Study Notes on Acute Respiratory Distress Syndrome (ARDS)

ACUTE RESPIRATORY DISTRESS SYNDROME (ARDS) OVERVIEW

  • ARDS is a form of respiratory failure characterized by:

    • Non-cardiogenic pulmonary edema

    • Refractory hypoxia

  • Pathophysiological characteristics of ARDS include:

    • Inflammation of lung tissue

    • Damage to pulmonary capillaries

    • Injury to alveoli, leading to impaired gas exchange.

  • Arterial Blood Gases (ABGs) typically show:

    • Rise in PaCO2 (partial pressure of carbon dioxide in arterial blood)

    • Decreased PaO2 (partial pressure of oxygen in arterial blood)

PATHOPHYSIOLOGY

  • ARDS can be caused by either direct or indirect lung injury:

    1. Direct Injury:

    • Lung tissue is damaged initially, causing a local inflammatory response.

    • This response leads to:

      • Damage to alveolar-capillary membrane

      • Increased permeability, resulting in fluid leakage into the alveoli, which causes ARDS.

    1. Indirect Injury:

    • A systemic inflammatory response occurs elsewhere in the body (e.g., Sepsis).

    • Inflammatory mediators circulate to the lungs, resulting in:

      • Alveolar-capillary damage and the onset of ARDS.

  • In both cases, inflammatory mediators elevate the permeability of the alveolar-capillary membranes, causing a leakage of protein-rich fluid into the alveoli, leading to:

    • Non-cardiogenic pulmonary edema

    • Decreased surfactant production due to damage to type II alveolar cells, resulting in:

    • Alveolar collapse (atelectasis)

    • Decreased lung compliance

  • Continued inflammation results in:

    • Formation of fibrin and cellular debris creating hyaline membranes

    • Severe ventilation-perfusion mismatch and refractory hypoxemia.

ETIOLOGY / RISK FACTORS

  • Direct Lung Injury can be due to:

    1. Pneumonia

    2. Aspiration of gastric contents

    3. Inhalation injuries

    4. Near drowning

  • Indirect Lung Injury can occur from:

    1. Sepsis

    2. Major burns

    3. Drug overdoses

    4. Pancreatitis

CLINICAL MANIFESTATIONS

  • Early Symptoms:

    • Dyspnea (difficulty breathing)

    • Tachypnea (rapid breathing)

  • Progressive Respiratory Distress:

    • Increased respiratory rate

    • Intercostal retractions and use of accessory muscles of respiration

    • Tachycardia due to oxygen demand increase

    • Development of crackles and rhonchi later in the progression

    • Potential for cyanosis

    • Altered mental status including agitation, confusion, and lethargy as respiratory failure advances.

  • Signs of Hypoxia:

    • Early Signs:

    • Neuro: Restlessness, anxiety, confusion

    • Respiratory: Tachypnea, dyspnea, use of accessory muscles, deep and labored breaths, mild to low SaO2 (oxygen saturation)

    • Cardiovascular (CV): Tachycardia, hypertension (HTN)

    • Skin: Pallor

    • Late Signs:

    • Neuro: Lethargy, stupor, decreased level of consciousness (LOC)

    • Respiratory: Bradypnea (slow breathing), shallow respirations, periods of apnea, low SaO2

    • CV: Bradycardia, hypotension, arrhythmias (related to ischemia and acidosis)

    • Skin: Cyanosis

    • Presence of metabolic acidosis.

DIAGNOSTICS

  • Berlin Criteria for ARDS diagnosis include:

    • Timing: ARDS condition precipitated by an acute event with symptoms developing within the last week.

    • Chest Imaging: Evidence of bilateral opacities on imaging (CXR or CT).

  • Edema Origin:

    • Primarily or exclusively non-cardiogenic.

  • Hypoxemia Severity Based on the P:F Ratio:

    • Mild: P:F ratio 200-300

    • Moderate: P:F ratio < 200

    • Severe: P:F ratio < 100 *Where P:F ratio is calculated by dividing the PaO2 by the FiO2 (fraction of inspired oxygen) as a decimal when on a ventilator with PEEP > 5 cm H2O.

  • Other diagnostics:

    • ABG analysis to determine oxygen levels

    • Blood tests (CBC, chemistries, cultures) to identify underlying causes

    • Sputum culture to identify infections contributing to ARDS.

COLLABORATIVE INTERVENTIONS

PHARMACOTHERAPY

  • No definitive drug therapy exists for ARDS, however, the following treatments may be employed:

    • Bronchodilators

    • Corticosteroids (considered for moderate to severe ARDS)

    • Antibiotics (if infection is present)

    • Paralytics in cases of ventilator asynchrony

    • Diuretics

    • Prophylaxis for Deep Venous Thrombosis (DVT) and gastrointestinal (GI) complications

    • Inhaled nitric oxide and prostacyclin to enhance pulmonary vasodilation, reducing pulmonary vascular resistance (PVR) and improving oxygenation.

VENTILATORY SUPPORT

  • The cornerstone of ARDS management involves mechanical ventilation strategies that may be either invasive or non-invasive.

**Non-Invasive Ventilatory Support:

**

  1. High Flow Nasal Cannulas

    • Deliver heated, humidified oxygen-air blend up to 100% FiO2 with distinct features:

      • The flow rate does not determine FiO2 (e.g., 50 L/min may deliver either 50% or 100% FiO2 depending on setting).

      • Flow and oxygen concentration are set separately.

      • Fit snugly in nares to minimize ambient air entrainment and allow for precise FiO2 delivery.

      • Provide low levels of positive pressure preventing atelectasis.

  2. Biphasic Positive Airway Pressure (BiPAP):

    • Delivers:

      • Higher positive pressure during inspiration (IPAP) and lower pressure during expiration (EPAP).

    • Sample settings: IPAP = 10 mmHg, EPAP = 5 mmHg, and FiO2 = 50%.

    • Advantages include prevention of atelectasis, CO2 flushing, reduced work of breathing (WOB), ability to deliver FiO2 up to 100%, and delaying intubation.

    • Disadvantages include:

      • High risk for aspiration if the patient vomits.

      • Potential leaks with patient movement.

      • Discomfort and risk of pressure injuries.

    • Contraindications:

      • Absolute: Cardiopulmonary arrest, inability to maintain patent airway, severe agitation/coma, facial trauma, severe refractory hypotension.

      • Relative: Altered level of consciousness (ALOC), vomiting, copious secretions, recent upper GI or respiratory surgery, right ventricular failure, mild hypotension.

Invasive Ventilatory Support:

  • Possible indications for endotracheal (ET) intubation include:

    • Altered mental status requiring airway protection

    • Anticipated airway obstruction

    • Copious secretions not amenable to suctioning

    • High-risk aspiration cases

    • Severe respiratory distress, bradypnea, apnea, code blue situations, or general anesthesia.

Preparation for Intubation

  • Supplies Needed:

    • Oxygen, ventilator, Ambu-bag for pre-intubation ventilation

    • Endotracheal (ET) tube (sizes 6 to 8 mm for adults)

    • Laryngoscope

    • End-tidal CO2 detector (yellow indicator confirms correct placement)

    • Tape or ET holder for stabilization

  • Nursing Responsibilities:

    • Positioning patient at the top of the bed

    • Hyperextending the neck using towels

    • Set up for suctioning to visualize vocal cords during insertion

    • Administer Rapid Sequence Intubation (RSI) with sedation (e.g., Propofol) and paralytic agent (e.g., Succinylcholine).

    • Preoxygenate the patient (to mitigate transient hypoxemia)

    • Limit intubation attempts to no more than 30 seconds.

    • Monitor vital signs during intubation.

Nursing Responsibilities After Intubation:

  • Assess pilot balloon inflation, stabilize ET tube, and measure at lip line.

  • Conduct respiratory assessment (lung sounds, chest rise, air emerging from tube).

  • Obtain chest X-ray to confirm tube position (should be 1-2 cm above the carina).

  • Employ soft restraints as necessary and potentially place a nasogastric tube (NGT).

  • Initiate sedation for comfort.

Ventilator Settings:

  • Tidal Volume (TV): Air delivered per breath, typically 8 to 10 mL/kg of ideal weight, approximately 400-500 mL in an average adult.

  • Respiratory Rate (RR): Generally set at 12 to 16, adjustable based on PaCO2 levels.

  • Fraction of Inspired Oxygen (FiO2): Adjustable between 21% to 100%, starting at a minimum of 30% and titrated to maintain PaO2 between 60 and 100 mmHg to avoid oxygen toxicity.

  • Positive End Expiratory Pressure (PEEP): Typically starts at 5 cmH20, can be increased for ARDS management, keeping alveoli open; excessive PEEP may induce barotrauma or pneumothorax.

  • I:E Ratio: Standard ratio is usually 1:2 (duration of inspiration to expiration).

Ventilator Strategies for Patients with ARDS:

  • Lung-Protective Ventilation:

    • Recommendations to prevent:

    1. Barotrauma from high pressures

    2. Volutrauma from large tidal volumes

    3. Atelectrauma from cyclical collapse and reopening of alveoli.

  • Ventilator Recommendations include:

    • Use low tidal volumes (4 to 8 mL/kg of ideal body weight against the norm of 6 to 8 mL/kg)

    • Respiratory rate up to 35 to compensate for low tidal volume

    • Maintain goal PaO2 between 55 and 80 mmHg.

    • SpO2 target between 88% to 95%.

    • Maintain pH levels between 7.30 and 7.45.

    • Reverse inspiratory-to-expiratory ratios as necessary.

    • PEEP can extend up to 24 cmH2O under specific treatment conditions.

VENTILATOR MODES

  • Assist-Control Mandatory Ventilation (ACMV):

    • Patients can initiate breaths with each being fully supported at:

      • Volume Control:

      • Preset tidal volume and respiratory rate.

      • Delivers full preset tidal volume regardless of patient spontaneity.

      • Pressure Control:

        • Preset respiratory rate and inspiratory pressure,

        • Delivers based on reaching a set pressure leading to variable tidal volumes dependent on compliance.

      • Utilized initially in ARDS when lung protection is critical.

  • Pressure Regulated Volume Control (PRVC):

    • Combines volume control with pressure protection to guarantee volume while preventing excessive pressure.

  • Airway Pressure Release Ventilation (APRV):

    • Features very long inspiratory times, high continuous pressure (similar to CPAP), with brief release phases for expiration.

    • Conceptualized as CPAP with intermittent release.

WEANING MODES

  • Synchronous Intermittent Mandatory Ventilation (SIMV):

    • Contains mandatory breaths (fully supported) interspersed with spontaneous breaths devoid of support.

  • Continuous Positive Airway Pressure (CPAP):

    • Requires spontaneous breathing without mandatory breaths, providing constant pressure to maintain airway patency.

  • Pressure Support Ventilation (PSV):

    • Covers scenarios where the patient initiates breaths with the ventilator boosting pressure during inspiration, significantly easing effort.

COMPLICATIONS OF MECHANICAL VENTILATION

  • Barotrauma/Pneumothorax:

  • Ventilator-assisted Pneumonia (VAP):

    • Potential sources of infection include:

    1. Aspiration of gastric contents

    2. Contaminated intubation procedure

    3. Biofilm development along the endotracheal tube

    4. Accumulated secretions.

  • Cardiovascular (CV) Effects:

    • Vena cava compression secondary to increased intrathoracic pressure may diminish preload and ultimately lower cardiac output (CO).

  • GI Effects:

    • Gastric distention attributable to excess air from intubation or PEEP and stress-induced gastric ulcers resulting from increased secretions.

VENTILATOR ALARMS

  • Regularly assess the patient prior to troubleshooting the ventilator. Look for signs such as:

    • Respiratory distress

    • Oxygen saturation

    • Chest rise

    • Breath sounds

    • Tube placement.

Low-Pressure Alarm (Low Tidal Volume)

  • Meaning: Indicates a loss of pressure in the ventilator circuit, generally due to an air leak or tubing disconnection.

  • Possible Causes & Interventions:

    1. Disconnection of ventilator tubing:

      • Reestablish connections.

    2. ET tube displacement:

      • Assess depth and tube placement, checking for breath sounds; notify respiratory therapist/MD if displaced.

    3. Self-extubation:

      • Immediately call for help, supply oxygen or utilize a bag-valve-mask, prepare for reintubation if necessary.

    4. Cuff leak:

      • Respiratory therapist may reinflate cuff or reintubate if cuff is ruptured.

    5. Air leak/damaged tubing:

      • Replace tubing as required.

High-Pressure Alarm

  • Meaning: Indicates increased airway resistance or an obstruction disrupting normal airflow.

  • Possible Causes & Interventions:

    1. Patient biting the tube:

      • Insert a bite block, adjusting sedation as needed.

    2. Coughing due to secretions:

      • Suction as needed; adjust sedation if cough is non-secretive.

    3. Kinked ventilator tubing:

      • Inspect and resolve obstructions.

    4. Excess secretions:

      • Perform suctioning.

    5. Mucus plug:

      • Immediate suction required.

    6. Decreased lung compliance (e.g., worsening ARDS):

      • Notify the provider; ventilator settings might require adjustment.

    7. Pneumothorax:

      • High-pressure alarm ominously appears with reduced breath sounds; notify the provider and prepare for chest tube placement.

    8. Patient fighting the ventilator (dyssynchrony):

      • Provide reassurance, encourage slow breathing, assess pain/anxiety/hypoxia, adjust sedation or ventilator settings as necessary.

NURSING CARE

Ventilator-associated Pneumonia Prevention Methods:

  1. VAP Prevention Bundle:

    • Suctioning as warranted (often q2-4 hrs).

    • Endotracheal (Tracheal) Suctioning Done through a closed (in-line) system to clear secretions from the trachea and bronchi.

    • Subglottis Suctioning should clear pooled secretions above the endotracheal tube cuff to avoid microaspiration and VAP.

    • Oropharyngeal Suctioning should address oral secretions.

  2. Oral Care:

    • Administer chlorhexidine typically twice daily as determined by facility policy.

  3. Elevate Head of Bed (HOB):

    • Position at 30-45° to reduce aspiration risk.

  4. Daily Spontaneous Awakening Trial (SAT):

    • Lighten sedation to evaluate neurologic status.

  5. Daily Spontaneous Breathing Trial (SBT):

    • Monitor readiness for extubation via ABGs and vital signs during SBT in pressure support mode.

  6. Strict Hand Hygiene:

  7. Rotate/Repositioning:

    • Every 2 hours to assist with lung expansion and secretion mobilization.

  8. GI & DVT Prophylaxis:

    • Implement measures to prevent stress ulcers and thromboembolic complications extending hospital stays.

  9. Monitor Descriptions of Secretions:

    • Assess color, consistency, and odor.

  10. Perform Chest Physiotherapy:

    • To facilitate secretions clearance.

  11. Monitor Kidney Function:

    • Conduct sequential studies as indicated.

  12. Consider Prone Positioning:

    • As prescribed for improved oxygenation.

NUTRITION MANAGEMENT

  • Initiate nutrition 12 to 24 hours post-intubation contingent on hemodynamic stability.

  • Calculate caloric requirements with a feeding formula determined by a dietician (e.g., Glucerna for diabetics, Jevity for standard nutrition, Nepro for renal patients).

  • RN responsibility involves tube insertion as ordered, utilizing options such as OG, NG, or post-pyloric tubes which reduce aspiration risk.

  • Begin feedings slowly, progressing gradually while monitoring tolerance. Flush with water every 6 hours.

SEDATION FOR INTUBATED PATIENTS

  • Propofol:

    • Class: Sedative Hypnotic

    • Indications: Rapid and easily adjustable sedation (onset within 30 seconds).

    • Nursing Considerations:

    • Watch for respiratory depression, hypotension, and hypertriglyceridemia.

    • Monitor blood pressure and triglycerides (hold for TG ≥ 500).

    • Replace tubing every 12 hours.

    • Dosing:

    • Start at 5 mcg/kg/min, titrate to effect at increments of 5 mcg/kg/min, up to 50-70 mcg/kg/min, reducing after effective sedation found. Lower doses may be required for elderly patients.

  • Dexmedetomidine (Precedex):

    • Class: Alpha-2 Agonist

    • Indications: Light sedation during ventilator weaning; maintains arousability without respiratory depression (can be used without mechanical ventilation).

    • Nursing Considerations: Good for SBT, may induce hypotension and bradycardia.

  • Fentanyl:

    • Class: Opioid analgesic

    • Indication: For pain-driven agitation.

  • Midazolam:

    • Class: Benzodiazepine

    • Indication: For deep sedation when other agents are inadequate.

    • Nursing Considerations: Beware of drug accumulation in renal/hepatic pathologies.

MONITORING PATIENTS ON SEDATION

  • Maintain RASS (Richmond Agitation-Sedation Scale) goals as ordered, typically between 0 and -2 for intubated patients.

  • Document RASS scores every 1-2 hours.

PRONATION THERAPY

  • Utilized for moderate to severe ARDS:

    • Enhances oxygenation through various mechanisms:

    • Alleviates mechanical pressure from the heart and abdominal viscera on lungs.

    • Promotes even blood and air distribution within the lungs.

    • Aids in the mobilization and drainage of secretions.

    • Facilitates oxygenation of dorsal lung areas (potentially more surface area available).

    • Patients are typically pronated for 12 to 16 hours, entailing considerable effort but capable of reducing mortality and ventilatory duration.

WEANING FROM VENTILATOR

  • Conduct SAT/SBT (sedation vacations) usually during day shifts.

  • Evaluate SAT safety to discern if a mechanically ventilated patient is prime for potential sedation duration halting. Criteria for failure necessitating continuous sedation infusion includes:

    • Requirement for excessive sedatives hindering safety in a spontaneous awakening trial.