Antidiuretic HormoneADH

ADH

Hypertonic Interstitial Fluid

Collecting Duct

H2O

Urine

Calcitonin

Calcium

Estrogen

Calcium

Parathormone

Calcium

Blood pH = 7.4(7.35-7.45)

Blood pH regulated by1. Kidneys2. Lungs

3. Buffers in blood

H+ Secreted HCO3

- Resorbed

Blood

Kidney Nephron

HCO3-

H+

Urine

Kidneys Regulate pH

• Excreting excess hydrogen ions, retain bicarbonate– if pH is too low

• Retaining hydrogen ions, excrete bicarbonate– if pH is too high

Lungs Regulate pH

• Breathe faster to get rid of excess carbon dioxide if pH is too low– Carbon dioxide forms carbonic acid in the

blood

• Breathe slower to retain carbon dioxide if pH is too high

Carbon Dioxide and Acid

CO2 + H2O H2CO3 H+ + HCO3-

Carbonic Acid

More Carbon Dioxide = More Acid = Lower pH

• Breathing slower will retain CO2 , pH will– decrease (more acid)

• Breathing faster will eliminate more CO2 pH will– increase (less acid)

Blood pH Drops to 7.3How does the body compensate?

• Breathe faster to get rid of carbon dioxide– eliminates acid

Blood pH Increases to 7.45How does the body compensate?

• Breathe slower to retain more carbon dioxide– retains more acid

The role of ADH:

• ADH = urinary concentration• ADH = secreted in response to ⇑

osmolality;

= secreted in response to ⇓ vol;• ADH acts on DCT / CD to reabsorb water• Acts via V2 receptors & aquaporin 2• Acts only on WATER

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Calculation of osmolality

• Difficult: measure & add all active osmoles

• Easy = [ sodium x 2 ] + urea + glucose

• Normal = 280 - 290 mosm / kg

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Fluid shifts in disease

• Fluid loss:– GI: diarrhoea, vomiting, etc.– Renal: diuresis– Vascular: haemorrhage– Skin: burns,sweat

• Fluid gain:– Iatrogenic:– Heart / liver / kidney failure:

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Prescribing fluids:

• Crystalloids:– 0.9% saline - not “normal” !– 5% dextrose– 0.18% saline + 0.45% dextrose– Others

• Colloids:– Blood– Plasma / albumin– Synthetics eg gelofusion

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The rules of fluid replacement:

• Replace blood with blood• Replace plasma with colloid• Resuscitate with crystalloid or colloid• Replace ECF depletion with saline• Rehydrate with dextrose

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How much fluid to give ?

• What is your starting point ?– Euvolaemia ? ( normal )– Hypovolaemia ? ( dry )– Hypervolaemia ? ( wet )

• What are the expected losses ?• What are the expected gains ?

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Signs of hypo / hypervolaemia:

Signs of …Volume depletion Volume overloadPostural hypotension Hypertension

Tachycardia Tachycardia

Absence of JVP @ 45o Raised JVP / gallop rhythm

Decreased skin turgor Oedema

Dry mucosae Pleural effusions

Supine hypotension Pulmonary oedema

Oliguria Ascites

Organ failure Organ failure

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What are the expected losses ?

• Measurable:– urine ( measure hourly if necessary )– GI ( stool, stoma, drains, tubes )

• Insensible:– sweat– exhaled

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• Electrolyte (Na+, K+, Ca++) Steady State• Amount Ingested = Amount Excreted.• Normal entry: Mainly ingestion in food. • Clinical entry: Can include parenteral

administration.

Case 1:

• A 62 year old man is 2 days post-colectomy. He is euvolaemic, and is allowed to drink 500ml. His urine output is 63 ml/hour:

1. How much IV fluid does he need today ?

2. What type of IV fluid does he need ?

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Case 2:

• 3 days after her admission, a 43 year old woman with diabetic ketoacidosis has a blood pressure of 88/46 mmHg & pulse of 110 bpm. Her charts show that her urine output over the last 3 days was 26.5 litres, whilst her total intake was 18 litres:

1. How much fluid does she need to regain a normal BP ?

2. What fluids would you use ?

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Case 3:

• An 85 year old man receives IV fluids for 3 days following a stroke; he is not allowed to eat. He has ankle oedema and a JVP of +5 cms; his charts reveal a total input of 9 l and a urine output of 6 litres over these 3 days.

1. How much excess fluid does he carry ?

2. What would you do with his IV fluids ?

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Case 4:

• 5 days after a liver transplant, a 48 year old man has a pyrexia of 40.8oC. His charts for the last 24 hours reveal:

• urine output: 2.7 litres• drain output: 525 ml• nasogastric output: 1.475 litres• blood transfusion: 2 units (350 ml

each)• IV crystalloid: 2.5 litres• oral fluids: 500 ml

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Case 4 cont:

• On examination he is tachycardic; his supine BP is OK, but you can’t sit him up to check his erect BP. His serum [ Na+ ] is 140 mmol/l.

• How much IV fluid does he need ?• What fluid would you use ?

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Case 5

• 30yo girl• SOB, moist cough, chest pain• ESKD• Very little urine output• Has missed dialysis last 3 sessions

Case 5

• What next?

– Current weight 78kg– IBW 68kg– JVP twitching her ear– No peripheral oedema– Coarse crackles to mid zones– BP 240/110– P 100– Gallop rhythm– 4cm of liver in RUQ

Case 5

• Assessment– Acute significant overload– Probably about 10kg

Case 6

• 55yo lady• Presents to dialysis for her routine session• BP 78/30

• History of dizziness for the last 6 hours• Current weight 58kg• IBW 59kg

Case 6

• P 120• Chest clear• HS dual• No oedema• Admits to 24hours of diarrhoea• Thirsty• No JVP visible

Case 6

• Dehydrated• Volume constricted• Hypotensive due to decreased circulating

fluid volume• Resuscitation?

The EndThe End

Acknowledgements

• Paddy Gibson – 4th year teaching ppt 2009

• Robert Harris – Fluid Balance ppt 2009• Heather Laird-Fick – Fluid and electrolyte

disorders ppt 2009• JXZhang Lecture 14 – ppt 2009• Dennis Wormington – fundamentals of

fluid assessment ppt 2009