Monday, June 13, 2011

Four Rs of fluids

Resuscitation Rehydration Rectification Regular (Maintenance)
  • Decreased blood pressure
  • Increased lactic acid
  • Decreased urine output
Hypovolemia +/- electrolyte abnormalities
  • "Pre-shock" (downtrends in blood pressure or urine output, increasing tachycardia)
  • Diabetic ketoacidosis
  • Rhabdomyolysis

  • Post-obstructive diuresis
  • Hypovolemic acute prerenal failure
  • Pancreatitis
Electrolyte abnormalities +/- hypovolemia
  • Hypovolemic hyponatremia
  • Hypernatremia
  • Hypokalemia
  • Hyperchloremic acidosis

Choice of fluids
  • NS
  • LR
  • Albumin
  • Hespan (but numerous contraindications)
Typically composition is directed by published guidelines (as in DKA) or fluids can be formulated by the considerations for maintenance fluids given in the column furthest to the right. Remember that 40 mEq of potassium in a peripheral line has a maximal infusion rate of 125 mL/hr Hypovolemic hyponatremia
  • 0.9% saline ("NS", 154 mEq Na/L)
  • 3% saline (513 mEq Na/L)
  • 0.45% saline ("1/2 NS", 77 mEq Na/L)
  • D5 (0 mEq Na/L)
  • Given normal renal function, assume 20 mEq of potassium increases serum potassium 0.25 mEq/L

Hyperchloremic acidosis

  • Assuming mild hyponatremia or normal sodium consider 150 mEq NaHCO3 in 1000 mL of D5 or free water (1)

Based on electrolytes, specifically: sodium, potassium, chloride, bicarbonate, and glucose (and occasionally phosphate) as well as blood pressure. If they are hypertensive consider hypotonic (1/2 NS) rather than isotonic (NS, LR) solutions even if they are mildly hyponatremic.
  • If Na is within normal limits < 140 use NS, > 140 use 1/2 NS
  • If K is within normal limits < 4 add 20 mEq KCl
  • If hypoglycemic or marginally hyperglycemic use the D5 variant of the 1/2 NS or NS chosen above
20 mL/kg of crystalloid (NS or LR) over 15-20 minutes (thus a pressure bag is needed) 100-1000 mL/hr titrated to whatever volume deficit you are correcting Hypovolemic hyponatremia
  • The initial rate to correct by 10 mEq/L in 24 hours with NS is by rough calculation 1.35 x wgt [kg] for the rate in mL/hr. If using 3% saline multiply by 0.3 (2)
  • Titrate the rate to serial BMP, if life threatening hyponatremia (e.g. seizures) correction may be more rapid for the first few hours but still < 10-12 mEq/L over 24 hours
  • The initial rate to correct by 10 mEq/L in 24 hours with D5 is by rough calculation 1.35 x wgt [kg] for the rate in mL/hr. If using 0.45% saline multiply by 2.
  • Titrate the rate to serial BMP, such that the rate of correction < 10-12 mEq/L over 24 hours
  • Maximal correction via peripheral line is 40 mEq/L in 500 mL NS over four hours or 125 mL/hr
Hyperchloremic acidosis
  • As per "rehydration" rates
40-20-10 "rule" (for patients with normal electrolyte hemostatic mechanisms)
  • 40 mL/hr for the first 10 kg
  • 20 mL/hr for the second 10 kg
  • 10 mL/hr for each additional 10 kg
How do you know it's working
  • Blood pressure increases
  • Lactic acid decreases
  • Urine output increases
  • Blood pressure, heart rate, and urine output improve ("preshock")
  • Anion gap decreases (diabetic ketoacidosis)
  • CK and renal function improve (rhabdomyolysis)
  • Replace 50% of urine output per hour (post-obstructive diuresis)
  • Urine output increases and renal function improves (hypovolemic acute prerenal failure)
  • Amylase and lipase improve (pancreatitis)
Hypovolemic hyponatremia
  • Sodium corrects by < 2 mEq/L every 4 hours, thus check BMP or I-STAT every 2-4 hours and titrate rate and composition of fluids appropriately
  • Sodium corrects by < 2 mEq/L every 4 hours, thus check BMP or I-STAT every 2-4 hours and titrate rate and composition of fluids appropriately
  • Electrolyte correction monitoring at most Q8H
Hyperchloremic acidosis
  • Electrolyte correction monitoring at most Q8H
The patient remains hemodynamically stable without electrolyte abnormalities or worsening renal function
  1. Assuming NaHCO3 comes in a stock solution of 1 mEq/mL, then [C] = solute osmolarity / solution volume

    = solute osmolarity / (solute volume + solvent volume)

    = 150 mEq / (0.150 L + 1 L) = 130 mEq NaHCO3/L

    In 850 mL of solvent, then [C] = 150 / 1000 = 150 mEq Na HCO3/L

  2. Assuming total body water [L] = 0.5 x wgt [kg] (acutally TBW fraction varies between 0.45 and 0.6 depending on gender and age). We want to change the current plasma sodium by 10 mEq/L/24 hours (i.e. the maximum safe change in serum sodium that will not precipitate central pontine myelinolysis) and recall that the concentration of sodium in 0.9% saline or NS is 154 mEq/L, then:

    infusion rate = 0.5 x wgt [kg] x 10 / 154 (L x mEq/L/24 hr) / (mEq/L)

    = 5 x 1000 x wgt [kg] / (154 x 24) mL/hr

    = 1.35 x wgt [kg] mL/hr for NS

    If we are using 3% saline, multiply by 0.9/3 (0.9% / 3%) or 0.3

    In the case of hypernatremia, we know that 1/2 NS is half the concentration of NS, such that if we did a similar infusion rate calculation the denominator would be half what is above, or simply multiplying by 2.

Sunday, June 12, 2011

Encephalopathy in a nutshell

Although not the definitive, all encompassing, reasons for encephalopathy/delirium/altered mental status, this short list certainly covers many of the most prevalent causes.
EtiologyPhysical ExamBedside Diagnostic TestsHistorySTAT Diagnostic Tests
Meningeal signs
Lines (vascular, GI, GU)
Productive cough
Vomiting / Diarrhea
Urinary changes
UA and urine c/s
Blood c/s
Sputum c/s
C. difficile toxin
Side effects of and withdrawal from drugs
Naloxone trialMAR (narcotics, corticosteroids, CNS agents)
Review home medications
Alcohol/substance abuse
Electrolyte abnormalities particularly hypo- and hyperosmolar states
Serum osmolarity
Inadequate pain control
Pain scale
Abdominal examination
Bladder scan
Cardiac arrhythmia and ischemia
Heart rate
Blood pressure
Jugular venous pulsation
Heart murmurs and additional sounds
I-STAT Troponin
Cardiac markers
Acute blood loss
Scleral pallor
Rectal exam
Fecal occult blood test
(ABG also has an H&H)
Recent surgery
Hypoxemia or hypercarbia
Acidosis or alkalosis
Respiratory rate
ABGHistory of hypercarbia
Previous ABG
Hypo- and hyperglycemia
Diabetes mellitus
Insulin or oral antihyperglycemic medications
Intracranial pathology (i.e. stroke, mass effect, traumatic brain injury)
Neurological examinationDocumentation of seizure-like activity without formal history of seizure
History of dementia or seizure
CT head without contrast