One lung ventilation kweq part 1
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  • Operated lung- non dependent/ upper lung Nonoperated lung- dependent/ lower lung Improved apparatus ~ Carlen’s tube to Robertshaw tube, single tube with blocker to double lumen tube, from rubber to PVC
  • Due to effect of gravity, pulmonary blood flow lowest at Apex, highest at Base. Decrease approximately 1cmH2O per cm of height because specific gravity (blood)1.05gm/mL ~ water 1.0gm/mL The pressure differences responsible for driving blood flow in each zone. PA, alveolar pressure; P a , pulmonary artery pressure; P v , pulmonary venous pressure Zone 1: at apex, Pa Pv. Blood vessel not compromised but the driven blood flow is by differences between Pa and PA (pressure flow characteristic). Pv has no influence on flow. This behaviour is called “Starling resistor/Sluice/Waterfall effect” Because Pa is increasing down the zone but PA is the same, thus the pressure difference responsible for flow increase. In addition increasing capilaries recruitment occurs down the zone. Zone 3: Gravity increase both Pa & Pv. Both > PA. Thus blood flow driven by diferrences between Pa>Pv (usual way by the arterial-venous pressure difference). In zone 3, greatest number of cappilaries is open and blood flow is highest. This is because the hydrostatic pressure in this zone causing distension of the cappilaries, recruitment also plays part in increasing the flow. Pa and Pv increasing down the zone but PA remains constant, thus transmural pressure increase. Transmural pressure is pressure difference inside and outside capillaries. Zone 4: Occur at base of lung, where parenchyma is least expanded. In this zone, due to low lung volumes, the resistance of the extra-alveolar vessel becomes significant, and reduction of regional blood flow is seen. Explaination: narrowing of extra alveolar vessels which occurs when the lung parenchymal is poorly inflated. Other factors causing uneven blood flow distribution: In animal study shows some region in lungs has intrinsically higher vascular resistance. It is evidence that blood decrease along the acinus with peripheral parts less well supplied by blood. Some suggest peripheral region receive less blood flow than central region. The complex and random arrangement of blood vessels and cappilaries contribute to uneven of blood flow distribution.
  • The lung- an elastic structur “tethered” to the chest wall, and is forced to adopt the shape of the chest cavity as it varies throughout the respiratory cycle. The apex- gravitationally superior alveoli are streched by the weight of the lung beneath them and have greater volume than alveoli at base, gravitationally inferior lung, which are compressed by the lung above them. Because gravity also causes a vertical gradient in pleural pressure (Ppl) in the LDP, ventilation is relatively increased in the dependent as compared with the nondependent lung (Fig. 48–10) . In addition, in the LDP the dome of the lower diaphragm is pushed higher into the chest than the dome of the upper diaphragm; therefore, the lower diaphragm is more sharply curved than the upper diaphragm. As a result, the lower diaphragm is able to contract more efficiently during spontaneous respiration. Thus, in the awake patient in the LDP, the lower lung is normally better ventilated than the upper lung, regardless of the side on which the patient is lying, although there remains a tendency toward greater ventilation of the larger right lung. 226 Because there is greater perfusion to the lower lung, the preferential ventilation to the lower lung is matched by its increased perfusion, so that the distribution of the V/Q ratios of the two lungs is not greatly altered when the awake subject assumes the LDP. Because perfusion increases to a greater extent than ventilation with lung dependency, the V/Q ratio decreases from the nondependent to the dependent lung (just as it does in upright and supine lungs).
  • Schematic presentation of relationship between perfusion and ventilation. Both Ventilation and perfusion increase as they approach the base of lung. The change in perfusion (blood flow) is greater than the change in ventilation. The ventilation-perfusion ratio decrease from tp to bottom. As it decrease, pO2 falls and pCO2 increase. Normal Alveolar ventilation ~ 4L/min Pulm capillary perfusion ~ 5L/min V/Q = ~0.8
  • Pulmonary Blood flow from bottom to apex decrease almost linearly. This changes affected by posture and exercise. Difference in Pulmonary artery hydrostatic pressure from top to base in a lung 30cm high will be about 30cmH2O (23mmHg). As these pressure is significant enough to cause changes for low pressure system in pulmonary circulation.
  • Lungs In Upright position (Awake): Compliance of apex of the lungs at flatter part of the cure. Compliance of base at steeper part of the curve. Thus compliance is increase down towards base. Lungs in Lateral Decubitus Position (Awake): Compliance of Nondependent lung at flatter part of the curve Compliance of Dependent lung at steeper part of the curve Thus more ventilation at Dependent Lung.
  • Distribution of blood flow and ventilation is similar to that in the upright position but turned by 90 degrees. Blood flow and ventilation to the dependent lung are significantly greater than to the nondependent lung. Good V/Q matching at the level of the dependent lung results in adequate oxygenation in the awake patient breathing spontaneously. In Lateral Decubitus Position (LDP) , ordinarily less Zone 1- due to vertical hydrostatic gradient is less in LDP than upright. % of Blood flow to lungs according to position; In upright/Supine-Rt 55% Lt 45%; In LDP Rt NDL 45% Lt DL 55%; In LDP Lt NDL 35% RT DL 65%
  • In Awake LDP, as DL receives >perfusion and >ventilation – V/Q is match.
  • Lateral Decubitus Position (LDP) in Anaesthetised Pt This position significantly alter the normal pulmonary Ventilation/Perfusion Relationship. Perfusion continue to favor dependent lung (Due to gravitational effect) Ventilation favor the less perfused lung. End result is V/Q mismatch(shunt) giving rise to hypoxemia. The changes further accentuated by several factors: 1)Induction of anesthesia 2)Initiation of mechanical ventilation 3)Use of neuromuscular blockade 4)Opening the chest/pleural space 5)Surgical Retraction/ Compression 6)Pressure by mediastinum/ Abdominal content Perfusion continue to favor dependent lung (Due to gravitational effect) Ventilation favor the less perfused lung. End result is V/Q mismatch(shunt) giving rise to hypoxemia.
  • nondependent (up) lung moving from a flat, noncompliant portion to a steep, compliant portion of the pressure–volume curve, and the dependent (down) lung moving from a steep, compliant part to a flat, noncompliant part of the pressure–volume curve anesthetized patient in the lateral decubitus position has most tidal ventilation in the nondependent lung (least perfusion) and less tidal ventilation in the dependent lung (most perfusion)
  • GA does not cause significant change distribution of blood flow but has change the distribution of ventilation. Most of the V T enters the nondependent lung, and this results in a significant V/Q mismatch. Pressure effect by mediastinal structure prevent DL expansion and further reduce lung FRC
  • Poor mucociliary clearance & absorption atelectasis with high FiO2 1.0 cause further lung volume loss.
  • 1)larger part of tidal ventilation going to the nondependent lung because the pressure of the abdominal contents (PAB) pressing against the upper diaphragm is minimal, and it is therefore easier for positive-pressure ventilation to displace this less resisting dome of the diaphragm 2)diaphragmatic displacement is maximal over the nondependent lung, least amount of resistance to diaphragmatic movement caused by the abdominal contents. - further compromises the ventilation to the dependent lung and increases the V/Q mismatch.
  • Alveolar O2 can diffuse to these pulmonary arteries and the rate of diffusion appears to be a controlling factor for HPV. HPV is immediate, sustainable response that is readily reversed by reoxygenation.

One lung ventilation kweq part 1 One lung ventilation kweq part 1 Presentation Transcript

  • ONE LUNG VENTILATION (OLV)- PART 1 DR. IKHWAN BIN WAN MOHD RUBI MD (UKM), MEDICAL OFFICER DEPT OF ANAESTHESIOLOGY AND INTENSIVE CARE UNIT HSNZ 01/31/12 HSNZ KT
  • OUTLINE OF PRESENTATION
    • INTRODUCTION
    • Indication/contraindication of OLV
    • Respiratory Physiology (Upright,LDP)- Pulmonary Blood flow & Ventilation
    • Respiratory Physiology in various LDP & OLV
    01/31/12 HSNZ KT
  • INTRODUCTION OF OLV
    • One lung ventilation (OLV) – thoracic anesthesia
    • Separation of 2 lungs, each lung ventilated independently
    • Collapse of the operated (nondependent) lung, ventilation of the non operated (dependent) lung
    • A ventilation technique used in thoracic surgery
    • Devices; 2 lumen tube; bronchial blockers; single lumen tube inserted beyond carina
    First described in 1932; Gale & Waters- using single-light tube, inserted into Rt/Lt mainstem bronchus. Since then various methods/ techniques proposed- safer and facilitate practices. 01/31/12 HSNZ KT
  • TUBES USED IN 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
    01/31/12 HSNZ KT
    • Distribution of perfusion (Pulmonary Bld Flow)
    • Distribution of ventilation
    • Ventilation/Perfusion Ratio
    RESPIRATORY PHYSIOLOGY (AWAKE UP RIGHT/ LATERAL DECUBITUS POSITION) 01/31/12 HSNZ KT
    • Pulmonary Bld flow uneven due to effect of gravity- decrease almost linearly from base to apex
    • In supine, bld flow evenly distributed (nearly uniform) as entire lungs at same gravitational level, apical blood flow increase but basal blood flow virtually unchanged
    • 3 principle pressure involved:
    • -PA, Pa, Pv
    • PA- approx equal to atm Pressure
    • Gravity increase Pulmonary Artery Hydrostatic Pressure
    Physiology Linda S.Costanzo Resp Physiology pg 219 01/31/12 HSNZ KT
  • DISTRIBUTION OF VENTILATION (AWAKE/CLOSED) 01/31/12 HSNZ KT
  • RELATIONSHIP OF VENTILATION & PERFUSION 01/31/12 HSNZ KT
  • RESPIRATORY PHYSIOLOGY (AWAKE UP RIGHT)
    • Principle changes occures:
      • Recruitment
      • Distension
      • Transudate
    Summary showing the role played by the pressure/ cappilaries in determining the distribution of blood flow in upright. 01/31/12 HSNZ KT
  • RESPIRATORY PHYSIOLOGY (LATERAL DECUBITUS POSITION) 01/31/12 HSNZ KT
  • COMPARING UP RIGHT & LATERAL DECUBITUS POSITION 01/31/12 HSNZ KT
  • VARIANT OF LDP DURING THORACIC SURGERY
    • LDP/ Awake/ Spont Breath/ Closed Chest
    • LDP/ Awake/ Spont Breath/ Open Chest
    • LDP/ Anaesthetized/ Spont Breath/ Closed
    • LDP/ Anaestehtized/ Spont Breath/ Open
    • LDP/ Anaesthetized/ Paralysed/ Open Chest
    • OLV/Anesthetized/ Paralyzed/ Open Chest
    01/31/12 HSNZ KT
  • 1)LDP/ AWAKE/ SPONT BREATH/ CLOSED CHEST 01/31/12 HSNZ KT
  • 1) LDP/ AWAKE/ SPONT BREATH/ CLOSED CHEST
    • Dependent lung (DL) receives
      • >perfusion (gravity)
      • >ventilation
    • Reasons why >ventilation:
      • Contraction of dependent hemidiaphragm became > efficient as it assumes higher position in the chest due to its disproportionate dome shape supporting the weight of abdominal content
      • Dependent lung > favorable part of compliance curve
    • Thus in LDP/ Awake/Spont/ Closed; -DL receives > ventilation regardless which side pt is lying
    01/31/12 HSNZ KT
  • 2) LDP/ AWAKE/ SPONT BREATH/ OPEN CHEST 01/31/12 HSNZ KT
    • 2 complications
    • Mediastinal shift , occurring during inspiration. Negative pressure more in intact hemithorax cause the mediastinum to move vertically downward and push into the dependent hemithorax.
      • create circulatory & reflex changes, result in a clinical picture similar to that of shock and respiratory distress.
      • Eg. Thoracoscopy  LA, pt may need intubated immediately, with initiation of positive-pressure ventilation
    2) LDP/ AWAKE/ SPONT BREATH/ OPEN CHEST 01/31/12 HSNZ KT
  • 2) LDP/ AWAKE/ SPONT BREATH/ OPEN CHEST 01/31/12 HSNZ KT
    • Paradoxical breathing :
      • During inspiration, movement of gas from the exposed lung into the intact lung and movement of air from the environment into the open hemithorax cause collapse of the exposed lung.
      • During expiration, the reverse occurs, and the exposed lung expands
    LDP/ AWAKE/ SPONT BREATH/ OPEN CHEST 01/31/12 HSNZ KT
  • RESPIRATORY PHYSIOLOGY (LATERAL DECUBITUS POSITION) IN ANAESTHETISED PT 01/31/12 HSNZ KT
  • FACTORS AFFECTING RESPIRATORY PHYSIOLOGY IN LATERAL DECUBITUS POSITION
    • The changes further accentuated by several factors:
    • Induction of anesthesia
    • Initiation of mechanical ventilation
    • Use of neuromuscular blockade
    • Opening the chest/pleural space
    • Surgical Retraction/ Compression
    • Pressure by mediastinum/ Abdominal content
    • Perfusion continue to favor dependent lung (Due to gravitational effect)
    • Ventilation favor the less perfused lung.
    • End result is V/Q mismatch(shunt) giving rise to hypoxemia.
    01/31/12 HSNZ KT
  • INDUCTION OF ANAESTHESIA
    • Reduce FRC
    • Non dependent lung moves to favorable part of compliance
    • Dependent lung moves to less compliance
    • Result in > ventilation in nondependent lung than dependent
    • But perfusion still favor the dependent lung (gravitational effect)
    • Thus V/Q mismatch occur causing hypoxia
    01/31/12 HSNZ KT
  • 01/31/12 HSNZ KT
  • OTHER FACTORS INVOLVED
    • Positive Pressure Ventilation (PPV in mechanical ventilation) favors ND lung as it is > compliant
    • Use of neuromuscular blockade- causing paralysis of the diaphragm. Allowing abdominal to push the dependent hemidiaphram & impede further ventilation of DL
    • Suboptimal positioning (usage of sand bag to maintain pt in LDP) further restrict movement of DL
    • Opening of NDL cause increase compliance of NDL, as the lungs less restricted. This further attenuates differences of compliance between two lungs.
    01/31/12 HSNZ KT
  • 3) LDP/ ANAESTHETIZED / SPONT BREATH/ CLOSED CHEST 01/31/12 HSNZ KT
  • 3) LDP/ ANAESTHETIZED / SPONT BREATH/ CLOSED CHEST 01/31/12 HSNZ KT
    • In awake/ anaesthetised- distribution of pulmonary blood flow influenced by gravitational effect
    • But Induction of GAC cause significant changes in distribution of ventilation
    • Reasons:
    • Ventilation favors NDL due to
    • GAC reduce both lungs FRC (both loss of volume)
      • Effect of muscle relaxation- paralysis of both hemidiaphragm. The curve effect of diaphragm gives no Advantages
      • Pressure effect by medialstinal structure- rest on dependent lung physically impedes DL.
    3) LDP/ ANAESTHETIZED / SPONT BREATH/ CLOSED CHEST 01/31/12 HSNZ KT
    • Weight of abdominal contents pushing cephalad against diaphragm (greatest effect to DL)- physically impedes DL expansion and reduce FRC
    • Effect more prominent if paralyzed
    • Suboptimal positioning- fails to provide room for DL expansion ; considerable compressing DL
    • Opening chest/ pleural space (pneumothorax) further increase ventilation to NDL as it is no longer restricted
    3) LDP/ ANAESTHETIZED / SPONT BREATH/ CLOSED CHEST 01/31/12 HSNZ KT
    • No changes in pulmonary blood flow - >perfusion to DL (gravitational effect)
    • But it caused significant changes on ventilation
    • NDL overventilation (remain unperfused)- increase compliance due to no restriction of chest wall/ free to expand
    • DL relatively non compliance (poor ventilation/ overperfused)
    • Surgical retraction/compression of NDL provide partial solution: expansion of NDL when externally restricted, ventilation will be diverted to dependent, and better perfused lung.
    4) LDP/ ANAESTHETIZED / SPONT BREATH/ OPEN CHEST 01/31/12 HSNZ KT
  • 5)LDP/ ANAESTHETIZED / PARALYSED/ OPEN CHEST 01/31/12 HSNZ KT
  • 6) OLV/ ANAESTHETIZED / PARALYSED/ OPEN CHEST 01/31/12 HSNZ KT
    • Creates an obligatory right-to-left transpulmonary shunt (nonventilated lung)
    • Assuming active HPV, blood flow to the nondependent hypoxic lung will be reduced by 50% and therefore is (35/2) = 17.5%.
    • To this must be added 5%, which is the obligatory shunt through the nondependent lung.
      • shunt through the nondependent lung is therefore 22.5%
    • Together with the 5% shunt in the dependent lung, total shunt during one-lung ventilation is 22.5% + 5 = 27.5%.
    • This results in a PaO2 of approximately 150 mm Hg (FIO2 = 1.0).
    6) OLV/ ANAESTHETIZED / PARALYSED/ OPEN CHEST 01/31/12 HSNZ KT
    • Dependent lung is no longer on the steep (compliant) portion of the volume–pressure curve because of reduced lung volume and FRC.
    • # create a low V®/Q® ratio and a large P(A-a)O2 gradient.
    6) OLV/ ANAESTHETIZED / PARALYSED/ OPEN CHEST 01/31/12 HSNZ KT
  • SUMMARY OF V/Q RELATIONSHIP IN AWAKE & ANAESTHETISED PT 01/31/12 HSNZ KT Awake/Closed Anaesthetised Closed Open V/Q V Q V Q V Q NDL DL
  • SUMMARY OF V-Q RELATIONSHIPS IN THE ANESTHETIZED, OPEN-CHEST AND PARALYZED PATIENTS IN LDP 01/31/12 HSNZ KT
  • SUMMARY OF FACTORS INFLUENCING PULMONARY/ LUNG PERFUSION 01/31/12 HSNZ KT
    • HPV, a local response of pulmonary vascular smooth muscle (PVSM), decreases blood flow to the area of lung where a low alveolar oxygen pressure is sensed.
    • Intrinsic response of lung, no neuronal control, immediately present in transplanted lung.
    • The mechanism of HPV is not completely understood. Vasoactive substances released by hypoxia or hypoxia itself (K+ channel) cause pulmonary artery smooth muscle contraction.
    • All pulmonary arteries and veins vasoconstric in response to hypoxia, but greatest effect is to small pumonary arteriesm(200mm)
    HYPOXIC PULMONARY VASOCONSTRICTION (HPV) 01/31/12 HSNZ KT
    • 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.
    • But effective only when there are normoxic areas of the lung available to receive the diverted blood flow
    HYPOXIC PULMONARY VASOCONSTRICTION (HPV) 01/31/12 HSNZ KT
  • FACTORS AFFECTING REGIONAL HPV
    • HPV is inhibited directly by volatile anesthetics (not N20), vasodilators (NTG, SNP, dobutamine, many ß2-agonist), increased PVR (MS, MI, PE) and hypocapnia
    • HPV is indirectly inhibited by PEEP, vasoconstrictor drugs (Epi, dopa, Neosynephrine) by preferentially constrict normoxic lung vessels
    01/31/12 HSNZ KT
  • FACTORS THAT WORSENED RIGHT TO LEFT SHUNT
    • HPV inhibition:
    • very high or very low pulmonary artery pressures
    • hypocapnia
    • vasodilators;
      • GTN, Nitroprusside
    • high or low mixed venous oxygen
    • pulmonary infection
    • volatile anesthetics
    •  FRC:
    • general anesthesia,
    • paralysis,
    • pressure from abdominal contents,
    • compression by the weight of mediastinal structures,
    • suboptimal positioning on the operating table.
    • Others:
    • absorption atelectasis,
    • accumulation of secretions,
    • formation of a fluid transudate in the dependent lung.
    01/31/12 HSNZ KT