1. Mechanical Ventilators
Dr. Masroor Afreedi

2. Early History of Ancient Times
Ancient writings by the Egyptians and Greeks described theories of respiration.
In the Old testament there is a mention of Prophet Elisha inducing pressure breathing from his mouth into the mouth of a child who was dying–(Kings 4:34-35). Hippocrates ( BC) wrote the first description of endotracheal intubation his book –‘Treatise on Air’ “One should introduce a cannula into the trachea along the jaw bone so that air can be drawn into the lungs”.

3. Modern History
Paracelsus ( ) used ‘Fire Bellows’ connected to a tube inserted into patient’s mouth as a device for assisted ventilation. This was the first study (1550) which credited him with the first form of mechanical ventilation.
Vesalius (1543) performed ventilation via a tracheostomy in a pig.
Hook (1667) used bellows via a tracheostomy in a dog.
John Fathergill in 1744 reported a successful case of ‘mouth to mouth’ resuscitation.

4. Modern History
John Hunter developed double bellows for resuscitation in one for blowing air in and the other for drawing bad air out

5. Origins of mechanical ventilation
The era of intensive care medicine began with positive-pressure ventilation
Negative-pressure ventilators (“iron lungs”)
Non-invasive ventilation first used in Boston Children’s Hospital in 1928
Used extensively during polio outbreaks in 1940s – 1950s
Positive-pressure ventilators
Invasive ventilation first used at Massachusetts General Hospital in 1955
Now the modern standard of mechanical ventilation
The iron lung created negative pressure in abdomen as well as the chest, decreasing cardiac output.
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Iron lung polio ward at Rancho Los Amigos Hospital in 1953.

6. Negative Pressure Ventilators
From the mid s a large number of devices were invented that applied negative pressure around the body or thoracic cavity – these devices became known as negative pressure ventilators or 'iron lungs'. Two successful designs became popular; in one, the body of the patient was enclosed in an iron box or cylinder and the patient’s head protruded out of the end.
The second design was a box or shell that fitted over the thoracic area only (chest cuirass). Patients with chronic paralytic disorders were successfully ventilated on this cuirass ventilators at home for years

7. Scandinavian Polio Epidemic - 1952
Between July-December of 1952, in Copenhagen, patients with poliomyelitis were treated in the Community Disease Hospital of which 315 patients required ventilatory support.
Many principles of IPPV were defined during that time –including the use of cuffed tubes, periodic sigh breaths and weaning by reduction of assisted breaths. Towards the end of the epidemic a few positive pressure ventilators were invented  (the Engstrom, Lundi and the Bang) which became popularly known as mechanical students.

8. Era of Respiratory Intensive Care
After polio epidemics, the 1960’s became an era of respiratory intensive care. Positive pressure ventilation with use of an artificial airway replaced the bulky and cumbersome negative pressure technology of respiratory support.

9. Era of Respiratory Intensive Care
Two types of ventilators and two modes of mechanical ventilation evolved during this period;
the first type of ventilator was pressure cycled (PCV). Two ventilators were commonly used for PCV in the 1960’s and 1970’s; the Bird Mark 7 and the Bennet PR2.

10. Era of Respiratory Intensive Care
The second type of ventilator that evolved from a historical perspective is the volume cycled ventilator – VCV.
The first fluidic ventilator utilizing moving streams of liquid or gas for sensing, logic, amplification and controls was designed for the US army in 1964 by Barila and
the first commercial versatile fluidic ventilator “Hamilton standard PAD” appeared in The term ‘weaning’ was used to explain various techniques to test the quality of patient’s spontaneous ventilation before extubation.

11. Present day
A mechanical change of substantial importance in the late 1960’s and early 1970’s that shaped the present era was the introduction of Positive End Expiratory Pressure (PEEP).
Two modes of ventilation Assisted Ventilation (AV) and Controlled Mechanical Ventilation (CMV) came together in a single piece of equipment and the modern era of multiple choice respiratory support was born.
The introduction of IMV permitted spontaneous respiration in the midst of substantial respiratory failure which paved the way for a means of weaning i.e. SIMV. PSV proved to be an addition to IMV that facilitated spontaneously breathing patients

12. MECHANICAL VENTILATION

13. INDICATIONS FOR MV Hypoxemia Acute respiratory acidosis
Reverse ventilatory muscle fatigue
Permit sedation and/or neuromuscular blockade
Decrease systemic or myocardial oxygen consumption

14. INDICATIONS CONTINUED
Reduce intracranial pressure through controlled hyperventilation
Stabilize the chest wall
Protect airway
Neurologic impairment
airway obstruction

15. TYPES OF CONVENTIONAL MV
Timed cycled
Home ventilators
Pressure cycled
Pressure controlled
Volume cycled
Flow cycled
Pressure support

16. VOLUME VENTILATION Controlled mechanical ventilation CMV
Assist-control AC
Synchronized intermittent mandatory ventilation SIMV
Which mode?

17. VENTILATOR SETTINGS Tidal volume Respiratory rate
10 to 15 mL/kg
Respiratory rate
10 to 20 breaths/minute
normal minute ventilation 4 to 6 L/min
Fraction of inspired oxygen
Flow rate and I:E ratio

18. PRESSURE SUPPORT VENTILATION
Flow cycled
preset pressure sustained until inspiratory flow tapers to 25% of maximal value
Comfortable
Used mainly as a weaning mode
Wean pressure until equivalent to air way resistance
peak - plateau pressure

19. PRESSURE CONTROLED VENTILATION
Pressure cycled
Volume varies with lung mechanics
Minute ventilation is not assured
Improves oxygenation
recruitment of alveoli
Lessens volutrauma?

20. SETTINGS FOR PRESSURE CONTROL VENTILATION
Inspiratory pressure
I:E ratio
1:2, 1:1, 2:1, 3:1
Rate
FIO2
Peep

21. PRESSURE REGULATED VOLUME CONTROLLED
Ventilate with pressure control
Preset volume
Inspiratory pressure is adjusted breath to breath
Minute ventilation is maintained

22. INDICATIONS FOR PEEP ARDS Stabilize chest wall Physiologic peep
Decrease Auto-peep?

23. CONTRAINDICATIONS FOR PEEP
Increased intracranial pressure
Unilateral pneumonia
Bronchoplueral fistulae

24. PEEP Increases FRC Recruits alveoli Improves oxygenation Best Peep
based on lower inflection of pressure volume curve

25. TROUBLE SHOOTING VOLUME VENTILATION
High pressure alarm
Breath sounds
CXR
Low tidal volume
disconnected
Desaturation

26. TROUBLE SHOOTING PRESSURE VENTILATION
Low tidal volumes or minute ventilation
Desaturation
Breath sounds
Patient agitation
CXR

27. Sedation in Mechanically Ventilated Patients
Benzodiazepines
Opioids
Neuroleptics
Propofol
Ketamine
Dexmedetomidine

28. Benzodiazepines Lorazepam Midazolam Half-life 12 to 15 hours
Major metabolite inactive
Midazolam
Half-life 1-4 hours, increased in cirrhosis, CHF, obesity, elderly
Active metabolite

29. Opioid
Morphine
Fentanyl
Hydromorphone

30. Neuroleptics Haloperidol Side Effects Mild agitation .5mg to 2mg
Moderate agitation 2 to 5 mg
Severe 10 to 20 mg
Side Effects
Acute dystonic reactions
Polymorphic VT
Neuroleptic malignant syndrome

31. Propofol Side Effect Anticonvulsant Expensive Use short term
Hypotension
Bradycardia
Anticonvulsant
Expensive
Use short term

32. Ketamine Dissociative anesthetic state Direct cardiovascular stimulant
Brochodilator
Side Effects
Dysphoric reactions
increased ICP

33. Dexmedetomidine Centrally acting alpha 2 agonist
Approved for 24 hours or less
Side Effects
Hypotension
Bradycardia
Atrial fibrillation

34. Maintenance of Sedation
Titrate dose to ordered scale
Motor Activity Assessment Scale MAAS
Sedation-Agitation Scale SAS
Ramsay
Rebolus prior to all increases in the maintenance infusion
Daily interruption of sedation

35. NEUROMUSCULAR BLOCKING AGENTS
Difficult to asses adequacy of sedation
Polyneuropathy of the critically ill
Use if unable to ventilate patient after patient adequately sedated
Have no sedative or analgesic properties

36. Neuromuscular Blocking Agents
Depolarizing
Bind to cholinergic receptors on the motor endplate
Nondepolarizing
Competitively inhibit Ach receptor on the motor endplate

37. Depolarizing NMBA Succinylcholine
Rapid onset less than 1 minute
Duration of action is 7-8 minutes
Pseudocholinesterase deficiency
1 in 3200
Side Effects
Hyperthermia, Hyperkalemia, arrhythmias
Increased ICP

38. Nondepolarizing Agents
Pancuronium
Drug of choice for normal hepatic and renal function
Atracurium or Cisatracurium
Use in patients with hepatic and/or renal insufficiency
Vecuronium
Drug of choice for cardiovascular instability

39. No bubble is so iridescent or floats longer than that blown by the successful teacher. Sir William Osler

41. MV IN OBTRUCTIVE AIRWAY DISEASE
Decrease barotrauma
related to mean airway pressure
Increase I:E
decrease TV and/or increase flow
Minimize auto-peep
auto-peep shown to cause most barotrauma
Permissive hypercapnea

42. ARDS
Set peep to pressure shown at lower inflection point of pressure volume curve
Tidal volumes set below upper inflection point of pressure volume curve
Use pressure control ventilation early
Minimize volutrauma

44. Ventilation With Lower Tidal Volumes
Tidal volume: 6 ml/kg
Male (centimeters of height-152.4)
Female (centimeters of ht )
Decrease or Increase TV by 1ml/kg to maintain plateau pressure 25 to 30.
Minimum TV 4ml/kg
PaO mm Hg. Sats 88 to 95%
pH 7.3 to 7.45

45. CASE EXAMPLE
34 y/o female admitted with status asthmaticus and respiratory failure
You are called to see patient for inability to ventilate
Tidal volume 800 cc, FIO2 100%, AC 12 Peep 5 cm
PAP 70, returned TV 200 cc

46. Case example continued
Examine patient
CXR
Sedate
Assess auto-peep
Increase I:E
Lower PAP and MAP
Reverse bronchospasm & elect. Hypovent.

47. CONCLUSION Three options for ventilation Peep, know when to say no
volume, pressure, flow
Peep, know when to say no
Always assess to prevent barotrauma
ventilate below upper inflection point
assess static compliance daily
monitor for auto-peep