Dengue fever, a mosquito-borne viral illness, can present a significant risk to patients even after the initial fever subsides, medical experts warn. While many patients recover as their fever declines, for some, this period marks the onset of a critical phase that requires close medical monitoring.

This phase, typically occurring around the time the fever resolves and lasting 24 to 48 hours, is characterized by a potentially dangerous process called plasma leakage. Plasma, the liquid portion of the blood, can escape from the bloodstream into surrounding tissues due to increased permeability of small blood vessels induced by inflammation. This leakage reduces the effective blood volume circulating through the body, concentrating the blood and sometimes causing fluid to accumulate in spaces around the lungs or inside the abdomen.

Severe plasma leakage can lead to a dangerous drop in blood pressure and impaired tissue perfusion, resulting in dengue shock syndrome. Shock signifies that vital organs such as the kidneys, liver, brain and heart are not receiving sufficient oxygenated blood, potentially causing organ dysfunction, multi-organ failure, and death if not promptly addressed.

Accurate monitoring during this critical period is essential. Physicians emphasize the importance of tracking haematocrit levels, which indicate the proportion of red blood cells in the blood. As plasma leaks out, haematocrit values rise due to the concentration of red blood cells. This metric, along with blood pressure, pulse pressure, urine output, peripheral circulation and overall clinical assessment, helps clinicians determine the severity of plasma leakage. While platelet counts—often a focus among patients and caregivers—provide some information, they do not alone reflect the full risk picture.

Fluid management is a cornerstone of dengue treatment during the critical phase. Careful administration of isotonic intravenous fluids is necessary to maintain adequate circulation without causing fluid overload. Underhydration can exacerbate shock and organ injury, whereas excessive fluids may lead to complications such as pulmonary edema, difficulty breathing, or cardiac problems when the blood vessels recover and reabsorb the leaked fluid. Patients who maintain adequate oral intake may not require intravenous fluids, but those showing warning signs or evidence of significant plasma leakage need fluids tailored and frequently adjusted based on clinical indicators.

Medical professionals also caution against premature discharge. Some patients may appear well enough to leave the hospital after their fever breaks, only to develop severe symptoms such as intense abdominal pain, repeated vomiting, unusual drowsiness or restlessness, cold extremities, breathing difficulties, bleeding, dizziness or reduced urine output shortly thereafter. These signs warrant immediate medical evaluation as they may indicate the beginning of the critical plasma leakage phase rather than a relapse of dengue.

Awareness of this critical period and adherence to vigilant monitoring protocols are vital to preventing life-threatening complications. Proper understanding of plasma leakage dynamics and fluid management strategies can significantly improve patient outcomes in dengue care.