Respiratory failure Yuanlin Song, MD
Yuanlin Song, M.D. Respiratory failure
Definition and classification 1. Definition Failure of gas exchange due to inadequate function of respiratory system 2. Classification Hypoxemia: lung edema, low FIO2, lung fibrosis Hypercarbia: excess of CO2 production Combination of hypoxemia and hypercarbia: COPD Type L, Il, Ill, IV respiratory failure
Definition and classification 1. Definition: Failure of gas exchange due to inadequate function of respiratory system 2. Classification Hypoxemia: lung edema, low FIO2, lung fibrosis Hypercarbia: excess of CO2 production Combination of hypoxemia and hypercarbia: COPD Type I, II, III, IV respiratory failure
Lung physiology Brain-stem 1. Controller: rhythm 2. Muscle: strong 3. Airway: patent 4. Alveolar: dry 5. Vasculature: intact BSec dl vati aton 2 Efec of Pacm haemoglobin on veat at CO2 normal haemoglobin Paco, erm Hg)
Lung physiology Brain-stem 1. Controller: rhythm 2. Muscle: strong 3. Airway: patent 4. Alveolar: dry 5. Vasculature: intact O2 CO2
Lung function test ERV FRC RV
Compliance (c) Static compliance measured in absence of flow o C=AV/AP= 1/E where e=elastance, V=volume, P=pressure =AV/(Pairspace-Ppleura) Pleura esophageal total=AV/(Pairspace-Patmospheric) total chest wall Etotal= Elmg Chest wall COPD, asthma 3100 normal Pulm Fibrosis. fibrothorax Pressure
C=ΔV/ΔP = 1/E where E=elastance,V=volume, P=pressure Clung = ΔV/(Pairspace –Ppleura), Ppleura = Pesophageal Ctotal = ΔV/(Pairspace-Patmospheric) . Ctotal Clung Cchest wall 1 1 1 Etotal Elung Echest wall % Predicted Volume Pressure 100 0 normal COPD, asthma Pulm. Fibrosis, fibrothorax Static compliance measured in absence of flow
Compliance Calculations C-42 High Compliance /目 △ 2000mL Low Compliance 100ml/cm △(Pmg-Pan)20cm-0cm △ 2000mL ngs△(Pngs-pena (20cm-5cm)-(0cm-(-5)cm) Pressure(cmH2O) 200 ml/cm cm cm resp +0cm +20c +0cm 100200200 2 liters 4 liters
+20 cm + 0 cm -5 cm + 0 cm +5 cm 2 liters 4 liters P V C mL cm cm cm mL P P V C lungs air lungs resp 100 / 2 0 0 2000 ( ) mL cm cm cm cm cm mL P P V C lungs pleura lungs lungs 200 / [ (20 5 ) (0 ( 5) ) ] 2000 ( ) Cresp Clungs Cchest wall 1 1 1 200 1 200 1 100 1 Pressure (cmH2O) Volume (mL ) Low Compliance High Compliance Compliance Calculations
Resistance(R) and Time Constant(t) Resistance measured in presence of flow o R=AP/F where f= flou elastic z=RxC⊥△P△FCmH2O sec F△Pml/ sec cmh2O Where t= time constant tiime it takes for 64% of volume to be exhaled. normally r-2cmh2o per ml of air per sec and c=0.1 liter/ cmH2O so that t=2 sec. About 4t(0. 8 sec) needed for complete expiration Assumption: single unit emptying Endotracheal tubes and inhomgeneous ventilation can greatly slow emptying- multiple compartments. Anything which increases R or C increases exhalation time(both occur in obstructive lung disea
R = ΔP/F where F = flow PLung = Presistance + Pelastic Where τ = time constant tiime it takes for 64% of volume to be exhaled. Normally R=2cmH2O per ml of air per sec and C= 0.1 liter/cmH2O so that τ = .2 sec. About 4 τ (0.8 sec) needed for complete expiration. Assumption: single unit emptying. Endotracheal tubes and inhomgeneous ventilation can greatly slow emptying – multiple compartments. Anything which increases R or C increases exhalation time (both occur in obstructive lung disease.) sec /sec 2 2 cmH O ml ml cmH O P V F P R C Resistance measured in presence of flow
Blood gas analysis o Normal blood gas: pH 7.4, 0285, CO2 40, HC○325 o Respiratory acidosis: pH 7.3, CO2 80, O2 58 HC○330 ◇ Respiratory alkalosis:pH7.48,○286,CO2 30,HC○320 o Metabolic acidosis: pH 7. 2, HCO3 8, CO2 38,0280 o Metabolic alkalosis: pH 7.56, CO2 45, O2 68,HCO335
Normal blood gas: pH 7.4, O2 85, CO2 40, HCO3 25 Respiratory acidosis: pH 7.3, CO2 80, O2 58, HCO3 30 Respiratory alkalosis: pH 7.48, O2 86, CO2 30, HCO3 20 Metabolic acidosis: pH 7.2, HCO3 8, CO2 38, O2 80 Metabolic alkalosis: pH 7.56, CO2 45, O2 68, HCO3 35
Respiratory rhythm control-nerve system RESPIRATORY CENTRES Inla lUkic apneustic area expiratory cen Itre inspirator centre expiate muscles to inspirator museles
Respiratory rhythm control-nerve system
Muscle contraction and relaxation Ramdagram Nose Trachea Resp System Ps=Pa·Pbs 0 Diaphragm Intercostals muscle. external internal intercostals muscle Accessory muscle: sternocleidomastoid, scalene muscle
Muscle contraction and relaxation Diaphragm Intercostals muscle: external, internal intercostals muscle Accessory muscle: stenocleidomastoid, scalene muscle
