NLE Foundations of Medical-Surgical Nursing — Homeostasis, Inflammation and Cellular ResponseSummary

Homeostasis is the body's dynamic tendency to maintain a stable internal environment within narrow physiologic ranges—temperature 36.5–37.5°C, pH 7.35–7.45, serum glucose 70–100 mg/dL fasting, and electrolyte concentrations precisely regulated. A negative feedback loop occurs when a deviation from the set point triggers a response that reverses that deviation, restoring balance. Example: if body temperature rises above 37.5°C, thermoreceptors signal the hypothalamus, triggering vasodilation and sweating to cool the body; as temperature returns to normal, these responses cease. This mechanism explains why postoperative patients' temperatures typically normalize within hours as cooling mechanisms activate. Positive feedback loops, which amplify responses, are rare but critical (labor contractions, blood clotting cascade). Understanding feedback loops helps you anticipate which interventions (e.g., tepid sponging, cooling blankets) support the body's own homeostatic mechanisms.

A stressor is any real or perceived threat to homeostasis—physiologic (trauma, surgery, infection, hemorrhage) or psychological (fear, anxiety). Hans Selye described the General Adaptation Syndrome as a three-stage nonspecific response to any stressor. Stage 1 (Alarm): The sympathetic nervous system activates; the hypothalamic-pituitary-adrenal (HPA) axis releases catecholamines (epinephrine, norepinephrine) and cortisol. Clinical signs include increased heart rate (tachycardia), elevated blood pressure, rapid respirations (tachypnea), pupil dilation, sweating, tremor, and heightened alertness—the 'fight-or-flight' response. Blood is shunted to vital organs (heart, brain, lungs) and away from the gut and skin. Stage 2 (Resistance/Adaptation): If the stressor is manageable, the body's compensatory mechanisms work to restore homeostasis. Cortisol levels remain elevated, promoting protein and fat breakdown for energy; glucose levels rise to fuel tissues. If the stressor resolves, recovery occurs. Stage 3 (Exhaustion): Prolonged or overwhelming stress depletes adaptive reserves. Physiologic decline, infection, organ failure, or death may ensue. In clinical practice, postoperative patients typically show Stage 1 and 2 responses: hyperglycemia (from cortisol and catecholamines), fluid and sodium retention (from aldosterone and ADH), and immunosuppression (from cortisol). Recognizing these as adaptive—not pathologic—helps you distinguish normal postoperative stress response from complications requiring intervention.

Cortisol (glucocorticoid) increases blood glucose by promoting gluconeogenesis and inhibiting glucose uptake by non-vital tissues; suppresses the inflammatory and immune response (why stress-exposed patients are prone to infection); and promotes catabolism of protein and fat for energy. Aldosterone (mineralocorticoid) promotes sodium and water reabsorption by the kidney, raising blood volume and pressure—explaining fluid retention, weight gain, and edema in stressed or postoperative patients. Antidiuretic hormone (ADH/vasopressin) conserves water by increasing aquaporin channels in the collecting duct, concentrating urine and raising blood osmolality initially, then diluting it as excess water is retained. The sympathetic nervous system releases epinephrine and norepinephrine, which increase heart rate, contractility, blood pressure, and redistribute blood to vital organs. These hormonal changes are adaptive in acute stress (ensuring oxygen delivery to the brain and heart) but become maladaptive if prolonged (hyperglycemia worsens in diabetic patients, immunosuppression increases infection risk, fluid overload stresses the heart in elderly or cardiac patients). In the Philippine healthcare context, where many patients present late with limited access to intensive monitoring, recognizing these stress responses early helps you anticipate complications and intervene promptly.

Cells adapt to stress by changing size, number, or structure. Atrophy is a decrease in cell size due to disuse (immobilized leg muscle), aging, or denervation; the tissue shrinks but maintains function if atrophy is not severe. Hypertrophy is an increase in cell size in response to increased workload (cardiac muscle enlarges in hypertension or aortic stenosis; skeletal muscle grows with exercise). Hyperplasia is an increase in the number of cells, seen in breast tissue during pregnancy (hormone stimulation) or in the endometrium in response to estrogen. Metaplasia is a reversible change from one mature cell type to another mature cell type, often in response to chronic irritation (respiratory epithelium in smokers changes from pseudostratified columnar to stratified squamous). Dysplasia is disordered, abnormal cell growth with increased nuclear-to-cytoplasmic ratio; it is not cancer but is considered premalignant and requires monitoring (dysplastic cervical cells on a Pap smear warrant colposcopy). All these responses—except dysplasia—are reversible if the stimulus is removed. When cellular stress exceeds adaptive capacity, cell death occurs by necrosis (uncontrolled, inflammatory death from injury) or apoptosis (programmed, orderly cell death). Understanding these adaptations helps you recognize early warning signs of tissue response to stress and counsel patients on preventing progression (e.g., smoking cessation to prevent metaplasia and dysplasia in respiratory epithelium).

Inflammation is the body's protective, nonspecific response to tissue injury or microbial invasion. It is distinct from infection: inflammation is the response; infection is inflammation caused by microorganisms. The inflammatory response aims to (1) neutralize and destroy harmful agents, (2) limit their spread, and (3) prepare tissue for healing. Upon injury, resident cells (mast cells, endothelial cells, macrophages) release chemical mediators: histamine (stored in mast cell granules, causes vasodilation and increased capillary permeability), bradykinin (causes vasodilation and pain), prostaglandins (cause vasodilation, pain, and fever), and leukotrienes (cause vasodilation and chemotaxis). These mediators trigger two main vascular events: vasodilation (arterioles then capillaries dilate, increasing blood flow—causing redness and heat) and increased capillary permeability (endothelial cell junctions widen, allowing plasma proteins and fluid to leak into tissue spaces, causing swelling). Simultaneously, white blood cells migrate to the injury site through chemotaxis (movement along a chemical gradient). Neutrophils arrive first, followed by macrophages. These cells engulf and digest debris and pathogens through phagocytosis. Systemic manifestations include fever (from prostaglandin action on the hypothalamic thermostat), leukocytosis (elevated white blood cell count, often with a 'left shift'—increased immature neutrophils indicating intense immune activation), malaise, and elevated acute-phase proteins (C-reactive protein, erythrocyte sedimentation rate). In the Philippine setting, where patients may delay seeking care, chronic low-grade inflammation can lead to complications such as chronic pain, functional impairment, and increased infection risk in immunocompromised individuals.

These Latin terms describe the local manifestations of inflammation at an injury site. Rubor (redness) results from vasodilation increasing blood flow to the area. Calor (heat) is due to the increased blood flow and metabolic activity of inflammatory cells. Tumor (swelling/edema) occurs as plasma proteins and fluid leak from permeable capillaries into tissue spaces. Dolor (pain) is caused by pressure from edema on nerve endings and by chemical mediators such as bradykinin and prostaglandins that directly activate nociceptors. Functio laesa (loss of function) is a consequence of swelling and pain limiting movement and use of the part. For example, in acute appendicitis: the inflamed appendix is red (rubor) and warm (calor), swollen (tumor), painful to palpate (dolor), and the patient guards the abdomen, limiting movement (functio laesa). In clinical practice, you assess these signs at wound sites, around injections, or in inflamed joints to judge the intensity of inflammation and response to treatment. A patient whose surgical wound shows decreasing redness, warmth, and swelling over days indicates resolving inflammation; persistent or worsening signs suggest infection and warrant notification of the physician.

Wound healing progresses through three overlapping phases. The inflammatory phase (0–3 days) involves hemostasis (clotting), vascular response, and migration of neutrophils and macrophages to clean the wound. The proliferative phase (3–21 days) is characterized by angiogenesis (new blood vessel formation), collagen deposition by fibroblasts, and epithelialization (epithelial cells migrate over the wound bed). Adequate protein, vitamin C (essential for collagen cross-linking), and zinc are critical nutrients; deficiency prolongs this phase. The maturation/remodeling phase (weeks to months or years) involves collagen remodeling, angiogenesis regression, and scar formation. Healing by primary intention occurs when wound edges are clean and well-approximated (e.g., a clean surgical incision closed with sutures); healing is fast with minimal scarring. Healing by secondary intention occurs in open wounds (e.g., pressure ulcers, infected wounds) that must heal from the base up by granulation tissue formation; this is slower and produces more scarring. Tertiary intention (delayed primary closure) is used when wound contamination or tension makes primary closure unsafe; the wound heals by secondary intention initially, then is closed later. Factors impairing healing include poor tissue perfusion (ischemia from atherosclerosis, diabetic microvascular disease, or shock), diabetes (hyperglycemia impairs immune function and collagen synthesis), corticosteroid use (suppresses inflammation and collagen synthesis), malnutrition (inadequate protein, vitamin C, zinc), infection, and advanced age (slower cell proliferation). In the Philippine context, many patients have delayed presentation with chronic wounds, diabetes, or malnutrition; recognizing these risk factors guides your interventions to optimize healing (nutritional supplementation, glucose control, infection prevention, pressure relief).

Third-spacing is the abnormal shift of fluid from the intravascular space (plasma) into a 'third' compartment—the interstitium (tissue spaces), peritoneal cavity (ascites), pleural space, or bowel lumen—where it is not readily accessible for circulation. This occurs in burns, sepsis, major surgery, bowel obstruction, and liver disease (hypoalbuminemia). The danger of third-spacing is that although total body water may be normal or even high, the intravascular volume is depleted, producing signs of hypovolemia: hypotension, tachycardia, oliguria (low urine output), and poor skin turgor—despite visible edema and weight gain. This paradox confuses the novice nurse: the patient looks 'wet' (swollen) but is hemodynamically 'dry' (depleted). Fluid movement is governed by two pressures: hydrostatic pressure (the 'pushing' force exerted by fluid against vessel walls) and oncotic (colloid osmotic) pressure (the 'pulling' force exerted by large plasma proteins, chiefly albumin). Normally, hydrostatic pressure in capillaries is about 35 mmHg at the arteriolar end (pushes fluid out) and 15 mmHg at the venular end (less pushing force). Plasma oncotic pressure is about 25 mmHg, which pulls fluid back into the capillary. The net effect is that fluid leaves the capillary at the arteriolar end and is mostly reabsorbed at the venular end. In third-spacing, either hydrostatic pressure becomes excessive (as in heart failure, where venous congestion raises capillary pressure) or oncotic pressure drops (as in hypoalbuminemia from liver disease, malnutrition, or nephrotic syndrome, where albumin is lost). The result is sustained fluid loss into the interstitium and edema formation. Nursing implications include meticulous intake and output (I&O) recording, daily weights (a 1 kg weight gain in 24 hours indicates 1 L fluid retention), serum albumin monitoring (normal >3.5 g/dL), and hemodynamic assessment (blood pressure, heart rate, central venous pressure if available). In severe burns or sepsis, expect a diuretic phase during recovery when fluid re-enters the circulation; this can precipitate hypervolemia and pulmonary edema, requiring careful fluid management and diuretics.

Shock is a life-threatening state of inadequate tissue perfusion and cellular oxygenation. When cells do not receive sufficient oxygen, they switch from aerobic to anaerobic metabolism, producing lactic acid. Lactic acidosis develops, and without prompt intervention, cells die and multiple organ dysfunction syndrome (MODS) ensues. Shock is classified by etiology: Hypovolemic shock (most common) results from loss of circulating volume—hemorrhage, severe dehydration, third-spacing, or major burns. The body attempts to compensate by vasoconstriction to maintain blood pressure and increase heart rate to increase cardiac output (CO = HR × stroke volume). Cardiogenic shock occurs when the heart fails to pump effectively—from acute myocardial infarction, acute heart failure, or severe dysrhythmias. The body's compensatory vasoconstriction actually worsens the problem by increasing afterload on a failing heart. Distributive shock results from massive vasodilation causing maldistribution of blood volume—blood pools in dilated vessels, the central circulating volume drops, and tissue perfusion fails despite adequate total blood volume. Subtypes: septic shock (from infection, endotoxins trigger vasodilation), anaphylactic shock (severe allergic reaction, mast cell degranulation causes vasodilation and increased capillary permeability), and neurogenic shock (spinal cord injury above T6 eliminates sympathetic tone, causing vasodilation). Obstructive shock results from physical obstruction to blood flow—cardiac tamponade (fluid in the pericardium compresses the heart), tension pneumothorax (collapsed lung collapses the other, compressing the heart), or pulmonary embolism (clot blocks pulmonary circulation). The stages of shock are: Initial stage (cellular changes begin; anaerobic metabolism starts; lactic acid accumulates—but obvious clinical signs are absent, making early recognition difficult). Compensatory stage (sympathetic nervous system activates; catecholamines increase heart rate and contract vessels to maintain blood pressure; the renin-angiotensin-aldosterone system [RAAS] activates to conserve sodium and water; ADH conserves water). Clinical signs: tachycardia, tachypnea, cool clammy skin (except in early septic shock, where skin is warm and flushed), narrowing pulse pressure (systolic minus diastolic), decreased urine output (<0.5 mL/kg/hr), and restlessness or anxiety (from cerebral hypoperfusion). Importantly, blood pressure is often maintained here—this is the critical window for intervention before irreversible damage occurs. Progressive stage (compensatory mechanisms fail; hypotension develops; acidosis worsens; altered mental status (confusion, drowsiness) signals cerebral hypoperfusion; organ hypoperfusion deepens—kidneys produce oliguria or anuria; liver fails to metabolize lactate; gut ischemia may allow bacterial translocation). Refractory (irreversible) stage (profound organ failure; widespread cellular death; recovery is no longer possible even with aggressive intervention). Understanding these stages is critical: the patient who is tachycardic, anxious, and cool but still normotensive is in compensatory shock—this is when nursing interventions can make the difference.

Classic signs across most shock types are hypotension (late sign, indicates compensatory mechanisms have failed), tachycardia (heart rate >100 bpm), tachypnea (respiratory rate >20 breaths/min—the body attempts to compensate for metabolic acidosis by hyperventilating), cool clammy skin (from cutaneous vasoconstriction and sympathetic activation), oliguria (urine output <0.5 mL/kg/hr or <30 mL/hr in adults), and altered level of consciousness (confusion, lethargy, or coma). Restlessness and anxiety are often the earliest signs of inadequate cerebral perfusion and must not be dismissed as pain or psychiatric symptoms; they should prompt immediate assessment of vital signs and perfusion status. Type-specific differences: Hypovolemic shock presents with signs listed above. Cardiogenic shock additionally shows signs of pulmonary edema (crackles on lung auscultation, dyspnea, pink frothy sputum) and elevated jugular venous pressure (JVP). Septic shock has a warm, flushed appearance in early stages (vasodilation) with warm extremities, rapid bounding pulse, and normal or elevated blood pressure initially—only later does it progress to the classic cool, clammy appearance. Anaphylactic shock presents with angioedema (swelling of face, throat, tongue), urticaria (hives), bronchospasm (wheezing, stridor), and often a clear history of exposure (food, medication, insect sting). Neurogenic shock (from spinal cord injury) is the key exception: it causes bradycardia (not tachycardia—due to loss of sympathetic innervation) with warm, dry skin (vasodilation without compensatory sweating), and hypotension. Many nurses mistake neurogenic shock for other types and give fluid boluses when the problem is vasodilation, not volume loss; recognizing bradycardia with warm skin and a history of spinal trauma is the key. Obstructive shock may show signs of the specific obstruction: cardiac tamponade causes muffled heart sounds and elevated JVP (Beck's triad); tension pneumothorax causes unilateral absent breath sounds, tracheal deviation, and severe distress.

Nursing care in shock follows the ABCs: Airway and breathing come first—assess airway patency, position the patient to maintain airway, and administer high-flow oxygen (target SpO2 >94%). The priority is oxygenation and perfusion, not avoiding oxygen toxicity in an acute emergency. Circulation: establish large-bore IV access (two 18-gauge or larger catheters), initiate fluid resuscitation with isotonic crystalloids (0.9% normal saline or lactated Ringer's), and monitor response. Isotonic crystalloids are the fluids of choice for hypovolemic and most distributive (septic) shock because they expand the intravascular and interstitial spaces. Blood products (packed red blood cells, fresh frozen plasma) are given for hemorrhage. Position the patient supine with legs elevated 30–45° (modified Trendelenburg) unless contraindicated by respiratory distress or head injury; this promotes venous return. Monitor vital signs continuously, urine output (aiming for at least 30 mL/hr in adults—a sign of adequate renal perfusion), mental status, and peripheral perfusion (skin color, temperature, capillary refill). Anticipate vasopressors (e.g., norepinephrine) once fluid resuscitation is underway; vasopressors are not started without fluid first, as they further worsen perfusion in hypovolemic patients. Treat the specific cause: administer epinephrine for anaphylaxis (IM if possible for rapid absorption), antibiotics for septic shock (broad-spectrum until culture results; follow DOH PhilPEN sepsis protocols), and arrange reperfusion (thrombolysis or PCI) for cardiogenic shock from MI. In cardiogenic shock, restrict fluid and monitor carefully for pulmonary edema; vasodilators and inotropes are preferred over fluid boluses. In neurogenic shock, position cautiously (immobilize spine), give fluids cautiously (the problem is vasodilation, not volume loss), and prepare for possible vasopressors if sympathetic tone does not recover.

Not all shock types are treated identically, and inappropriate treatment can be harmful. In cardiogenic shock, aggressive fluid administration can precipitate pulmonary edema and respiratory failure; fluid is given cautiously, monitoring for crackles, dyspnea, and elevated JVP. The focus is on improving myocardial contractility (inotropes like dobutamine) and reducing cardiac workload (vasodilators, diuretics). In hypovolemic shock, fluid is given more liberally (typically 30 mL/kg of crystalloid in the first 3 hours for trauma patients per trauma protocols). In neurogenic shock from acute spinal cord injury, bradycardia and hypotension are due to loss of sympathetic tone; fluids are given cautiously (the heart is not failing, just vasodilatation), and vasopressors may be needed. Immobilization of the spine is crucial to prevent further injury. In anaphylactic shock, epinephrine is the first-line medication (0.3–0.5 mg IM, repeat every 5–15 minutes if needed), not antihistamines or corticosteroids alone. In septic shock, antibiotics must be given within 1 hour of recognition (or 3 hours if the patient presents to a non-ICU setting per Surviving Sepsis Campaign guidelines); cultures are obtained before antibiotics, but do not delay antibiotics waiting for culture results. Lactate monitoring is increasingly used to guide resuscitation—persistent elevated lactate suggests tissue hypoperfusion despite apparently adequate perfusion parameters. In Philippine settings, where many patients present late and resources may be limited, recognizing shock early and initiating prompt intervention is lifesaving. Understanding that restlessness in a tachycardic, cool patient is not anxiety but a sign of cerebral hypoperfusion prevents sedation that would mask deterioration.