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65 Cards in this Set

  • Front
  • Back
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?
How quick does hypoventillation kill?
PaO2 < 60 mmHg
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?
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
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?
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?
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?
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
- 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