Artificial ( Mechanical) ventilation

Discusses the key concepts of Artificial and Mechanical Ventilation,
Distinguishes between Negative pressure ventilation and positive pressure ventilation. Explains Ventilator Settings, indications for Intubation and ventilation, and the complication that could arise. Also classifies the various control of ventilation and the modes of ventilation

1. Artificial Ventilation Dr John Afam PGDip.Ana Registrar II Department of Anaesthesia Federal Medical Centre 21st April,2021 ‹#›

2. Outline Introduction History Aims Indications Types Key Concepts Modes Management of Mechanical ventilation Complications References ‹#›

3. Introduction Artificial or Mechanical ventilation is a method of artificially assisting or replacing spontaneous breathing. A Mechanical ventilator is a machine that generates a controlled flow of gas into a patient’s airways. Artificial Ventilation is a commonly used technique in the operating rooms and intensive care unit (ICU) and knowledge and proper application can greatly impact patient outcome ‹#›

4. History Roman physician Galen first used mechanical breathing in the second century by blowing air into the larynx of a dead animal using a reed. First officially documented by Andreas Wesele Vesalius in the 15th Century “ B ut that life may ... be restored to the animal, an opening must be attempted in the trunk of the trachea, in which a tube of reed or cane should be put; you will then blow into this, so that the lung may rise again and the animal take in air. ... And as you do this, and take care that the lung is inflated in intervals, the motion of the heart and arteries does not stop..." Vesalius 1543 Author George Poe used a mechanical respirator to revive an asphyxiated dog. ‹#›

5. History contd. Drinker and Shaw tank type ventilators were introduced in 1929 Earliest widely used ventilators Extensively used during the polio outbreak of 1940s and 50s Medical students facilitated PPV during the polio outbreak in Copenhagen in 1950 Better Mortality rates than Iron Lungs Success led to adaptation of the anaesthesia machine for intensive care use ‹#›

6. Aims Improve ventilation by augmenting respiratory rate and tidal volume Assistance for neural or muscle dysfunction Sedated, comatose or paralyzed patient Neuropathy, myopathy or muscular dystrophy Intra - operative ventilation Correct respiratory acidosis Match metabolic demand Rest respiratory muscles Correct hypoxemia High F I O 2 Positive end expiratory pressure (PEEP) ‹#›

7. 2. Oxygenation Maximize O2 delivery to blood (PaO2) V/Q mismatching Patient position (supine) Airway pressure, pulmonary parenchymal disease, small-airway disease ‹#›

8. Types Negative pressure ventilators Positive pressure ventilators ‹#›

9. Negative Pressure Ventilation A vacuum pump creates a negative pressure in the chamber, resulting in chest expansion This change reduces the intrapulmonary pressure and allows ambient air to flow into the patient's lungs. When the vacuum was terminated, the negative pressure applied to the chest dropped to zero, and the elastic recoil of the chest and lungs permitted passive exhalation. Almost extinct ‹#›

10. ‹#›

11. Types contd Disadvantages Cumbersome Significant patient discomfort Pooling of blood in the lower limbs Limited access Advantages Does not require invasive methods ‹#›

12. Positive Pressure Ventilation Modern day ventilator design Airway pressure is applied at the patient's airway through an endotracheal or tracheostomy tube. The positive nature of the pressure causes the gas to flow into the lungs until the ventilator breath is terminated. As the airway pressure drops, elastic recoil of the chest accomplishes passive exhalation by pushing the tidal volume out. ‹#›

13. Non Invasive Positive Pressure Ventilation Ca n be achieved using a facemask, nasal mask, helmet. It should be considered first, if patient meets the criteria and has no contraindications Indications Respiratory failure in the absence of haemodynamic instability, neurologic compromise. Acute exacerbation of COPD. Acute cardiogenic pulmonary oedema. Post operative ventilatory failure. ‹#›

14. Contraindications to NIPPV Cardiac or respiratory arrest Non respiratory organ failure GCS < 10 Haemodynamic instability Facial surgeries/trauma/deformities Inability to clear secretions Un-cooperative patients Patients at risk of aspiration ‹#›

15. Invasive Positive Pressure Ventilation A fter instrumentation of the airway. Either via LMA, endotracheal tube or tracheostomy tube Indications Arterial oxygen tension <50 mm Hg on room air Arterial CO 2 tension >50 mm Hg in the absence of metabolic alkalosis Pa O 2 /F IO 2 ratio <300 mm Hg V D /V T >0.6 Respiratory rate >35 cpm or < 5cpm Tidal volume <5 mL/kg Vital capacity <15 mL/kg Maximum inspiratory force > −25 cm H 2 O (eg, –15 cm H 2 O) ‹#›

16. Indications for IPPV contd Drug overdose Following prolonged surgery Deteriorating LOC (GCS 8) Significant Chest Trauma Post cardiac arrest Use of NMB Thoracic surgery Inadequate ventilation via conventional methods Control/monitor arterial Paco2 ‹#›

17. Key Concepts Control - How much to deliver Trigger - When to Deliver Cycling - How long to deliver for ‹#›

18. Key Concepts contd Control (How much to deliver) Volume Controlled (volume limited, volume targeted) and Pressure Variable. Pressure Controlled (pressure limited, pressure targeted) and Volume Variable. Dual Controlled (volume targeted (guaranteed) pressure limited) Newer models. ‹#›

19. Key Concepts contd Cycling (How long to deliver) Pressure-cycled ventilators cycle into the expiratory phase when airway pressure reaches a predetermined level. V T and inspiratory time vary, being related to airway resistance and pulmonary and circuit compliance. Volume-cycled ventilators terminate inspiration when a preselected volume is delivered. Many adult ventilators are volume cycled but also have secondary limits on inspiratory pressure to guard against pulmonary barotrauma Time-cycled ventilators cycle to the expiratory phase once a predetermined interval elapses from the start of inspiration. ‹#›

20. Key Concepts contd Trigger (What triggers Inspiration) Time: the ventilator cycles at a set frequency as determined by the controlled rate. Pressure: the ventilator senses the patient's inspiratory effort by way of a decrease in the baseline pressure. Flow: Ventilators deliver a constant flow around the circuit throughout the respiratory cycle. A deflection in this flow, is monitored by the ventilator and it delivers a breath. Requires less work than pressure triggering. ‹#›

21. Modes of Mechanical Ventilation Controlled Mandatory Ventilation Assisted Control Mode Intermittent Mandatory Ventilation Synchronous Intermittent Mandatory Ventilation Pressure Support Ventilation Pressure Control Ventilation Inverse I:E Ratio Ventilation High Frequency Ventilation ‹#›

22. Controlled Mechanical Ventilation Determined entirely by machine settings No synchronisation with patient’s breathing. Require heavy sedation or neuromuscular block. ‹#›

23. Patient does not participate in ventilations Machine initiates inspiration, does work of breathing, controls tidal volume and rate Useful in apneic or heavily sedated patients Useful when inspiratory effort contraindicated (flail chest) Patient must be incapable of initiating breaths ‹#›

24. Assisted/Control Can be used in spontaneously breathing patients Delivers a set number of mandatory breaths Patient triggers machine to deliver breaths but machine has preset backup rate Patient initiates breath--machine delivers tidal volume If patient does not breathe fast enough, machine takes over at preset rate Each breath results in a pre-set flow rate and tidal volume Tachypneic patients may hyperventilate dangerously Can result in severe alkalosis and auto PEEP, So it is contraindicated on patients with potential for respiratory alkalosis e.g patients with end-stage liver disease, hyperventilatory sepsis, and head trauma. ‹#›

25. Intermittent Mandatory Ventilation Patient breathes spontaneously, and the ventilator intermittently delivers positive pressure breaths at a pre-set tidal volume and rate. During spontaneous breaths, flow rate and tidal volume are patient determined Less risk of barotrauma, not every breath is a positive pressure breath Can result in stacking ‹#›

26. Synchronous Intermittent Mandatory Ventilation The ventilator delivers the set tidal volume, synchronizing the mandatory breaths with the patients’ triggering efforts. Spontaneous efforts between ventilator delivered breaths are unassisted. ‹#›

27. Pressure Support Ventilation Patient determines RR, inspiratory time – a purely spontaneous mode. Clinician sets Pinsp and PEEP Triggered by patient’s breath Limited by pressure Affects inspiration only Used in conjunction with other modes Great for weaning ‹#›

28. Other Ventilation Modes Pressure control Ventilation Similar to PSV Does not guarantee Vt Inverse I:E Ratio Ventilation Useful in patient with reduced FRC Requires Deep Sedation High Frequency Ventilation HFPPV - 60-120cpm HFJV 120-600cpm HFO 180-3000cpm ‹#›

29. Initiating Mechanical Ventilation Machine check- model specific Initial settings – DEPENDS ON WHAT IS WRONG WITH THE PATIENT ABG should be obtained 30 mins after initial setting PH PaCO2, PaO2 Minute Ventilation - 100ml/kg LBW Respiratory rate –Range 12-18c/min. ↑Rates = Insufficient gas exchange and auto PEEP Tidal volume or pressure settings – 6-10ml/Kg (lower for ALI/ARDS, higher healthy lungs) Inspiratory flow – Varies with the Vt, I:E and RR. Usually 60 – 100L/min ‹#›

30. I:E ratio – 1:2, 1:3, Inverse in ARDS PEEP- 5cmH2O in critically ill FiO2 – Always start with 1 then scale down PIP – 45-50cmH2O, 25-35cmH20 elevated suggests need for switch from volume-cycled to pressure-cycled mode Maintained at <45cm H2O to minimize barotrauma ‹#›

31. Management of Patients on Ventilator Intubation Nasal vs oral Tracheostomy > 2weeks Monitoring Spo2, BP, ABG, CXR, ECG Arterial Lines, I/O Ventilator Parameters Sedation Humidification and Thermoregulation ‹#›

32. Positive End Expiratory Pressure P ressure is applied at the end of expiration to maintain alveolar recruitment Ensures airway pressure is kept above atmospheric pressure to prevent alveoli collapse It is the baseline airway pressure for the duration of the respiratory cycle ‹#›

33. Benefits Increases FRC Prevents progressive atelectasis and intrapulmonary shunting Prevents repetitive opening/closing (injury) Recruits collapsed alveoli and improves V/Q matching Resolves intrapulmonary shunting Improves compliance Enables maintenance of adequate PaO2 at a safe FiO2 level Decreases FiO2 needed to correct hypoxemia Useful in maintaining pulmonary function in non-cardiogenic pulmonary edema ‹#›

34. Disadvantages Increases intrathoracic pressure, thus ↓ venous return and CO May lead to ARDS Barotrauma from over distension Increases dead space if over distended Work of breathing may be increased, larger negative pressure required to trigger ‹#›

35. Discontinuing Mechanical Ventilation Occurs in 2 phases In the first, “readiness testing,” so-called weaning parameters and other subjective and objective assessments are used to determine whether the patient can sustain progressive withdrawal of mechanical ventilator support. The second phase,“weaning” or “liberation,” describes the way in which mechanical support is removed. ‹#›

36. Readiness Testing Precipitating illness treated? Any organ failure? Is there fever? Adequate nutrition Is there fluid, electrolyte imbalance? Is the patient sedated? Is there any haemodynamic instability ‹#›

37. Readiness Testing Assess respiratory function PaO2 >60 on FiO2 < .5, PEEP <8, Ph >7.25 RR < 35/min Tidal volume >5ml/kg Minute ventilation >6L and <10L Vital capacity >10-15ml/kg FRC >50% of predicted volume RSBI- Rapid Shallow Breathing Index (f/Vt) < 100 Intact Airway control Cooperative patient ‹#›

38. Weaning SIMV In this weaning mode, the number of mandatory mechanical breaths is progressively decreased Aim - IMV 2-4 PSV Accomplished by gradually decreasing the pressure support level by 2–3 cmH2O. Aim - pressure support level of 5–8 cm H2O SBT/T Piece Τ -piece trials allow observation while the patient breathes spontaneously For patients on prolonged ventilation, repeated trials may be required May Require CPAP ‹#›

39. Complications of Mechanical Ventilation Barotrauma P resence of extra alveolar air This air may escape (usually due to alveolar or bleb rupture) into the: pleura (pneumothorax) mediastinum (pneumomediastinum) pericardium (pneumopericardium) under the skin (subcutaneous emphysema or crepitus) May occur when the alveoli are over distended such as with positive pressure ventilation, high tidal volumes or PEEP Increased PIP, decreased breath sounds, tracheal shift, hypoxemia Could worsen to tension pneumothorax ‹#›

40. Complications Gastrointestinal Stress ulcers Hypomotility & paralytic ileus Malnutrition: atrophy of respiratory muscles, protein, albumin, immunity, surfactant production, impaired cellular oxygenation, and central respiratory depression Cardiovascular Decreased venous return and CO ‹#›

41. Complications Mechanical Complications Inadequate Ventilation Intubation of right mainstem bronchus ETT out of position/extubation Incompatible settings Operator error Tracheal Damage/Necrosis Leaks Artificial airway related Sub Glottic Stenosis Sinusitis Otitis Media Layngeal Oedema ‹#›

42. Complications Acid - Base Disturbances O2 Toxicity Aspiration Infection Fluid Imbalance Immobility (Muscle Weakness, DVT, PE) Psychological (Isolation, Lack of Autonomy, Sleep Disturbances) Ventilator Dependence ‹#›

43. Conclusion Mechanical ventilation is becoming increasingly important in critical care and extensive knowledge of this concept is important in Critical Care. ‹#›

44. References ‹#›

45. Thank you for Listening ‹#›