Distributive Shock

Distributive shock reflects pathologic vasodilation and impaired vascular responsiveness, producing inadequate effective arterial filling and tissue oxygen utilization. Common causes are sepsis, anaphylaxis, neurogenic shock, pancreatitis, and post-cardiotomy vasoplegia. Septic shock accounts for most distributive shock and may initially be hyperdynamic, but sepsis-associated myocardial dysfunction can convert the phenotype to mixed distributive-cardiogenic shock.ScienceDirect+1ScienceDirectShock (Circulatory) - an overviewPubMedShock - StatPearls - NCBI Bookshelf - NIH

Treat shock as a physiologic syndrome rather than a single diagnosis. Hypotension, elevated lactate, oliguria, altered mentation, delayed capillary refill, mottling, and cool extremities indicate hypoperfusion, although early septic shock can present with warm, flushed skin and preserved or high cardiac output.ScienceDirect+2ScienceDirectShock (Circulatory) - an overviewScienceDirectShock: causes, initial assessment and investigationsPubMedShock - StatPearls - NCBI Bookshelf - NIH

A presumed distributive cause does not exclude hemorrhage, acute coronary syndrome, pulmonary embolism, tamponade, tension pneumothorax, or medication-associated vasodilation. Reassess whenever vasopressor requirements escalate, lactate fails to improve, pulmonary edema develops, or bedside findings are discordant with the presumed phenotype.ScienceDirect+1ScienceDirectShock (Circulatory) - an overviewScienceDirectShock: causes, initial assessment and investigations

Septic shock is sepsis with vasopressor requirement to maintain MAP at least 65 mmHg and lactate above 2 mmol/L despite adequate fluid resuscitation.PubMed+1PubMed2023 Update on Sepsis and Septic Shock in Adult PatientsPubMedThe Japanese Clinical Practice Guidelines for Management of Sepsis and Septic Shock 2024 Antimicrobial therapy and source control are the time-critical disease-modifying interventions. Obtain blood cultures and source-directed specimens before antimicrobials when feasible, but do not permit testing to delay treatment in a patient with shock.PubMed+1PubMed2023 Update on Sepsis and Septic Shock in Adult PatientsPubMedThe Japanese Clinical Practice Guidelines for Management of Sepsis and Septic Shock 2024

Initial fluid therapy should address suspected reduced intravascular volume while avoiding fluid accumulation. Balanced crystalloids are preferred over normal saline in the cited sepsis guidance. Some patients require at least 30 mL/kg within 3 hours, but subsequent fluids should be individualized using response to a small bolus, dynamic measures of fluid responsiveness, bedside echocardiography, and evidence of fluid intolerance or congestion.PubMed+1PubMed2023 Update on Sepsis and Septic Shock in Adult PatientsPubMedThe Japanese Clinical Practice Guidelines for Management of Sepsis and Septic Shock 2024

Norepinephrine is first-line for septic shock and should be started early when hypotension persists during resuscitation; the cited review describes 0.1 to 1.2 micrograms/kg/min. A MAP target of 65 mmHg is appropriate initially for most patients. Vasopressin is an adjunct when norepinephrine alone does not achieve the target; epinephrine is generally reserved for inadequate pressure control despite norepinephrine and vasopressin or when inotropic effects are needed.PubMed+1PubMed2023 Update on Sepsis and Septic Shock in Adult PatientsPubMedThe Japanese Clinical Practice Guidelines for Management of Sepsis and Septic Shock 2024

Anaphylaxis is a rapid systemic hypersensitivity reaction characterized by airway, breathing, and/or circulatory compromise; cutaneous findings may be absent. The immediate first-line treatment is intramuscular epinephrine. Prompt administration is associated with better outcomes, and a second intramuscular dose should be administered after 5 minutes if ABC compromise persists.PubMedPubMedEmergency treatment of anaphylaxis: concise clinical guidance

Place the patient supine with legs elevated when feasible to maximize venous return. Give oxygen, establish IV or intraosseous access, and provide IV fluid resuscitation for shock or poor response to epinephrine. Refractory anaphylaxis is persistent ABC compromise after two appropriate intramuscular doses and warrants urgent critical care support and a titrated low-dose IV epinephrine infusion by clinicians experienced with vasopressors and continuous monitoring.PubMedPubMedEmergency treatment of anaphylaxis: concise clinical guidance

Neurogenic shock follows disruption of sympathetic pathways, most often after traumatic spinal cord injury, producing low vascular resistance, reduced venous return, and often bradycardia. Supportive care includes continuous hemodynamic and respiratory monitoring, treatment of the spinal injury, and vasoconstrictor support; norepinephrine may be useful when both vasoconstriction and inotropy are needed, whereas phenylephrine may be appropriate in selected circumstances.ScienceDirectScienceDirectShock (Circulatory) - an overview

Other nonseptic vasodilatory states include post-cardiopulmonary-bypass vasoplegia, pancreatitis, medication-associated vasodilation, adrenal crisis, and severe inflammatory states. These presentations require active evaluation for mixed shock and targeted treatment of the precipitant; generalized vasopressor escalation without diagnostic reassessment can miss pump failure, hemorrhage, or obstruction.ScienceDirect+2ScienceDirectShock (Circulatory) - an overviewScienceDirectShock: causes, initial assessment and investigationsPubMedShock - StatPearls - NCBI Bookshelf - NIH

A MAP target of 65 mmHg is a reasonable initial target in septic shock, but hemodynamic stabilization should be judged by end-organ perfusion. Follow urine output, mentation, capillary refill, skin temperature and mottling, lactate, acid-base status, and the trajectory of vasopressor requirement. Failure of these markers to improve should prompt a search for inadequate source control, occult hemorrhage, excessive sedation, myocardial dysfunction, obstruction, or ongoing hypoxemia.ScienceDirect+2ScienceDirectShock (Circulatory) - an overviewPubMed2023 Update on Sepsis and Septic Shock in Adult PatientsPubMedThe Japanese Clinical Practice Guidelines for Management of Sepsis and Septic Shock 2024

Fluid administration should stop when there is no evidence of benefit or when fluid intolerance emerges. Reassess after each intervention with dynamic testing or stroke-volume response when available, and use lung and cardiac ultrasonography to identify pulmonary congestion or impaired ventricular function. Positive fluid balance and elevated CVP have been associated with worse outcomes in septic shock, but observational associations should not be used as a substitute for individualized assessment.PubMedPubMed2023 Update on Sepsis and Septic Shock in Adult Patients