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One lung ventilation kweq part 1
- 1. 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
- 7. DISTRIBUTION OF VENTILATION (AWAKE/CLOSED) 01/31/12 HSNZ KT
- 8. RELATIONSHIP OF VENTILATION & PERFUSION 01/31/12 HSNZ KT
- 10. RESPIRATORY PHYSIOLOGY (LATERAL DECUBITUS POSITION) 01/31/12 HSNZ KT
- 11. COMPARING UP RIGHT & LATERAL DECUBITUS POSITION 01/31/12 HSNZ KT
- 13. 1)LDP/ AWAKE/ SPONT BREATH/ CLOSED CHEST 01/31/12 HSNZ KT
- 15. 2) LDP/ AWAKE/ SPONT BREATH/ OPEN CHEST 01/31/12 HSNZ KT
- 17. 2) LDP/ AWAKE/ SPONT BREATH/ OPEN CHEST 01/31/12 HSNZ KT
- 19. RESPIRATORY PHYSIOLOGY (LATERAL DECUBITUS POSITION) IN ANAESTHETISED PT 01/31/12 HSNZ KT
- 22. 01/31/12 HSNZ KT
- 24. 3) LDP/ ANAESTHETIZED / SPONT BREATH/ CLOSED CHEST 01/31/12 HSNZ KT
- 25. 3) LDP/ ANAESTHETIZED / SPONT BREATH/ CLOSED CHEST 01/31/12 HSNZ KT
- 29. 5)LDP/ ANAESTHETIZED / PARALYSED/ OPEN CHEST 01/31/12 HSNZ KT
- 30. 6) OLV/ ANAESTHETIZED / PARALYSED/ OPEN CHEST 01/31/12 HSNZ KT
- 33. 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
- 34. SUMMARY OF V-Q RELATIONSHIPS IN THE ANESTHETIZED, OPEN-CHEST AND PARALYZED PATIENTS IN LDP 01/31/12 HSNZ KT
- 35. SUMMARY OF FACTORS INFLUENCING PULMONARY/ LUNG PERFUSION 01/31/12 HSNZ KT
Hinweis der Redaktion
- 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<PA thus pulmonary capillaries will be compressed by the higher alveolar pressure outside capillaries causing them to close, reducing regional blood flow. Normally this doesn’t occur as Pa is just High enough to prevent closure (albeit at lower flow rate) but in two circumstances, this can change. If Pa reduced (shock/hemorrhage) or PA increases (PPV) bld vessel can collapse thus there is ventilation but no perfusion (physiological/alveolar dead space) Zone 2: Pa higher compare to Pa Zone 1 due to gravitational effect. But PA still > 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.