ECC2- Oxy-Vent

  1. Movement of air from environment to alveolus.
  2. Exchange of gas b/w alveolus and arterial blood.
    oxygenation (pulmonary function)
  3. What are the steps involved with taking a breath? (5)
    • 1. signal in resp center of brain
    • 2. signal travels down cervical spinal nerves
    • 3. connected with peripheral efferent nerves
    • 4. synapse with neuromuscular junctions of diaphragm and intercostal muscles
    • 5. muscles contract, thoracic cavity expands, creating negative intrathoracic pressure
  4. What are factors affecting ventilation? (7)
    • Tidal volume (VT), which is affected by dead space, lung compliance, airway resistance, neuromuscular function
    • Respiratory rate (f, RR), which is controlled by the central ventilatory drive
  5. The overall effectiveness of ventilation is determined by...
    minute ventilation= RR x VT
  6. How does blood gas analysis aid your assessment of ventilation?
    • PCO2 value: PCO2 is primarily a function of ventilation
    • increased= hypoventilation
    • decreased= hyperventilation
  7. Describe the difference b/w arterial and venous blood gas analysis for ventilation.
    • arterial is gold standard, normal PCO2 is lower
    • venous is easier, but normal PCO2 will be higher for a venous sample (has not returned CO2 to lungs for exhalation yet)
  8. How is capnometry used to assess ventilation?
    • measure end-tidal CO2 through a sensor attached to ET tube (infrared absorption technology)
    • ETCO2 correlates to arterial CO2
    • high ETCO2= hypoventilation
    • low ETCO2= hyperventilation
  9. What are the pros and cons of using capnometry to assess ventilation
    • Pros: continuous assessment, primarily reflects ventilation 
    • Cons: MIGHT be affected with severely impaired perfusion
  10. What are indications for capnometry? (3)
    • monitoring anesthetized patients: low ETCO2- patient is too light or CVS collapse, high ETCO2- patient too deep or rebreathing of CO2
    • patients requiring mechanical ventilation: monitor for over or under-ventilation
    • monitoring effectiveness of compressions during CPR: ETCO2 >20mmHg associated with better success
  11. What are 2 general causes of hypoventilation and 12 specific reasons?
    • Neuromuscular: CNS dz, cervical spinal cord lesion, peripheral neuropathies (botulism), neuromuscular junction dz, myopathy
    • Respiratory: airway obstruction, lower airway dz, parenchymal dz, pleural space dz, chest wall damage, abdominal distention
    • Other: compensatory for metabolic alkalosis
  12. What are causes of hyperventilation? (9)
    • hypotension
    • fever/ hyperthermia
    • sepsis/ SIRS
    • pain/ stress
    • eercise
    • anemia
    • hypoxemia
    • CNS dz
    • compensatory for metabolic acidosis
  13. Arterial oxygen pressure (PaO2) in arterioles that passed through/ by an alveolus should be about _____________.
  14. Hemoglobin O2 saturation is determined by...
    PaO2, which depends on amount of Hgb, O2 saturation of Hgb, temperature
  15. What factors shift the Oxy-Hgb dissociation curve to the left? (4)
    • decreased temp
    • decreased CO2
    • alkalosis
    • decreased 2,3-DPG
  16. What factors shift the oxy-Hbg dissociation curve to the right? (4)
    • increased temp
    • increased CO2
    • acidosis
    • increased 2,3-DPG
  17. Hypoxemia is defined as...
    PaO2 < 80mmHg
  18. What does a right shift of the oxy-Hgb dissociation curve indicate?
    reduced affinity of Hgb for oxygen- releases it to the tissues easier
  19. What does a left shift of the oxy-Hgb dissociation curve indicate?
    increased affinity of O2 for Hgb
  20. What are causes of hypoxemia? (5)
    • V/Q mismatch
    • hypoventilation
    • shunt
    • diffusion impairment
    • decreased inspired oxygen
  21. Describe high versus low V/Q mismatch and causes of each.
    • High: ventilation in excess of perfusion; caused by PTE, CVS collapse
    • Low: perfusion in excess of ventilation; caused by pneumonia, pulmonary edema, contusions, PTE, pleural space disease
  22. Hypoventilatory causes of hypoxemia are usually very responsive to ____________ due to ___________.
    oxygen supplementation; increased diffusion gradient
  23. What causes diffusion impairment, which leads to hypoxemia?
    • scarring, thickening of alveolar wall, resulting in significant impediment to O2 diffusion
    • chronic lung disease: infection, inflammation, congestion, idiopathic
  24. What causes of hypoxemia are very responsive to supplemental O2? (3)
    • hypoventilation
    • diffusion impairment
    • decreased inspired O2
  25. What causes of hypoxemia are NOT responsive to O2 supplementation? (2)
    • anatomical/ pulmonary shunts
    • bad V/Q mismatch
  26. Describe a shunt and causes of it.
    • extreme form of V/Q mismatch with perfusion in complete absence of ventilation--> venous admixture with arterial blood
    • anatomical: reverse PDA, tetralogy of fallot
    • pulmonary: atelectasis, severe alveolar dz
  27. How does pulse ox work?
    • measures arterial oxygen Hgb saturation by measuring the absorption of 2 wavelengths of light through a pulsatile vascular bed
    • normal SpO2= 97-98% (start to worry when <95%)
  28. What are limitations of pulse oximetry? (4)
    • late indicator of hypoxemia
    • overestimates with hyperventilation (left shift of curve)
    • measurement affected by motion, pigmentation, vasoconstriction/ hypothermia, tissue thickness, arrhythmias, abnormal Hgb
    • does not tell you about anemia or icterus
  29. The gold standard for assessing pulmonary function is...
    arterial blood gas
  30. What are the measured and calculated values on arterial blood gas?
    • Measured: pH, PaO2, SaO2, PaCO2
    • Calculated: A-a gradient, P/F ratio, rule of 120
  31. PaO2 should be equal to...
    • 5 x FiO2 (if on oxygen)
    • 90-100mmHg (if breathing atmospheric air)
  32. What is A-a gradient?
    • quantifies ability of O2 to go from alveolus to arterial blood, taking ventilation into account
    • hyperventilation will tend to increase PaO2
    • hypoventilation will tend to decrease PaO2
    • changes occur independently of pulmonary function
    • **can only interpret when obtained at FiO2 of 21% (room air)
  33. What is the equation for A-a gradient?
    • A-a= (150- PaCO2/0.9) - PaO2
    • Hypoxia d/t hypoventilation if A-a <10-20mmHg on room air
    • Hypoxia d/t poor pulmonary function if A-a > 20mmHg
  34. Describe the rule of 120.
    • [simplified approach to A-a gradient]
    • asserts that PaO2 + PaCO2 should be >120
    • if sum is <120, pulmonary dysfunction exists
    • if sum is >120, normal pulmonary function
    • **again, only used if patient is breathing room air
  35. What is the P/F ratio? What is the equation?
    • it reflects the impact of FiO2 on PaO2
    • P/F ratio= PaO2/ FiO2
    • P/F= 400-500 is normal
    • P/F= 300-400 mild pulmonary dysfunction
    • P/F <300 acute respiratory distress syndrome
  36. What are the limitations of using P/F ratio for assessing pulmonary function? (2)
    • need to know exact FiO2
    • does not take into account the effects of ventilation
Card Set
ECC2- Oxy-Vent
vetmed ECC2