# The Undifferentiated Acutely Ill Patient: A Resuscitation Framework

## Introduction

The **undifferentiated acutely ill patient** presents with hemodynamic instability, altered mental status, or respiratory failure without a clear diagnosis. A systematic resuscitation framework enables clinicians to stabilize the patient while simultaneously pursuing the underlying etiology. This approach prioritizes life-threatening conditions and employs rapid assessment, early intervention, and iterative reassessment.

## The Initial Approach: First 5 Minutes

### Primary Survey (ABCDE)

- **Airway**: assess patency; jaw thrust, oropharyngeal airway, or intubation if compromised
- **Breathing**: respiratory rate, SpO2, work of breathing; apply supplemental oxygen; auscultate bilaterally
- **Circulation**: heart rate, blood pressure, capillary refill, skin color and temperature; establish large-bore IV access (2 x 18G)
- **Disability**: GCS, pupil reactivity, point-of-care glucose, lateralizing signs
- **Exposure**: fully expose the patient; assess for rashes, wounds, surgical scars, drug patches; prevent hypothermia

### Immediate Actions

- Obtain **continuous monitoring**: cardiac telemetry, pulse oximetry, non-invasive blood pressure
- Draw **initial labs**: CBC, BMP, lactate, troponin, coagulation studies, blood gas, blood cultures (x2), type and screen
- Obtain **12-lead ECG** within the first 5 minutes
- Place a **Foley catheter** if hemodynamically unstable to monitor urine output
- **POCUS** within the first 10 minutes to assess cardiac function, IVC, lungs, and free fluid

![Primary survey and initial resuscitation algorithm](images/primary-survey-algorithm.png)

## Shock Classification and Recognition

### The Four Types of Shock

| Type | Mechanism | Exam Findings | Common Causes |
|------|-----------|---------------|---------------|
| Distributive | Low SVR, vasodilation | Warm extremities, wide pulse pressure, bounding pulses | Sepsis, anaphylaxis, neurogenic |
| Hypovolemic | Volume loss | Cold extremities, tachycardia, narrow pulse pressure | Hemorrhage, dehydration, third-spacing |
| Cardiogenic | Pump failure | Elevated JVP, pulmonary edema, cool extremities | MI, arrhythmia, acute valve failure |
| Obstructive | Mechanical obstruction | Elevated JVP, clear lungs (tamponade/PE), absent breath sounds (tension PTX) | Tamponade, massive PE, tension PTX |

- **Distributive (most common)**: warm extremities, wide pulse pressure, low SVR; sepsis, anaphylaxis, neurogenic
- **Hypovolemic**: hemorrhagic or non-hemorrhagic volume loss; tachycardia, cold extremities, narrow pulse pressure
- **Cardiogenic**: pump failure; elevated JVP, pulmonary edema, cool extremities; MI, arrhythmia, acute valvular disease
- **Obstructive**: mechanical obstruction to flow; tension pneumothorax, cardiac tamponade, massive PE

### POCUS-Guided Shock Assessment (RUSH Exam)

- **Pump**: LV function, RV dilation, pericardial effusion
- **Tank**: IVC size and collapsibility, lung B-lines, FAST for free fluid
- **Pipes**: aorta for aneurysm, DVT assessment for PE consideration
- POCUS narrows the differential within minutes and guides initial resuscitation

## Resuscitation Strategies

### Fluid Resuscitation

- **Crystalloid** (balanced solutions preferred: lactated Ringer's or Plasmalyte) as initial fluid
- **30 mL/kg bolus** for sepsis within the first 3 hours; reassess after each bolus
- Avoid fluid overload; transition to vasopressors if hypotension persists despite adequate volume
- Use **dynamic measures of fluid responsiveness**: passive leg raise, pulse pressure variation, IVC variability

### Vasopressor and Inotrope Selection

- **Norepinephrine**: first-line vasopressor for most forms of shock
- **Vasopressin**: second-line adjunct in septic shock to reduce norepinephrine requirements
- **Epinephrine**: first-line in anaphylaxis and cardiac arrest; second-line in cardiogenic shock
- **Dobutamine**: inotrope for cardiogenic shock with low cardiac output
- **Phenylephrine**: pure alpha-agonist; useful in tachyarrhythmia-associated hypotension

![Vasopressor and inotrope selection by shock type](images/vasopressor-selection.png)

## The Diagnostic Workup: Thinking While Doing

### Must-Not-Miss Diagnoses (The Killer Bs)

- **Blood**: hemorrhage (GI bleed, ruptured AAA, ectopic pregnancy)
- **Bugs**: sepsis from any source
- **Blocks**: tension pneumothorax, cardiac tamponade, massive PE
- **Bad pump**: acute MI, acute heart failure, arrhythmia
- **Brain**: stroke, status epilepticus, meningitis

### Systematic Approach to the Differential

- Use an **organ-system-based** approach when the diagnosis is unclear
- Consider **toxicologic** causes: overdose, withdrawal, environmental exposure
- **Endocrine emergencies**: adrenal crisis, myxedema coma, thyroid storm, DKA/HHS
- Review medication list for recent changes, new drugs, or missed doses
- Obtain collateral history from family, EMS, and prior records

## Reassessment and Escalation

- **Reassess every 15-30 minutes**: vital signs, mental status, urine output, lactate clearance
- **Lactate trends** are more valuable than single values; a failure to clear by 20% in 2 hours suggests inadequate resuscitation
- If not improving, reconsider the diagnosis and broaden the differential
- **Escalate early**: involve critical care, surgery, or specialty consultation when indicated
- **Communicate**: structured handoffs (SBAR) at transitions of care

## Team-Based Resuscitation

- **Designate a team leader** who maintains situational awareness and avoids task fixation
- Assign roles: airway manager, proceduralist, medication nurse, documenter
- Use **closed-loop communication**: order, repeat back, confirm
- **Debrief** after every resuscitation to identify what went well and opportunities for improvement

![Team-based resuscitation roles and communication framework](images/team-resuscitation.png)

## Key Clinical Pearls

- The ABCDE approach and early POCUS are the foundation of managing the undifferentiated acutely ill patient.
- Norepinephrine is the first-line vasopressor for nearly all forms of shock.
- Always consider the must-not-miss diagnoses before anchoring on a working diagnosis.
- Reassess frequently; failure to improve should prompt reconsideration of the diagnosis and treatment plan.
- Effective resuscitation is a team sport: clear roles, closed-loop communication, and structured debriefs improve outcomes.

## References

1. Seymour CW, Gesten F, Prescott HC, et al. Time to Treatment and Mortality during Mandated Emergency Care for Sepsis. *New England Journal of Medicine*. 2017;376(23):2235-2244.
2. Perera P, Mailhot T, Riley D, et al. The RUSH Exam: Rapid Ultrasound in SHock in the Evaluation of the Critically Ill. *Emergency Medicine Clinics of North America*. 2010;28(1):29-56.
3. Evans L, Rhodes A, Alhazzani W, et al. Surviving Sepsis Campaign: International Guidelines for Management of Sepsis and Septic Shock 2021. *Critical Care Medicine*. 2021;49(11):e1063-e1143.
4. Weingart SD, Levitan RM. Preoxygenation and Prevention of Desaturation During Emergency Airway Management. *Annals of Emergency Medicine*. 2012;59(3):165-175.