Microdialysis calibration

MenacherryS, Hubert W, Justice JB Jr. 1992. In vivo calibration of microdialysis probes for exogenous compounds. Anal Chem 64(6) 577-583. 

Calibration is necessary to allow correlation between collected dialysis concentrations to external sample concentrations surrounding the microdialysis probe. Extraction efficiency (EE) is used to relate the dialysis concentration to the sample concentration. The steady-state EE equation is shown in equation (6.1), where Coutiet is the analyte concentration exiting the microdialysis probe, Ci iet is the analyte concentration entering the microdialysis probe, CtiSSue> is the analyte tissue concentration far away from the probe, Qd is the perfusion fluid flow rate and Rd, Rm, Re, and Rt are a series of mass transport resistances for the dialysate, membrane, external... 

For any implanted device that is intended for long-term use, collagen encapsulation of the device will occur due to the immune response to the device.60 Collagen deposition typically begins at roughly 5-7 days postimplantation and takes up to a month to reach completion. In terms of calibration of the microdialysis probe, this layer of material will provide additional mass transport resistance and could be denoted as a trauma layer. 

Adipose tissue poses additional calibration differences for microdialysis sampling devices. The thickness of the tissue (e.g., lean versus obese individuals) and thus the capillary density will affect interindividual microdialysis sampling recovery values. This has been shown by Lutgers et al., who demonstrated decreases in glucose recovery of up to 50% between human volunteers with a skin fold thickness of 20 versus 45 mm.65 This points to how microdialysis sampling recovery is dependent upon analyte supply since glucose will be supplied better to the microdialysis probe in lean individuals with a higher density of capillaries per unit tissue than obese subjects with a lower density of capillaries and thus an increased mass transfer resistance to the probe. Additional reports have also shown less interindividual differences between microdialysis probes implanted in the forearm versus in the subcutaneous tissue.66... 

No Net Flux/Zero Net Flux Calibration The most time intensive of all the in vivo microdialysis calibration methods is the method of no net flux (NNF), which is sometimes referred to as the method of zero net flux (ZNF). The NNF calibration method requires the analyte to be in a steady state. So, for healthy... 

Stenken JA. Methods and issues in microdialysis calibration. Analytica Chimica Acta 1999, 379, 337-357. 

Wang Y, Wong SL, Sawchuk RJ. Microdialysis calibration using retrodialysis and zero-net flux application to a study of the distribution of zidovudine to rabbit cerebrospinal fluid and thalamus. Pharmaceutical Research 1993, 10, 1411-1419. 

Bouw MR, Hammarlund-Udenaes M. Methodological aspects of the use of a calibrator in in vivo microdialysis—further development of the retrodialysis method. Pharmaceutical Research 1998, 15, 1673-1679. 

Strindberg L, Lonnroth P. Validation of an endogenous reference technique for the calibration of microdialysis catheters. Scandinavian Journal of Clinical and Laboratory Investigation 2000, 60, 205-212. 

Sorg BS, Peltz CD, Klitzman B, Dewhirst MW. Method for improved accuracy in endogenous urea recovery marker calibrations for microdialysis in tumors. Journal of Pharmacological and Toxicological Methods 2005, 52, 341-349. 

Brunner M, Joukhadar C, Schmid R, Erovic B, Eichler HG, Muller M. Validation of urea as an endogenous reference compound for the in vivo calibration of microdialysis probes. Life Sciences 2000, 67, 977-984. 

In many cases, however, if only the monitoring of changes in concentration of a given analyte is of interest, determination of the absolute concentration may not be necessary and simpler calibration methods can be applied. For example, when microdialysis is used for monitoring the concentration of a substance in blood, the dialysate concentration may be calibrated against blood concentrations, assuming that there is a linear relationship between the dialysate and blood concentration. This approach has been used for subcutaneous glucose sensors [64,65]. 

Third, an in vitro calibration, which does not necessarily provide a good estimate of the recovery in vivo, was used for the microdialysis probe. In vitro calibration is only an approximate calibration technique because it does not always accurately represent what is happening in vivo. In addition, the efficiency of the microdialysis probe can change over time as the biological surroundings adjust to the presence of the probe. A final cause for the discrepancy could be due to the method of sampling for the conventional analysis. Because blood samples were taken from the rat, fewer samples could be taken within a given time. 

L Hernandez, NA Guzman, BG Hoebel. Bidirectional microdialysis in vivo shows differential dopaminergic potency of cocaine, procaine and lidocaine in the nucleus accumbens using capillary electrophoresis for calibration of drug outward diffusion. Psychopharmacology 105 264-268, 1991. 

A very promising and even more expanding field of application was opened up more than 15 years ago by the microdialysis technique, which is the most widely used dialysis technique in bioanalytical and clinical chemistry. The main advantages are in situ sampling, in situ calibration, and avoiding the influence of complex samples matrices on to the indicator reaction. Table 2 summarizes the application areas. Miniaturized dialysis probes with tip diameters smaller than 1mm are implanted into different... 

---