Exam 3: Lecture 20 - Mechanical Ventilation Flashcards
1
Q
What is normal ventilation?
A
-Movement of gas in & out of alveoli & defined as the maintenance of normal arterial blood carbon dioxide concentration (PaCO2) of 35-45mmHg
2
Q
Besides normal ventilation, patient should also have a normal
A
-Respiratory effort, rate & rhythm
3
Q
What is indicated by the blue star?
A
-Inspiratory reserve volume
4
Q
What is the inspiratory reserve volume?
A
-Extra bit you can breathe past the tidal volume
5
Q
What is indicated by the blue star?
A
-Expiratory reserve volume
6
Q
What is the expiratory reserve volume?
A
-Volume when you push all the air out
7
Q
What is indicated by the blue star?
A
-Residual volume
8
Q
What is the residual volume?
A
-The volume left over after exhaling everything you can
9
Q
What is indicated by the blue star?
A
-Functional residual capacity
10
Q
What is the functional residual capacity?
A
-Expiratory reserve volume + residual volume
11
Q
What is indicated by the blue star?
A
-Vital capacity
12
Q
What is the vital capacity?
A
-What your body can do
-Expiratory reserve volume + tidal volume + inspiratory reserve volume
13
Q
What is indicated by the blue star?
A
-Inspiratory capacity
14
Q
What is the inspiratory capacity?
A
-Tidal volume + inspiratory reserve volume
15
Q
What is indicated by the blue star?
A
-Total lung capacity
16
Q
What is indicated by the blue star?
A
-Tidal volume
17
Q
What is the tidal volume?
A
-Small amount of the total amount that the patient is breathing
18
Q
The air in the lungs can be divided into:
A
4 different volumes & 4 different capacities:
-Tidal volume (Vt)
-Inspiratory reserve volume (IRV)
-Expiratory reserve volume (ERV)
-Residual volume (RV)
-Inspiratory capacity (IC) = TV + IRV
-Functional residual capacity (FRC) = ERV + RV
-Vital capacity (VC) = IRV + TV + ERV + RV
-Total lung capacity (TLC) = IRV + TV + ERV + RV
19
Q
Tidal volume and minute ventilation can be measured with
A
-Spirometer
20
Q
What is minute ventilation?
A
-VE
-Tidal volume (Vt) x respiratory frequency (f)
21
Q
What is the VE of a patient that has a tidal volume of 250 mL & a respiratory rate of 12 bpm?
A
250 mL x 12 bpm = 3,000 mL/min
22
Q
Why do we care of ventilation?
A
-Anesthetic drugs can alter patient’s ability to normally ventilate
-Ventilation is required for inhalant anesthetics to be properly taken up & eliminated
23
Q
How can anesthetic drugs alter the patient’s ability to normally ventilate?
A
-Could lead to inadequate gas exchange, hypoventilation, & eventually respiratory arrest -> cardiac arrest!
24
Q
What is hypercapnia?
A
-CO2 level above 45 mmHg
25
What are the **direct** effects of hypercapnia?
-Causes vasodilation of peripheral arterioles & myocardial depression
-Associated w/ increased vagal tone -> slows heart rate, & could lead to cardiac arrest
-Increased intracranial pressure due to vasodilation
26
What are the **indirect** effects of hypercapnia?
-Increases circulating catecholamines -> cardiac arrhythmias, tachycardia, increased myocardial contractility, & BP elevation
27
Narcoses progresses with PaCO2 values above ____ mmHg and induces complete anesthesia at ____ mmHg
95 mmHg, 245 mmHg
28
What is IPPV?
-Intermittent positive pressure ventilation
-Positive pressure maintained **only** during inspiration
29
What is IMV?
-Intermittent mandatory ventilation
-Operator sets a predetermined number of positive breaths, but patient can also breathe spontaneously
30
What is PEEP?
-Positive end-expiratory pressure
-Airway pressure at end expiration is maintained above ambient pressure
-Applied when positive pressure is maintained between inspirations that are delivered by a ventilator
31
What is CPAP?
-Continuous positive airway pressure
-**Spontaneous** breathing with positive pressure during **both** inspiratory & expiratory cycles
32
What is HF(N)OT?
-High flow (nasal) oxygen therapy
-Administration of warm, humidified oxygen via nasal prongs, using a commercially available unit to deliver higher flow rates of oxygen & and FiO2 up to 100%
33
How can IPPV be performed?
-Closing/occluding pop-off valve & squeezing reservoir bag until 10-20 cm H2O reached, then pop-off valve is reopened so patient can passively expire (called "Manual IPPV")
-A machine (called mechanical ventilator)
34
What is the preferred method of performing a "manual IPPV"?
-To utilize the safety occlusion valve instead of actually closing APL valve (aka pop off valve)
35
What is the advantage of using a mechanical ventilator IPPV, but also what are downsides?
-It frees your hands to do other things, but can do harm to your patient if incorrectly used
-Most general practices do not own this piece of equipment so don't want to become dependent on having one
36
What are 6 reasons a patient may require mechanical ventilation?
1. **Respiratory center depression** (drugs, toxins, acidosis, head trauma)
2. **Inability to adequately expand thorax** (drugs, pain, chest wall trauma, etc.)
3. **Airway obstruction** (foreign object or body fluid, nerve damage, trauma, etc.)
4. **Inability to adequately expand lungs** (pneumothorax, pleural fluid, diaphragmatic hernia, etc.)
5. **Cardiopulmonary arrest**
6. **Pulmonary edema or pulmonary insufficiency**
37
What are some specific indications for IPPV during anesthesia?
-Thoracic sx (lungs can't inflate when chest is open, IPPV minimizes spontaneous chest wall movements)
-Neuromuscular blocking drugs
-Prolonged anesthesia (> 60 min) (especially in horses)
-Chest wall or diaphragmatic trauma ("flail chest" results in paradoxical breathing)
-Maintain more stable anesthesia plane
-Obesity & special patient positioning
-Control of intracranial pressure
-Convenience (i.e. treatment of hypoventilation to free hands)
38
In otherwise healthy SA patients, when would you start IPPV?
-When the ETCO2 reaches the mid 50s
39
Controversy exists about the routine use of IPPV in anesthetized patients, especially horses, just to keep the PaCO2 near _____
40 mmHg
40
What are the negative effects of mechanical ventilation?
-Neg. pressure not generated during inspiration, so venous return to heart is not enhanced
-IPPV may actually physically impede venous return to right side of heart -> decreased SV, CO, & arterial BP
-Exacerbated by prolonged inspiratory time, PEEP/CPAP, obstruction to exhalation, & excessively rapid respiratory rate
-CV effects can be overcome often w/ expansion of extracellualar fluid volume & admin. of inotropic drugs
41
With IPPV, excessive or sustained pressure can lead to _____
over expansion & volutrauma -> alveolar membrane disruption, development of interstitial air, & eventual transfer to air to mediastinum, pleural space, or abdomen
42
IPPV can alter what neurohormonal systems?
-ADH release
-Sympathetic outflow
-Renin-angiotensin axis
-Atrial natriuretic peptide production
43
What 2 things do mechanical ventilators need?
-Power source & driving force
44
What is the "driving force" of mechanical ventilators?
-Driving gas cyclically introduced into cylinder, but outside bellows, causing pressure to increase within cylinder
-Inspiratory phase occurs when bellows are compressed & air contained is delivered to the patient
45
How do mechanical ventilators work?
-Consist of compliant pleated compressible bellows connected to anesthesia breathing circuit
-Bellows are contained within airtight rigid plastic cylinder the can be pressurized to compress bellows
-Driving gas introduced into cylinder, but outside bellows, causing pressure to increase in cylinder
-When pressure is released, process reverses & elastic recoil of lungs causes bellows to expand during expiratory phase
46
What is a double-circuit ventilator?
Refers to two gas sources:
-Driving gas circuit outside bellows which compresses bellows
-Patient gas circuit inside bellows that originates in anesthesia machine & provides O2 & anesthetic gasses to patient
47
Why is the VT for IPPV usually increased above normal spontaneous VT?
-To compensate for pressure-mediated increases in volume of breathing system & airway
48
What patients on IPPV may need to have an increased respiratory rate to maintain VE without creating excessive inspiratory pressures?
-Patients w/ lung trauma, diaphragmatic hernia, or gastrointestinal distention
49
What s the Tidal Volume (VT) guideline for IPPV in small & large animals?
-SA: 10-20 mL/kg
-LA: 15 mL/kg
50
What is the inspiratory time guideline for IPPV in small & large animals?
-SA: 1 to 1.5 seconds
-LA: 1.5 to 3 seconds
51
What is the I:E ratio IPPV guidelines for small & large animals?
-SA: 1:2 to 1:3
-LA: 1:2 to 1:4.5
(Basically want to spend twice as long in expiration vs. inspiratory to allow blood return to heart)
52
What is the Peak Inspiratory Pressure (PIP) guideline for IPPV in small & large animals?
-SA: 15 to 20 cm H2O
-LA: 20 to 30 cm H2O
53
What is the Respiratory Frequency (f) IPPV guideline for small & large animals?
-SA: dogs= 8-14 bpm, cats= 10-14 bpm
-LA: horses & cows= 6-10 bpm, pigs & small rumin.=8-12 bpm
54
Q: You have a 70 kg MN Boer that is hypoventilating under inhalant anesthesia. You would like to set up a mechanical ventilator. What settings should you select?
A. VT= 700 mL; I:E ratio = 1:2; PIP = 15 cmH2O; f=6 bpm
B. VT = 900 mL; I:E ratio = 1:2; PIP = 15 cmH2O; f= 24 bpm
C. VT = 1050 mL; I:E ratio = 1:3; PIP = 20 cmH2O; f=10bpm
D. VT = 1400 mL; I:E ratio = 1:2; PIP = 35 cmH2O; f = 12 bpm
C.
-Can get rid of choice B. b/c f=24 bpm is very fast for goat
-Can get rid of D. b/c PIP= 35 cmH2O id s lot of pressure giving into the lung
55
What are the 8 steps for general IPPV setup?
1. Plug ventilator into oxygen & power source (ideally before induction) & leak test ventilator
2. Determine VT resp. rate & PIP needed to achieve effective ventilation. Preset dials if possible
3. Empty reservoir bag into scavenging system & replace w/ hose that connects ventilator to anesthesia machine
4. Close pop off valve
5. Increase O2 flow rate so bellows fill completely, then return O2 flow rate to maintenance level
6. Turn on ventilator
7. Closely monitor PIP, ETCO2 & chest wall excursions
8. Adjust inspiratory flow, resp. rate, & I:E ratio to achieve effective ventilation w/out causing barotrauma
56
What are the normal values of ETCO2, PaCO2, & PIP?
-ETCO2 ~35-45 mmHg
-PaCO2 ~40 mmHg
-PIP < 20 cm H2O
57
The amount of gas delivered to a patient during ventilation depends on
-Resistance & compliance of breathing system & patient's respiratory system
58
Although inspiratory pressure may not vary over time, the ____ may change as the compliance of the respiratory system changes
VT
59
What happens after IPPV is discontinued?
-If PaCO2 low, spontaneous ventilation may not return b/c certain level of PaCO2 required to stimulate ventilation
-Opioids, anesthetics, neuromuscular blocking drugs, hypothermia, or hypovolemia may delay return of consciousness & therefore spontaneous ventilation
-Patient should continue to receive supplemental O2 & can be manually ventilated at 1-4 bpm until spontaneous ventilation has returned & stabilized (i.e. normal VT & f)
60
How are ventilators classified?
-The power source, drive mechanism, cycling mechanism & type of bellows are used to classify anesthesia ventilators
61
What are the power sources of ventilators?
-Electricity, compressed gas, or both
62
What is the drive mechanism of ventilators?
-Compressed gas
63
What is the ventilator classification "volume cycled"?
-Inflate lungs to predetermined volume
64
What is the disadvantage of volume cycled ventilation?
-Inspiratory pressure may increase if compliance decreases during ventilation
65
What is the ventilator classification "pressure cycled"?
-Inflate lungs to predetermined pressure
66
What is the disadvantage of pressure cycled ventilation?
-VT delivered may decrease if respiratory compliance decreases in patient
67
What is the "time cycled" ventilator classification?
-Inflate lungs for a preset time at a predetermined gas flow rate
68
What are most anesthesia ventilators classification?
-Time cycled
69
What is used for IPPV of small animals with room or supplemental O2 components?
-Self-inflating resuscitation systems (e.g. Ambu bag)
70
____ is inserted on the proximal end of ET tube & delivers IPPV (O2 only) & works on demand from a patient-initiated breath or from operator assistance
-Demand valve
71
What are recruitment maneuvers?
-Used to reinflate collapsed alveoli by applying sustained pressure above normal PIP & using PEEP to prevent derecruitment
-Induces temp. improvement in lung function in healthy dogs under general anesthesia
