1. Concentration and second gas effect Dr. S. Parthasarathy MD, DA, DNB, Dip Diab.MD,DCA, Dip software based statistics, PhD (physiology)

2. N2O represents a special case in clinical anesthesia, because it is often the major constituent of the inhaled gas mixture. ( 65 % -- 35 % ) As a result, uptake of N2O from the alveolar space into blood produces significant shifts of alveolar gas volume

3. Concentration effect After absorption of the N2O in the blood, although the volume of N2O in the alveoli decreases, but the concentration does not diminish to the previous level, because the volume of the alveoli also decreases. Understand ??

4. N2O + volatile anaesthetic agents, then N2O quickly replaces the nitrogen, which was previously preset in the alveoli. So, the volume of N2O taken up by the blood is greater than the volume of nitrogen entering the alveoli from the blood. Therefore, the alveoli get smaller and the fractional concentration of the second volatile anaesthetic agent in the alveoli increases. This phenomenon is called the ‘second gas effect’

6. Concentration & Second Gas Effect 19% O 2 32.3% O 2 80% N 2 O 66.7% N 2 O 40% N 2 O 19% O 2 7.6% O 2 32% N 2 O 4000 (800 + 3200) 2400 (800 + 1600) 4000 800 + 1600 320 + 1280 Uptake of 50% of inspired N2O Absorbed gas replaced by Augmented ventilation This model assumes that O2 is not taken up. Drawn only to understand the process 1% of Sec. gas 1.6% of Sec. gas 1% of Sec. gas 0.4% of Sec. gas

8. Concentration effect After absorption of the N2O in the blood, although the volume of N2O in the alveoli decreases, but the concentration does not diminish to the previous level, because the volume of the alveoli also decreases.

9. N2O + volatile anaesthetic agents, then N2O quickly replaces the nitrogen, which was previously preset in the alveoli. So, the volume of N2O taken up by the blood is greater than the volume of nitrogen entering the alveoli from the blood. Therefore, the alveoli get smaller and the fractional concentration of the second volatile anaesthetic agent in the alveoli increases. This phenomenon is called the ‘second gas effect’

10. Thank you all