Mechanical Ventilation

Mechanical Ventilation

Instructor Information

  • Name: Dawn Hauck MSN, RN, CCRN, PHRN

Definition of Mechanical Ventilation

  • Mechanical Ventilation: A machine used to provide adequate ventilation and oxygenation to a patient who is unable to adequately ventilate or oxygenate.

Indications for Mechanical Ventilation

  • Reasons to Mechanically Ventilate a Patient:

    • Unable to maintain acceptable PO2 (partial pressure of oxygen).

    • Unable to maintain acceptable PCO2 (partial pressure of carbon dioxide).

    • Excessive work of breathing.

    • Patient fatigue.

    • Patient apneic due to neurologic conditions such as multiple sclerosis (MS), myasthenia gravis (MG), Guillain-Barré syndrome, or cerebrovascular accidents (CVA).

    • Apnea due to drug effects such as narcotics, overdose, or anesthesia.

Goals of Mechanical Ventilation

  • Primary Goals:

    • Improve ventilation.

    • Improve oxygenation.

    • Decrease work of breathing (support/rest respiratory muscles).

    • Correct life-threatening blood gas and acid-base abnormalities.

    • Ultimate Goal: Wean patient off mechanical ventilation.

Limitations of Mechanical Ventilation

  • Ventilators DO NOT:

    • Cure diseased lungs.

    • Complete gas exchange.

    • Oxygenate tissues.

  • Ventilators DO:

    • Support ventilation while underlying causes are explored and ideally resolved.

    • Administer necessary oxygen levels while therapy is undertaken.

Key Concepts

  • Key Terms:

    • Ventilation: The act of inspiring and exhaling.

    • Respiration: Gas exchange occurring at the alveolar-capillary level and at the cellular level.

Noninvasive Positive-pressure Ventilation

  • Purpose:

    • Keep alveoli open.

    • Improve gas exchange without invasive ventilation.

  • Types:

    • BiPAP (Bilevel Positive Airway Pressure): Provides noninvasive pressure support ventilation via nasal mask or facemask, used to assist patients with respiratory failure before considering intubation.

    • CPAP (Continuous Positive Airway Pressure): Maintains open alveoli and prevents collapse during expiration, improves gas exchange and oxygenation, decreases cardiac output, and is also non-invasive.

Equipment Requirements for Mechanical Ventilation

  • Required equipment includes:

    • A cuffed endotracheal tube.

    • A cuffed tracheotomy tube.

Mechanical vs. Spontaneous Breathing

  • Mechanical Ventilation:

    • Positive pressure pushes air into lungs, diaphragm pushed down, expiration occurs spontaneously.

  • Spontaneous Breathing:

    • Vacuum created by diaphragm dropping, creating negative pressure that pulls air into lungs, expiration occurs passively.

Cardiovascular Response to Controlled Ventilation

  • Effects of Positive Pressure:

    • Hypotension.

    • Fluid retention.

    • Increased intrathoracic pressure during inspiration inhibits venous return to the heart, leading to decreased preload, cardiac output, and blood pressure.

    • Decreased cardiac output leads to decreased renal blood flow, activating the Renin-Angiotensin-Aldosterone (RAA) system causing fluid retention.

Basic Ventilator Settings

  • Tidal Volume (Vt):

    • Volume of air patient receives with each breath, normal range is 7-10 ml/kg.

    • For ARDS patients, consider 5-8 ml/kg with an increase in PEEP.

  • FiO2: Fraction of Inspired Oxygen, can be from 21%-100%. Oxygen is warmed and humidified to prevent mucosal damage and facilitate secretion clearance.

  • Rate: Number of breaths delivered per minute (bpm).

Modes of Ventilation

  1. Assist Control (AC) / Continuous Mandatory Ventilation (CMV)

    • Tidal volume and rate are set, assists with patient's breathing.

    • May lead to hyperventilation if the patient's spontaneous breathing rate increases which delivers a preset tidal volume.

  2. Synchronized Intermittent Mandatory Ventilation (SIMV)

    • Similar to AC with preset tidal volumes and rates.

    • Allows spontaneous breathing at the patient’s own rate between controlled breaths to help weaning.

  3. Pressure Support Ventilation (PSV)

    • Used for weaning, provides preset inspiratory pressure in response to the patient’s effort.

    • Reduces workload of breathing; less pressure support increases workload.

  4. Continuous Positive Airway Pressure (CPAP)

    • Patient performs all work of breathing, ventilator provides pressure support during spontaneous breaths.

    • Improves oxygenation and helps keep alveoli open.

Advantages and Disadvantages of Ventilation Modes

  • Assist Control (AC):

    • Advantage: Reduced work of breathing.

    • Disadvantage: Potential for hyperventilation and adverse hemodynamic effects.

  • SIMV:

    • Advantage: Less interference with cardiovascular function.

    • Disadvantage: Increased work of breathing compared to AC.

  • PSV:

    • Advantage: Enhances patient comfort.

    • Disadvantage: Variable patient tolerance to support.

Positive End-Expiratory Pressure (PEEP)

  • PEEP: Pressure exerted in airways at end of exhalation.

    • 5 cm H2O is normal for simulating chest pressures.

    • 6-20 cm H2O is therapeutic to hold open difficult alveoli.

    • Higher pressures can cause barotrauma and decreased cardiac output.

Routine Checks and Patient Assessment

  • Basic Ventilator Check:

    • Mode, FiO2, respiratory rate, tidal volume, PEEP, pressure support, alarm system.

    • Must be documented by respiratory therapy every four hours or with changes.

  • Patient Assessment:

    • Vital signs at least every 2 hours.

    • Monitoring respiratory rate, chest movements, lung sounds.

    • Skin color, secretions, and need for suctioning.

    • Pulsatility of oximetry, evaluation of ABGs, ventilation awareness level.

Patient Management and Interventions

  • Anxiety Management:

    • Encourage family interaction for emotional support.

    • Ensure adequate sedation, using scales for assessment.

  • Nutritional Needs:

    • Begin nutritional supplementation immediately for strength to wean off the ventilator.

    • Use tube feeds or hyperalimentation based on bowel sounds.

Complications of Mechanical Ventilation

  • Ventilator Complications:

    • Barotrauma: leads to pneumothorax from excessive PEEP.

    • GI Complications: such as stress ulcers.

    • Ventilator Associated Pneumonia (VAP): occurs from secretions pooling; prevent via mouth care, HOB elevation, suctioning.

    • Venous Thromboembolism: managed with SQ heparin and TED stockings.

Weaning Process from Mechanical Ventilation

  • Weaning: Transfer of work of breathing back to the patient, trials begin when stable. Sedation must be lightened.

  • Weaning Criteria:

    • PEEP ≤ 5 cm H2O.

    • NIF ≥ -25.

    • Minute ventilation 4-10 L.

    • Respiratory rate < 24.

    • Tidal volume 5-10 ml/kg.

Post-Extubation Assessment

  • Key Post-Extubation Monitoring:

    • Vital signs frequently, assess level of consciousness, cardiac rhythms, and ABGs.

  • Take precautions against complications like decreased oxygenation or bronchial spasm.

Conclusion

  • Ventilator management is complex and requires continual assessment and intervention to ensure patient safety and effective breathing support.