Exam 2 Study Guide For Breathing, Breathing Circuits, Co2 Absorption

Front 1

1. Explain the basics of ventilation pertaining to the exchange of oxygen and carbon dioxide

Back 1

O2 needs carrier molecules.CO2 dissolved

Oxygen is inhaled diffuses across the alveolar-capillary membrane from alveoli at base of lung into the blood in exchange for carbon dioxide (waste) which diffuses from the blood into the alveoli and is subsequently exhaled. Ventilation: diaphragm, intercostal muscles contract, intrapleural and alveolar pressures decrease; alveolar pressure increases as air flows into alveoli from upper a/w (lungs from atmosphere) until equal to atmospheric prss and flow stops; resp muscles relax/recoil, intrapleural and alveolar pressures increase, gas flows out of alveoli to atmosphere

Front 2

2. How much oxygen does a normal adult need?

Back 2

230 ml/min

Front 3

3. How much CO2 does a normal adult produce?

Back 3

? 180 ml (0.008gm moleculues/min) @ 0 deg C; 204 ml @ 37 deg C

Front 4

4. How long can someone go without oxygen before complications ensue?

Back 4

4min if do not fill FRC w/ 100%; 10 min if fill FRC w/100% O2

Front 5

5. Why is it more common to have a right endobronchial intubation?

Back 5

? At the carina where the mainstem bronchi branch off of the trachea, the left mainstem branches at a sharper angle than the right causing any items sliding down the trachea to tend to slide into the right mainstem bronchus.

Front 6

6. Why is atelectasis a problem?

Back 6

Causes a decreased surface area available for gas exchange

Front 7

7. What mechanisms keep the airway clear?

Back 7

? Spasm (i.e., laryngospasm) =convulsive muscular contraction- type of reflex. Cough (reflex)- forcibly ejects items (larynx spams closing off a/w followed by diaphragm spasm increasing pressure in lungs). Mucus secretion (reflex)- cells lining tract. Ciliary movement along tract.

Front 8

8. What is laryngospasm and what might cause it?

Back 8

? “sudden involuntary movement or convulsive muscular contraction” of the larynx (a type of laryngeal reflex).

Front 9

9. How is the work of breathing generated?

Back 9

Active process of inhalation- energy or work produced by the diaphragm and other inspiratory muscles to expand (increase volume) the chest cavity/lungs and decrease the pressure within compared to atmospheric prss, such that air flows into the lungs.

Front 10

10. How does exhalation occur?

Back 10

? Exhalation is a passive process resulting from the natural tendency for elastic lung tissue to recoil, decreasing the size of the cavity/lungs, increasing the pressure within compared to atmospheric, causing the release of air into the atmosphere down its pressure gradient.

Front 11

11. Differentiate between ventilation and respiration.

Back 11

. Ventilation is the movement of gas into and out of the lung (inhalation and exhalation) based on pressure gradients. Respiration is the process of gas exchange that happens at the alveolar-capillary level (O2 and CO2).

Front 12

12. How do the variables of Fick’s Law relate to respiration?

Back 12

Fick’s law- diffusion of a gas across a membrane directly proportional to the partial pressure gradient, membrane solubility of the gas, and the membrane area. Diffusion is inversely proportional to membrane thickness and molecular weight of the gas. Higher partial pressure of O2 in alveoli facilitates its diffusion into capillary and higher partial pressure CO2 in capillary vs that in alveoli (neglible) facilitates its diffusion into alveoli. Membrane solubility of specific gas is measure of ability/ease of molecules to cross the lipid bilayer. Increased surface area gives more room for more O2, CO2 molecules to diffuse. Thicker membranes increase the distance for molecule diffusion and hinder their transport across membranes (i.e., consolidation of tissue- decreased gas exchange). Heavier gases (increase molecular weight) affect the ability to cross membranes (decreased exchange).

Front 13

13. Differentiate between how oxygen is delivered and how CO2 is removed in the blood.

Back 13

. Oxygen from atmospheric air is delivered to the alveoli, it then diffuses into the capillary across the alveolar-capillary membrane driven by the oxygen’s pressure gradient. O2 is mainly carried attached to hemoglobin, but also present dissolved in blood, for delivery to tissues. Deoxygenated blood that has returned to pulmonary circulation from the tissues is rich in CO2, a waste product of cellular metabolism, mostly dissolved in the blood and diffuses across the alveolar-capillary membrane driven by its pressure gradient. It is then exhaled by the lungs.

Front 14

14. What are the two main muscles involved in inspiration?

Back 14

Diaphragm and intercostal muscles. C345/phrenic innervation of diaphragm

Front 15

15. Under what conditions can expiration increase the work of breathing?

Back 15

When gas exchange is impaired – airway obstruction or pulmonary disease. Abdominal muscles must provide force/energy to move air out faster. Increases in airflow resistance. Noncompliant lung

Front 16

16. What is compliance?

Back 16

? Degree/ease of expandability of the lung.

Front 17

17. What is resistance?

Back 17

? Force that opposes the flow of gas in airways; affected by tube diameter (bronchoconstriction- increased a/w resistance)

Front 18

18. How does the Hagan –Poisieulle equation affect flow of gases in the lung?

Back 18

? Flow is directly proportional to the radius to the 4th power; flow is directly proportional to hydrostatic pressure; flow is inversely related to the viscosity of the gas; flow is inversely related to the length of the tube.

Front 19

19. How does Boyle’s Law apply in the respiratory cycle?

Back 19

? Boyles- temp constant, volume varies inversely with pressure. Inhalation, the thoracic cage expands (increase in volume), decreasing the pressure of air inside the lungs (in relation to atmospheric) such that air flows into the lungs. When the lungs recoil, increasing the pressure within the chest cavity in relation to atmospheric, air is forced out of the lung into the atmosphere, decreasing volume in the lungs.

Front 20

20. Normally, what is the relative humidity of the air that reaches the alveoli?

Back 20

100% saturated with water vapor. Accounts for 47mmHg of the atmospheric pressure of air inhaled.

Front 21

21. Why does a pneumothorax occur?…think in terms of a physicist

Back 21

Negative intrapleural pressure (created by inward recoil of lungs and outward recoil of chest cavity) helps pull the lungs toward the thoracic cage, keeping the lungs inflated when their normal elastic tendency is to collapse. When the pleural membrane is ruptured, intrapleural pressure increases, decreasing lung volumes (failing to keep the lungs inflated and therefore they collapse).

Front 22

22. What conditions can lead to V/Q mismatches?

Back 22

? Pulmonary embolus (thrombus, air, foreign material), atelectasis, pulmonary edema. Atelectasis- no ventilation (no air/gas exchange in these alveoli due to collapse) to blood that circulates through these alveoli causing shunt. Pulmonary embolism- no perfusion (blockage of blood flow through pulmonary circulation) to alveoli supplied by blocked blood vessels therefore no gas is exchanged (dead space created).

Front 23

23. Describe the normal sequence of events when it comes to delivering oxygen to the tissues.

Back 23

. O2 diffuses into capillary from alveoli; some dissolves in the blood, most of O2 binds to hemoglobin (Hgb has high affinity for binding O2 in the pulmonary capillaries); O2 travels through heart and arterial circulation to capillaries where it is released to tissues (Hgb has decreased affinity for O2 binding in peripheral tissues- once unloads one, the next unloads easier).

Front 24

24. Where is the respiratory center?

Back 24

? Brainstem – medullary respiratory center (spontaneous rhythm); pons – apneustic center and pneumotaxic center (both modify output of the medullary center, apneustic promotes [excitatory], pneumotaxic inhibits inspiration).

Front 25

25. How do neuromuscular blocking agents affect respiration?

Back 25

Leads to apnea (paralysis).

Front 26

27. How does the breathing pattern change with inhalation anesthesia?

Back 26

Generally produce rapid, shallow breaths. Most general anesthetics cause hypoventilation- lower tidal volumes. N2O causes tachypnea and decreases tidal volume. Halothane- rapid, shallow breathing. Isoflurane- respiratory depression with less pronounced tachypnea, but more pronounced decrease in minute ventilation. Desflurane- tachypnea, decreas Vt. Sevoflurane- depresses respiration similar to isoflurane. Decreased peripheral response to hypoxemia (increase alveolar ventilation in response to decreased PaO2, perfusion, increased H+ or CO2).

Front 27

28. How do narcotics affect the respiratory centers?

Back 27

Depressed ventilation (esp. decr RR); decreased sensitivity to rising PaCO2; apneic threshold (highest paCO2 at which patient remains apneic) elevates and the hypoxic drive decreases. Also can cause chest wall rigidity preventing adequates ventilation (depressing centrally mediated muscle contraction).

Front 28

29. What is the most powerful stimulus to breathe?

Back 28

? Increased PaCO2 to the brain (increased hydrogen ion concentration /acidosis of CSF).

Front 29

30. How does the supine position affect breathing?

Back 29

Reduced chest compliance from the abdomen pushing up against the diaphragm; proportion of breathing from rib cage excursion decreases and abdominal breathing predominates- diaphragm is higher in chest and allows it to contract more effectively. FRC decreases

Front 30

33. What are the advantages and disadvantages of insufflations?

Back 30

? Advantages- pediactric use because does not require placement of a face mask or IV line; can help avoid CO2 accumulation under head/neck draping with facial surgeries by providing high flow rates of O2/air; no rebreathing of exhaled gases if high enough flow because no direct patient contact with system; used to maintain arterial O2 during brief apneic periods through device placed in trachea (O2 directed into lungs). Disadvantages- ventilation cannot be controlled; unpredictable amounts of entrained atmospheric air is inspired

Front 31

32. How does ‘light anesthesia’ affect breathing?

Back 31

? Often results in irregular breathing patterns, commonly breath holding. (Deep anesthesia- breaths regular) Increased RR

Front 32

34. What is ‘open drop’ anesthesia?

Back 32

Highly volatile anesthetic is dripped onto a gauze-covered mask applied to the patients face. Patient inhales and air passes throught the gauze, vaporizing the liquid agent and carrying high concentrations of anesthetic to the patient.

Front 33

35. What are the advantages of draw-over anesthesia?

Back 33

? (non-rebreathing circuits that use ambient air as carrier gas or supplemental O2- pt’s inspiration draws air into vaporizer)- predictable and controllable concentrations of O2 and inspired vapor; can use with IPPV, CPAP or PEEP; simplicity and portability. Low resistance. Disadvantages – low sat w/RA, unknown tidal vol’s

Front 34

37. What are the major complications with a Bain system

Back 34

? Possibility of kinking or disconnection of the fresh gas inlet tubing (cann lead to rebreathing of exhaled gas); smaller, longer inner tubing can cause an increase in flow resistance; [**if inner tube detached/disconnected or fresh gas tubing kinked/twisted- exhalation limb becomes dead space**- from article]

Front 35

38. How do you check a Bain circuit for leaks?

Back 35

? (special testing)- setting low flow of O2 on a flowmeter and occluding the inner tube (with finger or syringe) at the patient end and observe the flowmeter indicator- the indicator will fall if intact; activate the O2 flush and observe the bag (high flow at patient end will create negative pressure in outer exhalation tubing and cause bag to deflate).

Front 36

42. What three factors must be met to make carbon dioxide absorption feasible?

Back 36

Absorbent granules should not be toxic themselves or when mixed with inhalation agents; low resistance to airflow; 100% efficiency in CO2 removal; [small granules with high absorptive surface area and larger granules with lower resistance to gas flow]

Front 37

43. Why should you ensure the carbon dioxide granules are NOT dry?

Back 37

Water is required for carbonic acid formation (absorbed by the base); prevents anesthesia agent absorption (and degradation- to possibly toxic byproducts) into granule

Front 38

44. How is rebreathing of CO2 prevented in a resuscitation bag?

Back 38

Contains a nonrebreathing valve and exhaled gas is vented to the atmosphere through exhalation ports in the patient valve.

Front 39

45. If the unidirectional valves in the absorber are not competent, what can happen?

Back 39

? Rebreathing of exhaled gas that still contains CO2 (has not gone through absorber) – hypercapnia. Increased FiCO2, incr ETCO2, incr PIP, incr resistance

Front 40

46. How do you know the carbon dioxide granules are exhausted

Back 40

? Color change- pH indicator dye converts when H+ concentration increases. Incr FiCO2 (hypercarbia, resp acidosis, SNS stimulation)  incr flow to 3-5lpm

Front 41

47. What does the term ‘mesh’ refer to?

Back 41

? Number of openings per linear inch in a wire screen used to grade particle size (granule size). [4-8 in soda lime and barium hydroxide lime]

Front 42

48. What are the advantages of carbon dioxide granules without strong bases?

Back 42

Breakdown of anesthetic agents to CO enhanced by strong bases; also, higher pH seen with strong bases. Strong bases can be very reactive and caustic to tissues.

Front 43

49. What is regeneration and what causes it

Back 43

? “Reversion/peaking”: Granules exhaust (color change) and after a period of rest without CO2 they regenerate (color changes back- false impression); however, only small amounts of CO2 will quickly exhaust regenerated granules.

Front 44

50. How do the solubility rules influence regeneration?

Back 44

Sodium carbonate (Sodasorb) is more soluble and able to regenerate vs barium hydroxide (Baralyme) which is insoluble an has no regeneration capacity. Amsorb doesn’t regenerate; CaCO3 only  insoluble (doesn’t have outer layer of NaOH, KOH like Sodasorb which has the color change/regeneration because of the faster chemical reaction). Carbonates insoluble; salts make it soluble.

Front 45

51. Why did APSF convene a meeting about carbon dioxide absorbers?

Back 45

? Increasing evidence that volatile anesthetic exposure to dessicated CO2 absorbents could result in exothermic reactions leading to fires in anesthetic breathing circuits and production of toxic products (CO, compound A, methanol, formaldehyde)- esp. w/sevo exposed to Baralyme.

Front 46

51. Why did APSF convene a meeting about carbon dioxide absorbers?

Back 46

Increasing evidence that volatile anesthetic exposure to dessicated CO2 absorbents could result in exothermic reactions leading to fires in anesthetic breathing circuits and production of toxic products (CO, compound A, methanol, formaldehyde)- esp. w/sevo exposed to Baralyme.

Front 47

52. Summarize the APSF recommendations regarding carbon dioxide absorption?

Back 47

? Use of only CO2 absorbents that do not contain a strong base (no KOH, Ba(OH)2, less NaOH); possible monitoring of CO gas in ciruit or carboxyhemoglobin through co-oxmimetry (watch for elevated baseline of inspired CO2 on capnnogram); use of absorbents with color change with dessication or those that have substances that delay total dessication; use of absorbents only containing Ca(OH)2 with CaCL2 or CaSO4 catalysts. Monitoring absorbent temperature; also, replace canisters if possibly dessicated (replace routinely), turn off flows at end of day and vaporizers when not in use, check for proper plastic packaging when changing canisters

Front 48

53. Be able to differentiate between anatomic, physiologic and mechanical dead space

Back 48

. Part of tidal volume that does not undergo alveolar ventilation is dead space. Gases in conducting (nonrespiratory) airways that do not participate in gas exchange are anatomic dead space. Alveoli (areas of gas exchange) that are not perfused (unable to participate in gas exchange) is alveolar dead space. Physiologic is the sum of anatomic and alveolar dead space. Mechanical dead space- space in the breathing circuit occupied by gases that are re-breathed without any change in composition; in a circle system it is the area distal to the point of inspiratroy and expiratory gas mixture at the Y-piece (limited by the unidirectional valves).

Front 49

54. What are the advantages of low flow anesthesia

Back 49

? Help prevent excess drying of granules; CO2 absorbent more efficient (from the channeling/flow pattern through the granules); less dust back to pt’s a/w. Gas more warm, humid; decreased cost; benefits patient

Front 50

55. What are the disadvantages of using Sevoflurane with strong bases?

Back 50

? Risk of exothermic rxns leading to fires in breathing circuits and formation of toxic products (compound A which is nephrotoxic in rats- increases renal markers in humans).

Front 51

56. How can carbon monoxide be formed in a CO2 absorber?

Back 51

When phosgene reacts with water (from use of choloroform in absorbers); formed from the **breakdown of desflurane, enflurane, isoflurane (many volatile agents) when react with desiccated absorbent** esp. one with a strong base

Front 52

57. What factors lead to inefficiency in carbon dioxide absorbers?

Back 52

Hardness of granules (more than 80 on scale of 100); drying of granules; tightly packed granules in the canister (resistant to flow); high flow rates and high pressure fluctuations within the circle system

Front 53

58. Summarize the fresh gas decoupling breathing circuit.

Back 53

. Separating fresh gas flow fromt the delivered tidal volume such that the delivered tidal volume will match the set tidal volume despite changes in fresh gas flow; compensates delivered tidal volume for fresh gas flow (so that Vt is not increased or decreased with a change in fgf)

Front 54

59. What are the advantages of fresh gas decoupling?

Back 54

Always deliver set tidal volume despite changes in fresh gas flow.

Front 55

60. What anesthesia machines have fresh gas decoupling?

Back 55

? Drager Julian, Narkomed 600, Fabius GS; Aestiva and S/5 ADU use fresh gas compensation

Front 56

Maplesons Hints-“A”

Back 56

you will let them do what they want  spontaneous ventilation

Front 57

Maplesons Hints-“D”

Back 57

– you will control them controlled ventilation
If a child is getting a “D” – you will control them controlled ventilation

Front 58

Maplesons Hints- - “E”

Back 58

- “E” stands for Easy  easy to ventilate, low resistance

Front 59

Maplesons Hints-- “F”

Back 59

- “F” stands for Friendly  friendly to spontaneous or controlled ventilation with moderately low resistance

Front 60

1. How much PEEP is created within the breathing circuit with the use of ascending bellows on the ventilator?

Back 60

2-3 cmH2O, Descending bellows/pistons - none

Front 61

2. Explain the difference between ascending bellows and descending bellows?

Back 61

Ascending bellows are standing and descending bellows are hanging (both ascend and descend have ‘e’ in them so look at bellows on expiration. Ascending rise expiration; descending collapse expiration

Front 62

3. Which bellow design is safer ascending or descending? Why?

Back 62

Ascending bellows because they will not fill in the event of a disconnection whereas descending bellow may still fill with room air.

Front 63

4. Explain is the difference between the drive mechanism of the Drager Anesthesia Machine and the Datex-Ohmeda Anesthesia Machine?

Back 63

? Drager (venturi) –O2 + air used for pneumatic power, O2 consumption reduced by Venturi device; manuf. Pressure limit 65-80 cmH2O (which we can reduce). Ohmeda – 100% O2 uses pneumatic power, pressure regulated down to 26 psig by 2nd stage regulator, O2 consumed at rate equal to minute ventilation

Front 64

5. Explain the difference between Double –Circuit and Piston Ventilators?

Back 64

? Double-circuit- the tidal volume is delivered from a bellows assembly; in a piston- an electrically driven piston is substitutied for the bellows and the vent requires minimal or no pneumatic (oxygen) power. 2 circuits – pt circuit and drive gas circuit

Front 65

6. What is the purpose of the Ventilator Relief Valve?

Back 65

? (“spill” or pop-off valve) relieve excess pressure

Front 66

7. What happens to the ventilator relief valve during inspiration? Why?

Back 66

Pneumatically closed during inspiration so that positive pressure can be generated. Prevents gas from bellows leaking out

Front 67

8. What happens to the ventilator relief valve during expiration? Why?

Back 67

? During exhalation the pressurizing gas is vented out and the ventilator spill valve is no longer pressurized closed- the bellows or piston refill during expiration and the **valve opens** as the circle system pressure rises.

Front 68

9. What happens to the reservoir bag and APL Valve when the anesthesia machine is turned to the Auto or Vent Mode?

Back 68

They are excluded from the breathing circuit. APL closed – if closed during spontanteous vent, incr in pressure

Front 69

10. What happens to (PIP) Peak Inspiratory Pressure during CMV?

Back 69

PIP is monitored but not controlled and varies according to the pt’s compliance and a/w resistance

Front 70

11. Explain the ventilator mode (PCV) Pressure Control Ventilation?

Back 70

? Vent operates as pressure is limited and time-cycled with a decelerating flow pattern. Inspiratory pressure is controlled rather than volume. Vent generates sufficient flow to reach target pressure early in inspiration then maintains this set prss t/o inspiratory time. Target prss is adjusted for the desired tidal volume, RR is adjusted to maintain a reasonable end-tidal CO2. Be aware of minute ventilation (tight control).

Front 71

12. When and why should PCV be utilized in anesthesia?

Back 71

Used in pts for whom high inspiratory pressure is dangerous (LMA, emphysema, neonates/infants). It can produce higher tidal volumes in pts with low compliance (pregnancy, laparoscopic, obese, ARDS). It can compensate for leaks (uncuffed ett, LMA) and can provide effective ventilation and lower a/w prss during one-lung ventilation.

Front 72

13. Explain Pressure Support Ventilation (PSV)?

Back 72

)? Like PCV in that it is a pressure-targeted vent mode but with a RR of zero. It can deliver a breath within a trigger window in response to the pts efforts as long as the pt’s negative inspiratory prss matches the sensitivity setting

Front 73

14. Explain (PEEP) Positive End Expiratory Pressure? When and why should it be used?

Back 73

Application of positive pressure during expiration as an adjunct to a mechanically delivered breath. PEEP valve provides a pressure threshold that allows expiratory flow to occur only when a/w prss equals or exceeds the selected PEEP level. Keep alveoli open I pts with atelectasis at end of expiration. Obese – weight causes closure of alveoli

Front 74

15. Which type of ventilator is standard on the Drager Fabius GS Anesthesia Machine? How does it work?

Back 74

? Piston vent. Uses electronic keypad to switch between modes. It corrects delivered tidal volume for compliance losses by measuring circuit compliance and fgf by fresh gas decoupling. Electronic peep. Piston is visible (visible indication of lung inflation and potential disconnects in that fresh gas is diverted to the manual breathing bag which inflates during mechanical ventilator inspiration and deflates during expiration). Piston design avoids negative end-exp prss by entraining room air if pressure in bellows is less than atm prss.

Front 75

16. What are three advantages and disadvantages of Piston Ventilators?

Back 75

Advantages- quiet, no PEEP, precision in delivered tidal volume, fewer compliance losses, capable of all modern vent modes. Disadvantages- harder to hear cycling (quiet), cannot easily accommodate nonrebreathing circuits, potential for NEEP and dilution of the pt’s inspired gas with room air.

Front 76

17. On the Drager Fabius GS Anesthesia Machine what helps to ensure the set and delivered tidal volumes are equal? How does this occur?

Back 76

Fresh gas decoupling- piston closes a decoupling valve, diverting fgf to the manual breathing bag during the inspiratory cycle (inflates) and the bag deflates during expiration, emptying the contents into the piston.

Front 77

18. What happens to the manual breathing bag motion during inspiration and expiration on the Drager Fabius GS while in ventilation mode?

Back 77

? Bag inflates during inspiration (due to fgf) and deflates during expiration as it empties into piston.

Front 78

19. How does the Piston Style Ventilator as utilized by the Drager Fabius GS avoid (NEEP) negative end expiratory pressure?

Back 78

? Entrains room air if pressure within bellows is less than atmospheric pressure. Neg prss pulmonary edema (laryngospasm after extubate)

Front 79

20. How does the safety relief valve incorporated in all ventilators by the manufacturer work?

Back 79

Closed inspiration- positive prss generated; opens during expiration (see #8)

Front 80

21. How does a double- circuit ventilator work?

Back 80

Tidal volume is delivered from a bellows assembly. Bellows takes place of the breathing bag in the anesthesia circuit. Pressurized oxygen/air from vent power outlet is routed to the space between the inside wall of the plastic enclosure and the outside wall of the bellows. Pressurziation of enclosure compresses the bellows forcing the gas inside into the breathing circuit and patient. Ventilator flow-control vavle regulates drive gas flow into the pressurizing chamber.