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What happens with ventilation under general anesthesia?
decrease in pulmonary performance
What is tidal volume?
the amount of air taken in with each breath
What does anesthesia do to tidal volume?
What can decrease tidal volume during anesthesia?
- rapid, shallow breathing
- airway resistance
- surgical posture
What do opioids and inhalants do to pulmonary performance under anesthesia?
- shift the CO2 response curve to the left
- this means that it takes higher levels of CO2 to trigger breathing, which means less breathing
- this is why opioids and inhalants cause respiratory depression
What is atelectasis?
What causes atelectasis during anesthesia?
absence of spontaneous deep breaths (sighing)
What does FRC stand for?
functional residual capacity
What is functional residual capacity?
the volume of gas in the lung that exists at the end of a normal expiration when there is no airfol and alveolar pressure equals the ambient pressure
What can cause a decreased FRC during anesthesia?
- relaxation of thoracic and diaphragmatic muscles due to drugs that cause muscle relaxation
- recumbent position of animal
- regular shallow breathing
What is the order of body position from greatest ability to breathe to least ability to breathe?
- sternal recumbency
- lateral recumbency
- dorsal recumbency
What can the head down position during surgery affect?
breathing, because when we slide everything forward it puts pressure on the lungs
What can cause impaired ventilation during recovery?
- pain when breathing
- filling up the lungs puts pressure on the abdomen, when we have done abdominal surgery the pressure can hurt
What is spontaneous ventilation?
the patient determines the breathing rate and tidal volume (depth)
Do patient's under anesthesia hypoventilate?
- small animals sometimes hypoventilate
- large animals almost always hypoventilate
What needs to happen every 5 to 15 minutes during spontaneous ventilation?
patient should be given a deep breath (sigh)
What does IMV stand for?
intermittent mandatory ventilation
What is intermittent mandatory ventilation (IMV)?
a periodic inflation of the lungs during spontaneous ventilation
What is the difference between IMV and a "sigh"?
IMV will be more frequent with less pressure than a sign
How much cm of H2O do we give during a sigh? During IMV?
- sigh: 25 - 30 cm of H2O
- IMV: 15 - 20 cm of H2O
When do we do IMV?
- when the patient is hypoventilating to give extra breaths to blow off the CO2.
- the higher the CO2 levels, the more breaths we give
What is assisted ventilation?
- the patient determines the breathing rate, but tidal volume is determined by the ventilator so that it will be more
- when the patient takes a breath, we push in more air
Doing IMV also gives more anesthetic gas, so what do we need to do?
turn down the vaporizer when doing IMV
What is assisted-controlled ventilation?
assisted until a patient drops below a set respiratory rate, then the machine switches over to controlled ventilation
What is controlled ventilation?
both the breathing rate and the tidal volume (depth) is determined
When would we do controlled breathing?
- when giving neuromuscular blockers of skeletal muscle
- thoracic surgery
- diaphragmatic hernia
- large animal surgery
What is manual ventilation?
We are ventilating the patient, not a machine
What are some advantages to manual ventilation?
- can customize ventilation for the patient and can change it at specific points in time
- does not require purchase of expensive ventilation machines
What is the disadvantage of manual ventilation?
The pop off valve must be _____ before the patient can be ventilated.
Inspiratory time should be _____.
1 - 1.5 seconds
The peak inspiratory pressure should be about _____.
15 - 20 cm of H2O
What happens if we forget to open the pop off valve after giving a breath?
venous return to the heart is compromised
The vena cava is normally _____.
0 - 5 cm of H2O
What is mechanical ventilation?
equipment is doing ventilating
What are the advantages of mechanical ventilation?
- provides continuous, uninterrupted ventilation
- allows anethetist to devote their attention toward monitoring the patient more closely
What are some disadvantages of mechanical ventilation?
- mechanical failure
- consumes large amounts of compressed gas
- expensive equipment required
- anethetist can not use breathing rate as an indicator of anesthetic depth
What are the goals of positive pressure ventilation?
- prevent or treat hypoxemia
- prevent or treat hypercapnia
- dilute inhalation anesthetics more effectively
What does PPV stand for?
positive pressure ventilation
When would we use positive pressure ventilation?
anytime there is an increase of pressure in the system
What are some examples of positive pressure ventilation?
- intermittent mandatory ventilation
- controlled ventilation
What is IPPV?
intermittent positive pressure ventilation
When do we need to worry about tidal volume?
- when choosing a bag size
- for the ventilator setting
How do we choose the bag size?
3 x tidal volume
What are the most important guidelines for positiveg pressure ventilation?
- selecting an appropriate breathing rate
- use appropriate peak inspiratory pressures (PIP)
What does PIP stand for?
peak inspiratory pressure
How much is a regular breath?
15 - 20 cm H2O
How much cm H20 for a sigh?
25 - 30 cm H20
How often do we give a sigh during controlled positive ventilation? During spontaneous ventilation?
- controlled ventilation: every 15 minutes
- spontaneous ventilation: every 5 minutes
How long should inspiratory time be?
1 - 1.5 seconds
What are some problems with positive pressure ventilation?
- impaired cardiovascular function
- increased ventilation perfusion mismatch
- increased anesthetic depth
- patient "fighting" or "bucking" the ventilator
How can we treat hypovolemia?
with balanced electrolye solutions
Whata do we need to make sure the manometer is at when we are not giving a breath?
What happens when the pressure exceeds 5 cmH20?
impedes venous function and return
At what cm H2O will there be damage to the lungs?
50 cm H20 - barotrauma
How do we know when the patient is hyperventilating?
- ETCO2 is low (hypocapnia)
- long endotracheal tubes
What can happen if we give too many sighs?
we can increase the anesthetic depth too much
What can cause the patient to fight or buck the ventilator?
- if the patient is too light
- hypercapnia or inadequate ventilation
What can we do to help the patient to not fight or buck the ventilator?
- increase the respiratory rate and/or tidal volume
- provide additional anesthesia if the patient is too light
- eliminate leaks in the system
- use neuromuscular blockers if the patient is adequately anesthetized and adequately ventilated
Define aveolar ventilation.
the portion of total ventilation that participates in gas exchange of O2 and CO2 with pulmonary capillary blood
Define deadspace ventilation.
the portion of total ventilation that does not participate in gas exchange of O2 and CO2 with pulmonary capillary blood.
Dead space ventilation may result in what?
- anatomic deadspace
- alveolar dead space
- dead space effect
- mechanical dead space
Define anatomic dead space.
the volume of gases in the respiratory conducting system that does not normally participate in gas exchange with pulmonary capillary blood.
What are the respiratory conducting systems?
- nasal passageways
Define alveolar dead space.
represented by areas of the lung where no gas exchange occurs but where gas exchange normally occurs
Define dead space effect.
when ventilation in excess of perfusion exists (due to overventilation and/or underperfusion of alveoli)
Define mechanical dead space.
an extension of anatomical dead space (masks, endotracheal tubes that extend beyond the nares, Y-piece, non-functioning unidirectional valves)
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