Thursday, July 20, 2017

Shock - A Brief Discussion



Shock is a condition of severe impairment of tissue perfusion leading to cellular injury and dysfunction. Rapid recognition and treatment are essential to prevent irreversible organ damage and death.

Different Causes And Categories Of Shock:

Hypovolemic shock

  • Hemorrhage
  • Intravascular volume depletion (e.g., vomiting, diarrhea, ketoacidosis)
  • Internal sequestration (ascites, pancreatitis, intestinal obstruction)

Cardiogenic shock

  • Myopathic (acute MI, fulminant myocarditis)
  • Mechanical (e.g., acute mitral regurgitation, ventricular septal defect, severe aortic stenosis, aortic dissection with aortic insufficiency)
  • Arrhythmic

Extracardiac obstructive shock

  • Pericardial tamponade
  • Massive pulmonary embolism
  • Tension pneumothorax

Distributive shock (profound decrease in systemic vascular tone)

  • Sepsis
  • Toxic overdoses
  • Anaphylaxis
  • Neurogenic (e.g., spinal cord injury)
  • Endocrinologic (Addison’s disease, myxedema)
Clinical Manifestations:

• Hypotension (mean arterial BP <60 mmHg), tachycardia, tachypnea, pallor, restlessness, and altered sensorium.
• Signs of intense peripheral vasoconstriction, with weak pulses and cold clammy extremities. In distributive (e.g., septic) shock, vasodilation predominates and extremities are warm.
• Oliguria (<20 mL/h) and metabolic acidosis common.
• Acute lung injury and acute respiratory distress syndrome with noncardiogenic pulmonary edema, hypoxemia, and diffuse pulmonary infiltrates.

Approach To The Patient: 

Obtain history for underlying causes, including 
  • cardiac disease (coronary disease, heart failure, pericardial disease), 
  • recent fever or infection leading to sepsis, 
  • drug effects (e.g., excess diuretics or ), 
  • conditions leading to pulmonary embolism and 
  • potential sources of bleeding.
Physical Examination
  • Jugular veins are flat in oligemic or distributive (septic) shock; 
  • jugular venous distention (JVD) suggests cardiogenic shock; 
  • JVD in presence of paradoxical pulse may reflect cardiac tamponade . 
  • Check for asymmetry of pulses (aortic dissection). 
  • Assess for evidence of heart failure , murmurs of aortic stenosis, acute mitral or aortic regurgitation, and ventricular septal defect. 
  • Tenderness or rebound in abdomen may indicate peritonitis or pancreatitis; high-pitched bowel sounds suggest intestinal obstruction.
  • Perform stool guaiac to rule out GI bleeding.
  • Fever and chills typically accompany septic shock. 
  • Sepsis may not cause fever in elderly, uremic, or alcoholic patients. 
  • Skin lesions may suggest specific pathogens in septic shock: petechiae or purpura (Neisseri meningitidis or Haemophilus influenzae), ecthyma gangrenosum (Pseudomonas aeruginosa), generalized erythroderma (toxic shock due to Staphylococcus aureus or Streptococcus pyogenes).
Investigations:

  • Obtain hematocrit, WBC, electrolytes, platelet count, PT, PTT, DIC screen, electrolytes.
  • Arterial blood gas usually shows metabolic acidosis (in septic shock, respiratory alkalosis precedes metabolic acidosis). 
  • If sepsis suspected, draw blood cultures, perform urinalysis, and obtain Gram stain and cultures of sputum, urine, and other suspected sites.
  • Obtain ECG (myocardial ischemia or acute arrhythmia) and chest x-ray (heart failure, tension pneumothorax, pneumonia). 
  • Echocardiogram is often helpful (cardiac tamponade, left/right ventricular dysfunction, aortic dissection).
Management: 

Aimed at rapid improvement of tissue hypoperfusion and respiratory impairment:
• Serial measurements of BP (intraarterial line preferred), heart rate, continuous ECG monitor, urine output, pulse oximetry, blood studies: Hct, electrolytes, creatinine, BUN, ABGs, pH, calcium, phosphate, lactate, urine Na concentration (<20 mmol/L suggests volume depletion). 
• Consider monitoring of CVP and/ or pulmonary artery pressure/PCW pressures in patients with ongoing blood loss, marked fluid shifts, or suspected cardiac dysfunction (the majority of patients do not require pulmonary artery catheter monitoring).
• Insert Foley catheter to monitor urine flow.
• Assess mental status frequently.
• Augment systolic BP to >100 mmHg: 
(1) Place in reverse Trendelenburg position;
(2) IV volume infusion (500- to 1000-mL bolus), unless cardiogenic shock suspected (begin with normal saline or Ringer’s lactate, then whole blood, or packed RBCs, if anemic); continue volume replacement as needed to restore vascular volume.
• Add vasoactive drugs after intravascular volume is optimized; administer vasopressors if systemic vascular resistance (SVR) is decreased (begin with norepinephrine [preferred] or dopamine; for persistent hypotension add phenylephrine or vasopressin).
• If heart failure is present, add inotropic agents (usually dobutamine) ; aim to maintain cardiac index >2.2(L/m2)/min [>4.0(L/m2)/min in septic shock].
• Administer 100% O2; intubate with mechanical ventilation if PO2 <70 mmHg.
• If severe metabolic acidosis present (pH <7.15), administer NaHCO3.
• Identify and treat underlying cause of shock.

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