SYSTEMIC EFFECTS OF INHALATIONAL AGENTS

SYSTEMIC EFFECTS OF INHALATIONAL AGENTS


Effect on respiratory system:

Bronchodilation: 

  • All inhalational agents.
  • Halothane – Maximum bronchodilatation.
  • DOC in asthmatics (intravenous anesthetics) = Ketamine.

Respiratory depression (minimal):

  • All inhalational agents.
  • Enflurane – Maximum depression.
  • Halothane – Maximum inhibition of ventilatory response to increased CO2 & hypoxia.

Vasodilation:

  • Vasodilate pulmonary vascular bed – All inhalational agents.
  • By blunting hypoxic pulmonary vasoconstriction (HPV) response. 
  • Halothane – Maximum effect; Also by isoflurane

Phosgene production:

  • By Trilene -> Causes ARDS.
Effects on CVS:
Cardiac output: 

  • CO best maintained with isoflurane.
  • Isoflurane – Most cardiostable inhalational agent & agent of choice for cardiovascular surgery.
  • Due to reflex tachycardia acting as protective baroreceptor reflex is minimally inhibited by isoflurane. 

CO decreasing drugs:

  • All inhalational agents decrease CO, except ether & cyclopropane.
  • Cardiovascular stability in decreasing order:Isoflurane (most stable) > desflurane > Sevoflurane > Halothane > Enflurane. 

Baroreceptor reflex:

  • Halothane – Only agent suppressing baroreceptor reflex –> causes tachycardia.

Myocardial contractility:

  • All inhalational agents cause directly depress contractility. 
  • Isoflurane, desflurane & sevoflurane cause minimum depression to similar level.
Systemic vascular resistance (SVR):

  • All inhalational agents decrease –> result in hypotension. 
  • Except cyclopropane, ether, halothane & N20 – Not decrease SVR.
  • Isoflurane, Desflurane & Halothane = Cause maximum hypotension.
  • Isoflurone – Inhalational DOC for controlled hypotension.
  • Note: Halothane causes hypotension by myocardial depression, not decrease SVR.
Cardiac adrenaline sensitization:

  • Halothane – Sensitizes heart to adrenaline –> Results in arrhythmias.
  • Contraindicated in pheochromocytoma along with adrenaline.

Sympathetic stimulation:

  • Cyclopropane & Ether -> maintain CO & not decrease SVR.
  • (Note: Other inhalational agents cause those effects).
Coronary steal phenomenon.

  • By Isoflurane
  • Mainly in patient with coronary artery stenosis.
  • Causes coronary artery vasodilatation in non-ischemic area & diverts blood away from ischemic zone.
  • N20 has no effect on BP, CO HR.

Effect on liver:

Hepatotoxicity:

  • Mild toxicity – All inhalational agents.
  • By decreasing hepatic blood flow.
  • Direct hepatotoxicity (hepatitis, hepatic necrosis)
  • Halothane, chloroform, trilene & methoxyflurane.

DOC in liver disease

  • Isoflurane – Due to least effect on hepatic blood flow.

Effect on kidney:

Renal function depression:

  • All inhalational agents.
  • By decreasing renal blood flow. 

Nephrotoxic agent:

  • Most nephrotoxic – Methoxyflurane causes high output (polyuric) renal failure.
  • Sevoflurane & enflurane – No renal toxicity in normal person; contraindicated in renal patients.
  • By producing nephrotoxic compound A.
  • Desflurane has no nephrotoxicity.

Note: 

  • Direct toxicity caused by fluorinated compounds due to inorganic fluoride (F-) production.
  • Renal threshold beyond which fluoride levels are toxic is 50 mm. 

Effect on Brain:

Increasing ICT:

  • All inhalational agents.
  • By increasing cerebral blood flow –> ICT.
  • Provide cerebral protection by decreasing cerebral metabolic rate.
  • Maximum cerebral protection – Isoflurane.
  • Inhalational DOC for neurosurgery.
  • Enflurane – Provokes seizure.
  • Contraindicated in epilepsy.

Neurotoxicity:

  • Dichloroacetylene involving most commonly 5th CN.

Effect on hematopoietic system:

  • Bone marrow depression (aplastic anemia) & Vit B12 deficiency – By nitrous oxide.
  • Vit B12 deficiency causes megaloblastic anemia & subacute degeneration of spinal cord.

Effect on muscle relaxation & analgesia:

Muscle relaxation:

  • All inhalational agents except N2O. 
  • By neuro-muscular blockade.
  • Maximum relaxation – By ether (unused), desflurane.

Analgesic action:

  • All inhalational agents except halothane.
  • Maximum – Trilene, N2O & ether. 
  • No analgesic action – Halothane.

Effect on uterine relaxation:

  • All fluorinated anesthetics.
  • Halothane (maximum), isoflurane, desflurane, sevoflurane, enflurane.

Halothane:

  • DOC for assisting external or internal version during late pregnancy.
  • Contraindicated during labor 4 – Due to post-partum hemorrhage.

Effect on Inflammability & reaction with sodaline:

Inflammable agents:

  • Ether, Cyclopropane, ethylene oxide, ethyl chloride.
  • Cautery should not be used in vicinity (up to 25 cms).

Inducing inflammability:

  • Agents can be made non-inflammable by adding fluorine atoms.
  • Trichloroethylene (Trilene) & sevoflurane reacts with soda lime -> Not be used in closed (circle) system.

Effect on metabolism:

  • Most inhaled anesthetics are eliminated from lung.
  • Hepatic metabolism also occurs in order:
  • Methoxyflurane (> 50%) > Halothane (20%)> Ether (10 -15%) > enflurane (3-5%) > sevoflurane (3%) > isoflurane (0.2%) > desflurane (< 0.1%) > N20 (0%). 
  • N20 does not have any metabolism in body.
  • Some agent cause hyperglycemia; chloroform (most profound), ether cyclopropane.

Effects on anesthetic circuit:

  • Corroding metals & vaporizing in breathing circuit – Halothane.
  • Halothane & methoxyflurane – Absorbed by rubber of anesthetic circuit & polyvinylchloride of ET tube.
  • Can be used only on replacing plastic tubing.

Exam Important

  • Halothane causes maximum bronchodilatation.
  • DOC in asthmatics (intravenous anesthetics) is ketamine.
  • All inhalational agents vasodilate pulmonary vascular bed, by blunting hypoxic pulmonary vasoconstriction (HPV) response. 
  • Halothane has maximum vasodilatory effect.
  • CO best maintained with isoflurane.
  • Isoflurane is most cardiostable inhalational agent & agent of choice for cardiovascular surgery.
  • Halothane, only agent suppressing baroreceptor reflex –> causes tachycardia.
  • Isoflurane, desflurane & sevoflurane depress myocardial contractility to similar level.
  • Isoflurane is inhalational DOC for controlled hypotension.
  • Halothane sensitizes heart to adrenaline resulting arrhythmias, contraindicated in pheochromocytoma along with adrenaline.
  • Isoflurane causes coronary steal phenomenon.
  • DOC in liver disease is Isoflurane, due to least effect on hepatic blood flow.
  • Direct hepatotoxicity (hepatitis, hepatic necrosis) are caused by Halothane, chloroform, trilene & methoxyflurane.
  • Most nephrotoxic is Methoxyflurane causes high output (polyuric) renal failure.
  • Desflurane has no nephrotoxicity.
  • Sevoflurane & enflurane causes no renal toxicity in normal person;contraindicated in renal patients.
  • Isoflurane provides maximum cerebral protection by decreasing cerebral metabolic rate, hence inhalational DOC for neurosurgery.
  • Enflurane provokes seizure & contraindicated in epilepsy.
  • Nitrous oxide causes bone marrow depression (aplastic anemia) & Vit B12 deficiency.
  • Vit B12 deficiency causes megaloblastic anemia & subacute degeneration of spinal cord.
  • Maximum analgesic action is seen with Trilene & nil analgesic action with halothane.
  • Halothane (maximum), isoflurane, desflurane, sevofluraneenflurane can cause uterine relaxation.
  • Halothane DOC for assisting external or internal version during late pregnancy.
  • Halothane is contraindicated during labor 4 – Due to post-partum hemorrhage.
  • Inflammable agents are ether, Cyclopropane, ethylene oxide, ethyl chloride & cautery should not be used in vicinity (up to 25 cms).
  • Trichloroethylene (Trilene) & sevoflurane reacts with soda lime, hence not be used in closed (circle) system.
  • Most inhaled anesthetics are eliminated from lung.
  • Neurotoxicity is caused by dichloroacetylene involving most commonly 5th CN.
  • Sevoflurane produces nephrotoxic compound A.
Don’t Forget to Solve all the previous Year Question asked on SYSTEMIC EFFECTS OF INHALATIONAL AGENTS
Click Here to Start Quiz

Module Below Start Quiz

Leave a Reply

%d bloggers like this:
Malcare WordPress Security