Prevention of irrigating fluid absorption during transurethral resection of the prostate.

This thesis contains studies on the prerequisites for fluid absorption during transurethral resection of the prostate (TURP) and suggestions on its prevention. The pressure gradient bladder-prostatic fossa to pelvic veins and its relation to fluid absorption were studied in patients using a sensitive detection technique with a radionuclide. It is concluded that to prevent fluid entering the vascular system, the bladder pressure should be kept below the pressure in the pelvic veins. The physical properties of the irrigating jet of resectoscopes were investigated in model experiments including an artificial, "bleeding" prostatic fossa. The dynamic pressure of the jet amounts to only 1-3% of the driving head and thus is of marginal importance in fluid absorption. The effect of various flow rates on the optical field was also demonstrated. In patients with prostatism epidural and spinal analgesia increased the bladder capacity but always with a corresponding increase in bladder pressure. In a preliminary study a correlation was found between the minimum urethral resistance and the compliance of the detrusor during epidural analgesia. This may suggest a relation between prostatic obstruction and changes of the viscoelastic properties of the bladder wall. The effects of various irrigating flow rates on the pressure-volume response of the bladder and its relation to the pressure in the pelvic veins was also investigated. From this study it was concluded that the detrusor response was unaffected by flow rates used during TURP. The critical bladder pressure above which fluid is absorbed changed with the position of the patient. In the Trendelenburg (20 degrees) position it was 0.25 kPa (approximately equal to 2.5 cmH2O), increasing to 1.25 kPa in the horizontal and 1.75 kPa in the half-sitting (20 degrees) position. To prevent absorption bladder pressure must be monitored. A simple pressure warning device with an adjustable warning level and which can be combined with any irrigating technique is presented. Irrigation with a large driving head may thus be combined with a low pressure resection.