MECHANICAL VENTILATION
Consider the NEED for Mechanical Ventilation if:
RR > 35
Rise in PCO2 >10
TV <5cc/kg
Negative inspiratory force <250mmH2O
VC < 10
A-a gradient >450
PaO2 <55
Minute ventilation <10L/min
PaO2/PAO2 <0.15
Unable to maintain airway or obvious respiratory distress
Ventilator Modes/Settings
Initial Settings: AC Rate 10-12 TV 6-10cc/kg (use IBW) FiO2 40-100% PEEP 0-5
AC—Assist Control: all breaths delivered from machine at set TV & rate but the preset rate can
be exceeded by a triggering effort from the pt to deliver the same TV breath
Indications: pts capable of spontaneous resp effort but with inadequate resp muscle strength to
achieve adequate tidal volume; pts who can’t maintain adequate oxygenation and/or ventilation
without significant work of breathing (pulm edema, ARDS, PNA)
Adv: allows pts to choose RR above preset rate while obtaining adequate TV w/breath
Disadvantages: pts with increased RR can develop resp alkalosis and auto-PEEP
SIMV—Synchronized Intermittent Mandatory Ventilation: a preset number of breaths are
mandatory and are delivered by machine at a specific TV, in between these pt may breathe
spontaneously at his/her own TV
Indications: should only be used with intact CNS function or helpful in weaning
Advantages: pt controls PaCO2 and ventilatory pattern of spontaneous breaths, thus decreases
auto-PEEP tendency and lowers mean airway pressures, keeps respiratory muscles active
Disadvantages: requires active respiratory muscles and more work for pt
PSV—Pressure Support Ventilation: with each pt initiated spontaneous breath, neg pressure
generated opens a valve to deliver flow cycled inspiratory support only at desired pressure until
inspiratory flow tapers off (pt controls RR, inspiratory time, flow rate)
Indications: reduces work of breathing in weaning (not for acute resp failure), more comfortable
Disadvantages: may not provide sufficient minute ventilation
CPAP—Continuous Positive Airway Pressure: ventilator maintains positive pressure at the
airway throughout respiratory cycle as end-expiratory pressure
Indications: in spontaneous breathing pt with refractory hypoxemia who has adequate control
over their PaCO2 (ventilation); weaning trials to monitor adequacy of oxygenation maintenance;
sleep apnea; neuromuscular or chest wall disease
PEEP—Positive End-Expiratory Pressure: maintains set amount of positive pressure at end of
expiration to combat collapsing tendency of small airways and alveoli to improve compliance
Indications: refractory hypoxemia, ARDS
Disadvantages: more difficult to wean if PEEP required, may increase risk of barotrauma
BIPAP—Bilevel Positive Airway Pressure: ventilator maintains inspiratory and expiratory
pressure support to help ventilate pts (ie CPAP and PEEP)
Indications: hypercarbia or hypoxemia, as a bridge before mechanical ventilation; COPD
Start settings at 8-12/ 4-6; repeat ABG in 30 minutes and adjust as needed; inc PEEP to a tital
volume of 5-7 L
Ventilator Weaning
DECREASE FiO2 after 24-48hrs to <0.60 as 100% will lead to O2 toxicity
1) Patients with acute respiratory failure should have a weaning trial daily (minimal or no CPAP)
once initial insult has stabilized and FiO2 is <0.6 with sats >92%.
2) Patients with chronic respiratory failure (trach, ETT >10-14days) have chronic daily weaning
trials (using PSV or CPAP) as tolerated to encourage lung mechanics (see Pre-Printed Orders)
Weaning Parameters after 30-120minute weaning trial
PaO2 > 60mmHg with FiO2 <0.6
PEEP <5
RR 12-30
TV >3.5ml/kg
PSV <20
PaO2/FiO2 >150-200
VC >10ml/kg
Minute Ventilation <10L/min
Rapid shallow breathing Index = RR/TV in liters < 100
Failure to Wean, Consider Causes:
1) General: pain control, fluid status, sedation, need for bronchodilators or steroids
2) Neurologic: CVA, OSA, metabolic
3) Respiratory: fatigue, incr O2 demands, poor nutrition, electrolyte abnormalities
4) Cardiac: ischemia, CHF
5) Psych: sleep problems, depression, anxiety, fear, drug withdrawal
Sedation on Mechanical Ventilation
Goal: to keep pt calm, cooperative, able to follow commands, should turn off for weaning
1) Ativan: 2-4mg IV prn to sedate OR 2mg bolus followed by 1mg/hr infusion (titrate as
needed for adequate sedation with max 5-10mg/hr)
2) Versed: 5-10mg IV prn to sedate OR 5mg bolus followed by 5mg/hr infusion (titrate by
1mg/hr or rebolus with 5mg for adequate sedation)
3) Propofol: initial 5-10mcg/kg/min for 10min and titrate at 5-10mcg/kg/min increments every
10-15minutes as needed for desired sedation to max 50mcg/kg/min
4) Fentanyl: 25-100mcg IV prn for sedation/analgesia OR 3mcg bolus followed by 25mcg/hr
infusion (titrate 25mcg/hr or rebolus as needed for adequate sedation)
Monitoring Lung Mechanics
Peak Inspiratory Pressure (at end of inspiration): reflects inflation volume, airway resistance,
lung and chest wall compliance
Plateau Pressure (after expiration): reflects elastic recoil pressure of lungs & chest wall
Incr in Peak Pressure with no change in Plateau Pressure = increased airway resistance
 aspiration, bronchospasm, secretions, tracheal tube resistance, obstruction
Increase in both Peak Pressure and Plateau Pressure = decreased lung compliance
 atelectasis, auto-PEEP, pneumonia, pneumothorax, pulm edema, abd distention, asynchronous
breathing