Quick Revision to Basics of Respiration:
- The term breathing means getting oxygen into lungs and removing carbon dioxide out of it.
- The lungs carry out the process of exchange of gases by the process of diffusion with the blood vessels.
- These blood vessels then ultimately carry out the same process in the body cells and hence completes the process of respiration.
What is a Ventilator ?
Ventilator is a life support device also known as breathing machine that helps a person breathe who is not able to do it naturally. A ventilator blows air into patient airways through a non-invasive breathing tube or endotracheal tube. One end of the tube is inserted into the windpipe and the other end is attached to the ventilator. The breathing tube serves as an airway by letting air and oxygen from the ventilator flow into the lungs.
The breathing tube may cause some discomfort so it is inserted after administration of anesthesia. It also affects patients ability to talk and eat, So for long term patients the breathing tube used is a invasive trach tube, patient may be able to talk. (A trach tube is put directly into the windpipe through a hole in the front of the neck.)
When Ventilator is required ?
During surgery when the patient is on anesthesia due to which all his breathing muscles are inactive so for this short period of time patient needs ventilator to carry out the process of breathing.
Ventilator is also used for both short term as well as long term depending on the patient disease condition. if the patient can’t recover enough to breathe on his own then he may even need portable ventilator for rest of the life.
Some disease that may impairs the lung function and hence require the need of ventilator to assist normal breathing includes:
- Pneumonia and other lung infections
- COPD (chronic obstructive pulmonary disease) or other lung diseases
- Upper spinal cord injuries, polio, amyotrophic lateral sclerosis (ALS), myasthenia gravis, and other diseases or factors that affect the nerves and muscles involved in breathing
- Brain injury or stroke
- Drug overdose
Terminologies in relation to Ventilator:
1). TRIGGER MODE AND SENSITIVITY: Trigger implies initiation breathing by the ventilator, which can be done in two ways:
- Pressure Triggering that is a ventilator-delivered breath is initiated if the demand valve senses a negative airway pressure deflection (generated by the patient trying to initiate a breath) greater than the trigger sensitivity.
- Flow-by Triggering that is a continuous flow of gas through the ventilator circuit is monitored. A ventilator-delivered breath is initiated when the return flow is less than the delivered flow, a consequence of the patient’s effort to initiate a breath.
2). TIDAL VOLUME: The tidal volume is the amount of air delivered with each breath. It is generally 500ml for adults but much lesser for neonates and the appropriate initial tidal volume depends on numerous factors, most notably the disease for which the patient requires mechanical ventilation.
3). RESPIRATORY RATE: In general, an initial respiratory rate between 12 and 16 breaths per minute is reasonable.
4). POSITIVE END-EXPIRATORY PRESSURE (PEEP): It is the pressure in the lungs (alveolar pressure) above atmospheric pressure (the pressure outside of the body) that exists at the end of expiration.
Applied PEEP is generally added to mitigate end-expiratory alveolar collapse. A typical and general initial applied PEEP is 5 cmH2O. However, up to 20 cmH2O may be used in patients undergoing low tidal volume ventilation for acute respiratory distress syndrome (ARDS).
5). FLOW RATE: The peak flow rate is the maximum flow delivered by the ventilator during inspiration. Peak flow rates of 60 L per minute may be sufficient, although higher rates are frequently necessary.
An insufficient peak flow rate is characterized by dyspnea (Difficult or labored respiration), spuriously low peak inspiratory pressures, and scalloping of the inspiratory pressure tracing.
6). INSPIRATORY TIME: EXPIRATORY TIME RELATIONSHIP (I:E Ratio): During spontaneous breathing, the normal I:E ratio is 1:2, indicating that for normal patients the exhalation time is about twice as long as inhalation time.
Usually it is 1:2 but depending on the disease process, such as in ARDS, the I:E ratio can be changed to improve ventilation.
7).FRACTION OF INSPIRED OXYGEN (FiO2): The lowest possible fraction of inspired oxygen (FiO2) necessary to meet oxygenation goals should be used. This will decrease the likelihood that adverse consequences of supplemental oxygen will develop, such as absorption atelectasis (Collapse of an expanded lung), accentuation of hypercapnia (high level of carbon dioxide in the circulating blood), airway injury, and parenchymal injury
What are the modes of ventilation ?
Assist Control Ventilation: A set tidal volume (if set to volume control) or a set pressure and time (if set to pressure control) is delivered at a minimum rate. Additional ventilator breaths are given if triggered by the patient.
Pressure Support Ventilation: The patient controls the respiratory rate and exerts a major influence on the duration of inspiration, inspiratory flow rate and tidal volume.
The model provides pressure support to overcome the increased work of breathing imposed by the disease process, the endotracheal tube, the inspiratory valves and other mechanical aspects of ventilatory support.
Synchronized Intermittent Mandatory Ventilation:
(i). Breaths are given are given at a set minimal rate, however if the patient chooses to breath over the set rate no additional support is given.
(ii). One advantage of SIMV is that it allows patients to assume a portion of their ventilatory drive.
(iii). SIMV is usually associated with greater work of breathing than AC ventilation and therefore is less frequently used as the initial ventilator mode.
(iv). Like Assist Control, SIMV can deliver set tidal volumes (volume control) or a set pressure and time (pressure control).
(v). Negative inspiratory pressure generated by spontaneous breathing leads to increased venous return, which theoretically may help cardiac output and function.
What Are the Risks of Being on a Ventilator?
One of the most serious and common risks of being on a ventilator is pneumonia. The breathing tube that’s put in the airway of the patient can allow bacteria to enter the lungs. As a result, patient may develop ventilator-associated pneumonia (VAP).
The breathing tube also makes it hard for patient to cough. Coughing helps clear airways of lung irritants that can cause infections.
VAP is a major concern for people using ventilators because they’re often already very sick. Pneumonia may make it harder to treat their other disease or condition.
VAP is treated with antibiotics. Patient may need special antibiotics if the VAP is caused by bacteria that are resistant to standard treatment.
Another risk of being on a ventilator is a sinus infection. This type of infection is more common in people who have endotracheal tubes. (An endotracheal tube is put into the windpipe through the mouth or nose) Sinus infections are treated with antibiotics.
Using a ventilator also can put patient at risk for other problems, such as:
- Pneumothorax. This is a condition in which air leaks out of the lungs and into the space between the lungs and the chest wall. This can cause pain and shortness of breath, and it may cause one or both lungs to collapse.
- Lung damage. Pushing air into the lungs with too much pressure can harm the lungs.
- Oxygen toxicity. High levels of oxygen can damage the lungs.
These problems may occur because of the forced airflow or high levels of oxygen from the ventilator.
Using a ventilator also can put patient at risk for blood clots and serious skin infections. These problems tend to occur in people who have certain diseases and/or who are confined to bed or a wheelchair and must remain in one position for long periods.
Another possible problem is damage to the vocal cords from the breathing tube. If patient find it hard to speak or breathe after patients breathing tube is removed.
When on Ventilation ?
Patient may need periodic chest x-ray and blood tests to check the levels of oxygen and carbon dioxide (blood gases) in the body to find out how well the ventilator is working for him. Based on the test results, they may adjust the ventilator’s airflow and other settings as needed.
Also, a nurse or respiratory therapist will suction patients breathing tube from time to time. This helps remove mucus from lungs. Suctioning will cause patient to cough, and he may feel short of breath for several seconds. He may get extra oxygen during suctioning to relieve shortness of breath.
What After Ventilation ?
“Weaning” is the process of taking patient off of a ventilator so that he can start to breathe on his own. People usually are weaned after they’ve recovered enough from the problem that caused them to need the ventilator.
Weaning usually begins with a short trial. Patient stay connected to the ventilator, but he is given a chance to breathe on his own. Most people are able to breathe on their own the first time weaning is tried. Once he can successfully breathe on his own, the ventilator is stopped.
If patient can’t breathe on his own during the short trial, weaning will be tried at a later time. If repeated weaning attempts over a long time don’t work, he may need to use the ventilator long term.
After patient weaned, the breathing tube is removed. He may cough while this is happening. His voice may be hoarse for a short time after the tube is removed.
References and Further reading:
- Kollef MH. Ventilator-associated complications, including infection-related complications. Crit Care Clin. 2013;29:33-50.
- MacIntyre NR. Principles of mechanical ventilation. In: Mason RJ, Murray JF, Broaddus VC, et al., eds. Murray and Nadel’s Textbook of Respiratory Medicine. 5th ed. Philadelphia, PA: Elsevier Saunders; 2010:chap 89.