Short Notes: Clinical Decision Rules in Emergency Medicine

a) NEXUS C-Spine Rule (2.5 Marks)

Background

The 5 NEXUS Criteria (ALL must be present to clear the C-spine without imaging):

Performance

• Sensitivity: 99.6% (95% CI, 98.6%–100%)
• Specificity: 12.9% (95% CI, 12.8%–13.0%)
• Negative predictive value: 99.9%

Notes on Elderly Patients

Limitations

• Low specificity (many false positives leading to unnecessary imaging)
• Developed before routine CT use for C-spine evaluation
• Subjective elements ("distracting injury," "intoxication") are the most common sources of misinterpretation

b) Canadian C-Spine Rule (CCR) (2.5 Marks)

Application

The Three Sequential Assessments:

• Age ≥65 years
• Dangerous mechanism of injury (fall from >3 feet; axial loading injury; high-speed MVC, rollover, or ejection; motorized recreational vehicle or bicycle collision)
• Presence of paresthesias in the extremities

• Simple rear-end motor vehicle crash
• Patient able to sit up in the ED
• Patient ambulatory at any time post-injury
• Delayed onset of neck pain
• Absence of midline cervical tenderness

Performance

• Sensitivity: 100% (95% CI, 98%–100%)
• Specificity: 42.5% (95% CI, 40%–44%)

CCR vs. NEXUS

• Sensitivity: 99% (CCR) vs. 91% (NEXUS)
• Specificity: 45% (CCR) vs. 37% (NEXUS)
• Negative likelihood ratio: 0.01 (CCR) vs. 0.25 (NEXUS)

c) Ottawa Knee Rule (2.5 Marks)

Indication

Key Points

• The rules were validated in adults; the original age cutoff was >55 years
• Validated for children >5 years of age per the most recent meta-analysis
• Their use reduces ED waiting times and costs
• For multisystem trauma patients unable to undergo gait testing, it is reasonable to order radiographs regardless
• The Pittsburgh Knee Rules are similar but may have greater specificity

Weight-Bearing Assessment

d) Ottawa Ankle Rule (2.5 Marks)

Background

The Rule - Two Zones:

• Bony tenderness along the posterior edge or tip of the lateral malleolus (distal 6 cm), OR
• Bony tenderness along the posterior edge or tip of the medial malleolus (distal 6 cm), OR
• Inability to bear weight both immediately after injury AND in the ED (4 steps)

• Bony tenderness at the base of the 5th metatarsal, OR
• Bony tenderness over the navicular bone, OR
• Inability to bear weight both immediately after injury AND in the ED

Diagram

Ottawa Ankle Rules for Ankle and Midfoot Injuries (Tintinalli's Emergency Medicine, Fig. 276-6)

Notes

• Can rule out ankle fractures without the need for radiography with high accuracy
• Applies to adults; discussed separately for children (Chapter 141 in Tintinalli)
• The ankle trauma series consists of three views: anteroposterior, 15-degree internal oblique, and lateral - ~95% of ankle fractures are detected with any two of these views
• In Rosen's: "The Ottawa Ankle and Foot Rules should be used to evaluate the need for x-rays in ankle and foot injuries. CT scans are indicated for negative x-rays when a high clinical concern of fracture remains."

Summary Comparison Table

Necrotizing Fasciitis - Structured Answer

a) Pathophysiology of Necrotizing Fasciitis, Including the Mechanism of Rapid Tissue Destruction (3 Marks)

Definition and Overview

Entry and Initial Infection

• Pathogens are most commonly introduced through a break in the skin - cuts, scrapes, sites of minor trauma, bug/animal bites, or injection sites
• Once the bacterial pathogen enters the skin and subcutaneous tissue, infection quickly tracks down to and spreads along the fascia

Mechanism of Rapid Tissue Destruction

1. Bacterial enzyme release: Bacteria release exotoxins and enzymes (including hyaluronidase, streptokinase, DNase, proteinases) that cause direct tissue breakdown and liquefactive necrosis of the fascia, assisting with rapid progression of disease along fascial planes
2. Synergistic polymicrobial activity: In polymicrobial (Type I) infections, aerobic organisms consume local oxygen, producing an anaerobic microenvironment that favors anaerobic growth. Anaerobes then produce gas (seen on CT as soft tissue air - classic sign) and further destructive enzymes. This synergy accelerates tissue necrosis far faster than either organism alone
3. Fascial plane spread without muscle barrier: Infection tracks along the superficial fascia overlying the muscle, where there are few anatomical barriers - allowing lateral and proximal spread to far exceed the area of visible skin involvement
4. Vascular thrombosis and ischemia: The inflammatory process triggers thrombosis of perforating vessels supplying the overlying skin. This produces ischemia and progressive necrosis of skin and subcutaneous tissue, despite the fascia being the primary site of infection
5. Superantigen-mediated toxicity (Type II / Group A Strep): In monomicrobial Group A streptococcal infection, bacterial pyrogenic exotoxins (SPE-A, SPE-B) act as superantigens, causing massive non-specific T-cell activation and cytokine storm (TNF-α, IL-1, IL-6), driving both local tissue destruction and systemic sepsis simultaneously
6. Host immune impairment: In this diabetic patient, impaired neutrophil function, reduced perfusion from microvascular disease, and relative immunosuppression allow unchecked bacterial proliferation and tissue destruction

Microbiology

• Type I (Polymicrobial - as in this case): Mixed aerobic + anaerobic organisms (e.g., E. coli, Bacteroides, Streptococcus, Klebsiella). Common in diabetics, perianal/bowel-origin infections, decubitus ulcers
• Type II (Monomicrobial): Group A Streptococcus (S. pyogenes) most common; also MRSA. Associated with streptococcal toxic shock syndrome
• In diabetic patients specifically, Klebsiella pneumoniae necrotizing fasciitis is described with increased frequency

b) Clinical Features, Signs, and Differentiation from Other Soft Tissue Infections (3 Marks)

Clinical appearance of necrotizing fasciitis - note the erythema, swelling, and tissue necrosis (Rosen's Emergency Medicine, Fig. 107.10)

Clinical Features - Progressive Stages

• Erythema, pain, and surrounding edema that closely resemble uncomplicated cellulitis
• Pain disproportionate to the visible skin findings - a critical early warning sign
• The skin may appear deceptively normal or mildly erythematous

• Deep erythema or violaceous (purple) discoloration of skin
• Pronounced, woody, firm induration of surrounding skin and subcutaneous tissue
• Progressive edema that extends beyond visible erythema
• Development of bullae (hemorrhagic or serous blisters)
• Subcutaneous crepitus - pathognomonic of gas-forming organisms (felt as crackling under the skin)
• Pain spreading outward as infection progresses

• Cutaneous anesthesia/hypesthesia over involved areas - paradoxically, the initially painful area loses sensation as nerves are destroyed (this distinguishes advanced NF from cellulitis, which remains painful throughout)
• Visible gangrene and tissue necrosis
• Skin sloughing

Systemic Features (Tintinalli's / Rosen's)

• High fever, rigors, malaise, nausea, vomiting
• Tachycardia, hypotension - progression to septic shock
• Disorientation and lethargy (septic encephalopathy)
• Marked systemic toxicity out of proportion to local findings - Tintinalli describes this as a hallmark

Investigations in this Patient

• CT scan showing gas in soft tissues - gas tracking along fascial planes is highly specific for necrotizing fasciitis
• CT may also show asymmetric fascial thickening and focal fluid collections
• MRI: sensitive but not totally specific; also useful but delays surgery
• Blood cultures: mixed Gram-positive and Gram-negative (polymicrobial = Type I NF)
• Laboratory: leukocytosis, raised CRP, hyponatremia, elevated creatinine, metabolic acidosis - LRINEC Score (Laboratory Risk Indicator for Necrotizing Fasciitis) uses these to risk-stratify

Differentiation from Other Soft Tissue Infections

c) Surgical Management, Role of Debridement, and Additional Considerations (4 Marks)

Principle: Surgical Emergency

Timing of Surgery

• Surgical intervention less than 24 hours following onset is associated with improved clinical outcomes
• Despite this, delays remain common in practice - ongoing need for physician education on this urgency
• Delayed surgical intervention and interhospital transfer are independently associated with increased mortality

Role of Surgical Debridement

• Wide, aggressive excision of all necrotic tissue is the primary intervention
• The surgeon opens skin and subcutaneous tissue widely and excises all necrotic fascia, skin, and subcutaneous fat down to and including the affected fascial layer
• Critical principle: The process usually extends beyond the area of clinical involvement - all tissue including areas that appear grossly normal must be explored, as infection tracks along fascia well ahead of visible skin changes

• Full surgical debridement of all necrotic areas is essential to therapeutic success
• This is not achieved in one operation - staged, daily debridements are performed until no further areas of involvement are found on surgical exploration
• Return to the operating theatre every 24-48 hours is standard

• "Dishwater fluid" - grey, thin, malodorous fluid in fascial planes
• Lack of bleeding when fascia is cut (thrombosed vessels)
• Lack of resistance to blunt dissection along fascial planes ("finger test" positive - finger sweeps through necrotic fascia without resistance)
• Necrotic grey fascia

• Amputation may be necessary for severe limb disease
• Patients with underlying diabetes mellitus have an increased risk of requiring surgical amputation
• Limb salvage is attempted but must not delay definitive control of infection

Wound Management Post-Debridement

• Vacuum-assisted closure (VAC/negative pressure wound therapy): Applied to large open wounds post-debridement; reduces edema, promotes granulation tissue, facilitates wound closure
• Delayed wound closure and skin grafting: After infection is controlled and wound bed is healthy, skin grafting is performed to achieve final closure
• Wounds are left open initially - primary closure is never appropriate in active NF

Antibiotic Therapy (Adjunctive - Critical Supplement to Surgery)

• Vancomycin
• Linezolid
• Daptomycin

• Piperacillin-tazobactam
• Carbapenem (imipenem/meropenem)
• Ceftriaxone + metronidazole
• Fluoroquinolone + metronidazole

• Final surgical debridement is completed
• Patient is afebrile for 48-72 hours
• Patient has clinically stabilized
• Culture-directed narrowing is performed based on intraoperative tissue cultures

Additional Considerations in Patient Care

• Aggressive IV fluid resuscitation (NF releases significant drainage/third-space losses)
• Close monitoring of vitals, urine output, electrolytes
• Most patients require ICU-level care with vasopressor support if septic shock develops

• Strict glycemic control reduces immunosuppression
• Assess for peripheral vascular disease - may need vascular surgery consultation
• Higher risk of amputation - early orthopaedic/vascular surgical involvement

• Some evidence suggests benefit (promotes angiogenesis, is directly bactericidal against anaerobes, enhances neutrophil function)
• There is insufficient data to support its routine use, but research is ongoing and it may be considered as an adjunct where available

• Early studies suggest some benefit (especially in streptococcal NF by neutralizing superantigens)
• However, data is limited - no strong evidence supports routine use

• Prolonged hospitalization and multiple surgeries demand early enteral nutrition to support wound healing and immune function

• Overall adult mortality remains 20-30% despite modern management
• Most deaths are secondary to underlying bacteremia, septic shock, and/or multiorgan failure
• Factors increasing mortality: older age, septic shock, acute renal failure, sacral involvement, delayed surgery, multifocal infection

Summary Box

Necrotizing Fasciitis - Comprehensive Answer

a) Pathophysiology of Necrotizing Fasciitis, Including the Mechanism of Rapid Tissue Destruction (3 Marks)

Definition

Portal of Entry

Microbiology in This Case

• Type I (Polymicrobial) - as indicated by the mixed Gram-positive and Gram-negative blood cultures. This is the most common type, accounting for 55-75% of all NSTIs
• A symbiotic interaction between aerobic and anaerobic organisms drives rapid tissue destruction
• Type II (monomicrobial) - Group A Streptococcus or MRSA; Type III - Vibrio vulnificus

Mechanism of Rapid Tissue Destruction (Step by Step)

• Facultative gram-negative organisms (e.g., E. coli, Klebsiella) consume local oxygen, lowering the oxygen-reduction potential of the tissue
• This anaerobic microenvironment facilitates anaerobic organism growth (e.g., Bacteroides, Clostridium spp.)
• Anaerobic organisms in turn impede phagocyte function, favoring further aerobic bacterial growth
• This mutual amplification produces gas (seen on CT as soft tissue air) and accelerates necrosis

• Tissue ischemia
• Liquefactive necrosis of the fascia and subcutaneous tissue
• Systemic toxicity
• Staphylococcus aureus and streptococci produce exotoxins that trigger TNF-alpha and cytokine release, producing systemic inflammatory response syndrome (SIRS) leading to septic shock, organ failure, and death

b) Clinical Features, Signs, and Differentiation from Other Soft Tissue Infections (3 Marks)

Clinical Features - Progressive Stages

• Severe pain, anxiety, and diaphoresis - classic early symptoms
• Pain out of proportion to physical examination findings, with tenderness extending beyond the area of visible erythema - "perhaps the single most important feature to make the diagnosis early" (Tintinalli, Chapter 152)
• Erythema and edema that can be indistinguishable from cellulitis
• About 10-40% of patients report trauma or a skin break ~48 hours before symptoms begin

• Brawny (woody, firm) oedema - non-pitting, indurated
• Crepitus from bacterial gas production (present in 13-31% of patients; its absence does NOT exclude the diagnosis)
• Erythema and tenderness extending well beyond the visible margins
• Violaceous (purple-brown) discoloration of overlying skin
• Development of haemorrhagic/dark bullae with serosanguineous or malodorous discharge - late sign

• Cutaneous anaesthesia/hypesthesia - as nerves are destroyed by ischaemia, the initially exquisitely painful area becomes numb (important differentiating sign)
• Overt skin necrosis and gangrene
• Malodorous "dishwater" discharge

Fig. 152-6: Necrotizing soft tissue infection - large cutaneous haemorrhagic bullae on the leg of a patient with necrotizing fasciitis (Tintinalli's Emergency Medicine)

• Low-grade fever with tachycardia out of proportion to the fever
• In fulminant cases: cardiovascular collapse, confusion, rapid deterioration of mental status
• Progression to septic shock and multiorgan failure

Differentiation from Other Soft Tissue Infections

Investigations Supporting Diagnosis

• CT with contrast: Fascial thickening of deep fascial planes; non-enhancing deep fascia (suggesting necrosis); presence of gas (highly specific but found in only ~1/3 of cases) - as in this patient
• MRI: Extensive thickening of intermuscular fasciae with incomplete vascularisation; absence of MRI abnormalities virtually rules out NF
• LRINEC Score (Laboratory Risk Indicator for Necrotizing Fasciitis): Uses CRP >150 mg/L, WBC >15,000/mm³, haemoglobin <13.5 g/dL, sodium <135 mmol/L, creatinine >1.6 mg/dL, glucose >180 mg/dL. Score ≥6 raises suspicion; however, LRINEC alone can miss many cases and should not be used to exclude the diagnosis
• Definitive diagnosis: Surgical exploration - finding grey necrotic fascia, lack of bleeding, no resistance to blunt finger dissection, and "dishwater fluid"

c) Surgical Management of Necrotizing Fasciitis (4 Marks)

Principle: Surgical Emergency - Life-Saving Priority

1. Immediate Surgical Debridement - Role and Technique

• Wide, radical excision of all necrotic tissue - all necrotic skin, subcutaneous fat, and fascia are excised down to and including the infected fascial layer
• The process always extends beyond the area of clinical involvement - the surgeon must probe adjacent tissue with a finger; if it sweeps through without resistance ("finger test" positive), that tissue must also be debrided
• Intraoperative findings confirming NF: grey necrotic fascia, "dishwater" fluid in fascial planes, lack of bleeding from tissues, lack of resistance to blunt dissection, absence of normal tissue attachment to overlying fat

• A single debridement is almost never adequate
• Patients return to theatre every 24-48 hours for re-exploration and further debridement until no further necrotic tissue is found
• This staged approach is essential - re-inspection is mandatory

• May be required for severe limb disease when infection cannot be controlled with debridement alone, or when limb viability is irretrievably lost
• Diabetic patients (as in this case) have an increased risk of requiring amputation
• Limb salvage should be attempted but must never take priority over life-saving debridement

2. Antibiotic Therapy - Critical Adjunct (Not Replacement for Surgery)

• Vancomycin OR Linezolid

• Piperacillin-tazobactam
• Carbapenem (imipenem/meropenem)
• Ceftriaxone + metronidazole

• Penicillin G + Clindamycin - clindamycin is added because it inhibits bacterial protein and exotoxin synthesis (even though bacteria may be resistant to clindamycin alone)
• Tintinalli: "Triple antibiotic therapy with penicillin or a cephalosporin, an aminoglycoside, and clindamycin probably should be used"

• Surgical debridement is complete
• Patient is afebrile for 48-72 hours
• Clinical stabilisation is achieved
• Narrowed based on culture results from intraoperative tissue samples

3. Wound Management After Debridement

• Wounds are left open - primary closure is never appropriate in active NF
• Negative pressure wound therapy (VAC - vacuum-assisted closure): Applied to large open wounds post-debridement; reduces oedema, promotes granulation tissue, bridges the gap to definitive closure
• Skin grafting: Once infection is fully controlled and wound bed is clean and healthy, delayed skin grafting achieves final wound closure
• This reconstruction phase may require input from plastic surgery

4. Hyperbaric Oxygen Therapy (HBO)

• Suppresses growth of anaerobic microorganisms
• Improves bactericidal action of leukocytes that function poorly in hypoxic conditions
• Enhances antibiotic penetration into target bacteria

5. Additional Considerations in Patient Care

• Aggressive IV fluid resuscitation (massive third-space losses from necrotic tissue)
• Close monitoring of urine output, vitals, and electrolytes
• Vasopressor support if septic shock develops
• Most patients require ICU-level care

• Strict glycaemic control - hyperglycaemia impairs neutrophil function and wound healing
• Assess for peripheral vascular disease - vascular surgery consultation may be needed
• Higher risk of amputation; higher mortality risk

• May be considered in Group A Streptococcal NF to neutralise bacterial superantigens
• Limited data - no strong evidence for routine use

• Early enteral nutrition supports immune function, wound healing, and recovery through the prolonged post-operative course

Mortality

Summary