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 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
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
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.