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HypoxiaZhihua Gao
Zhejiang University
Review of respirationMeasurements of O2
Hypoxia definition classification, etiology, mechanism
resultant changes in the body prevention and treatment
Overview
1. O2 intake
2. Hb carrying O2
3. O2 transport in circulation
4. O2 utilization in the tissue
Respiration-a process of gas exchange
External respiration
O2 dependence
Large amount of O2 consumption ---- 250ml/min (360L/day)
Small amount of O2 storage ---- 1.5L (sustain life only six minutes)
Continuous hypoxia
>6 min--life-threatening
PO2 (partial pressure of oxygen) 血氧分压
Oxygen tension 血氧张力 the tension produced by oxygen molecules
physically dissolved in the blood Arterial (PaO2): 100 mmHg (13.3kPa)
Venous (PvO2): 40 mmHg (5.33kPa)
Influence factors (IFs): Pressure of O2 in the air (空气氧分压) External respiratory function (外呼吸功能) Shunt of blood ( 血液分流 )
Measurements of O2 (1)
CO2max (oxygen binding capacity) ,最大血氧容量
Maximal amount of oxygen that can be potentially bound by the haemoglobin (Hb), a reflection of the ability of Hb carrying O2.
Under ideal condition, the binding capacity is ~1.34 ml/g Hb
IFs:
Quantity of Hb ( 血红蛋白的量 )
Quality of Hb or affinity of Hb ( 血红蛋白的质与亲和力 )
Measurements of O2 (2)
CO2: (oxygen content), 实际血氧含量 the actual O2 content in the blood, including the
oxygen bound to the Hb and O2 dissolved in the blood. Arterial CO2 (CaO2): 19 ml/dl
Venous CO2 (CvO2): 14 ml/dl
Differences of CO2 between arterial and venous (Da-vCO2): 5 ml/dl
IFs: PaO2
CO2 max-Hb quantity and quality
Measurements of O2 (3)
SO2 (oxygen saturation) , 血氧饱和度 the percentage of oxygen-bound form
(oxyhemoglobin) in total Hb. Arterial (SaO2): 97-99% Venous (SvO2): 75%
IFs: PO2
pH, temperature CO2, DPG
Measurements of O2 (4)
A curve reflecting the relationship between the PO2 and SO2
S (sigmoid) shape
SO2 , SDC left shift Hb affinity SO2 , SDC right shift Hb affinity
O2 saturation dissociation curve (SDC)
Right shift
Left shift
P50: the PO2 @ 50% SO2
Reflecting the flexibility of Hb carrying O2
SDC right shift , P50↑
SDC left shift, P50↓
P50-a value indicating the felexibilty of Hb
Hypoxia
Defintion:
A pathological process in which O2 supply to tissues is
inadequate to meet the demand of cells, or utilization of
O2 is insufficient in cells despite adequate O2 supply,
leading to changes in functions, metabolisms and
structures of cells and tissues in the body.
Inadequate supply of O2 ( 氧供不足 )
Insufficient utilization of O2 (用氧障碍)
1. O2 intake
2. Hb carrying O2
3. O2 transport in circulation
4. O2 utilization in the tissue
Classification of hypoxia
1. Hypotonic hypoxia
2. Hemic hypoxia
3. Circulatory hypoxia
4. Histogenoushypoxia
The most common type of hypoxia
Causes:
O2 supply Tibetan Plateau, mineral wells
Dysfunction in external respiration, a.k.a respiratory hypoxia Bronchial obstruction
Respiratory muscle paralysis
Venous-to-arterial shunts Congenital cardiac defects
Hypotonic/hypoxic hypoxia( 低张性缺氧 )
Features:
minor: PaO2 ↓ ; CO2 N
Severe:PaO2 ↓ ; CO2max N, CaO2 ↓ ; SaO2↓D(a-v)O2 ↓or N
Central cyanosisRespiratory compensation
Hypotonic/hypoxic hypoxia
Deoxyhemoglobin >5g/dl (central cyanosis)
Patients with hypoxia can show cyanosis, but cynosis does not mean hypoxia.
Hypoxia patients may not have cyanosis.
Enterogenous cyanosis ( 肠源性紫绀 ):
Cyanosis ( 发绀或紫绀 )
Hypoxia caused by abnormalities in hemoglobin (Hb)
Amount of Hb ↓ Altered binding capacity of Hb
Causes: Anemia CO poisoning Methemoglobinemia Higher affinity of Hb to O2
Hemic/isotonic hypoxia (血液性缺氧)
20 60 100 120
PaO2 , mmHg
300
200
150
Ca
O2,
ml/
l
100
100
anemiaHb = 10
normalHb = 15
100
Sa
O2,
%
polycythemiaHb = 20
Hb concentration &CaO2 relationship
CO poisoning
CO binds to Hb to form
COHb,
which cannot take up
O2.
Affinity of Hb to CO is
~210 times higher than
O2, dissociation of CO
from Hb is much slower
than O2.
Methemoglobinemia ( 高铁血红蛋白血症 )
正常血红蛋白的铁主要以二价形式存在,亚硝酸盐,过氧酸盐、磺胺衍生物等氧化剂可使血红蛋白中的二价铁氧化成三价铁,形成高铁血红蛋白血症 ( Methemoglobinemia , HbFe3+OH )。
Central cyanosis ( 紫绀 ) v.s. Enterogenous cyanosis ( 肠源性紫绀 ):
食用大量含亚硝酸盐的腌菜后,硝酸盐颈肠道细菌还原为亚硝酸盐,吸收入血后,使血红蛋白的二价铁氧化为三价铁,导致高铁血红蛋白血症。
当血液中 HbFe3+OH>1.5g/dl, 皮肤,粘膜可出现青紫,为肠源性紫绀。
Features:Normal PaO2
CO2 max ↓ and CaO2↓→ O2
delivery to tissue ↓CO2 max N but affinity ↑→ O2
release to tissue ↓
Hemic/isotonic hypoxia
Inadequate blood flow resulting in insufficient oxygenation of the tissue
Causes: General circulatory dysfunction-shock,
heart failure Local circulatory dysfunction-stenosis,
occlusion, thrombosis
Mechanisms---tissue perfusion ↓ ischemia hypoxia (缺血性缺氧) congestive hypoxia (充血性缺氧)
Circulatory/hypokinetic hypoxia (循环性缺氧)
Features: a. PaO2: N PvO2↓
b. CaO2: N CvO2↓
c. CO2max: N
d. SaO2: N
e. (Da-vCO2)↑
f. Peripheral cyanosis ( 外周性紫绀 )
g. Respiratory compensation
Histogenous/dysoxidative hypoxia ( 组织性缺氧 )
Causes: Cell poisoning
cyanide poisoning→histotoxic hypoxia
Mitochondria injury radiation ; ROS
Inadequate synthesis of biological oxidation coenzyme deficiency of vitamin B2 or PP
Mechanisms:
Aberrant biological oxidation or oxidative phosphorylation → deficiency in oxygen consumption →ATP↓.
Features: a. PaO2 = N, PvO2↑
b. CaO2 = N, CvO2↑
c. CO2max = N
d. SaO2 = N
e. (CaO2-CvO2)↓
f. No cyanosis
g. No respiratory compensation
Features of different types of hypoxia Type PaO2 SaO2 CO2 max CaO2 D(a-v)CO2
Hypotonic hypoxia ↓ ↓ N ↓ ↓ or N
Hemic hypoxia N ↓ or N ↓ or N ↓ or N ↓
Circulatory hypoxia N N N N ↑
Histogenic hypoxia N N N N ↓
Notes: ↓— decrease; ↑ — increase; N — normal.
Hypotonic hypoxia: PaO2
Hemic hypoxia: Normal PaO2, altered Hb quantity and quality, CO2max or
Circulatory hypoxia: Normal PaO2, Hb quantity and quality, blood flow
Histogenous hypoxia: normal O2 supply to the tissue, O2 utilization
Features of different types of hypoxia
Metabolic and functional changes
Respiratory system
Circulatory system
Hematologic system
Central nervous system
Tissues and cells
Compensatory reaction-hyperventilation ( 过度通气 )
PaO2 <8Kpa or 60 mmHg → chemoreceptors↑→respiratory rate and depth↑→ hypoxic ventilation reaction (HVR).
Consequences:respiratory surface↑, O2 diffusion↑, PaO2&SaO2↑
More fresh air into the lung, PaO2 ↑ , PCO2↓
blood volume returning to the heart↑
Respiratory system
Injury manifestation
High-altitude pulmonary edema
Respiratory failure
Severe hypoxia (PaO2 <30 mmHg)→ inhibition of respiratory center→ slow and periodic or irregular breathing → stop of breathing.
Circulatory system
Compensatory responses
Cardiac output ↑ : tachycardia (心动过速) → arrhythmia → myocardial contractility↑
Pulmonary vasoconstriction → pulmonary arterial hypertension → right heart failure
Redistribution of blood → ensure enough blood to heart and brain
Capillary hyperplasia
Injury manifestation
Pulmonary hypertension Decreased diastolic and systolic
myocardial function Arrhythmia Decrease in Venous blood return to
the heart
Hemic system
Compensatory responses Rightward shift of oxyhemoglobin dissociation
curve
Increase of red blood cell and erythropoietin(EPO)
Injury manifestation
Blood viscosity ↑
Brain is highly sensitive to hypoxia.
Blood redistribution to the brain
PaO<28 mmHg , mental disorder
Cerebral edema
Central nervous system
Cell
Compensation: increased ability to use O2
anaerobic glycolysis ↑
increase of myoglobin
Injury manifestation cellular membrane injury
mitochondria impairment
lysosome breakage
Factors involved in tolerance to hypoxia
Oxygen consumption rate Brain → oxygen consumption rate↑→
tolerance↓
Skin → oxygen consumption rate↓→ tolerance↑
Compensatory ability of the body
Prevention and treatment
Inhalation of oxygen ( 氧吸入 )
Efficiency: Hypotonic hypoxia — the best Histogenous hypoxia —the worst
When the patient inhaled high pressure of oxygen(PO2 is 2-3 times atmosphere) ,a series of toxic signs and symptoms was appeared, this condition is termed as oxygen toxication.
Oxygen toxication: 1. Pulmonary oxygen toxication 2. Cerebral oxygen toxication
The mechanisms of oxygen toxicity:
Reactive oxygen species or oxygen free radicals .
掌握各项血氧检测指标的意义。掌握缺氧概念,分类与特征。掌握紫绀,肠源性紫绀的概念。熟悉呼吸的基本过程。熟悉机体对缺氧的代偿反应。熟悉缺氧治疗的原则。了解氧中毒概念。
学 习 目 标 与 内 容