Dr Chaitanya VemuriInt.Med M.D Trainee
The choice of ventilator settings – guided by clearly defined therapeutic end points.
In most of cases : primary goal is to correct abnormalities of arterial blood gas tensions
Accomplished by adjusting minute volume - to correct
hypercapnea oxygen supplementation – to correct
hypoxemia
Choice of inspired gas composition
Means to ensure the machine’s sensing of patient’s demand
Definition of machine’s mechanical output
Confirm indication for mechanical ventilation
Invasive / Non invasive Check Connections & Circuit Self test Select mode Set variables Alarm settings Connect to patient Monitor and reassess
Patient not breathing Patient breathing but not enough Patient breathing enough, but pt
hypoxemic / hypercapneic Patient breathing with normal gas
exchange, but working hard Airway protection
LABORATORY CRITERIA
CLINICAL CRITERIA
OTHER CRITERIA
Blood gases : PaO2 < 55 mm Hg PaCo2 > 50 mm Hg pH < 7.32
PFT : Vital Capacity < 10 ml/Kg -ve inspiratory force <25cm H20 FEV 1 < 10 mL/Kg
Apnea / Hypopnea Respiratory distress with altered
mentation Clinically apparent increasing work of
breathing unrelieved by other interventions
Need for airway protection
Controlled hyperventilation ( eg head injury )
Severe circulatory shock
THERE IS NO ABSOLUTE CONTRAINDICATION FOR MECHANICAL VENTILATION
To check : - leak - compliance - resistance of circuit - sensors Needs to be done : - before connecting to
patient - once in 2 weeks - whenever circuit is changed
Depends on : Patients requirement User comfort Availability
For PO2 : adjust FiO2, PEEP
For PCo2 : adjust TV , RR
Tailored to need of the patient
SIMV / A/C – versatile modes for initial settings
In pts with good resp drive & mild – mod resp failure – PSV
Initial TV : 5 – 8 ml/Kg of ideal bd wt Lowest values are recommended in
presence of Obstructive airway ds & ARDS
Goal : to adjust TV so that plateau pressures are less than 35 cm H20
8 – 12 breaths per minute : pts not requiring hyperventilation for treatment of toxic/metabolic acidosis or intracranial injury
Initial rate may be low ( 5 – 6 breaths per min ) in asthmatic pts where permissive hypercapnic technique is used
Lowest FiO2 that produces an Sp02 > 90 % PaO2 > 60 mm Hg is recommended
Normal I:E ratio to start is 1:2
Reduced to 1:4 or 1:5 in presence of obstructive airway disease in order to air trapping
Inverse I:E – in ARDS
60 L/min is typically used
Increased to 100 L/min : to deliver TVs quickly and allow for prolonged expiration in presence of obstructive airway ds
Titrated according to PEEP and BP High PEEP ( > 10 H20 ) – pneumonia, ards PEEP – reduces risk of atelectasis - increase no of open alveoli ( decrease V/Q mismatch ) - in CHF : decrease venous return Physiological PEEP ( 3-5 cm H20 ) : to
prevent decrease in FRC in normal lungs
Set at -1 to -2 cm H20
NEWER VENTILATORS SENSE INSPIRATORY FLOW
and thereby reduce work of breathing associated with ventilator triggering
Mode : Complete / Partial . VCV/PCV Rate : titrate to Pco2 Tidal Volume : 5 – 8 ml / Kg Flow rate & Pattern : 4 – 8 times Minute
Ventilation I:E = 1:2 to 1:4 FiO2 : titrate to O2 Saturation / Pa O2 PEEP : titrate to PaO2 & BP Trigger : Adjust to synchronize
Fixed alarms : disconnection o2 sensor
Set alarms : volume pressure rate apnea
Patient Monitor : pulse , bp , rr, spO2 Ventilator Abg Volume Pressure Rate Patient comfort / synchrony
For Paralysed pts : CMV or A/C mode
For Non paralysed pts : SIMV mode
Pts with normal resp effort mild resp failure : PSV mode
Hypoxia corrected by High FiO2
Increase Expiratory Flow Time to max : to prevent increase intrinsicPEEP
RR : 6 -8 breaths / min ( permissive hypercapnia )
I : E : increased 1:2
A/C mode Tidal Volume : 6 ml/Kg PEEP : 5 Ventilatory rate : 12 titrated to maintain Ph > 7.25
Respond well to positive pressure ventilation (opens alveoli, reduces preload)
Many benefit from trial of noninvasive CPAP / BiPAP
Intubated pts usually manage to oxygenate well
But PEEP can be increased to improve oxygenation and reduce preload