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- Improves oxygenation
- Used to treat obstructive sleep apnea
- Also used to treat patients with COPD
Noninvasive positive pressure ventilation
- Used for patients with respiratory failure caused by various neuromuscular disorders, chest wall deformities, COPD, central ventilatory control abnormalities, and acute cardiogenic pulmonary edema
- Can reduce the need for intubation in 60 to 75% of patients
Advantages of Noninvasive positive pressure ventilation!
- Avoids complications associated with artificial airways
- Provides flexibility in initiating and removing mechanical ventilation
- Reduces requriements for heavy sedation
- Preserves airway defense, speech, and swallowing mechanisms
- reduces need for invasive monitoring
Disadvantages of Noninvasive positive pressure ventilation!
- Can cause gastric distention
- skin pressure lesions
- Facial pain
- Dry nose
- eye irritation
- poor sleep
- mask leaks can occur
Full ventilatory support
- Provides all the energy necessary to maintain effective alveolar ventilation
- Provided when ventilatory rates are high (8 breaths/min or more) and tidal volume is adequate for the patient
Partial ventilatory support
Any degree of mechanical ventilation in which set machine rates are lower than 6 breath/min and the patients partipates in the work of breathing to help maintain effective alveolar ventilation
Patient lung characteristics in volume controlled ventilation!
- Reduction in lung or chest wall compliance produce higher peak and plateau pressures
- Increases compliance produces lower peak and plateau pressures
- Increased airway resistance produces a higher peak pressure
- Reduction in airway resistance produces lower peak pressures
Inspiratory flow pattern in volume controlled ventilation!
- Peak pressures is higher with a constant flow and lower with a decelerating flow pattern
- Decelerating flow pattern has a higher mean airway pressure
- Constant flow generates the lowest mean airway pressure
- High inspiratory gas flow creates a higher peak pressure
Volume setting in volume controlled ventilation!
- High volume produces higher peak and plateau pressures
- Low volumes produce lower peak and plateau pressures
PEEP in volume controlled ventilation!
Increasing PEEP increases the peak and mean pressures
Auto PEEP in volume controlled ventilation!
Increases in auto PEEP increases the peak inspiratory pressure
Pressure setting in pressure controlled ventilation!
- Higher pressure setting produce larger volumes
- Lower pressure setting produce lower volumes
- Increasing the PIP while maintaining a constant EEP increases volume delivery
Pressure gradient in pressure controlled ventilation!
Increasing EEP (PEEP + auto PEEP) while keeping PIP constant reduces the pressure gradient (PIP - EEP) and lowers volume delivery
Patient lung characteristics in pressure controlled ventilation!
- Reduced compliance results in lower volumes
- Increased compliance results increased volumes
- Increased airway resistance (RAW) results in lower volume delievery
- Reduction in airway resistance results in higher volume delievery
Inspiratory time in pressure controlled ventilation!
When the inspiratory time is extended, volume delievery increases
Patient effort in pressure controlled ventilation!
Active inspiration by the patient can increase volume delievery
Continuous mandatory ventilation
- All breaths are mandatory and can be volume or pressure targeted
- Breaths can also be patient triggered or time triggered
Intermitted mandatory ventilation
- Involves periodic volume or pressure targeted breaths that occur at set intervals (Time triggering)
- The patient can breath spontaneously between mandatory breaths
CPAP may be helpful for...
Improving oxygenation in patients with refractory hypoxemia and a low FRC, which can occur with a acute lung injury
Pressure support ventilation
A pressure support breath is patient triggered, pressure limited, and flow cycled
Advantages of volume targeted or pressure targeted continuous mandatory ventilation! (CMV)
- Set minimum ventilation with volume tregeted breaths
- Guaranteed volume or pressure with each breath
- May synchronize with patient efforts
- Patient may establish rate
- Can provide full support in patients who are not breathing spontaneously
Advantages of volume targeted or pressure targeted synchronized intermittent mandatory ventilation! (SIMV)
- May lower mean airway pressure
- Variable work of breathing for patient may maintain muscle strength and reduce muscle atrophy
- Can be used for weaning
- May reduce alkalosis associated with CMV
- Full or partial support can be adjusted to meet patients needs
- Sedation and paralysis are not requried
Metabolic rate is directly related to...
Body mass and surface area
- Men- Ve = 4 x body surface area (BSA)
- Women- Ve = 3.5 x body surface are (BSA)
Calculating ideal body weight!
- Women: IBW= 105 +5(H-60)
- Where H is hieght in inches
- Men: IBW = 106 + 6(H-60)
- Reflects the volume (in milliliters) of gas compressed in the ventilator circuit
- Ct= change in volume divided by change in pressure
When setting tidal volume and rate, the goal is not to focus so much on the exact Vt and rate but to focus...
- On using setting that do not harm the patient
- Maintaining plateau pressures lower than 30 cm H2O is very important
- In some cases let PaCO2 rise and pH fall outside the patients normal values to avoid lung injury
When determining tidal volume for ventilated patients...
- A range of 5 to 8 mL/kg of IBW is typically used for adults
- 4 to 8 mL/kg IBW for infants and children
- 6 to 12 ml/kg IBW
- 5-10 ml/kg IBW
Mechanical dead space
- The volume of gas that is rebreathed during ventilation
- Adding dead space will increase dead space
- App 6 inch of tubing will increase CO2 by 2 to 3 ml/Hg
Gas flow during controlled mechanical ventilation
- High flows shorten Ti and may result in higher peak pressures and poor gas distrubution
- Slower flows may reduce peak pressures, improve gas distrubution, and increase Paw
- Shorter Te can lead to air trapping and longer Ti may cause cardiovascular side efects
A long Ti (requring 3 to 4 constants) has been shown to improve...
- Ventilation in nonhomogeneous lungs like those seen in ARDS
- good for patients with increased resistance
Fast Ti flows (requring fewer time constant to fill the lungs) may benefit...
Patients with increased airway resistance as in COPD, providing longer Te, which in turn will reduce or prevent the risk of air trapping
A maneuver that can be performed by preventing the expiratory valve from opening for a short time at the end of inspiration
The inspiratory pause maneuver is used to obtain...
Measurements of Pplateau, which helps to estimate alveolar pressure for the calculations of static compliance
The inspiratory pause provides a longer inspiratory time, which in turn provides...
- Optimum V/Q matching
- Reduces dead space to tidal volume ratios
In any pressure targeted breath the difference in what determines the set Vt delievery?
Pressure between baseline (PEEP + auto PEEP) and PIP
There are two ways to set the pressure in pressure targeted breath to provide the desired Vt!
- One way is to deliever a volume targeted breath to the patient at the desired Vt and measure the plateau and baseline pressures
- A second method to intiate pressure ventilation is to start at a low pressure (10-15 cm H2O) and check the Vt before readjusting the pressure to attain the desired volume
Pressure support ventilation
- The pressure is set at a level sefficient to prevent a fatiguing workload on the respiratory muscles
- Set the initial PSV level to equal the transairway pressure
The goal of adjusting pressure support ventilation!
- To help increase Vt (4-8 mL/kg)
- To decrease respiratory rate (to <30 breaths/min
- To decrease the WOB associated with breathing through an artificial airway
The goal of setting a specific FiO2 for a patient is to...
Achieve a clinically acceptable arterial oxygen tension(60-100 mm Hg)
If the PaO2 is not within the desired range, The equation for FiO2!
- If a baseline ABG is not available, it is advisible to select a high initial FiO2 setting > 0.50
- This can be a way of restoring normal oxygenation and replacing tissue oxygen storage when oxygen debt and lactic acid accumulation has occured
Extended use of 100% O2 is not recommended because...
It can lead to absorption atelectasis and long term oxygen toxicity
- Flow triggering is set in a range of 1 to 10 L/min below the base flow
- Pressure sensitivity is common between -1 and -2 cm H2O
When a FiO2 greater than 0.50 is requried to maintain oxygenation...
PEEP may be indicated
Many clinicians prefer using flow triggering because...
It provides a slightly faster response time compared with pressure triggering
If auto PEEP is present...
Patients might have trouble triggering a breath
Intrinsic PEEP can occur in three situation!
- Strong active expiration
- High minute ventilation where Te is too short
- expiratory flow limitations due to increased airway resistance
The humidification system used during mechanical ventilation should provide at least 30 mg H2O/L of absolute humidity at a temperature range of about 31 to 35 degrees C for all available flows up to Ve of 20 to 30 L/min
Heated Humidifiers devices!
- Vapor phase
- Active heat and moisture exchange
Typically include a servo controlled heater with a temperature probe that is placed close to the patient airway
Whenever the temperature in the patients circuit is less than the temperature of the gas leaving the humidifier...
- Condensate accumulates in the circuit
- This will increase as the room temp becomes cooler
To assess whether a humidity deficit is present...
The therapist should check the patients secretions
Heat moisture exchangers
Can provide up 10 to 14 mg/L of water at tidal volumes of 500 to 1000 mL
The dead space for most HMEs ranges from...
50 to 100 mL
Contraindications for heat moisture exchangers!
- The presence of thick, copious, or bloody secretion.
- The patients exhaled tidal volume is less than 70% of inhaled Vt
- Body temp below 32* C
- Spontaneous Ve is greater than 10 L/min
- An aerosolized medication must be given
- Very small Vt must be delievered
Most HMEs have a resistance to flow of...
Between 2.5 and 3.5 cm H2O/L/min
Low pressure alarms
- Usually set about 5 to 10 cm H2O below PIP
- These alarms are useful for detecting patient disconnection and leaks in the system
High pressure alarms
- Set about 10 cm H2O about PIP
- Usually end inspiration when activated
Low PEEP/CPAP alarms
- Usually set about 2 to 5 cm H2O below the PEEP
- Activation of these latter alarms usually indicates the presence of a leak in the circuit
Low minute ventilation alarm
10 to 15% below average minute volume
- A deep breath that occurs regular as a part of a normal breathing patterm
- Reduces atelectasis
Sighs or deep breaths may be appropriate in the following situations!
- Before and after suctioning
- Before and after bronchoscopy
- During an extubation procedure
- During CPT
- During low Vt ventilation
- As a recruitment maneuver in some patients with ARDs
Final consideration in ventilator equipment setup!
- Check ventilator and circuit function
- Fill the humidifier with sterile water and set the humidifier temp so that the final gas temp at the airways will be 31 to 35 *C or place an HME in line
- Place a temperature monitoring device near the patients connector when heated humidifier is used
- Check the FiO2, set Vt and F
- Adjust the alarms
- Ensure that the patient is connected to an electrocardiographic monitor
- Have an emergency airway tray avilable in case the patient airway is removed or damanged
- Check that the suctioning equipment is available and functioning
- Select a volume monitoring device and an oxygen analyzer if one is not available with the ventilator
- Ensure that a manual resuscitation is available
Once the decision has been made to connect the patient to a ventilator, several steps should be taken, including the following:
- Preparing the patient
- Establishing an airway interface
- Manually ventilating the patient
- Stabilizing the patient's cardiovascular status
- Meeting ventilation needs
- Treating the cause of respiratory failure
Guidelines for neuromuscular disorders!
- Full or partial support
- NPV or PPV
- Nonivasive or invasive ventilation
- Assist/control mode
- Volume control ventilation
- Vt of 700 to 1000 L while maintaining the Pplateau at less than 30 cm H2O
- F= 8 to 16 breaths/min
- Inspiratory flow rates greater than 60 L/min
- Flow waveform: constant or descending flow pattern
- PEEP = 5 cm H2O
- FiO2 = 0.21
Indications for mechanical ventilation in acute exacerbation of asthma!
- Exhaustion with developing metabolic acidosis and decresing pH
- If aidible bilateral wheezes become distant as air trapping increases
- Severe hypoxemia
- Altered mental status changes
Tidal volume and rate for patients with normal lungs?
- High tidal volume to low to normal rate
- Vt 10 to 12 mg/IBW
- Rate 8-12
Rate and tidal volume based on obstructive lungs (COPD)!
- Moderate Tidal volume 8-10 mg/IBW
- Rate 8-12
- I:E ratio 1:4
Rate and tidal volume based on restructive lungs (ARDs)!
- Small tidal volumes 4-8 mg/IBW
- maintain low alveoi pressure
- Rate 15-25
- Do not want auto PEEP with high rate decrease exhalation time
- CO2 will rise
A increase in gas flow, a decrease in I time and increase in PEEP pressure will...
Slow or no flow will...
Decrease in PIP will...
- Protect alveoli
- Increase I time
Better gas distrubtion
Increase in mean airway pressure which improves oxygenation
A decrease in E time will...
- Increase chance for cardiovascular effects
- Can lead to impression of inferior and vena cava which reduces venous return to heart
- destroys lung endothelium
- Alveoli capillarily thickens
CPAP only treats!
Ventilation and perfusion
- Normal drive to breath
- Risk of aspiration
- Weak muscles
- Cant protect airway
- Big tidal volumes at high flow
- The strength of the pulses will change when inhaling
- Change of PPl changes blood flow
- High flow
- Descending flow waveform
Allowing CO2 to go up to prevent lung damage
A increase in PEEP will...
Increase ICP which is bad
- Decrease in CO2 causes vasoconstruction of cerebral vessels which decreases ICP and swelling
- CO2 25-30
- Effective for 48 hours
Hypoxmia that does not respon to oxygen
- Keep FiO2 low
- Use PEEP higher to keep O2 low
- Longer I time to improve oxygenation
- make sure E time is long enought to prevent air trapping