AEP Episode 7: Coagulation- Key Concepts for Exams

AEQ 2: Pulmonary Function Tests (PFT)

Anaesthesia Exam Question 2
PFTs are done to evaluate the mechanical and gas exchange functions of the lung; most important of these include :
Spirometry
Lung Volumes & Elasticity
Gas Exchange Function Tests

SPIROMETRY
It’s the measurement of dynamic lung volumes during forced expiration and inspiration. It includes
Forced Vital Capacity (FVC)
Forced Expiratory Volume in one second (FEV1) &
Maximum expiratory flow during the middle 50% (25-75%) of the vital capacity- this is a sensitive index of small airway obstruction
The severity of COPD is graded based on the FEV1 values:
Mild COPD- FEV1 >70% of predicted
Moderate COPD- FEV1 50-69% of predicted
Severe COPD- FEV1 <50% of predicted
In COPD and asthma, the FEV1 will be reduced more markedly than FVC resulting in a reduction in FEV1/FVC ratio (>70%)
The response to bronchodilators in the form of an increase in FEV1 and FVC indicates reversibility and helps in diagnosis- a response >15% from the baseline value shows significant reversibility and points towards a diagnosis of bronchial asthma
TLC and RV will be increased in COPD
THE FLOW VOLUME(FV) LOOPS

The normal FV loop:
The patient takes a vital capacity breath and starts the test with a forced expiration
The loop rises rapidly to a flow rate of 8-10 l/sec followed by a steady decrease as the expiration continue from left to right- the patient will be unable to cross the maximal flow line because of the dynamic compression of the airways. So the normal loop represents the maximum flow rate at each lung volume
Then inspiration occurs from RV to TLC in a right to left direction to achieve a flow rate of 4-6 l/sec and has a squarer shape

FV loop: COPD
COPD reduces flow rates all through the expiration with increased concavity or a ‘scooped out’ appearance of the expiratory limb. PEFR is also reduced
Due to gas trapping, the RV (and TLC) is increased. The inspiratory flow rates are only slightly reduced

FV loop: Restrictive Diseases
Restrictive diseases shifts the left hand side of the curve towards right because of a marked reduction in TLC while preserving RV. PEFR is also reduced.

FV loop: Variable Extrathoracic Obstruction – Problem: during inspiration
e.g. Laryngomalacia, vocal cord paralysis, subglottic stenosis, goitres, tracheomalacia of extrathoracic trachea
The negative pressure generated in the airway during inspiration makes the airway collapse thus markedly reducing the inspiratory flow, but retains the square shape
The positive pressure generated during expiration, keeps the airway open. So the expiratory limb may be near normal
The TLC and RV are generally unaffected.

FV Loop: Variable Intrathoracic Obstruction
e.g. Tracheomalacia of intrathoracic trachea and tracheal tumours
If the obstruction is intrathoracic, the negative pressure generated in the intrapleural compartment during inspiration will help to pull and open up the airways. So the inspiratory limb will be near normal.
The positive pressure generated during expiration will make the airway further narrower. So the expiratory flow will be markedly reduced, similar to that happens in COPD.
The TLC and RV are generally unaffected.

FV Loop: Fixed Large Airway Obstruction
e.g. Tracheal stenosis
Here the peak expiratory and inspiratory flows are determined by the diameter of the orifice- so both the expiratory and inspiratory limbs show markedly reduced flow.
The TLC and RV are generally unaffected.

GAS EXCHANGE FUNCTION TESTS
TLCO measures the integrity and functioning of the gas exchange surface of the lung. This will be reduced in emphysema and is also a good indicator of the severity of the disease. PEFR is also reduced.
Arterial Blood Gas analysis and Exercise testing are additional tests that will reflect the functioning of lung function

Anaesthesia Exam Question:1
Revised Cardiac Risk Index (RCRI) is one of the commonly used perioperative risk indices
The RCRI determines preoperative risk based on risk of surgery, history of ischemic heart disease, congestive heart failure, cerebrovascular disease, preoperative use of insulin and creatinine greater than 2.0 mg/ dL.
The total score ranges from 0 to 6, with higher scores indicating a higher risk of major adverse cardiac events (MACE). The risk categories and their corresponding scores are as follows:
0 points: Low risk (MACE rate <1%)
1-2 points: Intermediate risk (MACE rate 1-5%)
3-6 points: High risk (MACE rate >5%)
RCRI is less accurate in patients undergoing vascular, noncardiac surgery. In addition, as RCRI does not capture risk factors for noncardiac causes of perioperative mortality, it does not predict all-cause mortality well

American College of Surgeons’ National Surgical Quality Improvement Program (ACS-NSQIP) is a universal surgical risk calculator model developed using a web-based tool . The ACS-NSQIP calculator incorporates 20 patient risk factors in addition to the surgical procedure. From this input, it calculates the percentage risk of a MACE, death, and 8 other outcomes. This risk calculator may offer the best estimation of surgery-specific risk of a MACE and death. It has excellent performance for predicting mortality and morbidity. It has not been validated in an external population outside the NSQIP. This classification has poor inter-rater reliability
Surgery-specific risk calculation using ACS-NSQIP report the rate of cardiac death or non-fatal MI and are noted to be greater than 5% in high-risk procedures, 1% to 5% in intermediate-risk procedures, and less than 1% in low-risk procedures. Emergency surgery is associated with higher risk of MACEs compared with elective procedures.