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Mechanical ventilation
This document is a primer on mechanical ventilation by Dr. Firas Rabi, outlining indications for use, ventilator origins, terminology, and various modes of ventilation. It details the mechanics of pressure and volume control, the role of positive end-expiratory pressure (PEEP), and the differences between CPAP and BiPAP. Additionally, it emphasizes the importance of initial settings, oxygenation strategies, high-frequency ventilation, and troubleshooting techniques related to mechanical ventilation.
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Mechanical ventilation
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- 2. Indications Airway Compromise Airway patency is in doubt Loss of gag or cough reflex Respiratory Failure Hypoxemic – generally, PaO2 ≤ 60 mmHg Needs help oxygenating Hypercarbic – generally, PaCO2 ≥ 50 mmHg Needs help ventilating
- 3. Origins of Ventilators Negative pressure ventilators “Iron” lung First used in Boston in 1928 Used extensively for polio
- 4. Mechanical Ventilators Dependon place of employment All have similar ventilator patterns, but may call them different names ALL MODES ARE HARMFUL TO THE LUNG Goal is always to extubate ASAP.
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- 11. Ventilator Terminology A/C– Assist/Control IMV – Intermittent mechanical ventilation SIMV – Synchronized IMV PRVC – Pressure regulated, volume control PEEP – Positive end-expiratory pressure CPAP NIPPV
- 12. Volume vs. Pressure Volume control – tidal volume is constant, pressure will vary Pressure control – pressure is constant, tidal volume will change based on lung compliance
- 13. Pulmonary Compliance Compliance= Volume/Pressure This equation is worth memorizing since it provides the basis for understanding pulmonary and ventilator interactions
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- 15. Control Mode Eachbreath has a pre-set volume, time, and flow rate Patient cannot generate spontaneous breaths
- 16. Assist/Control Mode Eachbreath has a pre-set volume, time, and flow rate Each patient generated respiratory effort over and above the set rate are delivered at the set volume and flow rate
- 17. Pressure Control Ifthe pressure is set at PC 16 above PEEP of 4, then the ventilator will deliver a top pressure (peak pressure) of 20 (PC level of 16 plus PEEP) with an end pressure of 4. This keeps the airways slightly open, making it easier to inflate them, and helps prevent collapse and consolidation
- 18. SIMV Each breathhas a pre-set volume, time, and flow rate Allows patient to generate own breaths with own volumes and flow rates If patient initiates a breath, machine will not initiate a ventilator breath no breath stacking
- 19. PRVC Each breathis volume controlled (you set the tidal volume) The machine decides how much pressure to use to deliver that tidal volume based on the required pressures for previous 2-3 breaths
- 20. PRVC You getto limit the amount of pressure used to deliver the volume. If this pressure is reached, the ventilator will alarm “regulation pressure limited”, switch to expiration, and will not be able to deliver the preset tidal volume
- 21. Automode (only inservo i) Automatically controls the transition between controlled (vent triggered) and support (patient triggered) mode in accordance with patient’s effort PC PS VC VS PRVC VS
- 22. Pressure Support Eachpatient-initiated breath is supported by the machine
- 23. Combo modes SIMVVC with PS SIMV PC with PS SIMV/PRVC with PS
- 24. PEEP Not aspecific mode but rather an adjunct to any of the other modes PEEP is the amount of pressure remaining in the lung at the END of the expiratory phase. Utilized to keep otherwise collapsing lung units open while hopefully also improving oxygenation
- 25. Improving oxygenation FiO2 Simplest maneuver Free radical damage with prolonged exposure to > 60% PEEP Reverses pulmonary shunting Atelectasis, pneumonia, ARDS, CHF, pulmonary hemorrhage
- 26. PEEP Side-effects Barotrauma Diminished cardiac output Regional hypoperfusion
- 27. CPAP This ISa mode and simply means that a pre-set pressure is present in the circuit and lungs throughout both the inspiratory and expiratory phases of the breath CPAP serves to keep alveoli from collapsing, resulting in better oxygenation and less WOB
- 28. CPAP The CPAPmode is very commonly used as a mode to evaluate the patients readiness for extubation
- 29. CPAP vs. BiPAP CPAP is essentially PEEP BiPAP is PEEP plus pressure support
- 30. Summary of Modes Controlled Modes Supported Modes Combined Modes Spontaneous breaths VCVS Automode: VC + VS CPAP PC PS Automode: PC + PS BiPAP PRVC Automode: PRVC + PS SIMV: VC/PS SIMV: PC/VS SIMV: PRVC/PS
- 31. Initial Settings Decideon mode Rate based on age Infants 30 Children 20 Adolescents 10 Most can start with tidal volume of 6mL/kg PEEP of 5
- 32. Inspiratory Trigger Normallyset automatically Two modes Airway pressure Flow triggering
- 33. I:E Ratio Normally1:2 Asthma 1:3 or 1:4 Severe hypoxia 1:1 or 2:1 (inverse ratio)
- 34. FiO2 Start 100% Target lowest possible for PaO2 > 60mmHg or sat > 90%
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- 36. Oxygenation in HFOV Oxygenation is primarily controlled by the Mean Airway Pressure (Paw) and the FiO2 Mean Airway Pressure is a constant pressure used to inflate the lung and hold the alveoli open. Since the Paw is constant, it reduces the injury that results from cycling the lung open for each breath
- 37. Ventilation in HFOV Generally controlled by frequency Increased frequency reduces amount of time for exhalation, so leads to decreased ventilation ↑ Hz ↑ pCO2 Increased amplitude/power will increase ventilation Not usually the primary reason for using HFOV
- 38. Troubleshooting Sudden deterioration Disconnection Obstruction Pneumothorax Equipment failure Anxious patient Appropriate mode Trigger set appropriately
- 39. Troubleshooting Call therespiratory therapist
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