Nursing care
Why sepsis drops blood pressure: vasodilation, leaky capillaries and lost volume
Written and reviewed by Maria Santos, ADN, RN, CMSRN · 4 min read · Updated October 2026
Short answer
Sepsis causes hypotension because inflammatory mediators dilate arteries and veins and make capillaries leak. The vessels suddenly hold more space while fluid escapes into tissues, so there is too little effective volume to fill them. This relative hypovolaemia lowers blood pressure and perfusion. The nurse tracks mean arterial pressure, lactate, urine output, mental status and skin to see whether resuscitation is working.
Inflammatory mediators widen the vessels
In sepsis the host response to infection releases a cascade of mediators. MSD explains that arteries and arterioles initially dilate, which lowers peripheral resistance, and cardiac output often rises in compensation. Because skin and extremities can stay warm, this early stage has been called warm shock, and it can be mistaken for a fever that is simply making the client flushed.
MSD's shock chapter classifies this as distributive shock: circulating blood volume may be normal, but arterial and venous dilation make it relatively inadequate for the enlarged vascular space. Blood is also diverted past capillary exchange vessels, so tissues receive less oxygen even when cardiac output is high. Low pressure and poor perfusion can therefore coexist with warm skin.
Capillary leak and relative hypovolaemia
Inflammation also increases capillary permeability. MSD lists sepsis among the causes of intravascular fluid moving into the extravascular space. Plasma leaves the circulation and collects in the tissues, so the client can become oedematous while the blood vessels are underfilled. This combination is the reason fluid resuscitation is a core early treatment.
Later, cardiac output may fall, and extremities become cool, pale and mottled. Microthrombi can block small vessels and add to poor capillary flow. As perfusion drops, organs begin to fail: the kidneys produce less urine, the brain becomes confused, and cells switch to anaerobic metabolism, which raises lactate.
Why fluids come before vasopressors
If the vessels are wide and partly empty, the first step is to put volume back so the heart has something to pump. MSD describes treatment as restoration of perfusion with IV fluids and sometimes vasopressors, alongside early antibiotics and source control. Vasopressors constrict vessels, but squeezing an underfilled circulation does little to restore flow.
MSD defines septic shock as sepsis with persistent hypotension requiring vasopressors to maintain a mean arterial pressure of at least 65 mm Hg and a serum lactate above 2 mmol/L despite adequate volume resuscitation. On the exam, persistent hypotension after fluids is the cue that vasopressor therapy, usually in critical care, is being considered under local protocol.
Reading MAP, lactate and urine output as a trend
Mean arterial pressure reflects the pressure that drives organ perfusion, so it is often more useful than systolic pressure alone. Track it with heart rate, respiratory rate, temperature, oxygen saturation, capillary refill, skin colour and level of consciousness. MedlinePlus notes that a change in mental status and very fast breathing may be the earliest signs of sepsis.
MSD describes urine output as a good indicator of renal perfusion. Improving trends are a rising MAP, falling heart rate, clearer mentation, warmer peripheries, better urine output and a falling lactate on repeat testing. Concerning trends are persistent hypotension after fluids, new mottling, decreasing urine output, rising lactate or new crackles and breathlessness that suggest fluid is not being tolerated.
Work a hypothetical sepsis scenario
Imagine a hypothetical client with pneumonia who is warm, flushed and newly confused, with a low blood pressure, fast heart rate and fast breathing. Options include giving an antipyretic and reassessing in an hour, placing the client flat and continuing to monitor, or escalating suspected sepsis and preparing for cultures, fluids and antibiotics per protocol.
Escalating is correct. Warm skin with hypotension and confusion fits early distributive shock, and delay worsens perfusion. An antipyretic treats the fever, not the falling pressure. Positioning alone does not correct vasodilation and leak. The prescriber decides fluid volume and rate; the nurse's job is recognition, escalation and close trend monitoring.
Sources and further reading
Sepsis and Septic Shock (MSD Manual Professional Edition). Arterial dilation and warm shock, shunting past capillaries, microthrombi; later cool mottled skin; septic shock definition with MAP and lactate; IV fluids and sometimes vasopressors; urine output as perfusion indicator.
Shock (MSD Manual Professional Edition). Distributive shock as relative inadequacy of volume from vasodilation; increased capillary permeability in sepsis moving fluid out of vessels.
Sepsis (MedlinePlus Medical Encyclopedia). Falling blood pressure and shock in sepsis; mental status change and fast breathing as possible early signs; warm skin.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our med-surg practice questions are the closest set to what this page covers.
One question from the med-surg set
A client with chronic obstructive pulmonary disease has an oxygen saturation of 88% on 2 L/min via nasal cannula and is alert with no distress. What should the nurse do first?
Rationale
In COPD a saturation of 88–92% is the therapeutic target, not an emergency, and this client is alert with no distress. The first action is the independent nursing intervention that is least invasive and most likely to help: sit them up and reassess. Turning the oxygen up to 6 L/min risks blunting the hypoxic drive, and calling rapid response or drawing an ABG escalates ahead of an assessment you have not finished.
Answer: B
Common questions
Why can a client in septic shock have warm skin?
Early sepsis dilates arteries and arterioles, so blood flows to the skin and extremities even as blood pressure falls. Later, as cardiac output drops and perfusion worsens, the skin becomes cool, pale and mottled.
Why does lactate rise in sepsis?
Poor capillary flow and low pressure reduce oxygen delivery to cells, so they rely more on anaerobic metabolism, which produces lactate. A falling lactate on repeat testing is one sign that perfusion is improving.
If sepsis causes leaky capillaries, why can fluid overload still happen?
Leaked fluid stays in the tissues and lungs, so large volumes can cause oedema and breathlessness, especially in clients with heart or kidney disease. Reassess breath sounds, oxygen saturation and work of breathing during resuscitation.
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