1. Modes of Mechanical Ventilation
Mohamad S Ahmad, M.D. Lecturer of Anaesthesia and Intensive CareAin Shams University Cairo, Egypt
2008

2. Introduction Ventilation
The goal of ventilation is to facilitate CO2 release and maintain normal PaCO2
Minute ventilation (VE)
Total amount of gas exhaled/min.
VE = (RR) x (TV)
VE comprised of 2 factors
VA = alveolar ventilation
VD = dead space ventilation
VD/VT = 0.33
VE regulated by brain stem, responding to pH and PaCO2

3. Oxygenation
The primary goal of oxygenation is to maximize O2 delivery to blood (PaO2)
Alveolar-arterial O2 gradient (PAO2 – PaO2)
A-a gradient measures efficiency of oxygenation
PaO2 partially depends on ventilation but more on V/Q matching

4. Adjustments VE MAP To affect ventilation, adjust: Respiratory Rate
To affect oxygenation, adjust:
FiO2
PEEP
I time
PIP
To affect ventilation, adjust:
Respiratory Rate
Tidal Volume VE
MAP

5. COMPLIANCE =  Volume /  Pressure
If volume is set, pressure varies…..if pressure is set, volume varies

6. Goals of Mechanical Ventilation
Achieve and maintain adequate pulmonary gas exchange
Minimize the risk of lung injury
Reduce patient work of breathing
Optimize patient comfort

7. Ideal Mode of Ventilation
Synchronizes with the patient’s spontaneous respiratory effort
Maintains adequate and consistent tidal volume and minute ventilation at low airway pressures
Responds to rapid changes in pulmonary mechanics or patient demand
Provides the lowest possible WOB

8. Ideal Ventilator Design
Achieves all the important goals of mechanical ventilation
Provides a variety of modes that can ventilate even the most challenging pulmonary diseases
Has monitoring capabilities to adequately assess ventilator and patient performance
Has safety features and alarms that offer lung protective strategies

9. MODES
Ventilator mode can be defined as a set of operating characteristics that control how the ventilator functions
Operating mode can be described by (1)the way a ventilator is triggered into inspir. and cycled into expir., (2)what variables are limited during inspiration, (3)and whether or not the mode allows mand., spont. breaths or both.
spontaneous, PEEP, CPAP, BiPAP, CMV, AC, IMV, SIMV, MMV, PSV, PCV, APRV, IRV

10. SPONTANEOUS
Not an actual mode since rate and tidal volume during spont. breathing are determined by patient
Role of ventilator during spont. vent. is to provide the (1) flow to the pt. in a timely manner, (2) flow adequate to fulfill a patient’s insp. demand, and (3) provide adjunctive modes such as PEEP to complement the spont. effort
Apnea ventilation is a safety feature used for spontaneous mode

11. PEEP
PEEP increases the end-expiratory or baseline airway press. to a value greater than atmos. and is often used to improve the pt.’s O2 status, esp. if refractory
PEEP is not a stand-alone mode, but is used in conjunction with other modes
Two major indication for PEEP are:
- Intrapulmonary shunt
- Decreased FRC and lung compliance
Complications assoc. with PEEP include
- Decrease venous return and C. O. - Barotrauma
- Incr. ICP - Alterations of renal, hepatic blood flow

12. CPAP
Is PEEP applied to a spont. breathing pt.
Indications are same as PEEP but in addition pt. must have adequate lung function to sustain eucapnic ventilation
Can use in with ET tube or facemask

13. BiPAP Allows one to apply IPAP and EPAP
IPAP provides positive pressure breaths and it improves hypoxemia and/or hypercapnia
EPAP (essentially PEEP) improves oxygenation by increasing the FRC and enhancing alveolar recruitment

15. Indications for BiPAP:
- preventing intubation of end-stage COPD patient
- supporting patients with chronic ventilatory failure
- patient’s with restrictive chest wall disease
- neuromuscular disease
- nocturnal hypoventilation

16. CMV
Ventilator delivers the preset tidal volume at a set time interval
should only be used when the pt. is properly medicated with a combination of sedatives, respiratory depressants and neuromuscular blockers
Indicated if pt. “fights” the vent., seizure, complete rest for pt. for 24 hr., chest injury

17. Assist Control (A/C)
Pt. always receives a mechanical breath, either timed or assisted

18. Indicated when full ventilatory support is needed, used when pt
Indicated when full ventilatory support is needed, used when pt. has a stable respiratory drive (10-12 spont. rate)
Advantages include a very small WOB when sens. and flow are set properly, and this mode allows the pt. to control the RR
Disadvantage include alveolar hypervent.

19. IMV
Pt. breaths spont. at any tidal volume between the mechanical breaths
Primary disadvantage is chance for breath stacking, therefore care should be taken to set high press. limit properly to reduce risk of barotrauma

20. SIMV
A mode in which the vent. delivers mandatory breaths to the pt. at or near the beginning of a spont. breath, mandatory breaths are synchronized with the pt.’s spont. efforts to avoid breath stacking

21. “synchronized window” refers to the time just prior to time triggering in which the vent. is responsive to the pt.’s effort (0.5 sec is typical)
Advantages include maintaining resp. muscle strength, reduces V/Q mismatch, decreases mean airway press., helps wean pt

22. PSV Used to lower the WOB and augment a patient’s spont. tidal volume
When PSV is used with SIMV, it lowers the O2 consumption because of the decr. WOB
Typically used in the SIMV mode to help weaning by (1) increasing spont. tidal volume (2) decreasing spont. RR (3)decreasing WOB

23. PCV
The pressure controlled breaths are time triggered by a preset resp. rate
Once inspir. begins, a pressure plateau is created and maintained for a preset inspir. time
Typically used in ARDS where it takes excessive press. in volume cycled modes to ventilate a pt., leading to barotrauma

24. ALTERNATIVE MODES OF MECHANICAL VENTILATION
Dual-control ventilation modes were designed to combine the advantages of volume-control ventilation with pressure-control ventilation
These dual-control modes attempt to increase the safety and comfort of mechanical ventilation

25. pressure-regulated volume-control (PRVC)
a desired tidal volume is preset and the ventilator delivers a pressure-limited (controlled) breath until that preset tidal volume is achieved
↑ Vt ↓ PIP & ↓ Vt ↑ PIP
provides the opportunity to deliver minimum minute ventilation at the lowest peak airway pressures possible

26. volume support ventilation (VSV)
The patient triggers every breath, controlling his own respiratory frequency and inspiratory time but the machine can guarantee minute ventilation
The pressure support is automatically adjusted up or down according to patient's lung compliance and/or resistance to deliver a preset tidal volume
This mode cannot be used in a patient who lacks spontaneous breathing effort
This mode is considered as a self-weaning mode

27. Automode
PRVC
VSV
designed for automatic weaning from pressure control to pressure support depending on the patient's effort

28. Volume-assured pressure support ventilation (VAPSV)
VCV
Advantages include a reduction in the work of breathing, lowered airway resistance, and lowered intrinsic PEEP

29. Automatic tube compensation(ATC)
Designed to overcome the resistance of the endotracheal tube by means of continuous calculations

30. Proportional assist ventilation(PAV)
This mode adjusts airway pressure in proportion to the patient's effort
If patient's effort and/or demand are increased, the ventilator support is increased, and vice versa, to always give a set proportion of the breath

31. High-frequency ventilation (HFV)
HFV is time-cycled positive pressure ventilation that delivers a high frequency (60–120 breathes per min) of small tidal volumes (1.5 mL/kg) that are usually less than the anatomic dead space
3 different modes: high-frequency positive-pressure ventilation (HFPPV), high-frequency jet ventilation (HFJV), and high-frequency oscillatory ventilation (HFOV)

32. APRV (airway pressure release ventilation)
Is similar to CPAP in that the pt. is allowed to breathe spont. without restriction

33. Combines two separate levels of CPAP and the pt. may breathe spont
Combines two separate levels of CPAP and the pt. may breathe spont. from both levels
Periodically, pressure is dropped to the lower level, reducing mean airway press.
During spont. expir. the CPAP is dropped (released) to a lower level which simulates an effective expiration

34. Thank
You