Fluids and Electrolytes Acids and Bases

Fluids and Electrolytes Acids and Bases

Principles of Surgery

July 25, 2012

May Tee, MD, MPH PGY-‐5 General Surgery

Outline

•  Fluids and Electrolytes – Homeostasis (normal physiology) – Effects of surgery (physiologic stress) and implicaKons for fluid and electrolyte shiMs

– Derangements of fluid / electrolyte balance (pathophysiology) and management

•  Acids and Bases – Physiology – Pathophysiology

Fluids and Electrolytes

Overview with Cases

Total Body Water

Source: CURRENT Diagnosis and Treatment Surgery: 13th Ed. (2010)

Water DistribuKon

TBW

(60%)

ECF -‐ 1/3

(20%)

IntersKKal 3/4 (15%)

Intravascular 1/4 (5%)

ICF – 2/3

(40%)


Electrolyte DistribuKon


Nephrology for Surgeons

•  Kidneys regulate constant volume and composiKon of body fluids. –  ReabsorpKon / excreKon of sodium –  RegulaKon of water re-‐uptake

•  Homeostasis maintained despite variable intake of sodium and water.

•  Analysis of urine can someKmes give insight on disorders of fluids / electrolytes.


Effect of Surgery

•  RetenKon of fluids and electrolytes is driven by the stress response induced by surgery: catecholamines and counter-‐regulatory hormones are upregulated.

Source: Sabiston Textbook of Surgery, 19th Ed. (2012)

Key Hormones

•  CorKsol –  Secreted by adrenal cortex, sKmulated by ACTH produced in

anterior pituitary due to decreased intravascular volume, pressure, and sodium.

•  Renin-‐Angiotensin-‐System –  Renin produced by juxtoglomerular complex of kidney in

response to decreased renal blood flow, which generates AI that converts to AII by lungs.

•  Aldosterone –  Produced by adrenal cortex in response to AII to sKmulate renal

recovery of Na and excreKon of K. •  AnK-‐DiureKc Hormone

–  Produced by the pituitary to re-‐absorb water in kidneys, effect usually wears off aMer about 2 days.


Clinical ImplicaKons

•  Decreased urine output immediately post-‐operaKve is part of the physiological response to stress.

•  Problems may arise when paKents have underlying cardio-‐respiratory, renal, and / or hepaKc dysfuncKon who cannot handle major fluid and electrolyte shiMs.

•  These paKents need to be resuscitated with appropriate fluids and electrolytes. How?

Case

•  70 year-‐old male undergoing open AAA repair.

•  PMHx: CAD, PVD, HTN, Hyperlipidemia, DM.

•  Meds: ASA, Ramipril, Metoprolol, AtorvastaKn, Meeormin.

•  All: None.

IV Fluids

What to order? •  How much fluid? •  What kind of fluid? •  Colloid versus crystalloid? •  How much electrolyte? •  What to do when there are problems with fluid and / or electrolyte status?

Water Requirements

•  For a 70 kg person, minimum obligate water requirement is about 800 mL / day, which would yield 500 mL of urine.

•  Normal intake: 2500 ml (1500 ml liquids, 700 ml solids, 300 ml endogenous).

•  Normal output: 1400-‐2300 ml (urine 800-‐1500 ml, stool 250 ml, 600-‐900 ml insensible losses).

Source: Clinician’s Pocket Reference, 10th Ed. (2004)

Source: Schwartz's Principles of Surgery, 9th Ed. (2010)

How Much Water is Needed?

•  These are basic requirements

•  4-‐2-‐1 Rule (see box from Sabiston) –  Can use for kids –  70 Kg adult: 110 ml / hr or 2640 ml / 24 hr.

•  EsKmate for adults: 35 ml / Kg –  70 Kg adult: 2450 ml / 24 hr or 100 ml / hr


Crystalloids


(+ 20 mEq KCl = 2 mEq K)

(provides 50g glucose)

Ringer’s versus D5 ½ NS with KCl

Ringer’s •  Fluid shiMs in major surgery

are due to leakage of intravascular fluid into the intersKKal space.

•  What is lost is PLASMA. •  The crystalloid that is most

similar to plasma is Ringer’s (also Plasmalyte).

•  However, the lacKc acid buffer may have detrimental effects.

D5 ½ NS with 20 mEq KCl •  Stress from surgery induces

catabolism and muscle breakdown.

•  IV glucose slows this down by providing some basal energy needs.

•  For a 70 Kg pt taking 2400 ml / 24 hrs, it provides: –  184 mEq Na (140 mEq req) –  48 mEq K (35 mEq req) –  120g Glucose (100g needed to

spare muscle breakdown)

Case

•  45 year-‐old male undergoing elecKve R Hemi, R nephrectomy, R adrenalectomy for retroperitoneal sarcoma excision.

•  PMHx: Healthy. •  Meds: None. •  All: None.

•  What is a good peri-‐op IV fluid?

•  What rate would you run this guy if he were 70 kg?

Case

•  55 year-‐old female with SBO, being admined with goal to trial non-‐operaKve management first.

•  PMHx: Hypertension, CAD.

•  Meds: Ramipril / HCTZ, ASA, AtorvastaKn.

•  All: None.

•  Would you bolus this paKent if she looked dry given CAD?

•  What IV fluid would you use and how much?

•  What about NG losses – would you replace them?

Colloids

•  Unlike crystalloids, colloids exert enough oncoKc pressure to stay within the intravascular space rather than redistribute to the intersKKal space.

•  Two types of colloids: –  (1) Biologic: red blood cells,

platelets, fresh frozen plasma, albumin.

–  (2) SyntheKc: starch (pentaspan, voluven) or glucose (dextran) polymers.


Case

•  55 year-‐old paKent with Hep B cirrhosis, POD #1 segmental liver resecKon for HCC.

•  Called re: low urine output.

•  PMHx: Hep B cirrhosis, portal hypertension.

•  Meds: Spironolactone, Propranolol, Lactulose.

•  All: None.

•  What maintenance IV fluid might be appropriate?

•  What fluid could be used to bolus the paKent?

Colloids versus Crystalloids

Case

•  18 year-‐old, previously healthy female, admined earlier today for 30% TBSA burns from apartment fire.

•  Called re: low urine output.

•  What is opKmal urine output?

•  Should we bolus the paKent?

•  What IV Fluid and how much?

Glucose / Electrolyte Requirements

•  Sodium: 80–120 mEq/d (children, 3–4 mEq/kg/24 h)

•  Potassium: 50–100 mEq/d (children, 2–3 mEq/kg/24 h)

•  Calcium: 1–3 g/d, most of which is secreted by the GI tract

•  Magnesium: 20 mEq/d

•  Glucose: 100–200 g/d (65–75 g/d/m2)

Source: Clinician’s Pocket Reference, 10th Ed. (2004)

Electrolyte AbnormaliKes

•  No perfect IV soluKon exists but you can choose the best one available based on what the paKent needs (e.g. replace what is lost).

•  Electrolyte can be too high

•  Electrolyte can be too low

Hyponatremia

•  Low sodium: very common problem, ADH is key. •  In addiKon to thinking of the problem based on volume, consider thinking of it based on physiology: –  Appropriate / AdapKve: recall that the stress response in surgery upregulates ADH, thus, you will see this as a surgeon in at least some of your post-‐op pts.

–  Inappropriate: SIADH (Syndrome of Inappropriate ADH), might see in head trauma, lung cancer, paraneoplasKc syndromes.

– MaladapKve: paKents with heart, liver, and kidney failure have decreased effecKve intravascular circulaKng volume, which leads to increased ADH secreKon that does not address the underlying pathology.

Hyponatremia

•  DefiniKon based on severity of Na deficit –  Mild (130 to 138 mEq/L) –  Moderate (120 to 130) –  Severe (<120 mEq/liter)

•  Classify by volume status –  Hypovolemic (e.g. burns,

open wounds, sweaKng, GI/renal losses)

–  Euvolemic (e.g. SIADH – look at brain and lungs)

–  Hypervolemic (e.g. CHF, cirrhosis)

•  Treatment –  Pseudo-‐Hyponatremia:

treat underlying cause (e.g. hyperglycemia, which dilutes extracellular sodium)

–  Hypovolemic: fluid resuscitate (e.g. normal saline boluses)

–  Euvolemic: water restrict –  Hypervolemic: diurese (e.g.

furosemide)


Central PonKne Myelinolysis

•  This is a devastaKng iatrogenic complicaKon of correcKng hyponatremia too quickly.

•  The pons swells leading to brainstem dysfuncKon.

•  Rate of Serum Na rise should be < 0.5 mEq/L per hour and < 12 mEq / L over 24 hours.

•  Example order: 3% hypertonic saline @ 10-‐30 cc / hr with electrolytes and neurovitals checked q 1-‐2 h.


Hypernatremia

•  Na > 145 mEq / L (up to 159 mEq / L is well-‐tolerated).

•  Treat by volume status: –  Hypovolemic: fluid

resuscitate (NS, RL, or D51/2NS) then correct free water deficit.

–  Euvolemic: correct free water deficit.

–  Hypervolemic: consider diuresis then correct free water deficit.

•  How much free water to give back is based on the free water deficit:

Free H20 deficit (L) = [(Serum Na – 140) / 140] x

TBW

TBW = Total Body Water (esKmate from body weight in Kg: 50% for men, 40% for women)

Source: Schwartz's Principles of Surgery, 9th Ed. (2010); Sabiston Textbook of Surgery, 19th Ed. (2012)

Cerebral Edema and HerniaKon

•  Again, do not correct Na too quickly.

•  Acute hypernatremia: correct at rate of 1 mEq / hr.

•  Chronic hypernatremia: correct more slowly at rate of 0.7 mEq / hr.

•  PO or IV free water replacement is okay.

•  Example order: D5W or D51/2NS @ 50-‐100 cc / hr with electrolytes and neurovitals checked q 1-‐2h.


Sodium Formulas


Potassium

•  While sodium is the main extracellular caKon, potassium is the main intracellular caKon (98% is in cells).

•  Excreted by kidneys. •  Acid-‐base balance also affects extracellular potassium due to H+/K+ ATP ion exchanger.


Hypokalemia

•  K < 3.5 mmol / L •  EKology: GI / GU losses,

meds, low Mg. •  Immediately post-‐op is

rare since cell lysis can predispose to hyperkalemia.

•  Aldosterone (secreted in stress response from surgery) will waste K in favor of reabsorbing Na.

•  How to replace K: –  Oral: KCl 20 mEq or 40 mEq

up to 3 doses per day (can be liquid or tablet form).

–  IV: 20 mEq or 40 mEq KCl in 250cc or 500cc bag of D5W or NS infused over at least 4 hours.

–  Remember to re-‐check potassium aMer replacement to ensure adequate therapy (at least 2 hours aMer replacement).


Hyperkalemia

•  PotenKally life-‐threatening (one of the H’s/T’s for cardiac arrest!).

•  Risk factors: renal failure, burns and trauma.

•  Acute life-‐threatening treatment: –  Insulin 10-‐20 units with 1 amp

D50W –  CaCl 1 amp IV –  NaHCO3 1 amp IV –  NS bolus –  Hemodialysis


Hyperkalemia Treatment OpKons


Magnesium

•  Present in bones and cells, important role in cellular metabolism. –  Co-‐factor in many enzymaKc reacKons. – Major role in acKvity of electrically excitable Kssues . –  Regulates movement of Ca into smooth muscle cells.

•  Normal range: 1.5-‐2.5 mEq / L. •  Excreted by kidneys. •  Metabolism closely related to Potassium. •  Serum Mg = Total body Mg.


Disorders of Magnesium

Hypomagnesemia

•  EKology: GI/GU losses, malabsorpKon, Ca, K, poor intake.

•  Treatment: –  MgSO4 2g or 5g IV qD x up to

3 days or

–  Milk of Magnesia 15 cc qD x 3 days (hold for diarrhea)

–  Re-‐check Mg daily for 3 days to ensure adequate replacement.

Hypermagnesemia

•  EKology: usually renal failure (inability of kidneys to clear excess Mg).

•  Treatment: –  NS IV infusion to promote

renal excreKon of Mg.

–  CaCl IV to antagonize neuromuscular effects of Mg.

–  May need hemodialysis with ECG changes, somnolence, coma.

Source: CURRENT Diagnosis and Treatment Surgery: 13th Ed. (2010); Schwartz's Principles of Surgery, 9th Ed. (2010)

Calcium

•  99% found in bones, only 1% in extra-‐cellular fluid.

•  Important role in neuromuscular funcKon and enzymaKc processes.

•  Normal serum Ca: 4.2-‐5.2 mEq / L (1.0-‐1.5 mmol / L).

•  Mediators of Ca metabolism: PTH (parathyroid), calcitonin (thyroid), vitamin D (kidneys / diet / sun).

•  Serum Ca measurements are affected by acid-‐base status and albumin ( H / alkalemia and albumin will lead to Ca).


Hypocalcemia

•  EKology: PTH, Mg, pancreaKKs, renal failure, trauma, rhadbomyolysis, necroKzing fasciiKs.

•  Symptoms: hyperacKve DTR, Chvostek sx, cramps.

•  Treatment: –  If symptomaKc: Calcium gluconate

2g IV over 1h or CaCl 1 amp IV x 1 –  If not severe: CaCO3 (TUMS)

500-‐1500 mg PO QID –  Re-‐check Ca q6h if severe or daily

for 3 days.


Hypercalcemia

•  EKology: PTH (primary or ectopic), bone mets, Vit D, sarcoidosis, milk-‐alkali sx, thiazides, prolonged immobilizaKon.

•  Moans, bones, stones and psychological overtones.

•  Treatment: –  IV NS and Furosemide to

increase renal excreKon. –  Calcitonin and

bisphosphonates an opKon. –  Tx underlying pathology.


Phosphate

Physiology

•  Primarily a consKtuent of bone (metabolism closely related with Ca).

•  Important intracellular funcKon (ATP and DNA require phosphate, important in surgical paKents for Kssue healing).

•  ExcreKon is by the kidneys and mediated by PTH.

Pathophysiology / Treatment •  Hypophosphatemia

–  EKology: PTH, poor diet, refeeding syndrome (neuromuscular effects including cardiac death).

–  Tx: Potassium or Sodium Phosphate 15 mmol IV q8h x 2-‐3 doses. PO form also available. Re-‐check levels.

•  Hyperphosphatemia –  EKology: usually renal dx. –  Tx: diuresis, Al(OH)3, HD.


Case

•  28 year-‐old male involved in rollover MVC who sustained closed head injury. Looks euvolemic. Urine osmolality > serum osmolality. Urine sodium concentraKon high. Normal thyroid, adrenal, and renal funcKon.

•  Sodium trending down and hovering around 125 mmol / L range – what could we do to prevent this from going down further?

Case

•  55 year-‐old female with primary hyperparathyroidism, POD #0 bilateral neck exploraKon and subtotal parathyroidectomy for presumed hyperplasia.

•  Ca 6 hours post-‐op = 0.9 mmol / L without symptoms.

•  What therapy can be iniKated?

Case

•  65 year-‐old female, POD # 2 for wide excision of melanoma on chest with rotaKonal flap graM.

•  Potassium = 5.5 mmol / L. No ECG changes. Stable. Cr increased from 80 at baseline to 150.

•  Management?

Acids and Bases

Basic Primer

Acids and Bases

•  Hendersen-‐Hasselbach EquaKon:

H2O + CO2 <-‐> H2CO3 <-‐> H+ + HCO3-‐

•  CO2 is directly proporKonal to H+.

•  CO2 is a product of metabolism that is removed by respiraKon.

Normal Values

•  pH = 7.36 – 7.44 (7.4) •  PCO2 = 35 – 45 mmHg (40) •  PO2 = > 80 mmHg •  HCO3-‐ = 21 – 25 mEq/L (24) •  Anion Gap = 10 +/-‐ 2

•  ABG report of results: pH / PCO2 / PO2 / HCO3-‐

Approach to Acid/Base Problems

•  What is the “emia”? (ACIDemia or ALKALemia) •  What is the major “osis”? (4 Categories)

•  Calculate the AG for metabolic acidosis

•  Is there a superimposed METABOLIC disorder?

•  Is there a superimposed RESPIRATORY disorder?

Acidemia

•  Increased H+ due to:

–  Increased CO2 (Respiratory)

OR

– Decreased HCO3-‐ (Metabolic)

Alkalemia

•  Decreased H+ due to:

– Decreased CO2 (Respiratory)

OR

–  Increased HCO3-‐ (Metabolic)

Anion Gap

•  Anion Gap (AG) = CaKons -‐ Anions – CaKons = calcium / potassium / magnesium

– Anions = proteins / acids / phosphates / sulfates

•  Normal AG = Na+ -‐ (Cl-‐ + HCO3-‐) = 10 mEq/L ± 2

Increased AG (Metabolic Acidosis)

•  M – methanol

•  U – uremia •  D – DKA / ETOH /starvaKon •  P – paraldehyde /phenformin

•  I – iron / INH •  L – lacKc acidosis •  E – ethylene glycol •  S – salicylates

K – keytones

U – uremia

S – salicylates

M – methanol

A – other alcohols

L – lactate

Normal AG (Metabolic Acidosis)

•  Normal Anion Gap = bicarb loss •  Renal loss – RTA I, II, IV – Carbonic anhydrase inhibitors – 1° hyperparathyroidism

•  GI loss Diarrhea •  Aldosterone deficiency / antagonism

•  NS fluid resuscitaKon

Metabolic Acidosis

•  Treatment: – Treat the underlying cause – Sodium bicarbonate may be needed

Example

•  60 year-‐old female, POD # 3 from radical cystectomy and ileal conduit neobladder reconstrucKon. Febrile, tachycardic and flushed with costovertebral angle tenderness.

•  pH / PCO2 / PO2 / HCO3-‐

•  7.27 / 29 / 50 / 13 •  Na – 138, K -‐ 5.0, Cl -‐ 102

Metabolic Alkalosis

•  Physiologic = Volume sensiKve/Cl-‐ responsive –  Cause: volume depleKon –  Clue: volume depleKon – Urine Cl-‐ < 15 mEq/L

•  Pathologic = Volume resistant/ Cl-‐ resistant –  Cause: aldosterone / renin –  Clue: HTN, K+ depleKon – Urine Cl-‐ > 25 mEq/L

•  Treatment: –  Volume Resuscitate so that kidneys can start wasKng excess HCO3

-‐

Respiratory Acidosis

•  Increased PCO2 due to hypovenKlaKon •  Causes: – Pulmonary disease

– CNS dysfuncKon – Neuromuscular disease – Drug induced hypovenKlaKon

•  Treatment: treat underlying cause, may need to iniKate mechanical venKlaKon.

Example

•  25 year-‐old male, POD #0 from R Kbia / fibula ORIF on PCA hydromorphone. Called to assess decreased LOC.

•  pH / PCO2 / PO2 / HCO3-‐

•  7.30 / 50 / 90 /24

•  What is the acid/base problem?

Respiratory Alkalosis

•  Decreased PCO2 due to hypervenKlaKon

•  Cardiorespiratory and non-‐cardiorespiratory causes

Respiratory Alkalosis

Cardiorespiratory

•  Hypoxia •  Early restricKve lung disease •  PE •  Pneumonia •  Mild CHF

•  Mechanical venKlaKon

Non-‐Cardiorespiratory

•  Fever •  Sepsis •  Drugs (ASA) •  Anxiety •  CNS disorders •  Hyperthyroidism

•  Pregnancy •  Liver failure

CompensaKon

Respiratory

•  Respiratory compensaKon occurs quickly by altering respiratory rate / panern.

•  Metabolic acidosis: decreased CO2

•  Metabolic alkalosis: increased CO2

Metabolic

•  Metabolic compensaKon occurs more slowly via kidneys correct acid-‐base abnormaliKes, usually from primary lung disease.

•  Chronic respiratory acidosis: increased HCO3

-‐

•  Chronic respiratory alkalosis: decreased HCO3

-‐

Fluids and Electrolytes Acids and Bases

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Fluids and Electrolytes Acids and Bases