Chapter 3
SPECIAL FUNCTIONS
Hint: It is possible to start a therapy in continuous mode and switch over to
PCA later on (in case the drug is dedicated for use with continuous and PCA application).
3.5 Target Controlled Infusion (TCI)
Introduction
In TCI the user is defining a desired concentration of drug in the human body
(target) rather than an infusion rate. The rates necessary to reach and maintain that said concentration are calculated by the pump using an algorithm based on a three-compartment pharmacokinetic model.
A pharmacokinetic model (PK model) is a mathematic model to predict the concentration of a drug in the human body (e.g. plasma level) after a bolus or a continuous infusion of different duration. A PK model is developed by measurement of plasma level values of a population of patients or volunteers and the respective statistical analysis. A PK model mostly is a 2- or 3- compartment model indicating the volumes of the compartments, indicating rates for the exchange amongst the compartments and indicating rates for elimination / metabolism of the drug.
A PK model can be parameterized to use it for different drugs as long as it is suitable for that said drug. The pharmacokinetic model and its parameters are schematically depicted by the following illustration:
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Chapter 3
SPECIAL FUNCTIONS
B. Braun Space is offering two modes for TCI:
•
TCI by targeting the plasma concentration
In this mode the user selects the desired concentration of a drug in the blood plasma and the PK model is used to calculate the infusion rates required to achieve that concentration as quick as possible (unless there is no restriction defined by the user).
• TCI by targeting the effect-site concentration
In this mode the user selects the desired concentration of a drug at the site of action and the PK model is used to calculate the infusion rates required to achieve that concentration as quick as possible (unless there is no restriction defined by the user). A certain overshoot of the concentration in the plasma is resulting from this mode.
For effect-site targeting there is a link between pharmacokinetics and pharmacodynamics necessary. As the effect-site compartment is considered to have no volume and the rate constant k
1e can be ignored the rate constant k e0 is the parameter necessary to perform effect-site TCI. A pharmacokinetic model modified in such way is schematically depicted by the illustration on the next page.
Chapter 3
SPECIAL FUNCTIONS
TCI with B. Braun Space is possible with two drugs: Propofol and Remifentanil.
For Propofol the user can choose between two parameter sets. The parameter sets used for these drugs are (Not all parameter sets allow effect-site targeting):
Drug / Parameter
V
1
[Litre] k k k k k k
10
12
13
21
31 e0
[min
[min
[min
[min
[min
[min
-1
-1
-1
-1
-1
-1
Reference
]
]
]
]
Effect-site targeting
]
]
0,228 * Weight
0,119
0,112
0,0419
0,055
0,0033
0,26
Marsh et al., Br. J.
Anaesthesia, Vol.
67, 1991, 41-48
No
Propofol
4,27
0,443 + 0,0107 * (Weight -
77) - 0,0159 * (LBM - 59) +
0,0062 * (Height - 177)
0,302 - 0,0056 * (Age - 53)
0,196
[1,29 - 0,024 * (Age - 53)] /
[18,9 - 0,391 * (Age - 53)
0,0035
0,456
Schnider et al., Anesthesiology, Vol. 88, 1998, 1170-
1182 Schnider et al.,
Anesthesiology, Vol. 90,
1999, 1502-1516
Yes
Remifentanil
5,1 - 0,0201 * (Age - 40) +
0,072 * (LBM - 55)
[2,6 - 0,0162 * (Age - 40) +
0,0191 * (LBM - 55)] / [5.1 -
0.0201 * (Age - 40) + 0.072 *
(LBM - 55)]
[2,05 - 0,0301 * (Age - 40)] /
[5.1 - 0.0201 * (Age - 40) +
0.072 * (LBM - 55)]
[0,076 - 0,00113 * (Age - 40)] /
[5.1 - 0.0201 * (Age - 40) +
0.072 * (LBM - 55)]
[2,05 - 0,0301 * (Age - 40)] /
[9,82 - 0,0811 * (Age - 40) +
0,108 * (LBM - 55)]
0.01402 - 0,0002085 *
(Age -40)
0,595 - 0,007 * (Age - 40)
Minto et al., Anesthesiology,
Vol. 86, 1997, 10-33
Yes
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Chapter 3
SPECIAL FUNCTIONS
Drug List
The pre-installed drug list offers the following values:
Available Concentrations
Short name
Default Max. Rate
Hard Limit Rate
Plasma Limit Default
Plasma Limit Hard Low
Plasma Limit Soft Max
Default Target
Target Soft Max
Target Hard Max
Decrement Concentration
Default
Default Parameter Set
Propofol
5 mg/ml
10 mg/ml
20 mg/ml
TCIProp
1.200 ml/h
Max of pump
400 %
100 %
450 %
0.0 µg/ml
8.0 µg/ml
15.0 µg/ml
1.0 µg/ml
Marsh
20 µg/ml
50 µg/ml
Remifentanil
TCIRemi
1.200 ml/h
Max of pump
400 %
100 %
450 %
0.0 ng/ml
8.0 ng/ml
20.0 ng/ml
1.0 ng/ml
Minto
Important note: Before installing an additional drug list please contact your local
B. Braun representative!
Setting up the pump
For TCI a drug list with at least one drug activating the profile TCI is necessary. The drug list in this version is pre-defined. By this the conditions for an effective and safe therapy are defined.
Switch on pump with o and wait until self-check is finished. Insert disposable and use the drug lib according to Instructions for Use.
Selecting a drug
Select drug list, category (the TCI drugs need to be selected from the category “TCI”) and desired drug by using q .
In this example: Propofol.
Chapter 3
SPECIAL FUNCTIONS
As a next step select the correct dilution (concentration) of the drug to be administered as well as the parameter set (model) and the Mode
(Effect-Site Targeting or Plasma
Targeting)
These steps are only necessary in case there are different options for that drug.
Input of patient data
Depending on the parameter set one or more of the following data are necessary:
• Weight
•
Height
• Gender
•
Age
Use q for editing the patient data.
Example.
The editing window appears with the initial setting “0” to make sure editing a value takes place (exemption: initial setting for gender is “male”).
Using effect-site targeting the weight may be limited due to the constraints of the
LBM calculation.
Important notes:
• Be sure to enter the data corresponding to the respective patient.
•
Once the TCI is started patient data can not be altered!
Editing a target and starting TCI
The editor window for setting the target comes up with the default value from the drug list.
Editing this parameter is guided by the dose error reduction system
“DoseGuard™” according to the limits defined in the drug list.
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Confirm target with k
. TCI can be started now with s
.
After TCI is started the screen looks the following:
Mode-Indicator
Drug short name
Current plasma an effect-site concentration Target and unit
In the top line there is an icon indicating the parameter set and the mode (Mode Indicator) with following meaning:
• “TCI Ma P”: TCI Marsh plasma targeting
•
“TCI Sc P”: TCI Schnider plasma targeting
• “TCI Sc E”: TCI Schnider effect-site targeting
•
“TCI Mi P”: TCI Minto plasma targeting
• “TCI Mi E”: TCI Minto effect-site targeting
In the bottom line the status parameters like flow rate, Cp/Ce, infused volume etc. can be displayed. The desired parameter can be selected by using t
. It is recommended to select Cp/Ce.
In case it is necessary to change the target press l to edit the value.
Useful information while pump is running
By pressing r additional information can be requested.
Pressing r a second time is offering a graphical overview.
The line describes the course of Cp over the time and the area describes the course of
Ce over the time. The time window is 20 min (15 min past, 5 min future).
Additional information is left with C .
