Concentration and second gas effect Dr S Parthasarathy
- Slides: 10
Concentration and second gas effect Dr. S. Parthasarathy MD, DA, DNB, Dip Diab. MD , DCA, Dip software based statistics, Ph. D (physiology)
• N 2 O 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 N 2 O from the alveolar space into blood produces significant shifts of alveolar gas volume
Concentration effect Understand ? ? • After absorption of the N 2 O in the blood, although the volume of N 2 O in the alveoli decreases, but the concentration does not diminish to the previous level, because the volume of the alveoli also decreases.
• N 2 O + volatile anaesthetic agents, then N 2 O quickly replaces the nitrogen, which was previously preset in the alveoli. • So, the volume of N 2 O 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’
Concentration & Second Gas Effect 1% of Sec. gas 1. 6% of Sec. gas 19% O 2 32. 3% O 2 19% O 2 80% N 2 O 4000 (800 + 3200) Uptake of 50% of inspired N 2 O 40% N 2 O 66. 7% N 2 O Absorbed gas replaced by Augmented ventilation 2400 (800 + 1600) 7. 6% O 2 32% N 2 O 0. 4% of Sec. gas 4000 800 + 1600 320 + 1280 This model assumes that O 2 is not taken up. Drawn only to understand the process
Concentration effect • After absorption of the N 2 O in the blood, although the volume of N 2 O in the alveoli decreases, but the concentration does not diminish to the previous level, because the volume of the alveoli also decreases.
• N 2 O + volatile anaesthetic agents, then N 2 O quickly replaces the nitrogen, which was previously preset in the alveoli. • So, the volume of N 2 O 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’
• Thank you all