What is a sign of early sepsis?

A Sign of Early Sepsis

Respiratory alkalosis is a sign of early sepsis (c).

Pathophysiology of Early Sepsis

In early sepsis, the body's initial response to infection triggers a cascade of physiological changes. According to the American College of Critical Care Medicine, one of the earliest respiratory manifestations is centrally mediated hyperventilation, which leads to respiratory alkalosis 1. This occurs before metabolic derangements become prominent.

The respiratory system responds to inflammatory mediators and cytokines by increasing the respiratory rate, which is one of the diagnostic criteria for sepsis according to multiple guidelines 1, 2. This hyperventilation causes:

• Increased elimination of CO2
• Decreased PaCO2 levels (<32 mmHg)
• Elevated pH (alkalosis)

Progression of Acid-Base Disturbances in Sepsis

The acid-base disturbances in sepsis follow a typical progression:

1. Early sepsis: Respiratory alkalosis due to centrally mediated hyperventilation 1

2. Progressive sepsis: Development of metabolic acidosis due to:

   • Lactic acidosis from tissue hypoperfusion
   • Hyperchloremic acidosis
   • Renal dysfunction

3. Late/severe sepsis: Combined respiratory and metabolic acidosis as respiratory compensation fails 3

Clinical Recognition

The Society of Critical Care Medicine and the Surviving Sepsis Campaign emphasize that early recognition of sepsis involves identifying:

• Respiratory rate ≥22/min (a key component of qSOFA) 2, 4
• Tachycardia >90 beats/min
• Temperature abnormalities (>38.3°C or <36°C)
• Altered mental status

The respiratory rate increase is a compensatory mechanism that initially leads to respiratory alkalosis before metabolic acidosis becomes predominant 2.

Diagnostic Implications

Understanding that respiratory alkalosis is an early sign of sepsis has important clinical implications:

• Blood gas analysis showing respiratory alkalosis in a patient with suspected infection should raise concern for early sepsis
• Waiting for metabolic acidosis to develop may delay diagnosis and treatment
• Early intervention based on respiratory changes can improve outcomes

Common Pitfalls

1. Misinterpreting acid-base status: Assuming that acidosis is always present in sepsis can lead to missed early diagnoses when only respiratory alkalosis is present.

2. Focusing only on lactate: While lactate is an important marker, it typically rises later than the respiratory changes.

3. Overlooking vital signs: Tachypnea (elevated respiratory rate) is one of the earliest and most sensitive indicators of sepsis and should prompt consideration of sepsis even before laboratory abnormalities develop.

Clinical Algorithm for Early Sepsis Recognition

1. Monitor for tachypnea (RR ≥20/min) in patients with suspected infection
2. Check arterial blood gases if available
3. Recognize respiratory alkalosis (low PaCO2, high pH) as an early warning sign
4. Initiate sepsis protocols promptly rather than waiting for metabolic acidosis to develop

Remember that as sepsis progresses, metabolic acidosis will eventually develop and may overshadow the initial respiratory alkalosis, but by then, the patient has already progressed beyond the early phase of sepsis.