1. PRESSURE CONTROL VENTILATION
Michael A. Venditto D.O., FACOI, FCCP

2. Traditional Ventilation
Volume ventilation (CMV) is designed to deliver mandatory breaths at a preset volume and peak flow
Adjustments in the three variables (tidal volume, respiratory rate and peak flow) results in a specific inspiratory time and generated a variable pressure dependent on the patient”s airway resistance and lung compliance

3. Traditional Ventilation
Inspiration is never longer than expiration and in fact rarely exceeded 1/3 of expiratory time
Flow rates were adjusted within a narrow range to keep the I:E within the limits and with the criteria that delivering the present tidal volume was most important

4. Volume Ventilation--Disadvantage
Ventilator air tends to take the path of least resistance
In disease, some lung units have longer time constants because of  airway resistance or  local compliance
This leads to over distention of normal alveolar units and under-ventilation of diseased unit
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5. PCV - History Uses in neonatal ventilation since the late 70’s
Technology allowed for a higher inspiratory flow and decreased expiratory resistance
When used with inverse ratio ventilation, was found to decrease Vd, increase paO2 and decrease shunt

6. Pressure Control Ventilation
Delivers a mandatory number of breaths but at a preset pressure limit and inspiratory time
Inspiratory time is set by establishing the I:E ratio
For example, if the respiratory rate is 20/min, each respiratory cycle is 3 seconds. If the I:E is 2:1, the inspiration is 2 seconds and expiration is 1 second
This results in variable volume and flow patterns dependent on the patients airway resistance and lung compliance

7. Pressure Control Ventilation
When the ventilator cycles into inspiration, airway pressure rises rapidly to the preset value
When the inspiratory time is elapsed, the airway pressure fall to baseline or the an established PEEP level
Tidal volume is variable

8. Pressure Control Ventilation
Airway pressure is at its highest from the beginning of inspiration
This longer airway exposure to higher pressure allows those lung units with long pulmonary time constants the driving force and time to expand
The “bad” lung units can catch up to the “good” ones
Creates a more equitable distribution of gas

9. Pressure Curves Comparison

10. Inverse Ratio Ventilation
Much more effective with pressure control than with volume ventilation
With IRV it is essential that
Critical alveolar opening pressure is overcome rapidly
Airway pressure are maintained for a sufficient time
No significant time should pass during expiration that would allow alveolar closure

11. PCV—What to set Inspiratory Pressure (above PEEP) in cm H2O
Respiratory Rate
FiO2
PEEP (if so desired)
I:E ratio
It is suggested that you start at 1:2
It could then be altered to 1:1, 2:1, 3:1, or even 4:1

12. PCV—Settings An Example
Inspiratory Pressure = 25 cm H2O
Rate = 10/min
Fio2 = .40
I:E = 1:2
This implies that there will be 6 seconds allotted for each breath of which 2 seconds will be for inspiration and 4 seconds will be for expiration

13. PCV - Monitoring
Since pressure is constant, tidal volumes are variable
Changes in lung compliance or airway resistance will change to tidal volume
ET tube kinking/obstruction, water in tubing—will decrease tidal volume
Intrinsic PEEP must be assessed since if it increases, the tidal volume will decrease

14. PCV - Adjustments
The initial inspiratory pressure should be ½ to 2/3 of original CMV pressure
Manipulate PIP and RR to influence paCO2
Manipulate I:E and RR to adjust intrinsic PEEP and thus influence paO2

15. Adjustments Volume Mode PCV Mode
To increase paO2
Increase FiO2
Increase PEEP
To decrease paO2
Decrease FiO2
Decrease PEEP
To increase paO2
Increase FiO2
Increase PEEP
Decrease expiratory time
To decrease paO2
Decrease FiO2
Decrease PEEP
Increase expiratory time

16. Adjustments Volume Mode PCV Mode
To decrease paCO2
Increase tidal volume
Increase respiratory rate
To increase paCO2
Decrease tidal volume
Decrease respiratory rate
To decrease paCO2
Increase pressure
Increase respiratory rate
To increase paCO2
Decrease pressure
Decrease respiratory rate

17. Transition Back to Volume Mode
ABG should be approaching normal and underlying pathophysiology should be resolving
Attempt to lower PIP to below 50 cm
Then lower FiO2
Once FiO2 is less than .50, intrinsic PEEP should be reduced by increasing expiratory time
When I:E is 1:1, can convert to volume ventilation

18. Airway Pressure Release Ventilation
An application of CPAP
Patient cycles between to levels of CPAP—the higher one call P High (P1), the lower P Low (P2)
The patient can breath spontaneously at either level
Maintains an optimal FRC
Occasional pressure releases augments CO2 removal

19. APRV
After a preset time (T high) at the higher CPAP setting (P High), a very low resistance valve opens and drops the airway pressure to the lower level (P Low). With the release of pressure, the patient exhales a volume determined by the difference between P High and P Low and the respiratory compliance.

20. APRV
After a brief period of deflation, P High is reapplied---expanding the lung
The respiratory rate is determined by adding T High and T Low and dividing that number into 60 seconds. Example: T High = 5.0 sec and T Low = 1.0 sec; therefore total time is 6.0 sec and the respiratory rate is 60/6 = 10 per minute

21. APRV

22. APRV - Indications Hypoxia in a spontaneously breathing patient
Risk of barotrauma – peak airway pressure is usually just above what mean airway pressure would be in CMV
Risk of cardiovascular compromise that can occur with higher pressures

23. APRV - Advantages
Improves pulmonary mechanics and paO2 and decreased dead space ventilation
Negates use of paralysis – don’t “buck” the vent
Decreases need for sedation
Improved ability to mobilize patient
Preserves active cough
Improves ability to identify complication that can be masked by sedation

24. APRV - Contraindications
Patients with increased airway resistance (bronchospasm) –they need to empty their lungs in a relatively short period, usually 2 seconds
Patients with audible wheezes on known anatomical narrowing of their airway would be poor candidates
Lack of spontaneous breaths

25. APRV Pressure settings Time Settings FiO2
P High –desired mean airway pressure + 3 cmH2O (range: 20 to 30 cm)
P Low – usually set at 0 cm H2O (range: 0 to 5 cm)
Time Settings
T High – usually set at 5.0 seconds (range: sec)
T Low – usually set at 0.6 seconds (range: sec)
FiO2

26. APRV Monitoring Release tidal volume at least 5 ml/kg
Arterial oxygen saturation
Hemodynamics
ABG 20 minutes after initial setup

27. APRV Monitoring
If the patient shows inspiratory activity, they are struggling to achieve good lung volumes---raise the P High
If the patient is actively exhaling, they are struggling to get down to FRC---either decrease P High or increase the T Low

28. APRV Adjustments To increase paO2: Increase FiO2
Increase P High by 2 cm H2O increments or increase T High by 0.2 seconds

29. APRV Adjustments To decrease paCO2:
Increase the T High in O.5 second increments
Allows for more CO2 accumulation in the airways before releasing
If the CO2 increases with this, there is inadequate lung volumes and P High should be increased
Increase T Low to achieve a larger tidal volume
Never let the expiratory flow fall to less than 25% of the peak expiratory flow

30. APRV Adjustments Never change: P High by more than 2 cm H2O
T High by more than 0.2 seconds
T Low by more than 0.1 seconds

31. APRV Weaning
Decrease P High in increments of 1-2 cm H2O while increasing the T High by 0.5 seconds per cm H2O drop in P High
When the P High reaches an acceptable CPAP level, the patient should be considered for extubation