1. Mechanical ventilation & Respiratory support therapy
DR.REZWANUL HOQUE BULBUL
MBBS, MS, FCPS, FRCSG, FRCS Ed
ASSOCIATE PROFESSOR
DEPARTMENT OF CARDIAC SURGERY
BSMMU, DHAKA, BANGLADESH

2. DEFINITION It refers to the gamut of artificial means used to support ventilation and oxygenation. They encompass all forms of Positive Pressure Ventilation and those modes used to increase airway pressure above atmospheric during spontaneous ventilation

3. GOALS OF VENTILATION Increase efficiency of breathing Increase oxygenation Improve ventilation/perfusion relationships Decrease work of breathing

4. Types of Systems Negative Pressure Ventilator “Iron lung” Allows long-term ventilation without artificial airway Maintains normal intrathoracic hemodynamics Uncomfortable, limits access to patient

5. Types of Systems Positive Pressure Ventilator Uses pressures above atmospheric pressure to push air into lungs Requires use of artificial airway Types Pressure cycled Time cycled Volume cycled

6. Positive Pressure Ventilators Pressure Cycled Terminates inspiration at preset pressure Small, portable, inexpensive Ventilation volume can vary with changes in airway resistance, pulmonary compliance Used for short-term support of patients with no pre-existing thoracic or pulmonary problems

7. Positive Pressure Ventilators Volume cycled Most widely used system Terminates inspiration at preset volume Delivers volume at whatever pressure is required up to specified peak pressure May produce dangerously high intrathoracic pressures

8. Positive Pressure Ventilators Time cycled Terminates inspiration at preset time Volume determined by Length of inspiratory time Pressure limit set Patient airway resistance Patient lung compliance Common in neonatal units

9. CLASSIFICATION / On the basis of three functions
INITIATION
CONTROL
Initiation triggered by machine at a predetermined time set regardless of patient effort
ASSIST
Supported breath is triggered when patient initiates a breath that develops negative pressure below a threshold termed sensitivity
LIMIT
VOLUME
Tidal volume is preset while peak airway pressure is variable
PRESSURE
Airway pressure is preset while tidal volume is variable
CYCLE OFF
Tidal volume delivered then converted to expiration
TIME
May be prolonged by inspiratory pause
FLOW RATE
Converted to expiration when flow rate declines to predetermined level

10. VENTILATOR MODES Defined by inspiratory events while expiration is treated as independent entity

11. CONTROLLED MECHANICAL VENTILATION(CMV)
Initiation is time dependent with a fixed rate
Tidal volume is delivered along with inspiratory pause
Tidal volume is delivered regardless of airway pressure
If pressure limit is set delivery will stop once the limit is
reached
Eliminates patients work of breathing
Requires an anaesthetized and paralyzed patient
Useful when inspiratory effort contraindicated (flail
chest)
Patient must be incapable of initiating breaths
Rarely used

12. ASSISTED MECHANICAL VENTILATION
Initiation is assisted when sensitivity is reached
Otherwise similar to CMV
Better tolerated in light sedation
Cannot be used in sedated or paralyzed
Work of breathing is greater
Can predispose to alkalosis if resp. rate is high

13. Assist Mode Assist/Control (A/C) 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 Tachypnea patients may hyperventilate dangerously

14. A/C mode

15. INTERMITTENT MANDATORY VENTILATION (IMV)
Assist Mode
INTERMITTENT MANDATORY VENTILATION (IMV)
Combination of CMV and Spontaneous
modified circuit allows continuous flow that allows patient to breathe between machine delivered breath with minimal work of breathing
Delivery is regardless of the stage of respiration
Patient breathes on own
Machine delivers breaths at preset intervals
Patient determines tidal volume of spontaneous breaths
Used to “wean” patients from ventilators
patient –machine dyssynchrony may lead to lung over
distension or fighting with the ventilator
Patients with weak respiratory muscles may tire from
breathing against machine’s resistance
Largely abandoned in favor of SIMV

16. SYNCHRONISED INTERMITTENT MANDATORENTILATION (SIMV)
Assist mode
SYNCHRONISED INTERMITTENT MANDATORENTILATION (SIMV)
IMV in assist mode
Machine timed to delay ventilations until end of spontaneous patient breaths
Avoids over-distension of lungs
Decreases barotrauma risk
However if patient does not breathe then IMV delivers
Relative work of breathing is less
Does not contribute to central hyperventilation syndrome
Does not require sedation or paralysis
In COPD patients, hypercarbia is preserved
Popular mode for weaning of patients

17. SIMV mode

18. PRESSURE SUPPORT VENTILATION
Applicable in spontaneous ventilation
Initiation of respiration cause rapid flow of gas until selected pressure is crossed and continues until inspiration drive is stopped
Advantage over SIMV being support is provided for each breath
Requires spontaneous ventilation but spontaneous breath in SIMV mode are also supported
Cannot be used in low pulmonary compliance
Central hyperventilation syndrome along with resp.alkalosis may develop
Monitoring of tidal volume is required

19. Pressure support ventilation

20. Volume control vs. pressure control
There are, effectively, two ways of assisting inspiration – by using positive pressure to deliver a certain amount of volume (volume control ventilation), or by delivering a certain amount of pressure (pressure control ventilation).
Volume control means volume constant and pressure variable.
Pressure control means pressure constant (or limited) volume variable ventilation.
The mode of ventilation, is the way in which the ventilator uses volume or pressure to bump the patient up the pressure-volume curve.
Patients may be given mandatory breaths (controlled ventilation) or may have their spontaneous breaths assisted (assist control ventilation).
An alternative mode (which is often used with controlled modes) is pressure support, which allows a patient breath spontaneously, start and finish breaths and determine the tidal volume.
 Mechanical ventilation that is achieved regardless of the patient's spontaneous breathing, but that uses pressure as the major determining variable, along with rate and time, of how much air the patient receives.

22. High Frequency Ventilation (HFV) Small volumes, high rates Allows gas exchange at low peak pressures Mechanism not completely understood High frequency positive pressure ventilation breaths/min High frequency jet ventilation--up to 400 breaths/min High frequency oscillation--up to 3000 breaths/min

23. High Frequency Ventilation (HFV) Useful in managing: Tracheobronchial or bronchopleural fistulas Severe obstructive airway disease Patients who develop barotrauma or decreased cardiac output with more conventional methods Patients with head trauma who develop increased ICP with conventional methods Patients under general anesthesia in whom ventilator movement would be undesirable

24. Alternative modes of ventilation
Non-invasive positive pressure ventilation using specialized face or nasal mask
Negative pressure ventilation using special apparatus in COPD patient
Airway pressure release ventilation- Lung is kept inflated at constant pre-set pressure to achieve alveolar recruitment and inflation, intermittent release of pressure to allow exhalation
Mandatory minute ventilation- Pre-set minute ventilation either by spontaneous or by supplemental breath by machine
Inverse ratio ventilation- normal I:E ratio is reversed from 1:2/1:3 to 1:1-3:1
Partial liquid ventilation- Perfluorocarbon liquid instilled into lung followed by standard mechanical ventilation
ECMO

25. POSITIVE END EXPIRATORY PRESSURE
commonly kept at 3 – 5 cm of water as a substitute for physiological PEEP provided by closed glottis
primary goals include:
1. increase functional Residual Capacity
2. distends patent alveoli
3. recruits previously collapsed alveoli
4. In pulmonary edema, may redistribute extra vascular
lung water from alveolar capillary interstitium to
peribronchial and perihilar interstitium

26. increases air trapping, CO2 retention and hypercapnia
Disadvantages
1. Alveolar distention and pulmonary dead space
increases air trapping, CO2 retention and
hypercapnia
2. Not useful in diseased lung
3. Not tolerated in awake patients
4. Increased work of breathing
5. Increased chances of barotrauma
Contraindications
1. Severe hemodynamic instability
2. Acute bronchospasm
3. Severe Emphysema
4. Pneumothorax Suspected or present

27. Continuous Positive Airway Pressure (CPAP) PEEP without preset ventilator rate or volume Physiologically similar to PEEP May be applied with or without use of a ventilator or artificial airway Requires patient to be breathing spontaneously Does not require a ventilator but can be performed with some ventilators

28. RATIONALE FOR MECHANICAL VENT.
Provides the time to reverse the adverse effects on lung function induced by anaesthesia and surgery
Allows aggressive pain control without concern for respiratory depression
Reduces the work of breathing and saves energy at the critical period
In patients who are hemodynamically unstable, ensures effective ventilation reducing the number of variables in management

29. INDICATION OF MECHANICAL VENTILATION
PLANNED POST OPERATIVE
Based on Surgical procedures
1. Cardiac Surgery
2. Major Vascular Surgeries
3. Procedures with major blood loss
4. High risk Surgical Incisions
Planned- other diseases
1. Neuromuscular and Mechanical dysfunction
2. Parenchymal lung diseases
3. Acute lung injury
4. Multi System Organ Failure
Unplanned
1. Depressed CNS response to hypoxia and hypercapnia
upper abdominal reduces FRC by 60%
thoracotomy reduces FRC by 40%

30. CARDIO PULMONARY COMPLICATION
INDICATION (CONT’D
CARDIO PULMONARY COMPLICATION
Acute Myocardial Infarction
Arrhythmias
Pulmonary edema
Severe bronchospasm
Lobar Atelectasis
SURGICAL COMPLICATIONS
Hemorrhage
Cardiac contusion following TEE, Phrenic Nerve injury
OPERATIVE CATASTROPHE
Cardiac arrest, Malignant hyperthermia, ABO mismatch
Gastric Acid aspiration, Major anaphylactic reaction
INADEQUATE REVERSAL OF ANAESTHESIA
inadequate elimination of anaesthetic agents
inadequate reversal of opioid analgesics
inadequate reversal of muscle relaxants

31. Ventilator Settings Tidal volume--10 to 15ml/kg (std = 12 ml/kg) Respiratory rate--initially 10 to 16/minute FiO to 1.0 depending on disease process 100% causes oxygen toxicity and atelectasis in less than 24 hours 40% is safe indefinitely PEEP can be added to stay below 40% Goal is to achieve a PaO2 >60 I:E Ratio--1:2 is good starting point Obstructive disease requires longer expirations Restrictive disease requires longer inspirations
Changes are made according to Arterial Blood Gas reports
Maintain with ACV, use sedatives & muscle relaxants if needed
Switch to Synchronized Intermittent Mandatory Ventilation (SIMV) mode, reduce respiratory rate gradually and finally switch to Spontaneous mode
Extubate the patients when the criteria's are met.

32. Ventilator Settings Ancillary adjustments Inspiratory flow time Temperature adjustments Humidity Trigger sensitivity Peak airway pressure limits Sighs

33. Quick Guide to Setup Self check and/or Calibration as needed Check circuit and connections Set Mode: Usually “Assist/Control” Adjust “I” time: Usually 1 second Set tidal volume: ml/kg is standard May need to set “Flow” based on “I” time Set ventilatory rate: Adult 12-16/min

34. WEANING FROM VENTILATOR Criteria 1. Mental Alertness
2. No active bleeding
3. Haemodynamic stability
4. Normothermic
5. Satisfactory Arterial Blood Gas report
PaO2 > 70 mm of Hg on an FIO2 <50%
PaCO2 < 45 mm of Hg
pH 7.35 – 7.45
For Extubation
Vital Capacity > 10 – 15ml / kg
Negative Inspiratory Force > 25 cm water
Spontaneous Respiratory Rate < 30 / min
D(A-a)O2 <350 TORR ON 100% O2

35. Ventilator Complications Mechanical malfunction Keep all alarms activated at all times BVM must always be available If malfunction occurs, disconnect ventilator and ventilate manually

36. Ventilator Complications Airway malfunction Suction patient as needed Keep condensation build-up out of connecting tubes Auscultate chest frequently End tidal CO2 monitoring Maintain desired end-tidal CO2 Assess tube placement

37. Ventilator Complications Pulmonary barotrauma Avoid high-pressure settings for high-risk patients (COPD) Monitor for pneumothorax Anticipate need to decompress tension pneumothorax low chance with peak airway pressure < 45 cm of water high tidal volume may injure alveolar capillary membrane Oxygen toxicity incidence and rapidity of oxygen related injury increases with FIO2 > 60%

38. Ventilator Complications Renal malfunction Gastric hemorrhage Pulmonary atelectasis Infection Oxygen toxicity Loss of respiratory muscle tone increased intra cranial pressure

39. -Ventilator malfunction, improper setting
Ventilator complications
Acute Respiratory Insufficiency
present when there is evidence of inadequate oxygenation (PaO2 <60 mm Hg on FIO2 0.5) or Ventilation (PCO2 >50 mm Hg) during mechanical ventilatory support.
Causes:
-Ventilator malfunction, improper setting
- Endotracheal tube malfunction
- Pulmonary Problems – Atelectasis, Pulmonary edema, Pneumonia, Pneumothorax, Haemothorax
- Low cardiac output states
- Aspiration Pneumonia

40. Management:
- Examine the ventilator setting and function, ET
Tube, ABGs, CXR
- Hand ventilate with 100% O2, increase FIO2 in
ventilator until problem is corrected
- May require repositioning of ET tube, insertion of
Intra thoracic tube
- Asses and optimise hemodyanmics
- Add Inverse Ratio Ventilation with PEEP increment
- Consider sedation and Paralysis in patient Ventilator synchronicity
- Treat identifiable causes

41. Chronic Respiratory insufficiency
inability to wean from ventilator within hours caused by problems that primarily impair oxygenation or produce primary Ventilatory insufficiency
Causes: Hypoxia, ARDS, Sepsis, Metabolic Abnormalities,
Phrenic nerve paralysis
Management:
Treat the primary cause
Patients may even require Tracheostomy for
further airway management

42. Thank you