2680 PFT Review Flashcards
Pack years eqn
# packs/day x # years (Usually 20 cig/pack)
PFT process/ order of steps
1) spiro pre-bronchodilator
2) administer bronchodilator
3) DLCO
4) spiro post-bronchodilator
Most common symptom/complication during spirometry
Fainting
absolute contraindications for PF testing (pre-read pckg)
MI within 1 month
3 primary factors req’d for determining the predicted value (re: reference elms/normals)
Age, height, sex
Age when peak lung function reached
20-25 y.o.
How do lung mechanics and volumes change with age?
Lungs become more compliant while chest wall more rigid…
- RV & FRC increases w age (harder to fully exhale)
- VC decreases
- TLC remains same
- PEF decreases
- DLCO decreases
describe FVC test via spirometry and how to coach
Effort dependent test to measure volume forcefully exhaled from max inspiration
Steps: calibrate + enter pt data, nose clip on, mouth sealed on mouthpiece, good positioning; relaxed normal breaths, then on cue pt quickly breathes in until full then forcefully out until completely empty, then another breath in until full
coaching: “Purpose: how much volume you can exhale and how quickly you can do it (FVC, FEV1, PEF) = speed and volume
Big breath in and fast breath out as fast as you can; keep pushing even if you think you are empty; when i see that you’re empty, as big a breath as you can “
What type of patient may a SVC (slow vital capacity) be suitable for? What steps are generally preferred to do the test and why?
COPD Pt/emphysema bc forced vital capacity could collapse the airways during forced exhalation. SVC will give same volume but not the peak flows.
Steps:
Prefer to do a max expiration then max inspiration (VC) bc they will have a stronger drive to breathe when starting empty
critical value for a VC
<15ml/kg is resp concern; means their Vt will be way too small and won’t keep alveoli recruited
define the EPP
equal pressure point - Where pressure outside airway = pressure inside airway = critical point called equal pressure point (EPP)
-Further downstream from EPP, pressure outside airway can then exceed pressure inside airway
-lead to airway collapse (if lung tissue integrity is disrupted due to emphysema, obstructive lung disease)
-EPP is reached in everyone at some point, but it happens much easier/earlier with ‘floppy’ or weak airways
E.g. emphysema or COPD
normal proportion of lung volume exhaled in FEV1
75 - 85% = most people exhale this amount of lung volume in the 1st second of FORCED exhalation; represents large + medium airways +/- small airways
how to use FEV1/FVC to determine if obstruction is present
obstruction likely present if FEV1/FVC is <70%
what forced flowrate is independent of Pt effort?
FEF 25 - 75%; reflects smaller airways and is independent of Pt effort
Describe the ATS criteria for BEV (back extrapolated volume)
BEV should be =100ml or =5% of FVC whichever is greater; if Pt delays the start of the maneuver, they can “cheat” by leaking out some volume before the maneuver starts. We want to minimize this.
3 ways to meet the EFE (end of forced effort) ATS criteria
1) after 15 seconds of exhaling the test ends
2) Pt plateaus (< 25mL change in volume for) 1 second during exhalation
3) If Pt cannot achieve a plateau, FVC is within repeatability criteria or a larger than any previous FVC (VC needs to be within 150mL of a previous FVC, or a larger than a previous FVC = repeatability criteria)
describe ATS repeatability criteria for > 6 yrs old
If >6 years old,
-minimum 3 successful attempts with the top 2 FEV1 and FVC being within <150ml difference
FIVC ATS criteria
if FIVC > FVC, must be within 5% of FVC or within <100mL (whichever greater)
max # attempts to try according to ATS spirometry criteria
8
List the ATS criteria final reported values
Of the 3 successful tests, report Largest FVC Largest FEV1 Largest FEV1/FVC% -----> doesnt have to be from the same attempt! Largest PEF Largest FIVC
All other values come from best single test (e.g. FEF50%, FEF25-75%)
Best test = largest combined FEV1 + FVC
how to identify variable vs. fixed obstruction
variable FEF will not = FIF;
-intrathoracic: FEF < FIF
-extrathoracic: FEF > FIF
fixed FEF/FIF = 1 (they are the same)
List the bronchodilator given for spirometry and onset action
Ventolin (SABA) Salbutamol; onset action 5 - 15 mintues (so given in MDI after the pre-bronchodilator spiro, then do DLCO test ~10 minutes, then ready to do post-bronchodilator test)
describe repeatability criteria for < 6 yrs old
minimum 3 successful FEV1 and FVC, difference between top 2 FEV1 must be = 100mL or within 10% of largest FEV1 whichever is larger; and top 2 FVC must be = 100mL or within 10% of largest FVC whichever is larger
indications for spirometry (6 - overall)
pre-reading pckg
1) discover presence/absence of lung disease
2) assess amount of lung function impairment present in a known lung disease
3) assess effects of environmental or occupational exposure (hazardous work environments, smoking)
4) determine if therapy is beneficial to patient
5) determine surgical risk for thoracic, abdominal or lung resection procedures
6) evaluate impairments or disabilities for insurance/legal, social security/compensation, pulm rehab
what other information would be used to discover presence/absence of lung disease to indicate the need for spirometry
(pre-reading pckg)
S&S Hx: dyspnea, orthopnea, wheeze, cough, mucus production, chest pain
Physical exam: diminished br/s, chest wall abnormalities
Lab data: CXR, ABG
List the lung diseases that may be indication for spirometry when you want to assess the amount of lung function impairment
(pre-reading pckg)
pulm diseases: asthma, COPD, interstitial lung disease, cystic fibrosis
NMD: Guillain Barre
Cardiac: CHF
What type of therapies may indicate the need for spirometry? (pre-reading pckg)
bronchodilators, cardiac drugs, pulm rehabilitation, resection/reduction/transplant of lung
6 indications for determining lung volume (pre-reading pckg)
1) aid in diagnosis of restrictive lung disease
2) distinguish b/w obstruction or restrictive lung disease
3) determine severity of restrictive lung disease
4) assess response to therapy (from steroid/bronchodilator, lung reduction/resection/transplant, radiation/chemotherapy)
5) determine if pre-surgical pt have compromised lung fx
6) evaluate or determine level of disability
6 indications for DLCO
pre-reading pckg
1) determine if systemic disease is compromising pulm system
2) assess/quantify extent of parenchymal lung disease due to dust, drugs, organic agents
3) evaluate obstructive lung diseases + predict exercise induced arterial desaturation
4) evaluate CV diseases: pulm HTN, pulm edema, CHF, acute/recurrent pulmonary thromboembolism
5) evaluate polycythemia, L-R shunt, pulm hemorrhage
6) determine extent of severity associated with ILD
What 5 systemic diseases could be compromising the pulm system and indicate need for DLCO?
(pre-read pckg)
sarcoidosis, rheumatoid arthritis, sclerosis, systemic lupus erythematosus, mixed connective tissue disease
List the obstructive lung diseases that DLCO would help distinguish between
(pre-read pckg)
asthma, emphysema, chronic bronchitis
which obstructive diseases would DLCO help follow the progress of
(pre-read pckg)
CF, emphysema
conditions where suboptimal lung fx results are likely (pre-read pckg)
chest/abdominal pain from any cause, oral/facial pain exacerbated by mouthpiece, stress incontinence, dementia/confusional state
relative contraindications for PF testing (pre-read pckg)
poses relative danger or affects validity of performance:
- hemoptysis of unknown origin
- pneumothorax
- unstable CV status (angina, BP)
- recent MI
- recent PE
- thoracic/abdominal/cerebral aneurysms
- recent eye surgery
- acute disorders affecting test performance like nausea/vomiting
- recent thoracic/abdominal procedures
compare flow-volume graph to volume-time graphs
flow-volume loops can be used to identify disease process, Pt effort, errors like early stop or excessive BEV but NO indication of time
volume-time graphs show time, can identify errors such as leaks, and volume plateaus, but cant show disease process or Pt effort
describe the approach to detect testing errors for spirometry
1) on expiration see quick rise up
2) sharp PEF = strong effort and blasting out
3) linear rate downward or SLIGHT concave as flow decelerates is good
4) see zero flow is reached = complete emptying
5) big breath in until hit plateau for 1 sec
6) PEF50 should = PIF50
7) FVC should have same volume as FIVC
what is the shoulder/knee on the FV loop?
frequently seen in adolescents/young adults but is NOT abnormal for this population. It is due to airways pinching during the forced maneuver causing flow to flatten for a bit
describe location and phase of breath affected by upper airway obstruction
trachea, vocal cords, mainstem bronchi
fixed = affects both inspiration + expiration flows consistently (e.g. vocal cords stiff; FEF50% = FIF50%)
variable = inconsistent flow limitation during inspo or expo
distinguish variable extrathoracic obstruction vs. intrathoracic obstruction
extrathoracic = occurs in neck/trachea + amplified narrowing + lower flows on inspiration intrathoracic = occurs in bronchi within pleural cavity + amplified narrowing + lower flows on expiration
define vocal cord dysfunction
hard to diagnose; often appears as an asthma attack
- severe dyspnea due to vocal cord paradoxically closing on inspiration
- often affects younger high performing individuals
ATS criteria for responsiveness/reversibility + formula to calculate (to bronchodilator)
for post-bronchodilator, still need min 3 successful attempts with top 2 FVC and FEV1 within 150mL
responsive if:
pre + post FEV1 increases min 200mL or more AND at least 12% more
OR
pre + post FVC increases min 200mL or more AND at least 12% more
formula for % change= (pre - post) / pre
What medications should Pts STOP taking before coming in for PF testing? What medications should they KEEP taking before the test?
STOP: SABAs, SAMAs, LABAs, LAMAs
KEEP: ICS bc it takes days/weeks to get full anti-inflammatory effects, they’d have to stop for a full week
how long to refrain from taking a SABA vs. SAMA vs. LABA vs. LAMA before PFT?
SABA = 4 - 6hr SAMA = 12 hr LABA = 24 hr LAMA = 36 - 48hr
describe the approach to interpret spirometry results
1) scan Pt info to make sure reading results of the intended person
2) scan FV loops and vol-time graphs for errors
3) FEV1/FVC < 70%? If yes = obstructive likely, if low FEV1 and FVC but ratio is normal = restrictive likely
4) if FEV1/FVC, FEV1, and FVC values normal = normal lung function
5) compare any differences between phases
6) look at post-bronchodilator results for responsiveness
Purpose of lung volume tests
Helps identify all volumes and capacities not identified via spirometry = RV, FRC, TLC
+ helps create more specific interpretation (e.g. obstruction with airtrapping)
List the 4 lung volumes and 4 capacities measured with lung volume test
volumes = IRV, RV, Vt, ERV capacities = FRC, IC, VC, TLC
define IRV
max able to inspire on top of a normal tidal inspiration
define ERV
volume that can still be forcefully exhaled following a normal tidal exhalation; can help diagnose NMD
define RV
volume left in lungs that cannot be exhaled; normal ~ 20 - 35% of TLC
2 main types of lung volume tests
plethysmography, gas dilution: He Dilution or N2 Washout
what gas law does plethysmography/body box employ? What does each parameter represent?
Boyle’s Law: constant T, P1V1 = P2V2
P1 = pressure at mouth when shutter closes
P2 = pressure of box due to panting
V2 = volume of box due to panting
solve for V1 = FRC
Body box then also uses the Vt, ERV, and VC measured to calculate TLC
describe general steps of plethysmography
Pt sits in closed box for ~30 seconds to stabilize temp, begin relaxed breathing for at least 3 Vt to establish FRC, at END of Vt the RT closes the shutter and Pt begins to slowly pant, after 3 seconds shutter opens and Pt breathes fully out until empty / RV, then fully in until full / VC
difference between linked vs. unlinked pleth
linked is when VC is done right away after shutter opens = ideal
unlinked = after shutter opens, Pt takes a few normal breaths before doing a VC or they do the VC separately = done for Pts who have bad obstructions and need a break
For plethysmography, how should VTG or TGV compare to FRCpl? What is a switch-in error?
TGV = total gas volume, it indicates the volume of the thorax when the measurement was done
TGV should = FRCpl, but differences will cause a “switch-in error” and will be due to closing the shutter too early or late
What will an early switch-in error do to the calculated FRC?
Will over-estimate the FRC (or VTG) bc the Pt was switched in before they reached their FRC
What will a late switch-in error do to calculated FRC?
If you switch someone in too late and they end up breathing out even more during that breath, this could result in a lower FRC than actual
What is an acceptable switch-in error?
<200mL difference between VTG and FRCpl
Describe the ideal plethysmography loop graph
small and closed loops created by steady, slow small pants; the best fitting slope to these loops determines the FRC value
What do incomplete plethysmography loops mean? What do large loops mean?
incomplete = leak occurring; often seen on 1st attempt
too large = too strong a pant and loop is going off screen; need to be softer/smaller
what rate of panting for plethysmography
0.5 - 1hz (about 1 per second); should get 3 - 4 pants with shutter closed
what is thermal drift?
happens in body box/plethysmography if temp in box is changing and loops are shifting to the right; need to wait for temp to stabilize for at least 30s-1min
ATS criteria for FRCpl
- at least 3 separate maneuvers
- the 3 FRCs must be within 5% (highest - lowest FRC / mean FRC of the 3 attempts = < 0.05 = acceptable)
- panting frequency 0.5 - 1 Hz or 30 - 60 pants per min
- report the MEAN FRC value
what eqn describes the relationship of gas volume vs concentration used in gas dilution method
C1V1 = C2V2; so use of an inert gas like He that does not get absorbed at the A/C membrane can be used to show the volume of the FRC by determining how the concentration of He changed after being breathed in and back out C1 = initial [He] V1 = system volume C2 = final [He] V2 = FRC
C1 = N2 at room air C2 = end N2 V2 = how much volume it took to dilute end N2 V1 = solve for FRC
Describe the He Dilution procedure
on spirometer, Pt breathes at least 3 tidal breaths to establish baseline; at end of relaxed breath, RT switches Pt into 10% He mixture, Pt breathes He in closed circuit while O2 is kept at 21%, Pt breathes He until concentration change is less than or = 0.02% for 30 seconds = indicates equilibrium achieved, then Pt breathes out fully to RV than max inspo to VC
ATS He dilution criteria
- only 1 successful test needed; must wait 5 minutes between tests if needs to be redone
- test stops when [He] change is = 0.02% for 30 seconds; max 10 min test
- if only 1 test done, that value reported; if more done than report the mean with values within 10% of each other
describe the difference between the He dilution vs. N2 washout method
With N2, need to account for body producing N2 at 0.04ml/min in eqns (software does it)
describe N2 general washout procedure
Pt connected to spiro and breathing 3 tidal breaths to establish baseline; at end of Vt (FRC) Pt switched into 100% O2, continues breathing until exhaled [N2] drops to = 1.5% for 3 consecutive breaths, then Pt breathes out fully to RV then maximum inspo to VC
ATS N2 washout criteria
-only 1 successful test
-[N2] exhaled should be = 1.5% for 3 consecutive breaths
-max test time = 7 minutes
-if N2 increases, stop test bc there is a leak
-if multiple tests, report the mean and ensure within 10% values
(not ATS but wait 15 mins between N2 tests)
How would a severe obstruction / air-trapping affect He or N2 tests
underestimate FRC; obstruction prevents gas from mixing = takes long time for dilution
normal RV/TLC
20 - 35%; increases with age
What disease process if: high FRC > 120% high RV > 120% normal TLC 80 - 120% high RV/TLC (>35%)
air trapping since TLC is NORMAL but FRC and RV have increased
what disease process if high FRC > 120% high RV > 120% high TLC > 120% high RV/TLC >35%
Since all volumes AND TLC are >120%, this is hyperinflation
what disease process if low FRC < 80% low RV < 80% low TLC < 80% normal RV/TLC (20 - 35%)
intrapulmonary restrictive disease (e.g. pulm fibrosis, lung resection)
what disease process if normal FRC high RV > 120% decreased TLC < 80% high RV/TLC > 35%
extrapulmonary restrictive due to NMD
lungs are not less compliant but muscles are weaker so cant breathe in and out as much; low RV bc cant force out air with low muscle strength
what would a mixed obstructive-restrictive lung disease present as with pleth?
would have reduced FEV1/FVC < 70% AND
reduced TLC < 80%
What is the DLCO test, what gas is used and why
diffusion capacity test, measures amount of CO (diffusion limited gas- CO amount in blood only affected by factors of diffusion) that diffuses in ml/min/mmHg to signify gas-exchange ability of the lungs
-CO used bc it will be rapidly diffused due to high Hb binding affinity + high pressure gradient from alveoli–> blood
DLCO testing steps
body box, door doesnt have to be sealed; Pt starts normal tidal breathing; when ready they exhale until empty (RV); then Pt switched into CO (0.3%) + methane (CH4, 0.3%) gas mixture and Pt takes quick, deep breath in until full and HOLD for 10 seconds, then quickly breathe all the way out to RV; initial 750ml - 1L discarded and next 500mL - 1L analyzed
Why does a DLCO full breath in need to be quick <4 sec and exhalation < 4sec?
Bc once switched into gas mixture and breathing in, diffusion begins right away; making these phases too long can affect how much gas is transferred during that period
how long should a Pt be OFF their supplemental O2 before DLCO testing? how long should they stop smoking before DLCO?
O2 = off for 10 minutes; this is bc it will underestimate the DLCO
before DLCO test
smoking = not within last 2 hours; also underestimates the DLCO
Why is having relaxed shoulders and not tensed shoulders during the DLCO breath hold important?
tensing up can increase intrathoracic pressure = limits venous blood return = limits pulmonary blood flow = can lower DLCO/underestimate DLCO value
how does exercising affect DLCO testing?
increases pulmonary blood flow, more CO picked up, overestimates the DLCO
describe DLCO breath hold timing via Jones and Meade Method
shows that breath hold is not the time at the TLC volume but rather starts at 30% Ti and the mid-point alveolar sampling collection - this is an estimation of when diffusion actually starts and stops since diffusion occurs as soon as gas hits the alveoli
Why is methane used in DLCO
it is an inert gas and helps calculate the RV by breathing in 0.3% and measuring how much it was diluted <0.3% after exhalation; higher RV = more methane dilution
In DLCO what does it mean if VA < TLC?
air trapping and hyperinflation (could be due to obstruction; VA is what was actually measured)
ATS criteria for DLCO
- min 2 tests, max 5 tests with 4 min in between
- repeatability: within 2ml/min/mmHg
- report average of the 2 tests
- Pt inspo needs to be 90% of best VC or 85% of best VC + VA is wi/in 200mL or 5% of largest VA
- inspo and expo quick <4sec
- breath hold 8-12sec
- appropriate discard and sample volumes given lung size
how to adjust washout and sample volumes from DLCO if the VA < 2L?
VA of 2L is small, so take <500mL washout and sample volumes
normal DLCO
25ml/min/mmHg
normal CO in the body
<2% COHb
how does high Hb vs. low Hb affect DLCO without adjustment?
High Hb = high DLCO
low Hb = low DLCO
(would need to use a correction factor to make sure this is accounted for)
how would high vs. low PaO2 affect DLCO results without correction factor?
high PaO2 = low DLCO
low PaO2 = high DLCO
How would high COHb vs. low COHb concentration affect DLCO results without correction factors?
high COHb = low DLCO
low COHb = high DLCO
how would high vs. low pulmonary blood flow affect DLCO
high pulm blood flow = high DLCO
low pulm blood flow = low DLCO
how would high alveolar volume vs. low alveolar volume affect DLCO
high alveolar volume = high DLCO
low volume = low DLCO
normal DLCO/VA ratio and what it is used for
normal = 4 - 5ml/min/mmHg/L
use: can help for restrictive diseases
- a high DLCO/VA indicates NMD (slightly lower DLCO vs. LOW VA)
- a low DLCO/VA indicates a pulmonary vascular disease
- a low DLCO and low VA but normal DLCO/VA ca n indicate pulmonary fibrosis
normal Raw and Raw indicating obstruction
normal = 0.6 - 2.4cmH2O/L/sec
obstruction >/= 3cmH2O/L/sec
Describe how to do testing for Raw
- plethysmography with body box SEALED and calibrated (wait for temp stabilize 30 - 60 sec)
- normal tidal breathing at least 3 breaths to establish FRC; at end of normal exhalation (FRC), they begin panting with shutter open; then they continue panting with shutter CLOSED, then they shutter opens and return to regular breathing then test END
- note: difference with FRC testing is that they pant with shutter open AND closed, the speed of panting is different (Raw faster), and they do NOT do a VC breath
why open and closed shutter for Raw testing?
open shutter = allows us to measure Ppeak (Pbox vs. flow), closed shutter = gets us Pplat (Palv or mouth vs. Pbox)
how to tell if you got good loops for Raw testing
closed loops, loops should go just past the +0.5 and -0.5L/sec flow lines so that average flow can be calculated
how to tell between high Raw on insp vs. high Raw on exp
high Raw insp = flattening of loop at top
high Raw exp = flattening loop at bottom (left side)
ATS criteria for Raw
- min 4 - 5 acceptable trials
- trials must be within 10% of the average (highest-lowestRaw / averageRaw)
- report the average of the accepted trials
- pant rate = 1.5 - 2br/sec = 90 - 120br/min for both open and closed shutter
What is conductance (Gaw) relationship to resistance?
1/Raw = Gaw = conductance = amount of flow it takes to generate 1cmH2O
how to calculate SRaw and SGaw and why is it important?
S = specific; to account for the fact that lung volumes can influence Raw (and Gaw) SRaw = Raw x VTG VTG = the volume in the thorax when test was done; for Raw testing the VTG = FRC
SGaw = Gaw/VTG
what type of flowmeter is the microloop spirometer
turbine; internal vane rotates to measure flow and convert to volume
formula used for the pressure differential flowmeter
flow = (P1 - P2) / R
where resistor creates a fixed resistance and the pressure difference on each side of the resistor is measured
how thermal flow sensor works
how much the flowmeter is cooled from original temp = indicator of flow
how do pitot tube flowmeters work
gas flows into device and enters a small precise tube; the pressure generated at this site is measured; more pressure = greater flow
note: flow can only go in one direction for these devices
how does the ultrasonic flowmeter work
a wave is transmitted down the device; breathing out the wave speed is faster; breathing in against the wave direction = slowed wave speed
how to use a peak flowmeter device
no nose clips needed, do 3 times and report highest value
what is quality control for spirometers (list the criteria)
daily 3L syringe check
- accuracy must be +/- 2.5% of 3L
- precision should be +/- 2.5% over multiple attempts
- capacity should show able to measure 8L volume + flows between 0 - 14L/sec
- linearity accurate for slow, medium, fast flow rates
Give examples of direct vs indirect bronchoprovocation
direct - methacholine which binds to M3 receptors resulting in direct bronchoconstriction
indirect - mannitol or hyperventilation which indirectly stimulates release of mediators resulting in bronchoconstriction
why do a MCT?
methacholine challenge test is to assess for airway hyperresponsiveness via signs of obstruction (which is sometimes associated with asthma)
describe MC testing steps
- perform pre-test FVC; if FEV1 = 60% predicted then do not proceed bc they already are obstructed enough
- saline/diluent delivery; stop if FEV1 falls by 20% or more; give again if FEV1 falls by 10-20%; continue if FEV1 only falls within 10%
- get post-diluent FEV1 = baseline
- repeat FEV1 procedure after 30 and 90 seconds post each dose of methacholine and always compare the higher value to baseline
- MC starting dose (stop when FEV1 falls at least 20%; continue if FEV1 falls less than 20%
- wait 5 minutes between each dose
max methacholine dose given for BPT
400ug for dose; or 16mg/mL concentration
compare PD20 to PC20; which is better to report and what is the significance?
PD20 = provocation dose of methacholine that causes FEV1 to drop 20% from baseline (e.g. 400ug)
PC20 = concentration of methacholine causing FEV1 to drop 20% from baseline (e.g. 16mg/mL)
-report the PD20% bc it is more specific
-If PC20 <1mgmL or PD20 <25ug = asthma
If PC20 1- 16mg/ml or PD20 25-400ug = potentially AHR
If >16mg/ml or >400ug = no AHR
methacholine dosing schedule
start 0.0625mg/mL and quadruple until 16mg/mL
indications of MCT
rule out asthma, screen AHR for occupational screening, assess severity of asthma/guide treatment
contraindications to MCT
same as FVC + pretest FEV1 < 60%, pregnant or nursing, inadequate staff, meds that reverse methacholine
what would a positive response to mannitol bronchoprovocation testing be?
positive for AHR if FEV1 drops by at least 15% overall or by more than 10% between 2 consecutive doses
what is a positive result for EIB?
If after 4-6 min high intensity exercise FEV1 tested at 1, 2 and every 5 minutes post exercise until 30 minutes will show a drop in FEV1 of 10 - 15% or more
describe how to perform MIP
with or without nose clips, Pt fully exhales down to RV and with tight mouthpiece seal they breathe in against a closed valve and “pull” in as hard as possible
how to perform MEP
Pt fully inhales to TLC then forcefully exhales against a closed valve “pushing” out as hard as possible
MIP/MEP optimal criteria (not ATS)
- MIP or MEP should be 1.5 - 2seconds of pulling or pushing with pressure plateau for at least 1 sec
- minimum 3 times, max 8 attempts
- report highest absolute value
- ensure highest 2 values are within 10 - 20%
- allow rest in between
normal male and female MIPs and MEPs
male MIP -100 to -150cmH2O
male MEP 125 to 175cmH2O
female MIP -75 to -125cmH2O
female MEP 75 to 125cmH@O
abnormal MIP and MEP value indicating severe weakness
MIP =20cmH2O, MEP = 40cmH2O
normal and low values of VC
normal >/= 60ml/kg IBW
low = = 15ml/kg IBW
normal Vd/Vt
- 2 - 0.4 (0.3 being dead normal)
- used Bohr eqn PaCO2-P(e)CO2 / PaCO2 *not use mixed expired gas not end tidal
define occlusion pressure + how to measure
P100 or P0.1 = pressure of mouth during first 100ms of inspiration against closed valve (from FRC) reflects central resp drive
-value is used for weaning and can be trended
normal P100
-1cmH2O to -3.5cmH2O
for every 1mmHg increase in CO2 past normal, how does P100 change?
P100 increases by -0.5cmH2O
advice to give to Pts at risk for high altitude hypoxia going on a flight
- could do a HAST = high altitude simulation test breathing 15%O2 for 20 mins, SpO2 should not drop by more than 4% at max altitude
- if on O2 already, turn flow up by 2LPM during flight
resting ABG and SpO2 Home O2 criteria
they breathed room air for 10 mins, PaO2 = 55mmHg on room air OR
PaO2 = 60mmHg on room air + they have CHF or PHTN
SpO2 < 88% for 6 consecutive minutes (use this is cant do ABG)
criteria for ambulatory O2
6MWT on room air, SpO2 < 88% for 1 minute and repeat 6MWT with O2 + observe SpO2 >90%
4 consequences of HLHS
Aortic valve atresia or stenosis, mitral valve atresia or stenosis, hypo plastic ascending aorta, ASD and PDA
