Boyle Department of Anaesthesia, St Bartholomew Hospital, West Smithfield, London EC1A 7BE, UK
* Corresponding author. E-mail: vmehta1971{at}hotmail.com
Accepted for publication April 25, 2004.
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Abstract |
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Keywords: arteries, cannulation ; complications, catheter misplacement ; complications, hyperkalaemia ; ions, potassium
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Introduction |
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Case report |
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Before the blood sample results were available, anaesthesia was induced with propofol and alfentanil i.v.. Pancuronium was given and the trachea intubated. The internal jugular vein was cannulated.
The arterial blood sample showed a potassium concentration of 9.3 mmol litre1. The ECG did not show signs of hyperkalaemia, and other observations were normal (Table 1). The blood potassium value was suspected to result from a fault in analysis. Another sample (sample 2) was obtained from the radial arterial cannula and analysed with a different apparatus, which gave a potassium value of 8.4 mmol litre1. The patient's vital signs and ECG remained unchanged. Two further samples were obtained simultaneously from arterial and venous cannulae and analysed on the first analyser. The arterial sample value was 7.4 mmol litre1 (sample 3) and the venous sample value was 4.4 mmol litre1 (sample 4). We suspected haemolysis had been caused by malposition of the arterial cannula. The cannula was slightly withdrawn. A further sample was obtained (sample 5), which gave a potassium concentration of 4.1 mmol litre1, and further blood samples obtained from the cannula had expected potassium values.
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Discussion |
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We suggest that in this patient the tip of the cannula could have impinged against the vessel wall so that red blood cells were damaged when a blood sample was obtained. During withdrawal of the sample, a high shear rate caused by narrowing of the cannula orifice or lumen could have caused haemolysis leading to an increased potassium concentration in the blood samples.
A high shear rate and static pressure can damage erythrocytes.5 A positive static pressure of 600 mm Hg alone did not cause haemolysis, but shear rates of 500 s1 and greater caused haemolysis with a static pressure of 0 mm Hg.5
We found hyperkalaemia with two different analysers. Arterial and venous samples obtained simultaneously and analysed on the same analyser showed that the samples had different values and that equipment failure was not possible.
Systemic hyperkalaemia caused by heparin is a rare but recognized complication and has been described during cardiopulmonary bypass.6 However, this was not the cause in our patient who was subsequently fully anticoagulated with heparin without hyperkalaemia.
A badly positioned aortic cannula during cardiopulmonary bypass has been described in a child, resulting in hyperkalaemia and renal failure.7
After we suspected the possible cause of hyperkalaemia, we repositioned and adjusted the arterial cannula and repeatedly flushed it with heparinized saline. Subsequent sampling gave satisfactory results. No harm came to the patient. Red cell haemolysis can be measured using a haemorheologic assay that includes estimates of erythrocyte mechanical fragility, plasma total protein and fibrinogen concentrations, blood viscosity, and free haemoglobin.8 We could not use these measures to confirm our suspicions of the cause of hyperkalaemia in this case, but they should be considered if haemolysis is suspected to be caused by hyperkalaemia. Awareness of this complication of arterial cannulation should prevent inappropriate therapy to adjust potassium concentration. Abnormal values in a sample from a cannula after difficult cannula insertion should be held in suspicion, and a venous sample should be withdrawn to check the analysis.
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References |
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7 Murukami J, Yamura K, Akata T, Takahashi S. Acute renal failure in an infant attributable to arterial cannula malposition during cardiopulmonary bypass via ministernotomy. Jpn J Anaesthesiol 2002; 51: 2649
8 Kameneva MV, Marad PF, Brugger JM, et al. In vitro evaluation of haemolysis and sub lethal blood trauma in a novel subcutaneous vascular access system for haemodialysis. ASAIO J 2002; 48: 348[ISI][Medline]
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