Fluid Balance: Thirst Mechanism (Bond University) PDF

02/11/2024 2 Acknowledgement of Country Bond University acknowledges the Kombumerri people, the...

02/11/2024 2 Acknowledgement of Country Bond University acknowledges the Kombumerri people, the traditional Owners and Custodians of the land on which the University now stands. We pay respect to Elders past, present and emerging. Copyright Warning. This material has been reproduced and communicated to you by or on behalf of Bond University in accordance with section 113P of the Copyright Act 1968 (Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act.  Body fluid compartments and thirst mechanism Tim Hodgson Learning outcome: Describe the major body compartments and explain the thirst mechanism  IV fluids  It won’t be long before you’ll be prescribing litres of these fluids to all these people  What type and volume of fluid should you prescribe to each of these patients? 3 month old Piper 82 year old has had 26 year old Liam Marion has a diarrhoea and is in ED with 50% bowel vomiting for 2 body surface obstruction, is nil days, she is pale, area burns by mouth and is quiet and awaiting surgery lethargic  Adult humans are 50-60% water Total body water distribution  Extracellular fluid = ECF  Intracellular fluid = ICF   The water in both the ICF and ECF compartments contain solutes  The most physiologically important solutes are: Composition  Electrolytes of  chemical compounds that dissociate into ions in water – these charged particles can conduct an electrical current compartmen  Glucose  Dissolved gases O2, CO2 ts  Proteins  Lipids  Products of metabolism i.e. creatinine, urea  ICF ECF Na 10 140 K 155 3.8 Cl 3 102 HCO3 10 28 Ca 20L/day if no ADH is being produced –  ADH gives the body the ability to loose large volumes of water or maximally conserve water according to physiological conditions  Renin angiotensin  ADH acts in the kidney to regulate output/conservation of water, the RAAS aldosterone acts to control volume status via system effects on Na reabsorption in the kidney (RAAS)  RAAS outline Hypovolaemia Renin is the rate stimulates the limiting step in the production of renin production of the by the renal granular hormone (juxtaglomerular) angiotensin II (AII) cells  Conservation of NaCl and water Actions of Regulation of angiotensin systemic blood II pressure Stimulates hypothalamic thirst centre  Angiotensin II Increases Na reabsorption in the kidney Via direct action on the nephron Stimulates production of aldosterone Powerful effect on Na reabsorption in the distal part of the nephron  Angiotensin II Systemic vasoconstriction via AT1 receptors Increases systemic BP At low levels acts to preserve renal function by selective vasoconstriction of some renal arterioles Maintains glomerular filtration  Naturetic peptides Inhibit secretion of Atrial and brain renin and naturetic peptides aldosterone (ANP, BNP) oppose the effects of the Production RAAS stimulated by volume overload  Clinical case: Burns A 26 year old male is brought into the emergency department after a house fire. He has sustained burns to 50% of his total body surface area. He has no other injuries. What implications do the burns have for his ongoing fluid management?  Burns and fluid management Patients with major burns loose a significant volume of fluid during the hours after their injury Systemic inflammatory response makes all capillaries throughout the body leaky – intravascular hypovolaemia results Fluid from leaky capillaries accumulates in the area of the burn – loss of the skin barrier results in loss of this fluid by evaporation Fluid from leaky capillaries internally results in oedema of tissues and organs Without intervention hypovolaemic shock will occur with potentially fatal consequences  Hypovolaemic shock Shock is a condition in which blood vessels are inadequately filled and blood cannot circulate normally Hypovolaemic shock: shock due to loss of intravascular volume; can be either whole blood (plasma and red cells) or just the plasma Common causes are: blood loss, vomiting, severe diarrhoea, extensive burns   The management for hypovolaemic shock is replacement of intravascular volume  If a major haemorrhage is the cause, then volume Hypovolae should be replaced with blood mic shock  In burns the shock is caused by loss of plasma and extracellular fluid – replacement is with intravenous fluids  Intravenous fluids  The most common type of fluid that you will encounter and prescribe in your clinical practice is called a crystalloid  Crystalloids consist of water and electrolytes  The most commonly used crystalloids have an osmolarity which is the same as that of ECF  Intravenous fluids  Sodium compound lactate; CSL (also called Hartmann's) and 0.9% NaCl (also called normal saline) are the two most commonly prescribed IV fluids in the hospital  Burns patients require infusion of large volumes of these crystalloids to manage the hypovolaemic shock which ensues after a significant burn injury  The Parkland formula is used to guide fluid management (also termed fluid resuscitation) in patients with major burns Fluid managemen Parkland formula:3-4mls/kg/%burn of t of burns CSL over the first 24 hrs. patients Assuming 70kg and 50% burns this means: 3 x 70 x 50 = 10500mls Half should be given in the first 8hrs, the other half over the following 16hrs 0.5 X 10500mls = 5250mls  The large fluid volumes that the Parkland formula calculation Fluid produces gives an managemen indication of the t of burns magnitude of fluid patients losses and fluid shifts that are encountered with burns patients.  Clinical case 2: the dehydrated infant  A 3-month-old female presents to ED. She has had diarrhoea and vomiting for 2 days, she is pale, quiet and lethargic  Clinical case 2: the dehydrated infant  A 3-month-old female presents to ED. She has had diarrhoea and vomiting for 2 days, she is pale, quiet and lethargic  Observations:  HR 180  Resp rate 70/min  Capillary refill 3-4 seconds  Weight 6kg   Decreased skin turgor  Looks unwell  Altered consciousness, lethargy, restless Signs and  Sunken eyes symptoms  Tachycardia of dehydration  Increased respiratory rate in an infant  Reduced urine output  Capillary refill > 2 seconds  Weight loss (need very recent weight) Normal ranges in infants and children  The patient is significantly dehydrated and needs volume replacement urgently – TBW = 65-70% at 3 months of age (= 650-700mls/kg) Managemen t Neonates and infants are at risk of hypoglycaemia because they have low glucose stores  Estimate % dehydration Clinical dehydration is detectable when a child is 2.5-5% dehydrated 5% dehydrated = lost 50 ml/kg of body weight If there are signs of shock (tachycardia, increased cap refill time) then dehydration is at least 10% This infant is likely to be >10% dehydrated (approx. fluid deficit = > 600mls)  How to approach paediatric fluid replacement 3. 1. Volume 2. Replacement 3 parts: resuscitation Maintenance of ongoing losses  Volume resuscitation Isotonic Repeat fluids: normal 10ml/kg until saline or CSL: signs of 20ml/kg shock resolve bolus  Maintenance Replacement of ongoing fluid requirements Ideally orally, - IV only if oral intake poor/contra-indicated Fluids should contain 5% glucose to prevent hypoglycaemia Fluids should be isotonic Calculated using 4:2:1 formula  4:2:1 formula Gives a rate of 24ml/hr. for a 6kg infant Useful guide, but over-estimates requirements  Replacement of ongoing losses Replace with Most GI tract Measure or fluids which are losses are estimate ongoing of similar isotonic so 0.9% losses composition to NaCl or CSL are that being lost appropriate Learning outcome: Describe the major body compartments and explain the thirst mechanism  Summary Total body water Thirst mechanisms – Distribution of water Osmolarity and it’s regulate water across body physiological intake compartments Osmoreceptors and Electrolyte composition significance volume (stretch) of compartments receptors Hypovolaemia Anti-diuretic hormone – regulates Cases: Fluid water output management in major burns and RAAS acts to paediatric fluid conserve NaCl and management water