S&P Lecture 6: Surgical Critical Care

What is the 60-40-20 rule of fluid compartments?

TBW = 60% of body weight; ICF = 40%; ECF = 20%

What % of body weight is total body water in an adult male, and how much is that in a 70 kg male?

~60% of body weight = 42 L

What % of body weight is intracellular fluid (ICF), and what fraction of TBW?

40% of body weight - 2/3 of TBW (~28 L)

What is the primary cation of the intracellular fluid?

Potassium

What % of body weight is extracellular fluid (ECF), and what fraction of TBW?

20% of body weight - 1/3 of TBW (~14 L)

What is the primary cation of the extracellular fluid?

Sodium

What % of body weight is interstitial fluid, and what fraction of ECF?

15% of body weight - 3/4 of ECF (~10.5 L)

What % of body weight is intravascular volume (plasma), and what fraction of ECF?

4-5% of body weight - 1/4 of ECF (~3.5 L)

What is total blood volume (including RBCs) as a % of body weight?

~7% of body weight (~5 L)

What are the typical IV fluid choices? (select all that apply)

1. Lactated Ringer's 2. Normal saline 3. D5NS (± KCl) 4. D5W 5. 1/2NS

What are crystalloids, and how much remains intravascular?

Water + electrolytes/dextrose that freely cross capillary membranes - only ~25% remains intravascular

Which IV fluids are ISOTONIC crystalloids? (select all that apply)

1. Lactated Ringer's (LR) 2. 0.9% Normal saline (NS)

Which IV fluids are HYPOTONIC crystalloids? (select all that apply)

1. 0.45% NaCl (1/2 NS) 2. D5W

What is the hypertonic crystalloid?

3% NaCl

How is isotonic bicarbonate made?

150 mEq NaHCO3 (3 amps bicarb) mixed in 1 L of D5W or sterile water

What are colloids?

Large molecules that remain in the intravascular space to maintain oncotic pressure

What are examples of colloids? (select all that apply)

1. Albumin (5% or 25%) 2. FFP 3. PRBCs

Why aren't colloids used over crystalloids for resuscitation (CRISTAL trial)?

No mortality benefit with colloids

Of 1 L of isotonic fluid (NS or LR), how much stays in the plasma?

~250 mL (1/4)

Of 1 L of D5W (free water), how much stays in the plasma?

~83 mL (1/12) - it distributes across both ECF and ICF

What is the Na and Cl content of 0.9% NS?

Na 154, Cl 154 mEq/L

What is the Na, Cl, and K content of Lactated Ringer's?

Na 130, Cl 109, K 4 mEq/L (plus lactate)

What is the goal of post-op fluid management in the first 24 hours?

Restore euvolemia and perfuse end-organs

What is the fluid of choice in the first 24 hours post-op?

Isotonic crystalloid (LR or 0.9% NS)

What UOP indicates adequate post-op resuscitation?

> 0.5 mL/kg/hr

Besides UOP, how is post-op resuscitation adequacy monitored? (select all that apply)

1. Vital signs (HR, BP/MAP) 2. Mental status 3. Lactate

Which fluid losses must be tracked post-op? (select all that apply)

1. Urine 2. NG tubes 3. Surgical drains 4. Ostomies 5. Insensible losses

When should a BMP be checked post-op (not routinely needed if uncomplicated)? (select all that apply)

1. Active diuresis 2. High GI/drain output 3. Renal dysfunction

What is the goal of post-op fluid management at 24-48 hours?

Transition to enteral hydration or basal maintenance

At 24-48 hr post-op, what do you do with IV fluids if the patient is tolerating PO/enteral feeds?

Discontinue IV fluids - most uncomplicated patients don't need IVF after 24-48 hrs

What maintenance fluid is used if the patient is NPO/unable to tolerate enteral nutrition?

D5 1/2NS + 20 mEq/L KCl

What is the safety rule before adding potassium to IV fluids?

Only add K after confirming normal renal function and adequate urine output

Should post-op maintenance fluids be routinely continued?

No - most patients don't need maintenance fluids after 24-48 hrs unless continued losses are present

Is volume excess or deficit more common in the post-op patient?

Volume excess

What is the best way to monitor for post-op fluid excess?

Patient weight - cannot rely solely on peripheral edema

What is normal post-op weight loss?

0.25-0.5 lb/day (0.11-0.23 kg/day)

What are the daily maintenance fluid requirements?

~30 mL/kg/day (1-1.5 mL/kg/hr) - 70 kg pt = 2100 mL

When can daily maintenance fluid requirements be calculated?

Not until resuscitation is complete

Volume DEFICIT vs EXCESS - generalized findings?

Deficit: weight loss, decreased skin turgor. Excess: weight gain, peripheral edema

Volume DEFICIT vs EXCESS - cardiac findings?

Deficit: tachycardia, orthostasis/hypotension, collapsed neck veins. Excess: increased CO, increased CVP, distended neck veins, murmur

Volume DEFICIT vs EXCESS - renal, GI, and pulmonary findings?

Deficit: oliguria, azotemia, ileus. Excess: bowel edema, pulmonary edema

Which electrolytes are most frequently deranged in the post-op patient?

Sodium and potassium

What are the normal ranges for Na and K?

Na 135-145; K 3.5-5.5

What is the daily basal SODIUM need?

1-2 mEq/kg/day (~70-150 mEq)

What is the daily basal POTASSIUM need?

0.5-1 mEq/kg/day (~40-70 mEq)

What is the daily basal CHLORIDE need?

1-2 mEq/kg/day (~70-150 mEq)

How is hyponatremia treated?

Free water restriction; 3% saline if severe or neuro symptoms

What is the maximum rate of serum sodium correction per day?

No more than 8-10 mEq/L per day

What complication results from correcting sodium too quickly?

Central pontine myelinolysis

How fast can SYMPTOMATIC hyponatremia be corrected, and to what level?

Up to 1 mEq/L/hr until Na reaches 130 mEq/L

How fast can ASYMPTOMATIC hyponatremia be corrected?

Up to 0.5 mEq/L/hr

How is hypernatremia treated?

Resolve the water deficit; avoid rapid correction

In a hypovolemic hypernatremic patient, how are fluids given?

Replace with NS first, then switch to D5W, D5 1/4NS, or enteral water

What are the two steps in treating hyperkalemia?

1. Obtain EKG 2. First shift K into the cell (temporary), then remove it from the body

Which treatments SHIFT potassium into cells? (select all that apply)

1. Glucose (1 ampule D50) + regular insulin 5-10 units IV 2. Bicarbonate 1 ampule IV

Which treatments REMOVE potassium from the body? (select all that apply)

1. Sodium polystyrene sulfonate (oral or rectal) 2. Dialysis

What is given to counteract the cardiac effects of hyperkalemia?

Calcium gluconate 5-10 mL of 10% solution

What are the EKG changes of hyperkalemia?

Peaked T waves and prolonged QRS

What is the EKG change of hypokalemia?

U wave

Patients with what chronic disease require slow and careful K replacement?

CKD

How is ASYMPTOMATIC hypokalemia treated?

PO repletion - 40 mEq KCl

How is SYMPTOMATIC hypokalemia treated?

KCl 20 mEq IV/hr × 4 bolus doses

Above what IV potassium rate must the patient be on a cardiac monitor?

> 10 mEq/hr

Why do hypokalemic patients often need multiple doses of K?

Total body potassium losses must be replaced

When managing a volume disorder in a surgical patient, what two things must be done at the same time?

Find the cause AND address the volume disorder itself

What are the causes of HYPOVOLEMIA in the surgical patient? (select all that apply)

1. Hemorrhage (most common) 2. GI loss (diarrhea/vomiting) 3. Sequestration of fluid in gut lumen (bowel obstruction, ileus) 4. Burn (3rd spacing) 5. Excessive diuretic use

What is the presentation of HYPOVOLEMIA? (select all that apply)

1. Dry mucous membranes 2. Increased cap refill time 3. Postural hypotension 4. Unclear speech/extremity weakness 5. Postural tachycardia (> 30 bpm increase)

What lab finding suggests hypovolemia, and is it definitive?

Elevated BUN/Cr ratio > 20 (prerenal azotemia) - suggestive, not definitive

How is HYPOVOLEMIA treated? (select all that apply)

1. Isotonic fluids (LR might be better than NS) 2. Frequent reassessments 3. Manage concurrent electrolyte derangements

What are the causes of HYPERVOLEMIA in the surgical patient? (select all that apply)

1. Iatrogenic 2. Physiologic response to surgery (ADH increase) 3. HF, renal, or hepatic disease exacerbation

How does surgery physiologically cause hypervolemia?

↑ ADH → decreased filtration of Na+ → greater water retention

What is the presentation of HYPERVOLEMIA? (select all that apply)

1. Hypertension 2. Decreased O2 sat 3. Basilar crackles 4. JVD 5. Dependent edema 6. Gallop 7. Rapid weight gain

How is HYPERVOLEMIA treated? (select all that apply)

1. Stop excess fluids 2. Diuretics if CHF or pulm edema 3. Mechanical ventilation if severe respiratory failure from fluid 4. Hemodialysis

What is the normal pH range?

7.35-7.45

What is the normal PaCO2 range?

35-45 mmHg

What is the normal HCO3 range?

22-26 mEq/L

What is the normal PaO2 range?

75-100 mmHg

What is the normal base excess/deficit range?

-4 to +2

What is the normal SaO2 range?

95-100%

Metabolic acidosis: direction of pH, HCO3, and PCO2?

pH ↓, HCO3 ↓, PCO2 ↓ (compensatory)

Metabolic alkalosis: direction of pH, HCO3, and PCO2?

pH ↑, HCO3 ↑, PCO2 ↑ (compensatory)

Respiratory acidosis: direction of pH, HCO3, and PCO2?

pH ↓, HCO3 ↑ (compensatory), PCO2 ↑

Respiratory alkalosis: direction of pH, HCO3, and PCO2?

pH ↑, HCO3 ↓ (compensatory), PCO2 ↓

How do pH and PaCO2 move in a RESPIRATORY disorder vs a METABOLIC disorder?

Respiratory: opposite directions. Metabolic: same direction

What is the pathophysiology of respiratory acidosis?

CO2 accumulates → converts to H2CO3 → acidosis

What are causes of RESPIRATORY ACIDOSIS? (select all that apply)

1. Respiratory arrest 2. Airway obstruction 3. Pulmonary edema 4. Pneumonia 5. Saddle PE 6. Aspiration 7. ARDS 8. Hypoventilation from excess sedation, pain, or ethanol 9. Head trauma

Which acid-base disorder is the fastest and most common result of respiratory failure?

Respiratory acidosis

What are causes of RESPIRATORY ALKALOSIS? (select all that apply)

1. Hyperventilation - anxiety, agitation, pain 2. Early sign of sepsis 3. Early sign of PE

How is respiratory alkalosis treated?

Treat the underlying condition - it will resolve

What are causes of METABOLIC ALKALOSIS? (select all that apply)

1. Loss of H+ ion - gastric losses 2. Hypovolemia 3. Total body K+ depletion

How is metabolic alkalosis treated?

Volume restoration with adequate crystalloid (kidney minimizes Na+ reabsorption and excretes excess bicarb) + replace lost K+

What are the two broad causes of METABOLIC ACIDOSIS?

Increased production of H+ ion OR excessive loss of HCO3 (bicarb)

What is calculated to narrow down the cause of metabolic acidosis?

Anion gap

What is the anion gap formula?

AG = Na - (Cl + HCO3)

How is metabolic acidosis treated, and is sodium bicarb needed?

Find and correct the underlying cause - *generally* do not need to add NaHCO3

ABG: pH 7.41, PaCO2 40, HCO3 24. Interpretation?

Normal ABG

ABG: pH 7.31, PaCO2 30, HCO3 15. Interpretation?

Metabolic acidosis with respiratory compensation

ABG: pH 7.55, PaCO2 30, HCO3 24. Interpretation?

Respiratory alkalosis

ABG: pH 7.12, PaCO2 40, HCO3 16, Na 140, Cl 100. Interpretation and anion gap?

Metabolic acidosis - AG = 140 - (100 + 16) = 24 (anion gap metabolic acidosis)

ABG: pH 7.22, PaCO2 55, HCO3 23. Interpretation?

Respiratory acidosis