Mechanical Ventilation 101 An Introduction to Ventilatory Support

OBJECTIVES The student will be able to: State the two purposes of mechanical ventilation. List three indications for mechanical ventilation. State the primary reason for oxygenation failure. List three complications of mechanical ventilation. Differentiate between positive and negative pressure ventilation. Differentiate between invasive and non-invasive ventilation. Differentiate between pressure- and volume-based breaths. Describe how the mode of ventilation is related to patient-ventilation interaction. Differentiate between minute ventilation and alveolar ventilation. Describe the relationship between alveolar ventilation and PaCO2.

OBJECTIVES State the two purposes of mechanical ventilation. The student will be able to: State the two purposes of mechanical ventilation. List three indications for mechanical ventilation. State the primary reason for oxygenation failure. List three complications of mechanical ventilation. Differentiate between positive and negative pressure ventilation. Differentiate between invasive and non-invasive ventilation. Differentiate between pressure- and volume-based breaths. Describe how the mode of ventilation is related to patient-ventilation interaction. Differentiate between minute ventilation and alveolar ventilation.

OBJECTIVES The student will be able to: Describe the relationship between alveolar ventilation and PaCO2. State the two primary methods for controlling alveolar minute ventilation. State the normal range for spontaneous tidal volume. State the normal range for tidal volume during mechanical ventilation. List the four primary causes of hypoxemia. State two methods for improving PaO2. Describe how PaCO2 is managed in patients with chronic airflow obstruction. Describe how PaO2 is managed in patients with chronic airflow obstruction.

Purposes of Mechanical Ventilators TWO FUNCTIONS: Remove Carbon Dioxide Deliver Oxygen Ventilate (Decrease PaCO2) WOB is excessive Increased airway resistance Reduced lung compliance Defect with neuromuscular control Post-operative support Oxygenate (Increase PaO2 [SaO2]) Shunt

Effects of Positive Pressure Ventilation Increased airway pressures Reduction in venous return/cardiac output. Reduced renal blood flow. Cerebral blood flow issues. Airway related issues

Ventilator Settings Positive vs. Negative Pressure Invasive vs. Non-Invasive Breath Type What is our focus: Volume or Pressure Mode Who is in control: Patient or Ventilator Is support full or partial? A/C, SIMV, Spontaneous Control of Alveolar Minute Ventilation

Alveolar Minute Ventilation . PaCO2 levels are inversely related to VA Increase minute volume, decrease PaCO2. Decrease minute volume, increase PaCO2. Minute Volume (VA) is (Tidal Volume minus Deadspace Volume) x respiratory rate. (Vt – Vd) x f Deadspace includes anatomic (doesn’t change), mechanical (stuff we add), and alveolar ( without ). We can control alveolar minute ventilation by: Changing Respiratory Rate (f) Changing Tidal Volume .

Tidal Volume Spontaneous tidal volume is 5-8 mL/kg. Set tidal volume on ventilator is patient dependent: Higher tidal volumes may lead to higher delivery pressures and lung damage. Use as small of a tidal volume as possible to reduce the PaCO2 to desired levels. A setting of 7-10 mL/kg of Ideal Body Weight (IBW) is considered a safe place to start. ARDS: 6-7 mL/kg Some simulations “like” 10-12 mL/kg Evaluate CST to determine if setting is appropriate.

Oxygenation Issues Causes of Hypoxemia Reduced barometric pressure (move) Hypoventilation (ventilate) V/Q imbalance (responds to increased FiO2) Diffusion Defect (find cause and correct?) Intrapulmonary Shunt RECRUIT COLLAPSED ALVEOLI . .

Steps in Correcting PaO2 Increase FiO2 Increase Mean Airway Pressure “Space under the table” Increase starting pressure (PEEP) Increase delivery (ending) pressure (PIP) Lengthen inspiratory time (tI)

tI PIP PEEP

Mechanical Ventilation: COPD & Asthma Treat increased PaCO2 (and low pH) Use caution with increasing tidal volume. Increased RV leads to overdistension. Extend expiratory time. Auto PEEP Shorten inspiratory time (increase inspiratory flow rate). Use respiratory rate to control PaCO2. Control patient (?) pharmacologically. Permissive hypercapnia and acidosis. Treat reduced PaO2 Usually a result of hypoventilation and V/Q imbalance. Responds well to increase in FiO2. . .

Determine Ventilator settings 5’10” male admitted to ICU. Determine Ventilator settings Mode Tidal Volume Respiratory Rate FIO2 PEEP

ABG pH: 7.31, PaCO2: 50, PaO2: 60, HCO3: 26

ABG: pH: 7.38, PaCO2: 38, PaO2: 62, HCO3: 27