7.21: Hypokalaemia
- Page ID
- 60136
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Hypokalaemia is a serum potassium less than 3.5 mmol/l.
Causes
It can occur from increased gastrointestinal loss (poor diet, nasogastric suctioning,diarrhoea and vomiting), increased renal loss (including diuretics, renal tubular disease, excess steroid) or from a shift of potassium into the cells (such as respiratory and metabolic alkalosis, insulin effect and hyperaldosteronism).Common causes include patients with diarrhoea and vomiting and patients receivingdiuretics.Potassium is mostly intracellular and maintained by the sodium/potassium pump.(Only 2% of potassium is extracellular). Uptake of potassium into the cell is increased by insulin, adrenaline and aldosterone. Uptake is decreased by acidosis. The usual potassium requirement is approximately 1 mmol/kg/day.Mild hypokalaemia is a serum potassium less than 3.0 mmol/l (or less than 3.4 mmol/L if the patient is receiving digoxin. Digoxin toxicity will worsen if combined with hypokalaemia). Severe hypokalaemia is a serum potassium less than 2.5 mmol/l.
Clinical Signs and Symptoms
Clinical signs and symptoms of hypokalaemia are uncommon unless there is a rapid fall in serum potassium or severe hypokalaemia.ECG abnormalities include small or inverted T wave, increased U wave, prolonged PR interval and ST segment depression. Arrhythmias and asystole can occur.Patients may develop muscle weakness, hypotonia, cramps and tetanus. There may be increased sensitivity to neuromuscular blocking drugs. Gastrointestinal activity is reduced and patients may develop an ileus.
Management
Rapid replacement of potassium may cause more problems than the hypokalaemia .Elective surgery can proceed if the serum potassium is greater than 3.0 mmol/l and there are no ECG changes, the patient has no symptoms of hypokalaemia and the patient is not receiving digoxin.Elective surgery should be delayed if the serum potassium is less than 3.0 mmol/l or there are ECG changes, or the patient is symptomatic or if the patient is taking digoxin. The patient be should be treated with oral potassium.For urgent surgery if the serum potassium is less than 2.6 mmol/l, the hypokalaemia should be corrected by intravenous potassium. (Potassium must be replaced as slowly as possible and the patient must be monitored with an ECG and repeated serum potassium test. If time, try to correct the potassium deficit over 24 hours. Aim to give1.5 to 2.0 mmol/kg/day (ideally less than 10 mmol/h and less than 200 mmol/24 hours). For extremely urgent cases with severe hypokalaemia, the rate of potassium replacement may be increased. Potassium infusion should not exceed 30 mmol/h.Potassium should be diluted to 60 mmol/l and infused though a central vein(maximum rate 30 mmol/h) or large peripheral vein (maximum rate 5 mmol/h).