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65 Cards in this Set

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Anatomic deadspace (define)
Dead space in conducting airways
Alveolar deadspace
Wasted ventilation
Physiologic deadspace (formula)
Anatomic + alveolar dead space
Mechanical deadspace
External breathing system
How quick does hypoxemia kill?
Quickly
How quick does hypoventillation kill?
Slowly
Hypoxemia
PaO2 < 60 mmHg
Hypoxia
Inadequate O2 supply
What can cause CO2 retention? (2)
- Increased CO2 production
- Decreased CO2 exhaust
3 things that increase CO2 production
- Shivering
- Increased body temperature
- Inotrope administration
4 reasons for inadequate CO2 elimination
- Hypoventilation
- V/Q mismatch
- Rebreathing
- Equipment problem (incompetent one-way valve for example)
Two causes of rebreathing
- Spent sodasorb
- Low gas flow in a non-breathing system
Two beneficial effects of hypoventilation
- Maintains arterial BP and CO
- Shifts oxyhemoglobin dissociation curve to right to improve offloading of O2 into tissue
Three unwanted effects of hypoventilation
- Myocardial depression
- CNS depression
- Increased CSF pressure --> herniation --> suboptimal evaluation
What is PaCO2 directly related to?
CSF pressure
At what level of CO2 produces anesthesia?
30%
Why is CO2 not used as an anesthetic?
Produces convulsions
At what point does CO2 cause respiratory depression (rather than being the drive to breathe)?
> 100 - 150 mmHg
3 ways that CO2 causes CNS depression
- Anesthetic at 30% CO2
- Depression of respiratory stimulation effects at >100 - 150 mmHg
- Catecholamine release (leads to vasodilation and causes arrhythmias)
Formula for carbonic acid equilibrium
CO2 + H2O <--> H2CO3 <--> H + HCO3
Three actions that affect the carbonic acid equilibrium
- Adding CO2
- Adding HCO3
- Not Removing CO2
Where does the carbonic acid equilibrium occur?
RBC level
- Does not involve kidneys
Average pH
7.4
PaO2 range
80 - 100 mmHg
Average PaCO2
40 mmHg
Average HCO3
24 mEq/L
Base Excess range
-4 - 4
What's the direct measure of respiratory component?
CO2
What's the direct measure of metabolic component?
Base excess
How do you treat a respiratory acidosis in general?
Increase minute ventilation
- Increase Rate of breathing or End Tidal volume (Vt)
How do you treat a respiratory alkalosis in general?
Decrease minute ventilation
- Decrease rate or Vt
At what pH is there a metabolic acidosis?
< 7.2
Formula for calculating a bicarbonate (HCO3) replacement
HCO3 (mEq/L) = BW (kg) * 0.3 * BE (mEq/L)
How should bicarbonate be administered?
Administer 1/2 to 1/3 of deficit intravenously slowly, then re-evaluate
9 unwanted effects of bicarbonate administration
- Negative inotropy
- Paradoxical CSF acidosis
- Alkalosis
- Hyperosmolarity
- Hypokalemia
- Hypocalcemia
- Vasodilation
- Shifts OHAC (oxygen-hemoglobin association curve)
- Volume overload
How do you treat a metabolic alkalosis?
Administer 0.9% NaCl
4 clinical signs of hypoventilation
- Brick red mucous membranes
- Bucking
- Tachycardia
- Arrhthmias
What percent saturation corresponds with 60 mmHg?
90%
What PaCO2 indicates a Hypoventilation?
PaCO2 > 45 mmHg
What PaO2 indicates hypoxemia?
< 60 mmHg
What PaO2 is P50% on the oxyhemoglobin dissociation curve?
28 mmHg
How do you get the oxyhemoglobin dissociation curve to shift right? (4)
- Decrease pH
- Increase CO2
- Increase Temperature
- Increase DPG
How do you get the oxyhemoglobin dissociation curve to shift left? (5)
- Increase pH
- Decrease CO2
- Decrease Temperature
- Decrease DPG
- Fetal hemoglobin
Formula for Bound O2 and dissolved O2
Bound O2 = % sat * [Hb] g/dl * 1.34 ml O2/g Hb

Dissolved O2 = PaO2 * 0.003 ml O2/dl
6 differentials for Hypoxemia
a. FIO2 < 0.2
b. Hypoventilation
c. Diffusion barrier
d. Anatomic shunt (R -> L)
e. V/Q mismatch
f. Decrease CO
What is the respiratory quotient, and what's normal?
Ratio of CO2 produced to O2 consumed

0.8 (so 20% more O2 is consumed than CO2 produced)
Two factors contributing to a V/Q mismatch
- Anesthesia depresses hypoxic pulmonary vasoconstriction (HPV) mechanism
- Abnormal positioning for surgery
What is strictly not a differential for hypoxemia?
Anemia
2 ways that decreased cardiac output (CO) causes hypoxemia
- Direct impairment of arterial oxygenation
- Exacerbation of existing V/Q abnormality
What should you use to diagnose absolute hypoxemia? (4)
- Arterial blood gas
- Pulse oximetry
- T wave and ST segment changes
- Severe bradycardia
Sequelae to hypoxemia (3)
- Blindness
- Neurologic deficits
- Death
4 goals of intermitten positive pressure ventilation (IPPV)
- Maintain arterial pCO2
- Maintain arterial pO2
- Speed induction or maintain anesthetic plane
- Control respiratory movements (during thoracic surgery)
4 reasons IPPV is used
&gt; Maintain PaCO2
&gt; Maintain PaO2
&gt; Speed induction or maintain stable anesthetic plane
&gt; Control respiratory movements
5 complications of IPPV
- Increased anesthetic depth
- Hyperventilation
- Alkalosis
- Barotrauma
- Impaired CV function
Tidal volume of a mechanical ventilator
10 - 20 ml/kg
Respiratory rate for a mechanical ventilator
6 - 15 breaths/min
- 6 - 10 in horses
- 8 - 12 in dogs
What should inspiratory pressure of mechanical ventilators be?
12 to 30 cm of water
Inspiratory to expiratory ratio with mechanical ventilators
1:2
- Should never have inspiratory greater than expiratory
Two ways to wean a patient off a mechanical ventilator
- Decrease frequency of breaths to allow the PaCO2 to increase
- Decrease anesthetic plane (restore CO2 drive to breathe, or secondarily, O2)
How do you solve anesthetic depth being too light?
- Increase rate of anesthesia
How do you solve a hypercarbic patient?
Increase ventilation
Three types of ventilators
- Pressure limited
- Volume limited
- Time cycled
Which ventilator is safer to use?
Pressure limited (has failsafes)
Which ventilator has a known Vt?
Volume limited
What type are most anesthesia ventilators in veterinary medicine?
Time cycled