EICU core review

1. Mechanical Ventilation 1
EICU core review 전임의 김태권

2. Reference

3.  Hypoxemix Respiratory Failure (Type 1) :
PaO2 < 60 mmHg
 Hypercapnic Respiratory Failure (Type 2) :
PaCO2 > 50 mmHg (acute), pH < 7.30 (acute on chronic)
 Perioperative Respiratory Failure (Type 3) :
FRC ↓, Atelectasis ↑ (subset of type 1 respiratory failure)
 Shock (Type 4) : Secondary to cardiovascular instability
(MV → unloading respiratory muscle, lowering O2 consumption, stabilizing gas exchange)
Indication of MV

4. Oxygenation
VILI ↓ & WOB ↓
Ventilation
 Aceptable Oxygenation : PaO2 > 60 mmHg or SaO2 > 90%
 Prevent Ventilaor Induced Lung Injury (VILI)
(consider “permissive hypercapnia strategy” : pH > 7.2 ~ 7.25)
 Reduce Work of breathing (WOB)
 Adequate Ventilation : usually pH > 7.30
Goal of MV

5. Mode of MV
Ventilation Mode 분류 기준
변수(variable)에 따라 Mode를 분류 : 3T
Trigger (흡기 시작) : 환자 노력 or 시간 (기계)
Target (흡기 목표) : Volume or Pressure
Termination (흡기 종료 시점) : 시간 or 유속
+
Together with spontaneous breathing (SIMV)

6. 2. Flow Trigger1. Pressure Trigger
환자의 흡기 노력 감지
Ventilation Mode (variable) : Trigger
설정된 시간에 기계에 의해 시작
3. Time Trigger

7. Ventilation Mode (variable) : Target
실제로는 flow control을 통해 target volume을 맞춤

8. Ventilation Mode (variable) : Termination
1. Termination by Time 2. Termination by Flow
20% of peak inspiratory flow

9. Conventional Ventilation Mode
Mode of MV

10. Advanced Ventilation Mode
Mode of MV
Pressure regulation
+
Volume assurance
Pressure regulation
+
Volume assurance

11. Non-invasive Positive Pressure Ventilation (NIPPV)
CPAP
(continuous positive airway ventilation)
BPAP
(Bilevel positive airway ventilation)
Mode of MV

12. Mode of MV

13. Volume control A/C mode
Trigger : Patient (flow, pressure) or Ventilator (Time)
Target : Volume
Termination : Ventilator (Time)
 Volume is independent & Pressure is dependent
 Trigger by patient (if patient’s RR is above set rate) or
by timer (if patient’s RR is below set rate)
 Set VT, minimum rate, Flow max or I:E ratio, Flow pattern (ramp or squre)
→ Inspiratory time is determined
Advantage
 Guarantee tidal volume & minute ventilation
 Good representation of lung mechanics
Disadvantage
 High airway pressure (Vulnerable barotrauma)
 Overdistension (Dynamic hyperinflation)
 Patient-ventilator asynchrony (esp. flow demand)
Mode of MV : VC (A/C)

14. Pressure control A/C mode
Trigger : Patient (flow, pressure) or Ventilator (Time)
Target : Pressure
Termination : Ventilator (Time)
 All breaths are PC breaths triggerd by patient or ventilator
 Tidal volume depends on inspiratory pressure, lung mechanics (lung
compliance and airway resistance)
 Set Inspiratory pressure, minimum RR, Inspiratory time or I:E ratio, PEEP
Advantage
 Prevent excessive airway pressure
 Flow varies with patient’s demand (more comfortable)
 Mean airway pressure ↑ : better oxygenation
 Better gas distribution
Disadvantage
 Variable tidal volume (by respiratory mechanic change)
 No guaranteed minute ventilation (hypoventilation risk ↑)
 Mean airway pressure ↑ : C.O ↓ (if preload is inadequate)
Mode of MV : PC (A/C)

15. VC vs PC

16. Pressure support mode
Trigger : Patient (flow, pressure) or Ventilator (back up)
Target : Pressure
Termination : Patient (flow)
 PS level is the pressure above PEEP (baseline)
 Volume is determined by pt’s effort, lung mechanics, PS level
 Maximum PS (minimum effort required by patient)
 Minimum PS (usually PS level : 2~ 6 cmH20)
- To compensate for ET tube resistance
 Used for weaning (decreased slowly from PSmax to PSmin)
 PS may support the spontaneous breaths in SIMV for tube compensation
Advantage
 Better ventilator–patient synchrony (comfortable)
 Weaning mode of ventilation
Disadvantage
 Variable tidal volume (by respiratory mechanic change)
 Respiratory muscle fatigue (if pressure support is too low)
Mode of MV : PSV

17. Mode of MV : APRV (Inverse Ratio Ventilation)

18. APRV mode + spontaneous breathingAPRV mode + No spontaneous breathing
Mode of MV : APRV

19. Mode of MV : APRV Viscoelasticity of lung tissue = Need Time

20. Mode of MV : APRV Spontaneous Breathing
Spntaneous breathing
Mechanical ventilation

21. Mode of MV : APRV

22. Mode of MV : APRV
APRV (Airway Pressure Release Ventilation) mode
Trigger : Ventilator (Time)
Target : Pressure
Termination : Ventilator (Time)
+
Allowing spontaneous breathing (± pressure support)
Advantage
 Lower PIP to maintain oxygenation & ventilation
(without compromising patient’s hemodynamics)
 Higher MAP : Improved Oxygenation & V/Q matching
 Lower minute ventilation (less dead space ventilation)
 Preservation of spontaneous breathing
(throughout entire respiratory cycle)
Disadvantage
 Variable VT (with change in lung compliance & resistance)
 Auto-PEEP is usually present
 Could be harmful to patients with high expiratory resistance
(i.e., COPD, asthma)
 Not completely support CO2 elimination
(relies on spontaneous bereathing)

23. Mode of MV : APRV
Intensive Care Med (2017) 43:1648–1659
Clinicaltrials.gov : NCT01862016 ~
 Early spontaneous breathing in ARDS
 Enrollment : 702
 Procedure : APRV
 Primary outcome : All cause hospital mortality (~60 day)
 Study completion : May, 2019

24. Initial MV Setting

25. MV Setting : Tidal Volume

26.  Tidal Volume is based on Predict Body Weight (PBW)
 Use the Height, Don’t use the actual body weight
 Predict Body Weight (PBW) ≈ Ideal Body Weight (PBW)
- Male = 50kg + 0.91 ( Height (cm) – 152.4 ) ≈ Height (cm) - 105
- Female = 45.5kg + 0.91 ( Height (cm) – 152.4 ) ≈ Height (cm) - 110
 Initial tidal volume should be set at 6 mL/Kg PBW (≈ PBW)
(Range : 4~8 mL/kg PBW)
 Can increased up to 8 mL/Kg PBW
(If patients is double triggering, or if inspiratory airway pressure decreased below PEEP)
 Can decreased down to 4 mL/Kg PBW
(If plateau pressure > 28~30 cmH2O, or if driving pressure > 15~18 cmH2O)
 Keep alveolar (plateau) pressure < 28~30 cmH2O (assumes thoracic compliance is normal)
 Keep driving pressure < 14~16 cmH2O
Acta Anaesthesiol Scand 2004;48:267-271
MV Setting : Tidal Volume

27. Ann Am Thorac Soc 2017;14:S271-9
MV Setting : Tidal Volume

28. MV Setting : Tidal Volume (PC mode)
PC above PEEP
PEEP

29. Transpulmonary pressure
(alveolar distending pressure)

30. MV Setting : Tidal Volume (PC mode)

31. Stress & Strain
 Stress : The distribution of internal forces per unit of area
induced by an external force applied onto a specific material
 Strain : Ratio of total deformation to the initial dimention of the material body
in which the forces (stress) are being applied

32.  Stress : Transpulmonary Pressure (PL ) at end-inspiration
 Strain : ∆V/EELV (End expiratory lung volume) = VT /FRC
 Transpulmonary Pressure (Stress) = ELspec × VT /FRC (Strain)
stress
strain
Stress & Strain

33. Strain & Transpulmonary pressure
AJRCCM 2008;178:345-55 Gattinoni et al. Critical Care (2017) 21:183
 Stress = ELspec × Strain (Strain = VT /FRC)
 FRC의 2배로 부피 증가 (≈ 80% of TLC) :
Strain = 1, Stress (PL ) ≈ 12~13 cmH2O
 FRC의 3배로 부피 증가 (≈TLC) :
Strain = 2, Stress (PL ) ≈ 24~26 cmH2O

34. Strain & Transpulmonary pressure
Gattinoni et al. Critical Care (2017) 21:183
(Transpulmonary pressure)

35. Driving pressure (strain)
Mild Moderate Severe
키 175cm로 동일한 3명의 ARDS 환자
실제 functional lung volume (FRC)은 서로 다름
Q. 동일하게 6 ml/kg PBW로 계산한 420 ml를
주는 것이 lung protective가 되겠는가 ?
Severe ARDS - FRC 280cc
Mild ARDS - FRC 3600cc

36. Higher Plateau Pressure : Not always Risky
Higher PEEP : Not always Protective
NEJM 2015;372:747-55
Driving pressure (strain)

37.  CRS (respiratory system의 compliance)는 residual aerated lung volume, 즉 functional lung size(FRC)와 strongly correlation한다
 Tidal volume / CRS 은 허탈된 폐를 제외한 실제 남아 기능하는 폐용량(baby lung)에 대비하여 투여되는 일회 호흡량의 비율를 의미하게 된다
 DP = VT /CRS ≈ VT /FRC = Strain (Normalized VT to functional lung size)
Driving pressure (strain)
Driving Pressure

38. NEJM 2015;372:747-55
Driving pressure (strain)

39. MV Setting : Minute Ventilation

40. 1. Diffusion of gases into and out of liquids
- Henry’s law : 기체의 용해도는 기체 분압에 비례한다
- Solubility coefficient (용해 계수) : CO2가 O2보다 약 24배 물에 더 잘 녹는다
2. Diffusion of gases through the respiratory membrane
- Partial pressure gradient of the gas : 기체 분압 차이가 클수록 확산 ↑
Room air : O2 Partial pressure = 760 mmHg × 0.21 = 159.6 mmHg
FiO2 0.6 : O2 Partial pressure = 760 mmHg × 0.6 = 456 mmHg
- Alveolar ventilation 증가할수록 폐포내 PO2 ↑ & PCO2 ↓ 잘 유지되어 가스 교환 촉진됨
- Diffusion coefficient : CO2가 O2보다 호흡막을 통한 확산이 약 20배 잘 일어남
- Thickness of membrane : 폐부종, 폐렴 등에서 호흡막의 fluid 축적은 확산 ↓
- Surface area of membrane : 폐절제, destructive lung, 무기폐 등의 면적 감소시 확산 ↓
Minute Ventilation (VT × RR) ↑ = PaCO2 ↓
Surface area (PEEP) ↑ = PaO2 ↑
Partial pressure gradient (FiO2) ↑ = PaO2 ↑
MV Setting : Minute Ventilation

41.  Minute Ventilation = VT × RR
 Minute Ventilation : 100 mL/kg IBW per minute (approximately)
 Initial Setting : 6~8 L/min
 Minute Ventilation must be adjusted for abnormal conditions
- Hyperthermia or Hypothermia
- Hypermetabolism and metabolic acidosis
- Lung disorder ( physiologic dead space↑)
MV Setting : Minute Ventilation

42.  만약 CO2 생성에 변화가 없다면,
- PaCO2 (Initial) x VA (1) = PaCO2 (Desire) x VA (2)
- PaCO2 (Initial) x (VT – VDphys)(1) x RR(1) = PaCO2 (Desire) x (VT – VDphys)(2) x RR(2)
 만약 CO2 생성에 변화가 없고 생리적 사강에도 변화가 없다면,
- 호흡수만 변경하여 PaCO2 교정 : PaCO2 (Initial) x RR(1) = PaCO2 (Desire) x RR(2)
- 호흡량만 변경하여 PaCO2 교정 : PaCO2 (Initial) x VT (1) = PaCO2 (Desire) x VT (2)
Minute Ventilation (VT × RR) ↑ = PaCO2 ↓
 VA :Alveolar ventilation
 VDphys : Physiologic Dead space
 VCO2 : CO2 Production
 VA = (VT – VDphys) x RR
 PaCO2 = 0.863 x VCO2 / VA
MV Setting : Minute Ventilation

43. Ex) 175cm, 75kg men with mechanical ventilation
PBW : 175cm – 105 = 70kg
Tidal volume : 70kg × 6mL = 420mL
Minute Ventilation : 70kg × 100mL/kg/min = 7000mL/min
Respiratory Rate : 7000mL/min / 420mL = 16~17/min
MV Setting : Respiratory rate

44. MV Setting : Inspiratory Time (I : E ratio)
 For most adults (good starting point) :
- Initial inspiratory time : approximately 0.8 ~ 1 sec (0.6~1.2 sec)
+
- Inspiratory-to-Expiraotry (I:E) ratio : 1:2 ~ 1:4
↓
 This value corresponds to an initial peak flow setting of
approximately 60 L/min (flow range 40~80 L/min)
 COPD : High flow rate up to 80~100 L/min can improve gas
exchange (providing long TE : risk of air trapping↓)

45. Time Constant

46. Raw = PTA / flow = 7 cmH20 / 0.6 (L/s) = 11.7 cmH20/(L/s)
PTA = PIP − Pplat = 30-23 = 7 cmH20
PTA
Cs = VT / (Pplat − PEEP) = 0.5 L / (23−5) cmH20 = 0.029 L/cmH20
Flow= 36 L/min = 0.6 L/s
τ = Raw × Cs = 11.7 cmH20/(L/s) × 0.029 L/cmH20 = 0.34 s
Time Constant

47. MV Setting : Inspiratory Flow Pattern

48. MV Setting : Inspiratory Flow Pattern

49.  Change from Constant waveform → Descending waveform
- Peak airway pressure↓ & Mean airway pressure (MAP)↑
- Gas distribution↑, Dead space↓ , Oxygenation↑
- Changing to descending waveform to reduce peak airway pressure may increased MAP
Mean airway pressureMean airway pressure
MV Setting : Inspiratory Flow Pattern

50. MV Setting : Inspiratory Flow Pattern

51. Mean Airway Pressure (Paw)
 PPV에 의한 cardiovascular의 harmful effect를 줄이려면 Mean Airway Pressure를 감소시켜야 한다
 PaO2는 Mean Airway Pressure에 절대적으로 영향을 받기 때문에 어느 정도의 Paw 유지는 반드시 필요
 ARDS에서 Mean Airway Pressure↑ → FRC ↑ → Oxygenation ↑

52. Mean Airway Pressure (MAP)

53. Mean Airway Pressure (MAP)

54. MV Setting : Inspiratory Rise Time (Flow rate)

55. MV Setting : Inspiratory Rise Time (Flow rate)
 Inspiratory Rise Time
- Time to peak inspiratory flow or pressure at
the start of each breath as a percentage of
total cycle time (TCT) or in second
- Clinician must carefully adjust the flow and
flow pattern to suit the patient’s ventilator
needs
 Inspiratory Flow Rate
- Initial peak flow setting : about 60 L/min (range 40~80 L/min)
- Flow is normally set to deliver inspiration in about 1 sec
(Range : 0.6~1.2sec , 일반적으로 1초를 넘기지 않는다)
- COPD : High flow rate up to 80~100 L/min can improve gas exchange
(providing long TE of 3~4 time constants : risk of air trapping↓)
- Flow must be set to meet a patient’s inspiratory demand
(lower inspiratory flow tend to increased patient’s work of breathing)

56. MV Setting : Inspiratory Rise Time (Flow rate)

57. MV Setting : Inspiratory Rise Time (Flow rate)
Servo ventilator와는 달리 PB 840에서는 Inspiratory rise time의 숫자가 클수록 초기에 많은 유량과 함께 setting pressure에 도달함

58. MV Setting : Trigger

59. MV Setting : Trigger
More Sensitivity
 Auto-trigger가 발생하지 않는 범위내에서 최대한 민감하게 세팅해야 함
 Flow Trigger : 1 ~ 2 L/min
(일반적으로 숫자가 낮을수록 민감, but Servo의 경우 숫자가 높을수록 민감)
 Pressure Trigger : - 1 cmH2O
 너무 민감하면 auto-trigger 발생함
 너무 둔감하면 trigger 되지 않아 asynchrony & WOB ↑
 일반적으로 Flow triggering이 pressure trigger 보다 WOB가 적다고
알려져 있으나 최근의 ventilator 들은 차이가 없다고 함

60. Uncaptured Trigger Proper Trigger Auto-Trigger
MV Setting : Trigger
WOB↓

61. MV Setting : FiO2

62.  Expected PaO2 with age : 109 – [0.4 xAge(yrs)]
 Oxygenation Goal : PaO2 55 ~ 80mmHg, SaO2 88 ~ 95%
MV Setting : FiO2

63. MV Setting : FiO2
FiO2
 Unless detailed information identifying precise FiO2 needed available
→ Initiation of treatment for most patients is with 100% O2
 FiO2 is tiltrated to achieve PaO2 of 60~80 mmHg
with SaO2 or SpO2 90% or greater
 Titration is followed by oximetry or measurement of blood gases
(when titrating FiO2↓, should wait at least 20 min for O2 level stabilizing)
 Using P/F ratio is not as accurate as using the PaO2/PAO2 ratio
 When minimal FiO2 is identified, further reduction in FiO2 should be
in steps of 5% to 10% followed by pulse oximetry measurements
(Decrements not to exceed 20%)

64. FIO2 농도 노출시간 특징
1.0
> 12h FVC 감소, 기침, 흉통
> 24h 내피세포 기능 변화
> 36h A-a DO2 증가, DLCO 감소
> 48h Alveolar permeability 증가, Pul.edema 발생
> 60h ARDS
0.8 > 24h Toxicity can occur (same as FiO2 1.0)
0.6 > 36h 경미한 흉통, 폐기능 불변
0.24 ~ 0.28 Months No clinical toxicity
MV Setting : FiO2 & O2 Toxicity