Department of Surgery Yong Loo Lin School of Medicine National University of Singapore

Total Body Water body wt%Total body water% total60100 intracellular4067 extracellular2033 intravas58 interstitial1525

Composition of Fluids plasmainterstitialintracellular Cations Na K44150 Ca5310 Mg217 Anions Cl HCO SO411- HPO Protein16540

Control of Volume Kidneys maintain constant volume and composition of body fluids Filtration and reabsorption of NaFiltration and reabsorption of Na Regulation of water excretion in response to ADHRegulation of water excretion in response to ADH Water is freely diffusible Movement of certain ions and proteins between compartments restrictedMovement of certain ions and proteins between compartments restricted

Osmoregulation F osmolality 289 mOsm/kg H 2 0 F osmoreceptor cells in paraventricular/ supraoptic nuclei F osmoreceptors control thirst and ADH F small changes in Posm - large response

Osmoregulation Excess free water (Posm 280)  thirst inhibited  ADH declines  urine dilutes to Uosm 100

Osmoregulation Decreased free water (Posm 295) Fthirst increased FADH increases Furine concentrates to Uosm 1200

Volume Control l osmoreceptors - day to day control l baroreceptors - respond to pressure change neural and hormonal efferents neural and hormonal efferents hormonal mediators hormonal mediators

Baroreceptors l Hormonal mediators aldosterone renin ANP dopamine l Hormonal effect  ECF  Na and water reabsorption

l Neural mechanism Autonomic nervous system Baroreceptors

Renin-angiotensin Renin secreted when l drop BP l drop Na delivery to kidney l increased sympathetic tone

Renin-Angiotensin

Angiotensin II Increases vascular tone F increases catecolamine release F decrease renal blood flow F increases Na reabsorption F stimulates aldosterone release

Aldosterone Release stimutlated by F Angiotensin II F increased K F ACTH Effect F Na and water absorption F in distal tubular segments

Control of Volume Effective circulating volume Portion of ECF that perfuses organsPortion of ECF that perfuses organs Usually equates to Intravascular volumeUsually equates to Intravascular volume Third space loss Abnormal shift of fluid for Intravascular to tissues eg bowel obst, i/o, pancreatitisAbnormal shift of fluid for Intravascular to tissues eg bowel obst, i/o, pancreatitis

Normal Water Exchange Avg daily mlMin daily ml Sensible urine intestinal up to 10,000 sweatup to litres500 Insensible lungs/skin mls/kg/D -  10%/ o rise in Temp

Normal Intake of Water 2000mls-1300 free water 700 bound to food additional water comes from catabolism

Water and Eletrolyte Exchange Surgical patients prone to disruption F nil orally F anaesthesia F trauma F sepsis

Fluid and Electrolyte Therapy Surgical patients need l Maintenance volume requirements l On going losses l Volume excess/deficits l Maintenance electrolyte requirements l Electrolyte excess/deficits

1. Maintenance Requirements This includes:insensible urinary stool losses Body weightFluid required 0-10Kg100ml/kg/d next 10-20Kg50 ml/kg/d subsequent Kg 20ml/kg/d 15ml/Kg/d for elderly

70 Kg Man Needs 1 st 10kg x 100mls = 1000mls 2 nd 10kg x 50mls = 500mls Next 50kg x 20mls= 1000mls TOTAL 2500 mls /d TOTAL 2500 mls /d

2. On Going Losses l NG l drains l fistulae l third space losses Concentration is similar to plasma Replace with isotonic fluids

3. Volume Deficit - Acute l vital signs changes Blood pressureBlood pressure Heart rateHeart rate CVPCVP l tissue changes not obvious l urine output low

3. Volume Deficit - Chronic l Decreased skin turgor l Sunken eyes l Oliguria l Orthostatic hypotension l High BUN/Creatine ratio l HCT increases 6-8 points per litre deficit l Plasma Na may be normal

4. Volume Excess l Over hydration l Mobilisation of third space losses Signs F weight gain F pulmonary edema F peripheral edema F S3 gallop

Fluid and Electrolyte Therapy Goal F normal haemodynamic parameters F normal electrolyte concentration Method replace normal maintenance requirements ongoing losses deficits

Fluid and Electrolyte Therapy Normal maintenance requirements Fuse BW formula On going losses Fmeasure all losses in I/O chart Festimate third space losses Deficits Festimate using vital signs Festimate using HCT

Fluid and Electrolyte Therapy The best estimate of the volume required is the patients response is the patients response After therapy started observe F vital signs F Urine output (0.5mls/Kg/hr) F Central venous pressure

Maintenance Electrolyte Requirements Na 1-2mEq/Kg/d K mEq/Kg/d l Usually no K given until after urine output is adequate and U/E done. l Always give K with care, in an infusion slowly - never bolus l Ca, PO4, Mg not required for short term

Time Frame for Replacement l Usually correct over 24 hours l For ill patients calculate over shorter period and reassess e.g. 1, 2 hours or 3 hours for e op cases l Deficits - correct half the amount over the period and reassess

Postoperative Fluid Therapy l Check i/v regime ordered in op form l Assess for deficits by checking I/O chart and vital signs l Maintenance requirements calculated l Usually K not started l Monitor carefully vital signs and urine output

Postoperative Fluid Therapy l Urine specific gravity may be used ( ) l CVP useful in difficult situations (5-15 cm H 2 0) l Body weight measured in special situation e.g. burns

Concentration Changes l changes in plasma Na are indicative of abnormal TBW l losses in surgery are usually isotonic l hypoosmolar condition usually caused by replacement with free water

Hyponatremia - Usually Excess Free Water l Free water replacement of isotonic losses l Increased ADH secretion l Low intravascular volume states like cirrhosis /low albumin l Excess solute e.g. glucose - intracellular water shifts to ECF

l Features - depends on rapidity acute drop below 120 weakness fatigue confusion cramps nausea/vomiting headache/delirium/seizures/coma permanent CNS damage Hyponatremia - Usually Excess Free Water

Diagnosis of Hyponatremia l assess circulating volume l exclude hyperosmolar states l check for losses l check for excess free water replacement l In difficult situations measure urine Na (> <20mEq/L)

Treatment of Hyponatremia l replace volume deficits in dehydration l restrict free water in overload Na required = [desired Na] - [actual Na] x (TBW) TBW = 0.6xWt Correct half the deficit over 12 hours and reassess

Hyperkalaemia l Fatal if undiagnosed l Trauma, burns, septic, acidotic patient l ECG-Peak T, widened QRS, ST depressed l Repeat serum K l Insulin/dextrose, correct acidosis with HCO3, calcium IV infusion, oral calcium resonium, dialysis

Hypokalaemia l Depressed neuromuscular function l Dietary, excess loss – vomiting, diuretics l Related to alkalosis l Repeat serum K l Correct primary problem, replace orally or IV

Fit pt lap cholecystectomy 1 st POD l Na121 mmol/l ( ) l K4.6 mmol/l ( ) l Cl90 mmol/l (98-108) l HCO322 mmol/l (23-33) l Urea3.5 mmol/l (3.0 to 8.0) l Creat50 umol/l (60 to 120)

60 yr colectomy 1 st POD l Na121 mmol/l ( ) l K2.6 mmol/l ( ) l Cl50 mmol/l (98-108) l HCO312 mmol/l (23-33) l Urea1.5 mmol/l (3.0 to 8.0) l Creat40 umol/l (60 to 120) l HCT27

QUESTIONS ?