Critical care - Mechanical ventilation: Nursing

Mechanical ventilation is a process that partially or fully assumes breathing for patients who can't independently maintain effective gas exchange.

It can be used in the short term such as during surgery when a patient is sedated or in the long term, like in cases of respiratory failure, airway obstruction or when a patient is comatose.

Mechanical ventilation requires the placement of an artificial airway such as an endotracheal tube or ett, which is a tube that's inserted through the mouth and into the trachea through a procedure called intubation.

Another artificial airway is a tracheostomy tube which is inserted directly through a surgical opening made in the skin of the neck that creates an opening into the trachea.

Once inserted, the tube is connected to a ventilator which is a mechanical device that pushes oxygen rich air into the patient's lungs.

Now, mechanical ventilators have modifiable settings to meet the needs of each patient based on their health status, comorbidities and goals of care.

First, the respiratory rate or frequency determines the number of breaths, the ventilator supplies and is typically set between 6 to 20 breaths per minute to mimic normal respiration.

Next, tidal volume or VT is the volume of air delivered during each breath, which for most patients is between 4 to 8 mL per kilogram of body weight.

So let's say your patient weighs 60 kg and is started on a VT of 6 mL per kilogram. The ventilator will deliver a VT of 360 mL of air with each breath.

Then there's oxygen concentration or the fraction of inspired oxygen called F IO two for short, which refers to the concentration of oxygen being delivered.

F IO two can be set anywhere from 21 to 100% to maintain a partial pressure of arterial oxygen or PA O2 between 6100 millimeters of mercury or oxygen saturation at 90% or more.

Next. The inspiratory to expiratory ratio or IE ratio is the length of inspiration compared to the length of expiration with a typical ie ratio of 1 to 2 to mimic normal spontaneous ventilation.

Since inspiration is shorter than expiration, next is positive end expiratory pressure called peep, which is the application of positive pressure at the end of exhalation to prevent the collapse of the small airways in alveoli peep tends to be set between 3 to 5 cm of water.

Lastly, sensitivity determines how much effort a patient needs to make when attempting a breath for the ventilator to be triggered, which will then assist the patient with the breath.

Ideally, this setting will enable detection of a weak effort while avoiding auto cycling where the ventilator delivers breaths without a patient effort, which can lead to patient ventilator asynchrony.

All right. So a ventilator mode refers to how the ventilator delivers breaths to the patient selection of a particular mode of ventilation determines how much the patient will participate in their own ventilatory pattern.

And is chosen based on the patient's condition and treatment goals. A common mode is continuous mandatory ventilation or CMV, which is also known as a cyst control or AC ventilation.

In this mode, the ventilator delivers a specific number of breaths at a set VT or pressure, but the patient can also initiate additional breaths on their own.

Mhm. This mode will also deliver a breath if a patient fails to take a breath on their own within a set period.

It can also be used in patients with conditions like decreased lung compliance like pulmonary fibrosis or those with severe respiratory muscle fatigue.

Another mode is intermittent mandatory ventilation or I MV. For short, which is also known as synchronous, intermittent mandatory ventilation or SI MV.

With this mode, the ventilator delivers breaths at a set VT or pressure and rate while also allowing the patient to breathe spontaneously.

So the ventilators breaths are synchronized with the patient's respiratory effort. This mode is indicated for patients who are ready to be weaned off the ventilator and breathe on their own, but can also be used in conditions like chronic obstructive pulmonary disease or COPD or asthma where patients have increased airway resistance and their spontaneous respiratory efforts need to be preserved.

One last type of mode is continuous, positive airway pressure called CPAP. This mode keeps the patient's airway open by delivering constant pressure throughout the respiratory cycle at a fixed preset level.

CPAP can also be used to improve oxygenation in conditions that cause alveolar collapse, like pleural effusion. It can also be used for ventilator weaning because it allows patients to breathe spontaneously while giving them some airway support.

Ok. So when a patient is placed on mechanical ventilation, they're at an increased risk of developing complications to start with mechanical ventilation increases the risk of developing an infection called ventilator associated pneumonia or vap, which can happen when microorganisms invade the lungs during the intubation procedure or when secretions are aspirated.

And because normal upper airway defense mechanisms like ciliary function and coughing are bypassed in patients undergoing mechanical ventilation.

The risk of colonization of the lower airways is increased. Patients can also develop ventilator induced lung injuries.

Air leaks develop due to mechanisms like excessive pressure in the alveoli called barotrauma, excessive volume in the alveoli known as volute truma or from the repeated opening and closing of the alveoli called atelec trauma.

These mechanisms are associated with stress to the alveolar wall and damage to the alveolar capillary membrane that can cause air to leak into surrounding areas around the lungs like the subcutaneous tissue leading to subcutaneous emphysema, chest cavity causing pneumothorax or heart causing cardiac tamponade.

In addition, the trauma caused by pressure and stretching during mechanical ventilation can cause the release of inflammatory mediators resulting in bio truma that can ultimately cause acute respiratory distress syndrome or A R DS.

Another ventilator complication is cardiovascular compromise. This is caused by positive pressure ventilation which raises intrathoracic pressure, increased intrathoracic pressure decreases blood flow to the right side of the heart, reducing preload and cardiac output.

Consequently, perfusion to vital organs like the liver and kidneys is decreased. The increased intrathoracic pressure can also increase right atrial pressure that can impair venous return from the brain and contribute to increased intracranial pressure or ICP, especially in patients with impaired cerebral autoregulation that aims to maintain a stable cerebral blood flow.

All right, is a quick recap. Mechanical ventilation is a process that partially or fully assumes breathing for patients who can't independently maintain effective gas exchange.

It requires the placement of an artificial airway like an et ventilators have settings and modes that allow modifications to meet patient needs based on their health status.

The presence of comorbidities and their goals of care. Mechanical ventilation can also lead to complications like infections, lung injuries and cardiovascular compromise.