ACUTE RESPIRATORY FAILURE ACUTE RESPIRATORY DISTRESS SYNDROME ARF ARDS 1 ARF / ARDS Definition A sudden and life threatening deterioration of the gas exchange function of the lung and indicates failure of the lungs to provide adequate oxygenation or ventilation for the blood Respiratory failure by itself is not a disease, but rather a symptom of alteration in lung tissue function Delivery of oxygen Cardiac output Hypoxemia Alteration in transfer of oxygen Results in decreased PaO2 and decreased sats Hypercapnia Alteration on CO2 removal Results in increase in PaCO2 When assessing for hypoxemia or hypercapnia you must keep in mind that the patient’s baseline may be an abnormal value i.e. COPD patients Common causes Asthma, COPD, Cystic Fibrosis, Drug overdose, Morbid obesity, and Cervical cord injury as some of these causes ARF / ARDS 2 Classifications Hypoxemic respiratory failure There are two classifications of ARF Hypoxemic respiratory failure – oxygen failure Most common form of respiratory failure Characterized by a PaO2 of less than 60 with a normal or low PaCO2 while receiving oxygen at greater than 60% Acute hypoxemic respiratory failure is severe arterial hypoxemia that is refractory to supplemental O2 The is inadequate transfer of O2 in the alveoli and the pulmonary capillary bed Causes Pneumonia, shock, PE Hypercapnic respiratory failure Hypercapnic respiratory failure – ventilatory failure There is insufficient CO2 removal Characterized by a PaCO2 of greater than 45 with an acidotic pH and the body is unable to compensate Common causes include drug overdose, severe airway disorders (asthma, COPD) Trauma due to poor ventilatory effort 3 ARF / ARDS V/Q mismatch Definition This is a mismatch between ventilation and perfusion A defect which occurs in the lungs whereby ventilation (the exchange of air between the lungs and the environment) and perfusion (the passage of blood through the lungs) is not evenly matched Perfect match is 1 mL of air (ventilation) in each portion of the lung is received for each 1 mL of blood flow (perfusion) 1:1 V/Q mismatch is the most common cause of hypoxemia and a component of most causes of respiratory failure. In a patient with V/Q mismatch, there will most likely be some areas of the lungs which are better perfused that ventilated and some areas which are better ventilated than perfused. While this occurs to some degree in the normal lung, in V/Q mismatch, it is increased significantly to the point of being pathological When ratio is decreased, what does it mean? Ventilation is not adequate and perfusion is greater When ratio is increased: ventilation is increased and the patient blows off CO2 Causes When not 1:1; mismatch occurs COPD, Pneumonia, Asthma Treatment 1st line of treatment is administer oxygen Oxygen administration causes increased O2 more oxygenated blood to mix with poorly oxygenated blood raising the PaO2 of blood leaving the lungs Identify cause and treat HYPOXEMIC RESPIRATORY FAILURE ARF / ARDS 4 Shunt Definition When blood exits the heart without having gas exchange Types Anatomic An anatomic shunt occurs when blood bypasses the lungs through an anatomic channel Such as from the right to the left ventricle through a ventricular septal defect Blood doesn’t pass through the lungs Intrapulmonary Blood flows through the pulmonary capillaries with having little or no gas exchange Alveoli are filled with fluid and little or no gas exchange takes place Causes Conditions that cause the alveoli to become filled with fluid such as in Pneumonia, Pulmonary edema Treatment Need increased means of administering oxygen: such as with mechanical ventilation 5 ARF / ARDS Diffusion limitation Definition Alveolar-capillary membrane is thickened or destroyed causing a compromise in the gas exchange Slows gas transport Causes Severe emphysema (COPD), Pulmonary fibrosis, ARDS Classic sign Hypoxemia during exercise but not at rest Treatment Identify cause, treat symptoms HYPOXEMIC RESPIRATORY FAILURE 6 ARF / ARDS Alveolar Hypoventilation Definition Decreased ventilation increased in PaCO2 and a decrease in PaO2 Causes Restrictive lung disease, acute asthma, alterations in chest wall Although alveolar hypoventilation is primarily a mechanism of hypercapnic respiratory failure, it also causes hypoxemia and is included in this discussion Usually hypoxemic respiratory failure will be a result of a combination of these four specific processes HYPOXEMIC RESPIRATORY FAILURE 7 ARF / ARDS Introduction Imbalance between ventilator supply and demand Hypercapnic respiratory failure is defined as acute respiratory distress resulting in a PaCO 2 greater than 45 mmHg. Typically, this involves abnormalities with CNS control of respiration, or the airways involved with gas transport. Hypercapnic respiratory failure is thus often called "respiratory pump failure" or "ventilatory failure." This is the primary problem Respiratory system is unable to remove adequate amount of CO2 to maintain a normal CO2 level Ventilator supply Ventilator demand Max amount of gas flow in and out of lungs without having respiratory muscle fatigue Amount of ventilation necessary to keep CO2 within normal limits Normally, supply is greater than demand which is why we are able to exercise with an increase in our PaCO2 HYPERCAPNIC RESPIRATORY FAILURE 8 ARF / ARDS Four categories of Hypercapnic Respiratory Failure Airways/Alveoli COPD and cystic fibrosis cause air flow obstruction and air trapping Because of this, places the patient at high risk for developing hypercapnic respiratory failure Develop respiratory fatigue because they have to work harder to breathe against the increased resistance CNS Conditions that can cause respiratory depression and depress the drive to breathe Such as drug overdose Other conditions that can cause interruption of the normal function of the respiratory center are Severe head injury Brainstem infarct (stroke) Any loss of consciousness can place patient at risk because they lose the ability to manage secretions and protect airway HYPERCAPNIC RESPIRATORY FAILURE 9 ARF / ARDS Chest Wall Conditions that limit chest wall movement and interferes with chest expansion Conditions that limit chest wall movement and ultimately gas exchange include Flail chest – a portion of the rib cage is separated from the rest of the chest wall Fractured ribs Morbid obesity Excess weight on chest and abdominal cavity can put undue pressure on diaphragm and limit lung expansion Neuromuscular Conditions that cause respiratory muscle weakness or paralysis Because of this muscle weakness and paralysis the patient is unable to maintain normal PaCO2 levels Muscular dystrophy Acute exacerbation of myasthenia gravis Multiple sclerosis After this discussion you can see that in the last three, the patient can have hypercapnic respiratory failure, yet have normal lungs In these 3; the medulla, the chest wall, or the respiratory muscles don’t function normally and the patient cannot remove a sufficient amount of CO2 HYPERCAPNIC RESPIRATORY FAILURE ARF / ARDS 10 Hypoxemia Respiratory Dyspnea, prolonged expiration Increased RR Retractions Decreased sats Late sign Cerebral Confusion, agitation, restless Decreased LOC Late sign Cyanosis Coma Cardiac Tachycardia, HTN Cool, clammy skin Late sign Dysrhythmias Hypotension Other Fatigue Can’t complete sentence without stopping to breathe CLINICAL MANIFESTATIONS ARF / ARDS 11 Hypercapnia Respiratory Dyspnea Decreased RR or increased and shallow Decreased tidal volume, Cerebral AM headache Disorientation Late sign Dysrhythmias, HTN, HR Neuromuscular Muscle weakness ↓DTR Late sign Coma Cardiac Volume of air inhaled and exhaled at each breath. Seizures Other Pursed lip breathing Tripod position CLINICAL MANIFESTATIONS ARF / ARDS 12 Respiratory rate either can be decreased or increased, but shallow Position of comfort – ask # of pillows patient uses to sleep – indication of distress Both contribute to inadequate removal of CO2 Position patient takes gives a good indication of the degree of respiratory distress Mild distress – patient may be able to lie down Moderate distress – prefers to sit Severe distress – can only breathe when sitting up Verbal communication Due to degree of distress patient may only be able to speak a couple of words without stopping to “catch their breath” May want an alternative means of communication Or ask questions in a way that they can be answered with yes or no, or only two or three words Inspiratory/expiratory ratio Normal is 1:2, meaning expiratory is twice as long as inspiratory Airflow obstruction causes changes and could be 1:3 or 1:4 Work of breathing can lead to respiratory muscle fatigue Retractions Paradoxical breathing – abd/chest move in opposite direction Move outward during exhalation – inward during inspiration SPECIFIC CLINICAL MANIFESTATIONS ARF / ARDS 13 Physical assessment ABG Determines respiratory function Ventilation and oxygenation status CXR Identify causes of respiratory distress such as pneumonia, atelectasis Pulse Ox Discuss Monitor O2 sats with or without exercise Labs Routine CBC, chemistry, UA Cultures Blood, sputum Determine source of infection DIAGNOSTIC STUDIES ARF / ARDS 14 Medications Bronchodilators via nebulizer Relief of bronchospasms and open airways Given with O2 in hospital to reduce risk of worsening the hypoxia that occurs when inspired gases are redistributed to areas with reduced perfusion Corticosteroids Antibiotics Reduce airway inflammation If infection is evident Analgesics/Anti-Anxiety Reduce pain Reduce agitation, anxiety Reduce pulmonary congestion Direct or indirect injury to the lung that causes decreased alveolar ventilation and hypoxemia For pulmonary congestion caused by heart failure give Lasix, morphine, and nitro to get rid of fluid and reduce oxygen demand For pulmonary congestion caused by A fib then beta blockers, calcium channel blockers MANAGEMENT to improve cardiac output by decreasing the heart rate ARF / ARDS 15 Respiratory Therapy Oxygen therapy 1-3 L with NC; 24-32% venturi mask Improve O2 sats Improve ventilation Assess patient to ensure they can tolerate the delivery device Use cautiously in COPD patients – hypoxia stimulates their breathing Mobilize secretions Position See page 1594 for different types of coughing CPT Humidification Suctioning Remove excess secretions MANAGEMENT ARF / ARDS HOB elevated; good lung down Effective coughing i.e. mask can cause anxiety which increases demands 16 Noninvasive Page 1596 ( Figure 67. 7) Positive pressure ventilation – process of forcing air into the lungs Non invasive used for acute or chronic respiratory distress Mask fits tightly over nose or nose/mouth, patient spontaneously breathes while the positive pressure is delivered Done to decrease the work of breathing without having to intubate the patient Types BiPAP Separate pressure levels for inspiration and expiration CPAP Constant pressure is delivered during inspiration and expiration POSITIVE PRESSURE VENTILATION ARF / ARDS 17 Indications Effective in treating patients with chronic respiratory distress caused by chest wall or neuromuscular conditions Non indicators Not appropriate for patients with excessive secretions, decreased LOC, those needing high oxygen requirements, facial trauma or those hemodynamically unstable POSITIVE PRESSURE VENTILATION ARF / ARDS 18 Invasive Apnea Acute respiratory failure Respiratory muscle fatigue Ventilators Negative pressure Mechanical ventilation in which negative pressure is generated on the outside of the patient's chest and transmitted to the interior to expand the lungs and allow air to flow in; used with weak or paralyzed patients. Chambers encase the chest or body and surround it with negative pressure Iron lung first form of negative pressure Positive pressure Method normally used with acutely ill, non stable patients Mechanical ventilation in which air is delivered into the airways and lungs under positive pressure, usually via an endotracheal tube, producing positive airway pressure during inspiration Page 1574; Figure 65 – 19 MECHANICAL VENTILATORS ARF / ARDS 19 Modes of Volume Ventilation Volume ventilation – a set tidal volume is delivered with each inspiration and pressure necessary to deliver the breath depends on compliance and resistance factors Vent settings will be based on several factors including: rate, depth, and patient status The tidal volume remains the same, but the pressure can vary Modes of Volume Ventilation Controlled mandatory ventilation – does all the work Breaths are delivered at a set rate per minute Used infrequently When patient has no drive to breathe Or cannot breathe spontaneously Anesthetized patients Paralyzed patients Assist-control mechanical ventilation Delivers a preset tidal volume at a preset frequency Assist the patient, when patient initiates a spontaneous breath, the vent delivers a preset tidal volume Patient can breathe faster than set rate on vent, but never slower MECHANICAL VENTILATORS 20 ARF / ARDS Synchronized intermittent mandatory ventilation Delivers a preset tidal volume at a preset frequency with the patient’s spontaneous breathing Like AC, SIMV delivers a minimum number of fully assisted breaths per minute that are synchronized with the patient's respiratory effort. However, any breaths taken between volume-cycled breaths are not assisted The volumes of these breaths are determined by the patient's strength, effort, and lung mechanics. Summary of difference With SIMV the breaths over the set amount only get the tidal volume the patient can muster on their own With AC the patient gets the same tidal volume with all breaths MECHANICAL VENTILATORS ARF / ARDS 21 Positive end-expiratory pressure Positive end-expiratory pressure is the pressure in the lungs (alveolar pressure) above atmospheric pressure (the pressure outside of the body) that exists at the end of expiration. A method of mechanical ventilation in which pressure is maintained to increase the volume of gas remaining in the lungs at the end of expiration Thus reducing the shunting of blood through the lungs and improving gas exchange Continuous positive airway pressure (CPAP) We defined this previously as constant pressure delivered during inspiration and expiration Bilevel positive airway pressure (BiPAP) Remember we defined this as separate pressure levels for inspiration and expiration MECHANICAL VENTILATORS ARF / ARDS 22 Complications Improper ET tube placement VAP – we discussed this when we discussed pneumonia Remember it is pneumonia developed after 2-3 days of intubation Barotrauma Damage to the lungs due to rapid or excessive pressure changes Mechanical ventilation can lead to barotrauma of the lungs. This can be due to Absolute pressures used in order to ventilate non-compliant lungs. Overdistended alveoli The resultant alveolar rupture can lead to pneumothorax, pulmonary interstitial emphysema (PIE) (collection of gas outside of normal air passages) and pneumomediastinum (air leaks from any part of the lung or airways into the mediastinum) Decreased cardiac output Because of the positive pressure it produces, positive pressure ventilation causes some degree of hemodynamic compromise (e.g., hypotension, decreased cardiac output). Controlled by administration of fluids, or, in severe cases, vasoactive drugs. GI Stress ulcers – patient stressed about illness, immobility, and the discomforts associated with being on a vent Gastric distention – excessive air swallowing, can be caused by irritation of the ET tube MECHANICAL VENTILATORS ARF / ARDS 23 ARDS Acute Respiratory Distress Syndrome 24 ARF / ARDS Definition ARDS is a type of ARF and is breathing failure that can occur in critically ill persons with underlying illnesses. It is not a specific disease. Instead, it is a life-threatening condition that occurs when there is severe fluid buildup in both lungs. The fluid buildup prevents the lungs from working properly— This fluid prevents enough oxygen from passing into the bloodstream. The fluid buildup also makes the lungs heavy and stiff, and decreases the lungs' ability to expand. Patients have severe SOB and often require mechanical ventilation ARDS often occurs along with the failure of other organ systems, such as the liver or kidneys. Cigarette smoking and heavy alcohol use may be risk factors. Incidence Death occurs in approximately 50% When associated with septic shock can be an increase of 70-90% mortality rate INTRODUCTION ARF / ARDS 25 Introduction Acute lung injury resulting from an unregulated systemic inflammatory response, damages alveolar capillary membrane Increased interstitial pressure and damage to alveolar membrane allow fluid into alveoli, dilutes and deactivates surfactant Atelectasis occurs, lungs lose compliancy and impaired gas exchange There are two main types of lung injuries: direct and indirect. Direct lung injuries are caused by infections, chemicals, and trauma that directly affect the lung, including: Pneumonia a severe lung infection Pulmonary aspiration Inhalation of harmful smoke or fumes Trauma to the lung, such as puncture wounds An indirect lung injury is caused by another condition elsewhere in the body. These include: Sepsis – infection that originated away from the lungs Severe bleeding from an injury or multiple blood transfusions. Burns Drug overdose Fat embolism PATHOPHYSIOLOGY ARF / ARDS 26 Three phases Injury/exudative phase 1 – 7 days after injury Interstitial and alveolar edema There is surfactant dysfunction Atelectasis occurs V/Q mismatch and shunting causes Refractory hypoxemia – not responsive to increased oxygen Diffuse limitation adds to the hypoxemia, making it worse Reduced lung compliance Reparative/proliferative phase 1 – 2 weeks after injury Proliferation of neutrophils, monocytes, lymphocytes, and fibroblasts due to inflammatory response When lung becomes dense and with fibrous tissue, phase is complete Lung compliance continues to worsen Hypoxemia gets worse Fibrotic phase – late phase and prognosis is poor 2 – 3 weeks after injury Remodeling has occurred Surface area for gas exchanged is reduced Pulmonary hypertension develops due to the vascular destruction PATHOPHYSIOLOGY ARF / ARDS 27 Progression If the patient is successful in surviving this stage, the pulmonary edema is resolved Patient recovers in a few days Chronic In this stage survival is poor Long term mechanical ventilator is required Factors that contribute to way the patient will or will not recover Mechanism of initial injury Any co-existing conditions and severity of that condition Any development of complications, specifically pulmonary ARDS PROGRESSION 28 ARF / ARDS Onset Insidious onset May take several hours or 1 – 2 days after the initial lung injury for the patient to exhibit any symptoms Respiratory symptoms include Dyspnea Tachypnea Cough May hear scattered rales Restlessness As ARDS Progresses Symptoms worsen due to increased accumulation of fluid, reduced lung compliance work of breathing with retractions Lung sounds (scattered crackles and rhonchi) Color changes pallor or cyanosis Profound distress Requires ET intubation CLINICAL MANIFESTATIONS ARF / ARDS 29 ABG Hypoxemia with PO2 < 60 and respiratory alkalosis due to hyperventilation Determine respiratory status CXR Compare to baseline After 24 hours of onset shows diffuse infiltration Profound distress may show “white out” So much consolidation – barely any notable air spaces PFT Determine patient respiratory status Decreased lung compliance and reduced vital capacity The amount of air that can be forcibly expelled from the lungs after breathing in as deeply as possible. DIAGNOSTIC TESTS ARF / ARDS 30 Infection Multiple organ dysfunction syndrome (MODS) is the major cause of death; mostly due to sepsis Vital organs involved: kidneys, liver, heart Systems affected: CNS, hematologic, GI, renal, respiratory VAP Up to 68% will develop VAP Risk factors include: altered immune system, cross contamination, multiple invasive devices, extended mechanical ventilation Strategies to prevent: infection control and VAP Bundle Oral care; HOB up; sedation holiday; Venous Thromboembolism prevention; stress ulcer prevention Barotrauma – we discussed this with ARF Absolute pressures used in order to ventilate non-compliant lungs. Overdistended alveoli that rupture The resultant alveolar rupture can lead to pneumothorax, pulmonary interstitial emphysema (PIE) and pneumomediastinum Can prevent by decreasing tidal volume on the vent COMPLICATIONS ARF / ARDS 31 Volutrauma Damage to the lung caused by overdistension by a mechanical ventilator set for an excessively high tidal volume in an effort to ventilate non compliant lungs Small tears in alveoli occur Smaller tidal volumes should be used in patients with ARDS Renal Failure The use of drugs that are toxic to kidneys, used to combat infection i.e. Vancomycin There is decreased renal tissue perfusion with the hypotension and hypoxia COMPLICATIONS 32 ARF / ARDS Respiratory Oxygen is your most important intervention Need to correct the hypoxemia Need higher concentrations of oxygen so face mask and n/c are not effective for this patient We discussed this earlier with ARF Positioning Continuous sat monitoring Mechanical Ventilation Lowest concentration to maintain PaO2 > 60 Prone positioning For those with refractory hypoxemia who do not respond to other strategies May improve the V/Q mismatch Heart rest on sternum, giving a more overall uniform in pleural pressures Not for all patients, close monitoring and evaluation Continuous lateral rotation therapy Bed actually moves patient from side to side 18 of the 24 hours/day Helps to mobilize secretions COLLABORATIVE ARF / ARDS MANAGEMENT 33 Supportive Medications When cardiac output falls Crystalloid (i.e. NS) or colloid (albumin) may be used Inotropic drugs i.e. dobutamine or dopamine Packed red blood cells Increase oxygen carrying capacity of the blood when hemoglobin decreases to less than 9 Nutrition Patient require high calorie and are started on enteral/parental feedings Accurate assessment of fluid balance to determine fluid status Patient may need some fluid restriction and diuretics COLLABORATIVE MANAGEMENT ARF / ARDS 34
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