CICM SAQ 2010.1 Q12

Question

12. A 68 year old man had both legs trapped under a heavy concrete slab for 4 hours. He has just been admitted to the ICU, 8 hours post injury, following adequate resuscitation and definitive operative wound debridement. His observations are that he is fully conscious, his blood pressure is 110/70 mmHg, pulse 86 beats/min and respiratory rate 24 breaths/min. He is anuric, and has been for the past 3 hours.

Relevant blood results at that time are:

12.1. In reference to the above results, what does the raised creatine kinase indicate and how would this affect the kidney?

12.2. You initiate CVVHDF in this patient. Following 24 hours of renal replacement therapy, you become concerned that you are not achieving optimal solute clearance. The dialysis settings are as given:

  • Blood Flow: 80 mls/min
  • Replacement fluid (post filter): 1000 mls/hr
  • Dialysate fluid: 1000 mls/hr
  • Effluent flow: 2000 mls/hr
  • Fluid removal: zero

(a) What changes would you make to these settings so as to enhance solute clearance?

12.3. An alarm has sounded on the dialysis machine. Access pressures are high. How would you respond to this problem?

12.4. Briefly outline the relationship between dose of dialysis and outcome


Answer

Answer and interpretation

12.1. In reference to the above results, what does the raised creatine kinase indicate and how would this affect the kidney?

  • Rhabdomyolysis secondary to crush injury
  • Direct injury from myoglobin (direct tubular toxicity/obstruction) and other haem related compounds and indirectly via hypovolaemia/shock (pre renal).

12.2. (a) What changes would you make to these settings so as to enhance solute clearance?

  • Increase blood flow, replacement fluid, dialysate and effluent flows
  • change replacement fluid to be pre filter

12.3. An alarm has sounded on the dialysis machine. Access pressures are high. How would you respond to this problem?

Check and manipulate vascular access

  • Malposition (catheter tip, sucking against vessel wall) and kinking (subclavian)
  • Change in patient position – side/supine/sitting
  • Site of catheter-  e.g. sitting up –femoral access problems
  • Type of catheter – geometry, length, diameter
  • Negative intrathoracic pressure – high intraabdominal pressures
  • Hypovolemic patient –poor flow
  • Catheter occlusion / thrombosis

12.4. Briefly outline the relationship between dose of dialysis and outcome

Candidates were not expected to list all of the literature but an understanding that this remains a controversial area – credit was given if they quoted relevant studies.

Although several clinical trials have suggested an improvement in survival with higher doses of CRRT results have not been consistent across all studies. To date five randomised trials have assessed the relationship between intensity of CRRT in terms of effluent flow rate and outcomes of acute kidney injury.

  • Ronco (Lancet 2000) and Saudan (Kid Int 2006) found that lower doses around 20 -25ml/kg/hr were inferior in terms of survival to higher effluent flows of around 35 to 45 mls/kg/hr.
  • Two other studies Bouman (Crit Care Med 2002) and Tolwani (J Am Soc Nephrol, 2008) however found no difference in survival with higher effluent rates.
  • The latest study (NEJM 2008, VA/HIH acute renal failure Trial Network or ATN study) found that mortality at 60 days was no different between two intensity arms. In the less intensive arm both IHD and SLED were used as standard practice of thrice per week and CVVHDF effluent flow at 20 mls kg hr. In the more intensive arm IHD and or SLED were used six times per week and CVVHDF at an effluent flow rate of 35ml kg hr.
  • The ANZICS CTG RENAL study just completed (25 v 40 ml kg hr). No difference in mortality between the two groups, a higher incidence of hypophosphatemia in the higher dose group.

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Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also the Innovation Lead for the Australian Centre for Health Innovation at Alfred Health and Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of two amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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