Chapter 23 - IV Fluids and Electrolytes Seth Christian, MD MBA Tulane University Hospital and Clinic Seth Christian, MD MBA Tulane University Hospital and Clinic

Overview of Fluid and Electrolyte Physiology Perioperative Fluid Balance Fluid Replacement Solutions Perioperative Fluid Strategies

Perioperative Fluid Balance Water represents 60% of TBW 1 Kg = 1 L 70 kg = 70 L 60% of 70 L = 42 L water

Perioperative Fluid Balance Intracellular Water (2/3 = 28 L) Extracellular Water (1/3 = 14 L) Blood Volume (5L) Interstitial Volume (9 L) Arterial Blood: Venous = 15:85 Oncotic Pressure = 20 mmHg

Perioperative Fluid Balance Maintenance Requirements 1.5 to 2.5 L of water mEq Na mEq K

Perioperative Fluid Balance

NPO Deficit Maintenance Rate Insensible Loss and 3rd Spacing Blood Loss

Fluid Replacement Solutions Crystalloids NS, LR, Plasmalyte Distribute freely within intravascular and interstitial compartments Only 1/3 remains intravascular

Fluid Replacement Solutions

0.9% "Normal" Saline Slightly hypertonic (154 mEq) Large volumes result in hyperchloremic (154mEq) non- gap metabolic acidosis Preferred for neurosurgery (Na) and ESRD patients(K) and for transfusions (no Ca) Hypertonic saline rarely used in OR, but has a role in trauma resuscitation to limit the total volume

Interesting Tid-Bit Daily Na Allowance = 2400 mg Big Mac w/Fries = 1500 mg 1 L 0.9% Saline = 9000 mg

Fluid Replacement Solutions Lactated Ringers (balanced salt solution) Slightly hypotonic (Na 130) Chloride ( ) K (4) Mg ( ) pH = 6.5 Lactate metabolized to bicarbonate

Fluid Replacement Solutions

Colloids (albumin, hetastarch) Oncotic Pressure = mmHg Replace blood loss with albumin 1:1 ratio Half life in circulation normally 16 hours. Half life can be as short as 2-3 hours in pathophysiologic conditions More expensive than crystalloid, but less expensive than blood Infectious complications are negligible

Fluid Replacement Solutions 5% Albumin Colloid oncotic pressure = 20 mmHg Preparation removes viruses and bacteria Albumin has minimal effects on coagulation

Fluid Replacement Solutions 6% Dextran 70 The last number indicates the molecular weight in kDa Polymers synthesized from sucrose by certain bacteria Dextran 40 is used in vascular surgery to prevent thrombosis Side effects: anaphylactic and anaphylactoid reactions and increased bleeding (>20ml/kg/day) and rouleaux formation (interferes with cross- matching blood) and rare cases of noncardiac pulmonary edema

Fluid Replacement Solutions Hydroxyethyl Starch (HES) Synthetic colloids that are modifications of natural polysaccharides Molecular weight Molar substitution (per 10 glucose units) C2 to C6 ratio Hetastarches have 7 substitutions per 10 glucose (0.7) The higher the molecular weight and molar substitution more prolonged intravascular time AND potential complications HES preparations with high C2 to C6 ratios have prolonged duration of action without increasing side effects

Fluid Replacement Solutions HES preparations are described by their concentration, average molecular weight, and molar substitution. Hespan is 6% HES 450/0.7 Hextend is 6% HES 670/0.7 Voluven is 6% HES 130/0.4

Fluid Replacement Solutions Hydroxyethyl Starch Complications Coagulation disturbances (interferes with vW factor, factor VIII, and platelet function) Renal toxicity (larger, older formulations) Tissue storage (pruritis)

Crystalloids versus Colloids Proponents of crystalloids argue that albumin molecules normally enter the pulmonary interstitial compartment freely and then are cleared through the lymphatic system returning to systemic circulation. Additional albumin merely increases the albumin poo cleared by the lymphatics. The largest RCT of saline versus albumin fluid resuscitation involved 7000 patients in the intensive care population and showed no difference in any major outcome. A subgroup of patients with traumatic brain injury had increased mortality rate in the albumin group. It may be prudent to minimize the use of albumin in this patient population.

Perioperative Fluid Strategies The traditional approach was developed over 40 years ago. The guidelines represent a starting point for initiating therapy. Conservative fluid strategies are often employed for patients undergoing lung surgery, liver resection, and bowel resection.

Perioperative Fluid Strategies Conservative Fluid Strategies Replace blood loss on a 1:1 ratio with colloid No replacement of insensible losses or urine output during surgery No fluid loading prior to epidural analgesia Administer colloid bolus for signs of hypovolemia Definitions of "liberal" and "restrictive" fluid regimens are not standardized.

Perioperative Fluid Strategies

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