fluids and electrolytes acids and bases
TRANSCRIPT
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
-‐