Conference Lectures
Pitfalls of Total Intravenous Anaesthesia
Dr.Renu Devaprasath,
HOD – Anaesthesia,
Dr.Jeyasekharan Medical Trust,
K.P.Road, Nagercoil.
TIVA is a technique of administering anaesthesia wherein combination of agents are given only by the intravenous(IV) route in the absence of all inhalational agents including Nitrous Oxide. TIVA techniques have been evolving continually and driven by better understanding of the pharmacokinetics of short acting anaesthetic agents and improvements in infusion pump technology TIVA has become popular and almost a mainstream anasthetic in many countries.
TIVA has many potential advantages.
- Rapid Induction of anaesthesia.
- Smooth maintenance of anaesthesia.
- Adequate pain control.
- Rapid emergence and clearheaded recovery
- Significantly reduced incidence of post operative nausea and vomiting [PONV].
- Reduced atmosphere pollution
- Easily titrated with TCI systems.
- Safe in malignant Hyperthermia and Myasthenia Gravis.
- Preserves the Hypoxic Pulmonary Vasoconstriction reflex.
- Reduces ICP if certain drugs are used.
- Can provide adequate depth of anaesthesia without use of muscle relaxants and yet allow Rapid Recovery.
The pharmacokinetic properties of certain aneasthetic drugs like propofol and remifentanyl make them very suitable for administration by continuous infusion. Once these drugs are given intravenously they follow the three compartment model, i.e.,First The Core or Central Compartment which is the blood volume, Second, The Peripheral Compartments, and Third,drug metabolism and elimination. In TIVA a Fourth Compartment is added since anaesthetic depth depends upon the effect - site concentration in the brain. To elaborate further, from the central compartment the drug gets redistributed to the peripheral compartments. Simultaneously metabolism and excretion occur and if,theoretically volumes and metabolism / excretion are known then the central compartment dosing can be predicted over time.
Drugs which are commonly used in TIVA are- Propofol, Remifentanyl, Alfentanyl, Sufentanyl, Ketamine, Dexmedetomidine and muscle relaxants.
It is important to note that it is not the drug concentration in blood which anaesthetises the patient but rather the 'effect site' concentration in the brain.
Currently TIVA, is used extensively in
1. Ambulatory Surgeries
2. Fast Track Anaesthesia
3. Day Care Surgeries
4. Surgeries on the Parotid glands
5. Surgeries on patients with Myasthenia Gravis / Video assisted
Thoracoscopic Thymectomies
6. Patients with Malignant hyperthermia
7. Major abdominal surgeries
8. Bariatric surgeries
9. Other surgical procedures
Even though TIVA, is very popular it is not used by every anaesthesiologist for every surgery. Which sets us thinking about the pitfalls with TIVA.
So, what are the theoretical and practical problems which exist with this technique.
- First and foremost, safe and effective use of TIVA requires the anaesthesiologist to have a sound understanding of the Pharmacokinetics of the drugs involved. In addition the anaesthetist needs to be aware of the Pharmacodynamics of the concerned patient and the varying intensity of the surgical stimulation. Only then, the advantages of TIVA will be available, else the anaesthetic may not be smooth, may be inadequate or toxic doses may be administered. The pitfall is that even though a target concentration in plasma may be obtained by using a Target Controlled Infusion [TCI] it is the concentration at the effect - site, namely the brain,which needs to be achieved. Practically speaking there are instances when the plasma concentration is achieved,but clinically the depth of anaesthesia is yet to be obtained.On the other hand,if the TCI is used to maintain the effect site concentration the haemodynamic consequences may be detrimental.Hence,there is a learning curve and clinical monitoring continues to be important.
- Target controlled infusion [TCI] systems are advisable for administering TIVA and they have an investment cost precluding their use in certain parts of the world.
- Since the delivery of drugs are by infusion via the intravenous route,incorrect dose settings of drugs,displaced cannulae,disconnections, leakages and obstructions at any point in the system can lead to sudden changes in the quality of anaesthesia.
- Inspite of there being theoretical mathematical models on which Drug Doses are based for achieving blood levels of Propofol, Remifentanyl etc.Review of literature shows that cost efficacy and rapid recovery depend more on the patient and the individual perioperative setting than the TIVA concept per se.
- Advances in computer technology and sophisticated delivery systems make control of TIVA straight forward and user friendly for the electronic savvy. The same advantages become handicaps for those anaesthesia practitioners not well versed with electronic equipments.
- The addition of multiple TCI systems for delivering anaesthesia increase the likelihood of error and of the anaesthetist getting distracted by equipments.
- When muscle relaxants are used during TIVA awareness is a possibility since patient movement as a clinical monitoring parameter is lost.This is often overcome by using the relaxant only for intubation.
- Bradycardia and hypotension are frequently noticed side effects of TIVA. The bradycardia is responsive to Atropine but the hypotension is due to the direct vasodilatation effect of the drugs and is patient dependent.
- Post operative analgesia in TIVA depends upon the drugs selected. Sufentanyl provides better post operative analgesia than Remifentanyl. Hence the anaesthetist needs to be sensitive and supplement and / or provide adequate pain relief post operatively based upon the drugs used.
- The TCI systems available allow the anaesthetist to either set a desirable plasma concentration or an effect site concentration. Both have their draw backs mainly because of the time lag between the plasma concentrations equilibrating with the effect site concentration.
- The pharmacodynamic variability observed between patients with respect to drug requirements for different levels of stimuli is 300-400%.This far exceeds the pharmacokinetic variability of 15-20%.
- Remifentanyl,which has the best pharmacodynamic profile amongst the short acting opioids,in the bolus dose of 1 microgram /kg used for induction may cause chest wall rigidity. the other problem is due to it's very short context sensitive half life leading to lack of post operative analgesia.
- Syringe Infusion Pumps play a major role in giving successful TIVA.These are subject to some common problems which must be avoided. Siphoning can be avoided by using a tight fitting syringe and not placing it high up.Backlash needs to be prevented by purging the line. Accidental injection of air can occur due to air being compressible and hence delaying the onset of the alarm.
- Propofol/Remifentanyl- based target controlled general anaesthesia for surgery is associated with a reduced pschomotor function upto the first post operative day.
Inspite of all these pitfalls,TIVA has become a mainstay anaesthetic technique which is being continually researched. Refining Target Controlled Systems,discovering newer drugs and adjuvants and advanced engineering for Automatic drug delivery and monitoring systems may assist in controlling these pitfalls.