Dosage of Foran in details
lsofurane has a slight pungent ethereal odour, which may limit the rate of gas induction but, despite this, induction and particularly recovery are rapid.
The use Foran-specific vaporisers will facilitate accurate control of the administered concentration of anaesthetic.
The minimum alveolar concentration (MAC) the standard measure of potency for anaesthetics is 1.15% in pure oxygen decreasing to 0.5% when given with 70% nitrous oxide for middle-aged humans. There is an age-relationship, the MAC is significantly higher in children and is lower in the elderly.
Premedication: Premedication drugs should be selected according to the needs of the patient. The ventilatory depressant effect of Foran should be taken into account. Anticholinergic drugs (eg, atropine, glycopyrrolate USP) may be used for their effects in drying oral secretions (antisialogogue) at the discretion of the anaesthetist, but they may enhance the weak effects of Foran in increasing heart rate.
Induction: As Foran has a mild pungency, inhalation should usually be preceded by the use of a short-acting barbiturate or other IV induction agent, to prevent coughing. Salivation and coughing may be troublesome in small children induced with Foran. Alternatively, Foran with oxygen or with an oxygen/nitrous oxide mixture may be administered. It is recommended that induction with Foran be initiated at a concentration of 0.5%. Concentrations of 1.5-3% usually produce surgical anaesthesia in 7-10 min. Blood pressure decreases during induction but this may be compensated by surgical stimulation.
Maintenance: Adequate anaesthesia for surgery may be sustained with an inspired lsoflurane concentration of 1-2.5% in an oxygen/70% nitrous oxide mixture. Additional inspired Foran (0.5-1%) will be required with lower nitrous oxide levels, or when Foran is given with oxygen alone or with air/oxygen mixtures. Blood pressure decreases during maintenance anaesthesia in relation to the depth of anaesthesia. That is, blood pressure is inversely related to the Foran concentration. Provided there are no other complicating factors, this is probably due to peripheral vasodilation. Cardiac rhythm remains stable. Excessive falls in blood pressure may be due to the depth of anaesthesia and in such circumstances can be corrected by reducing the inspired Foran concentration.
Induced hypotension can be achieved by artificially ventilating patients with Foran 2.5-4%. Pretreatment with clonidine significantly decreases the Foran requirement for maintaining induced hypotension.
Recovery: The concentration of Foran can be reduced to 0.5% at the start of closing the operation wound and then to 0% at the end of surgery, provided that the anaesthetist is satisfied that the effect of any neuromuscular blocking drugs has been reversed and the patient is no longer paralysed. After discontinuation of all anaesthetics, the airways of the patient should be ventilated several times with oxygen 100% until complete recovery.
Foran interactions
Muscle Relaxants: Foran produces sufficient muscle relaxation for some intra-abdominal operations. It is compatible with all commonly used muscle relaxants, the effects of which may be markedly potentiated by Foran. The effect is most notable in nondepolarising agents, thus lower doses should be used in the presence of Foran. The effect of nondepolarising muscle relaxants can be counteracted by administering neostigmine as this has no effect on the relaxant properties of Foran.
Adrenaline: Administration of adrenaline (epinephrine) by any route during Foran anaesthesia may cause supraventricular or ventricular arrhythmias. Where adrenaline is used, the amount used should be limited to a maximum of 3 mg/kg of body weight in patients with normal hearts and less in those with rhythm disturbances.
Concurrent use of other β-sympathomimetic drugs eg, amphetamines may predispose to arrhythmias. If possible, interrupt treatment a few days before surgery.
Calcium Antagonists (and Other Vasodilators): Foran can cause marked hypotension in patients receiving concomitant therapy with calcium antagonists, especially those of the dihydropyridine class. Patients receiving chronic therapy with other vasodilators eg, ACE inhibitors (eg, captopril, enalapril, lisinopril) or α1-adrenoceptor antagonists (eg, prazosin), may show unpredictable hypotension with any type of anaesthesia. Monoamine Oxidase Inhibitors (MAOI): Beta-Blockers:
Isoniazid: Isoniazid induces enzymes. Patients receiving isoniazid may be more susceptible to hepatotoxicity from volatile anaesthetics. If possible, cease isoniazid treatment 1 week before surgery. Opioid Analgesics:
References
- DailyMed. "ISOFLURANE: DailyMed provides trustworthy information about marketed drugs in the United States. DailyMed is the official provider of FDA label information (package inserts).". https://dailymed.nlm.nih.gov/dailyme... (accessed September 17, 2018).
- MeSH. "Anesthetics, Inhalation". https://www.ncbi.nlm.nih.gov/mesh/68... (accessed September 17, 2018).
- European Chemicals Agency - ECHA. "Isoflurane: The information provided here is aggregated from the "Notified classification and labelling" from ECHA's C&L Inventory. ". https://echa.europa.eu/information-o... (accessed September 17, 2018).
Reviews
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Information checked by Dr. Sachin Kumar, MD Pharmacology
