One-Lung Ventilation: physiology and practical approach

1. One-Lung Ventilation: physiology and practical approach Konstantin Balonov Department of Anesthesiology Boston Medical Center

2. Objectives • Indication/contraindication of OLV • Physiology changes of OLV • Selection of the methods for OLV • Management of common problems associated with OLV, especially hypoxemia

3. Introduction • One-lung ventilation, OLV, means separation of the two lungs and each lung functioning independently by preparation of the airway • OLV provides: • Protection of healthy lung from infected/bleeding one • Diversion of ventilation from damaged airway or lung • Improved exposure of surgical field • OLV causes: • More manipulation of airway, more damage • Significant physiologic change and easily development of hypoxemia

4. Absolute indication for OLV • Isolation of one lung from the other to avoid spillage or contamination • Infection • Massive hemorrhage • Control of the distribution of ventilation • Bronchopleural / - cutaneous fistula • Surgical opening of a major conducting airway • giant unilateral lung cyst or bulla • Tracheobronchial tree disruption • Life-threatening hypoxemia due to unilateral lung disease • Unilateral bronchopulmonary lavage

5. Relative indication • Surgical exposure ( high priority) • Thoracic aortic aneurysm • Pneumonectomy • Upper lobectomy • Mediastinal exposure • Thoracoscopy • Surgical exposure (low priority) • Middle and lower lobectomies and subsegmental resections • Esophageal surgery • Thoracic spine procedure • Minimal invasive cardiac surgery (MID-CABG, TMR) • Postcardiopulmonary bypass status after removal of totally occluding chronic unilateral pulmonary emboli • Severe hypoxemia due to unilateral lung disease

6. Physiology of the LDP • Upright position LDP, lateral decubitus position

7. Physiology of LDP Awake/closed chest Anesthetized . V Q V Q V Q ND     D      

8. Summary of V-Q relationships in the anesthetized, open-chest and paralyzed patients in LDP

9. Physiology of OLV • The principle physiologic change of OLV is the redistribution of lung perfusion between the ventilated (dependent) and blocked (nondependent) lung • Many factors contribute to the lung perfusion, the major determinants of them are hypoxic pulmonary vasoconstriction (HPV) and gravity.

10. Hypoxic pulmonary vasoconstriction • HPV is a physiological response of the lung to alveolar hypoxia, which redistributes pulmonary blood flow from areas of low oxygen partial pressure to areas of high oxygen availability. • The mechanism of HPV is not completely understood. Vasoactive substances released by hypoxia or hypoxia itself (activating K+, Ca++ and TRP channels) cause pulmonary artery smooth muscle contraction

11. HPV: oxygen sensors

12. HPV • HPV aids in keeping a normal V/Q relationship by diversion of blood from underventilated areas, responsible for the most lung perfusion redistribution in OLV • HPV is graded and limited, of greatest benefit when 30% to 70% of the lung is made hypoxic. • HPV is effective only when there are normoxic areas of the lung available to receive the diverted blood flow

13. Factors affecting regional HPV • HPV is inhibited directly by volatile anesthetics (not N20), vasodilators (NTG, SNP, NO, dobutamine, many ß2-agonist), increased PVR (MS, MI, PE) and hypocapnia • HPV is indirectly inhibited by PEEP; vasoconstrictor drugs (epinephrine, norepinephrine, phenylephrine, dopamine) constrict normoxic lung vessels preferentially

14. Gravity and V-Q • UprightLDP

15. Shunt and OLV • Physiological (postpulmonary) shunt • About 2-5% CO, • Accounting for normal A-aD02, 10-15 mmHg • Including drainages from • Thebesian veins of the heart • The pulmonary bronchial veins • Mediastinal and pleural veins • Transpulmonary shunt increased due to continued perfusion of the atelectatic lung and A-aD02 may increase

16. Two-lung ventilation and OLV

17. Cardiac output and OLV • Decreased CO may reduce SvO2 and thus impair SpO2 in presence of significant shunt • Hypovolemia • Compression of heart or great vessels • Thoracic epidural sympathetic blockade • Air trapping and high PEEP • Increased CO increases PA pressures which increases perfusion of the non-ventilated lung → increase of shunt fraction

18. Methods of OLV • Double-lumen endotracheal tube, DLT • Single-lumen ET with a built-in bronchial blocker, Univent Tube • Single-lumen ET with an isolated bronchial blocker • Arndt (wire-guided) endobronchial blocker set • Balloon-tipped luminal catheters • Endobronchial intubation of a single-lumen ET

19. DLT • Type: • Carlens, a left-sided + a carinal hook • White, a right-sided Carlens tube • Bryce-Smith, no hook but a slotted cuff/Rt • Robertshaw, most widely used • All have two lumina/cuffs, one terminating in the trachea and the other in the mainstem bronchus • Right-sided or left-sided available • Available size: 41,39, 37, 35, 28 French (ID=6.5, 6.0, 5.5, 5.0 and 4.5 mm respectively)

20. Left DLT… • Most commonly used • The bronchial lumen is longer, and a simple round opening and symmetric cuff Better margin of safety than Rt DLT • Easy to apply suction and/or CPAP to either lung • Easy to deflate lung • Lower bronchial cuff volumes and pressures • Can be used • Left lung isolation: clamp bronchial + ventilate/ tracheal lumen • Right lung isolation: clamp tracheal + ventilate/bronchial lumen

21. …Left DLT • More difficult to insert (size and curve, cuff) • Risk of tube change and airway damage if kept in position for post-op ventilation • Contraindication: • Presence of lesion along DLT pathway • Difficult/impossible conventional direct vision intubation • Critically ill patients with single lumen tube in situ who cannot tolerate even a short period of off mechanical ventilation • Full stomach or high risk of aspiration • Patients, too small (<25-35kg) or too young (< 8-12 yrs)

22. Right DLT: bronchoscopic view

23. Another indication for DLT: Reexpansion pulmonary edema

24. Univent Tube... • Developed by Dr. Inoue • Movable blocker shaft in external lumen of a single-lumen ET tube • Easier to insert and properly position than DLT (diff airway, C-s injury, pedi or critical pts) • No need to change the tube for postop ventilation • Selective blockade of some lobes of the lung • Suction and delivery CPAP to the blocked lung

25. ...Univent Tube • Slow deflation (need suction) and inflation (short PPV or jet ventilation) • Blockage of bronchial blocker lumen • Higher endobronchial cuff volumes +pressure (just-seal volume recommended) • Higher rate of intraoperative leak in the blocker cuff • Higher failure rate if the blocker advanced blindly

26. Univent Tube

27. Arndt Endobronchial Blocker set • Invented by Dr. Arndt, an anesthesiologist • Ideal for diff intubation, pre-existing ETT and postop ventilation needed • Requires ETT > or = 8.0 mm • Similar problems as Univent • Inability to suction or ventilate the blocked lung

28. Other methods of OLV • Single-lumen ETT with a balloon-tipped catheter • Including Fogarty embolectomy catheter, Magill or Foley, and Swan-Ganz catheter (children < 10 kg) • Not reliable and may be more time-consuming • Inability to suction or ventilate the blocked lung • Endobronchial intubation of single-lumen ETT • The easiest and quickest way of separating one lung from the other bleeding one, esp. from left lung • More often used for pedi patients • More likely to cause serious hypoxemia or severe bronchial damage

29. Management of OLV... • Maintain two-lung ventilation as long as possible • Start OLV with 100% O2 then start backing off the FiO2 if saturations are OK • Manual ventilation for the first few minutes of OLV to get a sense of pulmonary compliance / resistance • Be attentive to inspiratory pressures and tidal volumes and adjust the ventilator to optimize oxygenation and alveolar ventilation, with minimal barotrauma • Look at the surgical field to see if the non-dependent lung is collapsed

30. ...Management of OLV • Tidal volume = 8-10 ml/kg • Adjust RR (increasing 20-30%) to keep PaCO2 = 40 mmHg • No PEEP (or very low PEEP, < 5 cm H2O) • Continuous monitoring of oxygenation and ventilation (SpO2, ABG and ET CO2)

31. Management of hypoxemia during OLV • FiO2 = 1.0 • Manual ventilation • Check DLT position with FOB • Check hemodynamic status • CPAP (5-10 cm H2O, 5 L/min) to nondependent lung, most effective • PEEP (5-10 cm H2O) to dependent lung, least effective • Intermittent two-lung ventilation • Clamp pulmonary artery

32. Other causes of hypoxemia in OLV • Mechanical failure of O2 supply or airway blockade • Hypoventilation • Resorption of residual O2 from the clamped lung • Factors that decrease SvO2 (CO, O2 consumption)

33. Broncho-Cath CPAP system

34. Summary • OLV widely used in cardiothoracic surgery • Many methods can be used for OLV. Optimal methods depends on indication, patientfactors, equipment, skills and level of training • FOB is the key equipment for OLV • Principle physiologic change of OLV is the redistribution of pulmonary blood flow to keep an appropriate V/Q match • Management of OLV is a challenge for the anesthesiologist, requiring knowledge, skill, vigilance, experience, and practice