How to prevent volutrauma during anaesthesia ? New insights in the bloodblood-gas barrier of the lung. J P Mulier MD PhD az St Jan av Brugge Belgium JPMulier volutrauma Prague 19 02 2010 1 VILI: An aspect of Safety in anesthesia ventilation? • How to prevent volutrauma during anaesthesia ? New insights in the bloodblood-gas barrier of the lung. – J P Mulier MD PhD – az St Jan av Brugge Belgium JPMulier volutrauma Prague 19 02 2010 2 When disasters take place • Why waiting for a disasters before action? • Regulations and checklists are never 100% safe. • Why not using automatic safety issues? JPMulier volutrauma Prague 19 02 2010 3 History Lung trauma caused by mechanical ventilation • Past baro trauma: • high airway pressure rupture the alveolus to the pleura. • Since 1992 focus on volutrauma: • large tidal volume and not high airway pressure gives lung damage. – “Dreyfuss 1992 barotrauma is volutrauma but which volume is the responsible one?” • Mechanical Ventilation is Bio trauma and gives multimultiorgan failure: • release of mediators in the lung circulation due to lung damage affecting other organs. – Slusky ventilatorventilator-induced lung injury: from barotrauma to biotrauma. • What is pathophysiology of volutrauma? • Pulmonary capillary wall stress increases with rupture of alveolar, endothelial or basal membrane. – West J B Thoughts on the pulmonary bloodblood-gas barrier. Am J Physiol Lung Cell Mol Physiol. 2003 Sep;285(3):L501Sep;285(3):L501-13. JPMulier volutrauma Prague 19 02 2010 4 Old view: Alveolar anatomy • One alveolus or a group of alveoli behaves as an individual balloon. JPMulier volutrauma Prague 19 02 2010 5 Old Physiologic view of the alveolus • Alveolus = balloon • Laplace law P=T/R P = T/R P/2 = T/2R • Unequal balloon size gives collaps of smallest • • alveoli. Surfactant must change wall tension with a factor 2 when radius halves. Disruption of an alveolar wall always gives a pneumothorax. Impossible conclusions! JPMulier volutrauma Prague 19 02 2010 6 Real alveolar anatomy • Alveolus is part of one larger structure – The lung is not an agglomerate of independent balloons. – The lung is one structure and no alveolus has an independent wall. JPMulier volutrauma Prague 19 02 2010 7 Artist impression of alveolus at draeger • High airway pressure does not increase • • transmural pressure. Other side has same pressure. Rupture or pneumothorax is not possible. if alveolar wall between alveoli would rupture it gives no problems as the wall is full of holes. Surfactant needed only to lower wall tension of all alveoli. • Why is volutrauma dangerous? JPMulier volutrauma Prague 19 02 2010 8 Microscopic view of the alveolar wall capillary rupture and not alveolar is dangerous • • • • Small capillaries in the alveolar wall. Wall is very thin at these locations. Lungtrauma gives edema, protein and blood loss When or why will a capillary bursts???. JPMulier volutrauma Prague 19 02 2010 9 Electron Microscopy of the alveolar wall • Thinnest wall at – Capillary – alveoli: JPMulier volutrauma Prague 19 02 2010 10 Lung trauma = Capillary wall rupture • When do we have rupture? • Pathophysiology of the pulm capillary • High cardiac output gives high pulm cap pressure and creates lung edema, lung bleeding – Sport horse racing, running sport – High altitude edema – Extreme sport conditions = high cardiac output JPMulier volutrauma Prague 19 02 2010 11 Very high wall stress in pulmonary capillaries • R: 3,6 um • Thickness: 0,34 um • P: 52,5 cmH20 340 nm T 5,5 N m2 • T: Wall stress approaches the ultimate tensile strength of collagen. P 52,5 cmH20 • these extremely high values have not previously been recognized: • misled by the small radius of the capillary, which reduces circumferential tension . ( 25 dynes/cm [25 mN/m]) • the extreme thinness of the wall, which follows directly from the gas exchange function of the blood--gas barrier was overlooked. blood •J West 1991 JPMulier volutrauma Prague 19 02 2010 12 Strength of the Capillary Wall • the capillary endothelial layer, the alveolar epithelial layer, and the extra cellular matrix (ECM) = the fused basement membranes • the ECM ( type IV collagen ) has a central lamina densa with a lamina rara on either side • the great strength of the thin part of the bloodblood-gas barrier comes from an extremely thin layer of type IV collagen ( 50 nm thick) • 50 nm gives 38 Nm2 J West 1992 JPMulier volutrauma Prague 19 02 2010 13 Dilemma of the BloodBlood-Gas Barrier • Efficient gas exchange needs an extremely thin blood blood--gas barrier. – it cannot be any thicker because human athletes show diffusion limitation. J West 2003 – This is also true of thoroughbred racehorses. Fu 1992 – The extreme thinness of the barrier confers a survival advantage. • Blood Blood--gas barrier must be immensely strong because it forms the walls of the pulmonary capillaries, and the stresses become extremely high when the capillary pressure rises. – the barrier has evolved to be as thin as possible for maximum efficiency of gas exchange but to have just enough strength to maintain its integrity under the most challenging normal physiological conditions. – it is possible that the amount of type IV collagen in the capillary wall is continuously being regulated, possibly by the level of pressure within the capillary, and this explains why the extra cellular matrix increases in disease such as mitral stenosis when the capillary pressure is raised. – if the capillary transmural pressure rises to unphysiologically high levels, or wall stress is greatly increased by over inflation, or the wall is weakened by disease, alveolar edema, or hemorrhage, or both are inevitable. JPMulier volutrauma Prague 19 02 2010 14 Changes in Pulmonary Capillaries at High Pressures • a, Capillary endothelium is disrupted (arrow), but the alveolar epithelium and • • • the basement membranes are intact. b, Alveolar epithelial layer (right) and capillary endothelial layer (left) are disrupted. c, Disruption of all layers of the capillary wall, with a red cell apparently passing through the opening. d, Scanning electron micrograph showing breaks in the alveolar epithelium. J West 2003 JPMulier volutrauma Prague 19 02 2010 15 What determines acute changes in the Pulmonary Capillary Pressure ? •The pressure drop in the pulmonary circulation occurred in the capillary bed, so in upstream capillaries the pressure is close to pulmonary artery pressure. •Pulmonary artery pressure is dependent on •Cardiac output •Stimulated by intropes, high filling and exercise •Left atrial filling pressures and left ventricular filling pressures •Mitral stenosis and aortic or mitral regurgitation •Left ventricular failure, ventricular hypertrophy and ischemia •Capillary position relative to the heart. JPMulier volutrauma Prague 19 02 2010 16 Why is hyperinflation damaging the capillary wall? • Why is hyperinflation damaging the capillary wall? • Is volutrauma possible without pulmonary hypertension? • Is peep or high airway pressure not protecting against high capillary pressure? • Is peep not dropping the CO JPMulier volutrauma Prague 19 02 2010 17 Three forces act on the bloodblood-gas barrier •Pres cap •Tens tmp •Pres alv •Tens el •Vol alv •Tens st – Ttmp is the circumferential or hoop tension caused by the capillary transmural pressure. – Tel is the longitudinal tension in the alveolar wall elements associated with lung inflation; this is transmitted to capillary membrane. – Tst is the surface tension of the alveolar lining layer; It exerts an inward--acting force to support the capillary when the latter inward bulges into the alveolar space. J West 2003 JPMulier volutrauma Prague 19 02 2010 18 Hyperinflation increases wall stress • Capillary is flattened through increased alveolar stretching • Radius of ellips x 10 in flat part -> T x 10 • With normal capillary pressure capillary wall ruptures • Fu West 1992 JPMulier volutrauma Prague 19 02 2010 19 Some animals are protected against hyperinflation • Birds • Mammalians JPMulier volutrauma Prague 19 02 2010 20 Research studies • Overinflation of the Lung increases the permeability of pulmonary capillaries – Respiratory failure treated with high levels of positive end--expiratory pressure gives edema. Dreyfuss DAm end Rev Respir Dis. 1985;132:880 1985;132:880--884. – High lung volume rather than the increased alveolar pressure gives the increased permeability. Hernandez LA. J Appl Physiol. 1989;66:2364 1989;66:2364--2368. – If we increase lung volume while maintaining a constant capillary transmural pressure, the number of both endothelial and epithelial breaks is greatly increased. Fu Z. J Appl Physiol. 1992;73:123 1992;73:123--133. JPMulier volutrauma Prague 19 02 2010 21 lung trauma • Each time the epithelial layers disrupt – The basal membrane is stretched – The basal membrane exposes to • Blood (vascular endothelia) • Air (alveolar endothelia) – Spontaneous recovery exists • Each time the basal membrane disrupts – Leak of blood into the alveoli: red sputum – Connection between two alveoli, no problem – Connection between alveoli and interpleural space: bulla and possible pneumothorax JPMulier volutrauma Prague 19 02 2010 22 Clinical conditions at risk: • Large tidal volume ventilation • High peep • Long bagsqeezing to open lungs – No problem for collapsed lung but dramatic in healthy lung • Accidental over inflation: – no manual ventilation with semisemi-closed pop valve – Inflation over max lung vol • Pressure above normal ventilation pressure – Occluded expiratory tubing or valve JPMulier volutrauma Prague 19 02 2010 23 Most common accident is however a human error • Manual system is outside electronic ventilator and less protected • Forgetting to switch from manual to mechanical ventilation might happen – with a closed APL valve – with a high fresh gas flow • Most of the time not reported ! JPMulier volutrauma Prague 19 02 2010 24 Manual system • Manual system is outside electronic ventilator – Anesthetists prefer a pure mechanical system, capable of giving high pressures and large volumes – only recently some alarms in Ohmeda, not in Drager • Anesthesia Induction – high fresh gas flow: 15 liter or more – APL valve closed: different types – Manual breathing bag • Airway pressure rises very fast • Airway pressure monitor – High pressure alarm – Apnoe alarm – High peep alarm • But if anesthetist does not react immediately, risk for volutrauma exists • The APL valve, a large manual balloon with a high compliance protects against Prague 19 02 2010 high airway pressuresJPMulier but notvolutrauma against volutrauma. 25 APL // Man – Mech switch • APL (adjusted pressure limiting valve) valve • Mechanical switch • Electronic switch (older ventilators separated) JPMulier volutrauma Prague 19 02 2010 26 Human risk • the anesthetist assumes that he did start the correct mode while the ventilator did not and remained in the manual mode. – Verify ventilation mode • two anesthetist: one connects the end tracheal tube to the ventilator, assuming that the other starts the correct ventilation mode – The person who connects the tube always starts the ventilator • after a difficult intubation or other distracting event, the anesthetist finally relaxed, forget to change the ventilation mode – Set the mobile phone off – Stay alert, even when tube is finally in • Drapes over the ventilator, anesthetist staying between patient and ventilator, surgical procedures on the head requiring to turn the ventilator in opposite direction makes the ventilator invisible for the anesthetist. – Have a separate induction room? But risk doubles? – Request the place and position needed for the anesthetist JPMulier volutrauma Prague 19 02 2010 27 How frequently happens this type of human error ? • 90 % of all anesthetist know a case in their • hospital of this type of human error. 50 % of all anesthetist tell that at least one case a year happens in their hospital. – Most of the time no barotrauma and therefore not registered. • Low blood pressure no time to measure • Lung edema white lungs ? • We are all afraid that it might happen with us • We all assume that it is not traumatic ! JPMulier volutrauma Prague 19 02 2010 28 Definition of dangerous • A ventilation mode is considered to be at risk if the airway pressure stayed above 30 cmH20 for more than 5 seconds and dangerous if no alarm did go off in that time. • A ventilator is considered to be dangerous if a dangerous ventilation mode could take place. JPMulier volutrauma Prague 19 02 2010 29 Aestiva 5 DatexDatex-Ohmeda pressure time relation in aestiva 5 balloon pressure in cmH2O 50 40 30 mode 1 mode2 20 mode 3 10 0 -10 0 5 10 15 20 25 30 JPMulier volutrauma Prague 19 02 2010 time in seconds 35 40 30 Juliana Dräger pressure time relation in Juliana balloon pressure in cmH2O 60 50 40 mode 1 mode2 30 mode 3 20 10 0 -10 0 5 10 15 20 25 30 time in seconds JPMulier volutrauma Prague 19 02 2010 35 40 31 Comparison of different ventilators 1 ventilator APL valve alarm first alarm after excel 210SE 30 30 high pressure excel 210SE 75 30 high pressure 1 s At risk excel 210SE 75 100 sustained pressure 17 s dangerous excel 410 30 30 sustained pressure 15 s excel 410 75 30 high pressure 3 s At risk excel 410 75 100 sustained pressure 18 s dangerous datex as3 30 30 high pressure datex as3 80 30 high pressure 1 s At risk datex as3 80 80 high peep 5 s At risk aestiva5 30 30 apnoe aestiva5 70 30 high pressure 2 s At risk aestiva5 70 99 apnoe 9 s dangerous JPMulier volutrauma Prague 19 02 2010 risk 32 Comparison of different ventilators 2 drager AV1 30 30 high pressure drager AV1 106 30 high pressure 1 s drager AV1 106 133 titus 30 30 titus 70 30 titus 70 99 cato 30 30 cato 70 30 cato 70 98 julian 30 30 julian 70 30 julian 70 98 At risk dangerous high pressure 1 s At risk dangerous high pressure 1 s At risk dangerous high pressure 1 s JPMulier volutrauma Prague 19 02 2010 At risk dangerous 33 2 and 3 liter breathing bags • US EUR old rubber JPMulier volutrauma Prague 19 02 2010 34 Compliance of breathing bags 100 35 cmH20 60 cmH2O 2L USlatex free 2 L EURlatexfree 3 L EURlatex free 2 L black rubber 3 L black rubber cmH2O 80 60 40 20 0 0 5 10 15 liter JPMulier volutrauma Prague 19 02 2010 35 ANSI standard for anesthetic equipment--reservoir bags Z79.4 1983 equipment • Bag with volume greater than 1,5 l should – not exceed a pressure of 35 cmH2O when at 2 times its volume – not exceed a pressure of 60 cmH2O when at 6 times its volume • 2 l EUR latex free at 2 x is 51 cmH20 • 3 l EUR latex free at 2 x is 45 cmH20 • 2 L US latex free at 2 x is 29 cmH20 – European anesthetic equipment does not comply with the ansi standard of USA! JPMulier volutrauma Prague 19 02 2010 36 How to choose a breathing bag? • Never old black rubber balloons • Use the largest possible balloon – 2 liter or more • Pediatric balloon with fingertip hole – Contamination of room air • not available anymore! • Consider US type of balloons – No volutrauma protection! • Use VSV protection system JPMulier volutrauma Prague 19 02 2010 37 JPMulier volutrauma Prague 19 02 2010 38 Specifications of VSV 3 (safety frog) • Alarm and valve open when: – > 75 cmH2O – > 20 CMH2O and >6 seconds • VSV off – Variation less than 2 cmH2O and >60 seconds • VSV on – > 10 cmH2O JPMulier volutrauma Prague 19 02 2010 39 VSV 3 or safety frog effect 50 cmH2O 40 Euro 2l breathing bag Euro 2l breathing bag with VSV USA 2l breathing bag USA 2l breathing bag with VSV 30 20 10 0 0 10 20 30 40 50 seconds JPMulier volutrauma Prague 19 02 2010 40 How to use VSV (safety frog) ? • Connect VSV always in inspiratory limb of breathing circuit – Inspiratory limb protects manual and automatic modes – Manual bag position protects only manual mode – Expiratory limb position does not solve risk for tubing occlusion • No need to switch on or off – Switches on automatically when pressure rises during normal ventilation – Switches off when pressure stay zero longer than 1 minute • Never have to worry about VSV function – VSV is constant active during manual and mechanical ventilation without interference • VSV is working and protecting when you need it • VSV is warning you with an alarm each time it opens the airway and protects the patient JPMulier volutrauma Prague 19 02 2010 41 Also useful when technical error • APL valve closed or blocked during spontaneous ventilation • Not starting ventilator due to ventilator failure or human error • Blocked expiratory valve • Defect peep valve ( higher or occlusion) • Occluded expiratory tubing – Accident in univ Zurich (Markus Weiss) – No alarm is going off in Ohmeda ventilator ! JPMulier volutrauma Prague 19 02 2010 42 Safety frog • Is produced Medec nv Benelux • Prize of PGA New York for best anesthesiology invention • Prize of Bizidee for best product idea JPMulier volutrauma Prague 19 02 2010 43 Insufficient research on volutrauma • How to evaluate clinical damage ? • Are only excessive volumes dangerous ? • Should we limit tidal volumes ? • Is pulmonary pressure important ? • Is increasing cardiac output while lowering ventilation volume safer ? • Is Recovery of epithelial damage possible JPMulier volutrauma Prague 19 02 2010 44 Effect of 40 cmH20 during 4 x 30 seconds in rats preliminary data JPMulier 2008 JPMulier volutrauma Prague 19 02 2010 45 Effect of 40 cmH20 during 4 x 30 seconds in rats preliminary data JPMulier 2008 Burkitt chamber count of BAL • Without safety frog 11 RBC With safety frog 0 RBC JPMulier volutrauma Prague 19 02 2010 46 Effect of 40 cmH20 during 4 x 30 seconds in rats preliminary data JPMulier 2008 total number of erythrocytes in BAL per ml 5.000.000 4.500.000 4.000.000 3.500.000 3.000.000 2.500.000 2.000.000 1.500.000 1.000.000 500.000 0 no safety frog with safety frog JPMulier volutrauma Prague 19 02 2010 47 Conclusion:What to do during anesthesia • Prevent global hyperinflation or volutrauma – Reduce tidal volume, increase frequency Allow mild hypercapnia – No high peep. Allow mild hypoxia? – Use safety frog to prevent ventilator and human error • Prevent local hyperinflation – keep lung open, use low peep – Short time of bag sqeezing and look to lung during thoracotomy • Volume controlled mode is safer than Pressure controlled mode • Good volume alarms • Direct supervision • No change in lung compliance by surgery, position,.. • Use assist ventilation, it is more physiologic, but today still dangerous for hyperinflation – Better to use volume assist mode JPMulier volutrauma Prague 19 02 2010 48 ? JPMulier volutrauma Prague 19 02 2010 49 Obese patients are a challenge Our new abdominal model facilitates laparoscopy and prevents volutrauma JPMulier volutrauma Prague 19 02 2010 50 Effect of VSV 2 on ventilation • Interference only at freq of 4 breaths per minute ventilation of non elastic test lung C 11 ml/cmH2O high R 60 cmH2O 50 40 12x 1/2 VSV on 30 6x 1/1 VSVon 20 4x 1/1 VSV on 4x 1/1 VSV off 10 0 0,00 10,00 20,00 time in sec 30,00 JPMulier volutrauma Prague 19 02 2010 40,00 51 Prevent unequal alveolar distension • Try spontaneous ventilation whenever possible. • Use assist ventilation if tidal volume is to small – due to morphine, muscle relaxants, deep anesthesia or high work of breathing. • Use mechanical ventilation only if frequency is too low. Prevent volutrauma. – High frequency, small tidal volume and low peep? • Dead volume increases ! • Risk of atelectasis ! and hyperinflation of upper lung ! – Keep lung open with lowest peep possible ! – If airway pressure is high be alert ! – No recruitment maneuver: everyone does it although everyone find it dangerous and useless. JPMulier volutrauma Prague 19 02 2010 52 Prevent alveolar distension • Pressure controlled is more dangerous than volume • controlled ! Prevent hyperinflation – Lowest peep necessarily – Never forget to switch from manual to mechanical ventilation • Use safety frog to protect lung • No large tidal volumes – Accept hypercapnia, accept hypoxia ? • High Airway pressure does not mean high alveolar pressure. – Airway, tubing resistance • Danger of peep and long inspiratory times • High alveolar pressure does not mean distension of alveoli. – Thorax compliance and lung compliance • Danger in healthy lungs, thorax and in children JPMulier volutrauma Prague 19 02 2010 53 Clinical conditions . • Increased pulmonary capillary pressure causes – a highhigh-permeability type of pulmonary edema • Neurogenic Pulmonary Edema – "sympathetic storm" raises pulmonary vascular pressures intense peripheral vasoconstriction, which shifts blood to the thorax; acute left ventricular failure caused by overwhelming systemic hypertension; and reduced compliance of the left ventricle, necessitating very high filling pressures. Minnear FL J Appl Physiol. 1987;63:335 1987;63:335--341. • HAPE (High (High altitude pulmonary edema) – hypoxic pulmonary vasoconstriction is uneven, with the result that those capillaries not protected by arterial constriction are exposed to a high pressure given the high cardiac output. West JB. Eur Respir J. 1995;8:523 1995;8:523--529 • ARDS – when ARDS follows trauma, a large release of catecholamines gives a transient increase in pulmonary vascular pressures combined with high peep ventilation leading to stress failure of pulmonary capillaries. Bachofen M American Physiological Society; 1979:2411979:241-252. JPMulier volutrauma Prague 19 02 2010 54 World Health Organization diagnostic classification of pulmonary hypertension • 1 Pulmonary arterial hypertension – 1.1 Primary pulmonary hypertension(a) Sporadic(b) Familial – 1.2 Related to:(a) Collagen vascular disease(b) Congenital systemicsystemic-to to--pulmonary shunts(c) Portal hypertension(d) HIV infection(e) Drugs/toxins(1) Anorexigens(2) Other(f) Persistent pulmonary hypertension of the newborn(g) • 2 Pulmonary venous hypertension – 2.1 Left Left--sided atrial or ventricular heart disease – 2.2 Left Left--sided valvular heart disease – 2.3 Extrinsic compression of central pulmonary veins(a) Fibrosing mediastinitis(b) Adenopathy/tumours – 2.4 Pulmonary venoveno-occlusive disease • 3 Pulmonary hypertension associated with disorders of the respiratory systemand/or hypoxaemia – – – – 3.1 3.3 3.5 3.7 Chronic obstructive pulmonary disease 3.2 Interstitial lung disease Sleep disordered breathing 3.4 Alveolar hypoventilation disorders Chronic exposure to high altitude 3.6 Neonatal lung disease Alveolar–capillary dysplasia Alveolar– • 4 Pulmonary hypertension due to chronic thrombotic and/or embolic disease – 4.1 Thromboembolic obstruction of proximal pulmonary arteries – 4.2 Obstruction of distal pulmonary arteries(a) Pulmonary embolism (thrombus, tumour, etc.)(b) In situ thrombosis(c) Sickle cell disease • 5 Pulmonary hypertension due to disorders affecting the pulmonary vasculaturedirectly – 5.1 Inflammatory(a) Schistosomiasis(b) JPMulier volutraumaSarcoidosis(c) Prague 19 02 2010 – 5.2 Pulmonary capillary haemangiomatosis 55 Clinical conditions .. – alveolar hemorrhage • Exercise Exercise--Induced Pulmonary Hemorrhage – ExerciseExercise-induced pulmonary hemorrhage (EIPH) in racehorses is the most dramatic example of such a condition West JB, J Appl Physiol. 1993;75:1097--1109 1993;75:1097 • Catastrophic Increase in Pulmonary Venous Pressure – Occasionally, a catastrophic event such as rupture of the chordae tendineae or a papillary muscle of the mitral valve causes alveolar hemorrhage. Alveolar bleeding has also been described in patients with very high left atrial pressures who are awaiting cardiac transplantation. • Bleeding in Elite Human Athletes – anecdotal accounts of hemoptysis after extreme exercise West JB. Am Rev Respir Dis. 1991;143:A569. – a combination of edema and hemorrhage • Chronic Venous Hypertension – mitral stenosis where hemoptysis occurs in approximately one half of patients and the lungs contain large amounts of hemosiderin, alveolar type II cells replace type I cells that were damaged Kay JM. J Pathol. 1973;111:239--245 Wood P. Br Med J. 1954;1:1051 1973;111:239 1954;1:1051--1063, 11131113-1124 • Hemorrhagic Pulmonary Edema in Elite Athletes – prolonged intense exercise ex running the 9090-km Comrade's Marathon in South Africa (McKechnie JK S Afr Med J. 1979;56:261 1979;56:261--265) JPMulier volutrauma Prague 19 02 2010 56
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