TIVA can reduce the need for volatile anesthetics.
It can provide improved control over depth of anesthesia.
Reduced PONV
Decreased risk of postoperative nausea and vomiting.
Faster Emergence
Quicker recovery times compared to inhalation agents.
Hemodynamic Stability
Reduced cardiovascular depression during maintenance phase.
Pharmacokinetic and Pharmacodynamic Differences in Children
Pharmacokinetics:
Distribution:
Children have higher body water and lower body fat. This can lead to a larger central compartment (V1). Higher doses may be needed to reach the target plasma concentration. Neonates and infants may have immature organ function, affecting clearance.
Metabolism & Clearance:
Clearance is usually higher per kilogram in children. This is due to faster metabolic rates in school-age children. Neonates and infants exhibit slower clearance and prolonged half-life.
Context Sensitive Half-Time:
The active duration after infusion varies by age. In older children, it may be shorter versus adults. In neonates/infants, the drug may linger longer due to enzyme immaturity.
Pharmacodynamics:
Receptor Sensitivity:
Children may show sensitivity differences in GABA or opioid receptors. Dose-response curves can therefore differ. Propofol’s dose-response curve in adults may be more pronounced in young children.
Clinical Response:
Rapid anesthesia is desired in pediatric patients. However, overshooting is a risk, resulting in excessive sedation. Prolonged recovery may also occur.
Variability:
Greater interpatient variability is common in neonates and infants. Close monitoring and frequent adjustments are required.
Relevance of TIVA in Pediatrics
Advantages
TIVA provides smooth recovery, a key benefit in pediatric anesthesia.
- Reduced postoperative nausea.
- Less agitation.
- Improved patient comfort.
It's useful when volatile agents are not ideal.
Challenges
Manual dosing can be difficult in pediatrics. PK changes with age/size.
Monitoring limitations persist in younger children. Clinical judgment remains key.
Administering TIVA in Pediatric Cases
Calculate Dose
Determine the correct induction dose. Refer to age-specific guidelines for dosing.
Start Infusion
Begin infusion at the initial rate. Closely monitor sedation depth and hemodynamics.
Adjust Intervals
Progress through time intervals, reducing rate as recommended. Follow the schedule diligently.
Monitor Patient
Monitor depth and adjust rate. Maintain cardiorespiratory surveillance during the infusion.
Neonate to 3 years
Age 3-11 years.
Example Scenario: TIVA in a 2-Year-Old
This is an example of how to administer TIVA in a 2-year-old child (10 kg) undergoing a procedure.
Induction
Administer a propofol bolus of 30 mg IV slowly (3 mg/kg × 10 kg).
First 10 Minutes
Start infusion at 120 mg/h (12 mg/kg/h × 10 kg). Reassess depth and vitals at ~5 minutes.
10–20 Minutes
Decrease to 90 mg/h (9 mg/kg/h × 10 kg). Adjust if needed.
20–30 Minutes
Lower to 60 mg/h (6 mg/kg/h).
30–40 Minutes
Maintain 6 mg/kg/h or further reduce to 5 mg/kg/h if appropriate.
TIVA in Obese Patients
Weight-based dosing may overestimate required dose in obese patients. Consider lean body mass for calculations. Adjust based on clinical response and monitoring.
Reduced Clearance
Adipose tissue leads to altered drug distribution and clearance. This can result in prolonged drug effects.
Loading Dose
Use a smaller loading dose initially. Titrate carefully to avoid oversedation.
Maintenance Infusion
Reduce maintenance infusion rates. Regularly assess sedation depth and adjust accordingly.
Pharmacokinetic Differences in Obese Patients
Changes in Distribution
Increased fat mass leads to a larger volume of distribution for lipophilic drugs.
This can cause prolonged drug effects if dosing is not properly adjusted.
Altered Clearance & Metabolism
Obese patients often have altered hepatic blood flow and enzyme activity.
Use lean body weight during bolus for a more accurate dosing basis to avoid overdosing.
Context Sensitive Half-Time
Drugs may take longer to eliminate due to the larger adipose-rich compartment.
Prolonged infusions may delay recovery, so carefully monitor obese patients.
Manual vs. TCI Infusion in Obese Patients
Manual Infusion
Doses are based on adjusted or lean body weight. Start with a higher infusion rate, then gradually reduce. Frequent reassessment is required.
- Calculate bolus dose (1–2 mg/kg LBW).
- Start infusion, adapting the “12‑10‑6 rule according to LBW.”
- Reduce dose gradually based on monitoring.
Limitations: Challenging due to variability.
TCI Infusion
TCI allows precise dosing via individualized data and automatic corrections. It reduces the risk of oversedation or delayed recovery.
- Input patient data (LBW, age, height).
- Use Schnider (effect-site) or Eleveld.
- Set target Propofol (3–4 µg/ml).
Limitations: Models have less validation.
TCI Infusion Approach
Patient Data
Input lean body weight, age, height, and gender into the TCI pump.
Schnider Model
Use for effect-site targeting. It adjusts for age and lean body mass.
Eleveld Model
An alternative across a wide spectrum, including obese patients.
Target Concentration
Set effect-site concentration of Propofol to 3–4 µg/ml.
TIVA Dosing in Obese Patients
*Values are starting points using weight adjustments. Adjust based on clinical monitoring.
LBW and ABW Calculations
Lean Body Weight (LBW)
LBW formulas estimate body mass, excluding excess fat. The James and Janmahasatian formulas are common. Choose Janmahasatian for obese patients. Accurate dosing ensures optimal drug effect and minimizes the risk of toxicity. LBW provides a more reliable estimate of metabolically active tissue compared to total body weight, especially in individuals with a high proportion of adipose tissue.
James Formula
Separate formulas for men and women, incorporating TBW and height. Less accurate in extremely obese patients. The James formula, while widely used, may overestimate LBW in obese individuals, potentially leading to excessive drug administration. It is essential to consider the limitations of this formula, especially when dealing with patients at the extremes of the weight spectrum. The James formula is as follows:
- Men: LBW = (1.1 x weight(kg)) - (128 x (weight(kg) / height(cm))
- Women: LBW = (1.07 x weight(kg)) - (148 x (weight(kg) / height(cm))
Janmahasatian Formula
Uses TBW and BMI. More robust across a wider range of BMI values. Use this to dose obese patients. The Janmahasatian formula incorporates body mass index (BMI) to improve accuracy across diverse body compositions. This is particularly useful in obese patients where the relationship between weight, height, and lean mass is less predictable. It is also useful for calculating the dose required.
- Men: LBW = 9.27 x 10^2 x weight(kg) / (6.68 + (21.6 x BMI))
- Women: LBW = 9.27 x 10^2 x weight(kg) / (6.68 + (21.6 x BMI))
TIVA in the Elderly:
Introduction
TIVA provides benefits. These include smooth induction and rapid recovery.
Elderly Patients
They have comorbidities. There is decreased organ reserve and altered body composition.
Anesthetic Goals
Safe, effective anesthesia is required. Optimize drug choices and dosing.
Pharmacokinetic Differences in the Elderly
Distribution Changes
Reduced total body water decreases distribution volume for hydrophilic drugs. Increased fat leads to a larger volume for lipophilic drugs like propofol.
Metabolism and Clearance
Reduced liver and kidney function slow drug clearance. This necessitates lower doses to avoid oversedation and delayed emergence.
Context-Sensitive Half-Time
Reduced clearance prolongs the context-sensitive half-time. It is important to carefully reduce the infusion rate towards the end of surgery.
Pharmacodynamic Considerations in the Elderly
Increased Sensitivity
Elderly patients have greater sensitivity to anesthetics. Changes in receptor density and function cause this.
Hemodynamic Response
The elderly often show a blunted cardiovascular response. Small dose increases may cause hypotension.
Neurocognitive Effects
The elderly are at higher risk of POCD. Monitor depth of anesthesia to avoid deep sedation.
Dosing Strategies for TIVA in the Elderly
Manual Infusion Approach
Reduce the induction bolus to 1–1.5 mg/kg of propofol. Use ideal or adjusted body weight.
Modify the "12-10-6 rule." Start at lower rates. Reduce by 20–30% compared to younger adults.
Start with a lower infusion rate. Use BIS to monitor. Adjust infusion rates in small increments.
TCI Infusion Approach
Use models like Schnider or Eleveld. They adjust for age and lean body mass.
Carefully enter age, height, weight, and gender. Set lower target concentrations.
TCI automates titration and provides gradual changes. It reduces overdosage risk. Manual adjustments may be needed.
Practical Clinical Tips for TIVA in the Elderly
Monitoring is Key
Use depth-of-anesthesia monitors and blood pressure monitoring.
Start Low, Go Slow
Begin with lower doses than younger patients. Increase cautiously.
Hemodynamic Management
Prepare to use fluids, vasopressors if blood pressure drops.
Recovery Planning
Anticipate a prolonged recovery. Avoid over-sedation. Reduce POCD risk.
Key Differences & Dosing Recommendations
TIVA Algorithm for Elderly Patients
Elderly patients require special consideration when administering TIVA due to altered pharmacokinetics and increased sensitivity.
Pre-Induction Assessment
Evaluate cardiac function, renal status, and cognitive baseline. Consider reduced doses for patients >75 years.
Initial TCI Settings
Start propofol at 1-2 μg/ml effect-site concentration (30-40% reduction from standard adult dose).
Opioid Administration
Reduce remifentanil to 0.05-0.1 μg/kg/min or target 1-2 ng/ml if using TCI (50% reduction).
Titrate to Effect
Maintain BIS between 50-65 (higher than younger adults). Increase in 0.2-0.5 μg/ml increments.
Hemodynamic Management
Maintain MAP within 20% of baseline. Reduce propofol if hypotension occurs.
TIVA in Pregnant Women
Unique Challenges
Balance maternal safety and fetal well-being is key. Minimize drug transfer to the fetus.
Avoid Inhalational Agents
Inhalational agents may cause uterine relaxation. They could affect fetal oxygenation.
Precise Control
TIVA provides precise control over anesthesia depth. This is important during C-sections.
Rapid Recovery
Faster recovery aids maternal-fetal bonding. It supports immediate post-operative care.
Physiological Changes Affecting PK/PD in Pregnancy
Pharmacokinetic Changes
- Increased blood volume dilutes drug concentrations.
- Altered body composition affects drug distribution.
- Variable hepatic metabolism affects drug clearance.
- Increased renal clearance eliminates drugs faster.
Pharmacodynamic Changes
- Receptor sensitivity may be altered in pregnancy.
- TIVA drugs minimize fetal exposure due to rapid clearance.
- Maintain anesthesia depth to avoid maternal awareness.
Dosing Strategies for TIVA in Pregnant Women
Manual Infusion: Propofol Bolus
Administer 1.5–2 mg/kg based on ideal body weight. Adjust for increased cardiac output.
Manual Infusion: Maintenance
Use a step-down approach, like 12-10-6 mg/kg/h, adjusted to maternal response.
Manual Infusion: Opioids
Remifentanil at 0.05–0.1 µg/kg/min for analgesia. Titrate carefully.
TCI Model Selection
Use Schnider or Eleveld for propofol. Account for maternal changes.
TCI Target Concentration
Propofol target around 3–4 µg/ml. Remifentanil around 2–3 ng/ml.
Advantages of TCI in Pregnancy
TCI offers precise control. It helps quickly achieve desired anesthesia depth.
It reduces dosing errors versus manual infusion. Automated systems enhance safety.
TCI allows for smooth emergence. This is vital for maternal recovery and fetal safety.
Clinical Monitoring and Maternal-Fetal Considerations
Hemodynamic Monitoring
Monitor heart rate and blood pressure continuously. Invasive monitoring for high-risk cases.
Anesthesia Depth
Use BIS to maintain optimal anesthesia depth. Avoid over-sedation.
Fetal Monitoring
Monitor fetal heart rate if possible. Especially during C-sections.
Recovery Management
Expect rapid recovery due to drug clearance. Ensure maternal and neonatal stability.
Example Table: TIVA Dosing for Pregnant Women
Overview of MAC Using TIVA
Precise Titration
TIVA allows fine control of sedative and analgesic agents during MAC.
BIS Monitoring
BIS helps quantify sedation depth, ensuring optimal patient comfort and safety.
Optimal Balance
The goal is to maintain patient comfort while preserving airway reflexes.
Sedation Levels: Dosing and BIS Correlation
Sedation during MAC should reach specific levels. These include minimal, moderate, and deep sedation.
During minimal sedation, patients are relaxed and cooperative. Moderate sedation means the patient is sedated but responsive.
Deep sedation involves the patient being asleep with minimal response. Airway assistance may be needed.
- Minimal sedation: BIS ~80–90
- Moderate sedation: BIS ~60–80
- Deep sedation: BIS ~40–60
BIS values from EEG help monitor the sedation level. This helps ensure patient comfort and safety.
Practical Dosing Table for MAC Using TIVA
The table below lists typical infusion rates. It includes propofol and remifentanil during MAC. Propofol values are shown in µg/kg/min and mg/kg/h.
Why TCI Is Superior for MAC
Precision
TCI pumps use models and patient data. Infusion is smoother, with fewer changes.
Targeting
TCI maintains target effect-site concentration. It correlates with the sedation level better.
Workload
Automated adjustments reduce manual changes. This minimizes dosing errors and enhances safety.
Dynamic Response
TCI adjusts for changes in drug distribution. It offers safety and comfort to the patient.
Manual infusion is an option if TCI is not available. Vigilant monitoring is still needed.
TIVA for Monitored Anesthesia Care (MAC)
Set Appropriate Targets
Start propofol at lower effect-site concentration (0.5-1.0 μg/ml) for conscious sedation.
Titrate Carefully
Increase in 0.2 μg/ml increments. Allow 2-3 minutes between adjustments for equilibration.
Monitor Sedation Level
Maintain BIS between 65-80 for sedation. Ensure patient remains responsive to verbal commands.
Adjust for Procedural Stimulation
Add low-dose remifentanil (0.025-0.05 μg/kg/min) for painful procedures.
Prepare for Recovery
Reduce target concentration gradually. Expect prompt emergence with minimal residual sedation.
TIVA in ASA III Patients
Appropriateness
TIVA can be given to seriously ill patients whose systemic disease is not a constant threat to life (ASA III).
Drug Sensitivity
Pharmacokinetics and pharmacodynamics will be affected; ill patients are more sensitive to anaesthetic medication.
Protocol Adaptation
No specific protocols exist, but the algorithm for elderly patients can be adopted as both describe reduced drug concentration and dosage.
Monitoring Considerations
BIS may decrease during hypotensive episodes due to hypo-perfusion of the brain. Always keep BIS < 65 and propofol concentration > 1.2 µg/ml.
Relevance of TIVA in Pediatrics