Fluids and Electrolytes Acids and Bases Principles of Surgery July 25, 2012 May Tee, MD, MPH PGY5 General Surgery
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%)
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
Source: Schwartz's Principles of Surgery, 9th Ed. (2010)
(+ 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.
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.
• 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)
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.
• 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
• 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
-‐