Inhalational Anesthetics; Isoflurane and Sevoflurane.pptx

Isoflurane (Furane) 1979, Sevoflurane (Ultane) 1990s
general description ,physical properties and anesthetic properties .
Effects on organ system, contraindications, drug interaction.

1. Volatile Anesthetics Isoflurane , Sevoflurane Mahmood Hasan Taha HD/ Anesthesia Zakho General H. Aug/ 2022

2. Isoflurane (Forane) 1979

3. General Description: Non flammable . Non explosive. Pungent ethereal odor. Chemical isomer with the same molecular weight as Enflurane . MAC = 1.2 Blood/Gas : 1.43, Oil/ Gas: 91 (Blood / Gas: 2.3, Oil/ Gas: 224 for Halothane)

4. Color code: purple . Colorless liquid in brown glass bottle, without preservative. Boiling point: 48.5℃ SVP: 31.9 mmHg . (50.2 ℃, SVP 32.5 mmHg for Halothane). Soda lime: compatible.

5. Vaporizers: a specifically calibrated plenum vaporizers. The physical properties of boiling point and saturated vapor pressure are very similar to Halothane, so the vaporizer design is also closely related.

6. Effects on organ systems

7. Cardiovascular: Minimal left ventricular depression. SVR ↓↓ B.P ↓↓ H.R ↑ Coronary vasodilation → steal (diversion of coronary blood away from fixed stenosis). COP : no change.

8. Respiratory : As Halothane, except in less tachypnea. ( Net result more ↓ in Vm .) Even 0.1 MAC can blunt the normal ventilatory drive. Irritation to upper airway, increases bronchial secretions and salivary secretions . 2 MAC → irritation at 50% of patients. Good bronchodilator but < Halothane.

9. Cerebral : CBF ↑ ICP ↑ CMRO2 ↓↓ The CBF & ICP increased by > 1 MAC less than Halothane & can be reversed by hyperventilation. At 2 MAC → silent EEG. Anesthesia , no analgesia, not epileptogenic .

10. Neuromuscular: more than Halothane & can relax skeletal muscle. Renal : same as Halothane: RBF ↓ , GFR ↓, UOP ↓.

11. Liver: HBF ↓ ( Hepatic O 2 supply is better maintained than with Halothane & LFTs usually not affected). Safe for Liver & Kidneys functions.

12. Contraindications: Non absolute. Hypovolemia . It can trigger malignant hyperthermia.

13. Drug Interaction: Epinephrine safe up to 4.5 mcg/kg . > 1.5 mcg/kg should be avoided with Halothane. Non depolarizing NMBA ↑↑↑ by Isoflurane. Metabolism : Primarily via lungs, 0.2% in the liver.

14. Sevoflurane ( Ultane) 1990

15. General Description : Sweet . Excellent choice for smooth & rapid inhalational induction in pediatrics & adults . MAC = 2.0 Blood/Gas : 0.69, Oil/Gas : 53 Blood/Gas : 1.43, Oil/ Gas: 91 for Isoflurane. Color code: yellow.

16. No preservative, supplied in brown plastic bottles. Boiling point: 58.6 ℃, SVP:21.3 mmHg . 48.5℃ SVP: 31.9 mmHg for Isoflurane. Soda lime: compatible but may produce Compound A.

17. Effects on organ systems

18. Cardiovascular : Myocardium contractility mildly ↓. B.P ↓. SVR ↓. HR : no change or little ↑ → COP ↓ or maintained . Coronary vasodilatation < Isoflurane. QT interval prolongation even 60 minute following emergence. No myocardial sensitization to catecholamine.

19. Respiratory : Vt ↓. RR ↑. Bronchodilator like Isoflurane. No airway irritation.

20. CNS : Anesthesia , no analgesia, not epileptogenic. Slight ↑ in CBF & ICP but < Isoflurane. 1.5 MAC impair auto regulation. CMRO 2 ↓.

21. Neuromuscular : A dequate M.R for intubation of a child !!. NMBA (non depolarizing) ↑↑. Renal : RBF↓, GFR↓ , UOP↓.

22. A plasma fluoride ion concentration of 50 micromole/L is quoted as the threshold for renal toxicity , Sevoflurane metabolism can produce levels above this threshold, yet clinically significant renal dysfunction has not been associated with sevoflurane anesthesia .

23. Alkali such as barium hydroxide lime or soda lime (but not calcium hydroxide) can degrade sevoflurane producing another proven ( at least in rats) nephrotoxic end product (compound A), accumulation of compound A increases with increased respiratory gas temperature, low flow anesthesia, dry barium hydroxide absorbent (baralyme), high sevoflorane concentrations, and anesthetics of long duration.

24. Liver : Venous ↓ , Arterial ↑ : maintained Blood supply or mildly ↓. No immune- mediated hepatotoxicity. Safe for liver & kidneys. Uterus: uterine relaxation in pregnancy similar to isoflurane.

25. Contraindications : Sever hypovolemia. History of Malignant hyperthermia. I.C . hypertension.

26. Drug interaction : not sensitize the heart to catecholamine. Metabolism: predominantly via the lungs, 5% only metabolized by the liver.