Ventilator mode

welcome

LATEST VENTILATOR MODES

INTRODUCTIONPatient from an initial event such as an accident location all the way until he/she is released from hospital, mechanical ventilation is necessary and used in many areas of patient care. Even during transportation, ventilation is provided using an emergency ventilator. During the operation in the hospital an anesthesia machine provides ventilation. Intensive care ventilators are available during the critical stay in intensive care. Even during the subsequent treatment on intermediate care wards, some patients require mechanical breathing support.

HISTORYAndreas Vesalius (1555) is credited with the first

description of positive-pressure ventilation, but it took 400 years to apply his concept to patient care. The occasion was the polio epidemic of 1955, when the demand for assisted ventilation outgrew the supply of negative-pressure tank ventilators (known as iron lungs).

Invasive ventilation first used at Massachusetts General Hospital in 1955.

• Criteria for starting mechanical ventilation are difficult to define and the decision is often a clinical one.

Indication for mechanical ventilation

• Respiratory rate >35 or <5 breaths/ minute• Exhaustion, with laboured pattern of breathing• Hypoxia - central cyanosis, SaO2 <90% on oxygen

or PaO2 < 60 mmHg (8kPa)

• Hypercarbia - PaCO2 > 60 mmHg (8kPa)• Decreasing conscious level• Significant chest trauma• Tidal volume < 5ml/kg or Vital capacity <15ml/kg

Indication (Physical parameters)

• Control of intracranial pressure in head injury• Airway protection following drug overdose• Following cardiac arrest• For recovery after prolonged major surgery or

trauma

Indication (non- respiratory condition)

• Non-invasive ventilation - eg. Iron lung(negative pressure), Musk & adapter (positive pressure)

• Invasive ventilation- eg. IPPV

Type of ventilation

A. TriggerB. LimitC. Cycling

How a ventilator ventilates ?

A

B C

• Patient effort- pressure triggering• After a predetermined time-time triggering• Manually - manual/flow triggering

Start Inflation (Trigger)

Pressure Triggering

• Breath is delivered when ventilator senses patients spontaneous inspiratory effort.

• sensitivity refers to the amount of negative pressure the patient must generate to receive a breath/gas flow.

• If the sensitivity is set at 1 cm then the patient must generate 1 cm H2O of negative pressure for the machine to sense the patient's effort and deliver a breath.

• Acceptable range -1 to -5 cm H2O below patient s baseline pressure

Time triggering

Flow Triggering• The flow triggered system has two preset variables for

triggering, the base flow and flow sensitivity. • The base flow consists of fresh gas that flows

continuously through the circuit. The patient’s earliest demand for flow is satisfied by the base flow.

• The flow sensitivity is computed as the difference between the base flow and the exhaled flow

• Here delivered flow= base flow- returned flow• Hence the flow sensitivity is the magnitude of the flow

diverted from the exhalation circuit into the patient’s lungs. As the subject inhales and the set flow sensitivity is reached the flow pressure control algorithm is activated, the proportional valve opens, and fresh gas is delivered.

• Pressure• Volume• Flow• Time

Stop Inflation (Cycling)

• Terminates inspiratory phase at a preset PIP. TV varies directly with lung compliance and inversely with airway resistance.

• Advantages: reduced barotrauma which has been implicated secondary to high PIP.

• Disadvantages: if lung compliance is less, will lead to respiratory acidosis.

• Important to monitor patient’s expired TV.

Pressure Cycled Ventilation

• Terminates inspiratory phase at a preset TV.• Advantages: patient is guaranteed to receive a preset

TV under normal operating conditions.• Disadvantages: PIP may rise high enough to cause

barotrauma.

Volume Cycled Ventilation

• Terminates the inspiratory phase when inspiratory flow reaches a predetermined minimal level.

• Measured during spontaneous ventilation• Mostly seen in pressure support modes of

ventilation.

Flow cycled ventilation

• Terminates the inspiratory phase when a preset inspiratory time has been reached.

• Advantages: ease to regulate I:E ratio especially when inverse ratio ventilation is desired.

• Disadvantages: delivered TV is dependent on airway resistance and compliance characteristics.

Time Cycled Ventilation

Basic definitions

– Peak Inspiratory Pressure (PIP)– Plateau pressures– Positive End Expiratory Pressure (PEEP)– Continuous Positive Airway Pressure (CPAP)

• Peak Inspiratory Pressure (PIP)- The peak pressure is the maximum pressure obtainable

during active gas delivery. This pressure a function of the compliance of the lung and thorax and the airway resistance including the contribution made by the tracheal tube and the ventilator circuit.

– Maintained at <45cm H2O to minimize barotrauma

• Plateau Pressure-The plateau pressure is defined as the end inspiratory

pressure during a period of no gas flow. The plateau pressure reflects lung and chest wall compliance.

• Mean Airway Pressure- The mean airway pressure is an average of the

system pressure over the entire ventilatory period.

• End Expiratory Pressure- End expiratory pressure is the airway pressure at the

termination of the expiratory phase and is normally equal to atmospheric or the applied PEEP level.

PEEP • Positive end expiratory pressure (PEEP) refers to the

application of a fixed amount of positive pressure applied during mechanical ventilation cycle

• Continuous positive airway pressure (CPAP) refers to the addition of a fixed amount of positive airway pressure to spontaneous respirations, in the presence or absence of an endotracheal tube.

• PEEP and CPAP are not separate modes of ventilation as they do not provide ventilation. Rather they are used together with other modes of ventilation or during spontaneous breathing to improve oxygenation, recruit alveoli, and / or decrease the work of breathing

Advantages

• Ability to increase functional residual capacity (FRC) and keep FRC above Closing Capacity.

• The increase in FRC is accomplished by increasing alveolar volume and through the recruitment of alveoli that would not otherwise contribute to gas exchange. Thus increasing oxygenation and lung compliance

• The potential ability of PEEP and CPAP to open closed lung units increases lung compliance and tends to make regional impedances to ventilation more homogenous.

Physiology of PEEP• Reinflates collapsed alveoli and maintains alveolar

inflation during exhalationPEEP

Decreases alveolar distending pressure

Increases FRC by alveolar recruitment

Improves ventilation

Increases V/Q, improves oxygenation, decreases work of breathing

Dangers of PEEP

• High intra-thoracic pressures can cause decreased venous return and decreased cardiac output

• May produce pulmonary barotrauma

• May worsen air-trapping in obstructive pulmonary disease

• Increases intracranial pressure

• Alterations of renal functions and water metabolism

AutoPEEP

• During expiration alveolar pressure is greater than circuit pressure until expiratory flow ceases. If expiratory flow does not cease prior to the initiation of the next breath gas trapping may occur. Gas trapping increases the pressure in the alveoli at the end of expiration and has been termed:– dynamic hyperinflation;– autoPEEP;– inadvertent PEEP;– intrinsic PEEP; and– occult PEEP

Effects of autoPEEP can predispose the patient to:• Increased risk of barotrauma• Fall in cardiac output• Hypotension• Fluid retention• Increased work of breathing

Modes of Ventilation• Controlled

– Pressure Control (PC)– Volume Control (VC)

• Supported– Continuous Positive Airway Pressure (CPAP) – Pressure Support (PS)

• Combined– SIMV (PC) + PS– SIMV (VC) + PS

• CMV• SIMV• Spont• APRV• ASV• Duopap, BiPAP• NIV

Modes of latest ventilation

• Patient receives a preset TV at a preset RR.– Pt. Cannot increase RR or breathe spontaneously– Should only be used if the patient is properly medicated and

paralyzed

CMV (Continuous mandatory ventilation)mode

• Indications: - bucking during initial stages of vent support - flail chests - who otherwise need complete respiratory rest

• Complications: a disconnect will lead to apnea and hypoxia.

• Disadvantages: - Muscles of respiration weaken making weaning more

difficult.


- May lead to a rapid type of disuse atrophy involving the diaphragmatic muscle fibers, which can develop within the first day of mechanical ventilation.

- May cause atrophy in all respiratory related muscles during CMV


• Ventilator delivers a pre-set tidal volume at a pre-set respiratory rate when there is not respiratory effort from the patient.

• But if the patient triggers a spontaneous respiratory effort earlier than the time interval created by the set respiratory rate, the ventilator will still deliver the breath at the set tidal volume and then resets the time interval for the next breath.

• All breaths are delivered at the set tidal volume whether it was ventilator triggered or patient triggered.

AC ( Assist control ventilation) mode

• Indications: Myasthenia gravis, GBS, post cardiac / resp arrest, ARDS, pulmonary oedema.

• Advantages: minimal work of breathing and patient controls RR which helps normalize PaCO2.

AC ( Assist control ventilation) mode

• Ventilator delivers either assisted breaths to the patient at the beginning of a spontaneous breath or time triggered mandatory breaths.

• Synchronization window- time interval just prior to time triggering.

• Breath stacking is avoided as mandatory breaths are synchronized with spontaneous breaths.

• In between mandatory breaths patient is allowed to take spontaneous breath at any TV.

• It provides partial ventilatory support

SIMV(Synchronized Intermittent Mandatory Ventilation )

• Advantages:– Maintain respiratory muscle strength.– Reduce ventilation to perfusion mismatch.– Decreases mean airway pressure.– Facilitates weaning.


• Supports spontaneous breathing of the patients.• Each inspiratory effort is augmented by ventilator at

a preset level of inspiratory pressure.• Patient triggered, flow cycled and pressure

controlled mode.• Applies pressure plateau to patient airway during

spontaneous breathing.• Commonly applied to SIMV mode during

spontaneous ventilation to facilitate weaning

PSV (Pressure Support Ventilation) mode

• Indications:As an adjunct to SIMV. Not used during machine breaths. This will increase pts. Spontaneous TV, decrease spontaneous RR and decrease work of breathing

• Disadvantages-Not suitable for patients with central apnea. (hypoventilation)Development of high airway pressure. (hemodynamic distubances)Hypoventilation, if inspiratory time is short.


• Similar to CPAP as patient breathes spontaneously.• Airway pressure is maintained at moderately high level

(15-20 cmH2O) throughout most of respiratory cycle with brief periods of lower pressure to allow deflation of lungs.

• Increased pressure ensures alveolar recruitment & oxygenation & brief deflation allows CO2 elimination without alveolar collapse.

• Indicated as an alternative to conventional volume cycled ventilation for patients with decreased lung compliance (ARDS), as chances of barotrauma is less due to less PAW.

APRV (Airway Pressure Release Ventilation) Mode

APRV (Airway Pressure Release Ventilation) Mode

• a ventilator targeting scheme in which one variable is automatically adjusted to achieve a predetermined value of another variable.

• Patient body weight (deadspace) & percent minute volume are feed in ventilator.

• Inspiratory pressure is automatically adjusted by the ventilator to achieve a minute volume target.

• Automatically adjust the inspiratory flow to maintain a constant I:E ratio.

• Using artificial intelligence application to conduct ventilation

ASV (Adaptive Support Ventilation ) Mode

• Used in conjunction with other modes Prevents closing of alveoli by increasing baseline airway pressure.

• Indications: intrapulmonary shunt and refractory hypoxemia, decrease FRC and lung compliance.

• Complications: decrease venous return, barotrauma, increased ICP and alterations in renal functions and water metabolism.

PEEP (Positive end expiratory Pressure)

CPAP and BiPAPCPAP is essentially constant PEEP; BiPAP is CPAP plus PS

• ParametersCPAP – PEEP set at 5-10 cm H2OBiPAP – CPAP with Pressure Support (5-20 cm H2O)Shown to reduce need for intubation and mortality in COPD pts

IndicationsWhen medical therapy fails (tachypnea, hypoxemia, respiratory acidosis)

Use in conjunction with bronchodilators, steroids, oral/parenteral steroids, antibiotics to prevent/delay intubation

Weaning protocolsObstructive Sleep Apnea

- Decrease cardiac output- Barotrauma- Nosocomial pneumonia- Positive water balance- Decrease renal perfusion- Increase ICP- Hepatic congestion- Worsening of intracardiac shunt

Complications

• Unsupported spontaneous breathing trials. - The machine support is withdrawn - T-Piece (or CPAP) circuit can be attached .• Intermittent mandatory ventilation (IMV) weaning. - The ventilator delivers a preset minimum minute volume - Synchronized (SIMV) to the patient's own resp efforts.• Pressure support weaning. - Patient initiates all breaths and these are 'boosted' by the

ventilator. - Gradually reducing the level of pressure support, - Once the level of pressure support is low (5-10 cmH2O

above PEEP), a trial of T-Piece or CPAP weaning should be commenced.

Modes of Weaning

• Underlying illness is treated and improving• Respiratory function:

– Respiratory rate < 35 breaths/minute– FiO2 < 0.5, SaO2 > 90%, PEEP <10 cmH2O– Tidal volume > 5ml/kg– Vital capacity > 10 ml/kg– Minute volume < 10 l/min

• Absence of infection or fever• Cardiovascular stability, optimal fluid balance

and electrolyte replacement

Indication of weaning

Conclusion

Ventilator mode

Healthcare

Transcript of Ventilator mode