STVARNI VOLUMEN TJELESNE VODE U BOLESNIKA LIJEČENIH PERITONEALNOM DIJALIZOM

Marko Jakić

Sažetak. Volumen tjelesne vode (VTV), jednak volumenu raspodjele ureje (VRU), bitan je u procjeni doze dijalize iz klirensa ureje bolesnika liječenih peritonealnom dijalizom. Pouzdano se određuje samo praćenjem koncentracije vode obi¬lježene tricijem ili deuterijem u plazmi ispitanika. To nisu rutinske metode i umjesto njih rabi se niz alternativnih metoda ili mnoge antropometrijske formule, kojima se VTV pokušava odrediti iz tjelesne težine i visine bolesnika, njegove dobi i spola. Relativno su jednostavne, ali ne uvijek pouzdane. U ovom radu cilj nam je bio praćenjem VTV-a u bolesnika liječenih peritonealnom dijalizom, određenog najčešće korištenom Watsonovom formulom, iz razdoblja dok su bili liječeni ovom metodom i nakon prijelaza na hemodijalizu, odnosno nakon što su bili transplantirani, pokazati da je njihov VTV značajno veći od dobivenog formulom. Neposredno prije prijelaza na hemodijalizu ili neposredno prije transplantacije bubrega 39 bolesnika (14 žena, 25 muškaraca) imalo je, s trbuhom bez dijalizata prosječno 74,60±12 kg, a prema Watsonovoj formuli 37,90±5,80 litara tjelesne vode. U prvih mjesec dana nakon zamjene dijalitičke metode svi su smanjili tjelesnu težinu, prosječno za 3,35±2,55 kg. Prosječna tjelesna težina iznosila je tada 71,25±11,45 kg, a VTV 36,80±5,50 litara. Razlike tjelesne težine i VTV-a nisu bile statistički značajne (ttjelesna težina=1,25, ttjelesna voda=0,84, p>0,05). Gotovo je sigurno da je do smanjenja tjelesne težine u promatranom razdoblju došlo zbog eliminacije nakupljene tekućine. To nadalje znači da su bole¬snici liječeni peritonealnom dijalizom imali, neposredno prije prijelaza na hemodijalizu ili neposredno prije transplantacije bubrega, prosječno 3,35±2,55 litara tjelesne vode više od volumena dobivenog Watsonovom formulom te da njihov VTV nije bio 37,90±5,80 (50,80±7,75% tjelesne težine) nego 41,25±6,85 litara (55,16±9,15% tjelesne težine). Prema t-testu proizlazi da je njihov tadašnji stvarni VTV bio statistički značajno viši od dobivenog formulom (t=2,39, p<0,05), za 8,83%, da je za približno isti postotak lažno viši dobiveni Kt/V i da je onda i smanjenje VTV-a, nakon zamjene peritonealne dijalize bilo statistički značajno (41,25±6,85:36,80±5,50 litara; t=3,20, p<0,01). U zaključku možemo reći da retrogradna pro¬cjena VTV-a u bolesnika liječenih peritonealnom dijalizom pokazuje da je i VTV određen najpoznatijom antropometrij¬skom formulom značajno podcijenjen, a klirens ureje iz istog razloga precijenjen.

Summary. Body water volume (BWV) equals urea distribution volume (UDV), crucial for accurate calculation of dialysis dosage from urea clearance in patients treated with peritoneal dialysis. BWV is precisely determined only by monitoring tritium – or deuterium – labeled water concentration in patient plasma. These are not routine methods, thus a number of alternative methods and anthropometric formulas have been used instead trying to determine BWV from patient body weight and body height, age and sex. These methods are relatively simple but not fully reliable. In the present study, BWV being mostly determined by use of Watson formula at the time of peritoneal dialysis and upon switching to hemodialysis¬ or undergoing kidney transplantation, was monitored in peritoneal dialysis patients to demonstrate that it significantly exceeded the value obtained by the formula. Immediately before switching to hemodialysis or undergoing kidney transplantation, 39 patients (14 female, 25 male) without dialysate in the abdomen had a mean body weight of 74.60±12 kg and mean BWV of 37.90±5.80 L according to Watson formula. In the first month of switching to another dialysis method, all patients reduced their body weight by a mean of 3.35±2.55 kg. Now, their mean body weight was 71.25±11.45 kg and mean BWV 36.80±5.50 L. However, differences in the mean body weight and BWV did not reach statistical significance (t body weight=1.25; t body water=0.84; p>0.05). The body weight reduction during the period of observation could have almost certainly been ascribed to the accumulated fluid elimination. This in turn implies that immediately before switching to hemodialysis or undergoing kidney transplantation, peritoneal dialysis patients had a total body water greater by a mean of 3.35±2.55 L than the figure obtained by Watson formula. Thus, their BWV was not 37.90±5.80 L (50.80±7.75% of body weight) but 41.25±6.85 L (55.16±9.15% of body weight). According to t-test, then their true BWV statistically significantly (by 8.83%) exceeded the figure yielded by the formula (t=2.39; p<0.05), the Kt/V was falsely higher by approximately the same percentage, and the BWV reduction upon switching from peritoneal dialysis to another dialysis method or undergoing kidney transplantation was statistically significant (41.25±6.85 vs. 36.80±5.50 L; t=3.20; p<0.01). In conclusion, retrograde assessment of BWV in patients treated by peritoneal dialysis showed the BWV calculated by the most widely used anthropometric formula to be considerably underestimated and urea clearance overestimated for the same reason.