How Positive Pressure Ventilation Affects Vital Organs Functions

1
How Positive Pressure Ventilation Affects Vital
Organs Functions

• Shao-Hsuan Hsia, MD.
• Pediatric Critical Care Medicine, Chang Gung
  Childrens Hospital

2
Why is this topic important?

• Ones meal is another ones poison
• Respiration affects several major body
  compartments thorax, abdomen, cranium, muscle
  tissue spaces.
• Take care of the whole body, not only one organ
  system
• Adverse effects of mechanical ventilation exist
• Respiratory system dysfunction is potentially a
  cause of multiple organ dysfunction syndrome
  (MODS)

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How Positive Pressure Ventilation Affect Vital
Organs Functions

• Respiratory system-cardiovascular system
• Respiration as exercise
• Increased lung volume
• Intrathoracic pressure
• Respiratory acidosis/alkalosis, inhalation gases
• Respiratory system-vital organs
• Brain
• Liver
• Kidney
• Oxygen toxicity

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DO2CO?(1.34?Hb?SaO20.003PaO2)
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Increased Lung Volume

• Vtlt12ml/kg vagal withdrawal?tachycardia
• Vtgt15ml/kg sympathetic withdrawal? bradycardia
• Humoral factors cyclo-oxygenase inhibition, NO
• Mechanical compression of LV
• Pulmonary vascular resistance
• Ventricular interdependence

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Pulmonary Vascular Resistence
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Ventricular interdependence
Positive pressure ventilation can restrict RV
volume and decrease ventricular interdependence
effects Ventricular interdependence can be
worsened by pulmonary hypertension
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Intrathoracic Pressure

• Venous return
• RV preload and afterload
• LV preload and afterload
• Pulmonary resistence

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Systemic Venous Return(RV Preload)
Volume expansion shifts the line to right
PPV increases RAP
RAP
Spontaneous Breathing
Max
0
Systemic Venous Return
10
???????
Vena Cava
???????
???????
RA
RV
PA
??? ????
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???????
Thoracic pump augmentation
???????
???????
Lung
Lung
LA
LV
Ao
12
???????

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??????????
Effect of HFJV on PAH


(n13)
Plt0.01 vs. HFJV




Meliones Circ 1991
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???????????
Effect of pH on PVR
Plt0.01 vs hypoxia

PVR

Lyrene RK 1985
15
??????????
16
??????????
NO for PAH post OP for CHD
PAP (mmHg)
SaO2
Journois J T CVS 1994
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How Positive Pressure Ventilation Affect Vital
Organs Functions

• Respiratory system-cardiovascular system
• Increased lung volume
• Intrathoracic pressure
• Respiratory acidosis/alkalosis, inhalation gases
• Respiratory system-vital organs
• Brain
• Liver
• Kidney
• Oxygen toxicity

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??????
CBF vs. Glasgow outcome score 3 months post
injury Robertson et al. 1992
of Patients
CBF Groups
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Positive Pressure Ventilation and Cerebral
Perfusion

• Cerebral perfusion pressuremean arterial
  pressure?intracranial pressure
• CPPMAP ?ICP (CVP when CVPgtICP)
• PEEP ?ITP, ?VR, ?CVP
• Normal ICP PEEPgt10cmH2O ? ICP
• Increased ICP PEEPltICP is safe
• McGuire et al 1997
• PaCO2

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PEEP vs. normal ICP


plt0.05
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PEEP vs. elevated ICP
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?????????
Volume change(ml/100ml brain)
Palmer, Acta Paediatr 1995
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Impaired Pressure-Flow Autoregulation
Maximal Normal
Maximal Vasodilation Autoregulation
Vasoconstriction
Unexpected Hypermia
Unexpected Ischemia
CBF
Normal Autoregulation Disrupted
Autoregulation Partial Disrupted Autoreg
0 25 50 75 100 125 150
CPP (mmHg)
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???????????-TCD
Hyperventilation ? Vasoconstriction (Ischemia) ?
ICP but ? PI
ICP
Pulsatility Index (PI)
40 35 30 25 PaCO2
25
????CMRO2???
6.0

• hypo-
• perfusion

AVDO2(?mol/ml)
4.0
ischemia
CMRO2
normal
1.8
1.5
2.0
hyperemia
1.2
infarction
0.9
0.6
0.3
0
0
0.4
0.8
1.2
CBF(ml/gm/min)
Robertson J of Neurosurg 1989
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Positive Pressure Ventilation and Liver Function

• Patients with sepsis, trauma and ARDS usually
  combine liver dysfunctionendotoxin, shock,
  hypoxemia and DIC
• ?CO? ?hepatic artery and portal vein blood flow
• ?ITP??hepatic vein pressure (Phv)??hepatic flow
• Descending diaphragm compression? ?intrahepatic
  closing pressure (Pc)? ?sinusoidal cell-blood
  contact time
• ?Peak-inspiratory RAP? ?hepatic blood flow
  pressure gradient
• ?abdominal pressure? ?Ppv, and ?Pc

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Hepatic blood flow interactions
Qha
Pha
Diaphragm
QL
Qvc
Rha
Phv
Ps
Pc
Pra
Rpv
Pab
Ppv
Qpv
Matushak et al J Crit Care 1989
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Plt0.001
N6
plt0.05
Matuschak et al. J Appl Physiol 1987
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Positive Pressure Ventilation and Renal Functions

• PPV may decrease CO and MAP
• The partial occlusion of IVC increase renal vein
  pressure (RVP) and retention of Na and water
• Sympathetic nervous system/renin-angiotensin-aldos
  terone system/atrial natriuretic factor (ANF)
  system.

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Positive Pressure Ventilation and Renal Functions

• ?venous return?deactivate low pressure
  baroreceptor reflexes??renal blood flow, ?renin
• ?venous return? ?ANF?Na and water retention

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Renal Blood Flow vs. PEEP
ZEEP
PEEP 10
RVP 10
PEEP 20
RVP 20




Masahiro et al. CCM 1988
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PEEP and Hormones
Plt0.02
Plt0.0001
Pierre et al. J Appl Physiol 1991
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PEEP and Natriuresis
Plt0.0003
Plt0.0002
Pierre et al J Appl Physiol 1991
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Schuller et al. Chest 1991, 100(4) 1068
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P0.0005
Schuller et al. Chest 100(4) 1068, 1991
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Schuller et al. Chest 100(4) 1068, 1991
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Conclusions (1)

• DO2 CO ? (1.34 ? Hb ? SaO2 0.003PaO2)
• Use heart-lung interactions
• Restrict airway pressure for RV failure
• Expand fluid volume to compensate venous return
• Use positive pressure ventilation in LV failure
• Optimize PEEP?FRC to optimize PVR
• Avoid hypercapnea for pulmonary hypertension

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Conclusions (2)

• Avoid prolonged use of hyperventilation in IICP
• Monitor ICP and CPP vs. PEEP
• Avoid prolonged use of positive pressure
  ventilation in neonates with risk of ICH
• Watch liver function and coagulation factors
• Allow spontaneous (negative pressure) breath
  (IMV, SIMV)
• Watch fluid balance and Na
• Use constant flow in healthy lung

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Mean Airway Pressure
Decelerating Constant
Flow (l/sec)
MAP Area Under Curve
PIP
PIP
Airway Pressure (cmH20)
Gas Distribution