PHYSIOLOGY OF One lung ventilation.pptx

PHYSIOLOGY OF One lung ventilation
single lung ventilation ,
PRE ANESTHETIC EVALUATION OF A PATIENT UNDERGOING A PULMONARY RESECTION SURGERY

1. PHYSIOLOGY OF ONE LUNG VENTILATION PRE ANESTHETIC EVALUATION OF A PATIENT UNDERGOING A PULMONARY RESECTION SURGERY DR. ANANYA NANDA ASSISTANT PROFESSOR, Dept Of Anaesthesiology & Critical Care ESIC MEDICAL COLLEGE & HOSPITAL

2. Outline of Discussion RESPIRATORY PHYSIOLOGY IN SUPINE & LATERAL DECUBITUS POSITION CHANGES IN PHYSIOLOGY DURING ONE LUNG VENTILATION HYPOXIC PULMONARY VASOCONSTRICTION PREANAESTHETIC ASSESSMENT Cardiopulmonary Exercise T esting SUMMARY

3. Introduction… Principle of one lung ventilation is one lung for the surgeon and one for the anesthetist. Induction of anesthesia, one-lung ventilation (OLV) and opening of the chest progressively uncouple ventilation– perfusion (V/Q) matching.

4. Respiratory Physiology : ERECT versus LDP POSITION

5. In vivo perfusion scanning illustrating central-to-peripheral, in addition to gravitational blood flow distribution, in the upright position Classic West Zones of blood flow distribution in the upright position

6. P- V RELATIONSHIP OF LUNG

7. Ventilation-perfusion relationship V/Q ratio: The ratio of the amount of air reaching the alveoli and participating in gas exchange to the amount of blood reaching the alveoli. ZONE 1 : (V) >>> (Q) V/Q : 3.4 (High ) ZONE 2 : (V) = (Q) V/Q : 0.8 (Average ) ZONE 3 : (Q) >>> (V) V/Q : 0.63 (Low )

8. Respiratory Physiology – Lateral Decubitus Position LDP/ Awake/ Spontaneous Breathing/ Closed Chest LDP/ Anaesthetized/ Spontaneous Breathing/ Closed chest LDP/ Awake/ Spontaneous Breathing/ Open Chest LDP/ Anaesthetized/ Spontaneous Breathing/ Open chest LDP/ Anaesthetized/ Paralysed/ Open Chest OLV/Anesthetized/ Paralyzed/ Open Chest

9. LDP/ Awake/ Spontaneous Breathing/ Closed Chest Dependent lung has↑perfusion & ↑ventilation Perfusion- gravity , decreases linearly from base to apex V entilation ↑ at Dependent Lung Efficient Contraction of dependent hemidiaphragm Compliance of Nondependent lung at flatter part of the curve Compliance of Dependent lung at steeper part of the curve

10. 2 1 EFFECTS OF ANESTHESIA ON PULMONARY FUNCTION Pulmonary compliance decreases by 33% FRC decreases by 33% Vital capacity is decreased by 25% to 50% R e si d ual v o l u m e ( R V ) i n cre a ses by 1 3 %. Expiratory reserve volume decreases by 25% and 60% Tidal volume (VT) decreases by 20 %. T ot a l l u ng c a pacity (TL C ) can decrease

11. EFFECTS OF ANAESTHESIA IN LDP Reduces FRC ↑ ventilation in nondependent lung Positive Pressure Ventilation (PPV in mechanical ventilation) favors ND lung as it is more compliant N euromuscular blockade- diaphragm paralysis. Allows abdomen to push the dependent hemidiaphragm & impede further ventilation of DL Suboptimal positioning (usage of sand bag ) further restrict movement of DL

12. Non dependent lung moves to favorable part of compliance & Dependent lung moves to less compliant part

13. LDP / ANESTHETIZED / CLOSED CHEST Perfusion- no significant change in the distribution of blood flow Ventilation Significant change General anesthesia : ↓ FRC and lung vol. of both lungs Increased ventilation to non dependent lung 1) cephalad displacement of diaphragm more pronounced 2) mediastinal structures pressing on dependent lung move lungs to a lower volume on the S-shaped V/P curve. The nondependent lung moves to a steeper position on the compliance curve and receives most of the VT, whereas the dependent lung is on the flat (noncompliant) part of the curve

14. LDP / Awake / Spontaneous Breathing / Open Chest THORACOSCOPY under peripheral nerve block ( open pneumothorax) Two complications can arise

15. Mediastinal Shift S pontaneous V entilation I nspiration causes pleural pressure to become more negative on the dependent side, but not on the ND lung side. This results in a downward shift of the mediastinum during inspiration and an upward shift during expiration . The major effect of the mediastinal shift is to decrease the contribution of the dependent lung to the tidal volume.

16. Paradoxical respiration / Pendelluft To-and-fro Gas Flow between the dependent and nondependent lung( paradoxical respiration ( pendelluft ). During inspiration, the pneumothorax increases, and gas flows from the upper lung across the carina to the dependent lung. During expiration , the gas flow reverses and moves from the dependent to the upper lung Represents wasted ventilation- decreased amount of gas exchange

17. LDP/ Anaesthetized/ Spontaneous Breathing/ Open chest Opening chest has little impact on perfusion Upper lung is no longer restricted by chest wall and free to expand causing further increase in V/Q mismatch

18. LDP/ Anaesthetized/ Paralyzed/ Open Chest Perfusion: Dépendent Lung > non dépendent Lung Ventilation : High curved diaphragm no longer contracts & is no longer advantageous Mediastinum rests on lower lung & impedes lower lung expansion ↓ FRC significantly -pressure by abdominal contents Sub optimal positioning leaves no room for lower lung expansion Dependent lung better perfused and under ventilated → V/Q mismatch

19. The same phenomena …. But with OLV NO VENTILATION to NDL.. M aj o r dete r mi n a n t s of PERFUSION gravity, amount of lung disease, magnitude HPV, surgical interference nondependent , ventilation mode dependent

20. Arterial Oxygenation and Carbon Dioxide Elimination during OLV Greater decrease in oxygenation than during two-lung ventilation in LDP due to an obligatory Rt -Lt transpulmonary shunt through the nonventilated nondependent lung. Consequently, lower PaO2 & larger P(A-a) O2 gradient. Usually carbon dioxide elimination is not a problem; retention of CO2 by blood traversing the nonventilated lung is countered by the increased elimination of CO2 from blood traversing the ventilated lung .

21. Two Lung versus One Lung Ventilation V/Q Mismatch is due to creation of an OBLIGATORY RT TO LT TRANS PULMONARY SHUNT . During 2 Lung Ventilation in LDP-60% of Cardiac Output (CO) goes to dependent Lung and 40% to Non dependent Lung Normal Venous admixture is 10% and is equally shared(5%+5%) between two lungs. So average percentage of CO participating in gaseous exchange in Non-dependent-Lung is 35%; and in dependent Lung in 55%. HPV and OLV: reduce 50% of blood flow to the NONVENTILATED Lung - blood flow becomes 17.5% (35/2) and shunt will be also 17.5% If this is added to 5% of existing shunt the total shunt in NONVENTILATED Lung will be 22.5(17.5+5)%. So altogether in OLV the shunt will be 27.5% (22.5+5) causing impairement optimal PaO2.

22. Autoregulatory mechanism Tries to normalise V/Q relationship Decreases the blood flow to the nonventilated lung by about 50%. Rapid onset over the first 30 minutes and then a slower increase to a maximal response at approximately 2 hours. graded and limited HPV is, of greatest benefit when 30% to 70% of the lung is hypoxic HPV is effective only when there are normoxic areas of the lung available to receive the diverted blood flow . Hypoxic pulmonary vasoconstriction Von Euler and Liljestrand 1946 occurs in pulmonary arterioles of 200µm diameter PaO2- 30mmHg

23. Model of the effect of hypoxic pulmonary vasoconstriction (HPV) on PaO2 as a function of the percent of lung that is hypoxic. The model assumes an Fi O2 of 1.0, normal hemoglobin, cardiac output and oxygen consumption. The HPV benefit is maximal when 30–70% of the lung are hypoxic

24. MOA Primary stimulus is PAO2 principal pathways in the  in vivo  modulation of HPV- endothelin-1 , nitric oxide, cyclooxygenase and adenine nucleotide pathways. endothelin-1 and thromboxane A 2  may enhance, whereas nitric oxide and prostacyclin may moderate, HPV Pulmonary vascular smooth muscle cells( pvsmc ) and type 1 cells of the carotid body. Hypoxia causes inhibition of outward potassium current. Thus causing membrane depol . and calcium entry through voltage gated calcium channels.

25. FACTORS AFFECTING HPV DIRECT inhibition volatile anesthetics (less with Desflurane , isoflurane ), vasodilators (NTG, SNP, NO) increased Pulmonary vascular resistance mitral stenosis, volume overload, hypothermia, thromboembolism, large hypoxic lung segment INDIRECT inhibition PEEP vasoconstrictor drugs (epinephrine, norepinephrine, PE) constrict normoxic lung vessels preferentially

26. Potentiators of HPV Almitrine (respiratory stimulant) may potentiate HPV. Prostaglandins play a role in HPV inhibition, & therefore prostaglandin inhibitors have been investigated as potentiators of HPV.

27. EFFECT OF CARDIAC OUTPUT ON HPV Slinger and Scott showed a direct correlation between increasing CO and improving oxygenation in patients during OLV . CO augmented by a small dose of dobutamine (5 mg/kg/min) has been shown to improve arterial oxygenation and decrease shunt fraction BUT though increasING CO to supranormal level increases mixed venous oxygenation, this benefit is overridden by an increase in shunt fraction, resulting in impaired arterial oxygenation. The shunt fraction is likely increased due to weakened HPV in the face of increases in pulmonary arterial pressure Maintenance or restoration of “normal” CO is therefore important for oxygenation during OLV. The availability of noninvasive monitoring devices makes CO data more readily available and allows for appropriate titration of inotropes when required.

28. CO 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

29. Pre- anaesthetic evaluation Detailed History/ Allergies/ medications/ airway anatomy Evaluation of CVS Pulmonary function testing & evaluation for lung resectability Respiratory mechanics Lung parenchymal function Cardio pulmonary reserve assessment

30. Pre- anaesthetic Evaluation Detailed History/ Allergies/ medications/ airway anatomy Evaluation of CVS / renal and hepatobiliary systems Pulmonary function testing & evaluation for lung resectability Respiratory mechanics Lung parenchymal function Cardio pulmonary reserve assessment Cardiopulmonary exercise Testing LEVEL -2 LEVEL -3 LEVEL -1

31. History Age Patients functional status / METS score Dyspnea and cough – Characteristics of sputum exposure - Smoking – duration & frequency , asbestos or radiation IHD / CKD / CLD Recent infections Immobility and venous insufficiency metastatic disease- Mass effects and metabolic effects of lung cancers. Current medications

32. Physical Examination & Investigations Appearance – wasting, body habitus Cyanosis, clubbing Tracheal position Chest wall abnormalities Respiratory rate, pattern, breath sounds & use of accessory muscles of respiration Auscultation of lung fields Cardiac examination – Third heart sound, loud P2 Abdomen – liver size I nvestigations Pulmonary hypertension CHF IHD or VALVULAR disease RENAL FUNCTION TEST LIVER FUNCTION TEST

33. Assessment of suitability for lung resection Cardiac risk should be stratified All patients should have a preoperative ECG All patients with a cardiac murmur should undergo echocardiography Patients should wait 6 weeks after myocardial infarction before lung resection Cardiology opinion should be sought for all patients considered for lung surgery within 6 months of myocardial infarction  IMPORTANCE - Right ventricular dysfunction occur in 50% of COPD patients and in 30-40 % with post op pneumonectomy . • Recurrent hypoxemia is main cause of right ventricular dysfunction which increase the pulmonary vascular resistance. Cardiovascular Recommendations Before Resection

34. EVALUATION OF FITNESS FOR RESECTION LEVEL 1- Pulmonary function tests (FEV1 and DLCO) LEVEL 2- Stair climbing test , Shuttle Walk Test LEVEL 3 – Cardiopulmonary Exercise Testing (VO2 max )

35. How much lung tissue can safely be removed without making the patient respiratory cripple???? RISK ASSESSMENT – to identify patients who are at increased risk of respiratory morbidity and mortality / need short or long term ventilator support RISK REDUCTION – to institute corrective and preventive measures to minimize the risk of respiratory morbidity and mortality / respiratory cripple ** beneficial effects and reversibility of airway disease by bronchodilator therapy Pulmonary Function T ests - GOALS

36. Pulmonary function tests

37. SPIROMETRY FEV 1 an independent predictor of respiratory morbidity ( OR- 1.1 for every 10% decrease in FEV 1 ) corrected to patient’s age, height and sex and presented as a % of their predicted normal values Vital capacity FEV1 Residual volume / TLC MVV

38. Reduction of Pulmonary Function after Resection : Across various studies, postoperative pulmonary function values assessed at various time intervals after lobectomy or pneumonectomy : FEV1 : 84% - 91% of preoperative values for lobectomy, 64% - 66% for pneumonectomy DLCO : 89% - 96% of preoperative values after lobectomy 72% - 80% after pneumonectomy. VO 2 max: 87% - 100% of preoperative values after lobectomy 71% - 89% after pneumonectomy. P . Mazzone. Preoperative evaluation of the lung resection candidate. Cleveland Clinic Journal of Medicine May 2012; Vol 79, e-S17-22 THERE IS NO FEV1 PROHIBITIVE LIMIT FOR ANAESTHESIA ACC 2013 emphasize the importance of percentage of predicted postoperative values (% PPO) over absolute values

39. FEV1 & PpO FEV1 For a right lower lobectomy (% of functional lung tissue to be removed= 12/42 = 29%) a patient with a preoperative FEV1 70% of normal would be expected to have a postoperative FEV1 = 70% × (1 - 29/100) = 50 % This changes for a patient who has emphysema versus a person who has lung cancer coming for surgery. Pp o FEV1 estimates the WORKING FUNCTIONAL lung tissue 6 4 12 10 10

40. ABG - PaCO2 more than 45 mm Hg, PaO2 less than 60 mm Hg and SaO2 less than 90% being considered risk factors. Diffusing capacity for CO (DLCO) The DLCO correlates with the total functioning surface area of alveolo capillary interface. A PPO-DLCO < 40 % predicted correlates with both increased respiratory and cardiac complications and is relatively independent of the FEV1 The DLCO is negatively affected by preoperative chemotherapy and may be the most important predictor of complications in this subgroup of patients . P reoperative DLCO of 100% of the predicted value is associated with 11% risk of postoperative morbidity . A DLCO < 60% of predicted, holds a 40% risk of postoperative complications Lung Parenchymal F unction

41. Recommendation: FEV 1 and DLCO ACCP (2013) Both PPO FEV 1 and PPO DLCO > 60% * No further tests recommended ERS (2009) Both FEV 1 and DLCO 80% LOW RISK * PPO FEV 1 or PPO DLCO cut off values of 60% predicted values has been chosen based on indirect evidences and expert consensus opinion.

42. LEVEL - 2 TESTS 6-minute walk test - VO2max can be estimated from the 6MWT distance in meters divided by 30 ( 6MWT of 450 m: estimated VO2max = 450/30 = 15 mL/kg/min) Stair climbing test (SCT) - It is a first‑line functional screening test to select patients who can undergo surgery safely. If the height of ascent without any discomfort is more than 22 metre , then the patient is fit to undergo pulmonary resection . Shuttle walk test (SWT)- In this test the patient walks back and forth between two markers set 10 metres apart. A patient unable to complete 25 shuttles(250 metres ) on two separate occasions indicates a reduced maximum oxygen consumption (VO2max) < 10ml/kg/min

43. Maximum oxygen consumption (VO2max )- Most useful predictor of post-thoracotomy outcome. High risk- VO2max <15 mL/kg/min. Low risk = VO 2 max > 20 mL/kg/min  Moderate risk = VO 2 max 15 to 20 mL/kg/min  Oxygen desaturation - Patients with a decrease of SpO2 greater than 4% shows diminished ability to increase oxygen transfer through alveolar capillary membrane during exercise Cardiopulmonary Exercise Testing GOLD STANDARD

44. LEVEL-3 Cardio Pulmonary Exercise Testing Indications Positive high‑risk cardiac % PPO FEV1 or DLCO < 30%, SCT less than 22 m, or SWT less than 400 metre provides a global and integrated assessment of cardiovascular, respiratory, skeletal muscle, and neurophyschological system

45. Cardio Pulmonary Exercise Testing Maximum aerobic capacity (VO2max) Anerobic threshold (AT)- <11 ml/kg/min - poor postoperative outcome, 8 ml/kg/min - very poor postoperative outcome, Respiratory exchange ratio – The ratio between VCO2 and VO2 is known as respiratory exchange ratio (RER). This is a very accurate and reliable parameter of patient’s efforts. A peak value of ≥1.10 is indicative of excellent patient effort Oxygen pulse – The oxygen pulse gives assessment of stroke volume at peak exercise. It is the ratio of VO2max and maximum heart rate. > 80% of the predicted is considered normal. Ventilatory equivalents of carbon dioxide: The ratio of VE : VCO2 ( ≥34) at anerobic threshold is suggestive of gas exchange abnormality. Cardiac indices - peak heart rate achieved, arrhythmias , and electrocardiograph changes

46. Algorithm for preoperative pulmonary assessment for pulmonary resection

47. SPLIT LUNG FUNCTION TESTS Predicts post resection pulmonary function . If the lung region to be resected is nonfunctioning or minimally functioning, the prediction of postoperative function can be modified accordingly. REGIONAL PERFUSION TESTS- iv radioactive xenon-133 and look at degree of perfusion of each lung REGIONAL VENTILATION TESTS – radio- spirometry CT-PET SCAN

48. ASSESSMENT OF RISK OF SURGERY Thoracoscore is currently the largest and most validated global risk score . It is a logistic regression derived model which is based on nine variables

49. SUMMARY OF V/Q RELATIONSHIP IN LDP Awake / Closed Anaesthetised Clos ed O p e n V / Q N DL DL V Q V Q V Q 5 / 2 1/ 1 5 HSN Z KT

50. Summary of Preoperative A ssessment All patients: Assess exercise tolerance estimate predicted postoperative FEV 1 % discuss postoperative analgesia discontinue smoking Patients with predicted postoperative FEV 1 < 40%: Dl CO Cardiopulmonary reserve V o 2 max    Cancer patients: consider the “4 Ms”: m ass effects m etabolic effects M etastases m edications    COPD patients: Arterial blood gas analysis Physiotherapy bronchodilators    Increased renal risk: Measure creatinine and blood urea nitrogen

51. REFERENCES: Principles and Practice of Anesthesia for Thoracic Surgery- P.Slinger Miller’s Anesthesia 9 th edition Core Topics in thoracic anesthesia(Cambridge Medicine) Clinical consensus on preoperative pulmonary function assessment in patients undergoing pulmonary resection (first edition)2019.

52. Recommendations For all patients who may undergo radical surgery, it is recommended to measure both FEV1 and DLCO and calculate and evaluate PPO-FEV1 and PPO-DLCO according to the resection sizes (Category IB). For all patients who may undergo radical surgery, no further evaluation is required if the PPO-FEV1 and PPO-DLCO are greater than 60% predicted according to the resection size, and surgical resection can be scheduled (Category IC). For all patients who may undergo radical surgery, low-technology exercise tests [including stair climbing test (SCT) and shuttle walk test (SWT)] are recommended if either PPO-FEV1 or PPO-DLCO is less than 60% predicted and both are greater than 30% predicted according to the resection size (Category IC). For all patients who may undergo radical surgery, CPET is recommended to measure VO 2 max if either PPO-FEV1 or PPO-DLCO is less than 30% predicted according to the resection size (Category IB).

53. CARDIAC EVALUATION

54. Ventilation and Perfusion Lung Scanning with radioactive isotopes can be used to estimate the relative blood flow to each lung . If the predicted postoperative FEV1 is > 800ml a patient may be considered for pneumonectomy Unilateral Pulmonary Artery Occlusion If the predicted FEV1 is < 800ml, a “functional pneumonectomy” can be performed by testing the patient’s response to balloon occlusion of the operative lung’s pulmonary artery. Patients are excluded from pneumonectomy if the mean pulmonary artery pressure exceeds 35mmHg or the PaO2 falls below 45mmHg.

55. Spirometry for Lung Resection Maximal voluntary ventilation < 50% of predicted and FVC < 70% of predicted were associated with a 40% risk for death. Pneumonectomy : FEV1 >2L; MVV >55% of predicted; FEF 25–75% >1.6 L/s . Lobectomy : FEV1 >1L; MVV >40% of predicted; FEF 25–75% >0.6 L/s. Segmentectomy or wedge resection : FEV1 >0.6L; MVV >40% of predicted; FEF 25–75% >0.6 L/s. Chest 2003;123:2096-2103 Type of surgery FEV1 MVV PNEUMONECTOMY >2 LITRE (> 60%) >50% LOBECTOMY >1.5 LITRE 40-50% SEGMENTECTOMY >0.6 LITRE >40%