Definition

Mean arterial pressure (MAP) <65. Keep in mind that a patient who is usually hypertensive can experience hypoperfusion at higher MAPs.

Differential Diagnosis and Evaluation

Remember hypotension = death. Presence of normal mentation simply indicates that the patient still has a pulse and should not be reassuring in itself. Some patients with chronic conditions (end stage liver disease, chronic heart failure, and autonomic dysfunction) may have low baseline MAP, and elderly patients often have low baseline diastolic pressure. That said, treat all episodes of hypotension very seriously; all hypotensive patients should be seen and evaluated promptly.

Use this equation to think through the differential diagnosis of hypotension:

MAP = SVR x CO = SVR x HR x SV
(where Stroke volume = Preload x Contractility)

MAP - mean arterial pressure; SVR - systemic vascular resistance - HR, heart rate; SV - stroke volume.

History and physical exam (especially volume status) are the most important initial steps to narrowing down the diagnosis and determining initial treatment. Point-of-care ultrasound of the IVC can augment physical exam, and if used properly, predicts fluid responsiveness. Patients are predicted to be fluid responsive if IVC diameter (measured 1 cm distal to hepatic vein) is < 1.5 cm, with >40% collapse on inspiration if not intubated, or >15% distention during positive pressure ventilation (https://www.youtube.com/watch?v=qHWLFfXtGn8).

Decreased SVR: Exam = warm extremities, sometimes flushing.

• Sepsis: Common cause. Obtain blood cultures x 2, CXR, UA/micro/culture, and lactate. Rapid administration of IVF and antibiotics will be crucial. See Critical Care: early goal-directed therapy for sepsis.
• Medications: Look for antihypertensives, pain meds, sedatives, illicit drugs, and possible dosage errors; if concern for opiate overdose, give naloxone.
• Adrenal insufficiency: Is the patient on chronic steroids and unable to mount a stress response? Consider stress dose steroids (See Endocrine: Adrenal Insufficiency).
• Anaphylaxis: Look at medication list/diet for offending agent. Give epinephrine 0.2-0.5 ml (0.2-0.5 mg) of 1:1000 SC/IM q20 minutes (different from “code blue” dose), diphenhydramine 50 mg IV, hydrocortisone 100 mg IV.
• Neurogenic: “Spinal shock” rare cause in an already hospitalized patient. Spinal compression. Treatment is epinephrine.

Decreased preload: Exam = cool extremities, variable JVP

• Hypovolemia: bleed, diarrhea, third spacing, insensible losses. Get STAT CBC, consider Central Venous Pressure (CVP) monitoring, review Ins and Outs. Increase preload by putting the patient in Trendelenburg, giving IVF bolus (almost never wrong, though check if the patient has known heart failure).
• Pulmonary embolism: See Pulmonary: Pulmonary Embolism.
• Tension pneumothorax (PTX): Unequal breath sounds on exam. Do not wait for a CXR. Insert a 14 or 16-gauge needle into the second intercostal space at the midclavicular line ASAP.
• Tamponade: Remember Beck’s triad: elevated JVP, muffled heart sounds, and hypotension. Get pulsus, call cardiology to perform an echo and pericardiocentesis. See Cardiology: Tamponade.
• Right ventricular infarct: If you see inferior ST-segment elevation, obtain right-sided ECG. See Cardiology: RV Myocardial Infarction.
• Pulmonary hypertension: See Cardiology: Pulmonary Hypertension. 

Decreased contractility: Exam = listen for gallop, murmurs (especially new), and rales/crackles. Get ECG, Troponin, BNP, Comprehensive Metabolic Panel, and CXR.

• Myocardial dysfunction: New infarct vs. prior ventricular dysfunction and precipitating event. Review history of CAD/CHF and cardiac risk factors. Get STAT ECG, troponin, telemetry; see Cardiology: Rule out Myocardial Infarction, ACS, and Congestive Heart Failure.
• Medications: Look for β-blockers and CCBs.
• Valvular dysfunction (AS, AI, MR): Acute worsening of known valve disease? Infarction causing papillary muscle rupture? Endocarditis? Get STAT echo. Treatment is specific to the valvular abnormality (e.g. afterload reduction with nitroprusside drip for severe MR).
• Aortic dissection: Any history of peripheral vascular disease? Get STAT chest CT.

Abnormal heart rate/rhythm: Look at the ECG for pathologic tachycardia, bradycardia. Unlikely to be primary cause unless HR is very high or very low. Extreme tachycardia prevents LV filling.

Additional Points on Differential Diagnosis and initial evaluation: After using MAP=SVR x CO, consider the following:

• Overlap syndromes: Get more data with a bedside ultrasound. You can involve ICU/cardiology for consideration of CVP monitoring, mixed venous oxygen saturation, formal echocardiogram, and a pulmonary artery catheter if warranted.
• Consider other causes of hypotension:
• Increased cardiac output without sepsis: ESLD or fulminant hepatic failure, severe pancreatitis, trauma with SIRS, thyroid storm, AV fistula.
• Increased CVP without LV failure: pulmonary hypertension, PE, RV infarct, tamponade.
• Non-responsive hypovolemia: adrenal insufficiency, anaphylaxis, cold sepsis.
• Autonomic dysfunction: review past medical history

Management

Always start with: “Is the patient stable?” and go evaluate the patient promptly:

• Above all, stay calm. Crashing patients are scary. Do not try to manage shock by yourself. Discuss the case with other residents, ICU fellow, etc.
• Have a low threshold to transfer a hypotensive patient to the ICU for better nursing support, pressors, and/or intubation. Call a code blue for immediate help.
• If the BP is undetectable, palpate for pulses. A palpable femoral pulse indicates systolic blood pressure (SBP) > 80 mmHg and a palpable carotid pulse indicates SBP > 60 mmHg. If you are not sure you feel a pulse, call a Code Blue.
• Treatment is aimed at the underlying cause (see DDx and evaluation section above), but almost all cases call for fluid resuscitation. If suspicion of CHF is low, then give rapid isotonic fluid resuscitation.
  • If there is concern for mixed cardiogenic and septic shock, let your volume exam guide treatment. Keep fluid boluses small (i.e. 250ml and re-assess). Trend lactate and consider placing a central line to measure CVP and central venous saturation. While this is in process, you can use urine output as a surrogate.
• In general, start O2, additional large bore peripheral IVs, put patient in Trendelenburg, draw basic STAT labs (CBC, lytes, BUN, creatinine, glucose, LFTs, blood/urine cultures), and get STAT ECG, CXR, ABG/lactate.
• See Critical Care: Initial Choice of Vasopressor in Hypotension, Stepwise Approach to the ICU patient with septic shock for more information.
• If the patient is stable, then move on to these questions: 
  • Is this BP real? Measure the BP manually with the correct sized cuff. Get a repeat full set of vitals. Repeat on the opposite arm.
  • Is the BP different from prior values? If the patient usually has a BP of 80/40 mmHg, then the acuity may be decreased somewhat.
  • Is there associated hypoxemia, altered mental status, or increased respiratory rate (reasons for intubation)?
  • Access? Think about placing additional large bore peripheral IVs, a central line, or an intraosseous (IO) line in emergency situations.
  • Monitoring? Arterial line placement gives real time accurate blood pressure measurements. Foley catheter to measure urine output (renal perfusion).
  • Is the mean arterial pressure (MAP) < 60 mmHg?  MAP = (SBP + 2(DBP))/3. MAP less than 60 mmHg results in significant risk of hypoperfusion to vital organs.

Key Points

• “The patient is mentating fine” only signifies that the patient still has a pulse, and does not rule out hypoperfusion of other vital organs.
• Treat all episodes of hypotension seriously. Always go to evaluate the patient.
• Use the equation MAP = SVR x CO to help think through the DDx and initial management of hypotension. See Hypotension Algorithm for a quick review.
• Unless grossly volume overloaded, an IV fluid bolus is almost always an appropriate first step.

Wood Lawrence D, "Chapter 20. The Pathophysiology of the Circulation in Critical Illness" (Chapter).
Hall JB, Schmidt GA, Wood LDH: Principles of Critical Care, 3rd edition. 2005.
Soni NJ, Arntfield R, Kory P. Point-of-Care Ultrasound. 2nd Edition. Elsevier 2019.