Hypo/Hypernatremia. Stuart L. Goldstein MD. Director, Center for Acute Care Nephrology Cincinnati Children s Hospital

Transcription

1 Hypo/Hypernatremia Stuart L. Goldstein MD Director, Center for Acute Care Nephrology Cincinnati Children s Hospital

2 Objectives Understand Fluid cellular shifts Understand maintenance fluid and calculations Understand hyponatremic, isonatremic and hypernatremic dehydration and therapy

3 The Cell Has a Limited Repetoire H 2 0 moves passively Across cell membrane According to the osmotic gradient K+140 meq/l 280 milliosmoles/l Na+140 meq/l 280 milliosmoles/l

4 High Osmolality Outside The Cell=Shrinkage H 2 O K meq/l 280 milliosmoles/l Na meq/l 300 milliosmoles/l

5 Low Osmolality Outside The Cell=Swelling H 2 0 K meq/l 280 milliosmoles/l Na+120 meq/l 240 milliosmoles/l RUPTURE

6 ECF Na & ICF K+ Concentration, TBW distribution and body fluid osmolality A C Intracellular 280mosm/L H 2 O K+=140 28L Extracellular 280mosm/L H2O Na+=140 14L Normal Conditions B Intracellular 290mosm/L H 2 O K+=145 27L Extracellular 290mosm/L H 2 O Na+=145 15L 210 mm NaCl added to ECF Intracellular Extracellular Intracellular Extracellular 270mosm/L 270mosm/L 280mosm/L 280mosm/L H 2 O H H 2 O 2 O H 2 O K+=135 Na+=125 D K+=140 Na+=140 29L 14.5L 28L 15.5L 1.5 L H 2 0 added to ECF 1.5 L 0.9% NaCl added to ECF

7 HUMANS Lose insensible (unmeasured) water through skin and lungs at a predictable rate according to metabolic rate and size. Infant cc/kg/24hr Adult cc/kg/24hr This insensible water is almost always electrolyte free and therefore, every body requires replacement of free water. If you give solute, there is obligatory urine output 1400 milliosmoles per 1000cc urine

8 HUMANS cont. Small amounts of electrolytes are lost in stool and urine Maintenance intake is the amount of water and electrolytes needed to keep humans, and therefore, their cells in a stable state of adequate circulation and normal osmoles.

9 TABLE I INSENSIBLE WATER CALCULATIONS Age Weight Surface H2O Area Expenditure (kg) (M 2 ) (cc/kg/24hr) Newborn Week - 6 Months Months Years Years Years Years Adult

10 TABLE II Electrolyte Concentration of Various Body Fluids Fluid Na K Cl Protein (meq/l) (meq/l) (meq/l) (g/dl) Gastric Pancreatic Small Bowel Bile Ileostomy Diarrhea Burns rd Space Fl Variable Urine Variable <10 <5 <10

11 TABLE III Holliday Segar calculation of maintenance fluids and electrolytes Water Electrolytes (cc/kg) (per 100cc H 2 O) 1 st 10kg body weight 100 Na 3mEq 2 nd 10kg body weight 50 Cl 2mEq Each additional kg 20 K 2mEq through 70k Therefore: 10kg = 1000cc/24hr 20kg = 1500cc/24hr 70kg = 2500cc/24hr

12 TABLE IV Composition of commonly used IV solutions* Solution Ionic Concentration meq/l Total [Na + ] [K + ] [Ca 2+ ] [Cl - ] [HCO 3- ] mosmol/l 5% Dextrose in water Isotonic Saline (0.9%,normal) Dextrose in Saline 5% in 0.22% % in 0.45% Lactated Ringers *Adapted from A.Arieff, Clinical Disorders of Fluid and Electrolyte Metabolism, 2 nd ed.,m.h Maxwell and R. Kleeman (eds.). McGraw-Hill, New York, 1972.

13 Therefore in a 22kg 4-year-old, the maintenance fluid could be calculated by: 10kg X 100cc/kg = 1000cc 10kg X 50cc/kg = 500cc 2kg X 20cc/kg = 40cc Total H 2 O = 1540cc Na = 3mEq/100cc = 45 meq in 1.5 liters = 30mEq/liter K = 2mEq/100cc = 30mEq in 1.5 liters = 20mEq/liter These calculations can be made with a maximum weight of 70kg or a total volume of 2500cc/24hr

14 In order to utilize prepared IV solutions, you round off the electrolyte requirements to the closest solution available. All orders must be written with the quantities per liter as a standard. This makes it easy to compare the IV solution to what you know is in plasma water. You know D5.2NaCl contains 38mEq of NaCl per liter, so this is an effective solution to use. For the 22kg boy, your order would read: D5.2NaCl with 64cc/hr.

15 The Rules of the Road Cells require adequate circulation (vascular volume) and a stable iso-osmotic milieu to function Maintenance fluid has been calculated by understanding : Metabolic rate Body size It assumes: All homeostatic mechanisms are intact Lungs and kidneys are functional and there is adequate circulating volume

16 If these assumptions are not met, you must: Calculate insensible loss Calculate fluid and electrolyte loss Calculate rate based on previous slides

17 DEHYDRATION Measured by weight loss and clinical signs and symptoms Mild 4-5% Moderate 6-10% Severe 10% Death >25%

18 TABLE V Estimates of probable water and electrolyte deficits in individuals with approximately 10% dehydration Hellerstein 1993 Condition H 2 0 Sodium Potassium Chloride (ml/kg) (meq/kg) Hypotonic [Na]<130mEq/L Isotonic [Na]= mEq/L Hypertonic [Na]>150mEq/L

19 TABLE VI Correction of symptomatic electrolyte disturbances a. Formula: meq required = (CD-CA) x fd x Wt CD = concentration desired (meq/l) CA = concentration present (meq/l) fd = distribution factor as fraction of body wt Wt = baseline weight prior to illness (kg) b. Apparent distribution factor (D): Electrolyte fd HC Cl Na ** Correction of free H2O Deficit = 4cc/kg for every meq that the serum Na exceeds 145mEq/l

20 Types of Dehydration Isonatremic cells neutral Hypernatremic cells shrunken/and can have rebound Hyponatremic cells swollen

21 HYPERNATREMIA (Na > 150 MEq/L) ALWAYS means Serum osmolality is above normal

22 HYPONATREMIA USUALLY means Serum osmolality is below normal except for: - Hyperlipidemia - Hyperglycemia/mannitol which adds osmoles

23 mg/dl mg/dl Serum osmolality = Serum Na + X 2 + BUN + Glucose Urea moves passively across cell and therefore does not cause an osmotic gradient hyperosmolar but not hypertonic Glucose in diabetes cannot move intracellularly and therefore is an osmotic gradient and dilutes the sodium effect is hypertonic

24 TYPES ISONATREMIC 80% of all dehydration Proportional loss of salt and water Treatment - Calculate deficit from decreased weight - Replace intravascular volume with isotonic solution such as lactated ringers - From tables calculate estimate of water, sodium and potassium deficit

25 ORDERS STANDARD Isotonic rehydration cc/kg (more important is to restore vascular volume) Calculate deficit from tables Give ½ over 8 hours Give ½ over 16 hours Calculate maintenance Run piggyback Calculate ongoing losses Replace hourly

26 ORDERS IN REALITY Emergency Room isotonic rehydration 10-20cc/kg or until looks better Home on oral rehydration solution 5cc/minute = 300cc/hour

27 ORAL REHYDRATION: What You Need to Know Works well with vomiting and diarrhea Inappropriate with shock 5cc given every minute = 300cc/hour

28 APPROPRIATE FLUIDS CHO/mmol/L Na K Base Osmo WHO Formula Pedialyte Not appropriate Cola Apple Juice Chicken Broth

29 HYPONATREMIC DEHYDRATION 5% of all dehydration Usually occurs with a patient who has high GI losses accompanied by water replacement (jello/ pop, etc) Water shifts into the intracellular space to balance osmoles, so patient looks sicker since ECF is compromised Causes significant neurological problems as brain swells ** if Na<120mEq/l can cause permanent myelinolysis

30 If Na is above 120mEq/l Replace intravascular volume with isotonic solution Calculate Na Deficit 135 meq/l measured Na X TBW TBW = 0.6 X body weight Use D5 ½ NaCl = 75mEq/l of Na to replace deficit ½ over 8 hours ½ over 16 hours Add in maintenance = potassium Do not change serum more than 1 meq/hour

31 If Na<120mEq/l, Assess Hydration very Carefully If dry, give 20cc/kg of Isotonic solution You may use hypertonic saline if CNS signs are evident = 3%NaCl 514 meq/l = 1028 mosm/l or 0.5 meq NaCl per cc Risk of seizures

32 Calculate Deficit of Sodium to Get You to 120 In a 10kg child with sodium of 110 (CD-CA) X 0.6 wt/kg ( ) X 0.6 X X 0.6 X 10 = 60mEq 60 meq NaCl = 120 cc of 3% NaCl Give over 1-2 hours rechecking Na + every 30 minutes

33 HYPERNATREMIC DEHYDRATION 15% of all dehydration Seen in patients with deprivation of water Breast-feeding failure Patients with lossed replaced by high sodium foods (broth, etc) Elderly without adequate thirst mechanism Water moves out of the intracellular space and the ICF is compromised Na + >160mEq/l causes CNS effects With shrinking of the brain there can be tearing of bridging blood vessels causing subarachnoid or subdural bleeds

34 TREATMENT SLOW!!! If patient is stable and hypernatremic and got that way over weeks, you may take a week to correct it If patient is in shock, give isotonic solution 10-20cc/kg to get out of shock Calculate Water deficit 0.6L/kg*(SNa/145-1)*weight Replace deficit to correct SNa by 15mmol/L/day

35 Example: A 10kg child arrives with a history of dehydration. He now weighs 9.4kg. You give him 20cc/kg of L/R or 200cc. Labs return showing his lytes are: You want this child s Na to drop from 160 to 145 in 24 hours His water deficit is: 0.6*(160/145-1)*9.4 = 583cc

36 The safest way to give the water deficit is by using D5 1/2 NS. One liter of this solution contains 500cc of free water and 500cc of isotonic solution, so you have to give 1200cc of this solution for 600cc of free water. He will also have total body K + depletion, but his serum K is OK so you can simply give him that in his maintenance fluids. Orders should read D5 1/2NS 1200 to be given at 80cc/hr x 15hr His maintenance IV can be D5 1/4 NS with 40mEq KCL/l at 40cc/hr continuously These can be piggybacked together and run simultaneously. Serum Na should be measured every 4 hours to watch the rate of fall and adjustments made accordingly Remember ongoing losses

37 INAPPROPRIATE ADH Definitions: A state in which ADH is secreted and lowers serum osmolality despite adequate vascular volumes and hyponatremia. The following criteria must be fulfilled: - Hyponatremia < Normal intravascular volume - Low serum osmolality with urine osmolality that is inappropriately high Na + Osmolality Serum Urine

38 Diseases That Cause Inappropriate ADH CNS Abnormalities (meningitis/hemorrhage/neoplasm) Drugs intravenous cyclophosphamide Pulmonary disease Neoplasm Pain

39 Treatment of IADH Depends on acuity and severity 1. Water restriction 2. Diuretics 3. Diuretics with saline replacement

40 SUMMARY Cells need adequate circulating volume to survive: always assess and maintain adequate vascular volume which is part of the extracellular space Cells are at risk with rapid shifts in osmolality. Rapid expansion should always occur with istonic fluid K + is responsible for the electrochemical gradient in the cell and will cause cardiac abnormalities if too high or too low

41 Case #1 A 4-year old girl presents to the emergency center with a 2-day history of fever to 104F and vomiting. She has been unable to tolerate oral liquids for 48 hours. On examination, she is irritable, photophobic and pale. Her skin turgor is poor and she has a capillary refill of > 10 seconds. Vital signs: BP 60/40, HR 160, RR 60, Temp 105F. Weight is 20 kg. First questions: What is your first course of action? What tests should you order?

42 Case #1 cont d Initial labs reveal serum Na = 146, K = 3.2, Cl = 104, HCO3 = 20, BUN = 30, Cr = 1.0, CSF with bacteria, neutrophils, low glucose and high protein. After resuscitative effort, the patient now has the following vital signs: BP 110/40, HR 100, RR 45 Second questions: What are you next set of fluid orders? How would you expect the patient s electrolytes to change?

43 After 72 hours, she becomes confused and then has a generalized tonic-clonic seizure. She is afebrile and her volume status appears normal Third questions: What is the differential diagnosis? What tests would you order? Serum electrolytes reveal: Na = 118, K= 4.0, Cl = 96, HCO3 = 20. Fourth questions: What is the cause of the patient s hyponatremia? What lab tests could you order to confirm the diagnosis? What is the treatment? What are the risks of rapid correction of sodium?

44 Case #2 A 5 month-old girl presents to the emergency room after a 5-minute generalized tonic-clonic seizure. A set of stat electrolytes reveals a serum Na of 183. The patient s weight is 7.5 kg. First questions: What are the mechanisms by which patients develop hypernatremia? How could you distinguish between the mechanisms in this particular patient? What tests would you order at this time?

45 Case #2 Cont d Physical exam revels poor skin turgor, prolonged capillary refill and vital signs reveal BP 50/20, HR 170, RR 70. The patient s lung fields are clear to auscultation. The patient s pupils are unequally reactive to light. Urine specific gravity is Second questions: What are your initial fluid orders? What is the likely underlying cause of this patient s hypernatremia? How would you assess for a peripheral versus central cause of this patient s underlying cause of hypernatremia?

46 Case #2 cont d The patient has been adequately resuscitated with a resultant BP of 90/50 and restoration of skin turgor. In the last 2 hours, the patient has urinated 200 milliliters. Repeat serum sodium is 179. The patient s weight is now 7.7 kg. Third questions: What variables do you need to consider in writing this patient s fluid orders? What is this patient s free water deficit? What labs do you need to help guide your fluid orders? What is the danger of correcting the hypernatremia too quickly?

47 Case #2.1 Now, let s change the story a bit. The same aged patient presents with a serum Na of 183, but her skin appears doughy. You find on history that the patient s mother works the late shift at night, and she has her 7 year-old daughter mix the patient s formula Questions: What is the likely cause of the patient s hypernatremia? How can you prove this? How would your management change?