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Fluids & Electrolytes for Undergrads

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George G. Lim

on 18 September 2017

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Transcript of Fluids & Electrolytes for Undergrads

Hypernatremia
George G. Lim, MD, FPSGS, FPSCRS, FPCS
Fluid & Electrolytes
Professor I, Department of Surgery
Faculty of Medicine & Surgery
University of Santo Tomas

Preoperative Assessment
The dehydrated patient

Hypotension at the time of induction of anesthesia => MODS => MOF
Anesthesia interrupts normal baroreceptor reflexes
The over-hydrated patient
Edematous tissues
Normal patient
Good skin turgor
Moist mucous membranes
Normal vital signs
Stable body weight
Adequate urine output
Fluid deficit
Internal losses as in sequestration of extracellular fluid in injured tissues
Intestinal obstruction
Peritonitis
External losses
Diarrhea
Enterocutaneous fistulas
Detailed history

Duration and severity of losses
Gastrointestinal tract
THIRSTY!
Focused physical signs

Sunken eyes, dry tongue
Loss of skin turgor
Low BP, rapid pulse, low urinary output
Composition of Gastrointestinal Secretions
Thirsty
Sunken eyeballs
Dry mucous membranes
Depressed skin turgor
Decreased urine volume
Loss of 5% of body weight

Loss of ≥10% of body weight

Marked thirst
Shortness of breath
Labile BP
Tachycardia
Decreased urine output
Goal-Directed Therapy (GDT)
Urine volume of 0.5 cc/kg/hr
Stabilization of vital signs
Reversal of signs of dehydration

CVP line or Swan Ganz catheter
Urethral Foley catheter
Loss of
5% of body weight

(3.5 kg) will require about
3.5 L
to restore homeostasis
Loss of
10% of body weight
(7 kg) will require about
7 L
to restore homeostasis
Clinical approximation
0.5-1 L/hr (<2-3 L in a 4 hr OR)
Weight of blood soaked gauze
Measuring accurately the amount of blood suctioned out
Isotonic fluid replacement
Blood transfusion, if necessary
Maintenance Requirements
Insensible losses:
Lungs & skin: 600-1000 ml
Sensible water losses
Urine and feces: 1000-1500 ml
Water
30 ml/kg BW
70 kg male: 2100 ml/24 hrs
Sodium, potassium, chloride
1 mEq/kg BW
60-70 mEq/24 hrs each for a 70 kg patient
Sequestration
at operative site
Tissue edema due to manipulation
Magnitude of the surgery
Evaporation of water
from exposed viscera

Length of procedure
Blood loss
Both ends: hypotonic
Stomach: H+
Pancreas: HCO3-
Colon: K+
Postoperative Problems
Intravenous infusion of crystalloids
Physiologic responses
ADH mediated retention of water
Aldosterone mediated retention of Na & water
Catabolic response leading to release of water
Postoperative Fluid Excess
Manifestations of volume excess
Increase in BW
Increase in CVP
High pulse pressure
Swollen eyelids
Pulmonary edema
Hoarseness
Postoperative Fluid Deficit
Isotonic fluid losses
Gastrointestinal losses
Other sensible losses
NGT output, enterostomies, etc.
Inadequate fluid replacement
Inadequate intraoperative replacement
Manifestations of volume depletion
Weight loss
Tachycardia
Weak pulse
Dry mucosa
Hypotension
Oliguria
Hyponatremia
Hypotonic volume excess
Infusion of D5W
SIADH
Renal disorder
Catabolism
Water of oxidation
Manifestations
Cellular swelling
Confusion
Weakness
Nausea & vomiting
Convulsions
Coma
Treatment
Maximum change of Na per day:
12-16 mEq (0.7 mEq/L/hr)
Hypokalemia
K+ Abnormalities
Hyperkalemia
Release of K+ in immediate postoperative period
Tissue catabolism
Operative trauma
Blood transfusion
Normal neurohormonal response leads to loss of K+ in urine
K+ deficiency
Prolonged K+ free IV fluids infusion
Inappropriate replacement of daily K+ losses
Unsuspected / neglected GI losses
K+ excess
Renal dysfunction / disease
Manifestations

Cardiac
Bradycardia
Hypotension
Ventricular fibrillation / Cardiac arrest
Muscular
Weakness
Paresthesia
Treatment of hypokalemia
Ensure adequate renal function
Replacement should not exceed 150-200 mEq/day or 10-15 mEq/hr
Treatment of hyperkalemia
50 ml D50W + insulin 10-25 units IV infusion over 30 minutes (GIK)
Sodium bicarbonate
5-10 ml 10% Ca gluconate slow IV
Acidosis
Acid Base Disorders
Alkalosis
Metabolic acidosis
Primary decrease in [HCO3-]
Respiratory acidosis
Primary increase in pCO2
Cardiovascular effects
Decreased myocardial contractility
Decreased responsiveness of the peripheral vasculature to circulating catecholamines
Increased refractoriness of the fibrillating myocardium to defibrillation
Metabolic effects
O2-Hgb dissociation curve shifts to the right
Decreased affinity of Hgb for O2
Common postoperative causes

Inadequate ventilation
Pulmonary insufficiency
Poor tissue perfusion
Impairment of renal function
Diabetes mellitus
Loss of alkali via GI secretions
Respiratory causes of postoperative acidosis
Inadequate ventilation
Depression of respiratory center
Impaired thoracic excursion
Airway obstruction
COPD
Inappropriate ventilatory settings
Anion Gap
Change in unmeasured anions or cations
Increase in endogenously produced acids
Decreases in renal excretion of acids
Ingestion of toxins
= [Na+] - ([Cl-] + [HCO3-])
Normal value: 12 ± 2 mEq/L
Treatment
Correct tissue perfusion
Correct alveolar ventilation
Deep breathing and coughing
Suction of retained secretions
Humidification of air
Avoidance of over-sedation
Use of IV bicarbonate
Metabolic alkalosis
Primary increase in [HCO3-]
Respiratory alkalosis
Primary decrease in pCO2
Metabolic causes
Post-traumatic aldosteronism
Renal inhibition of bicarbonate excretion & excessive K+ excretion
Nasogastric suction
Removing H+ ions along with Cl-
Transfused blood with citrate being oxidized to bicarbonate
Respiratory causes
Hyperventilation secondary to apprehension or pain
Inappropriate respiratory therapy
Manifestations
Insidious onset
CNS: decreased cerebral blood flow
Dizziness, nervousness, confusion, obtundation, stupor, coma
Muscular: decreased ionized Ca++
Tetany & neuromuscular irritability
Treatment
Correction of the underlying cause
Correction of potassium depletion
Correction of volume depletion
Cl- containing solutions
Acid infusion
NH4Cl, arginine HCl, lysine HCl, or dilute HCl acid (0.1 N)
Treatment
Correction of respiratory alkalosis
Hyperventilation
Rebreathing CO2
Adjustment of tidal volume or respiratory rate
In a 70 kg patient with Na+ of 170 mEq/L
TBW = 60% x BW = 0.60 x 70 = 42 L
Manifestations
Severe thirst
CNS manifestations
Restlessness, irritability
Spasms, stupor, coma
Fever
Hypertonic volume deficit
∆ insensible loss of water
Renal disease
CNS trauma
Hyperosmolar dehydration
Solute loading (tube feeding)
In a 70 kg patient with a Na+ level of 120 mEq/L
Na+ required = (140 - 120) × TBW
Na+ required = (140 - 120) × (0.6 × [70])
= 20 × 42 = 840 mEq
Treatment
Restrict water intake
Serial monitoring of serum sodium
Na+ required (in mEq) = (desired serum Na - actual serum Na) × TBW
Na+ Abnormalities
Intraoperative
Ma
nagement
+ Hemodynamic changes
Tachycardia
Labile BP
Loss of 10% of body weight
Full transcript