Hypotension

1. 定義：低血壓+症狀，如lightheadedness, visual change, ↓mental status, syncope, shock。
2. 姿勢性低血壓：SBP↓≧10mmHg 且超過兩分鐘都還沒升回來。若病人服用特定藥物或有傳導異常會更嚴重。
3. 評估volume status。如 skin turgor, mucosal membrane moistness, axillary prespiration amount, jugular v. blood column height等，更進一步可測CVP，PCWP
4. 姿勢性低血壓也可能是嚴重的周邊神經病變。如DM, renal failure, amyloidosis, Wernicke's disease, syphilis, porphyria等等。
5. shock：低血壓+↓tissue perfusion→organ dysfunction。
   組織灌流不足會行無氧呼吸，產生lactic acid→ΔAG↑ metabolic acidosis。
   器官失能看↓MS，小腸失去peristaltic activity，肺部氣體交換↓，cool pale skin
6. 組織灌流正常的非姿勢性低血壓：transient vasomotor instability。通常為時不久。因vagal tone↑或刺激vagal n.而引起。
7. ↓volume status：可能是絕對／相對的。絕對的如RBC, plasma loss。相對的是因為：vasodilation。原因如：sepsis, neuropathy, anaphylatsis, drug。可能要測SVR, cardiac filling pressure才能區分
8. neuropathic form：脊髓descending pathway被阻斷。原因：SCI( transection, edema)，syringomyelia, spinal tumor, CP angle tumor, epidural/spinal 麻醉, drug (ex. barbiturate)
9.  瓣膜問題：critical AS, acute AR, acute MR 等等

Shock

EMPIRICAL CRITERIA FOR DIAGNOSIS OF CIRCULATORY SHOCK** Regardless of cause. Four criteria should be met.
Ill appearance or altered mental status
Heart rate >100 beats/min
Respiratory rate >20 breaths/min or Paco2 <32>4 mM/L
Urine output <0.5>20 minutes duration

DEFINITIONS AND CRITERIA FOR SEPTIC, HEMORRHAGIC, AND CARDIOGENIC SHOCK

• Septic Shock
  
  • Systemic Inflammatory Response Syndrome (SIRS)
  有兩個以上：
  1) Temperature >38℃ or <36℃>90 beats/min
  3) RR >20 breaths/min or Paco2 <32>12,000/mm3, <4000/mm3,>10% band neutrophilia
  
  • Severe Sepsis
  SIRS + suspected or confirmed infection + associated with organ dysfunction or hypotension; organ dysfunction may include presence of lactic acidosis, oliguria, or altered mental status
  
  • Septic Shock
    SIRS + suspected or confirmed infection + hypotension despite adequate fluid resuscitation; septic shock should still be diagnosed if vasopressor therapy has normalized blood pressure
• Hemorrhagic Shock
  
  • Simple Hemorrhage
    Suspected bleeding + pulse < 100
  • Hemorrhage with Hypoperfusion
    Suspected bleeding + base deficit <−4 mEq/L or persistent pulse >100 beats/min
  • Hemorrhagic Shock
    Suspected bleeding + Circulation Shock
  
  
• Cardiogenic Shock
  
  • Cardiac Failure
    Clinical evidence of impaired forward flow of the heart, including presence of dyspnea, tachycardia, pulmonary edema, peripheral edema, or cyanosis
    
  • Cardiogenic Shock
    Cardiac failure + Circulation Shock
    

CLINICAL MANAGEMENT GUIDELINES FOR FOUR COMMON CAUSES OF SHOCK

• Hemorrhagic Shock
  1) Ensure adequate ventilation/oxygenation
  2) Provide immediate control of hemorrhage, when possible (e.g., traction for long bone fractures, direct pressure)
  3) Initiate judicious infusion of isotonic crystalloid solution (10–20 mL/kg)
  4) With evidence of poor organ perfusion and 30-minute anticipated delay to hemorrhage control, begin packed red blood cell (PRBC) infusion (5–10 mL/kg)
  5) With suspected central nervous system trauma or Glasgow Coma Scale score <9, immediate PRBC transfusion may be preferable as initial resuscitation fluid
  6) Treat coincident dysrhythmias (e.g., atrial fibrillation with synchronized cardioversion)


• Cardiogenic Shock
  1) Ameliorate increased work of breathing; provide oxygen and positive end-expiratory pressure (PEEP) for pulmonary edema
  2) Begin vasopressor or inotropic support; norepinephine (0.5 μg/min) and dobutamine (5 μg/kg/min) are common empirical agents
  3) Seek to reverse the insult (e.g., initiate thrombolysis, arrange percutaneous transluminal angioplasty)
  4) Consider intra-aortic balloon pump counterpulsation for refractory shock


• Septic Shock
  1) Ensure adequate oxygenation; remove work of breathing
  2) Administer 20 mL/kg of crystalloid or 5 mL/kg of colloid, and titrate infusion to adequate central venous pressure and urine output
  3) Begin antimicrobial therapy; attempt surgical drainage or d?bridement
  4) Begin PRBC infusion for hemoglobin < 8 g/dL
  5) If volume restoration fails to improve organ perfusion, begin vasopressor support; initial choice includes dopamine, infused at 5–15 μg/kg/min, or norepinephrine, infused at 0.5 μg/min

Ref: Marx: Rosen's Emergency Medicine, 7th ed. Chp. 4 Shock