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What happens with ventilation under general anesthesia?
decrease in pulmonary performance
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What is tidal volume?
the amount of air taken in with each breath
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What does anesthesia do to tidal volume?
decrease it
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What can decrease tidal volume during anesthesia?
- rapid, shallow breathing
- airway resistance
- surgical posture
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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
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What is atelectasis?
collapsed alveoli
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What causes atelectasis during anesthesia?
absence of spontaneous deep breaths (sighing)
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What does FRC stand for?
functional residual capacity
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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
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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
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What is the order of body position from greatest ability to breathe to least ability to breathe?
- standing
- sternal recumbency
- lateral recumbency
- dorsal recumbency
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What can the head down position during surgery affect?
breathing, because when we slide everything forward it puts pressure on the lungs
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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
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What is spontaneous ventilation?
the patient determines the breathing rate and tidal volume (depth)
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Do patient's under anesthesia hypoventilate?
- yes
- small animals sometimes hypoventilate
- large animals almost always hypoventilate
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What needs to happen every 5 to 15 minutes during spontaneous ventilation?
patient should be given a deep breath (sigh)
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What does IMV stand for?
intermittent mandatory ventilation
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What is intermittent mandatory ventilation (IMV)?
a periodic inflation of the lungs during spontaneous ventilation
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What is the difference between IMV and a "sigh"?
IMV will be more frequent with less pressure than a sign
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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
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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
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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
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Doing IMV also gives more anesthetic gas, so what do we need to do?
turn down the vaporizer when doing IMV
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What is assisted-controlled ventilation?
assisted until a patient drops below a set respiratory rate, then the machine switches over to controlled ventilation
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What is controlled ventilation?
both the breathing rate and the tidal volume (depth) is determined
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When would we do controlled breathing?
- when giving neuromuscular blockers of skeletal muscle
- thoracic surgery
- pnumothorax
- diaphragmatic hernia
- apnea
- large animal surgery
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What is manual ventilation?
We are ventilating the patient, not a machine
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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
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What is the disadvantage of manual ventilation?
labor intensive
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The pop off valve must be _____ before the patient can be ventilated.
closed
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Inspiratory time should be _____.
1 - 1.5 seconds
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The peak inspiratory pressure should be about _____.
15 - 20 cm of H2O
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What happens if we forget to open the pop off valve after giving a breath?
venous return to the heart is compromised
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The vena cava is normally _____.
0 - 5 cm of H2O
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What is mechanical ventilation?
equipment is doing ventilating
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What are the advantages of mechanical ventilation?
- provides continuous, uninterrupted ventilation
- allows anethetist to devote their attention toward monitoring the patient more closely
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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
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What are the goals of positive pressure ventilation?
- prevent or treat hypoxemia
- prevent or treat hypercapnia
- dilute inhalation anesthetics more effectively
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What does PPV stand for?
positive pressure ventilation
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When would we use positive pressure ventilation?
anytime there is an increase of pressure in the system
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What are some examples of positive pressure ventilation?
- intermittent mandatory ventilation
- controlled ventilation
- sighs
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What is IPPV?
intermittent positive pressure ventilation
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When do we need to worry about tidal volume?
- when choosing a bag size
- for the ventilator setting
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How do we choose the bag size?
3 x tidal volume
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What are the most important guidelines for positiveg pressure ventilation?
- selecting an appropriate breathing rate
- use appropriate peak inspiratory pressures (PIP)
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What does PIP stand for?
peak inspiratory pressure
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How much is a regular breath?
15 - 20 cm H2O
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How much cm H20 for a sigh?
25 - 30 cm H20
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How often do we give a sigh during controlled positive ventilation? During spontaneous ventilation?
- controlled ventilation: every 15 minutes
- spontaneous ventilation: every 5 minutes
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How long should inspiratory time be?
1 - 1.5 seconds
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What are some problems with positive pressure ventilation?
- impaired cardiovascular function
- increased ventilation perfusion mismatch
- barotrauma
- hyperventilation
- increased anesthetic depth
- patient "fighting" or "bucking" the ventilator
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How can we treat hypovolemia?
with balanced electrolye solutions
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Whata do we need to make sure the manometer is at when we are not giving a breath?
0
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What happens when the pressure exceeds 5 cmH20?
impedes venous function and return
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At what cm H2O will there be damage to the lungs?
50 cm H20 - barotrauma
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How do we know when the patient is hyperventilating?
- ETCO2 is low (hypocapnia)
- long endotracheal tubes
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What can happen if we give too many sighs?
we can increase the anesthetic depth too much
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What can cause the patient to fight or buck the ventilator?
- if the patient is too light
- hypercapnia or inadequate ventilation
- hypoxemia
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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
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Define aveolar ventilation.
the portion of total ventilation that participates in gas exchange of O2 and CO2 with pulmonary capillary blood
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Define deadspace ventilation.
the portion of total ventilation that does not participate in gas exchange of O2 and CO2 with pulmonary capillary blood.
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Dead space ventilation may result in what?
- anatomic deadspace
- alveolar dead space
- dead space effect
- mechanical dead space
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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.
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What are the respiratory conducting systems?
- nasal passageways
- pharynx
- trachea
- bronchi
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Define alveolar dead space.
represented by areas of the lung where no gas exchange occurs but where gas exchange normally occurs
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Define dead space effect.
when ventilation in excess of perfusion exists (due to overventilation and/or underperfusion of alveoli)
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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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