Mechanical Ventilation Flashcards
list abbreviations that are important to know pertaining to ventilation
- PaO2
- MV → minute ventilation
- VC → vital capacity
- FIO2
- RR
- TV → tidal volume
- Intrapleural pressure
- Intra-alveolar pressure
- Transpulmonary pressure
- FRC → functional residual capacity
- Bradypnea/apnea
- Tachypnea
- PaCO2
- Negative/Positive Pressure
- Endotracheal tube
- Barotrauma
- PEEP → positive end expiratory pressure
what is minute ventilation (MV)?
the amount of air breathed per minute
normally = 5-8 L/min
equals TV x # of breaths per min
define VC
vital capacity
the max volume of air that can be expired following max inspiration
normal value 2-5 L
define FIO2
fraction of oxygen in a gas mixture
FIO2 of inspired air is 21%
define transpulmonary pressure
the pressure difference between intrapleural pressure and the intra-alveolar pressure
define FRC
functional residual capacity
the volume of air present in the lungs at the end of passive expiration
at FRC, the opposing elastic recoil forces of the lungs and chest wall are in equilibrium
distinguish between negative and positive pressure
Negative pressure = a pressure of gas less 760
Positive pressure = a pressure of gas greater than 760
define barotrauma
injury to your body because of changes in barometric (air) or water pressure
describe PEEP
a mode of therapy used in conjunction w/mechanical ventilation
- maintains the pt’s airway pressure above the atmospheric level by exerting pressure the opposes passive emptying of the lung
- limits alveolar collapse
when is PEEP effective?
when used in pts with a diffuse lung disease that results in an acute decrease in FRC
applying PEEP increases alveolar pressure and alveolar volume
how do we normally regulate respiratory function?
not known for sure with higher levels of exertion but the following are known factors that play a role:
- change RR
- change TV
- change intrapleural pressure
what is a mechanical ventilator?
a machine that assumes the work of breathing when a person is not able to breath well enough on their own
also called a ventilator, a vent, a respirator, a breathing machine
what are the most common reasons for a mechanical ventilator?
low oxygen levels or severe SOB from an infection such as pneumonia are the most common reasons
T/F: mechanical ventilation is curative
FALSE
the pt should have a correctable underlying problem that can be resolved with the support of mechanical ventilation
List Indications for mechanical ventilation
- Bradypnea or apnea with respiratory arrest
- acute lung injury
- tachypnea (RR >30)
- reduces TV which reduces air in alveoli
- MV greater than 10 L/min (normal is 6L/min)
- VC < 15 ml/kg (normal is 2-5L)
- clinical deterioration
- coma
- neuromuscular disease
- acute PaCO2 greater than 50 mmHg with an arterial pH less than 7.25
- normal PaCO2 = 35-45 mmHg
- normal blood pH = 7.35-7.45
list Types of mechanical ventilation
- Negative-Pressure Mechanical Ventilation
- Positive-Pressure Mechanical Ventilation
describe Negative-Pressure mechanical ventilation
- works by exposing the surface of the thorax to sub-atmospheric pressure during inspiration
- this pressure in turn causes thoracic expansion and decrease in intrapleural and alveolar pressures
- this in turn creates a pressure gradient favoring movement of air from the airway opening through the vascular tree and into alveoli
- “air is sucked into the lungs” much like normal breathing
T/F: negative pressure mechanical ventilation is used commonly
FALSE
- rarely used today
- bulky, cumbersome and poorly tolerated
- not suitable for use in the modern critical care unit
- blood tended to pool in the lower torso → reducing CO
describe Positive-Pressure mechanical ventilation
- airway pressure is applied at the pt’s airway (greater than atmospheric pressure)
- the positive nature of this pressure forces air to flow into and through the respiratory tract to the alveoli
- suspension of the positive pressure causes the elastic recoil of the chest to occur, pushing tidal volume out
- air is pushed into the lungs/alveoli and not “pulled” into the alveoli
how are modes of ventilation defined?
- the mode is one of the principle ventilatory settings
- a set of operating characteristics that control how the ventilator functions
- modes of ventilation describe the pattern of breath delivery to a patient
- a set of ventilator operations with one or more predefined mechanical breath types
list modes of non-invasive positive pressure mechanical pressure
- CPAP
- BiPAP
what is CPAP?
continuous positive airway pressure
- continuously delivers + air pressure created by a tabletop device and delivered through a tube connected to a face mask
- air is delivered at a constant pressure
- the constant + pressure helps to ensure that the airway remains open during exhalation
what is SDB?
sleep-disordered breathing
- an abnormal respiratory pattern during sleep
- repeated episodes of upper-airway obstruction during sleep, and nocturnal hypoxemia
- results range from fragmented sleep patterns to HTN to traffic accidents
T/F: CPAP is the preferred treatment of those with COPD
TRUE
also for sleep apnea
but pts can find it difficult to exhale against this constant pressure
describe BiPAP
the difference from CPAP is that on exhalation, the machine continues to deliver air at a predetermined pressure (less resistance to exhalation) → this helps keep the alveoli and smaller airways open
list disorders that BiPAP may be used with
- COPD
- Obstructive sleep apnea
- pneumonia
- post operative breathing difficulties
- neurological pathologies that disturbs breathing
invasive positive-pressure mechanical ventilation include the placement of what devices?
- endotracheal tubes
- tracheostomy tubes
- airway cuffs
what is an endotracheal tube?
a plastic tube that is placed through the mouth (or sometimes the nose) into the trachea to help a pt breath
- can be placed orally (most common) or nasally
- passes through the vocal cords to the trachea
what is tracheostomy?
a hole that surgeons make through the front of the neck and into the windpipe
the surgical procedure by which the tracheostomy tube is inserted into this opening is called a tracheotomy
describe a tracheostomy tube
- may have a cuff or may be without a cuff
- inserted above the vocal cords but extends inferiorly to the vocal cords (loss of voice)
- used in more long-term airway management
what are airway cuffs?
- assist with holding the airway in place
- allow +pressure ventilation without a loss of TV (prevents leakage)
- may reduce risk of aspiration of oral and gastric secretions
- if pt can talk or is losing TV → cuff may not be fully inflated
- may damage the trachea
immediate complications of a tracheostomy tube
- bleeding
- tube displacement
- air can become trapped in tissue under the skin of the neck (subcutaneous emphysema)
- buildup of air between the chest wall and lungs → pneumothorax
- a hematoma occurs in the neck which might compress the trachea
long term complications of tracheostomy tubes
- displacement of the tube from the trachea
- damage, scarring, or narrowing of the trachea
- development of an abnormal passage between the trachea and the esophagus
- infection → tracheostomy, trachea bronchial tubes and lungs (pneumonia)
list modes of ventilation
- controlled ventilation
- assist-control mode or pt initiated/supported ventilation
- volume controlled ventilation
- pressure control
- PRVC
- SIMV
- pressure support ventilation
- volume support
what is controlled ventilation?
a mode in which the ventilator initiates all breaths at a pre-set rate and TV volume
the ventilator will block any spontaneous breaths
describe the setup for controlled ventilation
assume ventilator was set up for controlled breaths at a RR of 10 bpm
every 6 seconds a breath will be delivered to your pt no matter what
when is controlled ventilation used?
mainly in the management of pts with severe neurologic conditions, are deeply sedated or are in shock or severe respiratory failure
there are diminished risks for hypo-or hyperventilation
T/F: spontaneous breathing is allowed with assist-control mode
TRUE
the pt triggers vent with an attempt to breath
benefits/risks of assist-control mode
- this mode maintains normal ventilatory activity by the pt and, therefore, prevents atrophy of the respiratory muscles
- pt does at least some of the work
- carries a risk for some pts to develop respiratory alkalosis or to reduce venous return and CO
describe volume controlled ventilation
preset TV is delivered at a set RR
in this mode the operator may control:
- TV
- RR
- TI (or I:E ratio or peak flow)
- pt trigger type and sensitivity
- PEEP
- FiO2
how is Ti or I:E ratio related/relevant to Volume Controlled Ventilation?
- I:E → the ratio of inspiratory time to expiratory time
- in normal spontaneous breathing it represents a compromise between ventilation and oxygenation
- Ti → inspiratory time
- characteristics of a spontaneous breath. these characteristics may stimulate the ventilator to initiate a breath, the flow of O2
T/F: PEEP prevents shunting
TRUE
and it allows for a decrease in FiO2
describe Pressure Control Ventilation
predetermined amount of pressure at a set rate
- ventilator determines inspiratory time
- pt has no spontaneous breathing
- PEEP used to increase arterial oxygen, improve lung compliance
- prevents collapse, makes lungs easier to inflate
describe PRVC
Pressure Regulated Volume Control
- combines pressure and volume controlled ventilation
- preset TV is delivered at set rate, but with lowest possible pressure
- helps prevent barotrauma
describe SIMV
Synchronous Intermittent Mandatory Ventilation
- Used to assist pts who have some, but not sufficient breathing
- pts can breath in between each machine assisted breath
- used for weaning
- delivers certain numbers of breaths in coordination with respiratory effort of pt
- does increase pt work of breathing
describe pressure support ventilation
small amount of pressure occurs on inspiration
- pts initiates all breaths
- assists pt in making a spontaneous breath
- delivers a specific pressure
- ventilator assists, but pt regulates the RR and TV
describe volume support ventilation
TV and PEEP are set
- pt initiates
- ventilator delivers support in proportion to pt’s inspiratory effort and target volume
what may trigger a red alarm on a mechanical ventilator?
- high pressure
- circuit disconnected
- apnea
what may trigger a yellow alarm on a mechanical ventilator?
- low TV
- high RR
- low MV
- low inspiratory pressure
list some complications of intubation
- injury to surrounding tissue
- upper airway
- nasal tissue
- vocal cords
- tracheal perforation
- intubation of the esophagus
- tracheal necrosis or stenosis
- ventilator associated pneumonia
T/F: barotrauma can be a ventilator induced injury
TRUE
what is ventilator associated pneumonia?
defined as a new infection of lung parenchyma that develops within 48 hours after intubation
- reported to occur in 8-28% of pts given mechanical ventilation
- mortality rates 33-50%
- risk for developing it is highest immediately after intubation
list cardiovascular effects of mechanical ventilation
- Positive-pressure ventilation can decrease preload, SV, and CO
- Reduces affects renal blood flow and function, resulting in gradual fluid retention
- positive pressure maintained in the chest may decrease venous return from the head, increasing ICP (worsening agitation, delirium, and sleep deprivation) and systemic edema
what is Auto PEEP
- pt doesn’t expire full TV and air becomes trapped
- also called breath stacking
- can cause increased alveolar damage
list other complications of mechanical ventilation
- anxiety/stress/sleep deprivation
- ulcers/gastric/malnutrition
- muscle deconditioning
- vent dependence
- increased intrathoracic pressure leading to systemic edema due to decreased venous return
list several ventilator induced lung injuries
- volutrauma → the local overdistension of normal alveoli
- sets off an inflammatory cascade that augments/perpetuates the initial lung injury
- oxygen toxicity → due to increased FiO2 and duration of use
- results in the production of oxygen free radicals
- associated with FiO2 >50%
