NT6 - Distúrbios do Metabolismo da Água e Sódio (1)

Question 1

Composição Fluidos Corporais?

Answer 1

★ Intracelular
★ Extracelular

★ Osmolalidade Plasmática, Posm (mOsm/Kg H2O)
==> 2 x [Na+ ] (mEq/L) + [Glucose] (mg/dL)/18 + [Ureia] (mg/dL)/6

★ Osmolalidade efectiva (Tonicidade)
1. Solutos efectivos: sódio, manitol
2. Solutos não efectivos: glucose*, ureia, etanol

★ Exemplo:
1. Um aumento de 10mEq/L na [Na+]plasma acarreta um aumento de ~20mOsm/Kg na Osmolalidade plasmática e na Tonicidade.
2. Um aumento de 110 mg/dL na [Ureia] plasma acarreta um aumento de ~20mOsm/Kg na Osmolalidade plasmática, mas a Tonicidade permanece intacta.

Question 2

Metabolismo Água?

Answer 2

★ Each day the body gains and loses fluids through several different processes
– Skin
– Lungs
– Kidneys
– Intestines
★ Regulating sodium and water
– serum sodium level decreases = thirst decreases = ADH release is suppressed = renal water excretion increases
– serum sodium level increases = thirst increases = ADH release increases = renal water excretion diminishes
★ Duto coletor é impermeável á agua na ausência de vasopressina ou outros anti-diuréticos

Question 3

Distúrbios por Défice Vasopressina (Produção ou Efeito)?

Answer 3

★ Central (Neurogenic) Diabetes Insipidus
★ Osmoreceptor Dysfunction
★ Increased AVP Metabolism
★ Nephrogenic Diabetes Insipidus
★ Primary Polidipsia (não é distúrbio da vasopressina)

★ Poliúria Hipotónica
★ Colheita Urina 24h:
- Volume > 50ml/kg H20
- Osmolaridade <300mOsm/Kg H2O
- Taxa excreção solutos (UOms x Uvol [L] < 15mOsm/Kg H2O

Question 4

Test for the diagnosis of Diabetes Insipidus?

Answer 4

★ Fluid Deprivation
★ Procedure:
1. take nothing by mouth after dinner the day before the test
2. obtain plasma and urine osmolality measurements, serum electrolyte levels, and a plasma arginine vasopressin level at the start of the test
3. measure urine volume and osmolarity hourly with each voided urine

Question 5

Therapies for the treatment of DI?

Answer 5

★ Water
★ Antidiuretic agents
★ Arginine vasopressin
★ Desmopressin
★ Antidiuresis-enhancing drugs

★ Défice corporal água
– 60% x Peso x [1 – (140 / [Na+])]
★ Exemplo:
– Homem 70Kg, [Na+]=160mmol/L, défice água estimado 5.25L.
★ Correcção do défice = 12mmol/L/dia.
★ Atenção à perda contínua de fluidos.

Question 6

Patogénese e Causas de Hiponatrémia?

Answer 6

★ Presence of ‘effective’ osmoles that raise serum osmolality and can cause hyponatremia
- glucose
- mannitol
- glycine
- maltose
★ Presence of ‘ineffective’ osmoles that raise serum osmolality but do not cause hyponatremia
- urea
- alcohols
- ethylene glycol
★ Presence of endogenous solutes that cause pseudohyponatremia (laboratory artifact)
- triglycerides, cholesterol and protein
- intravenous immunoglobulins
- monoclonal gammapathies

Question 7

Definition of Hyponatraemia based on biochemical severity?

Answer 7

★ We define ‘mild’ hyponatremia as a biochemical finding of a serum sodium concentration between 130 and 135 mmol/L as measured by ion-specific electrode
★ We define ‘moderate’ hyponatremia as a biochemical finding of a serum sodium concentration between 125 and 129 mmol/L as measured by ion-specific electrode
★ We define ‘profound’ hyponatremia as a biochemical finding of a serum sodium concentration <125 mmol/L as measured by ion-specific electrode

Question 8

Definition of Hyponatraemia based on time of development?

Answer 8

★ We define ‘acute’ hyponatremia as hyponatremia that is documented to exist <48h
★ We define ‘chronic’ hyponatremia as hyponatremia that is documented to exist for at least 48h
★ If hyponatremia cannot be classified, we consider it being chronic, unless there is clinical or anamnestic evidence of the contrary

Question 9

Definition of Hyponatraemia based on symptoms?

Answer 9

★ We define ‘moderately symptomatic’ hyponatremia as any biochemical degree of hyponatremia in the presence of moderately severe symptoms of hyponatremia
★ We define ‘severely symptomatic’ hyponatremia as any biochemical degree of hyponatremia in the presence of severe symptoms of hyponatremia

Question 10

Symptoms of Hypotonicity?

Answer 10

★ Moderately Severe
- nausea without vomiting
- confusion
- headache
★ Severe
- vomiting
- cardiorespiratory distress
- abnormal and deep somnolence
- seizures
- coma

Question 11

Drugs and conditions associated with acute hyponatraemia?

Answer 11

★ Postoperative phase
★ Post-resection of the prostate, post-resection of endoscopic uterine surgery
★ Polydipsia
★ Exercise
★ Recent thiazides prescription
★ MDMA
★ Colonoscopy preparation
★ Cyclophosphamide
★ Oxytocin
★ Recently started desmopressin therapy
★ Recently started terlipressin, vasopressin

Question 12

Treatment - Hyponatremia with severe symptoms - First-hour management, regardless of wether hyponatremia is acute or chronic?

Answer 12

★ We recommend prompt iv infusion of 150 ml 3% hypertonic over 20 min
★ We suggest checking the serum sodium concentration after 30 min while repeating an infusion of 150 ml 3% hypertonic saline for the next 20 min
★ We suggest repeating the first 2 steps twice or until a target of 5 mmol/l increase in serum sodium concentration is achieved
★ Manage patients with severely symptomatic hyponatremia in an environment where close biochemical and clinical monitoring can be provided

Question 13

Treatment - Acute Hyponatremia without severe or moderately severe symptoms?

Answer 13

★ Make sure that the serum sodium concentration has been measured using the same technique used for the previous measurement and that no administrative errors in sample handling have ocurred
★ If possible, stop fluids, medications and other factors that can contribute to or provoke hyponatremia
★ We recommend starting prompt diagnostic assessment
★ We recommend cause-specific treatment

Question 14

Chronic Hyponatremia without severe or moderately severe symptoms - General Management?

Answer 14

★ Stop non-essential fluids, medications and other factors that can contribute to or provoke hyponatremia
★ We recommend cause-specific treatment
★ In mild hyponatremia we suggest against treatment with the sole aim of increasing the serum sodium concentration
★ In moderate or profound hyponatremia we recommend avoiding an increase in the serum sodium concentration of >10 mmol/l during the first 24hrs
★ In moderate or profound hyponatremia we suggest checking the serum sodium concentration every 6h until the serum sodium concentration has stabilised under stable treatment
★ In case of unresolved hyponatremia reconsider the diagnostic algorithm and ask for expert advice

Question 15

Treatment - Patients with expanded extracellular fluid?

Answer 15

★ We recommend against treatment with the sole aim of increasing the serum sodium concentration in mild or moderate hyponatremia
★ We suggest fluid restriction to prevent further fluid overload
★ We recommend against vasopressin receptor antagonists
★ We recommend against demeclocycline

Question 16

Treatment in patients with reduced circulating volume?

Answer 16

★ We recommend restoring extracellular volume with an iv infusion of 0.9% saline or a balanced crystalloid solution at 0.5-1-0 ml/kg per h
★ Manage patients with hemodynamic instability in an environment where close biochemical and clinical monitoring can be provided
★ In case of hemodynamic instability, the need for rapid fluid resuscitation overrides the risk of an overly rapid increase in serum sodium concentration

Question 17

Patients with Syndrome of Inappropriate Antidiuresis (SIAD)?

Answer 17

★ In moderate or profound hyponatremia we suggest restricting fluid intake as fist-line treatment
★ In moderate or profound hyponatremia we recommend against lithium or demeclocycline
★ In moderate or profound hyponatremia we do not recommend vasopressin receptor antagonists
★ In profound hyponatremia we recommend against vasopressin receptor antagonist

Question 18

Tratamento da Hiponatrémia - Outros?

Answer 18

★ Fluid Rate (mL/hour) = [1000 X (rate of Na+ correction in mmol/L/hr)] / (change in serum sodium)

★ Rate of Na+ correction:
- Máximo de 12mmol/day
- Máximo de 0.5mmol/L/hr