INVASIVE
Mechanical ventilation is considered an invasive oxygen delivery method. It is deemed to be invasive because the mechanical ventilator or breathing machine is connected to either an endotracheal tube or tracheostomy tube that provides access to the trachea/lungs to ventilate, versus a noninvasive exterior route.
WHEN TO INITIATE MECHANICAL VENTILATION?
There are many different indications for mechanical ventilation. After all methods of noninvasive ventilation such as a heated high flow and a BIPAP machine have been trialed/failed or in emergent situations, mechanical ventilation is initiated.
The different indications for mechanical ventilation include apnea, inadequate alveolar ventilation, hypoxemia, impending ventilator failure, insufficient lung expansion, inadequate respiratory muscle strength, excessive work of breathing, and unstable ventilator drive. There are physiological components that drive these indications.
HOW TO INITIATE INTUBATION AND MECHANICAL VENTILATION?
Most acute care hospitals have a rapid sequence intubation protocol, which is precisely what the name says and is a particular protocol that has a fast sequence of pharmacological intervention administration to efficiently, effectively, and safely intubate the patient in acute respiratory failure.
Most facilities opt for sedative and amnesic medications before the paralytic is given to prevent the patient from being awake but paralyzed as they are attempting to intubate, which is not a situation you or I would ever want to be in.
Patient Vent System
The Patient-ETT/Trach/-Tubing-Vent system is a closed circuit.
The ventilator does the breathing for the patient and has inspiratory and an expiratory tubing circuits that are self-explanatory. The Inspiratory Tubing circuit provides appropriate heat and humidity to prevent drying of membranes and other things. The inspiratory tube can give aerosolized medications to the patient via metered-dose inhalers, nebulizer solutions, etc. The respiratory therapist can administer directly into the patients’ lungs.
Ventilator Settings/Parameters
There are so many different and complex settings and timing that the physician and the respiratory therapist keep track of. Still, for the purpose of the introduction to mechanical ventilation, the most important settings to focus on are the following: Mode, FiO2%, PEEP, Rate, Peak Pressures, and Volumes. These are typically available to be seen from the main screen of the ventilator.
Ventilator Modes
There are multiple ventilator modes; however, the most commonly used ones in the facilities I am from are SIMV, PS, CPAP, and this is what we will focus on for now.
SIMV (Synchronized Intermittent Mandatory Ventilation)
This is a vent setting that delivers a specific number of breaths of a particular volume every minute.
PS (Pressure Support)
This is a spontaneous breathing setting and is often used in conjunction with CPAP mode to wean patients. Think of pressure support as the higher the pressure support, the higher the amount of O2 is being delivered. It also provides the patient less resistance by helping the patient breathe through the endotracheal/tracheostomy resistance since it is relatively narrow.
CPAP and the Concept of PEEP
CPAP stands for continuous positive airway pressure. You might be familiar with CPAP machines for patients’ who have sleep apnea. This is the same physiological/intervention concept but delivered by the ventilator.
PEEP stands for Positive End-Expiratory Pressure, and standard physiological PEEP or the lungs’ pressure after expiration is just around 3-5.
Depending on the patients’ needs, the PEEP will be increased to recruit more of the alveoli. The increase in positive end-expiratory pressure allows for more alveoli to be open. This promotes alveolar recruitment and lung compliance, particularly for patients who have something called ARDS; we will touch on this and many other common to the ICU in the ICU Orientation Course in spring.
One of the essential PEEP points is that the patient should only get as much PEEP that is required to improve them physiologically. Too much PEEP can cause trauma called barotrauma. We should be aiming to keep PEEP and Peak Pressures <40, this is another typical setting that you will have to and be able to monitor usually from the main home screen of the ventilator machine.
When the pressure inside the chest is changed, and the intrathoracic pressure is increased from the PEEP, it has physiological effects on the heart. The increased intrathoracic pressure from PEEP can cause decreased venous blood return to the heart and reduce cardiac output. For cardiac patients, this can be enough of a change to put even further strain on the heart and should be monitored closely.
PEEP can also increase ICP, decrease renal perfusion, and worsen intracardiac shunts.
Complications of Mechanical Ventilation
The most important mechanical ventilation complications are Hemodynamic Compromise, Barotrauma/Volutrauma, VAP, and Upper GI Hemorrhage.
Hemodynamic Compromise
As mentioned in the PEEP section, mechanical ventilation increases positive end-expiratory pressure and affects the venous return to the heart and cardiac output. However, most ventilator systems are positive pressure ventilator systems, which is why this occurs. Our chest cavity is a negative pressure system. The pressures are opposite in the chest during inspiration and expiration when on a positive ventilator system, then they are during normal physiologic spontaneous breath.
One way to improve venous return and promote adequate cardiac output is to optimize preload (fluid volume/blood volume) going into the heart, of course if it is appropriate for that particular patient.
Barotrauma/Volutrauma
Barotrauma occurs trauma when the alveoli are stretched and overdistended from the PEEP settings. Volutrauma occurs to the whole lung tissue, and alveoli are damaged by the volumes delivered from the vent. These terms are generally used interchangeably, but remember the difference and, most importantly, how crucial it is not to have too much PEEP or Volumes for your patients’ condition or size.
Auto-PEEP
You have probably heard of this term or will hear of this term. Auto-PEEP/Intrinsic is also known as gas trapping or air trapping. It occurs when the next inspiration is delivered before the exhalation is complete leading to high and dangerous pressures in the lungs.
VAP
Ventilator-Associated Pneumonia occurs in the hospital from the ventilator from colonization and aspiration of bacteria. There are many interventions, preventions, and protocols to prevent the colonizations from happening, like performing oral cares and subglottic suction every two hours.
Upper GI Hemorrhage
This occurs secondary to gastric ulcers or stress ulcers. This is also the main reason you will see your patient who is intubated on a stress ulcer prophylaxis.
Weaning from Mechanical Ventilation
Once the patient is doing well enough to proceed to extubation, the patient has to be able to wean or practice to try breathing on their own successfully. This is important to determine if the patients’ lungs are healthy enough to breathe on their own before the endotracheal tube is removed.
The patient can wean a variety of different ways and methods.
Common Modes and Methods of Weaning
Common modes and methods are CPAP and Pressure Support combined or alone, and T-piece/blowby/or trach collar.
T-Piece/Blowby/Trach Collar
The patient is removed from the vent and then connected to an oxygen source via a T-Piece (connector).
Trach Collar Method uses a dome placed over the tracheostomy after the patient is removed entirely from the vent, the patient breaths on their own, and the dome is secured on top of the tracheostomy by an elastic cord typically.
CPAP
Same concept as mentioned before, continuous positive airway pressure that can be used alone or in conjunction with pressure support.
Pressure Support
The patient is connected to the vent, but the patient initiates their own breath, but with a predetermined level of pressure during inhalation to help with the ETT tube and ventilator tubing resistance.
Principles of Ventilator Management
While caring for a patient receiving mechanical ventilation, specific principles need to be kept in mind and managed well. These are ventilatory synchrony, patient airway maintenance, monitoring of O2 and vent status, physiotherapy, and weaning from mechanical ventilator.
How to Ensure Ventilator Synchrony
Starting right with the assessment is the patient breathing with or against the ventilator.
Look at the patient and the vent, is the patient fighting against the ventilator? You often hear the vent alarming, and the patient not really allowing for adequate help from the vent, and possible bad enough vent asynchrony that their oxygen saturation starts to drop.
One of the first things you can do is ensure that sedation is optimized and that the patient is comfortable by giving an ordered bolus or increasing the rate and making sure that they are at an appropriate RASS score.
If your patient remains asynchronous on the vent, then you should consult your respiratory therapist and physician to inquire if there are different settings/parameters with timing, triggers, and modes that they would suggest trying in an attempt to obtain vent synchrony.
How to Maintain a Patent Airway
One of the first ways to ensure that the patients’ airway is patent is to suction your patient with their inline endotracheal suction when clinically indicated, or when they are audible, or when their sats are dropping it should be one of the first things you do after you raise the head of bed.
Assess and auscultate for wheezes, and administer nebulizers as necessary.
Ensure optimal humidity for your patient from the humidifier that is connected to the inspiratory circuit. While the respiratory therapist manages this, you can keep an eye on it to make sure it isn’t dry.
Prevent the patient from biting on their endotracheal tube by placing a bite block! This is a plastic piece that goes around the endotracheal tube in their mouth so they can’t bite and occlude the tube.
How to monitor oxygenation and ventilator optimization
Monitor continuous pulse oximetry, watch trends and get an order for an ABG (arterial blood gas) if the patient is decompensating or has increased oxygen needs.
