复旦大学：《内科学 Internal Medicine MBBS》课程教学资源（课件讲稿）呼吸系统_Respiratory failure

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