Hypoxia

this PPT describes about all aspects related to hypoxia.

1. Dr Rajesh Reddy P Associate Professor Department of Physiology Mediciti IMS Hypoxia

2. Learning Objectives: Definition Etiology Types Stages Diagnosis Treatment

3. Hypoxia Hypoxia is defined as a deficiency in either the delivery or the utilization of oxygen at the tissue level.

4. Etiology High altitude Anemia Decreased oxygen supply to an area Low oxygen carrying capacity Poor tissue perfusion Impaired ventilation Decreased diffusion of oxygen

5. Etiology

6. Acute Hypoxia It can be due to : 1. Respiratory depression 2. Airway obstruction 3. Atelectasis 4. Ventilation/Perfusion mismatch 5. Reduced Functional Residual Capacity (FRC)

7. Direct Effects of Acute Hypoxia 1. Cyanosis 2. Confusion, Drowsiness 3. Excitement 4. Headache 5. Nausea 6. Myocardial Depression 7. Arrhythmias 8. Bradycardia 9. Renal Impairment

8. Indirect Effects of Acute Hypoxia These are mediated through stimulation of Carotid and Aortic Bodies : 1. Tachycardia 2. Hypertension 3. Hyperventilation

9. Degrees of Acute Hypoxia Acute Hypoxia manifestations depends on the degree of oxygen saturation in arterial blood: Saturation 1. 85 % = Mental Impairment 2. 75 % = Severe Mental Impairment 3. 65 % = Unconsciousness

10. Chronic Hypoxia Develops in, after adaptation for high altitude chronically developing lung diseases.

11. Effects of Chronic Hypoxia 1- Hyperventilation 2- Polycythemia 3- Increased 2-3-DPG 4- Proliferation of peripheral capillaries 5- Alteration in Intracellular Oxidative Enzymes

12. Types 1. Hypoxic / hypotonic hypoxia: PO2 of the arterial blood is low (less than 60mmHg) . 2. Anaemic / Hemic / isotonic hypoxia: amount of Hb to carry O2 is low 3. Stagnant / ischemic / circulatory / hypokinetic hypoxia: blood flow to the tissues is low 4. Histotoxic / histogenous hypoxia: tissue can not utilize 02.

13. Features of hypoxia Features Hypoxic H Anemic H Stagnant H Histotoxic H Arterial PO2 Decreases Normal Normal Normal Hb amount Normal Decreases Normal Normal Rate of blood flow to tissues Normal Normal Decreases Normal Arterial O2 content Decreases Markedly reduced Normal Normal Arterial %-02 saturation of Hb Decreases Decreases Normal Normal A-V O2 difference Decreases Normal More than normal Less than normal Cyanosis Present Absent Present Absent Stimulation of peripheral Chemoreceptors Present Absent Present Present

14. Stages of Hypoxia 1. Asymptomatic or indifferent 2. Compensatory 3. Deterioration or Disturbance 4. Critical

15. Asymptomatic or Indifferent Generally not aware about the effects. Primary symptoms: loss of night vision and color vision. These changes can occur at relatively modest altitudes (as low as 4,000 feet) and are most significant to pilots operating at night . Arterial O2 sat between 90 - 95%

16. Compensatory In healthy people, this stage may occur at altitudes between 10,000 and 15,000 feet. The body generally has the ability to starve off further effects of hypoxia by increasing the rate and depth of ventilation and cardiac output. Arterial O2 sat between 80 - 90%.

17. 3. Deterioration or Disturbance People are unable to compensate for the lack of oxygen. Unfortunately, not everyone recognizes or experiences the signs and symptoms associated with this stage. Arterial O2 sat between 70 - 80%. The signs that are associated with this stage:

18. ● Shortness of breath ● Incoordination ● Cyanosis ● Difficulty with simple tasks ● Drowsiness ● Diminished vision ● Headache ● Tingling ● Euphoria ● Numbness ● Aggression ● Hot/cold flushes ● Poor Judgment

19. 4. Critical This is the terminal stage leading up to death. People are almost completely incapacitated physically and mentally. People in this stage will lose consciousness, have convulsions, stop breathing and finally die. Arterial O2 sat are less than 70%.

20. Diagnostic parameters PO 2 CO 2max CO 2 SO 2 P 50

21. PO 2 partial pressure of oxygen PO2 is the tension produced by the oxygen molecules physically dissolved in plasma. Normal PaO 2 : 100mmHg PvO 2 : 40mmHg Determined by PiO2 and pulmonary function

22. CO 2max oxygen binding capacity of hemoglobin CO 2max refers to the maximal amount of oxygen that could be bound by the hemoglobin, which reflects the ability of hemoglobin carrying oxygen. Normal value: 20ml/dl Determined by quantity and quality of Hb

23. CO 2 oxygen content CO 2 includes oxygen that is bound to hemoglobin and physically dissolved in the blood (0.3ml/dl). Normal value: CaO 2 :19ml/dl CvO 2 :14ml/dl Determined by PO 2 and CO 2 max The A-V O2 content difference (CaO 2 -CvO 2 ) reflects the oxygen volume of tissue uptake.

24. SO 2 oxygen saturation SO 2 is the percentage of hemoglobin present as oxyhemoglobin. Normal value: SaO2: 95% SvO2: 75% The relation between O2 partial pressure and O2 sat is shown as oxygen dissociation curve (ODC).

25. P 50 P 50 means the oxygen partial pressure required to saturate 50% of the hemoglobin, which reflects the affinity of hemoglobin for oxygen. Normal value: 26-27 mmHg

26. Treatment Eliminating causes Oxygen therapy Hyperbaric oxygen therapy

27. Oxygen therapy Oxygen administration is of importance in hypoxic hypoxia. A. Inhalation of 100% O2 at normal atmospheric pressure B. Hyperbaric oxygen therapy

28. Oxygen therapy Indications: 1- Cardio Pulmonary Resuscitation (CPR) 2- Respiratory Failure 3- Cardiac Failure 4- Shock of any Cause 5- Increased Metabolic Demands 6- Carbon Monoxide (CO)-Poisoning 7- Postoperative States

29. Oxygen Toxicity 1- Retrolental Fibroplasia / retinopathy of prematurity: In Neonates (especially prematures) if breathing Oxygen Concentration more than 40 % (FiO2 more than o.4) 2- Lung Toxicity: In Adults if breathing Oxygen Concentration more than 60 % (FiO2 more than 0.6) for a long time

30. Oxygen toxicity will occur early Inhibits tissue enzyme activity Cerebral vasoconstriction Muscular twitches, tinnitus, convulsions and coma

31. Hazards of Oxygen Therapy 1. CO2 Narcosis / CO2 poisoning: hypercapnia will develop. 2. Barotrauma: by increased air pressure in the lungs.

32. Normobaric 100% O2 therapy It is useful in hypoxic hypoxia. Dangers of inhaling 100% oxygen: Nasal congestion, throat pain, cough, substernal discomfort. Bronchopneumonia if given for more than 24 hrs by inhibiting alveolar macrophages Newborns should not be given more than 40% oxygen

33. Hyperbaric O2 Therapy Hyperbaric oxygen therapy is defined as inhalation of oxygen at increased pressure for potential therapeutic benefit. Useful in anemic, stagnant and histotoxic hypoxia

34. Benefits of HOT Increased O2 tension Vasoconstriction Increased fibroblast replication Increased collagen response Angiogenesis Enhanced leukocyte function Attenuation of reperfusion injury

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