Pressure at point B is equivalent to the alveolar pressure and is determined by the volume inflating the alveoli divided by the compliance of the alveoli plus the baseline pressure (PEEP) Pressure at point A (equivalent to airway pressure measured by the ventilator) is the sum of the product of flow and resistance due to the tube and the pressure at point B. Flow, volume and pressure are variables while resistance and compliance are constants. Flow = Volume/time It follows from the relationships between pressure, flow and volume that by setting one of pressure, volume or flow and the pattern in which it is delivered (which includes the time over which it is delivered) the other two become constants. It also follows that it is not possible to preset more than one of these variables as well as time
Partial liquid ventilation is a complex and laborintensive procedure requiring a team approach, including meticulous nursing care to prevent adverse reactions. For his safety and comfort during PLV, your patient may receive a combination of neuromuscular blocking agents, sedatives, and antianxiety agents. Be sure to explain to him and his family beforehand what PLV will involve and answer their questions.
P.L.V Improvement in compliance may simply be due to recruitment of alveoli but may be also be due to a direct effect on surface tension Other postulated benefits: - barrier against infection – washes out inflammatory debris
P.L.V. Still an experimental technique Lung is partially filled with perfluorocarbon and patient is ventilated with conventional apparatus Perfluorocarbons are simple organic compounds in which all the hydrogen atoms have been replaced by halogens. There physicochemical properties include high density, relatively high viscosity, low surface tension and a remarkable ability to dissolve both oxygen and carbon dioxide
High frequency ventilation ventilation of lungs at a frequency > 4 times normal rate - Most important difference from conventional IPPV is that it requires tidal volumes of only 1- 3 ml/kg body weight to achieve normocarbia - 3 types: high frequency positive pressure (used in anaesthesia), high frequency jet (anaesthesia and ICU) and high frequency oscillation
Advantages - Reduced peak and mean airway pressures - Improved CVS stability due to above - Decreased risk of barotrauma - Allows adequate ventilation with a disrupted airway (eg bronchopleural fistula) - Permits mechanical ventilation during bronchoscopy - Improves operating conditions eg in thoracic surgery - Allows ventilation through narrow catheters and thus increases access during laryngeal and trachael surgery - Reduces sedation requirements when used in ITU - Avoidance of hypoxia during tracheobronchial toilet
Disadvantages - Specialized equipment required - Dangers of high pressure gas flows - Humidification of inspired gases difficult - Tidal volumes markedly affected by changes in respiratory compliance - Monitoring of ventilation parameters difficult - Difficult to predict minute ventilation from ventilator
Prone ventilation Probable mechanism is that when patient is turned prone the ventilation to the dorsal atelectatic parts of the lung is improved. However perfusion continues to pass preferentially to these regions and hence shunt is reduced Reduction in thoraco-abdominal compliance thought to play an important part in producing beneficial effects of prone ventilation Most common serious complication of turning prone is accidental extubation
ECMO Extracorporeal life support, or extracorporeal lung assist
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