The Science Journal of the American Association for Respiratory Care

2008 OPEN FORUM Abstracts

URINARY OXYGEN TENSION (PUO2) AS A TOOL FOR THE ASSESSMENT OF RENAL FUNCTION IN CRITICALLY ILL CANCER PATIENTS RECEIVING MECHANICAL VENTILATION: A CASE SERIES

Laura G. Withers1, Diego H. de Villalobos1, Shubhra Ghosh1, Clarence G. Finch1, Kristen J. Price1



Introduction: Mechanically ventilated critically-ill patients frequently develop ischemic injury as a consequence of hypoxemia. Kidneys have a high metabolic demand and need for oxygenation and are therefore very sensitive to changes in oxygen supply. More than 20% of the entire cardiac output flows through the kidneys every minute. However, even though the blood in the renal vein is oxygen -rich, the renal medulla is relatively hypoxemic. Therefore any compromise in the renal oxygen supply (e.g. in shock) has serious ramifications on the renal function. It has been shown that renal function is optimal in most people when the mean arterial pressure (MAP) is maintained within 65 - 70 mm Hg. Currently, a variety of tests are used for assessment of renal function ranging from the inexpensive but late markers including serum creatinine (Cr)/blood urea nitrogen (BUN)/electrolytes (which become abnormal after >60% of kidney function is lost) to accurate but invasive glomerular filtration rate (GFR), and expensive real-time renal ultrasounds requiring a radiologist.

Urinary oxygen tension (PuO2) is the partial pressure of oxygen in urine. In healthy adults, bladder urine PuO2 has been measured to be in the range of 25 - 80 mm Hg depending on hydration and diet. Since the renal function is largely dependent on its oxygen demand and supply, can the fluctuation of PuO2 therefore be utilized to assess renal function? If so, it could provide us with a relatively non-invasive, inexpensive tool to follow renal function in cases of suspected renal injury.

Case series Summary: Bladder urine PuO2 was measured via a probe inserted in foley's catheter in 3 critically ill cancer patients in acute respiratory failure requiring mechanical ventilation. The measured bladder urine PuO2, PaO2 and MAP are shown in figure 1. The electrolytes were within normal ranges in all cases. The titration of MAP closest to 65-70 mm Hg range was associated with PuO2 values in the range of 98 - 124 mm Hg. The changes in PuO2 did not coincide with changes in PaO2.

Discussion: In these three case studies, the PuO2 was observed to vary with changes in the MAP, BUN and GFR. Further studies on the use of PuO2 as a monitoring tool for assessment of organ function in critically ill patients are warranted since it is a relatively non-invasive, almost real-time and inexpensive tool.