DNB - ANESTHESIOLOGY, PMR
MD - ANESTHESIOLOGY, PMR
FINAL EXAM …!!!
Q 2 A ) DEFINE FUNCTIONAL RESIDUAL CAPACITY ( FRC ) ?
B ) ENNUMERATE THE EFFECTS OF AGE AND TRENDELENBERG POSITION ON FRC ?
C ) EXPLAIN ANAESTHETIC IMPLICATIONS OF THE CHANGES IN FRC ?
A 2 A ) DEFINITION
1 Is the volume of air present in the lungs at the end of passive expiration
2 Is the sum of Expiratory reserve volume ( ERV ) and Residual volume ( RV )
3 In this , the opposing elastic recoil forces of the lungs and chest wall is in equilibrium and there is no exertion by the diaphragm
4 It measures approximately 2100 ml in a 70 kg male
5 It can be measured through nitrogen washout , helium dilution or body plethysmograph
B ) 1 EFFECT OF AGING ON FRC
FRC increases with aging
A ) This change is due to an increase in relaxation volume of the respiratory system secondary to changes in the static recoil pressure of both chest wall and lungs
B ) A change in the lung size but no narrowing of airways
C ) A change in alveolar circumference
D ) Increases 1 to 3 % per decade
2 EFFECT OF TRENDELENBERG POSITION ON FRC
A ) Trendelenberg positioning or a head down tilt is routinely used especially while trying to establish a route for inserting central venous catheter to increase the caliber of jugular or subclavian vein and to prevent air embolus
B ) This position leads to a significant decrease in functional residual capacity ( 6 to 21 % ) and an increase in lung clearance index ( 2 to 19 % )
C ) ANESTHETIC IMPLICATIONS OF CHANGES IN FRC
1 This is important since during general anesthesia it is reduced to 20 % and this reduction is greater in obese patients and in patients with COPD - this occurs due to loss of inspiratory muscle tone
A ) This change in FRC creates or increases intrapulmonary shunt and areas of low ventilation or perfusion secondary to compression atelectiasis
2 It falls by 0.8 to 1 L by a change in position from upright to supine due to upward pressure from abdominal contents and more cephald position of diaphragm and it further decreases by 0.4 - 0.5 L due to relaxation of diaphragm and intercoastal muscles resulting in atelectiasis
3 Also in thoracic and abdominal surgeries it tends to decrease leading to postoperative hypoxemia
4 But it stays normal during ketamine induced anesthesia due to intact muscle tone