One Lung Ventilation

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One Lung Ventilation

  1. 1. Physiological Aspects of Hypoxemia During One Lung Ventilation Stanford T. Prescott, MD Staff Anesthesiologist Brooke Army Medical Center
  2. 2. Ventilation and Perfusion of the Normal Lungs <ul><li>Normal Distribution of Perfusion </li></ul><ul><ul><li>Mainly determined by gravity </li></ul></ul><ul><ul><li>Other (non-gravity) determinants </li></ul></ul>
  3. 3. Normal Distribution of Perfusion in the Lungs
  4. 4. Normal Distribution of Perfusion in the Lungs <ul><li>Recruitment of pulmonary vessels when P pa and P pv go from low to moderate </li></ul><ul><li>Distention of pulmonary vessels when P pa and P pv go from moderate to high </li></ul><ul><li>Transudation into ISF when P pa and P pv go from high to very high </li></ul>
  5. 5. Normal Distribution of Ventilation in the Lungs <ul><li>Gravitational determinants </li></ul><ul><li>Other (non-gravitational) determinants </li></ul>
  6. 6. Normal Distribution of Ventilation in the Lungs
  7. 7. Normal Distribution of Ventilation in the Lungs
  8. 8. The Ventilation to Perfusion Ratio <ul><li>V A /Q best expresses the amount of ventilation relative to perfusion in any given lung region </li></ul><ul><li>At the base of the lung V A /Q approaches zero </li></ul><ul><li>At the apex of the lung V A /Q approaches infinity (dividing by zero) </li></ul><ul><li>PaO 2 gradients are much higher than PaCO 2 gradients due to V A /Q mismatching </li></ul>
  9. 9. Normal Distribution of Perfusion in the Lungs <ul><li>Non-gravitational determinants </li></ul><ul><ul><li>Cardiac output </li></ul></ul><ul><ul><li>Alveolar hypoxia </li></ul></ul><ul><ul><li>Lung volumes </li></ul></ul><ul><ul><li>Alternate pathways of blood flow </li></ul></ul><ul><ul><li>Pulmonary compliance </li></ul></ul><ul><ul><li>Airway resistance </li></ul></ul><ul><ul><li>Work of breathing </li></ul></ul>
  10. 10. Non-Gravitational Determinants of Distribution of Perfusion <ul><li>Cardiac Output </li></ul><ul><ul><li>An increase in cardiac output causes an increase in pulmonary vascular pressures </li></ul></ul><ul><ul><li>Distensible pulmonary vasculature causes a decrease in pulmonary vascular resistance </li></ul></ul><ul><ul><li>Opposite effect occurs with decreases in pulmonary vascular pressures </li></ul></ul>
  11. 11. Non-gravitational Determinants of Distribution of Perfusion <ul><li>Alveolar hypoxia </li></ul><ul><ul><li>Alveolar hypoxia causes localized pulmonary vasoconstriction known as hypoxic pulmonary vasoconstriction </li></ul></ul><ul><ul><ul><li>Due to release of vasoconstrictor substances? </li></ul></ul></ul><ul><ul><ul><li>Direct effect of hypoxia on the pulmonary vasculature causes vasoconstriction? </li></ul></ul></ul><ul><ul><li>It is now thought that both of these theories are related to nitric oxide mediated vasoconstriction </li></ul></ul>
  12. 12. Non-gravitational Determinants of Distribution of Perfusion <ul><li>Alveolar hypoxia (continued) </li></ul><ul><ul><li>Three mechanisms of HPV in humans </li></ul></ul><ul><ul><ul><li>High altitude (decreased Po 2 ) or decreased Fio 2 </li></ul></ul></ul><ul><ul><ul><li>Hypoventilation or atelectasis (as in one lung ventilation) </li></ul></ul></ul><ul><ul><ul><li>COPD, asthma, pneumonia </li></ul></ul></ul>
  13. 13. Oxygen Transport and Causes of Hypoxemia <ul><li>Oxygen Dissociation Curve </li></ul><ul><ul><li>Shifts of curve have little effect when P O2 is in normal range </li></ul></ul><ul><ul><li>Shifts of curve have a greater effect on saturation when P O2 is on steep portion of curve </li></ul></ul><ul><ul><li>When P 50 is less than 27mm = Left shift </li></ul></ul><ul><ul><li>When P 50 is more than 27mm = Right shift </li></ul></ul><ul><ul><ul><li>Decreases cause left shift </li></ul></ul></ul><ul><ul><ul><li>Increases cause right shift </li></ul></ul></ul>
  14. 14. Oxygen Transport and Causes of Hypoxemia
  15. 15. Oxygen Transport and Causes of Hypoxemia <ul><li>Shunt fraction (Q s /Q T ) </li></ul><ul><ul><li>Shunt refers to right to left diversion of pulmonary blood flow </li></ul></ul><ul><ul><li>Blood does not get oxygenated </li></ul></ul><ul><ul><ul><li>Perfusion of underventilated alveoli </li></ul></ul></ul><ul><ul><ul><li>Bronchial blood flow </li></ul></ul></ul><ul><ul><ul><li>Intra-arterial and intra-cardiac shunts </li></ul></ul></ul><ul><ul><li>Increasing FiO 2 when Q s /Q T is greater than 50% is not helpful </li></ul></ul>
  16. 16. Oxygen Transport and Causes of Hypoxemia <ul><li>Calculation of Shunt Fraction </li></ul><ul><ul><li>Fick Equation </li></ul></ul><ul><ul><ul><li>Q s /Q t =[Cco 2 - Cao 2 ] / [Cco 2 - Cvo 2 ] </li></ul></ul></ul><ul><ul><ul><li>Cao 2 = (1.39)(Hb)(%sat) + (0.003)(Pao 2 ) </li></ul></ul></ul><ul><ul><li>Estimation using P(A-a) O2 </li></ul></ul><ul><ul><ul><li>P(A-a) O2 / 20 </li></ul></ul></ul><ul><ul><ul><li>If cardiac output is normal and Pao 2 is > 175 </li></ul></ul></ul>
  17. 17. Causes of Hypoxemia During Anesthesia <ul><li>Equipment malfunction </li></ul><ul><li>Hypoventilation </li></ul><ul><li>Hyperventilation </li></ul><ul><li>Decreased FRC </li></ul><ul><li>Decreased cardiac output </li></ul><ul><li>Inhibition of HPV </li></ul><ul><li>Increased right to left shunt </li></ul>
  18. 18. Physiology of One Lung Ventilation <ul><li>Effects of anesthetics on HPV </li></ul><ul><ul><li>Inhaled anesthetics inhibit HPV experimentally </li></ul></ul><ul><ul><li>Nitrous Oxide has only a small effect on HPV </li></ul></ul><ul><ul><li>Injectable anesthetics have no effect </li></ul></ul><ul><ul><li>Variability of effects experimentally likely related to the mechanism of HPV which is unknown </li></ul></ul><ul><ul><ul><li>Mechanism of HPV probably due to reaction of individual arterial smooth muscle cells to local O 2 conditions </li></ul></ul></ul>
  19. 19. Physiology of One Lung Ventilation and the Lateral Decubitus Position <ul><li>Blood flow distribution in both lungs in the lateral decubitus position (LDP) </li></ul><ul><ul><li>Gravity causes a vertical gradient as in the upright position </li></ul></ul><ul><ul><li>Blood flow is greater to the dependent lung </li></ul></ul>
  20. 20. Physiology of One Lung Ventilation in the Lateral Decubitus Position
  21. 21. Physiology of One Lung Ventilation and the Lateral Decubitus Position <ul><li>During one lung ventilation blood flow to the non-dependent lung is decreased by 50 percent due to HPV </li></ul><ul><li>Blood flow to the dependent lung is increased by 33 percent (from 60% to 80%) </li></ul><ul><li>Ratio of non-dependent to dependent lung blood flow is 20% : 80% </li></ul><ul><li>Shunt flow is therefore 20% and PaO 2 is 280mm Hg (100% O 2 ) </li></ul>
  22. 22. Physiology of One Lung Ventilation and the Lateral Decubitus Position
  23. 23. Physiology of One Lung Ventilation in the Lateral Decubitus Position <ul><li>Effects of anesthetics on HPV </li></ul><ul><ul><li>Inhibition of HPV by 1 MAC isoflurane is about 21% </li></ul></ul><ul><ul><li>Inhibition of HPV causes an increase in blood flow to the non-dependent lung of about 4% of total blood flow </li></ul></ul><ul><ul><li>This 4% increase in shunt causes PaO 2 to drop from 280 to 205 </li></ul></ul><ul><ul><li>This 4% increase in shunt flow is not usually clinically detectable </li></ul></ul><ul><ul><li>Inhaled anesthetics actually have little clinical effect on HPV </li></ul></ul>
  24. 24. Physiology of One Lung Ventilation in the Lateral Decubitus Position <ul><li>Other inhibitors of HPV </li></ul><ul><ul><li>Factors that increase PAP antagonize the effect of increased resistance caused by HPV </li></ul></ul><ul><ul><ul><li>Indirect inhibitors: MS, volume overload, thromboembolism, hypothermia, vasoconstrictors, and large hypoxic lung segment </li></ul></ul></ul><ul><ul><ul><li>Direct inhibitors: Infection, vasodilators, hypocarbia, and metabolic alkalemia </li></ul></ul></ul><ul><ul><ul><li>These actually have more of an effect on HPV than anesthetic agents </li></ul></ul></ul>
  25. 25. Physiology of One Lung Ventilation in the Lateral Decubitus Position <ul><li>Potentiators of HPV </li></ul><ul><ul><li>Almitrine, a respiratory stimulant drug </li></ul></ul><ul><ul><ul><li>Improves Pao 2 in patients with COPD </li></ul></ul></ul><ul><ul><ul><li>Actually non-specifically increases pulmonary vascular pressures </li></ul></ul></ul><ul><ul><li>Prostaglandin inhibitors </li></ul></ul><ul><ul><ul><li>Prostaglandins may inhibit HPV </li></ul></ul></ul><ul><ul><ul><li>Found to reverse HPV inhibition in dogs </li></ul></ul></ul><ul><ul><ul><li>Value in humans undetermined </li></ul></ul></ul>
  26. 26. Physiology of One Lung Ventilation in the Lateral Decubitus Position <ul><li>Potentiators of HPV </li></ul><ul><ul><li>Nitric Oxide </li></ul></ul><ul><ul><ul><li>Conflicting studies have shown either no improvement of oxygenation or has shown improvement of oxygenation with nitric oxide in OLV </li></ul></ul></ul><ul><ul><ul><li>A potent vasodilator </li></ul></ul></ul><ul><ul><ul><li>One theory suggests use of almitrine (non-specific vasoconstrictor in pulmonary vasculature) and nitric oxide to dependent lung </li></ul></ul></ul><ul><ul><ul><li>As yet unproven to be of benefit </li></ul></ul></ul>
  27. 27. Physiology of One Lung Ventilation in the Lateral Decubitus Position <ul><li>Distribution of perfusion </li></ul><ul><ul><li>Two lung ventilation </li></ul></ul><ul><ul><li>One lung ventilation </li></ul></ul><ul><li>Distribution of ventilation </li></ul><ul><ul><li>Two lung ventilation </li></ul></ul><ul><ul><li>One Lung ventilation </li></ul></ul>
  28. 28. Physiology of the Lateral Decubitus Position
  29. 29. Physiology of the Lateral Decubitus Position
  30. 30. Physiology of the Lateral Decubitus Position
  31. 31. Physiology of One Lung Ventilation and Causes of Hypoxemia <ul><li>The non-dependent lung is not ventilated which causes mismatch of ventilation and perfusion (V A /Q) </li></ul><ul><li>Blood flow to the non-dependent lung is shunt flow </li></ul><ul><li>Causes an obligatory right to left shunt </li></ul><ul><li>P(A-a)O 2 gradient is larger and PaO 2 is lower than in two lung ventilation </li></ul>
  32. 32. Physiology of One Lung Ventilation and Causes of Hypoxemia <ul><li>Factors that decrease blood flow distribution to the non-dependent lung </li></ul><ul><ul><li>Surgical compression </li></ul></ul><ul><ul><li>Retraction </li></ul></ul><ul><ul><li>Ligation of pulmonary vessels </li></ul></ul><ul><ul><li>Amount of disease in the non-dependent lung </li></ul></ul><ul><ul><li>Hypoxic pulmonary vasoconstriction </li></ul></ul>
  33. 33. Physiology of One Lung Ventilation and Causes of Hypoxemia <ul><li>Factors that increase blood flow distribution to the dependent lung </li></ul><ul><ul><li>Gravitational effects (zones of perfusion) </li></ul></ul><ul><ul><li>Hypoxic pulmonary vasoconstriction in the non-dependent lung </li></ul></ul>
  34. 34. One Lung Ventilation and Causes of Hypoxemia <ul><li>Factors that decrease ventilation to the dependent lung </li></ul><ul><ul><li>Reduced lung volumes </li></ul></ul><ul><ul><li>Absorption atelectasis </li></ul></ul><ul><ul><li>Difficulty of secretion removal </li></ul></ul><ul><ul><li>LDP for long period can increase transudation </li></ul></ul><ul><ul><li>Increases in HPV </li></ul></ul>
  35. 35. Treatment of Hypoxemia During One Lung Ventilation <ul><li>Conventional management </li></ul><ul><ul><li>Increase FiO 2 to dependent lung </li></ul></ul><ul><ul><ul><li>Helps to increase the PaO 2 </li></ul></ul></ul><ul><ul><ul><li>Causes vasodilation which increases blood flow to dependent lung </li></ul></ul></ul><ul><ul><li>Tidal volume of 10ml/kg and RR to keep CO 2 at 40mm Hg </li></ul></ul><ul><ul><ul><li>Lower tidal volume can cause atelectasis </li></ul></ul></ul><ul><ul><ul><li>Greater tidal volume may increase airway pressures </li></ul></ul></ul><ul><ul><li>Selective dependent lung PEEP </li></ul></ul>
  36. 36. Treatment of Hypoxemia During One Lung Ventilation <ul><li>Differential management of one lung ventilation </li></ul><ul><ul><li>Intermittent inflation of the non-dependent lung </li></ul></ul><ul><ul><li>Selective dependent lung PEEP </li></ul></ul><ul><ul><li>Selective non-dependent lung CPAP </li></ul></ul>
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