This document discusses perioperative fluid management and electrolyte balance. It begins by outlining the distribution of body water and fluid compartments. It then examines the factors that influence fluid movement such as osmotic gradients, Starling's law, and hormone regulation via ADH, RAAS, and ANP. Key concepts covered include fluid assessment, maintenance fluids, resuscitation fluids, and perioperative care domains like smoking cessation, frailty, nutrition, and medication management in the preoperative period.

1. Perioperative management and
Fluid
Neda Amini, MD
Northwell health
Surgical oncology Fellow

2. BODY WATER DISTRIBUTION
 Percent Of Body Weight
–Male: 55 – 60%
–Female: 50 – 55%
 Fluid Compartments
 intracellular volume : 2/3 of Body Water
 extracellular volume: 1/3 of Body Water
 Plasma: 25% of ECF
 Interstitial Fluid: 75% of ECF

4.  healthy 70-kg male predicted to have a TBW content of
42 L (60% of total body weight). The intracellular volume
is 28 L (two-thirds TBW) and the extracellular volume 14
L (one-third TBW)>>3.5 L plasma
 balance of TBW is directed by a complex interaction
between membranes and solutes
 Membranes separating intracellular and extracellular
compartments are freely permeable to water, such that
the osmolality of the intracellular, interstitial, and
intravascular compartments remains equal.

5. Albumin represents the most important osmotically active constituent of the ECV and is virtually excluded from the ICV.
Albumin is unequally distributed within the ECV; the serum concentration of albumin approximates 4.0g/dl, while the IF
concentration averages 1.0g/dl.
Capillary membranes are freely permeable to most small solutes (less than 50,000 kDA), including sodium, potassium, glucose,
and low-molecular-weight proteins.
They have the ability to create osmotic forces that direct the movement of water across a membrane. Water moves across
membranes via intercellular junctions or transcellular routes
These nonpermeable solutes are known as effective osmoles.

6.  Movement of water across
capillary membranes is directed
by competing forces known as
Starling’s law.
 Starling’s law states that net
filtration is the difference
between the hydrostatic and
oncotic pressures of both the
interstitial and the capillary
fluids.

7.  Although small solutes do not contribute to water movement across capillary membranes, they do
function as effective osmoles that direct water movement between the intracellular and
extracellular spaces across cell membranes.
 Sodium (Na+) : potassium (K+) are the principal determinants of extracellular osmolarity
 potassium (K+) are the principal determinants of intracellular osmolality
 Na+ and K+ are unable to passively diffuse across the lipid-rich membrane with a gradient
generated and maintained by the Na+/K+ adenosine triphosphatase (ATPase) pump mechanism.
 Manipulation of either of these ions results in water movement from lower to higher osmolality
compartment in order to reestablish equilibrium.

8.  For example, administration of hypotonic solution (e.g.,
0.45% NaCl solution) results in decreased extracellular
osmolality, so water moves from the extracellular space
to the intracellular space, resulting in cellular swelling.
 In contrast, administration of a hypertonic solution (e.g.,
3% NaCl solution) results in increased extracellular
osmolality, so water moves from the intracellular space
to the extracellular space, resulting in cellular
dehydration.

9. Serum
Osmolality
 Measure of solute (osmoles) per
KG of water
 –Only accounts for solute which
contributes to the solution’s
osmotic pressure
 Serum Osmolality–Formula:(2 X
[Na]) + [Glucose]/18 + [BUN]/2.8
 Normal: 278 – 300 mOsm/kg

10.  Elevations in plasma osmolality result in stimulation of thirst along with
antidiuretic hormone (ADH) secretion from the posterior pituitary gland.
 ADH release results in upregulation of aquaporin channels in the basolateral
membrane of distal collecting tubules in the kidney, promoting free water
resorption down an established gradient. As a result of increased aquaporin
insertion, urine osmolality increases, with variations from 100 to 1200 mOsm/kg
depending on the serum osmolality.
 ADH secretion is also triggered by central baroreceptors that detect decreased
plasma volume. The result of ADH secretion is free water reabsorption in the
body’s attempt to restore normal osmolality and maintain homeostasis.

11.  The renin-angiotensin-aldosterone (RAA) axis promotes volume expansion.
Renin is secreted by the juxtaglomerular cells in response to renal
hypoperfusion or low sodium concentration in the macula densa region of the
distal tubule.
 Renin secretion promotes formation of angiotensin from angiotensinogen and
the eventual production of aldosterone, which promotes sodium reabsorption.
 atrial natriuretic peptide (ANP) results in net diuresis. ANP is a systemic
hormone released in response to cardiac atrial stretch and results in increased
renal blood flow through dilation of the afferent glomerular arteriole and
inhibition of sodium reabsorption in the kidney.

13. Assessment of Fluid Status
 In the immediate postoperative period, patients may have fluid deficits resulting
from preoperative or intraoperative fluid losses. Continued fluid losses in the
extended postoperative period from urine, skin, and the gastrointestinal (GI) tract
are common.
 It should be recognized that intravenous (IV) fluids are a therapy capable of
providing benefit when utilized appropriately but also able to cause harm when used
inappropriately.
 Commonly seen in the postoperative period, inflammatory states result in a low
effective intravascular volume despite an overall positive fluid balance due to
cytokine-induced permeability, which increases extracellular volume.
 Common signs and symptoms of low effective circulatory volume include abnormal
mentation, excessive thirst, dry mucous membranes, poor skin turgor, tachycardia,
hypotension, orthostatic changes in vital signs, and oliguria.

14.  Daily weights
 serum and urine electrolyte levels
 acid-base balance
 invasive monitoring
 Urine output is an excellent measure of volume status; adults should produce at
least 0.5 mL/kg/hr, whereas children should produce nearly 1 to 2 mL/kg/hr.
 However, in the setting of renal insufficiency, those receiving diuretics, or those
in hyperglycemic states, urine output may be an inaccurate measure of volume
status and resuscitation.

15. Additional indicators of intravascular depletion:
elevated hematocrit
low serum bicarbonate level with a base deficit
blood urea nitrogen/creatinine ratio greater than
20:1 (prerenal azotemia)
fractional excretion of sodium (FENa) of less than 1%.

16.  Elevated urine osmolality may suggest intravascular hypovolemia, but in the
setting of renal insufficiency or use of diuretics it is often an inaccurate
measure. The equation for fractional excretion of sodium is as follows:

17. Maintenance Fluids and Daily Electrolyte
Requirements
 Sensible losses can be quantified and occur primarily in urine (∼800 to 1500 mL
daily) and stool (∼250 mL daily).
 Insensible losses are unable to be quantified and include cutaneous losses from the
skin (75%) and upper respiratory tract (25%). Insensible losses often are quantified
roughly at 8 to 12 mL/kg per day.
 Sensible and insensible losses vary greatly in different physiologic states and
pathologic conditions, including fever, hyperventilation, burns, tachycardia, and
other hypermetabolic states.
 Cutaneous insensible losses increase by 10% per day for each 1°C increase in body
temperature above 37.1°C. Laparotomy and thoracotomy increase insensible
losses from the operative site at rates that approach nearly 1 L/hr.

18.  Daily maintenance fluid administration in both pediatric and adult populations can be calculated for a
24-hour period utilizing the 100-50-20 rule or hourly utilizing the 4-2-1 rule
 By definition, maintenance fluids contain dextrose. Their electrolyte composition is variable and
allows for replacement of these lost from insensible and sensible losses but these levels should be
closely monitored in postoperative patients.
 In general, the most common postoperative maintenance fluid for adults consists of 5% dextrose in
one-half normal saline (D5 1⁄2NS) with 20 mEq/L KCl.


19.  In children the standard maintenance fluid is D5 1⁄2NS or D5 lactated Ringer’s
solution (LR). This is to avoid hyponatremia, which has been shown to be of
critical importance in the pediatric population.
 Children younger than 2 years usually receive D5 1⁄4NS, with 20 mEq/L. The
reason for this is that until age 2 years, the kidney has a glomerular filtration rate
(GFR) that is one-quarter the adult level, and the distal nephrons are unable to
effectively concentrate the urine, leading to a difficulty in excreting high sodium
loads.

22. GI SECRETIONS

23.  When administering maintenance fluids, utilizing a 4-2-1 dosing regimen in a
70-kg male (110 mL/hr) results in a total sodium load of 203 mEq in a 24-hour
period, which is greater than the required 1 to 2 mEq/kg/day.
 Although patients with normal kidney function are able to excrete the excess
sodium load, caution should be utilized in patients with underlying renal
dysfunction, cardiac failure, or other serious comorbidities to not cause
iatrogenic hypernatremia.
 In general, maintenance fluids should be reassessed at least daily to ensure
that correct electrolyte and fluid volume needs are met but not exceeded.

24. Resuscitative
Fluids
 Resuscitative fluids are most commonly used the
immediate postoperative period, after injury, and in
the setting of hypotension.
 The rate of fluid administration is determined by the
severity of the existing deficit, presence of ongoing
losses, and the patient’s comorbidities.
 NS and LR closely approximate the composition of
extracellular fluid and therefore are the most
commonly used resuscitative fluids.
 LR has a pH of 6.5 and provides 28 mEq of bicarbonate
(HCO3 −) per liter, making it preferential in the setting
of acidosis.
 NS, at a pH of 4.5, does not contain HCO3 − but has a
greater concentration of Na+ and Cl− (154 mEq),
making it preferential in patients with a metabolic
alkalosis.
 However, it can create hyperchloremic metabolic
acidosis in the setting of high volume resuscitation.

25.  Severe fluid losses resulting in hemodynamic instability should be replaced
with isotonic resuscitative fluid boluses of 0.9% sodium chloride (NS solution)
or LR solution at volumes of 10 to 20 mL/kg, with boluses repeated until
adequate resuscitation is reached.
 Colloid solutions, such as 5% albumin, theoretically provide an advantage
when restoring intravascular volume because of the oncotic pressure afforded
by the protein content. However, liberal use of colloid solutions is less cost
effective and has not demonstrated improved patient outcomes in
randomized studies.

26. Sydney Ringer, credited for the
development of lactated Ringer
solution.
In 1883, Sydney Ringer reported
influence exerted by the
the blood on the contractions of
ventricle

27. Perioperative Care Management Domains
 Smoking Cessation
▪ urge all patients to quit smoking prior to surgery
 Smoking cessation intervention for all smokers, ideally ≥6 weeks before
surgery

28. Frailty
 describe generalized poor functional status and reduced physiologic reserve
that results in increased vulnerability to adverse outcomes.
 Frailty should be evaluated before considering major elective surgery.
Common clinical assessments include questionnaires such as the Modified
Frailty Index (MFI) and Clinical Frailty Scale (CFS)
 6-minute walking distance (6MWD) or hand-grip strength test.
 Improvement in these objective measurements over time has been shown to
improve outcomes.

29. Nutritional Status
 Balanced diet for all surgical patients
 Preoperative screening for malnutrition to allow for referral to dietitian and
immediate intervention if screening positive

30. MEDICATION MANAGEMENT
 Take morning of surgery:
 b-Blocker
 Asthmatic medications
 GERD medications
 Statins
 Aspirin (for CV surgery)
 ACE Inhibitors (if for Heart Failure & BP adequate)
 Calcium Channel Blocker–Alpha 2 Agonists

31. ORAL HYPOGLYCEMIC AGENTS
 Hold the morning of surgery
 Metformin Exception: Stop 24 hrs prior to procedures with contrast dye
 Major Surgery: Reports of lactic acidosis (when taken postoperatively
 Minor Surgery: No studies

32. INSULIN
 Hold morning dose of short/rapid-acting Insulin
 Reduce long-acting agents by half when taken night prior
 Assess blood glucose at hospital in AM

33. ACE INHIBITORS
 Discontinue night before surgery
 Exception: CHF patients
 Issues–Suppresses renin-angiotensin pathway–Hypotension unresponsive to
normal pressorswith general anesthesia induction

34. ANTICOAGULANTS
 Discontinuation varies with drug–Warfarin: 5 days
 Clopidogrel: 7 days
 Enoxaparin: 12 – 24 hours

35. Cardiac Stents
 Elective Noncardiac Surgery–
 Defer 12 months if possible
 Can’t wait –BMS – 30 days
 DES – 6 months–Discontinue clopidogrel 7 days prior–Continue Aspirin through
perioperative period(except neurosurgery and retinal surgery)

36. Questions
 neda2466@gmail.com
 Namini@northwell.edu