Fluid and Acid-Base Balance

Fluid Balance

The state of equilibrium between the intake and output of fluids in the body.

Diffusion

The movement of particles from an area of higher concentration to an area of lower concentration.

Osmosis

The movement of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration.

Hydrostatic Pressure - Filtration

The pressure exerted by a fluid at rest due to the force of gravity, which drives fluid out of the capillaries.

Hypotonic fluids

Fluids with less concentration of solutes than cells.

Isotonic fluids

Fluids with the same osmolality as cells.

Hypertonic fluids

Fluids with more concentration of solutes than cells.

Fluid Spacing

The distribution of body fluids in different compartments.

First Spacing

Normal fluid distribution in the body.

Second Spacing

Increased interstitial fluid that is not normal but can be resolved.

Third Spacing

Fluid trapped in spaces where it is not easily exchanged with the rest of the body, such as in edema or ascites.

Fluid Volume Deficit - Hypovolemia

A condition characterized by a decrease in blood volume, often due to loss of fluids.

Causes of Hypovolemia

Includes diarrhea, vomiting, hemorrhage, polyuria, inadequate intake, and fluid shift to interstitial spaces.

Hypovolemia: Clinical Manifestations

Symptoms include tachycardia, dry mucous membranes, poor skin turgor, hypotension, thirst, and decreased urine output.

Fluid Volume Excess - Hypervolemia

A condition characterized by an increase in blood volume, often due to fluid retention.

Causes of Hypervolemia

Includes excess intake, fluid retention, heart failure, and renal failure.

Hypervolemia: Clinical Manifestations

Symptoms include hypertension, pulmonary congestion, pitting edema, dyspnea, and weight gain.

Nursing Management

Includes daily weights, monitoring intake and output, cardiovascular care, and respiratory care.

IV Fluid Solutions

Includes hypotonic, isotonic, and hypertonic solutions used for various medical conditions.

Mean Arterial Pressure

Measurement of perfusion calculated as MAP = (SBP + (2 x DBP)) ÷ 3, with a normal range of 70-100 mmHg.

Colloids

Volume expanders such as Albumin, FFP, PRBCs, Dextran, and Hetastarch.

Acid-Base Regulation

Three mechanisms to regulate acid-base balance and keep pH between 7.35 and 7.45: Buffer system, Respiratory system, Renal system.

Arterial blood gas (ABG) values

Give objective information about: Acid-base status, Underlying cause of imbalance, Body's ability to regulate pH, Overall oxygenation status.

Initial Steps for ABG Analysis

1) Determine pH: acidic normal alkalotic 2) Determine pCO2: high normal low 3) Determine HCO3: low normal high.

Understanding Full Compensation

Compensation is taking place when abnormal values for both pCO2 and HCO3 exist yet still have a normal pH.

pH Normal Range

pH must be back within normal range for A/B balance to be considered fully compensated.

Respiratory Acidosis

CO2 excess caused by: Hypoventilation, Respiratory failure. Compensation: Kidneys conserve HCO3- and secrete H+ into urine.

Respiratory Alkalosis

CO2 deficit caused by: Hypoxemia from acute pulmonary disorders, Hyperventilation. Compensation: Rarely occurs when acute.

Metabolic Acidosis

Accumulation of metabolic acids caused by: DKA, Lactic acidosis including shock, renal disease. Loss of base: Excessive diarrhea, fistulas.

Anion gap

Can help to distinguish cause for the metabolic acidosis: (Na+) - (Cl- + HCO3-). Normal: 8-12 mmol/L, gap increases with acid gain.

Metabolic Alkalosis

Ingestion of base: Antacid meds, NaHCO3-. Loss of acid and/or cations: Excessive vomiting/NGT suction.

Compensation in Metabolic Acidosis

Increased CO2 excretion by lungs (Kussmaul respirations, deep and rapid). Kidneys excrete acid.

Compensation in Metabolic Alkalosis

Lungs attempt to increase CO2 by slowing RR down (to a point). Kidneys excrete HCO3-.

ABG Interpretation Steps

Look at each of the values, Look at pH first, Use process to determine respiratory or metabolic, Determine if patient is compensating.

Partial Compensation

Occurs when two values are abnormal and pH is still abnormal.

Combined Disorder

Occurs when all three values are abnormal.

Compensated ABG

When pH is normal despite two abnormal values.

Uncompensated ABG

When pH is abnormal and at least one other value is abnormal.

pCO2

Represents carbon dioxide levels in the blood, indicating respiratory function.

HCO3

Represents bicarbonate levels in the blood, indicating metabolic function.

pH Interpretation

Determine if the pH is acidic, normal, or alkalotic.

Respiratory Rate in ABG

A patient with respiratory alkalosis may present with a respiratory rate of 36.

Patient Symptoms in ABG

Muscle cramping, warm flushed skin, and blood pressure of 94/52 may be expected in certain ABG results.