Fluids and Electrolytes Acids and Bases

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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%) ICF – 2/3 (40%) Intravascular 1/4 (5%) Source: CURRENT Diagnosis and Treatment Surgery: 13th Ed. (2010) Electrolyte DistribuKon Source: CURRENT Diagnosis and Treatment Surgery: 13th Ed. (2010) 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. Source: CURRENT Diagnosis and Treatment Surgery: 13th Ed. (2010) 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. Source: Sabiston Textbook of Surgery, 19th Ed. (2012) 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 Source: Sabiston Textbook of Surgery, 19th Ed. (2012) Crystalloids (+ 20 mEq KCl = 2 mEq K) (provides 50g glucose) Source: Schwartz's Principles of Surgery, 9th Ed. (2010) 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 •  What is a good peri-­‐op undergoing elecKve R IV fluid? Hemi, R nephrectomy, R adrenalectomy for •  What rate would you retroperitoneal sarcoma run this guy if he were excision. 70 kg? •  PMHx: Healthy. •  Meds: None. •  All: None. Case •  55 year-­‐old female with •  Would you bolus this SBO, being admined paKent if she looked dry with goal to trial non-­‐
given CAD? operaKve management first. •  What IV fluid would you •  PMHx: Hypertension, use and how much? CAD. •  Meds: Ramipril / HCTZ, •  What about NG losses – ASA, AtorvastaKn. would you replace •  All: None. 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. Source: Schwartz's Principles of Surgery, 9th Ed. (2010) 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. •  What is opKmal urine output? •  Called re: low urine output. •  What IV Fluid and how much? •  Should we bolus the paKent? 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) Source: Sabiston Textbook of Surgery, 19th Ed. (2012) 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. Source: Schwartz's Principles of Surgery, 9th Ed. (2010) 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. Source: Schwartz's Principles of Surgery, 9th Ed. (2010) Sodium Formulas Source: Sabiston Textbook of Surgery, 19th Ed. (2012) 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. Source: CURRENT Diagnosis and Treatment Surgery: 13th Ed. (2010) 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). Source: Schwartz's Principles of Surgery, 9th Ed. (2010) 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 Source: Schwartz's Principles of Surgery, 9th Ed. (2010) Hyperkalemia Treatment OpKons Source: Schwartz's Principles of Surgery, 9th Ed. (2010) 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. • 
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Normal range: 1.5-­‐2.5 mEq / L. Excreted by kidneys. Metabolism closely related to Potassium. Serum Mg = Total body Mg. Source: CURRENT Diagnosis and Treatment Surgery: 13th Ed. (2010) 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). Source: CURRENT Diagnosis and Treatment Surgery: 13th Ed. (2010) 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. Source: CURRENT Diagnosis and Treatment Surgery: 13th Ed. (2010); Schwartz's Principles of Surgery, 9th Ed. (2010) 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. Source: CURRENT Diagnosis and Treatment Surgery: 13th Ed. (2010); Schwartz's Principles of Surgery, 9th Ed. (2010) 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. Source: CURRENT Diagnosis and Treatment Surgery: 13th Ed. (2010); Schwartz's Principles of Surgery, 9th Ed. (2010) 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 • 
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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 • 
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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) • 
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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-­‐