Disorders of Salt and Water Balance

Blood Volume & Plasma Osmolality

* Tightly regulated
* Blood volume – saline balance
* Plasma osmolality – water balance

Blood Volume & Plasma Osmolality: Tightly Regulated

* Essential for normal function
* Frequently cause or contribute to hospitalization

Blood Volume & Plasma Osmolality: Blood Volume (Saline Balance)

* Assessed by physical exam
* Regulated by RAA, ANP, sympathetic nervous system

Blood Volume & Plasma Osmolality: Plasma Osmolality (Water Balance)

* Assessed by serum sodium and osmolality
* Regulated by osmoreceptors, vasopressin, thirst

Maintenance of Fluid Balance

* Antidiuretic Hormone (ADH)
* Renin – Angiotensin – Aldosterone System
* Sympathetic nervous system - VASOCONSTRICTION
* Thirst
* Normal responses to hypovolemia/hyperosmolality

Antidiuretic Hormone (ADH) and It’s Serum Calculation

* Water conservation hormone
* Calculated serum Osm = 2(Na) + (glucose)/18 + (BUN)/2.8

Maintenance of Fluid Balance: Antidiuretic Hormone (ADH)

* Increases water permeability of renal collecting duct
* Increases peripheral vascular resistance

Maintenance of Fluid Balance: Renin – Angiotensin – Aldosterone System

* Vasoconstriction → increased renal perfusion
* Increased reabsorption of sodium, chloride, and water

Maintenance of Fluid Balance: Thirst

* Osmoreceptors in the hypothalamus
* Baroreceptors - L Atrium, Carotid arteries, Macula Densa

Movement of solutions in the Body

* Osmotic Pressure
* Oncotic Pressure

Movement of solutions in the Body: Osmotic Pressure

* Ability of solutes to cause osmotic driving forces
* Osmolarity (mOsm/L)
* Osmolality (mOsm/kg)
* Tonicity = effective osmolality

Osmolality (mOsm/kg)

* Serum osm **≅ (2 x [Na]) + ([Glucose]/18) + ([BUN]/2.8)**


* Na-mEq/L; Glucose and BUN mg/dL

Tonicity

* Osmotic solutes that CANNOT freely move across membranes
* Serum tonicity = 2 x (Na) + (Glucose/18)

Movement of solutions in the Body: Oncotic Pressure

Plasma proteins

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Maintenance of Fluid Balance

Role of Water

* Solvent
* Delivery/removal of nutrients/wastes
* Medium for electrolyte/chemical Rxn

Body Water (TBW)

* Pediatrics > Adults > Geriatrics
* Children and men <70 years: 0.6L/kg x wt
* Men >70 and women <70 years: 0.5 L/kg x wt
* Women > 70 years: 0.45 L/kg x wt
* Dehydrated older patients: 0.4 L/kg x wt
* Muscle > Fat

Body Fluid Compartments

* Extracellular Fluid
* Intravascular Space (25%)
* Interstitial Space (75%)
* Intracellular Fluid

Body Fluid Compartment Percentages

* 1/3 ECF
* 2/3 ICF

Parenteral Fluid Therapy

* Dextrose solutions (water)
* Crystalloids (Salt containing)
* Colloids
* Blood and blood products

Parenteral Fluid Therapy: Dextrose Solutions (Water)

Electrolytes can be added as needed

Parenteral Fluid Therapy: Crystalloids (Salt containing)

* Additional electrolytes can be added
* Isotonic vs. Hypotonic

Parenteral Fluid Therapy: Colloids

* Hetastarch
* Dextran
* Albumin

Isotonic Crystalloids

* Lactated Ringer’s (LR)
* 0.9% “normal” saline – 300 mOsm/L

Isotonic Crystalloids: Distribution

* 100 % ECF
* Osmolality approximates that of the ECF
* No osmotic pul

Isotonic Crystalloids: 5 R’s

Resuscitate

Hypotonic Crystalloids

0\.45% normal saline, “half-normal saline”

Hypotonic Crystalloids: Distribution

½ H2O : ½ NS

Hypotonic Crystalloids: Routine Maintenance Fluid

* Inadequate for fluid resuscitation
* Dextrose added for isotonicity, calories

Dextrose

5% dextrose in water (D5W)

Dextrose Distribution

* Rapid dextrose metabolism/clearance
* “free water”
* Equal distribution throughout body

Dextrose: 5 R’s

Rehydrate

Colloid Solutions

* Fluids that contain high molecular weight substances
* Do not readily migrate across capillary walls
* Oncotic activity “pulls” fluid intravascularly

Colloid Solutions: Preparations

* Hetastarch 6%
* Iso-oncotic

Colloid Solutions: Uses

* Third-spacing
* Resuscitate

Colloid Solutions: ADE

* Bleeding/anaphylaxis
* Kidney injury

Colloid Solutions: Albumin

* NaCl content iso-osmotic
* Iso-oncotic 5% albumin: hypovolemia
* Hyperoncotic 25% albumin: Pull fluid for diuresis

Colloid Solutions: Albumin Cost

$$$ - Pooled Blood Product

Colloid Solutions: Albumin Leakage

* Leakage to interstitial space
* Hours to days

Colloid Solutions: Albumin Availability

* Shortages have been common
* Restricted use

Blood Replacement

* Replace blood with blood (PRBCs)
* Hemorrhage
* Anemia
* O2 carrying
* Goal hemoglobin?

Blood Products

* FFP
* Platelets

The 5 R’s

* Resuscitate
* Routine Maintenance
* Replacement & Redistribution
* Reassessment

Resuscitate For…

Hypovolemia

Hypovolemia Treatment Goal

Maintain/restore BP and tissue perfusion

Hypovolemia: Physiologic Compensation

* Physiologic compensation occurs
* Thirst, ADH, Renin, Aldosterone
* Sympathetic nervous system

Hypovolemia Interventions

* Oral or Intravenous intervention
* Electrolyte correction is often also needed

Hypovolemia: Signs & Symptom

* Consistent history
* Continuum of severity
* Variable dependant on age, rapidity, diseases, meds
* Mild thirst to shock

Hypovolemia Signs

* ↑pulse/resp rate
* ↓BP
* ∆mental status
* Agitation
* ↓capillary refill
* ↓urine output

Hypovolemia Symptoms

* Thirst
* Nausea
* Anxiety
* Weakness
* Dizzy/light headed

Hypovolemia: Sympathetic Activation

* Tachycardia
* Increased Systemic Vascular Resistance (SVR) shunts blood to $heart$ and $brain$

Hypovolemia: Sympathetic Activation Specificity

* Brain – light-headed to coma
* Heart – strain can cause demand infarct
* Skin – cyanosis with cold clammy skin
* Kidneys
* Muscle, GI tract, Liver

Hypovolemia: Sympathetic Activation of Kidney’s

* Decreased urine output (<500ml/day)
* Normal: 0.5\~1ml/kg/h
* Dark-yellow urine w/ increased spec grav
* BUN : Creatinine > 20-40 : 1

Hypovolemia: Laboratory Evaluation

* Increased BUN:creatinine ratio
* Hyper or Hypo-natremia
* Hyper or Hypo-kalemia
* Acidosis or Alkalosis
* Elevated hematocrit – unless acute blood loss

Causes of Hypovolemia

* GI Losses
* Renal Losses
* Skin Losses
* Third Spacing
* Bleeding

Causes of Hypovolemia: GI Losses

* Vomiting
* Diarrhea
* Fistula
* Bleeding
* Drainage

Causes of Hypovolemia: Renal Losses

* Diuretics
* Osmotic agents

Causes of Hypovolemia: Skin Losses

* Sweat
* Burns

Causes of Hypovolemia: Third Spacing

* Bowel obstruction
* Crush
* Fractures
* Pancreatitis

Treatment of Hypovolemia & Shock

Rate of repletion – as fast as possible

Treatment of Hypovolemia & Shock: Choice of Fluid

* Give blood if bleeding
* Isotonic crystalloid solutions – 0.9% saline preferred
* 250-500 mL NS over 15 min, reassess, repeat as needed
* Effective, inexpensive
* AVOID hetastarch – increased kidney injury & mortality
* AVOID colloid – does not improve outcomes
* Exception may be use of albumin in severe sepsis

Treatment of Hypovolemia & Shock: Monitoring

* Continuous assessment of vital signs, urine output, perfusion
* Others: physical exam, serum lactate, arterial pH

Hypovolemia: Special Populations (Elderly)

* Thirst
* Communication
* Impaired sensation
* Disabled, comatose
* ↓ TBW
* Kidney has ↓ concentrating ability
* ↓ response to ADH
* ↓ # of nephrons

Hypovolemia: Special Populations (Infants)

* Thirst
* Communication
* ↑ mL/kg water requirement
* ↑ TBW relative to weight
* ↑ metabolism (heat)
* Kidney has ↓ concentrating ability
* Immature

Daily Fluid Requirements: Sensible Losses

* GI output, urinary output


* Readily measurable

Daily Fluid Requirements: Insensible Losses

* From skin, lung, some GI losses
* Difficult to measure
* Variable
* Respiratory Rate
* Mechanical Ventilation
* Ambient Temperature
* Febrile illness
* Add 10% for each degree over 37 C°

Daily Fluid Requirements: Maintenance

Maintenance Monitoring

* Reevaluate IVF “prescription” at least daily
* Physical assessment
* Ins & outs, weight
* Laboratory assessment

Maintenance Adjustments

* Serum sodium dropping – decrease “free water”, D5NS
* Serum sodium increasing – increase “free water”, D5 ¼ NS
* Add or remove potassium as needed

Replacement & Redistribution: Electrolyte Loss From Fluids

Reassessment

Ongoing monitoring

Ongoing Monitoring

* Physical Exam
* Clinical Documentation
* Laboratory Assessment
* Other medications
* Determine need for continued therapy
* Alter prescription as needed

Ongoing Monitoring: Physical Exam

* Vital signs
* Neurologic status, lung exam, cardiac exam, extremities, skin

Ongoing Monitoring: Clinical Documentation

* Volume of fluid received, current rates and composition
* Urinary output – hourly, totals

Ongoing Monitoring: Laboratory Assessment

* Electrolytes
* Acid/base
* Renal function
* Lactate

Hypernatremia

* Hyperosmolar – always
* Hypervolemic
* Isovolemic
* Hypovolemic

Hyperosmolar

* Potent thirst stimulus (access to water?)
* Often associated with severe underlying disease

Hypervolemic

* Iatrogenic (illness cause by medical examination/treatment)
* Cushing’s Syndrome
* Hyperaldosteronism

Isovolemic

Nephrogenic or central diabetes insipidis

Hypovolemic

* Diuretics
* Osmotic diuresis (DKA)
* GI losses

Symptoms of Hypernatremia

* Neurologic
* Lethargy, confusion, seizures, myoclonus
* Due to alterations in cell volume
* Other (Due to volume depletion)
* Hypotension
* Tachycardia
* Oliguria, etc.

Hypernatremia: Lowering Na

Free water deficit: 3mls/kg of fluid will lower Na by 1mEq/L

Acute Hypernatremia

Acute Hypernatremia: Monitoring and Treatment

* D5W at 3-6ml/kg/hr to max of 666 mls/hr
* Monitor Na and glucose q 1-3 hours
* Continue at rate until 145mEq/L, then reduce to 1ml/kg/hr until \n normal Na

Acute Hypernatremia Goal

1-2mEq/L hr and normal Na at 24 hours

Chronic Hypernatremia

>48 hours

Chronic Hypernatremia: Monitoring and Treatment

* D5W at 1.35ml/kg/hr to a max of 150ml/Hr
* Monitor Na every 4-6 hours

Chronic Hypernatremia Goal

Reduce by 10mEq/L in 24 hours (max 12mEq)

Most Common Electrolyte Abnormality in the Hospital

Hyponatremia

Hyponatremia and Patient Outcomes

Associated with poor patient outcomes

Hyponatremia

* Primarily a Water abnormality with abnormal ADH
* Serum Na < 135 mEq/L

Symptoms of Hyponatremia

* Due to alterations in cell volume
* Acute vs. Chronic changes

Symptoms of Moderate Hyponatremia

* Nausea
* Confusion
* Headache

Symptoms of Severe Hyponatremia

* Vomiting
* Somnolence
* Seizures
* Coma
* Brain herniation
* Cardiorespiratory distress

Symptoms of Chronic Hyponatremia

* Gait disturbance
* Falls
* Conigitive deficits
* Osteoporosis/fractures
* Increased risk of death

Hyponatremia Classification

* Isotonic hyponatremia: normal serum osmolarity (\~280)
* Hypertonic hyponatremia: elevated serum osmolarity (>280)
* Hypotonic hyponatremia: Low serum osmolarity (<280)

Isotonic hyponatremia

* Pseudohyponatremia
* Elevated concentrations of serum lipids or proteins

Hypertonic Hyponatremia

* Excess effective osmoles
* Correction factor

Hypertonic Hyponatremia: Excess Effective Osmoles

* Hyperglycemia, mannitol, alcohols
* Diffusion of water from cells

Hypertonic Hyponatremia: Correction Factor

* For every 100 mg/dL ↑ in glucose the measured serum Na falsely decreases by 2.4 mEq/L


* Corrected Na=Measured Na + 0.024 \* (Serum Glucose-100)