History
A 74-year-old man has been referred to the emergency department following an assess-ment by his GP, who found him to be unable to get out of his chair and with a slow heart rate of 30/min. He has had a bout of diarrhoea and vomiting over the past couple of days.
Examination
On arrival an ECG is performed (Fig. 61.1). A chest X-ray shows cardiomegaly but clear lung fields. His jugular venous pulse (JVP) is visible 3 cm above the sternal angle with occasional cannon waves. He has dry mucous membranes. He has a midline sternotomy scar. The apex beat is displaced and the impulse diffuse. Heart sounds show a soft pan-systolic murmur at the apex. On chest auscultation there are no crackles. Abdominal examination is normal. His ankles are not swollen. He cannot lift his legs off the bed and is generally weak. He has ischaemic heart disease, having had a coronary artery bypass graft one year ago. His other medical history is hypertension, hypercholesterol-aemia, type 2 diabetes, gout, benign prostatic hyperplasia (BPH) and congestive heart failure. He has had no chest pains over the last year, although his exercise tolerance is limited to 40 metres on the flat and he has difficulty going up a flight of stairs due to breathlessness. He lives on his own in a flat, mobilizing with a frame. He is on aspirin, bisoprolol, ramipril, spironolactone, bumetanide, atorvastatin, omeprazole, metformin and allopurinol. He has no allergies. He does not smoke or drink alcohol. Observations:
temperature 36.4°C, blood pressure 156/78 mmHg, respiratory rate 18/min, SaO2 94 per cent on room air.
Figure 61.1
White cells 10.0 4–11 ¥ 109/L
Haemoglobin 13.3 13–18 g/dL
Platelets 199 150–400 ¥ 109/L
Sodium 145 135–145 mmol/L
Potassium 7.9 3.5–5.0 mmol/L
Urea 32 3.0–7.0 mmol/L
Creatinine 245 60–110 mmol/L
Venous blood gas pH 7.35 7.35–7.45
Questions
• What is the main life-threatening abnormality, given the biochemistry and ECG find-ings?
• What are the potential causes of this?
• How should this patient be further investigated and treated?
143
ANSWER 61
The main blood abnormality is hyperkalaemia. The level of 7.9 mmol/L is very high and this is the likely cause of his muscle weakness and complete heart block (shown on the ECG and indicated clinically by the bradycardia and cannon waves). He also has renal impairment.
Hyperkalaemia has several causes, so focusing investigations is crucial to allow timely and appropriate treatment. Often a combination of underlying problems may be the cause. In this case the most important to consider are:
• worsening chronic kidney disease;
• drug-related;
• obstruction;
• cardio-renal syndrome;
• volume depletion.
Urgent investigations should include a renal ultrasound scan to look for obstruction causing hydronephrosis. It will also help to assess renal size and give an indication as to whether there is likely to be pre-existing chronic renal impairment. A venous blood gas will show if there is metabolic acidosis. Although he has congestive heart failure he has no signs of it at present. He is likely to be dehydrated from the recent diarrhoea and vomiting.
He is on multiple medications that can cause hyperkalaemia directly or indirectly.
Spironolactone is a potassium-sparing diuretic and can raise potassium in some people who are sensitive to this drug. Ramipril can cause hyperkalaemia and in states of volume depletion from recent diarrhoea and vomiting this is exacerbated. Bumetanide, a loop diuretic, will exacerbate volume depletion but tend to lower serum potassium. Heart fail-ure is linked to renal impairment: the relationship is complex and it is known that one exacerbates the other. This phenomenon is termed cardio-renal syndrome.
Management should be based on the immediate need to lower his potassium level and treat his complete heart block. An assessment should be made of haemodynamic stability.
If he shows signs of hypotension or heart failure or reduced consciousness, he should be given atropine 500 mg intravenously to try to increase the heart rate. Further doses can be administered to a maximum of 3 mg. Isoprenaline infusion is a useful drug to use. If these measures do not work he will need initiation of transcutaneous pacing with a view to inserting a temporary pacing wire.
Ten per cent calcium chloride or gluconate should be given intravenously as soon as possible. Calcium works by stabilizing the cardiac sarcolemmal membrane, but its effects wear off in minutes so repeated doses may be necessary. Intravenous insulin/dextrose should be commenced to drive the potassium into cells; repeated doses are often required.
He is clinically dehydrated and fluid resuscitation should also be administered; normal saline is an appropriate fluid. A fluid challenge can be administered to determine the effect on blood pressure and urine output. He has a history of congestive cardiac failure, so careful fluid resuscitation is important. To help assess fluid balance, a central venous line may be required. He should be admitted to the intensive-care unit or coronary unit for continuous cardiac monitoring. If potassium is not improving with insulin/dextrose and fluid resuscitation, he requires renal replacement therapy.
Once potassium levels start to come down his rhythm may return to normal. Also his renal function should improve with fluids as this episode is likely to have been
precipi-lactic acidosis in the setting of significant renal failure.
Significant hyperkalaemia is defined as K >6 mmol/L, while moderate hyperkalaemia is 5–6 mmol/L; all levels above 6 should be treated. Treatment should be given between 5 and 6 if associated with ECG changes. ECG changes in hyperkalaemia include early changes (peaked T waves, shortening of the QT interval and ST segment depression). Later changes are widening of the QRS complex, prolongation of the PR interval and eventual loss of P waves. Eventually the QRS complex widens further to appear as a sine wave. At this point ventricular fibrillation or asystole can follow. However, any arrhythmia can be caused, including various degrees of AV block.
KEY POINTS
• Hyperkalaemia is life-threatening. When found, an ECG must be performed in all cases.
• Hyperkalaemia has many causes and the diagnosis is based on a focused history, examination and appropriate investigations.
145