Methods to Improve Oxygenation Flashcards
-PEEP ( Positive end Expiratory Pressure)
The establishment and maintenance of a preset airway pressure greater than ambient at end exhalation
-CPAP (Continuous Positive Airway Pressure)
The application of PEEP therapy to the spontaneously breathing pt. Both inspiratory and expiratory airway pressure are supra atmospheric.
Effects on Intrapleural (Intrathoracic) Pressures
-PEEP increases Intrapleural Pressure
-The extent of the increase is determined by: -The amount of PEEP that is being applied -The stiffness of the individuals lungs
PEEP and Compliance
-The greater the individual’s compliance, the greater the transmission of PEEP to the intrapleural space and the greater the increase in intrapleural pressure.
-In a PT with normal lungs, PEEP therapy causes a significant increase in intrapleural pressure -In PT with generalized diffuse pulmonary disease (ARDS) process resulting in decreased compliance, given levels of PEEP may not cause a significant increase in intrapleural pressure -PT with localized pulmonary disease (e.g., pneumonia, atelectasis) demonstrate a similar increase in intrapleural pressure as PT with normal pulmonary compliance
Effects on Functional Residual Capacity (FRC)
-PEEP therapy causes an increase in FRC regardless of the condition of the lung at the time of application
-FRC is increased by
-Increasing the transpulmonary pressure gradient. This occurs in all individuals.
-Recruiting collapsed alveoli
-In PTs with decreased FRC as a result of alveolar collapse due to surfactant instability. PEEP maintains the alveoli inflated. -This is accomplished by PEEP maintaining a back pressure exceeding the force of surface tension and lung elastance, which tend to collapse alveoli -The actual re expansion of alveoli is accomplished by the force of normal inspiration or positive pressure. PEEP simply maintains the alveoli open once the are re expanded
Effects on Pulmonary Compliance
-Since PEEP therapy increases FRC, it may alter pulmonary compliance
-In normal lungs, the increased FRC will probably cause a decrease in compliance -In PT with adult respiratory distress syndrome (ARDS), the application of PEEP therapy increases compliance or improves it.
Effects of PEEP on the Cardiovascular System
-Since PEEP therapy increases intrapleural pressure, it can decrease venous retainer and thus decrease cardiac output
-The greater the increase in intrapleural pressure, the greater the potential detrimental effect on cardiac output
-PEEP causes a decrease in cardiac output by
-Decreasing venous return (decrease preload)
-Increasing right ventricular afterload -Resistance to flow the ventricle during systole
-When evaluating the effect of PEEP on Cardiac output, it is important to
place the decreased cardiac output into proper perspective
-May need fluid or pharmacological support to fix and adverse reaction on the heart to PEEP therapy
Hemodynamic Effects of PEEP Therapy
-Since PEEP therapy decreases venous return and cardiac output, a decrease in systemic blood pressure is noted as PEEP is applied
-Usually the decrease is minimal or moves the blood pressure to a more acceptable level -However, with PEEP levels that significantly interfere with cardiac output, systemic blood pressure may drop rapidly
-As PEEP therapy increases intrapleural pressure, it abates the thoracic pump mechanism. As a result, the pressure gradient distending intrathoracic blood vessels decrease, thereby increasing resistance to blood flow. This causes:
-Decrease in volume of blood returning to the right ventricle
-An alteration in pressure measured within the intrathoracic vessels (hemodynamics)
-If the increased intrapleural Pressure does not significantly alter blood flow, hemodynamic readings taken within the thoracic cavity will slightly increase
-Increased CVP= central venous pressure
-Increased PAP= Pulmonary artery pressure -Increased PAP= Pulmonary wedge pressure
-If, on the other hand, the increased intrapleural pressure does significantly alter blood flow, hemodynamic readings taken within the thoracic cavity will decrease. The extent of decrease is a result of interrelationship among myocardial capabilities, vascular volume and intrapleural pressure
-Decrease CVP
-Decreased PAP -Decreased PWP
Effects of PEEP on PaO2
-Since PEEP causes a minor increaser in the partial pressure if oxygen in the lugs, a small increase in PaO2 may be noted even in healthy lungs
-In the PT with ARDS, PaO2 levels also demonstrate only small increase as the PEEP level is increased and will not markedly rise until a significant number of alveoli have been recruited. When appropriate numbers of alveoli have been recruited, PaO2 values may increase 20-40 mmHg or more.
-PaO2 values may continue to increase slightly, remain the same or decrease if PEEP levels inhibit cardiac output
-A continual increase in PEEP will eventually affect cardiac output. However the blood that is capable of perfusing the lung will still be oxygenated and its oxygenation state may continue to improve slightly as cardiac output s=decreases
-When monitoring appropriateness of PEEP therapy, PaO2 must be evaluated, however, PaO2 provides no indication of the adequacy of cardiovascular function or of systemic oxygen delivery .
Optimal PEEP Study
-The level at which the maximum beneficial effects of PEEP occur without profound cardiopulmonary side effects
Effects on Intrapulmonary Shunt
-Increasing PEEP levels result in a decrease in intrapulmonary shunt
-AS alveoli are recruited, ventilation/ perfusion ,matching improves and shunting decreases
-Intrapulmonary shunt may continue to decrease even when cardiac output is significantly decreased
-The occurs because any blood that is presented to the lung may be better oxygenated
-When monitoring the appropriateness of PEEP therapy, intrapulmonary shunt should be evaluated, however, the intrapulmonary shunt provides no indication of adequacy of cardiovascular function or systemic oxygen delivery
Effects on ICP
-Since PEEP impedes venous return, it can be expected to increase intracranial pressure by causing blood pool in the cranium
-If the PEEP therapy is required in PT with ICP, el;evation of head of the bed can minimize effects of PEEP on ICP
Barotrauma and PEEP
-Anytime positive pressure is applied to the lung, likelihood of barotrauma is increased
-However barotraumas normally occur when PT simulate cough, fight vent, or engage in any activity that markedly increase intrapulmonary pressure -When high levels of PEEP are applied, careful monitoring for barotrauma must be maintained. This is necessary because of the lung requiring high levels of PEEP is significantly diseased and any increase in airway pressure may result in barotraumas
-The primary indication of PEEP is ARDS
-Refractory hypoxemia
-PEEP is an oxygenation tool
-PEEP is truly indications only in PT with a generalized diffuse acute restrictive disease process characterized by
-Decreased pulmonary compliance
-Decreased FRC -Refractory hypoxemia (increasing levels of O2= no change) -Increased intrapulmonary shunting
-PEEP does not correct the refractory hypoxemia associated with a localized disease process such as
-Pneumonia
-Pleural effusion
-Localized atelectasis
