Isoflurane

Isoflurane is the anaesthetic drug of choice in renal failure.

It is useful in all degrees of renal impairment.

Due to minimal hepatic metabolism resulting in very low levels of inorganic fluorides and

because of its low cardiac arrythmogenicity isoflurane is an ideal agent for patients with renal failure.

Ref: Drug Dosage in Renal Insufficiency By G. Seyffart, Page 313 ; Meyler’s Side Effects of Drugs Used in Anesthesia By Jeffrey K. Aronson, Page 19 ; Foye’s Principles of Medicinal Chemistry By William O. Foye, 6th Edition, Page 500

Isoflurane causes least vasodialation and hence helps to moderate the cerebral blood flow.

It reduces the ICT and hence is useful in neurosurgery.

It is more potent than halothane and has rapid onset of action and induction.

Reference
1. Quick Review of Pharmacology,  By Dr J G Buch, Page 204

B i.e. Isoflurane

C i.e. Isoflurane 

Isoflurane has least & methoxyflurane has highest fluride contentQ. Methoxyflurane causes vasopressin resistant high output renal failure.Q.

D i.e. Isoflurane

Ans:D i.e. Isoflurane.

CARDIAC EFFECTS OF ANESTHETIC AGENTS :
Anticholinergic agents – Atropine/glycopyrrolate: will cause an increase in heart rate, contractility, cardiac output and myocardial oxygen consumption. Often there will be no change
in blood pressure and a decrease in right atrial pressure.
Thiopental – Barbiturate
Reduction in blood pressure – peripheral vasodilation is the main action. Compensatory rise in heart rate – barorecptor response. Commonly associated with ventricular arrhythmias .
Benzodiazepines
Midazolam and diazepam: Cause little or no direct myocardial depressant effects.
Hypnotics- Etomidate: no direct myocardial depression. Safe to use with cardiac, critical and septic patients. .
Mu opioids– Fentanyl is a pure mu agonist causes dose dependant bradycardia (increase in vagal tone).
Mixed agonist/antagonist agents= Buprenorphine: a partial mu agonist/antagonist. Slow onset of action, duration of 6-8 hours.

Cardiovascular depression and respiratory depression not as profound as pure mu agonists. Butorphanol: partial agonist/antagonist. Similar to buprenorphine in cardiovascular/respiratory effects.
Dissociative Agents:Ketamine- Heart rate and arterial pressure increase due to an increase in sympathetic tone .
Inhalational Anesthetics:

• Isoflurane and sevoflurane preserved cardiac index, and isoflurane and fentanyl-midazolam preserved myocardial contractility at baseline levels in this group of patients with congenital heart disease.
• Halothane depressed cardiac index and myocardial contractility.

B i.e. Isoflurane

Isoflurane increases ICT but less than halothane & enflurane; which can be reversed by hyperventilation. So isoflurane is a preferable agent in raised ICT. Isoflurane is anaesthesia of choice (AOC) for neurosurgical procedureQ as it does not increase cerebral blood flow & CSF pressure.

Of various inhalation agents available, isoflurane has the advantage of providing stability of cardiac rhythm & lack of sensitizention of the heart to exogenous & endogenous adrenalineQ.

In coronary artery disease isoflurane should be avoided Wt coronary steel phenomenonQ.

In ischemia of cardiac muscle selective vasodialation of vessels of Ischemic zone and maintained tone of non ischemic zone //t selective increase of blood supply to ischemic areas.

But in coronary steal phenomenon (Isoflurane & Dipyridomole) there is dialation of vessels of non ischemic zone also so there is decrease of flow in ischemic zone.Q That is why isoflurane is avoided in ischemic heart disease.

• In Myocardial Infarction operation should be with held for 6 monthsQ.
• Goldman Index is for cardiac risk factor and when it is > 13 it is associated with poor prognosis.
• In hypertension, halothane is AOC (for hypotensive surgery)

In hypovolumia, Light G.A. (preferably Ether and Cyclopropane) with IPPV is method of choice

Isoflurane increases ICT but less than halothane & enflurane; which can be reversed by hyperventilation. So isoflurane is a preferable agent in raised ICT. Isoflurane is anaesthesia of choice (AOC) for neurosurgical procedureQ as it does not increase cerebral blood flow & CSF pressure.

Of various inhalation agents available, isoflurane has the advantage of providing stability of cardiac rhythm & lack of sensitizention of the heart to exogenous & endogenous adrenalineQ.

In coronary artery disease isoflurane should be avoided Wt coronary steel phenomenonQ.

In ischemia of cardiac muscle selective vasodialation of vessels of Ischemic zone and maintained tone of non ischemic zone //t selective increase of blood supply to ischemic areas.

But in coronary steal phenomenon (Isoflurane & Dipyridomole) there is dialation of vessels of non ischemic zone also so there is decrease of flow in ischemic zone.Q That is why isoflurane is avoided in ischemic heart disease.

• In Myocardial Infarction operation should be with held for 6 monthsQ.
• Goldman Index is for cardiac risk factor and when it is > 13 it is associated with poor prognosis.
• In hypertension, halothane is AOC (for hypotensive surgery)

In hypovolumia, Light G.A. (preferably Ether and Cyclopropane) with IPPV is method of choice

B i.e. It is a structural analogue of isoflurane 

Desflurane’s structure is very similar to that of isoflurane. The only difference is substitution of a fluride atom for isofluranes chlorine atom. Q

A i.e. Propofol, Fentanyl, isoflurane

A i.e. Opioids > B i.e. Isoflurane

Anaesthesia in ischemic heart disease

Induction agents

– Propofol, barbiturate, etomidate, benzodiazepines, opioids & combinations are used

Ketamine is relatively contraindicated because its indirect sympathominetic effect can adversely affect the myocardial oxygen demand-supply balance. When combined with a benzodiazepine or propofol, however, ketamine does not appreciably increase sympathetic activity and results in relatively stable hemodynamics with minimal myocardial depression. The combination of benzodiazepine and ketamine may be most useful in patient with poor ventricular function (ejection fraction <30%) and in frail patient with hemodynamic compromise.

High dose opioid anesthesia had previously been used widely for patients with significant ventricular dysfunction4. With the exception of meperidine (in large doses), opioids alone are generally associated with minimal or no cardiac depression. Apparent cardiac depression may also occur wth pure high dose opioid inductions : this likely represents withdraw of an elevated baseline sympathetic tone. Patients with poor ventricular function often rely on an elevated sympathetic tone to maintain their cardiac output & may decompensate even with pure high dose opioid anaesthesia. (That’s why now mixed I.V & inhalation anaesthesia is used) 

Maintenance agents

– Patients are generally managed with n opioid-volatile anaesthetic technique – Patients with ejection fraction < 40% may be very sensitive to the depressant effects of potent volatile agents or large bolus of opioids

– N₂0, Particularly in presence of opioids, can also produce significant cardiac depression

– All volatile agents generally have favorable effect on myocardial oxygen balance, reducing demand more than supply. Isoflurane dilates intramyocardial arteries more than the larger epicardial vessels but there is little evidence that isoflurane causes an intracoronary steal phenomenon in clinical practice.

C i.e. Isoflurane 

–  IsofluraneQ is volatile anesthetic agent of choiceQ in patients with liver disease because it has the least effect on hepatic blood flow.

– CisatracuriumQ is neuromuscular blocking agent of choiceQ owing to its unique non hepatic metabolism.

B i.e. Isoflurane

Ans. c. Isoflurane