Respiratory Physiology 9-5-24 Final.pptx

Respiratory physiology, one lung ventilation

1. Respiratory Physiology One lung ventilation Moderator : Dr. Gaganjot Presenter : Dr. Gurleen

2. OLV Separation of two lungs with collapse of one lung Each lung function independently by preparation of airway

3. One lung ventilation Purpose: To provide surgical exposure in the thoracic cavity . Isolating ventilation to one lung OR protecting one lung from ill effects of fluid from the other lung ( blood, lavage fluid, or malignant or purulent secretions form bronchopleural fistula ) T o provide differential patterns of ventilation in cases of unilateral reperfusion injury (after lung transplantation or pulmonary thromboendarterectomy ) or in unilateral lung trauma

4. Persisting perfusion through the non ventilated lung causes a shunt and decreases PaO2. Two main contributors to impaired oxygenation: The persisting blood flow through non ventilated lung Development of a telectasis in the dependent lung, resulting in local shunt and low PaO2

5. S ix circumstances that are encountered during thoracic surgery - Lateral position, awake, breathing spontaneously Chest closed Blood flow and ventilation of DL >> NDL Perfusion is gravity dependent Zone 1 less extended ( as vertical hydrostatic pressure gradient smaller in lateral than upright position ) DL hemidiaphragm pushed higher into chest by abdomenal contents, but due to spont. ventilation diaphragm can contract normally --> adequate distribution of Vt to dependent lung Good V/Q matching at DL

6. Lateral Position ( LP), Awake, Breathing Spontaneously, Chest open - Thoracoscopy using intercostal blocks Two complications - Mediastinal shift - circulatory and reflex changes result in clinical features similar to shock and respiratory distress, treatment is immediate intubation Paradoxical breathing - increased by large thoracotomy

7. LP, Anesthetized, Breathing Spontaneously, Chest closed - No significant change in perfusion Vt enter NDL result in significant V/Q mismatch Induction of GA --> reduction in volumes of both lungs ( DL > NDL ) due to decrease of FRC Why ? Cephalad displacement of dependent diaphragm by abdomenal contents more pronounced and increase by paralysis Mediastinal structures pressing on DL and poor positioning of DL

8. LP, Anesthetized, Breathing Sontaneously , Chest open - Perfusion not much effected NDL not restricted by chest wall so freely expand Increase V/Q mismatch as NDL preferentially ventilated due to increased compliance Lateral position, Anesthetized, Paralyzed, Chest open - During paralysis and PPV diaphragmatic displacement is maximum over NDL as it is least resisted by abdomenal contents. Compromises ventilation to DL so inc V/Q mismatch

9. OLV, Anesthetized, Paralyzed, Chest open TLV in lateral position blood flow to NDL is 40% of CO and rest 60% of CO to DL Shunt in lateral position 10% of CO and divide equally as 5% to each lung CO participating in gas exchange 35% in NDL and 55% in DL OLV --> obligatory R to L transpulmonary shunt through non ventilated non dependent lung V/Q ratio of lung is 0 So, theoratically 35% added to the total shunt But d/t HPV, blood flow to NDL reduced by 50% therefore total shunt in NDL 35/2 = 17.5% + 5% ( obligatory shunt to NDL ) = 22.5%

10. 22.5% shunt of NDL + 5% shunt of DL = 27.5% total shunt in OLV So perfusion to DL = 100%-27.5% = 72.5% so matching of ventilation is important in this lung for adequate gas exchange But DL has reduced FRC - GA Muscle relaxant Pressure from abdomenal contents Compression by weight of mediastinal structures Suboptimal positioning on OT table Absorption atelactasis Accumulation of secretions and formation of transudate in DL Low V/Q ratio

11. Factors affecting blood flow in OLV It involves the body’s ability to redistribute pulmonary blood flow to the ventilated lung. AIM -- to optimize pulmonary blood flow redistribution during OLV by maintain the ventilated lung as close as possible to its FRC while facilitating collapse of the non ventilated lung to increase its PVR ( Pulmonary Vascular Resistance ) .

12. Relationship between FRC and PVR Hyperbolic fashion

13. HPV and collapse of NDL/NVL --> increases PVR --> blood flow toward the ventilated lung /DL The airway pressure gradient between the ventilated and nonventilated thoraces tends to encourage blood flow to the non ventilated lung .

14. Effect of cardiac output Increasing CO --> Inc Pulmonary artery pressure and passive dilatation of pulmonary vascular bed which oppose HPV --> inc shunt E ven with optimal anesthetic management there is usually a shunt of 20% to 30% during OLV, it is very important to maintain cardiac output.

15. Choice of anaesthetic The gas mixture in the nonventilated lung immediately before OLV has a significant effect on the speed of collapse of this lung. Because of its low blood-gas solubility, nitrogen (or an air-oxygen mixture) will delay collapse of this lung. It is important to thoroughly denitrogenate the operative lung, by ventilating with oxygen, immediately before it is allowed to collapse In doses of less than or equal to 1 MAC, the modern volatile anesthetics ( isoflurane , sevoflurane , and desflurane ) are weak, and equipotent, inhibitors of HPV.

16. HYPOXIC PULMONARY V ASOCONSTRICTION HPV is a compensatory mechanism that diverts blood flow away from hypoxic lung regions toward better oxygenated regions . The major stimulus for HPV is low alveolar oxygen tension (PAO2), whether caused by hypoventilation or by breathing gas with a low PO2 HPV is thought to decrease the blood flow to the NDL by 50 %. HPV is also a reflex that has a preconditioning effect

17. HPV response HPV has a biphasic temporal response to alveolar hypoxia. The rapid-onset phase begins immediately and reaches a plateau by 20 to 30 minutes. The second (delayed) phase begins after 40 minutes and plateaus after 2 hours .

18. The offset of HPV is also biphasic and PVR may not return to baseline for several hours after a prolonged period of OLV . HPV is decreased by vasodilators such as nitroglycerin and nitroprusside which are expected to cause a deterioration in PaO2 during OLV . In doses of less than or equal to 1 MAC are weak, and equipotent, inhibitors of HPV.

19. Recruitment maneuver During the period of two-lung anesthesia before the start of OLV, atelectasis will develop in the DL . R ecruitment maneuver to the DL (similar to a Valsalva maneuver, holding the lung at an end- inspiratory pressure of 20 cm H2O for 15–20 seconds) immediately after the start of OLV to decrease its atelectasis . Recruitment is important to maintain PaO2 levels during subsequent OLV.

20. Acceptable Sp02 during OLV A saturation greater than or equal to 90% (PaO2 > 60 mm Hg) is commonly accepted, and for brief periods a saturation in the high 80%s may be acceptable in patients without significant comorbidity . Hypoxemia events have reduced due to Improved lung isolation techniques. Routine use of fiberoscopy to prevent lobar obstruction from DLTs , Improved anesthetic drugs that cause less inhibition of HPV .

21. LUNG ISOLATION TECHNIQUES Lung isolation can be achieved by three different methods: DLTs Bronchial blockers S ingle-lumen endobronchial tubes (SLTs)

22. DLTs ADVANTAGES DISADVANTAGES Easy to place successfully Size selection more difficult Repositioning rarely required Difficult to place in patients with difficult airways or abnormal tracheas Bronchoscopy to isolated lung Not optimal for postoperative ventilation Suction to isolated lung Potential laryngeal trauma CPAP easily added Potential bronchial trauma Can alternate OLV to either lung easily Placement still possible if bronchoscopy not available

23. Bronchial blockers (BBs) ADVANTAGES DISADVANTAGES Size selection rarely an issue More time needed for positioning Easily added to regular ETT Repositioning needed more often Allows ventilation during placement Bronchoscope essential for positioning Easier placement in patients with difficult airways and in children Limited right lung isolation due to RUL anatomy Postoperative two-lung ventilation by withdrawing blocker Bronchoscopy to isolated lung impossible Selective lobar lung isolation possible Minimal suction to isolated lung CPAP to isolated lung possible Difficult to alternate OLV to either lung

24. Endobronchial tube ADVANTAGES DISADVANTAGES Like regular ETTs, easier placement in patients with difficult airways Bronchoscopy necessary for placement Longer than regular ETT Does not allow for bronchoscopy , suctioning, or CPAP to isolated lung Short cuff designed for lung isolation Difficult right lung OLV

25. Double-Lumen Tubes The most common design of the DLT used in the current practice of thoracic anesthesia is the Robertshaw design . It comprises  2 semicircles placed back to back to form 2 independent lumens that can be ventilated independently. It is available in left- and right-sided types and in varying sizes from 26 Fr to 41 Fr. The size denotes the external diameter of the tube in cm.

26. The right-sided DLT has a curve to the right, and the left-sided DLT has a curve to the left. The  DLT cuffs are high-volume and low-pressure cuffs. Size Selection of DLT

27. Methods of Insertion The blind technique : DLT passed with direct laryngoscopy and then turned 90 degrees counterclockwise (for a left-sided DLT placement) after the endobronchial cuff has passed beyond vocal cords. DLT should pass the glottis without any resistance.

28. The direct vision technique uses bronchoscopic guidance , in which the tip of the endobronchial lumen is guided into the correct bronchus after the DLT passes the vocal cords using direct vision with a flexible fiberoptic bronchoscope

29. Positioning of Double-Lumen Tubes Auscultation and bronchoscopy should both be used each time a DLT is placed and again when the patient is repositioned. Fiberoptic bronchoscopy is performed first through the tracheal lumen to ensure that the endobronchial portion of the DLT is in the left bronchus. Through the tracheal view, the blue endobronchial cuff ideally should be seen approximately 5 to 10 mm below the tracheal carina in the left bronchus. It is crucial to identify the take-off of the right upper lobe bronchus through the tracheal view.

30. Indications of Right sided DLT L eft-sided DLT is used more commonly for most elective thoracic procedures, there are specific clinical situations in which the use of a right-sided DLT is indicated: Distorted anatomy of the entrance of left mainstem bronchus External or intraluminal tumor compression Descending thoracic aortic aneurysm Site of surgery involving the left mainstem bronchus Left lung transplantation Left-sided tracheobronchial disruption Left-sided pneumonectomy

31. BRONCHIAL BLOCKERS An alternative method to achieve lung separation involves blockade of a mainstem bronchus to allow lung collapse distal to the occlusion

32. V entilation parameters for OLV

33. FLUID MANAGEMENT - Excessive administration of i.v. fluids -->inc hydrostatic pressure --> PE of DL Total fluid balance in first 24 hr perioperative period should not exceed 20ml/kg UO of 0.5 ml/kg/hr Invasive monitoring and inotropes postoperatively if inc tissue perfusion required TEMPERATURE - Heat loss from open hemithorax HPV inhibited during hypothermia So proper monitoring of temoerature is necessary

34. BRONCHOSPASM Inc chances because of airway manipulation Prevented by - Avoid airway manipulation in lighter anesthesia Use bronchodilating anesthetic - propofol or ketamine Avoid drugs that release histamine PROPER POSITIONING OF PATIENT

35. Factors predicting desaturation during OLV Poor Pa O 2 during two lung ventilation intraoperatively , particularly in the lateral position. Right sided thoracotomy Restrictive lung disease. Supine position during OLV 5. High percentage of Ventilation or Perfusion to the operative lung on pre operative V/Q scan

36. Partial ventilation methods for NDL Standard bacteristatic filter - 66 ml oxygen via intermittent positive airway pressure using CO2 port

37. Ventilation of the operative (nondependent lung) with a small tidal volume via another ventilator connected to a limb of a DLT to the nondependent lung ( brief period of IPPV with tidal volume 70 mL and respiratory rate of 6/min ) was effective in improvingPaO2 and SpO2 during OLV without interference with the surgery Selective lobar collapse of only operative lobe of NDL using blocker

38. PHARMACOLOGICAL METHODS Eliminating known potent vasodilators such as nitroglycerin, halothane, and large doses of other volatile anesthetics will improve oxygenation during OLV NO and other pulmonary vasoconstrictors such as phenylephrine has been shown to improve oxygenation D exmedetomidine, continuous infusion during OLV with sevoflurane anesthesia improved oxygenation and increased the PaO2/FiO2 ratio during the intraoperative period

39. MECHANICAL RESTRICTION OF PULMONARY BLOOD FLOW Directly compress or clamp the blood flow to the nonventilated lung . Inflation of a pulmonary artery catheter balloon in the main pulmonary artery of the operative lung . The pulmonary artery catheter can be positioned at induction with fluoroscopic guidance and inflated as needed intraoperatively .

40. THANK YOU