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Mechanical Ventilation: The Basics and Beyond

Mechanical Ventilation: The Basics and Beyond

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Mechanical Ventilation: The Basics and Beyond

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  1. Mechanical Ventilation: The Basics and Beyond Presented By: Diana Gedamke, BSN, RN, CCRN Marion College - Fond du Lac Masters of Nursing Student

  2. Module 3 Ventilator Wave Forms

  3. Positive Pressure Ventilation Two Main Types of Ventilators with Positive Pressure • Volume-cycled ventilation – With a set volume of air delivered per breath; Pressure to deliver breath will vary • Pressure-preset ventilation – With a set volume of pressure to open airways; Volume delivered will vary

  4. Volume-cycled Ventilation • Delivers a preset volume of gas with each machine breath—airway pressures increase in response to the delivered breath • Airway pressures are higher in patients with low compliance or high resistance—high pressures indicate risk of ventilator-induced lung injury

  5. Spontaneous Breathing vs. Positive Pressure Ventilation

  6. Volume-cycled Ventilation • Assist Control (AC) • Synchronized Intermittent Mandatory Ventilation (SIMV)

  7. Assist-control (AC) • Most widely used mode of MV • Delivers a minimum number of fixed-volume breaths • Patients can initiate extra assisted breaths (will get full set volume with each effort)

  8. Pressure-time TracingsAssist Control Mode

  9. Synchronized Intermittent Mandatory Ventilation (SIMV) • Delivers preset number of fixed-volume breaths • Patient can breathe spontaneously between breaths (rate and depth determined by patient) • Patients often have trouble adapting to intermittent nature of ventilatory assistance

  10. Pressure-time TracingsSIMV Mode

  11. Pressure-preset Ventilation • Delivers a predefined target pressure to the airway during inspiration • Resulting tidal volume (VT) and inspiratory flow profile vary with the impedance of the respiratory system and the strength of the patient’s inspiratory efforts • Includes pressure-control (PC) and Pressure support (PS)

  12. Pressure-control (PC) Ventilation • Delivers a preset gas pressure to the airway for a set time and at a guaranteed minimum rate • Patient can breathe in excess of set rate • Tidal volume achieved depends on pressure level, lung mechanics, and patient effort • Inspiratory flow rate variable

  13. Pressure Support (PS) • Delivers preset airway pressure for each breath • Variable parameters: Inspiratory and expiratory times (respiratory rate), flow rate, and tidal volume (VT)

  14. Synchronized Intermittent Mandatory Ventilation (SIMV) + Pressure Support (PS) • A set number of Mandatory breaths are delivered per minute. • Remainder of patients breath are at his own rate and volume • Spontaneous breaths allowed in SIMV are assisted by PS

  15. New Modes of MV • New modes often introduced • Involves nothing more than a modification of the manner in which positive pressure is delivered to the airway and of the interplay between mechanical assistance and patient’s respiratory effort • Goals: enhance respiratory muscle rest, prevent deconditioning, improve gas exchange, prevent lung damage, improve synchrony, foster lung healing

  16. Ventilator Settings • Respiratory rate • Tidal volume • FiO2 • Inspiratory:Expiratory (I:E) ratio • Pressure limit • Flow rate • Sensitivity/trigger • Flow waveform

  17. Inspiratory Flow (V) Waveform Square waveform Decelerating Waveform (constant flow) (decelerating flow)

  18. Inspiratory Flow (V) Waveform • Square waveform: volume of gas is evenly distributed across inspiratory time. Has highest peak pressure and lowest mean airway pressure. Ideal for those at risk for autopeeping due to short inspiration time

  19. Inspiratory Flow (V) Waveform • Decelerating waveform: Volume of gas flow is high at the beginning of inspiration then tapers off toward the end of the breath. Has lowest peak pressure and highest mean airway pressure. Increased inspiratory time; useful in ARDS.

  20. Patient-Ventilator Synchrony • Check for: • Symmetric chest inflation • Regular breathing pattern • Respiratory rate < 30 bpm • Synchrony between patient effort and machine breath • Paradoxical breathing

  21. Patient-Ventilator Synchrony • Inspiratory effort expended by patients with acute respiratory failure is 4 - 6 x normal • Don’t eliminate respiratory effort: causes deconditioning and atrophy

  22. Patient-Ventilator Asynchrony • Possible causes: • Anxiety or pain • Ventilator settings may not be appropriate: check ABG and alert individual responsible for ventilator orders • Auto-PEEP • Pneumothorax

  23. Ventilator Alarms and Common Causes

  24. Definitions • PEEP – positive-end-expiratory pressure applied during mechanical ventilation • CPAP - continuous positive airway pressure applied during spontaneous breathing

  25. PEEP • Improves oxygenation - increases functional residual capacity (FRC) above closing volume to prevent alveolar collapse • permits reduction in FIO2 • Reduces work of breathing • Increases intrathoracic pressure - decreases venous return to right heart - decreases CO • Titrate to least amt. necessary to achieve O2 sat > 90% or PO2 > 60 mm Hg with FiO2 < 0.6

  26. Auto-PEEP • Auto-PEEP/intrinsic PEEP (PEEPi)/inadvertent PEEP/occult PEEP - positive end expiratory alveolar pressure occurring in the absence of set PEEP. Occurs when expiratory time is inadequate.

  27. Assessing Flow Waveform for Presence of Auto-PEEP

  28. Resistance and Compliance

  29. Definitions • Peak Airway Pressure (Ppk) • An increase in Ppk indicates either an increase in airway resistance or a decrease in compliance (or both). • Plateau Pressure (Ppl) - end-inspiratory alveolar pressure

  30. Airway Pressure Analysis

  31. Ventilator-Induced Lung Injury • High volumes and pressures can injure the lung, causing increased permeability pulmonary edema in the uninjured lung and enhanced edema in the injured lung • Alveolar overdistention + repeated collapse and re-opening of alveoli

  32. Mechanical Ventilation in Obstructive Lung Disease • resistance to expired flow • results in air trapping/hyperinflation • hyperinflation may result in cardiopulmonary compromise • Goal: meet minimal requirements for gas exchange while minimizing hyperinflation • Allow increased time for expiratory flow

  33. Increasing Time for Exhalation • Decrease inspiratory time • Increase flow rate • Square waveform • Decrease minute ventilation (VE) • RR x TV

  34. Monitoring Patients with Obstructive Lung Disease Requiring Mechanical Ventilation • Monitor plateau pressure: in general, Pplat < 30 cm H20 to decrease risk of hyperinflation and alveolar overdistension • Permissive hypercapnia

  35. Respiratory Failure Due to Asthma • Watch for overventilation post intubation • High Ppk common • May require sedation to establish synchronous breathing with ventilator • Avoid paralytics • Ventilate as stated above (Increase exhalation time by decreasing RR and TV, increasing inspiratory flow rate, and using square waveform) • May want to use SIMV

  36. Respiratory Failure Due to COPD • Ppk typically not as elevated as in asthma; when it is, think other pathologic processes • Many patients with COPD have chronic hypercapnia; ventilatory support titrated to normalize pH and not PCO2 • Small levels of set PEEP may decrease WOB • May try NIPPV

  37. Noninvasive Positive Pressure Ventilation (NIPPV) • Cooperative patient • Functionally intact upper airway • Minimal amount of secretions • Done by full face or nasal mask • Watch for gastric distension; may increase risk of aspiration • May use standard ventilators • Monitor patients closely for decompensation and need for intubation

  38. ARDS: A Three Lung Unit Model Normal Non-recruitable Recruitable

  39. Respiratory Failure Due to ARDS • Refractory hypoxemia • Avoid ventilator induced lung injury • pressure-limited approach • keep Pplat < 30 cm H20 • small tidal volumes (6 ml/kg) • permissive hypercapnia • Avoid O2 toxicity; apply moderate levels of PEEP

  40. ARDS • May need to increase inspiratory time • Inverse ratio ventilation (IRV) • I:E > 1:1 • May require sedation/paralysis • Use as second-line strategy if PEEP fails to improve oxygenation

  41. Mechanical Ventilation in Patients with Neuromuscular Weakness • Present with acute or subacute respiratory failure, usually with hypercapnia • progressive neurologic dysfunction (amyotrophic lateral sclerosis, muscular dystrophies, Guillain-Barre, CNS dysfunction due to head injury or drug ingestion) • usually ventilated without difficulty unless RF is complicated by secondary conditions (atelectasis or pneumonia) • lung compliance and gas exchange remain relatively normal