1. Impairs venous return and cardiac output 2. May cause hypotension especially in hypovolemic patients 3. Pneumothorax and lung injury

Mechanical Ventilation Flashcards by Fiona Lair

How does anesthesia affect ventilation?

Alters CO2 sensitivity
Relaxes respiratory muscles
Develops atelectasis
Worsens V/Q match issues

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How can ventilation affect anesthesia?

Uptake depends on ventilation

2. Controlled ventilation facilitates reliable uptake and smooth plane of anesthesia

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What is ventilation defined by?

PaCO2

Patient should have normal resp rate, rhythm and effort

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What is oxygenation?

Process of oxygenation of arterial blood

Defined by PaO2

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What is oxygenation monitored by?

Arterial blood gas or pulse oximetry

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What does oxygenation depend on?

Inspired O2%

100% O2 typically insures good oxygenation

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What are the two phases of respiration?

Inspiration and expiration

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What does resistance do?

Limits flow

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What does compliance do?

Limits volume

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Indications for mechanical ventilation?

Need to decrease PaCO2
Need to increase PaO2
Need to decrease respiratory effort (mostly ICU)

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Indication for mechanical ventilation during anesthesia

Control of respiratory function
Prolonged anesthesia
Maintain stable anesthesia plane
Neuromuscular blockade
Thoracic surgery, chest wall, hernia
Obesity, increased abdomen pressure
head down positioning
Laparoscopy
Control ICP

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Side effects of MV

Impairs venous return and cardiac output
May cause hypotension especially in hypovolemic patients
Pneumothorax and lung injury

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Direct effects of hypercapnia

Peripheral vasodilation
Decreased myocardial contractility
Bradycardia and possible arrest
Increased ICP

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Indirect effects of hypercapnia

Tachycardia, arrhythmias
Increased myocardial contractility
Increased blood pressure

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CO2 narcosis levels

> 95 mmHg progressive narcosis

>245 mmHg complete narcosis

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What may happen if not ventilating properly?

CO2 accumulation, hypoxemia, sudden death

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Should horses be ventilated?

Debated issue

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Types of ventilation

Spontaneous- patient breathing
Assisted- patient timed, machine assists
Mandatory/Controlled- ventilator controls
Manual- bag
Mechanical- machine driven

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Ventilation modes

Volume controlled

Pressure controlled

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What can result from volume ventilation?

Pneumothorax if compliance is decreased

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Which ventilation mode is preferred if lung volume changes during a procedure?

Pressure controlled

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Which ventilation mode is preferred if trans-pulmonary pressure changes during a procedure?

Volume controlled

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Which ventilation mode works well for all patient sizes?

Pressure controlled

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Classification of ventilators

Source of driving power
Control variable
Cycle variable
Trigger variable
Limit variable

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Source of driving power

1. Electronically driven | 2. Pneumatically driven (pressurized gas)

Which source of driving power is more common?

Pneumatically driven

Control variables

1. Flow- delivers constant flow | 2. Pressure- delivers constant patient

Cycle variables

Triggers expiration when a set value is reached 1. Volume 2. Pressure 3. Time 4. Flow- diminishing flow

What is flow variable useful for?

Pressure support ventilation- helps accommodate the patients breathing pattern

Trigger variable

Triggers inspiration when a set value is reached 1. Pressure- negative pressure 2. Flow- inpiratory flow

Trigger variables are used during what ventilation modes?

Assisted

Limit Variable

When value is reached, inspiration will be terminated 1. Volume limit 2. Pressure limit

What does a pressure limit prevent?

Barotrauma if ventilator is set inappropriately

How can volume controlled ventilation be achieved?

Flow controlled, time cycled ventilator OR Flow controlled, volume limited, time cycled ventilator

How can pressure controlled ventilation be achieved?

- Pressure controlled, time cycled ventilator - Pressure controlled, pressure cycled ventilator - Flow controlled, pressure cycled ventilator

I:E Ratio

Ratio of inspiratory/expiratory times

What does the I:E ratio define?

Tidal volume (Vt)

Does the RR affect inspiratory time and Vt?

Nope

PIP

Peak inspiratory pressure- inflates alveoli

PEEP

Positive end expiratory pressure- keeps alveoli open

Indications for PEEP

1. Open thorax 2. Lung parenchymal disease 3. Following alveolar recruitment maneuver

Should PEEP be used during routine anesthesia?

Benefits are questionable

IMV

Intermittent mandatory ventilation- allowed to breath freely between mechanical breaths

SIMV

Synchronized IMV- each spontaneous breath is assisted

PSV

Pressure Support Ventilation- patient is breathing freely but supported with pressure Flow termination, better synchrony than SIMV

CPAP

Continuous Positive Airway Pressure- assisted ventilation mode when both insp/exp pressures are positive

Ventilating healthy lung values

``` Tidal volume : 10-15mL/kg RR: 10-15 bpm Inspiratory time: 1-2sec PIP: 10-20 cmH2O PEEP: 0-2 cmH2O ```

Ventilating sick lungs

``` Tidal volume : 4-8mL/kg RR: up to 60 bpm Inspiratory time: may be increased but watch expiration PIP: 35-60max cmH2O PEEP as needed: 5-20 cmH2O ```

Which lung typically collapses during anesthetic procedures?

The most dependent one very rapidly after induction

Can a collapsed lung persist for hours/days after surgery?

Yes

What is cyclic recruitment?

Opening and collapse of alveoli with each breath, may lead to lung injury

Mechanisms of atelectasis formation

1. Compression 2. Absorption 3. Lack of surfactant

Alveolar recruitment maneuver (ARM)

Therapeutic maneuver aiming to open lung atelectasis and improve oxygenation

Types of ARM

CPAP and Cycling Should be followed by PEEP

Open Lung concept

Therapeutic approach aiming to reverse atelectasis, prevent cyclic recruitment, and ventilator inducted lung injury ARM followed by optimal PEEP

Clinical application of ARM

Safe airway pressures are highly individual variation Should only be performed if you have sufficient monitoring/equipment and clinical indication

Patient-ventilator asynchrony

Patient attempts to breath out of phase with the ventilator

Common causes of patient-ventilator asynchrony

Inadequate anesthetic depth Inadequate lung volume or tidal volume ICU: pneumothroax, atelectasis, hypotension, hyperthermia

Treatment for patient-ventilator asynchrony

Treat underlying cause; may cause rapid deterioration of oxygenation and ventilation

Weaning from ventilator after surgery

If a normal healthy animal it's simple Decrease ventilator setting or continue ventilating until fully awake May use opioid antagonists if necessary

Weaning from ventilator in the ICU

More difficult since lungs are probably not healthy Spontaneous ventilation trials may be used

Mechanical Ventilation Flashcards

(61 cards)