1. MECHANICAL VENTILATION: Initiation Parameters, Complications
Safety and the Blood Gas Connection
“connecting the dots”
RET 2264C Dr. J.B. Elsberry Prof J.N. Newberry Special Thanks to: Antonio SVCC

2. Control Ventilation (Today, its an Idea not an active mode)
The ventilator delivers a pre-determined VT (volume or pressure targeted) at a preset frequency
Advantages
Guaranteed minute ventilation or peak pressure
Disadvantages
No patient interaction. The patient cannot initiate a breath
Time

3. Assist/Control Ventilation
The ventilator delivers a pre-determined VT (volume or pressure targeted) with each inspiratory effort generated by the patient. A back-up frequency is set to insure a minimum VE
Advantages
Patient can increase VE by increasing respiratory rate
Disadvantages
Dys-synchrony
Respiratory alkalosis
Dynamic hyperinflation

4. Synchronized Intermittent Mandatory Ventilation (SIMV)
The ventilator delivers a pre-determined VT (volume or pressure targeted) at a preset frequency and allows the patient to take spontaneous breaths between ventilator breaths. Spontaneous breaths may be augmented with pressure support.
Advantages
Decreased mean airway pressure
Improved venous return
Disadvantages
Increased oxygen consumption
Increased work of breathing

5. Pressure Control Ventilation (PCV)
The practitioner sets the maximal pressure obtained by the ventilator (preset Pressure), frequency and time the pressure is sustained (inspiratory time). Inspiratory time is set as a percent of the total cycle or absolute time in seconds.
Advantages
Tidal volume variable with constant peak airway pressure
Full ventilatory support
Decreased mean airway pressure
Control frequency
Disadvantages
Requires sedation or paralysis
Ventilation does not change in response to clinical changing needs

6. High Frequency Ventilation
High frequency ventilation is broadly defined as ventilatory support using small tidal volumes with high respiratory rates. Initially used in children, now used in adults who cannot be effectively ventilated with conventional methods.
Advantages
Use small tidal volumes at very lower peak inspiratory pressures
May be associated with lower incidence of pneumothorax
Improves gas exchange with infants with RDS at lower airway pressures than conventional ventilation
Can reduce flow through a bronchopleural fistula and may promote its healing
Disadvantages
Gas trapping
Necrotizing tracheobronchitis when used in the absence of adequate humidification

7. Pressure Support Ventilation (PSV)
The ventilator delivers a predetermined level of positive pressure each time the patient initiates a breath. A plateau pressure is maintained until inspiratory flow rate decreases to a specified level (e.g. 25% of the peak flow value).
Advantages
The flow rate, inspiratory time, and frequency are variable and determined by the patient
Decreased inspiratory work
Enhanced muscle reconditioning
Disadvantages
Requires spontaneous respiratory effort
Delivered volumes affected by changes in compliance

8. Positive End Expiratory Pressure (PEEP)
PEEP is the application of positive pressure to change baseline variable during CMV, SIMV, IMV and PCV. PEEP is primarily used to improve oxygenation in patients with severe hypoxemia.
Advantages
Improves oxygenation by increasing FRC
Decreases physiological shunting
Improved oxygenation will allow the FIO2 to be lowered
Increased lung compliance
Disadvantages
Increased incidence of pulmonary brotrauma
Potential decrease in venous return
Increased work of breathing
Increased intracranial pressure

9. Continuous Positive Airway pressure (CPAP)
Continuous Positive Airway Pressure is simply a spontaneous breath mode, with the baseline pressure elevated above zero.
Advantages
Improves oxygenation by increasing FRC
Decreases physiological shunting
Improved oxygenation will allow the FIO2 to be lowered
Increased lung compliance
Disadvantages
Increased incidence of pulmonary brotrauma
Potential decrease in venous return
Increased work of breathing
Increased intracranial pressure

10. Inverse Ratio Ventilation (IRV)
The ventilator delivers a prolonged inspiration with a proportionately shorter expiratory time. The I:E ratio of each respiratory cycle is  1:1.
IRV ventilation may be accomplished in a pressure controlled, time cycled mode (PCVV-IRV) or a volume cycled mode (VCV-IRV)
PCV-IRV
Peak pressure and I-time or I:E ratio are set
Flow is decelerating
Tidal volume is variable
VCV-IRV
Achieved by applying an inspiratory pause, decreasing the flow rate or applying a decelerating flow pattern
Today, used primarily for short-term recruitment of alveoli

11. Inverse Ratio Ventilation (IRV)
Advantages
Maintains elevated mean airway pressure, while maintaining safe peak alveolar pressures
Recruitment of lung units with decreased compliance
Disadvantages
Auto - PEEP
Exacerbation of hemo-dynamic instability
Barotrauma
Requires deep sedation and paralysis
Changes in lung compliance result in changes in delivered VT (PCV - IRV)

12. Airway Pressure Release Ventilation (APRV)
The ventilator cycles through a high and low CPAP level while the patient breathes spontaneously
APRV uses intermittent decreases (rather than increases) in airway pressure
VT varies depending upon pulmonary compliance, airway resistance, and the duration of the airway pressure release
Alveolar ventilation is augmented by the brief releases in the higher CPAP level to the lower CPAP level
APRV was developed to provide ventilatory support to
spontaneously breathing patients with acute lung injury.

13. Airway Pressure Release Ventilation (APRV)
Advantages
Lower peak airway pressures
Recruitment and stabilization of collapsed alveoli(intrinsic PEEP due to short expiratory phase)
Reduced deadspace ventilation
Allows spontaneous breathing
Disadvantages
Tidal volume varies with changes in the resistance and compliance properties of the lung
Synchrony  airway pressure release is not synchronized with spontaneous breathing

14. Clinical Review: Common Types of Ventilation Strategies Modes
Volume Control (CMV and IMV modes)
Pressure Control (CMV and IMV modes)
Pressure Support-CPAP (CSV and IMV modes)
Pressure-Regulated Volume Control (VC-CMV)
Airway Pressure Release Ventilation (PC-CSV)

15. Volume Control VC-CMV & VC-IMV
The patient is given a specific volume of air during inspiration.
The ventilator uses a set flow for a set period of time to deliver the volume: TV (cc) = Flow (cc/sec) x I-time (sec)
The PIP observed is a product of the lung compliance, airway resistance and flow rate. The ventilator (and staff) does not react to the PIP unless the alarm limits are violated.
The PIP tends to be higher than during pressure control ventilation to deliver the same volume of air.
With SIMV, the patient can breath spontaneously between vent breaths. This mode is often combined with PS.

16. Review of the Triggering Window in SIMV

17. What about Flow? (VC vs PC)

18. Pressure Control PC-CMV & PC-IMV
Patient receives a breath at a fixed airway pressure.
The ventilator adjusts the flow to maintain the pressure.
Flow decreases throughout the inspiratory cycle.
The pressure is constant throughout inspiration.
Volume delivered depends upon the inspiratory pressure, I-time, pulmonary compliance and airway resistance.
The delivered volume can vary from breath-to-breath depending upon the above factors. MV not assured.
Good mode to use if patient has large air leak, because the ventilator will increase the flow to compensate.

19. Pressure Control Ventilation (PC-IMV) vs PC-CSV

20. Volume vs Pressure Target Comparison
Flow
Cycle
Advantage
Disadvantage
Volume Target
(Volume control)
Fixed
Volume
Guaranteed
volume
Potentially
dys-synchronous
Pressure Target
(Pressure control)
Initially rapid, then
variable
Time
Rapid mixing
assist synchrony
No guaranteed
volume

21. Typical Volume vs. Pressure

22. Full Ventilatory Support Modes
CMV
- control - assist/control
SIMV Volume (VC-IMV)
SIMV Pressure (PC-IMV)
PCV (PRVC) (DC-CMV)

23. Partial Vent. Support Modes
Low-rate SIMV
PSV
VSV (Volume Support Ventilation) - Servo 300 and Servo i
(PSV to deliver certain volume)
APRV (Airway Press. Release ventilation)

24. Spontaneous Ventilation ?
PSV
APRV
BiPAP
CPAP
T-Tube (T-piece)

25. What about Sighs? (10-15 ml/kg)
Before and after suctioning
Before and after bronchoscopy
During an extubation procedure
During chest physiotherapy
During low VT ventilation (< 7 mL/kg)
As a recruitment maneuver in some patients with ARDS

26. CPAP-Pressure Support PC-CSV
No mandatory breaths
Patient sets the rate, I-time, and respiratory effort.
CPAP performs the same function as PEEP, except that it is constant throughout the inspiratory and expiratory cycle.
Pressure Support (PS) helps to overcome airway resistance and inadequate pulmonary effort and is added on top of the CPAP during inspiration.
The ventilator increases the flow during inspiration to reach the target pressure and make it easier for the patient to take a breath.

27. SIMV + PS VC-IMV + PS & PC-IMV + PS

28. Pressure-Regulated Volume Control VC-CMV +PC = (DC-CMV)
In this mode, a target minute ventilation is set.
The ventilator will adjust the flow to deliver the volume without exceeding a target inspiratory pressure.
Decelerating flow pattern.
No change in minute ventilation if pulmonary conditions change.
Can ventilate at a lower PIP than in regular volume control.
Hard to use on a spontaneously breathing patient or one with a large air leak.
Not a “weaning” mode.

29. PRVC algorithim from Maquet

30. Let’s Review General Initial Ventilator Settings
f: in neonates (higher with HFJV)
20-24 for infants and preschoolers for grade school kids for adolescents
8-14 for adults (SIMV-AC)
PEEP: 3-5cm H2O
FIO2: 100%
I-time: 0.7 sec for higher rates, 1 sec for lower rates (adults)
PIP (for pressure control): about 24cm H2O.
Pressure Support: 5-10cm H2O.

31. Basis for Minute Ventilation Setting or Targeting the Tidal Volume
Adults Vol. (ml/kg)
Normal lungs – 12*
COPD
Restrictive ≤ 8
ARDS (ARDSnet)
Children based upon age PC Target

32. Managing Ventilator Settings
Manipulating PaCO2
Alveolar Ventilation
Frequency (f or T E)
Tidal volume (in PC Modes: TI & PIP)
Manipulating PaO2
Fraction of inspired oxygen (FIO2)
Mean Airway Pressure (MAP)
Inspiratory flow rate
Inspiratory time and I:E ratio
PEEP : Auto PEEP
Extrinsic PEEP

33. Revisit the Indicators for Adjusting the Ventilator
pCO2 too high
pCO2 too low
pO2 too high
pO2 too low
PIP too high
What to do next…

34. pCO2 Too High Patient’s minute ventilation is too low.
Increase rate or TV or both.
If using PC ventilation, increase PIP.
If PIP too high, increase the rate instead.
If air-trapping is occurring, decrease the rate and the I-time and increase the TV to allow complete exhalation.
Sometimes, you have to live with the high pCO2, so MDs may use THAM or bicarbonate to increase the pH to >7.20.

35. pCO2 Too Low Minute ventilation is too high.
Lower either the rate or TV.
Don’t need to lower the TV if the PIP is <20.
PIP <24 is fine unless delivered TV is still >15ml/kg.
TV needs to be 8ml/kg or higher to prevent progressive atelectasis
If patient is spontaneously breathing, consider lowering the pressure support if spontaneous TV >7ml/kg.

36. pO2 Too High Decrease the FiO2.
When FiO2 is less than 40%, decrease the PEEP to 3-5 cm H2O.
Wean the PEEP no faster than about 1 every 8-12 hours.
While patient is on ventilator, don’t wean FiO2 to <25% to give the patient a margin of safety in case the ventilator quits.

37. pO2 Too Low
Increase either the FiO2 or the mean airway pressure (MAP).
Try to avoid FiO2 >70%.
Increasing the PEEP is the most efficient way of increasing the MAP in the PICU.
Can also increase the I-time to increase the MAP (PC).
Can increase the PIP in Pressure Control to increase the MAP, but this generally doesn’t add much at rates <30bpm.
May need to increase the PEEP to over 10, but try to stay <15 if possible.

38. Changes in ARDS (Decreasing CL)
Volume Control Pressure Control

39. PIP Too High Decrease the PIP (PC) or the TV (VC).
Increase the I-time (VC).
Change to another mode of ventilation. Generally, pressure control achieves the same TV at a lower PIP than volume control.
If the high PIP is due to high airway resistance, generally the lung is protected from barotrauma unless air-trapping occurs.

40. Complications Gastrointestinal Renal Nutritional Pulmonary
Barotrauma
Ventilator-induced lung injury
Nosocomial pneumonia
Tracheal stenosis
Tracheomalacia
Pneumothorax
Air Trapping (Auto PEEP)
Cardiac
Myocardial ischemia
Reduced cardiac output
Hypotension
Gastrointestinal
Ileus or Reflux
Hemorrhage
Pneumoperiteneum
Renal
Fluid retention
Electrolyte Disturbances
Nutritional
Malnutrition
Overfeeding

41. Acute Deterioration DIFFERENTIAL DIAGNOSES Pneumothorax
Right mainstem intubation
Pneumonia
Pulmonary edema
Loss of airway
Airway occlusion
Ventilator malfunction
Mucus plugging
Air leak

42. Physical Exam Findings
Tracheal shift
Pneumothorax
Wheezing
Bronchospasm
Mucus plugging
Pulmonary edema
Pulmonary thromboembolism
Asymmetric breath sounds
Pneumothorax
Mainstem intubation
Mucus plugging with atelectasis
Decreased breath sounds bilaterally
Tube occlusion
Ventilator malfunction
Loss of airway

43. How Do You Know… Target Limits
Tidal Volume or Minute Ventilation Changes
Limits
Flow or Time of Inspiration Insufficient for Pt.
Pressure an indicator of changing Raw or CL in VC
An established consistent pressure limit in PC
An adjusted Variable in Dual Modes
Baseline Pressures violated (Low PEEP/CPAP)

44. Pressure Patterns That May Indicate Complications
Elevated peak and plateau pressures
Pneumonia
Pulmonary edema
Pneumothorax
Atelectasis
Right mainstem intubation
Elevated peak pressure, normal plateau pressure
Airflow obstruction
Mucus plugging
Partial tube occlusion
Reduced peak and plateau pressure
Cuff leak
Ventilator malfunction
Large bronchopleural fistula
Ventilator Disconnect

45. Levels of Alarm and Example Events during Mechanical Ventilation
Level 1: Immediately Life-Threatening
electrical power failure
no gas delivery to patient
exhalation valve failure
excessive gas delivery to patient
timing failure
Level 2: Potentially Life-Threatening
circuit leak
circuit partially obstructed
heater/humidifier malfunction
inspiratory to expiratory
(I:E) ratio inappropriate
inappropriate oxygen level (gas/blender failure)
autocycling
inappropriate (CPAP) level

46. Levels of Alarm and Example Events during Mechanical Ventilation cont.
Level 3: Not Life-Threatening but a Potential Source of Patient Harm
changes in lung characteristics (compliance/resistance)
auto-PEEP (air trapping)
changes in ventilatory drive (e.g., CNS or muscle function)
Classification of Common Conditions in Lab Today…

47. Pt. “Fighting with the Ventilator”
Causes
1. Inadequate ventilation (Hypercarbia)
2. Acidemia
3. Inadequate oxygenation
4. CNS malfunction
5. Pain or anxiety
6. Asynchrony (I time and or Peak Flow)

48. Neurologic
Patient must be able to protect his airway, e.g, have cough, gag, and swallow reflexes.
Level of sedation should be low enough that the patient doesn’t become apneic once the ETT is removed.
No apnea on the ventilator.
Must be strong enough to generate a spontaneous TV of 5-7ml/kg on 5-10 cm H2O PS or have a negative inspiratory force (NIF) of 25cm H2O or higher.
Being able to follow commands is preferred.

49. Cardiovascular
Patient must be able to increase cardiac output to meet demands of work of breathing.
Patient should have evidence of adequate cardiac output without being on significant inotropic support.
Patient must be hemodynamically stable.

50. Pulmonary Patient should have a patent airway.
If no air leak, consider decadron and racemic epinephrine.
Pulmonary compliance and resistance should be near normal.
Patient should have normal blood gas and work-of-breathing on the following settings:
FiO2 <40%
PEEP 3-5cm H2O
Rate: 6bpm for infants, 2bpm for toddlers, CPAP/PS for 1hr for older children and adolescents
PS 5-8cm H2O
Spontaneous VT of 5-7ml/kg

51. Critical Care ABGs Rules Of Interpretation
∆ in pCO2 of 10mm Hg should ∆ pH by 0.08.
pH ∆ of 0.15 is equal to ∆ in HCO3 of 10mEq/L.
Normal pCO2 in the face of respiratory distress is a sign of impending respiratory failure.

52. Review Respiratory Disturbances
Acute respiratory acidosis occurs when CO2 is retained acutely.
Chronic respiratory acidosis occurs when the retained CO2 gets buffered by renal retention of HCO3. The pH is higher than in acute respiratory acidosis, but it is still <7.4.
Acute respiratory alkalosis occurs when CO2 is blown off acutely.
Chronic respiratory alkalosis occurs when the reduction of CO2 is compensated for by the renal excretion of HCO3. The pH is lower than in acute respiratory alkalosis, but it is still >7.4.

53. Metabolic Disturbances
Acute metabolic acidosis gets compensated by CO2 reduction within hours. The pH is still usually <7.4.
Metabolic alkalosis is rare. Usual causes are pyloric stenosis, chronic diuretic use, and bicarbonate infusions.
Otherwise healthy people do not usually retain CO2 to compensate for metabolic alkalosis.
Patients who are severely dehydrated or have lung disease will retain CO2 to compensate for metabolic alkalosis.

54. Adjusting for low PaO2 Low Compliance Pts.
Goal Generally is a PaO2 between 60 and 100 mm Hg.
Is PaO2 and FIO2 a linear relationship?
Calculate with this Relationship:
Current PaO2/ FIO2 = Desired PaO2/New FIO2
What about PEEP?

55. Clinical Approaches to PEEP Ranges
Minimum or Physiologic PEEP (3-5)
Moderate PEEP (5-15) Trial and error
Maximum PEEP > 15
Optimum or “Best PEEP”:
Compliance, C.O., PVO2 , Inflection Points…
We will revisit all of this later in the course