Introduction to Mechanical Ventilation

The mechanical ventilation is basically a replaement of assistance to the spontaneous ventilation/ breathing.

The concept of mechanical ventilation was first introduced by a scientist "Andreas Vesalius in 1555"

He said that : "an opening must be attempted in the trunk of the trachea, into which a tube of reed or cane should be put; you will then blow into this, so that the lung may rise again . . . and the heart becomes strong"

This was the fundamental of development of mechanical ventilation and intubation but it took 400 years to apply this and actually use it in medical field.

Now a days mechanical ventilation has been the very vital part of medical sciece and has been used for many purposed in daily basis for saving millions of the lives worldwide.

Mecahnical ventilation and mechanicala ventilators have been used to save lives in emergency situations as well as in elective and emergency surgeries. They are the majr part of modern day ICU care.

The first use of assisted ventilation (nt mechanical ventilations) was done in Europe during Polio outbreak (Read more about polio here).

Back then even human were used to a rtificailly ventilate the lung of sick people making them the human ventilators, and they even worked upto 8 hours a day and the medical schools were shut down for same purpose.

Later a company named "Ëmerson company" made a prototype positive pressure ventilator which was used in the Massachusetts General Hospital and it became instant succcess and started the era of Modern day intennsive care medicine.

What is Mechanical Ventilation? What happens when youre on a ventilator?

The basic concept of mechanical ventilation or positive pressure ventilation is to create a positive pressure the moves air/oxygen into the lungs. DUring breathing the pressure in our alveoli keeps on changing and during inspiration it becomes subatmospheric which drags air into the lungs and aveoli.

But if a person is not able to breathe by themselves in that condition positive pressure more than that of alveoli and lungs needs to be created by using artificial means and air or oxygen is pushed into the lungs.

A ventilator machine labelled different parts

Mechanical Ventilation Definition

By undertanding above concept, mechanical ventilation can be difined as a process in which the lungs of a person who is not able to breath by oneself are inflated using external force, person or machine in order to push air into them and pull it back, in order to complete gaseous exchange, or for purpose of delivering medicine (in case of anesthesia or other critical care).

Understanding Mechanical Ventilation Settings

a bag-valve-mask

In general there are two methods of positive pressure ventilation:

Volume controlled ventilation VC mode:

In this mode the initially the volume of air that is needed to be pushed into the ungs is selectd and ventilator selects the pressure needed to push that much volume into lungs by itself. Depending on that the rate of lung inflation, that if respiratory rate can be kept constant ot adjusted.

Pressure control ventilation PC mode:

In this mode the pressure at which the air/oxygen is pushed into lungs is preselected and duration and rate of lung inflation can be adjusted on the basis of need by the operator or doctor. by this desired tidal volume and sufficient oxygenation can be achieved.

The rate of lung inflation is initially high then is reduced so that presssure is same throughout(constant).

In other classification it can be classified as invasive and noninvasive ventilation:

Invasive ventilation

Invasive ventilation means ventilation with intubation in which a person a person has Endotrachea tube (ET Tube) placed in his trachea and through this air is supplied or his lungs are ventilated.

Endotracheal tube

Non-inasive ventilation

Non invasive ventilation consists of CPAP and BiPAP. CPAP standa for continuous positive pressure ventilation and BiPAP mean bilevel positive pressure ventilation.

These both are achieved through a fitting mask kept covering nose and mouth of the patient.

Though these types of ventilation can also be achieved in invasive ventilation as well, unless not necessary a person is not intubated but CPAP / BiPAP mas is used for this purpose.

Volume control Vs Pressure control technique in mechanical ventilation

Invasive Mechanical Ventilation: Benefits and Risks

Indication of mechanical ventilation

Respiratory failure

Hypoxemic respiratory failure : low oxygen saturation (sa02 or sp02)
Hypercarbic respiratory failure: High carbondioxide content in blood (paCO2)
Acute respiratory failure

Ventilatory failure
To reduce cerebral blood flow in case of raise ICP
Prevent aspiration of gastric content or other foreign body
Protect airway in seerely ill patient
In intoxicated, poisoned patients
To delever medicine and artificially breathe in case of general anesthesia
Hemodynamic instability
Heart attack
Head, face and neck surgery
Unstable or risky airway
Cardiac arrest
Encephalopathy
Coma or deterirating GCS

Ventilated patient depiction drawing

Befefits of mechanical ventilation:

Proper and adequate oxygenation
Accurate measurement of pressure and volumes
Decreases work of breathing
Improves gas exhange
Reduces mortality
Low failure rate than noninvasive ventilation
Improves general pulmonary function
Multiple modes available and settings can be changed according to need
Stabilize and protects the airwat from collapse or obstruction
Prevents aspiration
Prevents atelectasis
No airleaks

Risks associated with mechcanical ventilation:

High pressure related lung injury : Barotrauma
Volume trauma
Oxygen toxicity
Ventilator dependence
Infection of airway
Pneumonia, also called VAP : Ventilator associated pneumonia
Mucus plug and lung collapse
Airway trauma, mediastinal perforation
Cuff presure injury to trachea and fistula formation, tracheal necrosis
Hemodynamic collapse
Tube malposition
Electrolyte and aid base imbalance
Mouth, teeth and lip trauma
Infection of sinuses
Muscle weakness and wasting and difficulty breathing after intubation later
Position related complication
Deep venous thrombosis and Pulmonary embolism (PE)
Presure sores, ulcers
Psychaitric problems
Vocal cord injury and difficulty prducing speech

Mechanical Ventilation Systems: Types and Components

Invasive ventilator with modern mamchine
Bag-valve-mask ventilator (manual)

Though bag valve mask can also be connected to endotracheal tube.

ventilator

Components of mechanical ventilator:

Connector tube
circuits
t-piece
HME filter
monitor
air and oxygen ports and supply
ventilator machine
power supply
control knobs and butttons

ventilator parts

Instruments needed for mechanical ventilation

Ventilator machine
Connecting tubes for oxygen deivery
Endotracheal ET tube
Syringes
Stethoscope
Direct laryngoscope
Bag-Valve-Mask
Suction machine
Suction tube
Source of oxygen
Fixating tapes/dresings
Medications for anesthesia and muscle relaxation
Monitor for vitals monitering
Trained manpower

Process of putting one into mechanical ventilator or starting mechnical ventilation

The patient is decided for mechanical ventilation on basis of above mentioned criteria
Patient is preoxygenatied
Rapid sequence intubation is done using anesthetic agent and muscle relaxants
Once intubation is done then patient is connected to ventilator machine with appropriate setttings
The settings of the ventilator can be changed as need and patiend is intensively monitored
Regularly check ABG to maintain arterial blood ga and electrolyte in limits
Keep arterial blood pH 7.35-7.45
Reularly check patient efforts, improvements, and treat the condition and cause of patiet's need of intubation
Follow strict precaution for infection prevention
Prevent other complication
How does a ventilator work

Method of ventilation-Lung Protective ventilatory strategy

Set tidal volume to 6ml/kg

calculate ideal body weight
use VC and set initial tidal volume Vt to 8 ml/kg
set RR to match baseline minute ventilation but not >35 bpm
set PEEP to 5 cm of H2O
reduce Vt by 1 ml/kg every 1-2 hr till its 6ml/kg
adjust PEEP and FiO2 to maintain SpO2 88-95%

Prevent plateau pressure exceedig 30 cm of water

if plateau pressure .30 cm of water and Vt 6 ml/kg decrease vt 1 ml/kg until plateau pressure falls below 30 cm of water or Vt reached minimum of 4ml/kg

use least possible concentreation of oxygent (fraction of inspired oxygen or FiO2) to maintain saturation more than 90%
Adjust PEEP to maintain alveolar potency while preventing overdistention and closure reopening
Ph goal to 7.30 to 7.45

if pH 7.15-7.30 increase RR until ph >7.3, paco2 <25 or RR = 35
if pH <7.15, increase RR=35. if still remains <7.15, increase Vt in 1ml/kg until pH>7.15
if pH>7.45 decrease RR if possible

Read Normal ABG finding of a health person here:

Care during mechanical ventilation:

Sedation and muscle relaxants or paralysis
Analgesia
Intensive monitoring
Chest physiotherapy
Suctioning and secretion clearing
Nutrition
Humidification
Prevention of infection: common site of infections include lungs, urine, oral cavity, skin, and blood
Mobilization
Pressure prevention
Thromboembolic prophylaxis
Skincare
Oralcare
Eye care
Other general care

ventilator in action

Indication for discntinuation mechanical ventilation or indication of extubation

Patients recovery
Weaning
Completion of indication
Death

Technique of weaning:

   SIMV wean
   PS wean
   T-piece trial

Some terminlogies related to mechanical ventilation:

Respiratory rate RR

Number of breathes (insiration and expiration = one breathe) per minute

Tidal volume Vt

The volume of air inhaled or exhaled in each breath / respiration by the person

Minute ventilation MV

Total volume inhald or exhaled by the person in a minute

FiO2

Fraction of the inhaled oxygen i.e percentage of oxygen in inhaled air

Peak pressure

The maximum pressure during inspiration generated by machine to push air into the lungs.

PEEP

Positive end expiratory pressure. It is the pressure at aveoli at the end of the expiration cycle before beginning of inspiration.

ACMV

Assist controlled mechanical ventilation

IMV

Intermittent mandatory ventilation

SIMV

Synchronized intermittent mandatory ventialtion

PSV

Pressure Support Ventilation

A/C, PCV

Assisted/Controlled, Pressure Controlled Ventilation (time cycled)

A/C, VCV

Assisted/Controlled, Volume Cycled Ventilation.

IRV

Inverse ratio ventilation

TCV

TIme controlled ventilation

ZEEP

Zero end expiratory pressure

NEEP

Negative end expiratry pressure

I:E ratio

Ratio of inspiratory time to expiratory time

SIMV + pressure support

Synchronized Intermittent Mandatory Ventilation with PEEP

CPAP

Continuous positive airway presssure

BiPAP

Bilevel positive aiway pressure

If you want to read more about above termnologie write us at mail@chaitanya.com.np

Some non-convetional ventilation strategies

HFOV- high frequency oscillatory ventillation
APRV- airway pressure release ventilation
PLV- partial liquid ventilation
ECMO- extracorporeal membrane oxygenation
PAV- proportional assist ventilation
NAV- neurally adjusted ventillatory-assist ventilation
PAV-NAV : proportional assist ventilation-neurally adjusted ventillatory-assist ventilation

Read my friend's blog at doctorhealthrx.com

Conclusion: Importance of Mechanical Ventilation

Mechanical ventilation is a medical technique that replaces or assists spontaneous breathing. The concept was first introduced in 1555 by Andreas Vesalius, but it took 400 years to develop mechanical ventilation into a medical practice.

Today, mechanical ventilation and ventilators are widely used for various purposes in medical care, including elective and emergency surgeries and emergency situations. There are two main methods of positive pressure ventilation, volume-controlled and pressure-controlled ventilation, which can be invasive or noninvasive.

Mechanical ventilation has many benefits, such as improving gas exchange, reducing the work of breathing, and improving general pulmonary function, but there are also risks, such as high pressure or lung damage. Overall, mechanical ventilation has been a crucial part of modern-day intensive care medicine and has saved millions of lives worldwide.

Mechanical Ventilation: Definition, Settings, benefits of invasive mechanical ventilation