to view the course of the expiratory flow curve. Takes the expiratory flow until the next breath, or go to the thorax not before the next breathing cycle in the starting position, there is an intrinsic PEEP. From an increase in intrinsic PEEP is an increased work of breathing at the same time a depreciation of venous return flow, which can lead to decreased cardiac function and hypotension results. The detection of an intrinsic PEEP should immediately to search for the causes of respiratory flow reduction give rise (for example, secretions in the airways;. Reduced elastic recoil; bronchospasm), although a high minute volume (> 20 l / min), even without the presence of airway obstruction may lead to an intrinsic PEEP. If a boundary of the breath stream are present, can be reduced by shortening the inspiration time of the intrinsic PEEP (eg. As by increasing the inspiratory flow, or by decreasing the respiration frequency). This results in that a greater proportion of the breathing cycle is the expiration available. Ways and forms of mechanical ventilation ventilators are adjusted so that they with each breath, a constant volume (volume mode), providing a constant pressure (pressure control) or a combination of both. Ventilation holding a minimum breathing rate, regardless of whether the patient initiates a spontaneous breathing, (A / C) are referred to as assisted-controlled ventilation. Pressures and volumes are connected in the pressure-volume curve. Thus, each predetermined volume results in a corresponding pressure value and vice versa. This is regardless of whether the fan pressure or working volume mode. For fans, various ventilation parameters can be set: respiratory rate, tidal volume (tidal volume), trigger sensitivity, flow rate, type of ventilation curve and respiratory time ratio (inhalation / exhalation ratio, “I / E Ratio”). In this mode, ventilation volume, comprising the volume-controlled ventilation (A / C) and the SIMV ventilation ( “synchronized intermittent mandatory ventilation”), the ventilator delivers an adjustable tidal volume, respectively. The resulting airway pressure is not fixed from the outset, but varies as a function of resistance and elastance of the respiratory system and is also affected by the selected flow rate. V / C ventilation thus provides the easiest and most effective way for a fully mechanical ventilation. Here, each respiratory drive, which exceeds a set threshold value to a preset breath. Performs If the patient does not trigger this system often enough, the fan administered breaths independently and thus represents a desired minimum of breaths per time unit safely. SIMV allows the setting of a frequency and a volume that is synchronized with the breathing efforts of the patient. Unlike the V / C mode, the patient located above a selected respiratory rate respiratory efforts, not assisted. Nevertheless, the inspiration valve is open and the patient can breathe freely. This ventilation mode is still popular, although hereby can not be ventilated fully controlled (as with the V / C ventilation), it is not easy to wean the patient from mechanical ventilation, and the mode is not the patient’s comfort erhöht.Druckbeatmung This form of mechanical ventilation comprises the pressure-controlled ventilation (PCV), the pressure support ventilation (PSV) as well as various non-invasive modes that can be applied via a sealing patch face mask. However, all these methods have in common is that the fan administered a preset inspiratory pressure. This means, the tidal volume is determined by the resistance and the elasticity of the respiratory system. In this ventilation mode mechanical changes in the respiratory system can lead to unnoticed changes in minute ventilation. However, because it is here in a limitation of the expansion pressure on the lungs, this ventilation mode can theoretically just for patients with ALI / ARDS (Acute hypoxic respiratory failure (AHRF ARDS)) be favorable. Nevertheless, clear clinical advantages over A / C ventilation have not been proven yet. In addition, the expansion pressure is the same as when the volume that is supplied with pressure ventilation and A / C-ventilation, is the same. Pressure ventilation is a pressure-controlled form the A / C-ventilation. Every breath of the patient approach that exceeds a set threshold is answered with a full printing support through the respirator. The duration of the inspiration is also set as a minimum ventilation rate. In pressure support ventilation breaths triggered by the patient. PSV no minimum number of breaths is set. The fan helps the patient by providing a pressure which is maintained at a constant level until the inspiratory flow of the patient drops below a predetermined algorithm. This means the longer or extended breathing attempt by the patient, the greater is the draw volume. This ventilation is the most common method to wean patients from mechanical ventilation. Here, the patient may gradually more and take on more work of breathing itself. However, it is not proved that this method successful ist.Nichtinvasive positive pressure ventilation (NIPPV) In the NIPPV ( “noninvasive positive pressure ventilation”) is a positive pressure ventilation through a tightly seated mask, nose or nose and mouth covered administered. Helmets that provide NIPPV be investigated as an alternative for patients who can not tolerate the standard, tight-fitting respirators. Because of its use in spontaneously breathing patients NIPPV is usually applied as a form of PSV, although it can be ventilated and volume controls. Noninvasive positive pressure ventilation (NIPPV) using “bilevel positive airway pressure” Video created by Hospital Procedures Consultants, www.hospitalprocedures.org. var model = {videoId: ‘3903722519001’, playerId ‘SyAEZ6ptl_default’, imageUrl ‘http://f1.media.brightcove.com/8/3850378299001/3850378299001_4412116893001_vs-55c8fc48e4b097d1c2d5213a-672293880001.jpg?pubId=3850378299001&videoId=3903722519001’ title: ‘non-invasive positive pressure ventilation (NIPPV) using “bilevel positive airway pressure “‘

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