Exam 2 Review for NSC 325

Exam 2 Review for NSC 325

Immunology

Components of Immune Response

  • Red Blood Cells (RBC)

  • Neutrophils

  • Blood Platelets

  • Mast Cells

  • Cytokines: Signaling pathways that guide immune cells to injury sites.

Steps in Immune Response to Injury

  1. Entry of Pathogens: Bacteria and other pathogens enter a wound.

  2. Platelet Activity: Platelets from blood release blood-clotting proteins at the wound site.

  3. Mast Cell Activity: Mast cells secrete factors that mediate vasodilation and vascular constriction. This delivery of blood, plasma, and cells increases to the injured area.

  4. Neutrophil Activity: Neutrophils secrete factors that kill and degrade pathogens.

  5. Pathogen Elimination: Neutrophils and macrophages remove pathogens through a process known as phagocytosis.

  6. Cytokine Secretion: Macrophages secrete hormones called cytokines that attract more immune system cells to the site and activate cells involved in tissue repair.

  7. Inflammatory Response: The inflammatory response continues until the foreign material is eliminated and the wound is repaired.

Autoimmune Diseases

  • Autoimmune diseases occur when the immune system attacks the body's own tissues.

  • Examples include:

    • Systemic Lupus Erythematosus

    • Rheumatoid Arthritis

    • Insulin-Dependent Diabetes Mellitus

    • Multiple Sclerosis

Gut Immunology

Humoral Defense Mechanisms

  • Secretory Immunoglobulin A (IgA): Primary role is to prevent adherence of bacteria to mucosal surfaces and penetration of antigens.

Mucosal Barrier Function

  • Epithelial Surface: Resists microbial invasion.

  • Mucosal-Associated Lymphoid Tissue (MALT):

    • Small concentrations of lymphoid tissue located in the small intestine, breast, lung, eye, skin, etc.

    • 80% of immunologically active cells belong to MALT.

    • Cell interactions are complex and poorly understood. They respond to food and food antigens.

Gut-Associated Lymphoid Tissue (GALT)

  • Composed of lymphocytes, macrophages, and granulocytes present in the GI tract.

  • Lymphocytes produce secretory IgA.

  • Pathogen Degradation: Proteolytic and lipolytic enzymes degrade pathogens.

  • Mucin: Limits bacterial proliferation.

  • Peristalsis: Propels pathogens through the GI tract.

  • Tight Junctions: Prevent microbial invasion.

Mucosal Atrophy

  • Factors leading to mucosal atrophy include:

    • Starvation

    • Stress

    • Parenteral Nutrition (PN)

    • Bowel Rest

Fluid Balance

Fluid Distribution

  • Total Body Water: Approximately 50% of total body weight.

  • Composition is altered by age and gender:

    • Premature Infants: 80%

    • 6 Months Old: 70%

    • 1-2 Years: 60%

    • 11-16 Years: 58%

    • Adults: 58-60%

    • Older Adults: 50-60%

    • Malnourished Adults: 70-75%

Cell Classification of Total Body Water

  • Total Body Water (TBW): 50%-60%

    • Interstitial Fluid

    • Intravascular Fluid

    • Intracellular Fluid: Comprises 66% of TBW.

    • Transcellular Fluid: Represents 3% of TBW.

    • Extracellular Fluid: Comprises 30% of TBW.

Osmotic Pressure and Fluid Distribution

  • Intracellular Fluid: Fluid within cells.

  • Extracellular Fluid (ECF):

    • Interstitial Fluid: Fluid surrounding cells.

    • Intravascular Fluid: Fluid within blood vessels.

    • Transcellular Fluid: Fluid within body cavities.

  • Osmotic Pressure: Drives fluid distribution.

  • Sodium: Dominant extracellular osmole that maintains water in ECF.

Fluid Pressures: Starling's Law

  • Fluid shifts between ECF and ICF occur with changes in pressure.

  • Types of Body Fluids:

    • Isotonic: Equal concentration of solutes.

    • Hypotonic: Lower concentration of solutes compared to the cell.

    • Hypertonic: Higher concentration of solutes compared to the cell.

Examples of Fluid Distribution Mechanisms

  • Water Distribution:

    • Infusion of 1 liter of 5% dextrose: Water distributes as:

    • 2/3 to ICF

    • 1/3 to ECF

    • 25% remains in the intravascular space.

    • Infusion of 1 liter of 0.9% NaCl (isotonic): Remains in ECF with 25% in the intravascular space.

    • Infusion of 1 liter of 3% NaCl (hypertonic): Causes water to move out of cells (ICF) to ECF to equilibrate.

    • Hypotonic Solutions: Best for treating dehydration.

Oncotic and Hydrostatic Pressures

  • Oncotic Pressure: Allows fluid movement into the interstitial space, controlled by albumin.

  • Hydrostatic Pressure: Drives fluid movement across capillary walls.

  • Third-spacing: Accumulation of excess fluid in interstitial spaces (edema) which can lead to severe volume depletion.

Maintaining Fluid Balance through Kidneys

  • Kidneys regulate fluid through capillary pressure:

    • Forces fluid out of blood vessels into renal tubules.

    • Sodium and water reabsorption or excretion occurs; water follows sodium.

  • Urine can be diluted or concentrated accordingly.

Hormonal Regulation of Fluid Balance

  • Anti-diuretic Hormone (ADH) / Vasopressin:

    • Produced in the hypothalamus and stored in the pituitary gland.

    • Controls blood volume by increasing water reabsorption in the kidneys.

    • Release is stimulated by decreased blood volume or increased osmolality.

  • Aldosterone:

    • Secreted by adrenal glands in response to angiotensin II.

    • Promotes sodium and water retention, thus increasing blood volume and blood pressure.

  • Atrial Natriuretic Peptide:

    • Cardiac hormone released due to increased atrial pressure.

    • Opposes the renin-angiotensin-aldosterone system by promoting excretion of sodium and water.

Fluid Shifts

  • 1st Space Shifting: Normal fluid distribution between ICF and ECF.

  • 2nd Space Shifting: Accumulation of fluid in interstitial tissue.

  • 3rd Space Shifting: Fluid accumulation in spaces that normally contain little fluid.

Fluid Requirements and Losses

  • General Requirement: 1.5-3 liters per day; fluid needs vary by age:

    • 35 mL/kg up to 55-60 years.

    • 30 mL/kg for ages 60-75 years.

    • 25 mL/kg for >75 years.

  • Fluid losses account for approximately 1.5 liters/day through urine, skin, and GI tract.

Physical Manifestations of Fluid Balance Alterations

  • Indicators include changes in body weight, skin turgor, vital signs (blood pressure, heart rate, temperature), and level of consciousness.

Indicators of Dehydration

  • Weight Loss: Laboratory data may show increased sodium, chloride, BUN, albumin, and hemoglobin.

  • Physical Signs: Dry mucous membranes and poor skin turgor.

Indicators of Overhydration

  • Edema: Abnormal fluid accumulation in tissues or body cavities.

    • Pitting Edema: Indentation upon pressure.

    • Non-pitting Edema: Swelling without indentation, often in extremities.

    • Other Forms: Pulmonary edema and ascites (excess abdominal fluid).

Acid-Base Balance

  • Acid: Any substance that releases hydrogen ions in a solution.

  • Base: Any substance that accepts hydrogen ions in a solution.

  • pH Range: Arterial blood levels maintain between 7.35-7.45.

  • Regulating Organs:

    • Kidneys: Regulate hydrogen ion secretion and bicarbonate (HCO3-) resorption.

    • Lungs: Control alveolar ventilation and alter breathing rates to maintain balance.

  • Acid-Base Disorders: Can arise from renal or pulmonary causes.

Enteral Nutrition Support

Introduction to Enteral Nutrition (EN)

  • EN: Nutrition delivered via a feeding tube into the GI tract.

  • Preferred Route: Enteral nutrition is favored over parenteral nutrition due to benefits for gut immunology.

Benefits of Enteral Nutrition

  • Maintains GI barrier function and morphology.

  • Promotes normal gall bladder function and secretion of IgA, which helps in reducing bacterial translocation.

  • Results in fewer infectious complications and lower overall costs compared to total parenteral nutrition (PN).

Timing for Enteral Nutrition

  • Critically ill patients should receive feeding within 24-48 hours to reduce complications and length of stay (LOS).

  • Clinical Stability: Patients must be hemodynamically stable before enteral feeding is initiated.

  • Individualized Approach: Fluid intake and medication must be stable before starting feeds.

Objectives of Nutrition Support

  • Goals:

    • Provide adequate nutrition when oral intake is not possible.

    • Preserve or improve nutritional status (weight and lean tissue mass).

    • Promote wound healing and avoid nutrient deficiencies.

    • Maintain gut integrity through enteral routes.

    • Ensure no harm is done to the patient.

Assessment for Feeding Candidates

  • The acronym CAN WE FEED? is used:

    • C: Critical illness severity

    • A: Age

    • N: Nutrition risk screen

    • W: Wait for full resuscitation

    • E: Energy requirements

    • F: Formula selection

    • E: Enteral access

    • D: Determination of tolerance

Contraindications for Enteral Nutrition

  • Absolute Contraindications:

    • GI tract not available or accessible.

    • Total bowel obstruction.

    • Aggressive support not warranted or desired.

  • Relative Contraindications:

    • Vomiting or diarrhea.

    • High output fistula.

    • Ileus or GI bleeding.

Enteral Feeding Administration Routes

  • Short-term Feeding (<4 weeks):

    • Naso/orogastric (NG)

    • Naso/oroduodenal (ND)

    • Nasojejunal (NJ)

  • Long-term Feeding (>4 weeks):

    • Gastrostomy, PEG, or jejunostomy.

Feeding Methods

  • Bolus Feeding: Administered via syringe, generally for gastric feeds.

  • Intermittent Feeding: Administered over a predetermined duration.

  • Continuous Feeding: Administered slowly over several hours; requires a feeding pump.

Formula Selection for Enteral Nutrition

  • Standard Formulations:

    • Polymer-based containing intact nutrients.

    • Examples include Ensure (1 kcal/mL, 9 g protein), Boost (1 kcal/mL, 10 g protein).

    • Formulas such as Osmolite and Jevity provide specific caloric and protein content targeted for patients' needs.

Disease Specific Formulations

  • Diabetes:

    • Low carb formulations help achieve blood glucose control (80-150 mg/dL).

  • GI Disorders/Malabsorption: Use of peptide-based formulas and prebiotics to enhance absorption.

Clinical Guidelines for Critically Ill Patients

  • Start with standard polymeric formula where applicable; avoid specialty formulas unless warranted in specific cases such as immune-enhancing formulas post-surgery.

Complications of Enteral Nutrition

  • Mechanical Complications: Tube dislodgment or blockage.

  • Metabolic Complications: Electrolyte imbalances, acid-base disorders, hyperglycemia, and refeeding syndrome.

  • GI Complications: Distention, nausea/vomiting, aspiration, diarrhea/constipation, and potential GI bleeding.

Troubleshooting Feeding Problems

  • Strategies for slow motility include using small bowel feeding.

  • Diarrhea: Assess formula components; adjust according to findings.

  • Constipation: Increase water and fiber intake and evaluate medications.

Monitoring and Evaluation of Patient Feeding

  • Thorough documentation of all aspects of patient feeding is critical for safe and effective EN management.

Case Scenarios and Recommendations

  1. 70-Year-Old Female with Dysphagia: Recommend PEG with bolus feeding.

  2. 21-Year-Old Male in ICU: NGT or NDT if hemodymamically stable; continuous feeds if MAP is acceptable.

  3. 32-Year-Old Female Post-Pancreatic Surgery: Initiate J-tube feeds based on MAP status.

  4. 62-Year-Old Male Intubated Due to Sepsis: Do not initiate enteral feeding due to low MAP.