My presentation

Interpretation of Pulmonary Function Tests

The Perioperative Surgical Home

A patient-centered, physician-led system of coordinated care that guides patients throughout the entire surgical experience. From the decision for surgery to discharge from a medical facility and beyond, the PSH model of care is structured to improve patient care and outcomes.

PPCs are common and a major cause of overall perioperative morbidity and mortality.

Even more often than cardiac complications.

The National Surgical Quality Improvement Program (NSQIP) found that PPCs were the most costly of major postoperative medical complications (including cardiac, thromboembolic, and infectious) and resulted in the longest length of hospital stay.

Postoperative Pulmonary Complications

Postoperative Pulmonary Complications

Atelectasis

Infection, including bronchitis and pneumonia

Prolonged mechanical ventilation and

respiratory failure

Exacerbation of underlying chronic lung

disease

Thromboembolic disease

The impact of PPCs has become increasingly apparent,

Estimation of their risk should be a standard element of all preoperative medical evaluations.

This is increasingly driven by evidence-based medicine, rather than expert opinion.

Anesthesiologists should balance the risks and costs of these evaluations against their benefits.

• History and Clinical examination

• Preanesthesia Chest Radiographs

• Consultation with specialists

• Pulmonary function tests

Pulmonary function tests

What Functions We Should Test?

• Airways

– Small

– Large

• Parenchyma

– Alveoli

– Interstisium

• Pulmonary Vasculature

• Bellows & Pump mechanism

– Diaphragm

– Chest wall

• Neural Control of Ventilation


Tests for Assessment of Mechanical VentilatoryFunctions of the Respiratory System:

• Dynamic Lung Volumes (Spirometry)

• Static Lung Volumes

• Respiratory Muscle Function

– Maximum inspiratory & expiratory pressures


Tests for Assessment of Gas Exchange:

• Diffusion Capacity DLCO

• Arterial blood gases

• Overnight oximetry


Tests for Assessment of Cardiopulmonary Interaction:

• Cardiopulmonary exercise testing.

• 6-minute-walk test.

• Right Heart Catheterisation.

Goals of Preoperative PFTPredict the likelihood of PPCs in lung resection surgery or cardiac surgery.

Obtain quantitative baseline information concerning pulmonary function that guides decision making, and identify patients who may benefit from therapy preoperatively.

Obtain baseline pulmonary function data so assessment for liberation of MV and/or tracheal extubation might be based on.

SPIROMETRY

• Spirometry is the most commonly used lung function

screening study.

• It’s role is well established in lung resection or cardiac surgeries.

• Spirometry has NO effective risk prediction value for PPCs.

• There are NO prohibitive threshold for spirometric values below which the risk for surgery would be unacceptable.

• Changes in clinical management due to findings from preoperative spirometry were not reported.

Perioperative Indications of Spirometry

Studies:

1. Routine preoperative spirometry: abnormal

findings in 15.0–51.7% of cases.

2. Indicated preoperative PFT’s were reported as

abnormal in 17.0–27.1% of cases, and

3. Indicated preoperative spirometry were

reported as abnormal in 33.1–45.0% of cases.

The authors reported that a predicted FEV1 of

less than 61%, and a PaO2 less than 70 mmHg

each were independent risk factors for PPCs.

1. Maximal pressures generated in the thorax impact on abdominal and thoracic organs/tissues.

2. Large swings in blood pressure.

3. Expansion of the chest wall and lungs.

4. Active communicable diseases.

Myocardial infarction within the last month

Unstable angina

Recent thoraco-abdominal surgery

Recent ophthalmic surgery

Thoracic or abdominal aneurysm

Current pneumothorax

SPIROMETRY

Modern Spirometry

SpiroSmart

The main spirometry tests are:

FVC (Forced Vital Capacity)

VC (Vital Capacity or Slow Vital Capacity)

MVV (Maximum Voluntary Ventilation)

SPIROMETRY

FVCForced Vital Capacity

Tidal breathing

The patient starts with some tidal breathing.

Maximum inspiration

The patient fills his lungs entirely (TLC). No need to be forced but must be

as deep as possible.

Forced expiration

Immediately after, the patient performs a maximal expiration as fast, as

hard and as long as he can.

Forced inspiration

Immediately after, a second inspiration is performed as forced and as

quickly as possible.

(Slow) Vital Capacity

Inspiratory Vital Capacity: The patient inspires fully and than

slowly expires all the air in his lungs

Expiratory Vital Capacity: the other way around: the patient

expires fully and inspires slowly to a maximum

This test used to be performed to get VC and to be able to calculate the

FEV1/VC ratio (FEV1% or Tiffeneau index).

(Slow) Vital Capacity

The expiratory SVC > FVCIn patients with obstructive small airways disease &

a collapse of the small airways is suspected

Inspiratory VC = Expiratory SVC

= Expiratory FVC

Two graphs:

Volume-time curve

The flow-volume loop

SPIROGRAM

Volume-Time Tracing and Flow-Volume Loop

Identify the anatomic location of airflow

obstruction

Ascertain the

technical

adequacy of a

manoeuvre

They provide important graphic and numeric data regarding the

mechanical properties of the lungs.

Volume Time Graph

A healthy subject will

expire between 70

and 90% of the FVC

in the first second of

the test.

It takes roughly

about 5 sec to expire

the last 10-30 % of

the FVC.

Numeric Data

Volume parameters:

These parameters represent volumes and can be read from the volume-time graph:

• FVC

• FEV1

• FEV.5

• FEV3

• FEV6

• FEV1/FVC ratio (FEV1%)

• FEV3/FVC ratio (FEV3%)

• FEV1/FEV6 ratio (FEV6%)

FVC

FVC is a measure of lung volume.

• Restrictive disorders: ↓↓ FVC

(pulmonary fibrosis, kyphoscoliosis, neuromuscular disease, and pleural effusion).

• Pseudorestriction: ↓↓ FVC with hyperinflated lungs

(due to severe airflow obstruction and air trapping, as in emphysema.)

Forced Expiratory Volume in 1 Second

• Reflects mechanical properties of the large and the medium-sized airways

• It is reduced in obstructive and restrictive disorders

• In normal persons, the FEV1 accounts for the greatest part (80%)

of the exhaled volume from a spirometric manoeuvre

• FEV1%=FEV1/VC X100

• FEV1%=FEV1/FVC X100

• FEV1%=FEV1/FEV6 X100

Nowadays the value is compared to LLN

Tiffeneau index

FEV1 FVC FEV1 %

Obstructive

Lung Disease

Normal(very mild Obstruction)

Or

Decreased(Mod./severe Obstruction)

Normal(Mild/Mod. Obstruction)

Or

Decreased(severe Obstruction)

Decreased

(<70%)

Restrictive

Lung Disease

Normal

Or

Decreased

Decreased Normal

Or

Increased

(≥ 70%)

The Flow-Volume

loop

• It is the most important

graph in spirometry

• The morphology tells

immediately if the test was

well done.

• Begins at ZERO volume & flow.

• The curve rapidly (150 msec) mounts to a peak (PEF) = air expired from the large upper airways (trachea-bronchi).

• The curve descends (=the flow decreases)

FEF25 FEF50 FEF75

• FEF2575: The mean flow between the points FEF25 and FEF 75

• The flow reaches zero & the FVC is reached

No time axis on

the flow-volume loop

Maximal Mid-Expiratory Flow (MMEF)

The maximal flow rates between 25%-75% of the forced vital capacity (FEF25-75%).

• These may provide

information regarding small airway function.

• The lower limit of normal falls significantly with age.

FEV3/FVC ratio

• FEV3% is a new

parameter to assess

small airways function.

• FEF25–75 measurements can

be misleading (false-negative

results and false-positive

results).

Numeric Data

Flow parameters:

These parameters represent flows and can be read from the flow-volume loop:

• PEF

• PIF

• PEF 2575

• PEF 25

• PEF 50

• PEF 75

Obstructive Lung

Disease

• The small airways are partially obstructed

• FEV1 will be too low

• A normal FVC at the early stages

• FEV1% < 70%

• FET (Forced Expiratory Time) is prolonged

• The disease generally affects the expiratory limb (Airflows that are independent of effort is reduced)

• The descending limb of the expiratory loop is typically concave.

• FEF25-75 is low.

• The effort-dependent PEF may be normal or reduced.

Bronchodilator Testing

• Following the administration of a bronchodilator such

as 2.5mg of nebulised salbutamol.

• A positive response: a 12% increase in FEV1 with an increase of 200mls or more.

• When the baseline spirogram is relatively normal. Bronchial challenge testing may also be considered

• PC20FEV1: The provocative concentration dosage level of the inhalational agent (methacholine) required to produce a 20%

reduction in the FEV1.

• PC20FEV1 < 8 mg/mL suggests clinically important airway hyperreactivity

• GOOD –VE TEST

Restrictive Lung Disease

• ↓↓ FEV1

• ↓↓ FVC

• FEV1% is normal or even elevated

• ↓↓ TLC


• The F/V loop is narrowed, but the shape is generally the same as in normal.

• Flow rates are greater than normal at comparable lung volumes because the increased elastic recoil of lungs holds the airways open.


Static Lung Volumes

• Spirometry is an expiratory maneuver.

• ↓↓ VC during spirometry should prompt measurement of TLC to confirm the presence or absence of a true restrictive ventilatory disorder.

• FRC is usually measured by:

1. A gas dilution technique.

2. Body plethysmography.

3. Imaging Techniques.

Residual Volume

Total Lung Capacity

Functional Residual Capacity

↑↑ in patients with

obstructive defects such

as emphysema

↓↓ in patients with

restrictive abnormalities as

kyphoscoliosis.

Nitrogen washout or helium dilution.

Gas dilution techniques

• Measure of all air in the lungs that communicates with the airways.

• A limitation of this technique is that it does not measure air in non-communicating bullae, and therefore it can underestimate TLC, especially in patients with severe emphysema.

Whole body plethysmography

• The patient sits inside an

airtight box, inhales or exhales to a particular volume, and then a shutter drops across their breathing tube. The subject makes respiratory efforts against the closed shutter.

• The changes in pressure in a constant volume box or volume in a constant pressure box is measured.

• The primary advantage of body plethysmography is that it can

measure the total volume of air in the chest, including gas trapped in bullae.

• Another advantage is that this test can be performed quickly.

Whole body plethysmography

• Drawbacks include the complexity of the equipment as

well as the need for a patient to sit in a small enclosed

space.

Diffusion Capacity - DLCO

Diffusion capacity (DLCO) or transfer factor gives important information regarding the integrity and size of:

Single breath technique:

• where 10% helium and 0.3% carbon monoxide are rapidly inspired,

• held for 10 seconds and

• then expired with

• The measurement of the remaining carbon monoxide.

• Comparison of the inspired and expired CO fractions

The alveolar

blood

membrane

Adjustments of DLCO

• Normally the value is corrected for the patient’s haemoglobin (DLCOc).

• The transfer coefficient (KCO) is DLCOc corrected for alveolar volume:

– DLCOc after pneumonectomy will be reduced but

– KCO will be normal

Interpretation

1. Predicted values: spirometry values are compared to the predicted values that are calculated from age, gender, ethnicity and height

2. Lower Limits of Normal (LLN): is the lower fifth percentile of the Gaussian bell curve. This also applies to the Tiffeneauindex.

3. Historical Data: healthy patients will lose up to 25 mL of FEV1 every year from the age of 25. A patient that has blown 120% of his predicted values and blows 100% of his predicted values one year later may have a very big problem

Pathological

Spirometry

One should first make sure that the test was done according to standard, before interpreting the results of the test.

Quality Assessment of the

Spirogram

The volume-time tracing is most useful in assessing

whether the end-of-test criteria have been met,

whereas the F-V loop is most valuable in evaluating the

start-of-test criteria.

Good Quality Flow volume loop:

Typical shape inspiration & expiration

Quality Assessment of the Flow-Volume Loop

A frequent variation of the normal flow-volume loop:

Shoulder in spirometry loops from young females.


Reproducibility

To be sure that the patient has blown his maximal values during the FVC spirometry test, it is necessary to let him blow at least twice.

Reproducibility is calculated on three parameters:

1. FEV1

2. FVC

3. PEF

The patient will need to repeat the test until he has blown two reproducible tests or until he has tried 8 times.


1. Couphing

The flow to suddenly fall to zero and rise again


2. Expiration Too

Slow

The peak flow is not within

the first 100 milliseconds and

there is a dent in the loop

3. Patient hesitates

At the start of the loop

Common Errors

The technique of back-extrapolation of the start of the test to establish a zero time point on the volume-time tracing.

It corrects for delayed or hesitant starts that might otherwise be mistaken for a falsely reduced FEV1.


Incomplete Expiration


Larger Inspiration Than Expiration

The patient did not fill his lungs

completely before the test:

inspiration>expiration

A sudden drop at the right end

of the loop, the loop is 'cut off‘

FVC is underestimated.

Expiratory Time Not Sufficient:

According to the ATS criteria (American Thoracic Society) expiratory time should be equal to or exceed 6 seconds.

(3 seconds is set as a minimum)

Quality Assessment of the Spirogram

Pulmonary function tests in patientsundergoing lung resection

The British Thoracic Society guidelines:

• Pneumonectomy can be considered with FEV1> 2.0 L

• Lobectomy if FEV1> 1.5 L in the absence of any interstitial lung disease or unexpected disability due to shortness of breath.

As absolute values may be lower in older patients and women, patients are generally considered suitable for resection if

FEV1> 80% predicted and DLCO > 80% predicted.

In case of borderline lung function

The post operative predicted FEV1 and DLCO

(calculated either with knowledge of the number of lung segments to be resected or through quantitative lung perfusion scanning).

Patients with a post operative predicted FEV1 or DLCO < 40%

Patients undergoing lung resection

Are deemed at high risk of peri-operative

death and complications.

• CPET may be necessary for further risk stratification.

• Patients with PFTS below 30% predicted may potentially be considered for lung transplantation assuming no other contraindications are present.

Patients undergoing lung resection

• DLCO should be routinely measured during pre-operative

evaluation of lung resection candidates, regardless of

whether the spirometric evaluation is abnormal.

Large Airway Obstruction

• Tracheal stenosis, goiter

• The top and bottom of the loops are flattened (rectangle).

• Fixed obstruction limits flow equally during inspiration and expiration, and MEF = MIF.

Fixed obstruction of the upper airway

• Unilateral vocal cord paralysis

• When a single vocal cord is paralyzed, it moves passively with pressure gradients across the glottis.

• Therefore, MIF < MEF

• Tracheomalacia

• During a forced inspiration, negative pleural pressure holds the “floppy” trachea open.

• With forced expiration, loss of structural support results in tracheal narrowing of the trachea and a plateau of diminished flow.

• Flow is maintained briefly before airway compression occurs.

Pred. PRE %FVC 5,7 5,01 88%

FEV1 4,75 4,26 90%

FEV1% 82,5 85%

FEF2575 5,19 4,46 86%

PEF 10,45 1,02 97%

FET 5sec

a. The test was not properly executed

b. Normal spirometry

c. Obstructive lung disease

d. Restrictive lung disease

e. Mixed lung disease

f. Upper airway obstruction







Pred. PRE %FVC 5,44 5,39 99%

FEV1 4,57 4,20 92%

FEV1% 82,7 78%

FEF2575 5,14 4,47 87%

PEF 10,19 9,68 95%

FET 7sec







Pred. PRE %FVC 5,12 5,17 101%

FEV1 4,23 3,68 87%

FEV1% 80,9 71%

FEF2575 4,69 3,09 66%

PEF 9,7 4,07 42%

FET 7sec







Pred. PRE %FVC 3,47 3,48 100%

FEV1 3,07 3,14 102%

FEV1% 88,5 90,2%

FEF2575 4,17 3,84 92%

PEF 7,18 7,25 101%

FET 2,8sec







Pred. PRE %

FVC 5,49 5,55 101%

FEV1 4,61 3,32 72%

FEV1% 82,7 60

FEF2575 5,16 3,30 64%

PEF 10,25 10,34 101%

FET 12sec







Pred. PRE %FVC 3,9 3,91 100%

FEV1 3,41 3,51 103%

FEV1% 84,4 89%

FEF2575 4,17 4,57 109%

PEF 7,38 6,8 92%

FET 5sec







Pred. PRE %FVC 4,63 0,60 13%

FEV1 3,97 0,55 14%

FEV1% 82,7 92,6%

FEF2575 4,86 1,02 21%

PEF 9,33 2,99 32%

FET 3sec







Pred. PRE %

FVC 4,79 4,02 84%

FEV1 4,03 3,40 84%

FEV1% 82,7 84,6%

FEF2575 5,1 4,69 92%

PEF 10,07 8,67 86%

FET 7sec

Date post:	16-Jul-2015
Category:	Health & Medicine
Upload:	ghada-bashandy
View:	87 times
Download:	2 times

My presentation

Health & Medicine