Clinical Quick Reference Monthly Newsletter / October 2022 / Let's Talk About Vents!
Clinical Quick Reference Guides - Concept Review/ Mechanical Ventilation
This review will assist the learner by introducing fundamental basics associated with mechanical ventilation.
Why Do Patients Receive Mechanical Ventilation?
The primary indications for mechanical ventilation according to the NIH are:
Airway protection in a patient suffering from airway difficulties e.g., injury; infection
Hypercapnic respiratory failure d/t a decrease in minute ventilation
Hypoxemic respiratory failure d/t a failure of oxygenation
Cardiovascular distress and mechanical ventilation would help by offloading the energy requirements of breathing
Expectant course: for example a patient with an anticipated decline or impending transfer
Photo by Bagoes Ilhamy on Unsplash
Mechanical ventilation assists patients that require support by applying a positive pressure breath to them. It is dependent on the compliance and resistance in the airway system; and these factors help determine how much pressure must be generated by the ventilator to provide a given tidal volume (TV).
Tidal Volume refers to the volume of air entering the lung during inhalation.
There are four stages in mechanical ventilation;
the trigger phase
(initiation of inhalation either triggered by an effort from the patient or by set parameters of the ventilator)
the inspiratory phase
(inhalation of air into patient defines their inspiratory phase)
the cycling phase
(brief period when inhalation has ceased but before exhalation begins)
and the expiratory phase
(passive exhalation of air from the patient receiving ventilation)
Cardiovascular and Hemodynamic Concerns
Healthcare professionals need to be cognizant of the potential for side effects related to the use of mechanical ventilation. In particular, note that individuals receiving care with mechanical ventilation experience a shift in their natural negative pressure ventilation to one of positive pressure ventilation.
This affects the heart-lung physiology and can alter their hemodynamic status.
Three clinical strategies may be considered when providing mechanical ventilation.
Lung Protective Strategy
Intermediate Strategy
Obstructive Strategy
Lung Protective Strategy
This strategy is the best choice for a patient at high risk to develop acute lung injury (ALI) as well as, individuals whose disease state may progress to acute respiratory distress syndrome (ARDS).
This low tidal volume (LTV) approach launched after the landmark ARDSnet trials. These studies indicated that low tidal volume ventilation in patients with ARDS improved mortality.
Intermediate Strategy
In a trial known as “PreVENT,“ research found no significant difference in an intermediate tidal volume strategy (10ml/kg) compared to the low tidal volume strategy (6ml/kg) in patients who did not have ARDS.
For a patient placed on mechanical ventilation who has no obstructive physiology and no chance of developing ACL, the intermediate tidal volume strategy could be used.
Obstructive Strategy
Patients with COPD or other obstructive conditions have lung disease which is characterized by narrowed airways, increased secretions, and/or collapse of the small airways on expiration. Even though patients with obstructive lung diseases can usually be treated successfully with non-invasive ventilation methods, there are times when they may need to be intubated and receive mechanical ventilation.
Given the needs and physiologic conditions in obstructive lung disease patients, the strategy used must offset these factors and should be combined with other medical therapies and nebulizers to reverse obstructive processes.
Additional Considerations
Prior to the procedure, the clinician assesses which medications to use in post-intubation pain control and for sedation. The approach generally recommended is the analgesia first methodology, whereby meds are given prior to starting.
After initiating, the patient receives a chest x-ray and blood gases should be evaluated. These will insure proper endotracheal placement and assess minute ventilation.
Should the patient suddenly begin to desaturate (decreasing oxygenation), the healthcare team and providers needs to quickly work to determine the cause. A mnemonic known as DOPES can assist in finding issues.
D displacement
O obstruction of the ETT or airways
P pneumothorax/pulmonary embolism/pulmonary edema
E equipment failure
S stacked breaths
The care of mechnically ventilated patients is both complex and dynamic. Excellent care requires a team of professionals; this team consists of dedicated nurses, physicians and respiratory therapists. Commuication is key to maximizing patient health outcomes.
Medical Terminology
ALI - syndrome characterised by acute inflammation & tissue injury which affects normal gas exchange in the lungs
ARDS - acute, diffuse, inflammatory form of lung injury; life-threatening condition of seriously ill patients, characterized by poor oxygenation, pulmonary infiltrates, and acute onset
Hypercapneic respiratory failure - a frequent problem in critical care and mainly affects patients with acute exacerbation of COPD and ARDS; in this variety, the respiratory failure is caused by mechanical dysfunction (such as lung hyperinflation in COPD), central nervous system abnormality, or respiratory muscle dysfunction--- the issues lead to elevation of PaCO 2 levels
Hypoxemic respiratory failure – or type I, is characterized by arterial oxygen tension (PaO2) lower than 60 mm Hg with a normal or low arterial carbon dioxide tension (PaCO2); it is the most common form of respiratory failure & can be associated with virtually all acute diseases of the lung (e.g. generally involve fluid filling or collapse of alveolar units)
Minute ventilation - volume of gas inhaled (inhaled minute volume) or exhaled (exhaled minute volume) from an individual’s lungs per minute
Postive pressure ventilation - process of either using a mask or a ventilator to deliver breaths and decrease the work of breathing
Tidal Volume - amount of air moving in or out of the lungs with each respiratory cycle
Helpful Video:
Comprehensive Video (Not for the faint of heart!)
Resources:
CDC, Medscape, NIH
This study guide represents study materials and is not intended as medical advice. Always follow the advice and practice guidelines of your institution and/or provider.