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Respiratory Fysiology and Mechanical Ventilation

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Respiratory Fysiology and Mechanical Ventilation Respiratoire Insufficiëntie en Beademing Begrijp de fysiologie! Dr. Pieter Roel Tuinman, intensivist-epidemioloog; EDIC 1 voorbereiding 2019 met dank aan Leo (niet alleen) voor deel vd slides Causes of hypoxemia 1. Shunt 2. Hypoventilation 3. V/Q mismatch 4. Diffusion limitation 5. Low Svo2 6. Low Pbar or low Fio2 alveolar gas equation PAo2 = Fio2 (Pb-P,H2O) - (Paco2/RQ) Effect of O2 administration Causes of hypercapnia 1. Pump failure (reduced VE) • reduced drive • neuropathy • muscle weakness • mechanical disadvange 2. Dead space ventilation 3. Increased CO2 production Mechanical disadvantage excessive loads on the mechanical system • Mass of the respiratory system • Elastic loads (system is stiff) • Resistive loads R= L/radius⁴ Fig 1: O'Donell et al. COPD Research and Practice 2015: 1:4 Moving a lot of air • Increased CO2 production (fever: per 1 C 10% increase energy expenditure) • Acidosis • Dead space ventilation (fraction: Vd/Vt) https://pulmccm.org/ards-review/icu-physiology-1000-words- high-flow-oxygen-therapy/ Rapid shalow breathing they are going to fail Vt 1000 500 Vdana 150 150 Vdalv 300 300 Vtalv 550 50 https://pulmccm.org/ards-review/icu-physiology-1000-words- high-flow-oxygen-therapy/ Copyrights apply ETCO2 www.respironics.com ‘CADET face right’ Left shift Right shift ↓ PCO2 C: ↑PCO2 Alkalosis (↑ pH) A: Acidosis (↓pH) ↓ 2,3DPG D: ↑ 2,3DPG Hypothermia E: Exercise HbCO T: ↑ temperature Effects of PPMV on hemodynamics Cortes-Puentes et al. Ann Transl Med 2018;6(18):353 Effects of weaning on cardiac function Lemaire et al. Anesthesiology 1998 INDICATORS for SUCCESFUL DISCONTINUATON OF MV: • Respiratory rate <30 breaths per minute • Tidal volume >5 ml/kg or >325 mL • FVC >15 mL/kg predicts success • Minute ventilation <15 L/min • Maximum inspiratory pressure (PImax) < -30 cmH20 • Rapid shallow breathing index (RSBI) = f/VT <105 breaths/min/L • P0.1 x f/VT <300 • CROP index (dynamic compliance, respiratory rate, oxygenation, maximum inspiratory pressure index) >13 ARDS: Berlin Definition ARDS BASICS Guerin Intensive Care Med 2016 ARDS: Characteristics of pathophysiology 1. Dysregulated inflammation 2. Accumulation and activation of L and PLTs 3. Coagulopathy 4. Altered permeability of alveolar endo- and epithelial barriers “Baby lungs” not stiff but small vd Hoeven MMM 2018 Diagnostic work-up Standard of Care: Respiratory settings support of respiratory system: “minimize firstly, the mechanical power applied to the lungs and secondly, lung inhomogeneity” (Gattinoni). • PC or VC¹ • Tidal Volume: 4-6 mL/kg PBW² • Plateau Pressure <30 cm H2O • Respiratory Rate: 20-30/min • I:E ratio Keep it simple, keep it 1:2? • Higher PEEP to optimize oxygenation³ (vs overdistention) • Recruitment maneuvres³? ²PBW: Man: (lengte [cm] – 152) * 0.9 + 50 Vrouw: (lengte [cm] – 152) * 0.9 + 45 Prone positioning Guerin NEJM 2013; Gattinoni AJRCCM 2013 Who, when and how to prone? 1. Severe hypoxemia at entry (P/F <150) 2. < 48 hrs of meeting entry criteria 3. > 16 hrs/day RR 0.75-0.77 (±CI 0.60-0.0.99) Bloomfield Cochrane 2015 Contraindications for proning Bein ICM 2016 ARDS and TBI Frisvold et al. Intensive Care Med 2019 NMBs • P/F ratio < 150 and Pplat > 32 for 10 min • Early application • Effect through: - More gentle MV? - Antiinflammatory effects? Papazian NEJM 2014 Results are published after exam has been made Bein ICM 2016 Effects PEEP on respiratory mechanics Side effects of MV in ARDS Slutsky NEJM 2013 VILI Ventilation (and not ventilator) induced lung injury Slutsky NEJM 2013 Pes to determine Ppl Driving pressure Compliance of lungs • The compliance of the lungs demonstrate lung hysteresis; that is, the compliance is different on inspiration and expiration for identical volumes • ARDS/fibrosis lower compliance: indicates a stiff lung and means extra work is required to bring in a normal volume of air • Emphysema increase compliance: due to the poor elastic recoil. They have extreme difficulty exhaling air. In this condition extra work is required to get air out of the lungs Driving pressure & respiratory compliance ∆P best stratifies risk mortality ∆V CRS = ml / cmH2O ∆P Controlled ventilation TV ml = = cmH2O = driving pressure (∆P) CRS ml/cmH2O Driving Pressure ∆P= Pplat - PEEP Mortality PPlat PEEP ΔP rising same rising rising rising rising same same same rising falling falling Amato NEJM 2015 Risk of death versus driving pressure Bugedo et al. Crit Care (2017) 21:199 Is my patients respiratory drive (too) high? Telias et al Quantification of respiratory drive: P0.1 P0.1 intubated patients: P0.1 < 1.5 cmH2O: over-assist P0.1 > 3.5 cmH2O: under-assist Telias, ICM, 2018 ‘ Oxygenation is not the only treatment for hypoxemic ARF. The cause of ARF must be identified and cured, and then the respiratory state of the patient will be able to improve’ De Jong Intensive Care Med (2018) 44:2248–2250 Pathophysiologic effects of AECOPD Aaron. BMJ 2014;349:g5237 Treatment of AECOPD NIV in AECOPD Physiologic effects Effects on outcome • Decreased work of breathing • Reduced mortality • Decreased respiratory rate • Shorter hospital stay • Improved resp acidosis • Decreased need for intubation • Lower rates of VAP Factors associated with NIV failure HACOR score: Heart rate, Acidosis (pH), Consciousness (GCS), Oxygenation, Respiratory rate Duan et al Intensie Care Med (2017) 43:192-199 Controlled mechanical ventilation in AECOPD • Low respiratory rate • Alter I:E ratio (decrease to e.g. 1:5) • Air-dumping • What to do with PEEP? Guided by VEI? Ward et al. Crit Care Med 2008 Paradoxal Biphasic Overinflation Camarez et al. Crit Care Med 2008 Jul; 33(7): 1519-28 End inspiratory lung volume (Vei) Pulmonary embolism: risk stratification ESC Guideline 2014 Trach Esperanza ICM 2019 FRC Ward et al. Crit Care Med 2008; Vol 36. No 5 Na stoppen NMBs: wat gebeurt er? Succes Inhalation trauma Clinical signs of CO poisoning according to the level of COHb 3-0.7% None ⇓ blood flow to vital organs, angina by 2.5-5.0 exertion Headache, slight dyspnea, lethal to 10-20 fetus Nausea, headache +++, throbbing 20-30 temples, glushing, manual dexterity Severe headache, vertigo, nausea, 30-40 vomiting, weakness, irritability, impaired judgement, syncope Above but more severe, syncope, 40-50 collapse Coma, convulsions, Cheyne-Stockes 50-60 respiration Depressed respiration and cardiac 60-70 function, death possible 70-80 Generalised depression, death Diagnostic studies SpO2 unreliable: falsely high or normal Treatment Cyanide Pathophysiology Symptoms Treatment • Treatment for cyanide poisoning in the emergency setting should be given based on the clinical diagnosis only • The specific antidote hydroxycobalamin can be given I.V. with almost no side effects. (5 gr iv or 70 mg/kg; repeat when necessary) Succes Causes of hypocapnia • Hypoxemia • Metabolic acidosis • Mechanical abnormalities • Neurologic disorders • Voluntary due to psychological disturbance • Pregnancy Rapid shalow breathing they are going to fail Vt 1000 500 Vdana 150 150 Vdalv 300 300 Vtalv 550 50 https://pulmccm.org/ards-review/icu-physiology-1000-words- high-flow-oxygen-therapy/ Side effects of MV in ARDS.
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