mechanical ventilation S&H Flashcards
definition of oxygenation
movement of O2 from alveoli into the pulmonary capillaries
oxygenation primarily dependent on …?
- on the surface area available for gas exchange
- on the preservation of the gas exchange barrier
ventilation is primarily dependent on …?
fresh gas flow into the alveoli
definition of compliance
change in lung volume for a given change in pressure
what is an assisted breath?
the patient determines the respiratory rate, but tidal volume is generated by the machine
what is a controlled breaht?
the machine determines respiratory rate and tidal volume
what are the 2 basic ways a ventilator can generate breaths by
- volume controlled
- pressure controlled
what settings are made for the volume controlled breath
preset tidal volumes and inspiratory time
peak inspiratory pressure in volume controlled breaths depend on …?
…on tidal volume chosen and compliance of the respiratory system
what settings are made for the pressure controlled breath?
preset airway pressure and inspiratory time
tidal volume in pressure controlled breaths will depend on …?
…on airway pressure chosen and compliance of the respiratory system
what is the normal tidal volume in healthy dogs and cats?
10-15 ml/kg
what is the initial setting for FiO2
100%
what is the initial setting for tidal volume if the lungs are normal?
8-12 ml/kg
what is the initial setting for tidal volume in patients with lung disease
6-8 ml/kg
what is the initial setting for the respiratory rate in patients with normal lungs?
10-20 breaths/minute
what is the initial setting for the respiratory rate in patients with lung disease?
15-30
what is the initial setting for minute ventilation in patients with normal lungs?
150-250 ml/kg
what is the initial setting for minute ventilation in patients with lung disease?
100-250 ml/kg
What is the initial setting for pressure above PEEP in patients with normal lungs?
8-10 cm H2O
what is the initial setting for pressure above PEEP in patients with lung disease
10-15 cm H2O
what is the initial setting for positive end-expiratiory pressure in patients with normal lungs?
0 - 4 cm H2O
what is the initial setting for positive end-expiratory pressure for patients with lung disease?
4-8 cm H2O
what is the initial setting for inspiratory flow rate in both patients with normal lungs or lung disease?
40-60 L/min
what is the initial setting for inspiratory time in both patients with normal lungs or lung disease
0.8 to 1 seconds
what is the initial setting for rise time in both aptients with normal lungs or lung disease?
0.1 to 0.5 seconds
what is the initial setting for inspiratory-to-expiratory ratio in patients with normal lungs?
1:2
what is the initial setting for inspiratory-to-expiratory ratio for patients with lung disease?
1:1 to 1:2
what is the initial setting for inspiratory trigger in both patients with normal lungs or lung disease?
airway pressure drog by 1-2 cm H20
gas flow change by 1-2 L/min
- lower triggers in smaller patient
- don’t set too sensitive –> movements like patient handling could initiate breaths
what is rise time? in what type of ventilation is it set?
time in which airway pressure increase from baseline to peak pressure –> setting in pressure-controlled ventilation
what is the inspiratory time determined by?
the flow rate (40-60 L/min)
how high may the inspiratory pressure be set to in patients with lung disease and decreased compliance?
may be set as high as 30 mm Hg (normally kept under 20, ideally closer to 10)
what is PEEP (positive end-expiratory pressure)?
maintains positive pressure in the airway during exhalation and therefore prevents complete emptying of the lungs
- initially often set at 2-5 cm H2O and then tirtrated
how is PEEP though to increase oxygenation?
- recruits previously collapsed airways
- prevents further alveolar collapse
- reduces ventilator-induced lung injury
what is the definition of hypoxemia and severe hypoxemia?
hypoxemia –> PaO2 < 80 mm Hg and SpO2 < 95%
severe hypoxemia –> PaO2 < 60 mm Hg and SpO2 < 90%
when does PCO2 fail to be an accurate predictor of hypoventilation?
in a patient that is not hemodynamically stable
definition of severe hypoventilation?
PaCO2 > 60 mm Hg
what are common causes for sever hypoventilation/hypercapnia
- increased dead space in the breathing circuit
- upper airway obstruciton
- sedative overdose
- neurologic or neuromuscular disease
- post CPA
indications for mechanical ventilation
- severe hypoxemia despite O2 therapy
- severe hypoventilation despite therapy
- dysnpea with impending respiratory fatigue or failure
- severe hemodynamic compromise
- patients requiring > 60% FiO2 over prolonged period of time –> to prevent O2 toxicity
important monitoring during mechanical ventilation
- ECG
- core body temperature
- arterial blood pressure
- end-tidal carbon dioxide
- pulse oximetry
- serial arterial blood gas measurements
maximum tracheal cuff pressure
25 mm Hg
goals of mechanical ventilation (PaCO2 and PaO2)
PaCO2 35-50 mm Hg and PaO2 80-120 mm Hg
with the least aggressive setting possible
equation for V
equation for VT
VT = respiratory rate x tidal volume
equation for VA
VA = alveolar minute ventilation = VT - dead space volume
what is dead space?
part of tidal volume that doesn’t participate in gas exchange
what is the main determinant of PCO2?
VA = alveolar minute ventilation
things to assess in hypercapnia and how to respond
- check for increased dead space from excess tubing etc.
- check for airway obstruction, e.g., kinked tube or obstruction from secretion
- if those are not the case –> hypercapnia likely from decreased VA
next step –> increase respiratory rate and/or tidal volume –> reevaluate PCO2
what to do if CO2 is lower than reference range?
decrease respiratory rate and/or tidal volume
what is the goal FiO2 during mechanical ventilation?
< 60%
(risk of O2 toxicity if FiO2 > 60% for > 24 hours)
what should you do if the patient becomes hypoxemia?
- increase FiO2 to 100%
- if still hypoxemic –> increase PEEP, peak inspired airway pressure/tidal volume or respiratory rate
- Keep animal in prone position/sternal recumbency
groups of complications from mechanical ventilation
- cardiovascular compromise (impairment of intrathoracic blood flow)
- ventilator-induced lung injury
- ventilator-induced pneumonia
- pneumothorax
pneumothorax during mechanical ventilation is likely a cause of …?
underlying lung disease
indicators of pneumothorax during mechanical ventilation
- acute decline in oxygenating ability
- elevstion in PCO2
- decreased chest wall movement and compliance
- patient-ventilator asynchrony
causes of patient-ventilator asynchrony
- hypoxemia
- hypercapnia
- pneumothorax
- hyperthermia
- inappropriate ventilator settings
- full urinary bladder or colon
- inadequate depth of anesthesia
causes of decreases in oxygenation during mechanical ventilation
- loss of O2 supply
- machine or circuit malfunction
- deterioration of the underlying pulmonary disease
- development of new pulmonary disease
causes of hypercapnia during mechanical ventilation
- pneumothorax
- bronchoconstriction
- obstruction of endotracheal or tracheostomy tube
- inceased apparatus dead space
- incorrect assembly of the ventilator circuit
- increased pulmonary dead space (increases in PaCO2-ETCO2 gradient)
- inadequate ventilator setting (low tidal volume, inspiratory or expiratory time)
prognosis for successful weaning from mechanical ventilation and survival to discharge in animals with pulmonary parenchymal disease
- 30% weaned off
20% survive to discharge
prognossi for successful weaning from mechanical ventilation and survival to discharge in animals with intracranial or neuromuscular disease
50% weaned off, 40% survive to discharge
