MECHANICAL VENTILATION.ppt

1、MECHANICAL VENTILATION,Mechanical Ventilation,Indications for Intubation and Ventilation Principles of Mechanical Ventilation Patterns of Assisted Ventilation Ventilator Dependence: Complications Liberation from Mechanical Ventilation: Weaning Troubleshooting Arterial Blood Gases,Indications for Mec

2、hanical Ventilation,“.An opening must be attempted in the trunk of the trachea, into which a tube or cane should be put; You will then blow into this so that lung may rise again.And the heart becomes strong.” -Andreas Vesalius (1555),Indications for Mechanical Ventilation,1. “Thinking” of Intubation

3、: elective v/s emergent 2. “Act of weakness?” 3. Endotracheal tubes are not a disease and ventilators are not an addiction 4. And the usual elective and emergent indications that you all know!,Objectives of Mechanical Ventilation,Improve pulmonary gas exchange Reverse hypoxemia and Relieve acute res

4、piratory acidosis Relieve respiratory Distress Decrease oxygen cost of breathing and reverse respiratory muscle fatigue Alter pressure-volume relations Prevent and reverse atelectasis Improve Compliance Prevent further injury Permit lung and airway healing Avoid complications,Strategies for Mechanic

5、al Ventilation,Monitoring Lung Mechanics,Proximal Airway Pressures (end-inspiratory) 1. Peak Pressure Pk Function of: Inflation volume, recoil force of lungs and chest wall, airway resistance 2. Plateau Pressure Pl Occlude expiratory tubing at end-inspiration Function of elastance alone,Use of Airwa

6、y Pressures,Pk increased Pl unchanged: Tracheal tube obstruction Airway obstruction from secretions Acute bronchospasm Rx: Suctioning and Bronchodilators,Use of Airway Pressures,Pk and Pl are both increased: Pneumothorax Lobar atelectasis Acute pulmonary edema Worsening pneumonia ARDS COPD with tach

7、ypnea and Auto-PEEP Increased abdominal pressure Asynchronous breathing,Use of Airway Pressures,Decreased Pk: System air leak: Tubing disconnection, cuff leak Rx: Manual inflation, listen for leak Hyperventilation: Enough negative intrathoracic pressure to pull air into lungs may drop Pk.,Compliance

8、,Static Compliance (Cstat): Distensibility of Lungs and Chest wall Cstat = Vt/Pl Normal C stat: 50-80 ml/cm of water Provides objective measure of severity of illness in a pulmonary disorder Dynamic Compliance: Cdyn: Vt/Pk *Subtract PEEP from Pl or Pk for compliance measurement Use Exhaled tidal vol

9、ume for calculations,Patterns of Assisted Ventilation,Assist Control Intermittent Mandatory Ventilation Pressure Controlled Ventilation Pressure Support Ventilation Positive end-expiratory ventilation Continuous Positive Airway Pressure,Assist Control Ventilation,Volume-cycled lung inflation Patient

10、 can initiate each mechanical breath or Ventilator provides machine breaths at a preselected rate Maintain I:E ratio to 1:2 to 1:4. An increase in Peak flow decreases the time for lung inflation and increases the I:E Ratio I:E ratio of 1:2 can cause hyperinflation by air trapping Diaphragmatic contr

11、action continues during ACV and increases the work of breathing.,Assist Control Ventilation,Adverse effects: In a tachypneic patientLead to overventilation and severe respiratory alkalosis Hyperinflation and Auto-PEEP Lead to Electromechanical dissociation,Intermittent Mandatory Ventilation,Delivers

12、 volume cycled breaths at a preselected rate with spontaneous breathing between machine breaths Less Alkalosis and Hyperinflation Synchronized IMV,Intermittent Mandatory Ventilation,Disadvantages: Increased work of Breathing: Spontaneous breathing through a high resistance circuit Solution: Add Pres

13、sure support Cardiac Output Changes: C O decreased by decreasing ventricular filling C O increased by reducing ventricular afterload More significant decrease in patients with LV dysfunction,IMV vs. ACV,Switch to IMV for: Rapid breathers with alkalosis and over- Inflation Switch to ACV for: Patients

14、 with respiratory muscle weakness and LV dysfunction,Pressure Controlled Ventilation,Pressure cycled breathing, fully ventilator controlled Inspiratory flow rate decreases exponentially during lung inflation (+)Reduces peak airway pressure and improves gas exchange (-)Inflation volume varies with ch

15、anges in mechanical properties of the lungs. Suited for patients with neuromuscular diseases and normal lung mechanics,Inverse ratio Ventilation,PCV combined with prolonged inflation time Inspiratory flow rate is decreased I:E ratio reversed to 2:1 Helps prevent alveolar collapse (-) Hyperinflation,

16、 Auto-PEEP and decreased cardiac output Use: ARDS with refractory hypoxemia or hypercapnia ?mortality benefit,Pressure Support Ventilation,Pressure augmented breathing Allows patient to determine the inflation volume and respiratory cycle duration Uses: augment inflation during spontaneous breathing

17、 or overcome resistance of breathing through ventilator circuits (during weaning) Popular an a non-invasive mode of ventilation via nasal or face masks,Positive end-expiratory pressure,Alveolar pressure at end-expiration is above atmospheric pressure : PEEP Extrinsic PEEP Auto PEEP,Positive end-expi

18、ratory pressure,EXTRINSIC PEEP Applied by placing pressure limiting valve in the expiratory limb of ventilator circuit Prevents end-expiratory alveolar collapse and recruits collapsed alveoli This decreases intrapulmonary shunting, improves gas exchange and improves lung compliance, allowing the FiO

19、2 to be reduced to less toxic levels,Positive end-expiratory pressure,Cardiac Performance: Greater reduction in cardiac filling and cardiac output (Q), irrespective of level of PEEP! It is a function of PEEP induced increase in mean intrathoracic pressure Oxygen transport Do2: Do2 = Q X 1.3 X Hb X S

20、aO2 Systemic O2 delivery may vary with the effect of PEEP on the Cardiac Output.,Positive end-expiratory pressure,Best PEEP: Monitor Cardiac Output Another measure: Venous Oxygen Saturation If VOS decreases after PEEP applied= Drop CO Swan-Ganz catheter may be indicated in most patients on PEEP,Posi

21、tive end-expiratory pressure,CLINICAL USES: Reduce toxic levels of FiO2 (ARDS not pneumonia) Low-volume ventilation Obstructive lung disease (Extrinsic=Occult PEEP),Positive end-expiratory pressure,CLINICAL MISUSES: Reducing Lung Edema Routine PEEP Mediastinal Bleeding after CABG,Continuous positive

22、 Airway Pressure,Spontaneous breathing Patient does not need to generate negative pressure to receive inhaled gas CPAP replaced spontaneous PEEP Use: Non-intubated patients (OSA, COPD),Occult PEEP,Intrinsic or Auto-PEEP or Hyperinflation Incomplete alveolar emptying during expiration Ventilator Fact

23、ors: High inflation volumes, rapid rate, low exhalation time Disease factors: Asthma, COPD Consequences: Decreased CO/EMD, Alveolar rupture, Underestimation of thoracic compliance, increased work of breathing. If extrinsic PEEP does not increase Pk, then occult PEEP is present,Complications of Mecha

24、nical Ventilation,Toxic effects of Oxygen Decreased cardiac output Pneumonia and sepsis Psychological problems Ventilator dependence,Complications of Mechanical Ventilation,Purulent sinusitis Laryngeal Damage Aspiration :Value of routine tracheal suctioning Tracheal Necrosis (pressure below 20mm wat

25、er) Alveolar rupture: Pneumothorax, pneumomediastinum, subQ emphysema, pneumoperitoneum Basilar and sub-pulmonic air collections in the supine position, as seen on X-ray,Liberation from Mechanical Ventilation: Weaning,Weaning: Gradual withdrawal of mechanical ventilation Misconceptions: Duration- lo

26、nger duration, harder to wean Method of weaning determines ability to wean Diaphragm weakness is a common cause of failed weaning Aggressive nutrition support improves ability to wean Removal of ET tube reduces work of breathing,Bedside Weaning Parameters,Bedside Weaning Parameters,Maximal Inspirato

27、ry Pressure,Pmax: Excellent negative predictive value if less than 20 (in one study 100% failure to wean at this value) An acceptable Pmax however has a poor positive predictive value (40% failure to wean in this study with a Pmax more than 20),Frequency/Volume ratio,Index of rapid and shallow breat

28、hing RR/Vt Single study results: RR/Vt105 95% wean attempts unsuccessful RR/Vt105 80% successful One of the most predictive bedside parameters.,T-Piece Weaning,On-off toggle switch that circulates between on and off the ventilator Inhaled gas is delivered at a high flow rate Varied protocols: like 3

29、0min-2hr on and off, or keep as long as possible and if tolerated for 2-4hr. Deemed successsful (RR, TV, HR, diaphoresis, sat) Failed T piece: Resume Vent support till comfortable, 24h,vent,Airflow with CPAP,patient,T-Piece with Ventilator,Drawback: increased resistance due to vent tubing and actuat

30、or valve in circuit Provide minimum pressure support (PSV) :Pmin Pmin= PIFR X R PIFR is during spontaneous breathing R is airflow resistance during mech ventilation R= Pk-Pl/Vinsp (Vinsp:inspiratory flow rate delivered by the vent),IMV Weaning,Gradual decrease in no of machine breaths in between the

31、 spontaneous breaths False security: It does not adjust to patients ventilatory demands to maintain constant MV End point in IMV weaning is the T-piece trial Most important to recognize when a patient is capable of spontaneous unassisted breathing T-piece more rapid than IMV,Complicating Factors,DYS

32、PNEA Anxiety and dyspnea are detrimental (low dose haloperidol or morphine) CARDIAC OUTPUT Increased LV afterload can reduce CO, impair diaphragm function, promote pulmonary edema (Use Swan to monitor CO, may use dobutamine) ELECTROLYTE DEPLETION OVERFEEDING,The Problem Wean,RAPID BREATHING: Check TV Low TV Resume vent support TV not low. Check arterial pCO2 Arterial pCO2 decreasedsedate (anxiety) Arterial pCO2 not decreased Resume vent,The Problem Wean,ABDOMINAL PARADOX Inward displacement of the diaphragm during inspiration is a sign of diaphragmatic muscle fatigue