Principles of mechanical ventilation 2

PRINCIPLES OF MECHANICAL

VENTILATION

and

BLOOD GAS INTERPRETATION

SAMIR EL ANSARYICU PROFESSOR

AIN SHAMSCAIRO

[email protected]

Global Critical Carehttps://www.facebook.com/groups/1451610115129555/#!/groups/145161011512

9555/ Wellcome in our new group ..... Dr.SAMIR EL ANSARY

Definitions

• Tidal Volume (TV): volume of each breath.

• Rate: breaths per minute.

• Minute Ventilation (MV): total ventilation per minute. MV = TV x Rate.

• Flow: volume of gas per time.

Definitions

• Compliance:The distensibility of a system. The

higher the compliance, the easier it is to inflate the lungs.

• Resistance:Impediment to airflow.

Definitions

SIMV

Patient breathes spontaneously between ventilator breaths.

• Allows patient-ventilator synchrony

• Making for a more comfortable experience.

Definitions

• PIP: maximum pressure measured by the ventilator during inspiration.

• PEEP: pressure present in the airways at the end of expiration.

• CPAP: amount of pressure applied to the airway during all phases of the respiratory cycle.

Definitions

• PS: amount of pressure applied to the airway during spontaneous inspiration by the patient.

• I-time: amount of time delegated to inspiration.

Types of Ventilation

• Volume Control

• Pressure Control

• Pressure Support-CPAP

• Pressure-Regulated Volume Control

Volume Control

• The patient is given a specific volume of air during inspiration.

• The ventilator uses a set flow for a set period of time to deliver the volume:

• TV (cc) = Flow (cc/sec) x i-time (sec)

Volume Control

• The PIP observed is a product of :

• lung compliance, airway resistance and flow rate.

• The ventilator does not react to the PIP unless the alarm limits are violated.

Volume Control

• The PIP tends to be higherthan during pressure controlventilation to deliver the same volume of air.

Volume Control

• With SIMV, the patient can breath spontaneously between vent breaths.

• This mode is often combined with

PS.

Triggering the Ventilator

Pressure Control

• Patient receives a breath at a fixed airway pressure.

• The ventilator adjusts the flow to maintain the pressure.

• Flow decreases throughout the inspiratory cycle.

Pressure Control

• The pressure is constantthroughout inspiration.

• Volume delivered depends upon the inspiratory pressure, I-time, pulmonary compliance and airway resistance.

Pressure Control

• The delivered volume can vary from breath-to-breath depending upon the

above factors. MV not assured.• Good mode to use if patient has large

air leak, because the ventilator will increase the flow to compensate it.

Volume vs. Pressure

Changes in ARDS

Volume Control Pressure Control

ARDS ARDS

CPAP-Pressure Support

•No mandatory breaths• Patient sets the rate, I-time, and

respiratory effort.

• CPAP performs the same function as PEEP, except that it is constant throughout the inspiratory and expiratory cycle.

CPAP-Pressure Support

• Pressure Support (PS) helps to

overcome airway resistance and inadequate pulmonary effort and is

added on top of the CPAP

during inspiration.

CPAP-Pressure Support

• The ventilator increases the flow during inspiration to reach the target pressure and make it easier

for the patient to take a breath.

SIMV + PS

Pressure-Regulated Volume Control

• In this mode, a target minute ventilation is set.

• The ventilator will adjust the flow to deliver the volume without exceeding a

target inspiratory pressure.

•Decelerating flow pattern.

Pressure-Regulated Volume Control

•No change in minute ventilation if pulmonary

conditions change.

• Can ventilate at a lower PIP than in regular volume control.

Pressure-Regulated Volume Control

•Hard to use on a spontaneously breathing

patient or one with a large air leak.

•Not a “weaning” mode.

Initial Ventilator Settings

•Rate:•20-24 for infants and

preschoolers

•16-20 for grade school kids

•12-16 for adolescents

Initial Ventilator Settings

• TV: 10-15ml/kg

• PEEP: 3-5cm H2O

• FiO2: 100%

• I-time: 0.7 sec for higher rates, 1sec for lower rates

Initial Ventilator Settings

•PIP (for pressure control)

about 24cm H2O

•Pressure Support

5-10cm H2O

Adjusting The Ventilator

• pCO2 too high

• pCO2 too low

• pO2 too high

pO2 too low

PIP too high

pCO2 Too High

• Patient’s minute ventilation is too low.

• Increase rate or TV or both.

• If using PC ventilation, increase PIP.

• If PIP too high, increase the rate instead.

pCO2 Too High

• If air-trapping is occurring, decrease the rate and the I-time and increase the TV to allow complete exhalation.

• Sometimes, you have to live with the high pCO2, so use THAM or bicarbonate to increase the pH to >7.20.

pCO2 Too Low

• Minute ventilation is too high.

• Lower either the rate or TV.

• Don’t need to lower the TV if the PIP is <20.

• PIP <24 is fine unless delivered TV is still >15ml/kg.

pCO2 Too Low

• TV needs to be 8ml/kg or higher to prevent progressive atelectasis

• If patient is spontaneously breathing, consider lowering the pressure support if spontaneous TV >7ml/kg.

pO2 Too High

• Decrease the FiO2.

• When FiO2 is less than 40%, decrease the PEEP to 3-5 cm H2O.

• Wean the PEEP no faster than about 1 every 8-12 hours.

pO2 Too High

• While patient is on ventilator,

don’t wean FiO2 to <25%

to give the patient a margin of safety in case the ventilator quits.

pO2 Too Low

• Increase either the FiO2 or the mean

airway pressure (MAP).• Try to avoid FiO2 >70%.• Increasing the PEEP is the most efficient

way of increasing the MAP in the PICU.

• Can also increase the I-time to increase the MAP (PC).

pO2 Too Low

• Can increase the PIP in Pressure Control to increase the MAP,

but this generally doesn’t add much at rates <30 bpm.

pO2 Too Low

• May need to increase the PEEP to

over 10, but try to stay <15 if possible.

PIP Too High

• Decrease the PIP (PC) or the TV (VC).

• Increase the I-time (VC).• Change to another mode of

ventilation. Generally, pressure control achieves

the same TV at a lower PIP than volume control.

PIP Too High

• If the high PIP is due to high airway resistance, generally the lung is protected from

barotrauma unless air-trapping occurs.

Weaning Priorities

• Wean PIP to <35cm H2O

• Wean FiO2 to <60%

• Wean I-time to <50%

• Wean PEEP to <8cm H2O

• Wean FiO2 to <40%

Weaning Priorities

• Wean PEEP, PIP, I-time, and rate towards extubation settings.

•Can consider changing to volume control ventilation when PIP <35cm H2O.

Complications

•Pulmonary–Barotrauma

–Ventilator-induced lung injury

–Nosocomialpneumonia

Tracheal stenosis

Tracheomalacia

Pneumothorax

Complications• Cardiac–Myocardial

ischemia– Reduced cardiac

output• Gastrointestinal–Ileus

–Hemorrhage

–Pneumoperiteneum

Complications

•Renal–Fluid

retentionNutritional

Malnutrition

Overfeeding

Acute Deterioration• DIFFERENTIAL DIAGNOSES

PneumothoraxRight mainstemintubationPneumonia Pulmonary edema

Acute Deterioration• DIFFERENTIAL DIAGNOSES

Loss of airwayAirway occlusionVentilator malfunctionMucus pluggingAir leak

Physical Exam• Tracheal shift–Pneumothorax

• Wheezing–Bronchospasm

–Mucus plugging

–Pulmonary edema

–Pulmonary thromboembolism

Physical Exam

• Asymmetric breath sounds

–Pneumothorax

–Mainstem intubation

–Mucus plugging with atelectasis

Physical Exam

• Decreased breath sounds bilaterally

–Tube occlusion

–Ventilator malfunction

–Loss of airway

Pressure Patterns

• Elevated peak and plateau pressures

–Pneumonia

–Pulmonary edema

–Pneumothorax

–Atelectasis

–Right mainstem intubation

Pressure Patterns

• Elevated peak pressure, normal plateau pressure:

–Airflow obstruction

–Mucus plugging

–Partial tube occlusion

Pressure Patterns

• Reduced peak and plateau pressure :

–Cuff leak

–Ventilator malfunction

–Large bronchopleural fistula

Extubation Criteria

•Neurologic

•Cardiovascular

•Pulmonary

Neurologic

• Protect his airway, e.g, have cough, gag, and swallow reflexes.

• low Level of sedation

• No apnea on the ventilator.

Neurologic• Must be strong enough to generate a

spontaneous TV of 5-7ml/kg on 5-10 cm H2O PS

• or have a negative inspiratory force

(NIF) of 25cm H2O or higher.

• Being able to follow commands is preferred.

Cardiovascular

• Patient must be able to increase cardiac output to meet demands

of work of breathing.

• Adequate cardiac output without being on significant inotropic support.

• Hemodynamically stable.

Pulmonary

• Patient should have a patent airway.

• If no air leak, consider decadron and racemic epinephrine.

• Pulmonary compliance and resistance should be near normal.

Pulmonary

• Patient should have normal blood gas and work-of-breathing on the following settings:

– FiO2 <40%

–PEEP 3-5cm H2O

–PS 5-8cm H2O

–Spontaneous TV of 5-7ml/kg

–Adequate RR

Global Critical Carehttps://www.facebook.com/groups/1451610115129555/#!/groups/145161011512

9555/ Wellcome in our new group ..... Dr.SAMIR EL ANSARY

GOOD LUCK

SAMIR EL ANSARYICU PROFESSOR

AIN SHAMSCAIRO

[email protected]