Exam 3 · Week 6 · BIO 280 Pathophysiology
M6 · Musculoskeletal · Skin · Burns
Bone, muscle and skin: what breaks, what erodes, and why a major burn is a fluid problem before it is a skin problem.
▸M6Musculoskeletal · Skin · BurnsWeek 6
💡 The one idea
Skin is an organ, and losing it is a systemic event. A large burn kills through fluid shift, heat loss and infection long before the wound itself matters.
First 24 hours = fluid. After 48 hours = infection.
🦴 Bone — osteoporosis vs osteoarthritis vs osteomyelitis
| What it is | Key point | |
|---|---|---|
| Osteoporosis | Bone resorption outruns formation — less bone, normal composition | Silent until it fractures. Post-menopausal estrogen loss is the biggest driver. Vertebral, hip and wrist. |
| Osteomalacia | Vitamin D deficiency — bone is soft, not thin | Rickets in children; bone pain and bowing |
| Osteoarthritis | Cartilage wear | Asymmetric, weight-bearing, <30 min stiffness, worse with use |
| Osteomyelitis | Bone infection, usually S. aureus | Bone has poor blood supply — needs weeks of IV antibiotics |
| Gout | Uric acid crystals in a joint | Sudden, exquisitely painful, classically the great toe at night |
🚨 Compartment syndrome & fat embolism
Pain out of proportion to the injury, unrelieved by opioids, and worse on passive stretch is compartment syndrome until proven otherwise. Do not elevate the limb above the heart and do not apply ice — both reduce perfusion further.
The six Ps: Pain (first and most reliable), Pressure, Paresthesia, Pallor, Paralysis, Pulselessness. Pulselessness is last — waiting for it means waiting until the muscle is dead.
Fat embolism follows long-bone and pelvic fractures, usually within
24–72 h: the triad is hypoxia, confusion and a petechial rash over
the chest and axillae.
🩹 Skin — pressure injuries
| Stage | What you see |
|---|---|
| 1 | Intact skin, non-blanchable redness |
| 2 | Partial thickness — shallow open ulcer or an intact/ruptured blister. Dermis is visible. No slough. |
| 3 | Full thickness — subcutaneous fat visible; slough may be present; bone/tendon/muscle not exposed |
| 4 | Full thickness — bone, tendon or muscle exposed |
| Unstageable | Base obscured by slough or eschar — you cannot stage what you cannot see |
| Deep tissue | Persistent maroon or purple discoloration of intact skin |
Pressure, shear, friction and moisture are the four forces. Bony prominences are where they meet: sacrum, heels, ischium, trochanters, occiput.
⭐ Burn depth
| Depth | Layers | Looks like | Pain |
|---|---|---|---|
| Superficial | Epidermis | Red, dry, blanches | Painful |
| Partial thickness | Into dermis | Blisters, moist, weeping | MOST painful |
| Full thickness | Through dermis | White, leathery, waxy, dry | Painless — nerves destroyed |
| Deep full thickness | Into muscle and bone | Charred, blackened | Painless |
A patient who cannot feel the burn has destroyed nerve endings. Painless is worse, never better.
💧 Rule of Nines and Parkland
- Head & neck 9% · Each arm 9% · Each leg 18%
- Front torso 18% · Back torso 18% · Perineum 1%
Children have proportionally bigger heads, so pediatric charts shift percentage from the legs to the head.
4 mL × kg × %TBSA Lactated Ringer's over 24 hours, timed from the moment of the burn, not from arrival. Half in the first 8 hours, the other half over the next 16.
70 kg, 50% TBSA: 4 × 70 × 50 = 14,000 mL → 7,000 mL in 8 h (~875 mL/h), then 7,000 mL over 16 h (~437 mL/h).
The best indicator that fluids are working is urine output — adults
30–50 mL/hr, children 1 mL/kg/hr. Not blood pressure,
not heart rate.
🔥 Airway comes before all of it
Suspect inhalation injury with facial burns, singed nasal hair, soot in the mouth, hoarseness, stridor or a fire in an enclosed space. The airway swells over hours — intubate early, because after the swelling you cannot.
Circumferential burns of the chest or a limb act like a tourniquet as edema builds
— they need escharotomy. Carbon monoxide poisoning gives a normal pulse
oximetry reading with a hypoxic patient: treat with 100% oxygen.
🎯 Module quiz
Questions for this module.
Nothing here yet — drop it in when you have it