1、DISEASE-ORIENTED VENTILATION STRATEGIESObjectives of Ventilation ACCP Standards (Slutsky, 1993)CLINICAL1. Reverse hypoxemia2. Reverse respiratory acidosis3. Relieve respiratory distress4. Prevent or reverse atelectasis5. Reverse respiratory muscle fatigue PRIMARYAvoid Iatrogenic Lung InjuryRespirato
2、ry Failure Pathology OBSTRUCTIVE (Resistance) Asthma Bronchitis Emphysema Smoke Inhalation Small ET tube RESTRICTIVE (Lung Compliance) ARDS Pneumonias CHF PneumothoraxNeuromuscularAbdominal distensionChestwall deformityDisease-Oriented Ventilation StrategiesObjective: To avoid the adverse effects of
3、 +ve pressure ventilation: barotrauma or volutrauma cardiovascular compromise other complications e.g. overventilation Tailor ventilator settings specific to the pathophysiology of the patient.Ventilator Settings And Hemodynamics Tidal Volume Inspiratory Pressure Respiratory Rate I:E Ratio PEEP Clos
4、ed Loop Modes PRVC, ASV, VAPSPathophysiological StatusHow Does Blood Return To The Heart ? Venous Valves Muscular Pump“Respiratory Pump”RESPIRATORY PUMPInspiration - thoracic cavityPressure - abdominal cavityPressure MECHANICAL BREATH DELIVERYPositive Pressure Breath DeliveryMechanical VentilationRE
5、VERSES ITIntrathoracic Pressure ?COPD/Asthma Asthma airway resistance1. bronchospasm2. airway edema3. secretions COPD terminal bronchiole collapse during expiration bronchospasm secretions (infection) Expiratory Time ConstantAir trapping & auto-PEEPHyperinflated lungsCXR - Hyperinflated LungsPatient
6、 with Airway ResistanceGas flow is greatest where resistance is low, hence overinflation of normal lung units. V/QPvCO2 = 46 mmHgPvO2 = 40 mmHgPaO2 = 70 mmHgPaCO2 = 45 mmHgPaCO2 = 43 mmHgPaO2 = 60 mmHgMarvin Mah MSc, RRT123456SEC120120V.LPMAuto PEEPWhat is it? How do you measure it?Air trapping and
7、auto-PEEPCardiovascular Compromisefrom Auto-PEEP Combination of: high filling pressures (PAP) reduced C.O. hypotension Mistaken for LEFT VENTRICULAR FAILURE Continued ventilation PEA and cardiac arrestMartens et al, 1993 (Lancet); Kollef, 1992 (Heart Lung); Myles et al, 1995 (Br J Anaesth); Lapinsky
8、 & Leung, 1996 (NEJM)Detecting Auto-PEEP1. Waveforms (Flow, Pressure, Volume)2. Expiratory pause on ventilator (passive patient)3. Diff. b/w pts RR and the ventilators response rate4. Esophageal balloon pressure5. Central venous pressure line6. Arterial pressure line7. Pulse oximetry (sometimes)Some
9、 cases are very obvious!Pressure Triggering with Auto-PEEP Patient efforts not recognized by the ventilator-20Paw (cm H20)Marvin Mah MSc, RRTDepiction of a patient experiencing no auto-PEEPTime (s)(L/min)123456V.120-120INSPEXHZero flow at end exhalation indicates equilibration of lung and circuit pr
10、essure, ie, no auto-PEEPFlow Waveform with Auto-PEEPMarvin Mah MSc, RRTDepiction of a patient experiencing auto-PEEP (flow will not move into the lung until PWYE PLUNG)123456V.(L/min)120-120INSPEXHTransition from exhalation to inspiration occurs before expiratory flow returns to zero, ie, auto-PEEP
11、existsTime (s)Flow Waveform with Auto-PEEPPulse Oximetry Waveform Depicting Auto-PEEPTreating Auto-PEEP Suction thick secretions, bronchodilator Tx I:E Ratio 1. RR = expiratory time 2. VT (Permissive Hypercapnia)3. Flow rates ? Add external PEEP to 80% of observed auto-PEEP McIntyre, 1997; Ranieri &
12、 Giuliani, 1993 Am Rev Respir Dis Flow Triggering to reduce triggering asynchronyExpiratory W.O.B. and auto-PEEP in the COPD PatientMJ Tobin. NEJM 2001; 344: 1986-96.PS and WOB during ExpirationPRESSUREEsens allows the clinician to adjust the ventilators onset of expiration to match the patients bre
13、athing pattern.FLOWPS overshoots targetEsens fixed 25%Esens adjusted to 50%NormalProblem resolved0100015Ventilator Settings for COPD/Asthma Pathophysiology airway resistance and expiratory time constants Ventilator Settings SIMV or CPAP + PS - better for spont. breathing pt. Low VT, Low RR longer Ex
14、piratory Time Permissive Hypercapnia Reduce patients WOB: PEEP auto-PEEP Flow TriggeringAcute Respiratory Distress SyndromeFu et al, J Appl Physiol 1992; 73:123-133Ranieri et al, JAMA 1999; 282:54-61Lung Stretch and BAL Cytokines in ARDS Patients0510152025303540TNF-alpha (ng/mL)controllow stressentr
15、y24 hrs36 hrs Patient groups: VT for PaCO2 35-40 mm Hg PEEP to optimize SaO2 with lowest FIO2 (11 mL/Kg; 6.5 cm H2O) PV curve; Pplat lower Pflex (7.5 mL/Kg; 15 cm H2O) BAL for cytokinesMECHANICAL VENTILATIONBiochemicalBiophysical Injury - Shear - Overdistension - Intrathoracic Pressure- Alveolar-Cap
16、illary Permeability - Cardiac Output - Organ PerfusionDistal Organs - Tissue injury 2 to inflammatory mediators/cells - Impaired oxygen delivery - BacteremiaNeutrophilsCytokines, Proteases, Singlet O-, ComplementM MSOF (Slutsky & Tremblay, 1998)BacteriaMarvin Mah MSc, RRTEffect of a protective-venti
17、lation strategy on mortality in the acute respiratory distress syndromeAmato et al, 1998 N Engl J Med 53 Patients with early ARDS Randomly assigned to either Conventional or Protective ventilation strategy All patients were treated with identical hemodynamic and general support. Conventional Ventila
18、tion Protective-ventilation strategyVt 12ml/kg 1:1?Prevention of Ventilator-Associated Lung Injury Treat underlying disease Limit FIO2 to lowest acceptable level PEEP high enough; Pplat not too high Permissive hypercapnia Pressure control ventilation Prone positioning Recruitment maneuver Inhaled ni
19、tric oxide Partial liquid ventilation Tracheal gas insufflation Extracorporeal CO2 elimination Surfactant replacement High frequency oscillationOptimize PEEP using P-V Curve The greatest resistance occurs at the lowest lung volume (i.e. the distending pressure) Atelectasis may occur in this situatio
20、n, creating airway collapse at end exhalationLung Recruitment Maneuver Prolonged high alveolar pressure to recruit collapsed lung units Method used at Massachusett General Hospital, BostonPEEP 30 - 40 cm H2O PC of 20 cm H2O, Rate 10/min; I:E 1:11/2 - 2 min PEEP to maintain recruitmentRecruitment Man
21、euver 32 yr old woman transferred with severe ARDS secondary to streptococcal sepsis: BP 50/30; pH 7.00, PaCO2 78, PaO2 21; PC 34 (VT 300), PEEP 15, FIO2 1.0, rate 20 Recruitment maneuver: PEEP 40, PC 20, rate 10, I:E 1:1 for 2 min Dramatic improvement in PaO2 and tidal volume PEEP 25 cm H2O needed
22、to maintain recruitment Extubated 6 days after arrival; discharged after 2 weeksMedoff et al, Crit Care Med 2000 (April)Lapinsky, Intensive Care Med 1999; 25:1297-1301Marvin Mah MSc, RRTILVWhat About New Modes?What Is BILEVEL? Intermittent CPAP (Dr. John Downs, 1987)CPAP (cm H2O)Time02010Marvin Mah
23、MSc, RRT44BiLevel Ventilation (Normal I:E Ratios)By setting PEEPH , TH, and respiratory rate close to the patients typical ventilation settings, BiLevel looks similar to PCV/SIMVThis capability has been commonly referred to as BIPAP in EuropeSynchronized TransitionsSpontaneous BreathsPPressure Suppo
24、rtPLPHTMarvin Mah MSc, RRT45What Is APRV? APRV - Airway Pressure Release Ventilation utilizes a very short Exp. time for Pressure Release short time release time allows for CO2 removal All spontaneous breathing at upper pressure levelSpontaneous BreathsPT“Release” Auto-Flow, PRVC, VAPS and ASV Benef
25、its patients who require a target volume, but have variable flow demands and changing lung compliance helps to avoid barotrauma, IF Pressure Limit setting set correctly by staff 840/760 Smart Rise Time is automatic - maintains constant airway pressure despite changes in airway resistance or complian
26、ce Major Problem Feedback loop used in S300, Evita-4 and Galileo can under support ventilation needs of the patient in some clinical conditions. e.g. acidosis, fever, distress, etc. American Thoracic Society Conference 2000, Toronto - Dr. BrochardHigh Press LimitTidal Volume (reference centre)Tidal
27、Volume (exhaled)Dependent on CL and RawPi Delivered to patientClosed Loop Feedback System Does not think!Marvin Mah MSc, RRTStudy on WOB in High Demand Patients using VC, PCV and AutoFlowResults : PCV was most effective in decreasing WOB in patients with high Vt demand“At high Vt demand, AF is super
28、ior to volume ventilation at reducing WOB but not as effective as PC. In critically ill patients, the decrease in flow and mean airway pressure as demand rose could result in a significant loss of mean airway pressure and elevated WOB. The inability of AF to differentiate between actual improvements
29、 in dynamic compliance illustrates a potential limitation of closed loop ventilation.”Crit Care Med 1999 Vol. 27, No. 1Marvin Mah MSc, RRTSummary“The ventilator mode should be set to the clinical requirement and the settings adjusted to match the specific pathophysiology of the patient.” (ACCP Guidelines, 1994)
