Skip to Main Content

++

INTRODUCTION

++

Anesthesiologists must be able to evaluate and optimize volume status and electrolyte balance in the perioperative period. The primary goals of intravenous fluid therapy are the preservation of intravascular volume and the maintenance of left ventricular filling pressure and cardiac output to ensure adequate oxygen delivery to tissues.

++

FLUID COMPARTMENTS

++

The average adult man is approximately 60% water by weight, whereas the average woman is approximately 50%. This is referred to as total body water, and it is divided into two major fluid compartments: intracellular fluid (ICF = 40% total body weight) and extracellular fluid (ECF = 20% total body weight). ECF is further subdivided into the interstitial (15% total body weight) and intravascular components (5% total body weight).

++

Blood plasma is the major component of intravascular fluid volume contained in the vascular endothelium. Electrolytes are freely exchanged between the intravascular space and the interstitium, maintaining near-equilibrium state between the two compartments. Plasma proteins such as albumin do not cross the endothelium freely and therefore provide osmotic forces.

++

PREOPERATIVE EVALUATION OF INTRAVASCULAR FLUID VOLUME

++

Determining the fluid volume status of a patient can be challenging. Detailed patient history, physical examination, and laboratory data aid in accurately gauging volume status.

++

Nil per os (NPO) status, nausea and vomiting, diarrhea, bowel preparation, hemorrhage, burns, history of weight change, and high urine output are all common causes of preoperative hypovolemia. Hyperventilation, fever, and diaphoresis are often overlooked causes of hypovolemia. Tachycardia, orthostatic hypotension, and low urine output with concentrated urine are nonspecific signs of dehydration. Physical examination findings, suggestive of hypovolemia, include dry mucous membranes, flat neck veins, orthostatic hypotension, concentrated urine, and poor skin turgor. In babies, sunken fontanelles indicate hypovolemia.

++

Hematocrit is often elevated with dehydration. Hypovolemic shock can cause tissue hypoperfusion leading to metabolic acidosis and elevated lactate production. If renal function is normal during dehydration, sodium is retained, leading to low urine sodium and high urinary specific gravity (>1.025 in adults), and an elevated blood urea nitrogen: creatinine ratio (BUN/creatinine ratio >20).

++

PERIOPERATIVE FLUID THERAPY

++

Perioperative fluid therapy entails the replacement of preexisting fluid deficits, administration of maintenance fluids, and replacement of surgical losses.

++

Compensatory intravascular volume expansion (CVE) counteracts venodilation and cardiac depression from anesthesia as well as the hemodynamic effects of positive-pressure ventilation. CVE with 5-7 mL/kg of a balanced salt solution should occur prior to, or simultaneously with induction of general anesthesia provided there are no patient comorbidities prohibiting fluid administration.

++

Hourly maintenance of fluid requirements can be estimated using the “4-2-1 rule” (Table 92-1). This hourly rate can also be calculated for any person weighing more than 20 kg as [weight (in kg) + 40]. Maintenance fluid requirements take into account ongoing losses secondary to continued urine production, gastrointestinal ...

Want remote access to your institution's subscription?

Sign in to your MyAccess profile while you are actively authenticated on this site via your institution (you will be able to verify this by looking at the top right corner of the screen - if you see your institution's name, you are authenticated). Once logged in to your MyAccess profile, you will be able to access your institution's subscription for 90 days from any location. You must be logged in while authenticated at least once every 90 days to maintain this remote access.

Ok

Create a Free MyAccess Profile

* Required Fields

Note: If you have registered for a MyAccess profile on any of the Access sites, you can use the same MyAccess login credentials across all sites.

Passwords must be between 6 and 40 characters long (no whitespace), cannot contain characters #, &, and must contain:
  • at least one lowercase letter
  • at least one uppercase letter
  • at least one digit

Benefits of a MyAccess Profile:

  • Remote access to the site off-campus on any device
  • Notification of new content via custom alerts
  • Bookmark your favorite content such as chapters, figures, tables, videos, cases and more
  • Save and download images to PowerPoint
  • Self-Assessment quizzes saved for quick review
  • Custom Curriculum access for both instructors and learners

Subscription Options

AccessAnesthesiology Full Site: One-Year Subscription

Connect to the full suite of AccessAnesthesiology content and resources including procedural videos, interactive self-assessment, real-life cases, 20+ textbooks, and more

$995 USD
Buy Now

Pay Per View: Timed Access to all of AccessAnesthesiology

24 Hour Subscription $34.95

Buy Now

48 Hour Subscription $54.95

Buy Now

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.