Mechanical Ventilation

1. Mechanical Ventilation INTRODUCTIORY OVERVIEW

2. Today’s Agenda • Indications for mechanical ventilation: Acute Respiratory Failure • Hypoxic • Ventilatory • Ventilator Modes- VC, PC, SIMV, PS, CPAP • Vent orders for specific situations • Management of the ventilated patient • Adjustments for hypercapnea and hypoxia • PEEP

3. Indications for Mechanical Ventilation • O2? • CO2? • pH? • Combination of above plus the ever-important “eyeball test”

4. Acute Respiratory Failure • Severe oxygen deficit (gas exchange): Hypoxic respiratory failure • Impending or acute ventilatory failure: Hypercapneic respiratory failure • Apnea • (Other indications: Protect airway, refractory shock, acute reduction of ICP…)

5. Physiologic Mechanisms of Hypoxia • Shunt (V/Q ~ 0) • V/Q mismatch (dead space) • Hypoventilation • Diffusion Impairment • Reduced FIO2

6. Optimal V/Q matching

7. Dead Space

8. Shunt

9. Mechanisms of ventilatory failure • Balance between load on the lungs and the ability of bellows to compensate • Excess load • Inadequate bellows

10. Load Resistance Lung compliance Chest wall compliance Minute ventilation load Bellows Respiratory drive Neuromuscular transmission Muscle weakness Ventilatory Failure

11. Load Resistance Lung compliance Chest wall compliance Minute ventilation load Bronchospasm Secretions Airway Edema Upper Airway Obstruction Ventilatory Failure

12. Load Resistance Lung compliance Chest wall compliance Minute ventilation load Edema Pneumonia Atelectasis Auto-PEEP Ventilatory Failure

13. Load Resistance Lung compliance Chest wall compliance Minute ventilation load Pleural Effusion PTX Obesity Ascites Rib fracture Abdominal distention Ventilatory Failure

14. Load Resistance Lung compliance Chest wall compliance Minute ventilation load Sepsis Pulmonary Embolism Ventilatory Failure

15. Bellows Respiratory drive Neuromuscular transmission Muscle weakness Drug overdose Hypothyroid Brain-stem lesions Central sleep apnea Ventilatory Failure

16. Bellows Respiratory drive Neuromuscular transmission Muscle weakness Cord lesions Phrenic nerve injury Guillain-Barre ALS MG paralytics Ventilatory Failure

17. Bellows Respiratory drive Neuromuscular transmission Muscle weakness Malnutrition Electrolytes Fatigue Myopathy Hypoxia Hypoperfusion Ventilatory Failure

18. “This guy’s not doing well…Does he need the tube?” Alternatives to intubation?

19. Non-invasive Positive Pressure Ventilation (NPPV) • CPAP- Continuous Positive Pressure Ventilation and Bilevel (“BiPap”) • CPAP: one pressure; O2 • Bilevel: Inspiratory pressure (IPAP); expiratory pressure (EPAP); O2 • Machine • Ventilator, Vision, Quantum, BiPap • Patient interface • Full face mask, nasal mask • RT, RN, monitoring

20. KEY: patient selection • COPD guidelines • Selection criteria (2 of 3) • Moderate-severe dyspnea • Moderate acidosis (7.30-35) and hypercapnea (45-60) • RR >25

21. Severe acidosis or hypoxemia Severe dyspnea Respiratory arrest CV instability (BP, arrythmias, MI) Aspiration risk Copious/viscous secretions Recent facial/GE surgery Extreme obesity Exclusionary Criteria

22. “He wants the tube”

23. Ventilator Orders • Ventilator Mode • RR • VT or Pressure • FIO2 +/- PEEP • Other: flow pattern, I:E, inspiratory hold, patient trigger mode/sensitivity

24. Basic Ventilator Modes • “Control” modes • Volume control (Assist control): VC (AC) • Pressure control: PC • Mixed • Synchronized Intermittent Mandatory Ventilation (SIMV) with support (controlled and spontaneous) • “Spontaneous” Modes • Pressure Support (PS) • CPAP • T-Piece

25. Mode characteristics • What parameters do I have to set/order? • What initiates a breath? • What terminates a breath (i.e. how the ventilator cycle)? • What are the flow characteristics? • What are the pressure characteristics? • What are the determinants of VT?

26. Volume control (VC) • Orders: RR, VT, (VI:E), FIO2 +/- PEEP • Initiate: Patient or controlled • Breaths beyond set rate get the set VT • Termination: VT – “volume-cycled”

27. Volume control (VC) • Flow: constant (20-120 L/min); can change by adjusting %I time (e.g. 33% = 1:2 I:E ratio) • Shorter % I time = higher flows • Pressure: Increases as lungs distend until inspiration terminates; varies with load • VT: Fixed

28. Volume Control • Advantages: • Reduced work of breathing • Allows patient to increase minute ventilation; can’t decrease below set VE • Minimal VE is ensured • Disadvantages • potential adverse hemodynamic effects or inappropriate hyperventilation • airway pressures vary with changes in lung compliance • Fixed flows – High flow demands from pt may not be met (ventilator dependent)

29. Volume Control curves

30. Pressure Control (PC) • Orders: RR, Pinsp level above PEEP, I time, FIO2 +/- PEEP • Initiate: Patient or controlled; breaths beyond set RR get full set Pinsp/I time • Termination: Set pressure at the I time • Default I time is usually 1 second (time-cycled)

31. Pressure Control (PC) Flow: decelerating rate; can vary with patient demand • Pressure: constant • Volume: Pinsp, I time; varies with lung + chest wall compliance (C = V/P)

32. Pressure Control Advantages -Reduced work of breathing -Allows patient to increase minute ventilation; can’t decrease below set VE -Peak pressures are limited • Disadvantages • Potential inappropriate hyperventilation • VT varies with changes in lung and/or chest wall compliance • Minimal VE is not ensured

33. Pressure Control curves

34. Pressure Support (PS) • Orders: Pinsp above PEEP, FIO2 +/- PEEP • Initiate: Patient only • Termination: Flow is 25% of max (flow cycled) • Flow: decelerating rate; patient can increase • Pressure: constant • Volume: varies with pressure, effort, and compliance of lung and chest wall

35. Pressure Support • Potential advantages • Patient comfort • Decreased work of breathing • May enhance patient-ventilator synchrony • Potential disadvantages • Variable VT if pulmonary resistance/compliance changes rapidly • If sole mode of ventilation, apnea alarm mode may be only backup • Gas leak from circuit may interfere with cycling

36. CPAP (via ETT) • Orders: FIO2 and “PEEP” • Initiate: patient • Termination: patient • Flow: patient • Pressure: oscillates around the “PEEP” • Volume: varies with pressure, effort and compliance Patient breathing spontaneously at a higher end expiratory pressure

37. CPAP • No machine breaths delivered • Allows spontaneous breathing at elevated baseline pressure • Patient controls rate and tidal volume

38. T-piece (T-tube) • Orders: FIO2 • Initiate: Patient • Termination: Patient • Flow: Patient • Pressure: negative with inspiration • Volume: varies with effort and compliance Spontaneous breathing through an ETT

39. T-piece • Same as spontaneous ventilation • “Breathing through a long straw” • Uses- same as CPAP • SBT; protect airway w/out need for ventilation

40. SIMV(VC or PC)/PS • Orders: RR; VT (VI:E) or Pinsp, FIO2 +/- PEEP; add PS (for breaths beyond set rate) • Initiate: Patient or controlled (synchronized) • Termination: • Controlled breath (VC or PC) • PS breath (beyond set RR): Flow is ~25% of peak flow (flow-cycled) • Flow: • Controlled breath (VC or PC) • PS breath: Decelerating rate; varies with demand

41. SIMV(VC or PC)/PS • Pressure: • Controlled breath (VC or PC) • PS breath: constant at whatever you set • VT: • Controlled breath (VC or PC) • PS breath: patient effort; lung compliance • Try to match spontaneous VT with controlled VT

42. SIMV with PS • Potential advantages • More comfortable for some patients • Less hemodynamic effects • Potential disadvantages • Increased work of breathing, especially with T-piece

43. SIMV (VC with PS)

44. Basic Ventilator Modes

45. Managing the ventilated patient • Initial orders • Normal lungs • Obstructive lung disease • Acute Lung Injury/ARDS • Neuromuscular disease • Ventilator adjustments • Hypoxia • Hypercapnea

46. Suggested guidelines for mechanical ventilation • Maintain Alveolar Pressure < 30-35 cm H2O (plateau pressure) • Avoid dynamic hyperinflation (auto-PEEP) • PS during spontaneous breaths • Use lowest FIO2 to maintain acceptable arterial PaO2 • Keep patient comfortable • Anxiety, pain, WOB (RR < 20-30)

47. Post-op, procedures, drug overdose VC or SIMV/PS VT: 10-12 cc/kg (IBW) RR: 10-15 I:E – 1:2 (default) PEEP 5 cm H2O (optional) FIO2: 30-50%; keep sat > 90% HOB up >30 (ALL pts) Bottom line Many different strategies could be used Don’t need ‘lung protective strategy’ Short-Term: Normal Lungs

48. Closed head injury Same guidelines as normal lungs Avoid PEEP unless need for hypoxemia Hyperventilate? PaCO2 30-35 (controversial) Sedation during suctioning (cough) PEEP increases “downstream” pressure Raise HOB, especially if PEEP Avoid chest PT esp. with HOB down Elevated ICP: Normal lungs

49. COPD, asthma VC, SIMV/PS VT: 5-8 cc/kg RR: 6-8 I:E – shorter I time PEEP: ~80% of auto-PEEP Sats > 90% Good sedation for first 24h (rest) Avoid dynamic hyperinflation (auto-PEEP) Higher flows increase expiratory time Lower VT Avoid alkalemia (7.30-7.35); acidosis is OK! COPD Try bilevel first Most extubated in 48h Obstructive Lung Disease

50. ALI/ARDS VC, PC, SIMV/PS VT: Start at 8 cc/kg Goal is 6 cc/kg I:E- 1:2 Rarely need 1:1 RR: 15-25 PEEP: >8-10 Sats 86-92% Sedation ARDSnet Keep plateau < 30 cm H2O PEEP often ~15+ May affect CO Acidosis is OK! HCO3 for pH <7.2? High RR auto-PEEP; higher flows HFOV? Acute Lung Injury