Hypochloraemic Metabolic Alkalosis

Also known as: Hypochloremic alkalosis

Hypochloraemic metabolic alkalosis is a raised bicarbonate with a low chloride, most characteristically arising from loss of gastric hydrochloric acid through vomiting or nasogastric aspiration, or from loop and thiazide diuretic use.

Two mechanisms sustain it, and understanding both explains why treatment is what it is. The initial event generates the alkalosis; but the kidney would normally excrete excess bicarbonate rapidly, so the alkalosis only persists because something maintains it; usually chloride depletion, volume depletion, hypokalaemia, or mineralocorticoid excess.

Correcting the maintenance factor, principally by replacing chloride and volume, is therefore the treatment, rather than attempting to give acid.

The classic clinical picture is the patient with prolonged vomiting or gastric outlet obstruction, who is volume deplete, hypochloraemic, hypokalaemic and alkalotic, and who has a paradoxical aciduria : an acidic urine despite systemic alkalosis, because avid sodium reabsorption in the volume-deplete state obligates hydrogen ion excretion.

Venous or arterial blood gas showing raised pH and raised bicarbonate, with an appropriate compensatory rise in PaCO₂ (roughly 0.7 mmHg for each 1 mmol/L rise in bicarbonate)
Electrolytes showing low chloride and, characteristically, low potassium
Urine chloride is the single most useful discriminating test, and is preferred to urine sodium, which is unreliable in alkalosis because bicarbonate excretion obligates sodium loss:
- Urine chloride below 20 mmol/L ; saline-responsive: vomiting, nasogastric aspiration, prior diuretic use, post-hypercapnia. These correct with chloride and volume replacement
- Urine chloride above 20 mmol/L ; saline-resistant: current diuretic use, hyperaldosteronism, Cushing's syndrome, Bartter and Gitelman syndromes, severe potassium depletion. These do not correct with saline and require treatment of the underlying cause
Assess volume status clinically, since it drives both diagnosis and treatment
Consider surreptitious vomiting or diuretic use where the cause is not apparent, and hyperaldosteronism where alkalosis coexists with hypertension and hypokalaemia
Magnesium, which is frequently low and impairs potassium correction

Saline-responsive (low urine chloride):

Intravenous 0.9% saline is the treatment, restoring both volume and chloride, and allowing the kidney to excrete the excess bicarbonate. This is the one setting where the high chloride content of normal saline is an advantage rather than a drawback
Potassium chloride replacement, which is almost always required and which corrects both the hypokalaemia and part of the chloride deficit. Alkalosis will not fully correct while potassium remains depleted
Replace magnesium, without which potassium correction fails
Treat the cause: antiemetics, management of gastric outlet obstruction, and review of nasogastric losses with appropriate replacement

Saline-resistant (high urine chloride):

Saline will not correct the alkalosis and risks volume overload; treat the underlying cause instead
Review and adjust diuretics; potassium-sparing diuretics such as spironolactone or amiloride are useful where diuretic-induced alkalosis must be managed alongside continued diuresis
Acetazolamide promotes bicarbonate excretion and is useful particularly in diuretic-associated alkalosis in patients who cannot tolerate a saline load, such as those with heart failure
Investigate and treat hyperaldosteronism or Cushing's syndrome
Correct profound potassium depletion, which can itself maintain alkalosis

Severe alkalosis (pH above approximately 7.55) may warrant more aggressive measures, including hydrochloric acid infusion via a central line in extremis, or haemodialysis, though these are rarely needed and should involve critical care.

Referral: nephrology for saline-resistant alkalosis or suspected tubular disorders; endocrinology for hyperaldosteronism; surgery for gastric outlet obstruction.

Clinical toolsCalculators

BMI GCS EDD Parkland Formula

Corrected Sodium Corrected Calcium Anion Gap Creatinine Clearance Insulin Calculations qSOFA Wells PE Wells DVT CHA₂DS₂-VASc HAS-BLED CURB-65 Centor/McIsaac

Indications for Dialysis

Also known as: Renal replacement therapy

Dialysis is a renal replacement therapy used to remove waste products, correct electrolyte and acid base derangement, and manage fluid balance when native kidney function is insufficient to do so, whether in the context of acute kidney injury or end stage chronic kidney disease.

The two principal modalities are hemodialysis, in which blood is circulated through an external filter against a dialysate fluid across a semipermeable membrane, typically performed several times weekly in a dialysis unit or, in selected patients, at home, and peritoneal dialysis, in which the patient's own peritoneal membrane serves as the filtering surface, with dialysate instilled into and drained from the peritoneal cavity, typically performed daily at home either manually or via an automated overnight cycler.

The indications for urgent dialysis in acute kidney injury are commonly recalled using the mnemonic AEIOU, reflecting the specific, time critical complications that dialysis is used to correct when they fail to respond to medical management.

Acidosis, specifically severe metabolic acidosis that is refractory to medical correction, is an indication, since uncorrected severe acidosis carries significant cardiovascular and metabolic risk.

Electrolyte abnormality, most commonly severe or refractory hyperkalemia not adequately controlled by medical measures (calcium, insulin and glucose, salbutamol, potassium binders), is one of the most common acute indications given the immediate arrhythmic risk of significant hyperkalemia.

Intoxication with a dialyzable substance, such as certain overdoses (for example lithium, salicylates, or methanol and ethylene glycol among others), is an indication where dialysis can meaningfully accelerate toxin clearance.

Overload of fluid, causing pulmonary edema refractory to diuretic therapy, particularly in an oliguric or anuric patient where diuretics have limited further effect, is an indication.

Uremia, specifically the clinical complications of uremia rather than a biochemical urea level in isolation, including uremic encephalopathy, uremic pericarditis, and significant uremic bleeding tendency, is an indication, since these represent the clinical manifestations that dialysis is specifically intended to reverse.

Dialysis initiation in progressive chronic kidney disease is generally guided by a combination of eGFR trajectory and the development of specific symptoms or complications, rather than by an eGFR threshold in isolation, since the timing of initiation based on symptoms rather than a fixed number has been shown not to disadvantage patients and avoids unnecessarily early initiation.

Indications include the same AEIOU categories as above when they occur in the context of progressive, irreversible chronic kidney disease rather than resolving acute injury, alongside the development of significant uremic symptoms (nausea, anorexia, pruritus, cognitive change), malnutrition attributable to advanced renal failure, and an eGFR that has fallen to a very low level (generally in the range of 5 to 10 mL per minute per 1.73 m squared) even in the relative absence of overt symptoms, given the recognized risks of delaying initiation too long in this setting.

Planning for chronic dialysis, including the choice of modality and, for hemodialysis, the creation of vascular access such as an arteriovenous fistula well in advance of anticipated need, should ideally begin once a patient's chronic kidney disease trajectory suggests dialysis is likely to be required within the coming months to a year or so, since late referral and unplanned dialysis initiation, often via an emergency central venous catheter, carries worse outcomes than planned initiation with established access.

The choice between hemodialysis and peritoneal dialysis is guided by a combination of patient preference, lifestyle, comorbidity, and specific contraindications. Peritoneal dialysis is generally contraindicated or relatively unsuitable in patients with extensive prior abdominal surgery, significant abdominal wall hernia, or an inability to manage the technique either independently or with adequate support. Hemodialysis requires adequate vascular access and the ability to attend a dialysis unit regularly, unless home hemodialysis is being pursued.

Renal transplantation remains the optimal form of renal replacement therapy where feasible, offering superior long term survival and quality of life compared with either dialysis modality, and should be actively considered and discussed with suitable candidates, ideally well before dialysis becomes necessary, to allow for pre-emptive transplantation where a suitable donor is available.

Referral: nephrology for planning of renal replacement therapy in progressive chronic kidney disease, ideally well in advance of anticipated need; urgent nephrology involvement for any acute indication for dialysis in the context of acute kidney injury.

Hypochloraemic Metabolic Alkalosis

Overview

Diagnosis

Management

Overview

Indications in Acute Kidney Injury

Indications in Chronic Kidney Disease

Choice of Modality