Mechanical Ventilation

Khaled Hadeli, M.D.

HistoryHistory

• 18th century, the Danish fire place bellows

• 1920s, the “Iron Lung”

• World War II, demand for flow valves “pilots”

• polio epidemic

• Bennett & Bird “pressure-cycled ventilators”

• Emerson “volume-cycled ventilators”

Criteria for mechanical ventilation

• Clinical Criteria, i.e. A.B.C

• Profound respiratory failure– RR >35– MIF < 25 cm H2O– VC < 10-15 cc/kg– PaO2 < 60mm Hg with FIO2 > 60%– PaCO2 >50 mm Hg with pH < 7.35

Physiology of MV

• Air moves in and out of the lung according to pressure gradient

• -ve pressure ventilation = creating negative intra thoracic pressure, i.e suck air in.

• +ve pressure ventilation = providing high pressure at the mouth, i.e push air in

Types of Ventilators

• -ve pressure ventilators– Iron lung– Rocking bed– Ventilator vest

Types of Ventilators cont.• +ve pressure ventilators

– Pressure triggered (cycled)• Pressure control (PC)

• PC/IRV

– Volume triggered (cycled)• Asses control (AC)

• SIMV

• CMV = PC and AC

• PS

AC

• CMV, all breaths are machine breaths

• Back up rate

• Decrease work of breathing

• Complications: hyperventilation, Auto peep, ptx, patient need Sedation…

• You can start MV with this mode but you can’t wean.

SIMV

• Patient can breath- on his own- more than the set rate

• May boost with PS

• Increased work of breathing

• You can start MV and wean with this mode

PC

• You set the pressure limit• You set the I:E OR TI

• Variable Vm achieved

• Need to adequately sedate the patient

• Be careful how to put the order, “ total pressure v.s. pressure over the peep”

PC/IRV

• Normal I:E ratio = 1:2

• IRV= 1:1, 2:1, 3:1

• Use in ARDS when you can’t adequately oxygenate

• By trapping air increases the iPeep and improves oxygenation

• Heavy Paralysis and /or heavy sedation

PS

• Spontaneous breathing but each breath is boosted

• If patient don’t “trigger” the ventilator he will not get the breath

• Can be used in combination with SIMV

Ventilatory Settings

I. Mode: PC, SIMV, AC, etc.

II. Rate

III. TVIV. Peep

V. Fio2

VI. PS

Mode of Ventilation

• PC ventilation is more physiologic

• VC ventilation is used more because it is easy to operate

• AC ventilation if you want to rest the patient completely

• SIMV is an ok mode if added PS

Rate/ TV

• Corrects hypercapnea (respiratory alkalosis)• TV 8-10-12 cc/kg• Correct for height/ gender• Be aware of breath “stacking”• Low TV ventilation/ ARDS

Fio2

• Start with 100%

• Use peep to augment

• Decrease Fio2 to less than 40% ASAP

• 40%-60% low risk for ARDS

• More than 60% Dangerous zone

Peep

• Physiologic peep about 3 cm

• Increase as needed up to 25cm

• Peep above 10cm may affect CO

• Decrease peep no more than 2.5cm at a time

PS ventilation

• Can be an effective mode of ventilation if used solo

• Other uses include: combination with SIMV, overcome the ETT resistance,

• No PS if pt is on CMV or if pt has no spontaneous breathing

• Type of weaning

Special issues

• Permissive hypercapnea

• Recruitment maneuvers

• Best Peep

• Lung protective ventilation

• Triggering the ventilator

• Proning

CPAP

• Not a mechanical ventilation

• Pt provides the work of breathing

• Helps to keep air ways open– Rx sleep apnea (proximal air ways)– Improves oxygenation ( distal air ways)

• You can add PS to cpap

NIPPV

• CPAP wit /without PS• Bilevel ventilation• Neuromuscular diseases• COPD• Pulmonary edema (CPAP)• High maintenance, needs the cooperation of

MD, nurse, RT, and the patient

New modes of ventilations

• NO proven efficacy.

Weaning

• Should be started ASAP

• PS wean

• SIMV wean

• CPAP/T piece trial

• Wean to NIPPV

Liberation from MV

• Reversal of the primary condition leading to the respiratory failure

• Mental status

• Adequate strength “MIF”

• F/TV index ( rapid-shallow index)

• Spontaneous TV, rate, VC, Compliance

Sedation

• Adequate sedation, short acting sedatives with/without pain meds.

• Optimize the environment.

• Improve sleep cycles.

• TERN OF THE TV IN PATIENTS ROOM!!

• ICU psychosis

Paralytics

• Depolarizing (intubation), CI in denervated patients and with hyperkalemia.

• Non-depolarizing. Critical illness paralysis vs. steroid induced narcotizing myositis.

• Use minimal doses, avoid steroids, always sedate patients.

Care of the ventilated patient

• Nutrition

• DVT prophylactics

• GI prophylactics

• Daily* CXR

• Cuff leak

• Patient/ventilator synchrony ( sedation, paralysis, triggering, PS…)