Mechanical Ventilation Flashcards
Mechanical Ventilation
• Mechanical ventilatory support
provides positive pressure to
inflate the lungs.
• Pts w/ acute illness, serious
trauma, exacerbation of chronic
illness, or progression of chronic
illness may require mechanical
Indications
- Apnea
- Acute hypercapnia (not quickly reversible w/ standard treatment)
- PaO 2 <50 mmHg w/ supplemental oxygen
- RR>30 breath per minute
- Vital capacity <15 mL/kg normally ~ 50 mL/kg )
- Negative inspiratory force <25 cm H 2 O (normally > 60)
- Protection of airway from aspiration of gastric contents
- Reversal of respiratory muscle fatigue
Noninvasive
(Types of Mechanical Ventilatory Support)
- Includes continuous positive airway pressure (CPAP) and bi level positive airway pressure (BiPAP)
- Interface to connect the pt to the ventilator tubing.
- 6 types: full face (or oronasal) mask, total face mask, mouthpieces, nasal mask, nasal pillows orplugs, and a helmet.
- Sleep apnea, exacerbations of or hypercarbic COPD, or cardiogenic pulmonary edema when the airway cannot be protected
Invasive mechanical ventilation
(Types of Mechanical Ventilatory Support)
- Use of an artificial airway
CPAP
(Noninvasive Mechanical Ventilation)
- Continuous positive pressure (> atmospheric) throughout the respiratory cycle.
- To decrease the work of spontaneous breathing by reducing the airway pressure necessary to generate inspiration.
BiPAP
(Noninvasive Mechanical Ventilation)
- Two levels of positive pressure support triggered during spontaneous breathing
- Higher pressure (IPAP) to augment inspiratory airflow.
- Lower pressure (EPAP) to maintain airway patency & prevent collapse.
Intubation
(Invasive Mechanical Ventilation)
- A passage of an artificial airway (tube) into the pt’s trachea:
- Through the mouth (endotracheal)
- Through the nose (nasotracheal)
- Intubation indications:
- Presence of upper airway obstruction
- Inability to protect lower airways from aspiration
- Inability to clear pulmonary secretions
- Hypoxemia despite supplemental oxygen
- Respiratory acidosis
- Progressive fatigue including mental status deterioration
- The need for positive pressure ventilation
Cuff
(Invasive Mechanical Ventilation)
- A cuff (balloon) is located ~ 0.5 inches from the end of endotracheal or tracheal tube.
- The cuff is inflated to:
- Ensure that all of the supplemental O2 enters the lungs.
- Hold the artificial airway in place.
- Cuff inflation pressure should be adequate to ensure that no air is leaking around the tube (should not exceed 20 mm Hg)
- High cuff pressures –> tracheal damage & scarring –> tracheal stenosis.
Cuff (Clinical Tip)
(Invasive Mechanical Ventilation)
If the pt is able to phonate from mouth, a cuff leak is suspected. If so, the RT or the nurse should be notified.
Three basic cycling methods:
(Invasive Mechanical Ventilation)
- Pressure cycled: Ventilators stop inspiration at a preset pressure.
- Volume cycled: Ventilators stop inspiration at a preset volume.
- Time cycled: Ventilators stop inspiration at a preset time interval.
Modes of Ventilation
- Range from providing total support to minimal support.
- Goal: allow the pt to do as much of the breathing as is physiologically possible, while meeting the intended objectives of ventilatory support.
- Even short periods (11 days) of complete dependence can lead to respiratory muscle atrophy, reductions in diaphragm strength (25%) & endurance (36%)
Spectrum of Patient Participation
Ventilatory Settings
- Parameters established to provide the necessary support to meet the pt’s individual ventilatory and oxygenation needs.
- Settings are according to pt’s
- Arterial blood gas levels
- Vital signs
- Airway pressures
- Lung volumes
- Pathophysiologic condition (ability to spontaneously breathe).
Oxygenation
(Ventilatory Settings)
- Fraction of inspired oxygen (FiO 2
- 21% yields a normal PaO2 of 95 100 mmHg. (Threshold:
- Positive end expiratory pressure (PEEP)
- Pressure maintained in the airways at the end of expiration (normally 5 cm
Ventilation
(Ventilatory Settings)
- RR (s et according to the amount of spontaneous ventilatory by the pt) (12 20)
- V T ((↑volume leads to ↑airway pressures barotrauma
- Inspiratory flow rate (too slow, pt may attempt to continue to inhale against a closed circuit; too fast –> ↑peak airway pressure –> barotrauma)
- Inspiratory to expiratory ratio (set as synchronous as possible with pt’s ratio)
- Sensitivity (poor –> respiratory muscle fatigue. Too sensitive –> hyperventilation)
Auto PEEP
(Complications of Mechanical Ventilation)
- Occurs when lung volumes fail to return to functional residual capacity before the onset of the next inspiration.
- The process leading to auto PEEP is referred to as dynamic hyperinflation
- Dynamic hyperinflation →↑air trapping → physiologic dead space →↓gas exchange →↑work of breathing due to higher demand.
Auto PEEP can occur due to:
Barotrauma
(Complications of Mechanical Ventilation)
- Damage to the lungs caused by excessive airway pressure.
- Normally, spontaneous inhalation takes place because of negative pressure.
- The volume of inhaled air is limited by the return of intrapulmonary pressure back to atmospheric pressure in the lungs during inhalation.
- Mechanical ventilation is predominantly delivered with positive inspiratory pressure (normal physiologic mechanisms are bypassed).
Barotrauma Possible complications
- May exacerbate acute lung injury associated with ARDS (ventilator induced lung injury (VILI)).
- Pneumothorax and subcutaneous emphysema.
Cardiovascular
(Complications of Mechanical Ventilation)
- high positive pressures can result in decreased cardiac output from compression of great vessels by overinflated lungs.
Oxygen Toxicity
(Complications of Mechanical Ventilation)
- Oxygen toxicity: too high O2 for a prolonged time can result in:
- Substernal chest pain, dry cough, tracheal irritation, dyspnea, nasal stiffness & congestion, sore throat, eye and ear
Improper intubation can result in …
(Complications of Mechanical Ventilation)
Improper intubation can result in esophageal or tracheal tears.
Weaning from Mechanical Ventilation
- The process of decreasing or discontinuing mechanical ventilation in a pt.
- A key factor is the resolution or stability of the condition that led to the need for ventilatory support.
- A spontaneous breathing trial (SBT) is typically performed to evaluate the pt’s readiness.
- The pt breathing spontaneously for 15 to 30 minutes while being closely monitored.
Criteria for Weaning Attempt
- Spontaneous breathing with a tidal volume of 5 L/kg
- Adequate gas exchange (O2 sat >90%) w/ FiO 2 of <50% & PEEP <5 cm H2O
- MIP> −20 to −30 cm H2O (>−30 is associated w/ successful extubation).
- RR <35 bpm
- Minute ventilation of 5 to 10 L/min
- Respiratory rate/VT ratio <105. (A ratio >105 indicates shallow & rapid breathing and is powerful predictor of an unsuccessful wean)
SIMV
(Examples of Weaning Meathods)
- Decreasing the # of breath per minute the ventilator provides requires the pt to increase spontaneous breaths.
- Commonly used after surgery, while pts are waking up from anesthesia.
- Pt have not been on support for an extended time.
- Once spontaneous breathing returns, ventilatory support can be removed.
PSV
(Examples of Weaning Methods)
- Pt spends periods of time w/ ↓pressure support to ↑spontaneous ventilation.
- Two factors can be manipulated:
- To increase strength load on the respiratory muscles –> reduce the PSV.
- To increase endurance requirement on the respiratory muscles –> increase the length of time that PSV is reduced.
Factors to Consider During a Ventilator Wean
- Respiratory demand & the ability of the neuromuscular system to cope w/ the demand
- Oxygenation
- Cardiovascular performance
- Psychological factors
- Adequate rest & nutrition
Signs of Increased Distress During a Ventilator Wean
- Increased tachypnea (>30 bpm)
- Drop in pH to <7.25 to 7.30 associated with increasing Pa CO 2
- Paradoxical breathing pattern
- O2 saturation of <90%
- Change in HR of more than 20 bpm
- Change in BP of >20 mm Hg
- Agitation, panic, diaphoresis, cyanosis, angina, or arrhythmias
PT Considerations
- Pts who require prolonged ventilatory support are at risk for developing pulmonary complications , skin breakdown, joint contractures, & deconditioning.
- PT intervention of pulmonary hygiene & functional mobility training can help prevent or reverse these complications despite mechanical ventilation.
- During the weaning process , the PT can play a vital role on an interdisciplinary team responsible for coordinating the wean.
PT Considerations Continued.
•
PTs offer a combined understanding of the respiratory difficulties
faced by the pt , the biomechanics of ventilation , the principles of
exercise (weaning is a form of exercise), and the general energy
requirements of functional activities .
•
Pts should be placed in a position that facilitates the biomechanics of
their ventilation.
–
For many pts , this is seated & may also include the ability to sit forward w/ the
arms supported.
•
Inspiratory muscle resistive training –> weaning success particularly
in pts who have previously demonstrated a failure to wean.
