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
Other Indications For PEEP
-Includes the treatment of noncardiogenic pulmonary edema or early ARDS. The capillary endothelial changes associated with the early phase are
-Diffuse -Generalized -Causes of decrease in FRC, however, decrease is minimal -Hypoxemia, which is normally somewhat responsive to oxygen therapy
Other Indications For PEEP
-PEEP therapy has also been recommended for the following pathophysiological conditions. However data established its efficacy are questionable
-Chest trauma (such as failed chest)
-Cardiogenic pulmonary edema -Following open heart surgery
Physiologic PEEP
-The application of 3 to 5 cmH2O of PEEP to replace the glottic mechanism
-The placement of a foreign body between the vocal cords result in a reflexive decrease in FRC
-This occurs in all individuals but has only been demonstrated to be clinically significant in two populations
-Neonate/ pedi -PTs with severe COPD
-PEEP of 3-5 is often used in average PT requiring short term artificial airway. The effect of such treatment has not been established nor have any adverse reactions been documented
Physiologic PEEP
-Neonate/ pedi
-The group should have a short term artificial airway in place with 3-5 PEEP. If extubation is indicated, they are extubated from 3-5 cmH2O PEEP rather than from atmospheric pressure
Physiologic PEEP
-PTs with severe COPD
-Again establishment of an artificial airway under acy=ute conditions results in a significant decrease in FRC, causing hypoxemia. It is advisable to maintain 5CMH2O PEEP in these PTs until extubated
Prophylactic PEEP
-PEEP has been used to prevent ARDS or postoperative pulmonary complications
-No definitive data for or against this application of PEEP are available
Clinical Goals of PEEP Therapy
-The end point of PEEP therapy is defined by:
-Adequate arterial oxygenation
-Minimal FIO2 -Adaequare cardiovascular function
Clinical Goals of PEEP Therapy
-Adequate arterial oxygenation
-Defined as a PaO2> 60 mmHg. This normally results in a 90% Spo2
-Normal hemoglobin content
Clinical Goals of PEEP Therapy
-Minimal FIO2
-The specific FiO2 that is safe to inspire over a period of time has not been determined
-Most suspect that an FIO2>50% is necessary. Maintaining an FIO2 below 40% is ideal
Clinical Goals of PEEP Therapy
-Adequate cardiovascular function
-Entails maintaining an appropriate cardiac output for the particular PT
-Entails maintaining adequate tissue perfusion -Normal skin temp -Normal urinary output -Intact sensorium -The goal of PEEP therapy is to adequately oxygenate someone with minimal FiO2 and maintain cardiovascular function
Monitoring PEEP Therapy
-With the application of PEEP or the altercation of PEEP levels, extensive monitoring of PT cardiopulmonary status must be performed
-Monitoring should be done 10-20 min after each PEEP adjustment and periodically thereafter
Monitoring gas exchange
w/ PEEP
-Arterial blood gas
-Intrapulmoary shunt if accessible
-Monitoring pulmonary mechanics
w/ PEEP
-Evaluation of tidal volume, RR, and WOB
-Dynamic and static compliance
Monitoring Cardiovascular function
w/PEEP
-Pulse and blood pressure
-Skin color -Skin temp -Urinary output -Sensorium -Cardiac output -PAP -CVP PCWP -Note: If PEEP levels exceed 15 cmH2O it is advisable to insert a pulmonary artery cath for proper elevation cardiovascular function
Periodic Discontinuation of PEEP
-The periodic discontinuation of PEEP should be avoided. This is particularly true when higher levels of PEEP are employed
-Discontinuation of PEEP on a periodic basis results in -Significant decrease in PaO2 -Increase in intraocular shunt -Possible increase in venous return -Decrease in FRC -Decreased pulmonary compliance -A complete reversal of the changes accomplished with the application of PEEP -Once PEEP levels reach or exceed 15 cmH2O, PEEP should be maintained on the manual vent during suctioning and transport -PEEP should not be discontinued when hemodynamic monitoring is boeing performed
Clinical Application of PEEP
-Regardless of severity of disease all adults PT should be started on 3-5 cmH2O PEEP. Pedi and neonatal PT should be started on 3-5 PEEP (If PT is currently on CPAP, set at same level)
-PEEP levels should be increased in 3-5 cmH2O increments in adults, 3-5 increments in neonatal and pedi PTs, followed by complete monitoring of effects of PEEP -If an increase in PEEP results in adverse cardiovascular effects, fluid therapy. And or pharmacological support should be used to stabilize cardiovascular function before PEEP level is again increased -AS PEEP is applied, a significant increase in PaO2 should be noted. If s 20-40 cmmmHg is not seen the optimal level of PEEP for Pt may not have been attained
-When you wish to increase a low PAO2
-First thing you want to do is increase FIO2 by 5-10% (up to 60%)
-Then increase PEEP levels by 2-5 cmH2O until -Acceptable oxygenation is achieved or -Inacceptable side effects occur (decreased compliance, decreased cardiac output function, barotrauma, increased C9a-v)O2, etc.)
