Perioperative hypoxia
- 1. Perioperative Hypoxia Osama Elazzouny (PGY4 , Resident Anesthesiology) Dr. Satya Bhat ( Consultant Anesthesiology) August 2019 HMC, Doha, Qatar
- 2. Objectives: • Introduction • Preoperative hypoxia • Intraoperative Hypoxia • Postoperative hypoxia • Diagnosis • Management
- 3. Objectives: • Introduction • Preoperative hypoxia • Intraoperative Hypoxia • Postoperative hypoxia • Diagnosis • Management
- 4. What is the classification of hypoxia? • Hypoxic hypoxia • Pulmonary hypoxia • Anemic hypoxia • Stagnant hypoxia • Cellular hypoxia
- 5. What are the most sensitive organs to hypoxia? • Brain and the eyes
- 7. How does the body detects hypoxia? • Chemoreceptor activity: carotid bodies and the aortic bodies • Chemoreceptors respond to a decrease in oxygen tension rather than to a decrease in oxygen content
- 8. What are the defense responses against hypoxia? • Ventilatory compensation: tachypnea and hyperpnea • Circulatory compensation: increase in cardiac output or an increase in blood flow to a limited area. • Reserves of oxygen in the body • Tolerances to hypoxia by specific tissues Redistribution of blood flow
- 9. What is oxygen reserve? • That amount of oxygen which is available in the body for continued metabolism, if the supply of oxygen from ambient air is interrupted. • Should not be confused with oxygen stores, which refer to oxygen present in the body, whether or not this oxygen is available for metabolic purposes.
- 10. Four storage sites of oxygen in the body • Alveolar air (FRC) • Arterial blood • Venous blood • Tissue water contains oxygen in physical solution. • Muscle tissue contains approximately ten times this amount of oxygen, stored in myohemoglobin
- 12. What are the requirements for adequate oxygen transport? • Fraction of oxygen in inspired air (FiO2 ) • Partial pressure of oxygen in inspired air ( PiO2 ) • Alveolar ventilation (VA) • The relation of ventilation to perfusion in the lungs (VA/Q) • CO, and blood volume • Hb content • Arterial blood pH, body temperature
- 13. Objectives: • Introduction • Preoperative hypoxia • Intraoperative Hypoxia • Postoperative hypoxia • Diagnosis • Management
- 14. What is the etiology of hypoxia before anesthesia? • Pre-existing cardiopulmonary disease • Most important factor in promoting postoperative respiratory complications • Already low Pa02 + Decreased respiratory and Circulatory compensation. • Trauma : • May involve ventilatory and circulatory systems • May cause atelectasis and shunting imposed by immobilization, restrictive influences, and pain medication.
- 15. What is the etiology of hypoxia before anesthesia? • Old age : • PaO2(mmHg) =106 - Age/2 • after age of 60 the range is from 70 to 80 mm Hg. • Reduced compensatory increase in CO • Reduced ventilatory response to hypoxia is limited by reduced pulmonary volumes and capacities in old age • Obesity
- 16. What is the etiology of hypoxia before anesthesia? • Severe anemia : • rarely present at operation, except in the worst emergencies • Restriction of respiratory motion : • in the form of tight binders or abdominal distension can cause significant reductions in Pa02 • cause of decrease in available ventilatory compensation • Drug administration
- 17. Objectives: • Introduction • Preoperative hypoxia • Intraoperative Hypoxia • Postoperative hypoxia • Diagnosis • Management
- 18. What is the etiology of hypoxia during anesthesia? • Decreased oxygen in inspired air • Decreased PAO2 • Decreased oxygen tension in arterial blood Pa02 • Decreased oxygen content in arterial blood (Ca02 ) • Decreased cardiac output • Increased tissue metabolism
- 19. • Classified into two I.Problems with oxygen delivery system II.Problems with patient
- 20. Problems with oxygen delivery system? • at the level of central oxygen supplies • at the level of pipeline distributing system • at the level of oxygen cylinders attached to anaesthesia machine • at the level of anaesthesia machine • at the level of anaesthesia ventilator • at the level of anaesthesia circuit • at the level of endotracheal tube
- 21. Problems with oxygen delivery system • At level of central Oxygen • Liquid tank may be filled with nitrogen or argon • Gas leak • Inadequate pressure at central supply • Decreased oxygen level at the tank • Depleted cylinders • Failure of master alarm system • At the level of pipeline distributing system • Leak • Contamination of gases • Cross connection • Connecting wrong hose to Oxygen yoke • Inadvertent switching of schrader adapter of piped lines
- 22. Problems with oxygen delivery system • At the level of oxygen cylinders attached to anaesthesia machine • Empty cylinders • Substitution of non oxygen cylinder at the yoke • Insufficiently opened cylinder • At the level of anaesthesia machine • Incorrect setting of flow meter • Crack in the oxygen flow meter tubes • Transposition of rotameter tubes • Leak in machine
- 23. Problems with oxygen delivery system • At the level of anaesthesia Ventilator • Low tidal volume • Low respiratory rate • Inadequate minute volume • Disconnection of tubing • At the level of the anaesthesia circuit • Disconnection • Leak • At the level of Endotracheal tube • Esophageal intubation • Endobrochial intubation • Accidental extubation • Kinking of tube
- 24. II. Problems with patient? • Hypoventilation • Reduced functional residual capacity • Increased airway resistance • Atelectasis • Absorption atelectasis • Diffusion defect • Shunt • Inhibition of hypoxic pulmonary vasoconstriction • Poor oxygen delivery to tissues • Increased oxygen demand
- 25. II. Problems with patient? • A.Hypoventilation : • A spontaneously anaesthetised patient may hypoventilate due to drug induced respiratory depression. • In patient who is paralysed and ventilated ,hypoventilation may occur due to inadequate IPPV B.Reduced functional residual capacity: • Induction of GA will cause reduction in FRC by 15-20% invariably • This will be more in patients with preexisting lung disease, obese patients. • continue in post operative period. • causes increase in PAO2 –PaO2 gradient. • The reduction in FRC may be restored normal by application of PEEP.
- 26. II. Problems with patient? C. Increased airway resistance • Reduction in FRC • Decrease in calibre of airways • Endotracheal intubation • Anaesthesia apparatus • Laryngospasm , bronchospasm • Obstruction of ETT
- 27. D. Atelectasis • It is a condition of alveolar collapse . • It may be micro atelectasis,macro atelectasis or lobar collapse. • Leads to V/Q mismatch , R-L shunting and arterial hypoxemia • occur due to airways secretions, compression packs, wedge and prolonged procedures • PEEP may be useful in such situation
- 28. E. Absorption atelectasis • Alveloar collapse occur when the patient is getting high FiO2. • When PAO2 rises , the rate at which O2 moves from the alveoli to capillary blood increases.When the absorption rate is more than the inspired flow gases , lung unit collapses • So, absorption atelectasis occurs when • Fio2 is high • V/Q is low • time of exposure of lung unit low V/Q ratio to high FiO2 is long • CvO2 is low
- 29. F. Diffusion defect: • Thickened alveloar membrane • Thickening of air-blood interface • Inflammation • Edema • Fibrosis or loss of alveolar surface area (Eg:sarcoidosis ,Emphysema)
- 30. • G.Shunt: I) inadequate ventilation : • Absorption atelectasis • Airway secretions • Pulmonary aspiration • Pulmonary edema • Inhibition of HPV- vasodilators(SNP, NTG)
- 31. H. Inhibtion of hypoxic pulmonary vasoconstriction (HPV) • It is a protective phenomenon. When PaO2 decreases in a region pulmonary vasoconstriction occurs at that particular region. • HPV diverts blood flow from the hypoxic regions of the lung to better ventilated normoxic regions , thus decreases V/Q mismatch maintaning PaO2 • Inhibition of HPV lead to arterial hypoxemia • Factors inhibit HPV • Inhaled anaesthetics • vasodilators(SNP, NTG) • Hypocapnia • Hypothermia • Thrombo embolism
- 32. I. Poor oxygen delivery to tissues: • Systemic hypoperfusion • Embolus • Sepsis • Local problems ( cold limb , Reynaud phenomenon , sickle cell disease ) J.Increase oxygen demand : • Malignant hyperpyrexia • Shivering • Sepsis
- 33. Objectives: • Introduction • Preoperative hypoxia • Intraoperative Hypoxia • Postoperative hypoxia • Diagnosis • Management
- 34. Postoperative hypoxia: 1. Diffusion hypoxia • The solubilities of nitrogen and nitrous oxide differ sufficiently to reduce PAo2 when nitrous oxide anesthesia is stopped and the patient allowed to breathe room air. • Nitrous oxide comes out of solution and enters the alveoli more rapidly than nitrogen leaves the alveoli to become dissolved. • the period of greatest PA02 decrease is approximately 10 minutes • after 30 minutes the impairment is insignificant
- 35. 2. Prolonged effect of muscle relaxants 3. Pain • Dominant factor in determining postoperative respiratory function. • promoting atelectasis by restricting ventilatory excursions 4. Pain relieving drugs, typified by morphine • result in an increased incidence of respiratory complications. • Not restricted to high doses which depress ventilation • morphine may reduce the reflex activity, which provides for periodic hyperinflation
- 36. Objectives: • Introduction • Preoperative hypoxia • Intraoperative Hypoxia • Postoperative hypoxia • Diagnosis • Management
- 37. Diagnosis: • During early days of anaesthesia , defective oxygenation of the patient was identified by cyanosis &dark blood in the surgical field . • Cyanosis occurs when the deoxygenated hb is >5g /100ml • Cyanosis usually observed when Hb saturation is 85%.this corresponds to PaO2 of 45-50mm hg in adults 35-40mm hg in infants • Cyanosis may be observed when there is no hypoxemia Eg : methemoglobinemia • Cyanosis may not be apparent in the presence of anaemia or peripheral vasoconstriction
- 38. • Pulse oximeter is most commonly used one • Other monitors – a) oxygen analyser b) ABG c) Scvo2 d) Capnography e) Airway pressure monitor
- 39. Objectives: • Introduction • Preoperative hypoxia • Intraoperative Hypoxia • Postoperative hypoxia • Diagnosis • Management
- 42. References: • Bendixen, H. H., and M. B. Laver. "Hypoxia in anesthesia: A review." Clinical Pharmacology & Therapeutics 6, no. 4 (1965): 510- 539. • https://www.wfsahq.org/components/com_virtual_library/media/e8 cf1db1c025a18fa8a05f562082f29f-Management-of-Hypoxia-During- Anaesthesia-Algorithm--Update-2.pdf