IV Fluids

1. IV Fluids

2. Homeostasis Fluid levels in the body are controlled by homeostatic mechanisms VOLUME TONICITY ELECTROLYTES WASTE PRODUCTS In the obese patient there is a lower portion of body water In children there is a higher portion of total body water

3. Body Fluid Water content of the entire body The total amount of water in a man of 70 kg is approximately 40 litres, averaging 57 percent of his total body weight. In a newborn infant, this may be as high as 75 percent of the body weight, but it progressively decreases from birth to old age, most of the decrease occurring during the first 10 years of life . Also, obesity decreases the percentage of water in the body, sometimes to as low as 45 percent In diseased states where body water is affected, the compartment or compartments that have changed can give clues to the nature of the problem. Body water is regulated by hormones, including anti-diuretic hormone (ADH), aldosterone and atrial natriuretic peptide. There are many methods to determine body water. One way to get a simple estimate is by calculation. Body water is broken down into the following  compartments : - Intracellular fluid  (2/3 of body water). In a body containing 40 litres of fluid, about 25 litres is intracellular - Extracellular fluid  (1/3 of body water). In a 40 litre body, about 15 litres is extracellular ,  which amounts to 37.5 % Plasma (1/5 of extracellular fluid). Per Guyton's illustration, of the 15 litres of extracellular fluid, plasma volume averages 3 litres .   (20%) Interstitial fluid (4/5 of extracellular fluid) Transcellular fluid (a.k.a. "third space," normally ignored in calculations) Contained inside organs, such as the gastrointestinal, cerebrospinal, peritoneal, and ocular fluids.

4. Intracellular V Extracellular 2/3 intracellular 1/4 intravascular 3/4 interstitial Colloids stay in intravascular space: GOOD FOR EXPANSION OF FLUID VOLUME *** Fluids can move freely between the 2 compartments

5. Fluid Comparments *** Na primarily EXTRACELLULAR, K primarily EXTRACELLULAR

6. Tonicity ADH 300 mOsmols When tonicity falls below 270mOsmols ADH secretion is switched off ADH reduces the

7. ADH / Vasopressin Neurohypophysial , peptide hormone Derived from a preprohormone precursor that is synthesised in the hypothalamus and stored in vesicles at the  posterior pituitary. Regulates retention of water; it is released when the body is dehydrated and causes the kidneys  to conserve water; concentrating the  urine and reducing urine volume . Vasopressin has two effects by which it contributes to increased urine osmolality (increased concentration) and decreased water excretion: 1.) Increasing the water permeability of distal tubule and collecting duct cells in the kidney, thus allowing water reabsorption and excretion of more concentrated urine, i.e., antidiuresis. This occurs through insertion of water channels (Aquaporin-2) into the apical membrane of distal tubule and collecting duct epithelial cells. Aquaporins allow water to move down their osmotic gradient and out of the nephron, increasing the amount of water re-absorbed from the filtrate (forming urine) back into the bloodstream. Vasopressin also increases the concentration of calcium in the collecting duct cells, by episodic release from intracellular stores. 2 .) Increasing permeability of the inner medullary portion of the collecting duct to urea by regulating the cell surface expression of urea transporters, which facilitates its reabsorption into the medullary interstitium as it travels down the concentration gradient created by removing water from the connecting tubule, cortical collecting duct, and outer medullary collecting duct. Vasopressin increases peripheral vascular resistance (vasoconstriction) and thus increases arterial blood pressure. This effect appears small in healthy individuals; however it becomes an important compensatory mechanism for restoring blood pressure in hypovolemic shock such as that which occurs during haemorrhage .

8. Volume Renin Angiotensin If the volume drops too low, renin is activated which converts ansiotensinogen to angiotensin I. Ace converts if to angiotensin II. Angiotensin II is a potent vaso -constrictor - bvs constrict, i ncreasingblood pressure. Angiotensin II stimulates the secretion of aldosterone from adrenalcortex   => tubules of the kidneys increase the reabsorption of sodium and water into the blood.

9. Renin Angiotensin System

10. Indications to give Fluid To replace lost volume Maintenance of daily requirements Replace haemoglobin Replace blood component Diluent for d rugs Physical effect – promotion of a diuresis *** After surgery, vomiting, diarrhoea, dehydrated, bleeding...

11. The things that must be given Water Sodium Potassium Look at U&E’s any abnormalities detected will help you decide if the patient needs extra Na or K supplementation

12. Water Prescription Daily maintenance fluids Replacement of any remaining defecit Allowance for predicted excess (insensible) losses - Normal fluid balance for 70-80 year old male *** Insensible losses = respiration and sweating. Fluid given should appear to be more than that lost to allow for these losses

13. Maintenance Prescription Average person requires 2-3 litres/day Can be calculated by 30mls/kg/day For thin patients 30mls/kg/day is the best to use For obese patients, and estimate between 2-3 litres is best In paediatric patients maintenance prescriptions are calculated by weight: -100 mls /kg/day for first 10kg -50mls/kg/day for second 10kgs -20mls/kg/day for the rest

14. Prescribing Generally prescribed at 1.2ml/kg/hr However some fluids may be given at set rates EG 70kg patients requires fluids at 84ml/hr totalling 2016ml/day

15. Types of Fluids Saline  Sodium Chloride 5% dextrose Hartmann’s solution Colloids – good for expanding the volume Colloids 0.9% NaCl 5% Dextrose Plasma Interstitial Fluid Intracellular Fluid

16. Saline  NaCl 0.9% 77 molecules of Na and Cl Exchange Na for H. Pee the Na out If you give lots of Na it causes you to keep the fluids and therefore dilutes the volume, leading to a hyponatraemic state. (more sodium you give, the more water you hold onto) Rapid infusion of NS can cause metabolic acidosis The solution is 9 grams of sodium chloride ( NaCl ) dissolved in water, to a total volume of 1000 ml. It has a slightly higher degree of osmolarity (i.e. more solute per litre) than  blood Uses: hypovolaemia (threatening blood circulation) and maintenance fluids resuscitation

17. Saline with KCl Saline normally has no KCl in it and is available in 500ml or 1000ml bags Can add in KCl : -500mls NaCl with 20mmol KCl -1000mls NaCl with 40mmol KCl KCl added in when U&E show hypokalaemia or in maintenance if K is at the lower end of normal, to prevent a hypokalaemia Saline with KCl cannot be given in resus because K can only be given at a rate of 10mmol/hour

18. 5% Dextrose 50 grams of sugar dissolved in 1000mls water Kidneys filter glucose out, sugar draws water out with it so the whole volume is lost Not used for resuscitation

19. Hartmann’s Solution  Compound Sodium Lactate Closest to physiological normal. Has a lower Cl content to reduces the likelihood of a hyperchloraemic acidosis Source of K, only enough for a maintenance dose, not replacement: if U&E show hypokalaemia no point giving it Less Na. Very similar to GI losses. Used to replace GI losses, for maintenance, resuscitation

20. Sodium and Potassium Daily requirement Na: 1-2mmol/kg Daily requirement K: 1mmol/kg K  available in 20mmol aliquots Maximum rate of infusion is 10mmol/hr Maximum concentration in any 1 litre is 40mmol Usual prescription script: - 0.5-1l normal saline (75-150mmols Na) -1.5-2l 5% dextrose 60mmol KCl (distributed between these fluids)

21. Normal Saline / Hartmann’s Normal Saline - 154mmol Na/l (normal plasma level 135-145) -154mmol Cl /l ( normal plasma level 98-108) Hartmann’s - 131mmol Na -111mmol Cl 29mmol lactate -5mmol K -2mmol Ca Large volumes of saline will give considerable excess of chlorine. So using Hartmann’s will incur much less hyperchloraemic acidosis

22. GI losses ALL: Isotonic Gastric: acid (only if pure gastric losses) Lower GI: alkaline, small intestine especially ALL POTASSIUM RICH  10-20 mmol /l

23. Assessment of Defecit Blood loss, vomiting, diarrhoea, diuresis, sweating Fasting (before admission and during) Symptoms and signs Urinalysis: osmolality (>300, decreased Na <10) Bloods: Urea, Na , haematocrit Daily weight, any decrease in CVP or increase in pulse P: good estimate of circulating volume Estimate of insensible losses Skin turgor , mucous membranes

24. Estimating the defecit SHOCK

25. Replacement Estimate % deficit eg mild = 5% Calculate volume of deficit, = %deficit/100 x weight kg Eg 0.5 x 70 = 3.5 litres Tends to slightly overestimate deficit Replace lost fluids over 1-2 days, this allows you to assess the response of the patient and adjust the regime if necessary

26. Insensible (Excess) Losses Vomiting NG aspiration Diarrhoea Stoma output Intestinal Fistulae Rich in ions so need careful measured/ estimated

27. Gastric and Lower GI Losses Sodium 80mmol/l Remaining anoin is H+ Potassium will be substituted for H+ Can be replaced as normal saline May use 1 in 4 bags of 5% dextrose – because of the overload on Na+ *** Be generous with potassium!!! Lower GI Similar approach. Replace some with 1.4% bicarbonate if needed Potassium at 10 to 20 mmol . Over zealous use of N saline may cause hyperchloraemic acidosis look at plasma chlorine replacement ACIDIC ALKALINE

28. Monitoring the response Assess fluid status: thirst, mucous membranes (signs of dehydration), urine output, U&E, oedema, lung fields Urinalysis: urinary electrolytes (especially is low urine output) Skin turgor OBS Invasive monitoring (if required)

29. Fluid replacement  water, Na, K. At a safe rate. Consider content carefully

30. Common Problems Hyponatraemia : usually caused by excessive water Hypokalaemia: usually caused by under-prescription of potassium or excessive losses from the gut. Requires urgent replacement. Max rate 10mmol/hr

31. Renal Failure No safety valve, for excretion of excess fluids Avoid potassium unless low Total volume: - yesterday’s urinary output plus measured and insensible losses -WEIGH DAILY -advice from a nephrologist

32. Monitoring Daily U&E If excess losses, watch for low MG and acid-base balance If malnourished, watch for low PO4 Acidosis may be caused by excessive saline Switch to oral fluids ASAP

33. TUTORIAL When prescribing fluids need to know... weight, fluids since he came in/surgery, losses: blood, vomiting, diarrhoea, insensible. U&Es, BP, pulse, urinary output, renal function, diabetes? Old? CURRENT OBS PMHx : cardiac or renal problems DHx : diuretics etc

34. Prescribing fluids Read full paragraph. Work out maintenance: 30mls/kg/day Look at U&E – any hypoNa /K? Yes: what ion? How can you replace it? Saline plus KCl etc No: plain saline or hartmanns Over what time period fluids to be given?