Mechanical ventilation Flashcards
what are the indications to begin mechanical ventilation?
- severely impaired gas exchange
- rapid onset of respiratory failure
- inadequate response to less invasive medical treatments
- increased work of breathing with evidence of respiratory muscle fatigue
- absent gag or cough reflex
what parameters indicate increased work of breathing with evidence of respiratory muscle fatigue?
- RR > 35
- inspiratory force 25 cm H2O
- vital capacity < 10-15 ml/kg
- PaO2 < 60 mm Hg with FiO2 > 60%
- PaCO2 > 50 mm Hg with pH < 7.35
what are the different mechanical ventilation modes?
- assist control ventilation (ACV)
- intermittent mandatory ventilation (IMV)
- synchronized intermittent mandatory ventilation (SIMV)
- pressure support ventilation (PSV)
- inverse ratio ventilation (IRV)
- pressure targeted, lung protective ventilation
- high frequency oscillatory ventilation
- partial liquid ventilation
- mechanical ventilation with inhaled NO
what is assist control ventilation? what is a potential concern?
- produces ventilator-delivered breath for every patient-initiated inspiratory effort
- respiratory alkalosis is a concern
what is intermittent mandatory ventilation?
- allows patient to breath at a spontaneous rate and tidal volume without triggering ventilator
- ventilator adds additional mechanical breaths at a preset rate and tidal volume
what is synchronized IMV? what is a major benefit?
- allows ventilator to become sensitized to patient’s respiratory efforts at intervals determined by the frequency setting
- helps prevent stacking
what is pressure support ventilation? when is it mainly used?
- augments each patient-triggered respiratory effort by an operator-specified amount of pressure that is usually between 5-50 cm H2O
- used primarily to augment spontaneous respiratory efforts during IMV mode during weaning trials
what is inverse ratio ventilation? when is it mainly used?
- uses an inspiratory-to-expiratory ratio that is greater than the standard 1:2-1:3 to stabilize terminal respiratory units (alveolar recruitment)
- considered in patients iwth a PaO2 < 60 mm Hg despire an FiO2 > 60%, peak airway pressures > 40-45 cm H2O, or need for PEEP > 15 cm H2O
what is lung protective pressure targeted ventilation (permissive hypercapnia)?
allowed to occur with elevation of PaCO2 to minimize detrimental effects of excessive airway pressures
what are the important ventilator settings?
- FiO2
- minute ventilation
- PEEP
- inspiratory flow rate
- trigger sensitivity
- flow by
what is minute ventilation?
RR x tidal volume
close monitoring of minute ventilation is important to observe in what patients?
- COPD
- CO2 retention
definition: PEEP
maintenance of positive airway pressure at the end of expiration
what is the main goal of PEEP?
to achieve a PaO2 > 55-60 mm Hg with an FiO2 < 60% while avoiding significant cardiovascular sequalae
how should PEEP be weaned?
3-5 cm H2O increments while oxygenation is monitored closely
what is flow by?
triggering of the ventilator by changes in airflow as opposed to changes in airway pressures
what should you consider with low pressure alarms with decreased exhaled tidal volumes?
leak in the circuit
what should you do if you suspect gas trapping and auto-PEEP?
reduce minute ventilation
an acute increase in the peak airway pressure usually implies:
- decrease in lung compliance or
- increase in airway resistance
loss of tidal volume, indicated by a difference between the tidal volume setting and the delivered tidal volume, implies:
a leak in either the ventilator or the inspiratory limb of the circuit tubing
when should muscle paralysis be considered?
patients in whom effective gas exchange and ventilation cannot be achieved with other measures
what is auto PEEP?
development of end-expiratory pressure casued by airflow limitation in patients with airway disease, excessive minute ventilation, or inadequate expiratory time
what could be the end detrimental result of auto PEEP? why?
- organ hypoperfusion
- impairs CO: increases work of breathing, contributing to barotrauma
when should pneumothorax be suspected?
- airway pressures rise acutely
- breath sounds are diminished unilaterally
- BP falls abruptly
what are the acid base complications of mechanical ventilation?
- non anion gap metabolic acidosis
- metabolic alkalosis
- respiratory alkalosis
how does non anion gap metabolic acidosis render weaning difficult?
minute ventilation must increase to normalize pH
how does metabolic alkalosis compromise weaning?
blunts ventilatory drive to maintain a normal pH
what is a method to slow minute ventilation?
switch from ACV to SIMV or PSV
what are the detrimental sequelae of respiratory alkalosis?
- arrhythmias
- CNS disturbances (seizures)
- decrease in CO
what are the weaning strategies?
- IMV
- T tube
- PSV
how does IMV facilitate weaning?
allows progressive change from mechanical ventilation to spontaneous breathing be decreasing ventilator rate gradually
how does T tube facilitate weaning?
intersperses periods of unassisted spontaneous breathing through a T tube with periods of ventilator support
how does PSV facilitate weaning?
reduces work of breathing through the endotracheal tube and the ventilator circuit
once a PSV leve of _________ cm H2O is reached, the patient can be extubated without further decreases in PSV
5-8 cm H2O
what is the WEANS NOW acronym for failure to wean reasons?
W - weaning parameters E - endotracheal tube A - arterial blood gases N - nutrition S - secretions
N - neuromuscular factors
O - obstruction of airways
W - wakefulness
what are the guidelines for assessing withdrawal of mechanical ventilation?
- mental status
- PaO2 > 60 mm Hg with FiO2 < 50%
- PEEP 5 cm H2O
- PaCO2 and pH normal
- spontaneous tidal volume > 5 mL/kg
- vital capacity > 10 mL/kg
- minute ventilation < 10 L/min
- maximum voluntary ventilation double of mechanical ventilation
- maximum negative inspiratory pressure (MIP) 25 cm H2O
- RR < 30
- static compliance > 30 mL/cm H2O
- rapid shallow breathing index < 100
- stable vital signs following a 1-2 hr spontaneous breathing trial
what are troubleshooting considerations with respect to the endotracheal tube when assessing failure to wean?
- use largest tube possible
- consider supplemental PSV
- suction secretions
what are troubleshooting considerations with respect to ABG when assessing failure to wean?
- avoid or treat metabolic alkalosis
- maintain PaO2 at 60-65 mm Hg to avoid blunting of respiratory drive
- for patients with CO2 retention, keep CO2 at or above baseline
what are troubleshooting considerations with respect to nutrition when assessing failure to wean?
- ensure adequate nutritional support?
- avoid electrolyte deficiencies
- avoid excessive calories
what are troubleshooting considerations with respect to secretions when assessing failure to wean?
- clear regularly
- avoid excessive dehydration
what are troubleshooting considerations with respect to neuromuscular factors when assessing failure to wean?
- avoid neuromuscular depressing drugs
- avoid unnecessary corticosteroids
what are troubleshooting considerations with respect to obstruction when assessing failure to wean?
- use bronchodilators when appropriate
- exclude foreign bodies within airway
what are troubleshooting considerations with respect to wakefulness when assessing failure to wean?
- avoid oversedation
- wean in morning or when patient is most awake
