MECHANICAL VENTILATION

I. Indications for mechanical ventilation:

    A. Extrapulmonary

    1. CNS - OD sedatives, Coma, failure of resp centers
    2. Neuromuscular - injury, MG, GB, diaphragmatic dysfunction, ALS, electroly imbalances
    3. Musculoskeletal - injury, flail chest

    B. Pulmonary - airway obstruction, non-compliant lung tissue

    C. Goals

    1. maintain alveolar ventilation
    2. deliver oxygen
    3. administer gases under pressure
    4. main positive end expiratory pressure (PEEP)
    5. reduce the work of breathing

    D. Criteria

    1. Apnea
    2. deteriorating alveolar ventilation: pH <7.2 or> 7.6 ; Resp rate <8 or> 30; pCO2 > 50 torr

II. Negative vs Positive Ventilation

    A. Negative pressure ventilation - Normal Ventilation is negative, some mechanical vent can deliver negative pressure, not common, Example is use of a Turtle ventilator with COPD pt.
    B. Positive pressure ventilation - most common form of mechanical vents, delivers inspiration by positive pressure, Examples: MA I and II, Servo, Bennett 7200, Bird

III. Types of Positive pressure ventilators

    A. Pressure Limited - cycles off when a preset pressure reached; volume varies.

    1. examples - Servo, Bear Cub
    2. Uses - neonatal and pediatric vents

    B. Volume Limited - delivers a preset tidal volume within a pressure limit. * Most common ventilator type for adults is Volume Limited.

    1. examples - MA I ,II, Bennett 7200
    2. Uses - all those listed under I

IV. Modes of Ventilation - distinguishing factor is the amount of work or spontaneous effort is required to sustain adequate ventilation

    A. Control Mode - total control of rate and tidal volume; prevents effective spontaneous ventilation; used infrequently

    1. Indications - clients without resp effort or when spontaneous effort is to be prevented
    2. Adv/Disadv - cannot be used with a conscious or spontaneously breathing client, must use paralyzing agents;

    B. Assist-Control Mode - assists clients own spontaneous effort with a preset tidal volume; preset minimum rate setting; infrequently used

    1. Indications - used to decrease the work of breathing
    2. Adv/Disadv - does not alter tidal volumes, if resp rate is increased, preset tidal volume will be delivered, hyperventilation can occur

    C. Synchronized Intermittent Mandatory Ventilation (IMV) or (SIMV) - most commonly used, delivers preset minimum breaths at preset tidal volume but allows for clients own spontaneous breaths at spontaneous tidal volumes

    1. Indications - most of the conditions listed in I
    2. Adv - useful in weaning and allowing for return of spontaneous breaths

    D. Pressure Support - "newer" mode, May be used alone or with SIMV. assists spontaneous breaths with a preset amount of pressure ; decreases work of breathing, useful in weaning off the ventilator

    E. Positive End Expiratory Pressure (PEEP) - not really a mode but an adjunct to other modes; maintains a preset amount of pressure in the alveoli at the end of expiration; allows for more gas exchange without increasing O2 delivery

    1. increases FRC :

        a. prevents avleolar collapse b. increases diffusion time and surface area c. decreases work of breathing

    2. used for patients receiving large amounts of oxygen with low pO2s, Helps prevent oxygen toxicity

    F. Continuous positive airway pressure (CPAP) - similar to PEEP but applied to spontaneous breaths

V. Initial Set-Up of the Ventilator: General Guidelines

    A. Mode
    B. Tidal volume: 12 - 15 ml/kg body weight
    C. Oxygen (FIO2 = fraction of inspired oxygen)
    D. Rate (frequency)
    E. Set Pressure Limits (High Pressure) - peak inspiratory pressure
    F. Peak Flow//Inspiratory Flow Rate - speed at which the volume is delivered
    G. Inspiratory/Expiratory Ratio (normal I/E ratio = 1:1 or 1:2)
    H. Sensitivity - degree to which he ventilator is sensitive to spontaneous breaths
    I. Set Alarms: NEVER TURN ALARMS OFF!

    1. High pressure alarm - indicates increased airway resistance
    2. Low pressure alarm - indicates decreased airway pressure
    3. Low volume alarm/ Spirometer alarm
    4. Ratio Alarm

VI. Potential Complications from Mechanical Ventilation

A. Effects on the cardiovascular system - decreased cardiac output due to decreased venous return, increased right ventricular afterload and decreased left ventricular compliance
B. Barotrauma (esp. with PEEP) - consequence of high pressure in airways - overdistention of the alveoli causing rupture; gas escapes into interstitial spaces leading to subcutaneous emphysema, pneumothorax
C. Oxygen toxicity
D. Acid-Base Disturbances
E. Water Imbalances (fluid volume excess)
F. GI Bleeding
G. CNS Disturbances
H. Potential Infection
I. Fighting the Ventilator - breathing out of synchrony with ventilator

  1. Reasons - hypoxia, airway obstruction, ventilator malfunction, anxiety, etc.
  2. Intervention - ALWAYS ASSESS FIRST, then troubleshoot, consider sedation

J. Sleep deprivation & Psychological consequences
K. Mechanical Failure

VII. Weaning from the ventilator

    A. Patient Preparation - rested (don't attempt weaning at night), comfortable but not sedated, explain the procedure, decrease anxiety ; Criteria : Resp rate <25; Peak pressure < 25-35 cmH2O; NIF> 20 cm H2O; VC 10-15 ml/kg; min volume <= 10 L/m; PaO2> 60 torr on fIO2 <.40; PEEP <="5" cm

    B. Methods of Weaning - depended on the patient situation, underlying pathology, time on the vent

    1. Cold Turkey
    2. SIMV +/- PS
    3. PEEP

VIII. Nursing Care of the Ventilated Patient

    A. Use of Paralyzing Agents
    B. Possible Nursing Diagnostic stems for the Patientreceiving mechanical ventilation

    1. Impaired communication
    2. Alteration in nutrition
    3. Ineffective airway clearance
    4. Impaired Gas Exchange (actual/ Potential)
    5. Ineffective breathing pattern (actual/ potential)
    6. Anxiety

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