Approach to the Patient with Critical Illness¶
Chapter 311 | Part 8: Critical Care Medicine
KEY CLINICAL POINTS¶
- SOFA and APACHE II scoring systems are critical for assessing severity of illness and predicting outcomes in critical care.
- Shock is categorized into hypovolemic, cardiogenic, and high-cardiac-output types with distinct pathophysiology and management strategies.
- Respiratory failure is classified into types I-IV, with Type I (acute hypoxemic) and Type II (hypercapnic) being most clinically relevant.
- Mechanical ventilation requires careful management of tidal volumes, PEEP, and patient-ventilator synchrony to prevent ventilator-induced lung injury.
- Early recognition and intervention for sepsis, ICU-acquired weakness, and delirium are essential to improve outcomes.
1. DEFINITION & OVERVIEW¶
Critical illness severity is assessed using scoring systems like SOFA and APACHE II. These tools help define patient populations for clinical trials and guide ICU resource allocation. SOFA evaluates six organ systems, while APACHE II incorporates age, chronic disease, and physiologic parameters.
Table 311-1: Calculation of SOFA Score¶
| SYSTEM | 0 | 1 | 2 | 3 | 4 |
|---|---|---|---|---|---|
| Respiration | Pao2/FiO2 ‡400 (53.3) | Pao2/FiO2 <400 (53.3) | Pao2/FiO2 <300 (40) | Pao2/FiO2 <200 (26.7) with respiratory support | Pao2/FiO2 <100 (13.3) with respiratory support |
| Coagulation | Platelets ‡150 | Platelets <150 | Platelets <100 | Platelets <50 | Platelets <20 |
| Liver | Bilirubin <1.2 (20) | Bilirubin 1.2–1.9 (20–32) | Bilirubin 2.0–5.9 (33–101) | Bil3.0–11.9 (102–204) | Bilirubin >12.0 (204) |
| Cardiovascular | MAP ‡70 mmHg | MAP <70 mmHg | Dopamine <5 or Dobutamine (any dose) | Dopamine 5.1–15 or Epinephrine £0.1 or Norepinephrine £0.1 | Dopamine >15 or Epinephrine >0.1 or Norepinephrine >0.1 |
| Central Nervous System | GCS 15 | GCS 13–14 | GCS 10–12 | GCS 6–9 | GCS <6 |
| SYSTEM | 0 | 1 | 2 | 3 | 4 |
|---|---|---|---|---|---|
| Renal | Creatinine <1.2 (110) | Creatinine 1.2–1.9 (110–170) | Creatinine 2.0–3.4 (171–299) | Creatinine 3.5–4.9 (300–440) | Creatinine >5.0 (440) or urine output <500 mL/day |
Table 311-2: Calculation of APACHE II Score¶
| Acute P hysiolo gy Score | +4 | +3 | +2 | +1 | +0 | +1 | +2 | +3 | +4 |
|---|---|---|---|---|---|---|---|---|---|
| Rectal te mperatur e (°C) | ‡41 | 39.0–40. 9 | 38.5–38. 9 | 36.0–38. 4 | 34.0–35. 9 | 32.0–33. 9 | 30.0–31. 9 | £29.9 | |
| Mean blood pressure (mmHg) | ‡160 | 130–159 | 110–129 | 70–109 | 50–69 | £49 | |||
| Heart rate (bea ts/min) | ‡180 | 140–179 | 110–139 | 70–109 | 55–69 | 40–54 | £39 | ||
| Respirat ory rate ( breaths/ min) | ‡50 | 35–49 | 25–34 | 12–24 | 10–11 | 6–9 | £5 | ||
| Arterial pH | ‡7.70 | 7.60–7.6 9 | 7.50–7.5 9 | 7.33–7.4 9 | 7.25–7.3 2 | 7.15–7.2 4 | <7.15 | ||
| Oxygena tion | If FiO2 >0.5, use (A – a) Do ‡500 | If FiO2 >0.5, use (A – a) Do 350–499 | If FiO2 >0.5, use (A – a) Do 200–349 | If FiO2 >0.5, use (A – a) Do <200 | If FiO2 £0.5, use PaO2 >70 | If FiO2 £0.5, use PaO2 61–70 | If FiO2 £0.5, use PaO2 55–60 | If FiO2 £0.5, use PaO2 <55 | |
| Serum sodium (meq/L) | ‡180 | 160–179 | 155–159 | 150–154 | 130–149 | 120–129 | 111–119 | £110 | |
| Serum p otassium (meq/L) | ‡7.0 | 6.0–6.9 | 5.5–5.9 | 3.5–5.4 | 3.0–3.4 | 2.5–2.9 | <2.5 | ||
| Serum c reatinine (mg/dL) | ‡3.5 | 2.0–3.4 | 1.5–1.9 | 0.6–1.4 | <0.6 | ||||
| Hematoc rit (%) | ‡60 | 50–59.9 | 46–49.9 | 30–45.9 | 20–29.9 | <20 | |||
| WBC count (103/mL) | ‡40 | 20–39.9 | 15–19.9 | 3–14.9 | 1–2.9 | <1 | |||
| Glasgow Coma Score | 15 | 13–14 | 10–12 | 6–9 | <6 |
1.1 SOFA Scoring System¶
SOFA (Sequential Organ Failure Assessment) scores each of six organ systems (respiration, coagulation, liver, cardiovascular, central nervous system, renal) on a scale of 0–4. Total SOFA score ≥ 2 indicates organ dysfunction. qSOFA (quick SOFA) is a simplified version used for sepsis prognosis.
1.2 APACHE II Scoring System¶
APACHE II (Acute Physiology and Chronic Health Evaluation) combines physiologic scores, chronic health status, and age. Higher scores correlate with increased mortality. It is widely used in North America for ICU risk stratification.
2. EPIDEMIOLOGY¶
Critical illness is common in ICUs, with ≥ 75% of patients requiring mechanical ventilation. Sepsis is a leading cause of mortality in noncoronary ICUs. Risk factors include advanced age, chronic comorbidities, and prolonged ICU stays. Mortality rates vary by shock type and underlying conditions.
2.1 Sepsis and Mortality¶
Sepsis accounts for significant ICU mortality, with case fatality rates up to 30–70% in ARDS. Mortality increases with the number of failing organs and prolonged ICU stays.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
Critical illness arises from systemic inflammation, organ dysfunction, or failure. Shock is classified into hypovolemic, cardiogenic, and high-cardiac-output types. Respiratory failure is categorized by pathophysiology (e.g., alveolar flooding, ventilation-perfusion mismatch).
3.1 Types of Shock¶
Hypovolemic shock (fluid loss), cardiogenic shock (heart failure), and high-cardiac-output shock (e.g., sepsis, anaphylaxis) are distinguished by hemodynamic parameters and underlying mechanisms.
3.2 Respiratory Failure¶
Type I (acute hypoxemic) involves alveolar flooding and shunting. Type II (hypercapnic) results from impaired CO2 elimination. Type III (atelectasis) and Type IV (metabolic demands) are less common but clinically significant.
4. CLINICAL FEATURES¶
Clinical presentation varies by shock type. Hypovolemic shock presents with tachycardia and hypotension. Cardiogenic shock has pulmonary edema and elevated JVP. High-cardiac-output shock features warm extremities and bounding pulses. Respiratory failure manifests as tachypnea, hypoxia, or hypercapnia.
4.1 Shock Signs¶
Cold shock (low cardiac output): cool extremities, JVP elevation, crackles. Warm shock (high cardiac output): warm extremities, bounding pulses, rapid refill. Sepsis presents with altered mental status, tachypnea, and hypotension.
5. DIFFERENTIAL DIAGNOSIS¶
Differential diagnoses include sepsis, pulmonary embolism, heart failure, and metabolic derangements. For respiratory failure, consider pneumonia, ARDS, and pulmonary edema. For shock, differentiate between hypovolemic, cardiogenic, and distributive causes.
5.1 Sepsis vs. Other Causes¶
Sepsis is distinguished by systemic inflammation, organ dysfunction, and infection. Contrast with cardiogenic shock (pulmonary edema) and hypovolemic shock (fluid loss).
6. INVESTIGATIONS & DIAGNOSIS¶
Diagnostic tools include SOFA/APACHE II scores, arterial blood gases, chest imaging, and echocardiography. qSOFA is used for sepsis screening. Mechanical ventilation parameters (e.g., tidal volume, PEEP) guide ventilator settings.
6.1 Laboratory Tests¶
Arterial blood gas analysis, lactate levels, and complete blood count are critical. Chest X-ray and ultrasound assess for pulmonary edema, pneumothorax, or pleural effusion.
7. MANAGEMENT & TREATMENT¶
Management includes fluid resuscitation, vasopressors, mechanical ventilation, and source control. For sepsis, early antibiotics and surgical debridement are essential. Ventilator strategies (low tidal volumes) reduce ARDS mortality.
7.1 Shock Management¶
Hypovolemic shock: fluid resuscitation. Cardiogenic shock: inotropes, diuretics. High-cardiac-output shock: vasopressors, source control. Monitor for fluid responsiveness using dynamic parameters (e.g., pulse pressure variation).
7.2 Mechanical Ventilation¶
Use low tidal volumes (6 mL/kg) to prevent volutrauma. Adjust PEEP to optimize oxygenation. Avoid auto-PEEP with appropriate ventilator settings. Consider prone positioning in severe ARDS.
8. PROGNOSIS & COMPLICATIONS¶
Prognosis depends on severity of organ dysfunction, response to treatment, and comorbidities. Complications include ventilator-associated pneumonia, ICU-acquired weakness, delirium, and multiorgan failure. Mortality rates vary by shock type and ICU setting.
8.1 Long-Term Outcomes¶
ICU survivors may experience prolonged ICU stays, cognitive impairment, and reduced quality of life. Early mobilization and rehabilitation improve functional outcomes.
9. SPECIAL CONSIDERATIONS¶
Special populations include pregnant patients (risk of maternal/fetal complications), pediatric patients (different growth requirements), and elderly (increased frailty). ICU-acquired weakness and delirium require targeted interventions.
9.1 Nutrition and Glycemic Control¶
Early enteral feeding is preferred over parenteral nutrition. Tight glucose control ( ≤ 180 mg/dL) is recommended to reduce complications like infections and ARDS.
10. KEY POINTS & CLINICAL PEARLS¶
- Use SOFA and APACHE II scores to stratify critical illness severity. 2. Early recognition of sepsis and shock is critical for survival. 3. Low tidal volume ventilation reduces ARDS mortality. 4. Monitor for fluid responsiveness using dynamic parameters. 5. Address ICU-acquired weakness and delirium with early mobilization and sedation reduction.