Principles of Mechanical Ventilation: RT 244

1. Principles of Mechanical Ventilation: RT 244 Abby Erickson, RRT Review of RT 110

2. Ventilation Delivery • Performed by: • Hand • Machine • Available for: • Short term • Long term • Acute care • Extended home care

3. Gas Exchange

4. OxyhemoglobinDissociation Curve • S-shaped curve, relationship of plasma PO2 and O2 bound to Hb (SO2) • Flat portion: minor changes in PO2 have little effect on SO2 Strong Affinity! • Steep portion: small drop in PO2 causes a large drop in SO2 Weak Affinity!

5. Alveolar ventilation • Normal: 4-5L/min • VA= Vt-VD • VA= (Vt-VD)x f • ↑ VA = ↓PaCO2, ↑PaO2 • Hyperventilation • ↓VA = ↑PaCO2,↓PaO2 • Hypoventilation • Alveolar air equation • As PaCO2 ↑ by 1mmHg, PaO2 ↓ by 1.25mmHg . . .

6. ABG Interpretation • Degree of compensation • Acid-base balance • Cause: respiratory, metabolic, mixed • Oxygenation – degree of hypoxemia • Must interpret in the context of the clinical picture!! • Requires ventilation status • History, signs, symptoms • Acute changes versus chronic

7. Ventilation Gradients • Pawo: zero* • Pbs: zero* • Ppl: -5cmH2O -10cmH2O • PA: +1cmH2O -1cmH2O *unless pressure applied

8. Lung Characteristics: Compliance • Relative ease with which a structure distends • opposite of elastance • Used to describe the elastic forces that oppose lung inflation • V/P = L/cmH2O • 50-170ml/cmH2O normal • 35/40 -100ml/cmH2O intubated patient • Static Compliance • Dynamic Compliance

9. Lung Characteristics: Resistance • Frictional forces associated with ventilation • Anatomic structures • Tissue viscous resistance • Ability of air to flow depends on • Gas viscosity • Gas density • Length and diameter of the tube • Flow rate of the gas through the tube • Raw = PTA/flow cmH2O/L/sec • PTA ≈ PIP – Pplat • Assumes constant flow • Normal 0.6-2.4 cmH2O/L/sec • Intubated patients 5-7cmH2O/L/sec (and higher!)

10. Negative Pressure Ventilators • Attempts to mimic normal physiology • Types: • Iron lung – tank ventilator • Chest cuirass • Maintained without the need for ETT, tracheostomy, able to talk and eat • Cardiovascular concerns, access to patient

11. High Frequency Ventilation Above normal ventilating rates with below normal ventilating volumes HFPPV HFJV HFOV

12. Positive Pressure Ventilators • Requires airway interface • Applies pressure to create gradient between mouth and lung

14. Power Source : provides the energy to perform the work required to ventilate a patient Electrically Powered Pneumatically Powered • Relies on electricity • Wall outlet (AC), battery (DC) • Powers internal motors which provide gas flow to the patient • High pressure gas source • Usually 2 -50psi sources, air and oxygen • Built in reducing valves • Pneumatic • Fluidic

15. Combined Power Ventilators • Pneumatically powered – 50 psi gas sources • Mixture of air and oxygen allow variable FiO2 • Energy to deliver the breath • Electrically powered • Controls the internal function • May be controlled by a microprocessor (1980’s)

16. Control Systems Open Loop Closed Loop • “unintelligent” systems • Does not respond to changes in patient condition • Does not measure variables or change them • “intelligent” systems • Compares the set variable to the measured variable

17. Basic Elements of a Patient Circuit • Main inspiratory line • Adapter • Expiratory line • Expiratory valve • Adjuncts • Device to warm/humidify air • Thermometer • Nebulizer • Bacteria filters

18. Mechanics of Breathing • Muscle Pressure • Action of the respiratory muscles • Ventilation Pressure • Produced by the ventilator These pressures produce motion (flow) to deliver a volume of gas to the lung; the volume delivered depends on the lung’s characteristics

19. Control Variables Pressure Controlled Breathing Volume Controlled Breathing • Maintains the pressure waveform in a specific pattern • Pressure waveform is unaffected by changes in lung characteristics • Volume and flow waveforms vary with changes in lung characteristics • Maintains the volume waveform in a specific pattern • Volume and flow waveforms remain unchanged • Pressure waveform varies with changes in lung characteristics

20. 4 Phases of a Breath Change from exhalation to inspiration Inspiration Change from inspiration to exhalation exhalation

21. Phase Variable • Signal measured by the ventilator • Begins, sustains and ends each of the four phases of the breath • Trigger variable • Limit variable • Cycle variable

22. Types of Breaths Mandatory Spontaneous • Ventilator determines start time • Ventilator determines tidal volume • Ventilator determines both • Machine triggers and/or cycles the breath • Patient determines start of breath • Patient determines tidal volume delivery

23. Noninvasive Ventilation • Does not require an endotracheal tube • Use of NPPV has the potential: • to avoid complications of intubation • decrease mortality rates • decrease length of stay

24. Monitoring • Achieve exhaled tidal volume 5-7ml/kg • Patient ventilator synchrony • Rise time • Inspiratory sensitivity • Expiratory flow cycling • EPAP to offset autoPEEP • Oximetry • Alleviating disease/disorder signs and symptoms

25. Set-up and Preparation Requires patient cooperation and tolerance Selection of appropriate interface Starting with low pressure initially Allow the patient to hold the mask Reassurance Requires secure fit, leaks are acceptable

26. Complications Mask discomfort Air pressures/Gas flows –gastric insufflation Aspiration pneumonia Pneumothorax Hypotension Hypoxemia, Mucus plugging Respiratory arrest

27. Weaning Reversal of the cause of respiratory failure Stabilization of the patient's condition Gradually decreasing the level of support (both ventilatory and oxygenation) Gradually increase the amount of time off NPPV

28. Where do we go from here….. The rest of the book! Stay on top of the reading, this term moves fast Come and see me for questions, concerns and further review, I am here to help Class time is limited so plan on additional time for independent study