INITIATION OF

MECHANICAL
VENTILATION
Referrences
◦ Chang mechanical ventilation fourth edition
◦ Pilbeams mechanical ventilation 5 th edition
◦ Miller 9th edition
 Discussion

◦
Indications
◦ Types
◦ Terminologies
. Modes
◦ Settings
◦ Hazards
Indications
patient cannot maintain spontaneous ventilation
provide adequate oxygenation
carbon dioxide removal.

◦ 4 groups
◦ 1) acute ventilatory failure
◦ 2) impending ventilatory failure
◦ 3) severe Hypoxemia
◦ 4) prophylactic ventilatory support
Acute respiratory failure
Definition
◦ sudden increase in PaCO2 to greater than 50 mm Hg with accompanying respiratory acidosis (pH
<7.30)

Causes
◦ Reduced drive to breath or increased drive
◦ Neuromuscular disorder
◦ Disorder increases work of breathing
Impending Ventilatory failure

maintain marginally normal blood gases, but only at the expense of increased work of breathing

.
prolonged excessive work of breathing

muscle fatigue ventilatory failure

PaCO2 will rise

pH will fall - pathology not corrected

Assessment of impending Ventilatory failure
Severe hypoxamia
◦ PaO2 is less than 60 mm Hg on 50% or more of oxygen or less than 40 mm Hg at any FIO2.

◦ P(A-a)O2 is the difference of PAO2 And Pa02

◦ P(A-a)O2 = PAO2 –PaO2
◦
◦ PAO2 = (PB -PH2O) × FIO2 -(PaCO2/R)
threshold for ALI P/F value ≤300 mm Hg. ARDS ≤200 mm Hg
calculated by:P/F = (PaO2 / FIO2) mm Hg
Prophylactic Ventilatory Support
minimize hypoxia of the major body organs, reduce the work of breathing, oxygen
consumption ,rest cardiopulmonary system, and promote patient recovery
Contraindication
untreated tension pneumothorax

◦ patient’s informed refusal

◦ medical futility,

◦ reduction or termination of patient pain and

suffering
 Goals
Physiological objective Clinical objective

◦ support pulmonary gas exchange ◦ Reverse Respiratory distress

◦ increase lung volume ◦ Reverse acute respiratory failure
◦ Reduce work of breathing ◦ Reverse hypoxemia
◦ Reduce systemic/myocardial oxygen
consumption
Types of mechanical ventilation
◦ Negative pressure ventilation

◦ Positive pressure ventilation

◦ Invasive
◦ Non invasive

◦ Full ventilatory support

◦ Partial ventilatory support
Indication of invasive ventilation
◦ Apnea or impending respiratory arrest
◦ Acute exacerbation of COPD/asthma
◦ Acute ventilatory insufficiency in neuromuscular disorder
◦ Acute hypoxemic respiratory failure
◦ Flail chest
◦ Traumatic brain injury
 Non invasive ventilation
Indications Contraindications
RR>25/min ◦ Cardiac /respiratory arrest
PH-7.25 to 7.30 ◦ Cardiovasular instability
PCo2_45 to 60mmhg ◦ Uncooperative/ Head or facial trauma
Accessory mucle use/paradoxical breath At ◦ Tracheo esophagial fistula
least any 2
Non invasive ventilation

Advantages Disadvantages

◦ Avoids Artificial airwaycomplication ◦ Gastric distension

◦ Reduce heavy sedation ◦ Facial pain, dry nose
◦ Preserve airway ◦ Eye irritation
defense/speech/swallow ◦ Poor sleep
◦ Reduces Invasive monitoring ◦ Mask leak
When to change ??
Variables
◦ Control variables
◦ Pressure /volume /flow/time
◦ Phase variables
◦ Control phases of respiration
◦ Trigger (begins inspiration)
◦ Limit(restrict magnitude of variable )
◦ Cycle (end the inspiration)
◦ Baseline(parameter control during expiration)
Initial ventilatory settings
◦ Mode
◦ Frequency
◦ Tidal Volume
◦ Pressure Support
◦ FIO2
◦ PEEP
◦ I:E Ratio
◦ Flow Pattern
Mode
◦ decide whether the patient should receive full ventilatory support (FVS) or partial ventilatory support
(PVS).

◦ Dual Control Mode

. combines two control variables (e.g., pressure and volume)
.
patient receives mandatory breaths - volume-targeted, pressure-limited, time-cycled
Types
◦ Basic modes
◦ 1. Continuous mandatory ventilation (CMV)
◦ Controlled Ventilation
◦ Assist/Control Ventilation

◦ 2. Synchronized intermittent mechanical ventilation (SIMV)

◦ 3. Spontaneous modes
◦ Spontaneous breathing
◦ • Continuous positive airway pressure (CPAP)
◦ • Pressure support ventilation (PSV)
◦ Bilevel Positive Airway Pressure (BPAP or BiPAP)
Additional modes
◦ Pressure Regulated Volume Control (PRVC)
◦ Pressure Augmentation
◦ Volume-Support Ventilation
◦ Mandatory Minute Ventilaton
◦ Airway Pressure-Release Ventilation
Continuous Mandatory Ventilation
◦ all breaths are mandatory ,volume or pressure targeted.
◦ patient triggered or time triggered.

◦ Controlled Ventilation (time-triggered)

◦ appropriate only when patient can make no effort
Minute Ventilaton is determined by set RR and tidal volume
◦ Indications
◦ Patients obtunded with drugs,
◦ cerebral malfunction,
◦ Spinal cord or phrenic nerve injury,
◦ motor nerve paralysis
◦ closed head injury
 Assisted control mode
◦ operator sets minimum breathing rate, sensitivity level, and type of breath (volume or pressure).

Pt increase minute Ventilaton by triggering additional breaths

◦ ventilator senses a slightly negative pressure (−1 cm H2O) or drop in flow (1-2 L/min below expiratory bias flow),
inspiratory cycle begins
◦
◦ Disadvantage
◦ ventilator’s sensitivity (autotriggering)
◦ Response time
◦
 Synchronized intermittent mandatory
ventilation
Intermittent mandatory ventilation (IMV)
◦ volume or pressure-targeted breaths occur at set intervals (time triggering).
pt breathe spontaneously between mandatory

synchronized IMV (SIMV)

mandatory breaths normally – patient triggered
Predetermined interval (i.e., respiratory rate),
Ventilator waits for patient’s next inspiratory effort ,
senses, assists synchronously delivering mandatory breath
Volume Control Pressure control
 Settings- VCV Pressure Ventilation
◦ Minute Ventilation
◦ Men-4×BSA, women-3. 5×BSA ◦ Pressure support
◦ Increase ◦ Plateau pressure_ 5 to 10 cmh20
◦ 5%/ °F >99°F, 10%/F >37°c ◦ Pressure control
◦ 20%-metabolic acidosis ◦ I : E ratio > /= 1:2
◦ 50 to 100%_resting energy uses high
◦ Decrease
◦ 10%/C( 35 to 37° c)
◦ Tidal volume- 6ml/kg
◦ Frequnecy-12 to 18/min
 Spontaneous modes
1) Spontaneous Breathing
breathe spontaneously through ventilator circuit ( T-piece method)
spontaneous breathing trial (SBT) _used to evaluate patient’s readiness

2)Continuous Positive Airway Pressure

delivers continuous level of positive airway pressure, similar to PEEP
improving oxygenation in patients with refractory hypoxemia and low FRC
◦ Pressure-Support Ventilation
operator sets inspiratory pressure, PEEP, flow-cycle criteria,sensitivity level
◦ patient establishes the rate, inspiratory flow, TI.
◦ High pressure support - large tidal volume and
◦ low Respiratory rate decrease work of breathing

◦ Bilevel positive airway pressure ventilation

◦ two pressure - inspiratory and expiratory positive airway pressure
. Inspiration - patient triggered Or time triggered,
flow or time cycled,
Tidal volume- difference between IPAP and EPAP.
Frequency
◦
Sets between 10 and 12/min, coupled with a 10 to 12 mL/kg tidal volume
. Frequency = Estimated minute volume/Tidal volume
. Minute Volume (Male) = (4)(BSA)
◦ Minute Volume (Female) = (3.5)(BSA)

◦ High ventilator frequency, inadequate inspiratory flow, air trapping-auto-PEEP.

◦ Increase frequency if the PaCO2 is too high; decrease frequency if PaCO2 is too low.
 Tidal volume
◦ Set between 10 and 12 mL/kg of predicted body weight.
◦
◦ 6 mL per kg for ARDS patients-minimize the airway pressures and the risk of barotrauma
◦ COPD- benefit from a reduced tidal volume by100 to 200 mL , reduces the expiratory time requirements
Pressure Support
augment patient’s breathing effort by reducing the airflow resistance during spontaneous
breathing(artificial airway, ventilator circuit, and secretions)

PS level = [(PIP - Pplat)/Vmach] × Vspon

weaning
reduced 2 to 4cm H20 increments until achieving spontaneous frequency of 20 to 25/min , spontaneous
tidal volume of 8 to 10 mL/kg

Extubation
reaches 5 to 8 cm H2O for 2 hours with no signs of respiratory distress.
FIO2
severe hypoxemia or abnormal cardiopulmonary functions
◦ (e.g., post-resuscitation, smoke inhalation, ARDS) - initial FIO2 set at 100%.

◦ After stabilization- below 50%

mild hypoxemia or normal cardiopulmonary functions - 40%

Positive end expiratory pressure (peep)
◦ Positive pressure >zero after end of exhalation
◦ Extrinsic peep_ set by operator
◦ Intrinsic peep(auto) _pressure inside lung, incomplete exhalation
◦ Total- extrinsic+intrinsic
◦ initial PEEP at 5 cm H2O, Increase FRC, treat refractory hypoxemia
I:E Ratio
◦ ratio of inspiratory time to expiratory time, kept between 1:2 and 1:4.

◦ A larger I:E ratio (longer E ratio) - needs additional time for exhalation because of possibility of air
trapping , auto-PEEP

◦ checked by occluding expiratory port of ventilator circuit at the end of exhalation

◦ I:E ratio altered by manipulating any one or a combination of the following controls:
◦ (1) flow rate,
◦ (2) inspiratory time,
◦ (3) inspiratory time %,
◦ (4) frequency
◦ 5) minute volume (tidal volume and frequency).
Effects of Flow Rate Change on I Time, E Time, and I:E Ratio

◦ Using Flow to Change the I:E

◦ minute volume=12 L/min , desired I:E Ratio = 1:3
◦ Calculate: The flow rate for an I:E ratio of 1:3

◦ Solution- flow=Minute Volume × Sum of I:E Ratio

◦ . 12 L/min ×(1+ 3)
◦ 12 L/min × 4= 48 L/min
Inspiratory time

◦ Using I Time to Change the I:E Ratio

. Given: F=16/min. Desired I:E Ratio 5 1:4
◦ Calculate: The I time needed for an I:E ratio of 1:4

◦ Solutionl: f 16/min, time for each breath 60 sec/16 or 3.75 sec

◦ I Time = Time for Each Breath × [I Ratio / Sum of I:E Ratio]
◦ =3.75 sec ×[1/(1 + 4)]
◦ = 3.75 sec× [1/5]
◦ =3.75 sec/5 =0.75 sec
 Inspiratory time %
Using I Time % to Set the I:E Ratio
◦ Given:Desired I:E Ratio = 1:3.5
◦ Calculate: The I time % needed for an I:E ratio of 1:3.5

Solution: ITime% = Iratio/Sum of I:E Ratio

◦ =1/(1 + 3.5).
◦ =1/4.5 ,= 22%
Effects of tidal volume,Frequency on
I:E ratio
Flow Pattern
square flow pattern accelerating flow pattern

◦ increasing flow throughout respiratory cycle

constant peak flow during the entire inspiratory
phase ◦ improve distribution of ventilation in patients with
partial airway obstruction
◦ overcome airway resistance, parenchymal
elastance
◦ remaining peak flow enhance gas distribution
 decelerating flow pattern sine wave flow pattern

◦ high initial inspiratory pressure decrease in

◦ more physiological
flow help improve distribution of tidal volume
and gas exchange ◦ improve the distribution of ventilation and
◦ example-COPD improve gas exchange.
Special settings
Newer modes
volume-assured pressure support (VAPS).
◦
◦ pressure-limited ventilation with volume delivery targeted for every breath
◦ operator -desired volume, minimum rate, set pressure level above baseline, inspiratory gas flow,
sensitivity setting
◦ patient _triggers breath, ventilator delivers set pressure level
◦ monitors flow and volume
◦
Pressure-Regulated Volume Control

◦ delivers pressure breaths that is patient- or time-triggered, volume-targeted, time cycled breath
 Airway Pressure-Release Ventilation
◦ provide two levels of CPAP and to allow spontaneous breathing at both levels when spontaneous effort is present.

◦ pressure levels – time triggered and time cycled

VENTILATOR ALARM SETTINGS
◦ Low Exhaled Volume Alarm
◦ 100 mL lower than expired mechanical tidal volume. detect a system leak or circuit disconnection

◦ Low Inspiratory Pressure Alarm

◦ 10 to 15 cm H2O below observed peak inspiratory pressure
◦

◦ High Inspiratory Pressure Alarm

◦ 10 to 15 cm H2O above observed peak inspiratory pressure
◦ Once alarm is triggered by airflow obstruction, inspiration is immediately terminated,ventilator goes
into expiratory cycle.
◦ Apnea Alarm
◦ low volume and low pressure alarms are triggered in apnea and circuit
disconnection
. 15- to 20-sec time delay, with less time delay at higher frequency

High Frequency Alarm

10/min over observed frequency
indicate patient in respiratory distress

High and Low FIO2 Alarms

high FIO2 alarm – 5% to 10% over the analyzed FIO2
Low FIO2 alarm - 5% to 10% below the analyzed FIO2
HAZARDS AND COMPLICATIONS