What is the 10 8 6 Rule for Propofol?
The 10 8 6 rule for propofol, also known as the Roberts or Bristol regimen, is a historical manual dosing scheme for administering propofol during total intravenous anesthesia (TIVA). This technique was developed to approximate the stable blood concentration of propofol that could be achieved with more sophisticated computer-controlled pumps. It is a manually controlled, step-down infusion scheme designed to account for the redistribution of propofol from the central compartment (blood) to peripheral tissues over time.
The rule suggests a specific sequence of steps for adult patients undergoing general anesthesia:
- Initial Administration: An initial amount is given to rapidly induce unconsciousness and help achieve a therapeutic blood level.
- Initial Infusion Rate: An initial infusion rate is started immediately after the first administration and maintained for a set period. This rate is intended to help counteract the initial rapid redistribution of propofol out of the blood and into well-perfused tissues.
- Second Infusion Rate: After the initial period, the infusion rate is decreased for another set period. This adjustment accommodates the continued redistribution of the drug.
- Subsequent Infusion Rate: After a total specified time, the infusion is further reduced and maintained at this rate for the remainder of the anesthetic. This lower rate is intended to help maintain the steady-state plasma concentration once the slower redistribution phases are active.
The Pharmacokinetic Basis for the Rule
The rationale behind the 10-8-6 rule lies in the multi-compartmental pharmacokinetics of propofol. When propofol is first injected, it rapidly distributes from the blood (the central compartment) to highly vascular organs like the brain, potentially causing an anesthetic effect. However, the drug also begins to distribute to less vascular, peripheral compartments such as muscle and fat. This redistribution from the central compartment can cause the blood concentration to change, and without continued infusion, the anesthetic effect might diminish.
By stepping down the infusion rate, the 10-8-6 rule aims to help counteract these shifts in drug concentration. The initial high infusion rates are intended to compensate for the rapid redistribution, while the progressively lower rates are intended to help maintain the target plasma concentration as the body approaches a steady state. This manual approach was a significant innovation before the widespread availability of computer-controlled infusion pumps (TCI).
How the 10-8-6 Rule Compares to Modern Methods
The 10-8-6 rule was a valuable tool for decades, especially in settings where advanced equipment was not available. However, it is a simplified model that does not account for individual patient variability. Modern anesthesia has largely shifted towards more precise methods, such as Target-Controlled Infusion (TCI) systems.
Manual Infusion (10-8-6 Rule) vs. Target-Controlled Infusion (TCI)
| Feature | Manual Infusion (10-8-6 Rule) | Target-Controlled Infusion (TCI) |
|---|---|---|
| Mechanism | Relies on pre-programmed, timed step-downs to adjust for propofol's pharmacokinetic profile. | Uses a computer algorithm to continuously calculate and adjust the infusion rate based on the patient's individual factors. |
| Precision | Less precise due to fixed infusion rates at set time intervals. Can potentially lead to periods of over- or under-dosing. | High precision, as the pump adjusts the infusion rate in real-time (e.g., every 10 seconds) to help maintain a specific target plasma or effect-site concentration. |
| Adaptability | Not designed to be adaptable to individual patient variations in drug clearance, age, or weight without manual clinician adjustment. | Designed to be highly adaptable, potentially using patient data (e.g., age, weight, sex) to tailor the infusion, which may lead to greater stability and fewer complications. |
| Equipment | Typically requires a standard infusion pump and manual adjustments by the clinician. | Requires specialized, computer-controlled infusion pumps. |
| Potential for Error | Higher potential for human error due to manual calculation and adjustment of infusion rates. | Lower potential for manual calculation errors; however, requires careful setup and programming. |
| Hemodynamic Stability | Can potentially result in more pronounced hemodynamic changes, such as hypotension, especially in sensitive patients. | Generally designed to provide more stable hemodynamics due to smoother, more controlled administration. |
Limitations and Considerations for Patient Care
While the 10-8-6 rule provided a valuable framework, its broad application without considering key physiological factors can potentially lead to complications.
- Patient Variability: Factors such as age, body habitus, and co-morbidities significantly influence propofol pharmacokinetics. The elderly, for example, may have reduced clearance and be more sensitive to propofol's effects, potentially requiring adjustments. The 10-8-6 rule, as a standard, does not automatically account for these individual differences.
- Pediatric Dosing: The rule is not considered suitable as a standard for pediatric patients, who have different metabolic rates and volume compartment distributions compared to adults. Separate approaches, which may be based on manual infusion principles, exist for children and require careful consideration.
- Adverse Effects: Propofol, when not precisely managed, can cause significant side effects. The potential for variations in administration with manual techniques might increase the risk of adverse events like hypotension, respiratory depression, and apnea. In cases of prolonged administration, a rare but potentially fatal condition known as Propofol Infusion Syndrome (PRIS) is a concern, though it is often associated with high infusion rates.
Conclusion
The 10 8 6 rule for propofol was a foundational technique in the history of manual total intravenous anesthesia, providing a structured approach to help maintain a steady plasma concentration through a stepped-down infusion rate. Its development was a crucial step towards understanding the complex pharmacokinetics of propofol and potentially enabling safer administration. However, with the advent of sophisticated computer-controlled infusion systems (TCI), manual techniques like the 10-8-6 rule are less common in modern routine practice. While it serves as a valuable teaching tool, TCI generally offers superior precision and adaptability, which may minimize the risk of over- or under-dosing and potentially improve patient safety and hemodynamic stability. Clinicians must always consider individual patient factors and utilize appropriate monitoring and technology to ensure the best possible outcomes. A pivotal study discussing aspects of this manual scheme was published in the British Journal of Anaesthesia.(https://pubmed.ncbi.nlm.nih.gov/3259089/)
