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道 : Airway compromise
力 : Ventilation, Fatigue of the inspiratory muscles
呼吸力道是否足夠
呼吸力道是否足夠
氣 : Oxygenation
Oxygenation and ventilation are different
If you breathe a high concentration of oxygen
but don't increase or decrease your respiratory rate
your arterial oxygen content (PaO2) will greatly increase,
but your PaCO2 won't change.
but your PaCO2 won't change.
- Oxygenation mostly changes PaO2.
- Ventilation mostly changes PaCO2.
- Hypercapnia is exclusively caused by alveolar hypoventilation
舉例 :
Hypoventilation 的 baby
breathing tidal volumes 10 ml
Dead space 8ml, 到肺泡的只剩 2 ml
若我們給予 extra oxygen
會延緩 hypoxic
(enough oxygen will still reach her alveoli to maintain saturation)
But ventilation is still poor, Hypoventilation leads to increased PaCO2.
Type 1 : Hypoxemia with normocapnia or hypocapnia
Typically caused by a ventilation/perfusion (V/Q) mismatch
- Low ambient oxygen (High altitude)
- V/Q mismatch (Pulmonary embolism)
- Alveolar hypoventilation
(Decreased minute volume due to reduced respiratory muscle activity,
e.g. acute neuromuscular disease)
e.g. acute neuromuscular disease)
- Can also cause by severe type 2 respiratory failure
- Diffusion problem (Oxygen cannot enter the capillaries
due to parenchymal disease, e.g. pneumonia or ARDS)
due to parenchymal disease, e.g. pneumonia or ARDS)
- Shunt (Oxygenated blood mixes with non-oxygenated blood
from the venous system, e.g. R to L shunt)
from the venous system, e.g. R to L shunt)
Type 2 : Hypoxemia with hypercapnia
Inadequate alveolar ventilation
- Increased airways resistance (COPD, Asthma)
- Reduced breathing effort
(Drug effects, brain stem lesion, extreme obesity)
(Drug effects, brain stem lesion, extreme obesity)
- A decrease in the area of the lung available for gas exchange
(such as in chronic bronchitis)
(such as in chronic bronchitis)
- Neuromuscular problems (GBS, motor neuron disease)
- Deformed (kyphoscoliosis), Rigid (ankylosing spondylitis), or flail chest
http://jerryljw.blogspot.com/2016/04/shunt.html
* 有灌流 沒通氣 = 分流 Shunt
* 有通氣 沒灌流 = 死區 Dead space
* 用通氣灌流比 (V/Q) 就知道發生什麼問題
有通氣 + 沒灌流 = 通氣灌流比 高, 例如死區
有灌流 + 沒通氣 = 通氣灌流比 低, 例如分流
記 :
Pulmonary embolism 會死人 = Dead space
Pulmonary embolism = 有通氣 + 沒灌流 = Dead space
Physiologic Dead Space :
- Cardiovascular shock (decreased blood flow to lungs)
- Emphysema (lots of enlarged alveoli with less surface area and fewer alveolar capillaries)
- Pulmonary embolus (flow blocked by clot)
Shunt :
- Pneumonia and pulmonary edema : alveoli filled with fluid
- Tissue trauma : alveolar wall swelling
- Atelectasis : collapse of alveoli failure to expand,
taking deep breaths or sighs easily treats atelectasis
* Painful breathing from surgery or trauma
* Depressed levels of consciousness
- Mucous plugging : air can't get into the alveoli
- Pulmonary arteriovenous fistulas
A- a graient 正常 < 15 mmHg ( 超過 30 歲, 每增加 10 y/o 增加 3 mmHg )
A- a graient = 肺泡的氧分壓 - 血液的氧分壓
如果 A- a graient 增加, 就代表 氣體交換介面有問題 ( 通氣, 灌流有問題 )
導致肺泡的氧無法給血液
或是記 PAO2 = 150 - 1.25* PaCO2
Hypoxemia
1. Hypoxic hypoxia :
- Lowered FiO2 or PiO2
- Hypoventilation 神經肌肉問題, 嗎啡中毒
- V/Q mismatch : pneumonia ( V 減少而 Q 不變)
COPD (發燒時 Q 大量增加, 而 V 增加有限)
- Diffusion defect : ARDS, 肺纖維化
- Shunt : 包括intrapulmonary或extrapulmonary, 血流繞過了氣體交換
2. Circulatory hypoxia ：
低血壓, 低血容積導至低心輸出量, 沒有足夠的血液行氣體交換
Correct underlying disease前, 給予氧氣治療, 可延緩組織缺氧
- Decreased heart rate
- Decreased cardiac output
- Shock
- Emboli
3. Anemic hypoxia：
治療時不僅給予氧氣治療, 須 correct underlying
- Decreased Hb
- CO poisoning：use 100% O2
- Excessive blood loss
- Methemoglobin：results from toxic drug reaction
4. Histotoxic hypoxia：cyanide poisoning, alcohol poisoning
5. Demand hypoxia ：高代謝導致組織需氧量增加, 例如 fever
Hypoxemia 之 Approach :
若是 Pa CO2 增加 + Aa gradient 正常沒增加
代表只有 Hypoventilation
低血氧 & 高二氧化碳單純是因為換氣不足
可以是 :
- CNS drive
- Neuromuscular disease ( MG.. )
- Chest wall / pleura / Diaphragm : Scoliosis, fibrosis
- Airway : COPD, Asthma, ILD...
若是 Pa CO2 增加 + Aa gradient 增加
除了 Hypoventilation 外還要再考慮氣體交換介面問題
看是 shunt or V/Q mismatch
* Shunt : V/Q = 0 完全堵住
small airway 到 alveoli Total occlusion
- Lung collapse 當然 有灌流 沒通氣
- 肺泡被占滿滿 ( pneumonia, CHF ) 當然也是 有灌流 沒通氣
- ASD, VSD 也是一個血流沒有交換到氣體的狀況 ( 有血流但沒遇到通氣 )
完全堵住的 shunt 狀況, 給了氧氣當然也不會改善 -> non correctable
就是極端版的 V/Q mismatch
* V/Q mismatch
V/Q mismatch 不是單純指相對於 shunt 的 deadspace
而是很廣義的任何通氣灌流間不平衡
Shunting 就是最嚴重的 V/Q mismatch ~~
把 shunt 歸一類, 其他 mismatch 都在這邊
Asthma, COPD small airway partial obstruction
肺泡被部分塞住 ( pneumonia, CHF )
PE : 屬於有通氣沒有灌流, 是 dead space
不是完全堵住的狀況, 給了氧氣會改善 -> correctable
https://airwayjedi.com/2017/01/06/ventilation-perfusion-mismatch/
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