Oliguria in a surgical patient

1. Applied Sciences Lecture Course Oliguria in a surgical patient Mahesh Nirmalan MD, FRCA, PhD Consultant, Critical Care Medicine Manchester Royal Infirmary

2. Case history 1 A 68 years old; open repair of a 7cm diameter infra-renal aortic aneurysm; 2litre blood loss; transfused 5 Units of packed red cells; duration of the surgery was 250 minutes; admitted to ICU post-op; mechanically ventilated. Hourly urine output was approximately 15-20 ml.hr-1 for 8 hours. What are your initial thoughts and considerations?

3. Case History 2 70 Years old female Radical Cystectomy Difficult dissection due to adhesions 4 hour procedure 1 litre blood loss In ward…….called to review 5 hours post surgery No urine output since surgery What are your initial thoughts and considerations?

4. When managing a patient with reduced urine output after major surgery your first response should be: • Give fluids • Give diuretics • Give dobutamine • Give vasopressors • None of the above

5. PRE POST Parenchymal organ

6. New problems Exacerbation of pre-existing problems Systematic approach to oliguria • Pre renal causes • Renal flow, perfusion pressure • Renal causes • Acute tubular necrosis(ATN) • Neprotoxicity • Post renal causes • Obstruction: ureters, bladder, prostate, urethra, catheter

7. GFR UOP = Volume filtered at the glomerulus – Volume reabsorbed by the renal tubules GFR Vs Clearance

8. What is the relationship between Mean Arterial Pressure (MAP) and urine output in a patient?

9. RBF→ GFR→UOP Vs MAP • RBF= 25% of cardiac output • Way in excess of metabolic needs • Marked regional differences • Cortices: luxury perfusion • Medullary flow is low: why? • Autoregulation of RBF and GFR • UOP is proportional to the MAP Regulation curve is shifted to the right in patients with chronic hypertension

10. Renal blood supply Cortical Vs Juxtamedullary nephrons

11. Pressure diuresis and pressure natriuresis • Auto-regulation of GFR is not absolute • Small differences in GFR leads to large differences in UOP • Increased venous pressure in the vasa-recta • Reduced production of angiotensin

12. Cardiac output Peripheral vascular resistance Contractility Effective Blood volume Vascular tone Reduction in MAP is the most frequent cause for reduced UOP in the immediate peri-operative period.

13. Renal perfusion pressure Net Filtering pressure Cardiac output or Renal blood flow Afferent & Efferent Vascular Tone Direct and Indirect effects Other than reduced MAP what other physiological factors may account for reduced UOP in the above patient?

14. Net filtering pressure • Afferent arteriolar constriction reduces NFP • Pain • Hypovolaemia • Anxiety

15. Cardiac Output Effective Renal Functions MAP Local Glomerular Factors

17. 500 ml “Gelafusine” fluid challenge

18. What do you think of the choice of a colloidal solution and the volume (500ml) that was used during the above fluid challenge?

19. Colloids vs crystalloids and tissue oxygen tension after major abdominal surgery *p < 0.05 vs HES group Lang et al. Anesth Analg 2001;93:405–9

20. Glomerulo-Tubular Feedback Renin-Angiotensin system Myogenic autoregulation How is auto-regulation of glomerular filtration rate achieved?

21. Angiotensin II Flow rate in loop of Henle Macula Densa NaCL Glomerular Hydrostatic pressure Glomerular Filtration Pressure Na Cl resorption Arterial Pressure Renin Afferent arteriole Resistance GFR Efferent Arteriole Resistance

22. Glomerulo-tubular feed back

23. If the patient complained of severe pain, would you consider the use of nonsteroidal anti-inflammatory drugs?

24. Which is the correct statement: Most non-steroidal anti-inflammatory drugs: • Increase the synthesis of prostaglandins • Increases the conversion of arachidonic acid into prostaglandins and thromboxane • Act as non selective COX inhibitors • Act as selective COX-1 inhibitors • Act as selective COX-2 inhibitors

25. The functions of the kidneys • Excretion of metabolic waste • Regulation of water and electrolyte balance • Regulation of ECF volume and osmolality • Regulation of arterial pressure: Long and short term • Regulation of Acid-base balance • Hormones: secretion, metabolism and excretion • Gluconeogenesis

26. Glomerular Filtration Tubular Re-absorbtion Pre-Renal MAP CO Post-renal Blocked catheter Retention Damage to ureters Renal Renal parenchymal damage Pre-existing Acquired during the peri-operative period Sepsis Neprotoxic agents “Acute Tubular necrosis” Very Rarely the primary cause of the problem in the immediate post-operative period Urine production

27. Thank you