Terminology mechanical ventilation

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Description of basic terminologies in assisted mechanical ventilation

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Terminology mechanical ventilation

  1. 1. Basic Terminology Mechanical Ventilation
  2. 2. CO2 Elimination • Alveolar ventilation = (Tidal volume – Dead space) x Respiratory rate/min • Volume-controlled ventilator : Preset Tidal volume • Pressure-limited : lung compliance, Pressure gradient (PIP - PEEP)
  3. 3. O2 Uptake • Depends on Mean Airway pressure (MAP) • MAP - Area under airway pressure curve divided by duration of the cycle • MAP = K (PIP – PEEP) [Ti/(Ti – Te)] + PEEP
  4. 4. MAP MAP can be augmented by: o Inspiratory flow rate (increases K) o Increasing PIP o Increasing I:E ratio o Increasing PEEP
  5. 5. Conventional Ventilator Settings • The key settings are: PIP PEEP RR I:E ratio Flow rate • MAP – net outcome of all parameters except Fio2 and RR; true measure of average pressure; should be maintained between 8-12 cm H20 .
  6. 6. Fio2 • Inspired oxygen concentration • Fraction of O2 in inspired air-oxygen mixture • Regulated by blenders • Fio2 – kept at a minimum level to maintain PaO2 of 50-80 mm Hg. • Initial Fio2 – 0.5
  7. 7. Peak Inspiratory Pressure (PIP) • Neonate with normal lung requires PIP of about 12 cm H2O for ventilation • Appropriate to start with PIP of 18-20 cm H2O for mechanical ventilation • Primary variable determining tidal volume • High PIP - Barotrauma
  8. 8. Positive End Expiratory Pressure (PEEP) • Most effective parameter that increases MAP. • Has opposite effects on CO2 elimination. • PEEP range of 4-8 cm H2O is safe and effective. • Excess PEEP decreases compliance, increase pulmonary vascular resistance
  9. 9. Respiratory Rate (RR) • Main determinant of minute ventilation • Rate to be kept within normal range or higher than normal rate, especially at the start of mechanical ventilation • Hyperventilation – used in treatment of PPHN
  10. 10. I:E Ratio (Inspiratory-Expiratory ratio) • Primarily effects MAP and oxygenation • Physiological ratio : 1:1 or 1:1.5 • Reversed ratio (2:1 or 3:1) – FiO2 and PEEP can be reduced. • Prolonged expiratory rates (1:2 or 1:3) – MAS and during weaning
  11. 11. Flow Rate • Usually flow rate of 4-8 L/min is sufficient • Minimum flow of at least two times minute ventilation volume is required • High-flow rate – increased risk of alveolar rupture
  12. 12. • Respiratory rate • Tidal volume • PEEP • FiO2 • Auto PEEP • Barotrauma • Cardiac output • O2 toxicity

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