Introduction to Hemodynamics

Topic Progress:
Ernstl / CC BY-SA

Pearls for the Fundamentals of Hemodynamics

1. Cardiac output is determined by the squeeze of the pump, the volume in the tank, the squeeze of the pipes and the heart rate.
2. Hemodynamics can be measured using a variety of surrogate end points like urine output, respiratory rate, etc.
3. Assess the patient first; numbers can lie.

The Oxygen Supply-Demand Framework

We will be focusing on the green shaded area.

General Framework to Hemodynamics

It is best reviewed in a series of case studies. Our biggest recommendation is to use a systematic method to assess a patient to find problems, identify objectives and build a plan to meet those objectives.

72 year old admitted to critical care with hypoxemia secondary to COVID-19. She is intubated and mechanically ventilated.

She has a blood pressure reading of 70/40, MAP of 50 via blood pressure cuff, HR 110, urine output 15 ml/hr x 3 hours. She is on large amounts of sedation and analgesia for coughing and restlessness while on the ventilator.

How do you assess hemodynamics?

Build a POP

Find Problems

  • Hypotension NYD – MAP 50
  • Decreased urinary output NYD
  • Tachycardia NYD

Identify Objectives

  • MAP >65
  • HR <100
  • Urine output >30 ml/hr

Build a Plan

  • Start vasopressors (eg. norepinephrine)
  • Consider 250 ml IV bolus
  • Check lactate
  • Ensure foley catheter is not obstructed
  • Calculate ins/outs
  • Check blood pressure on different arm
  • Alert ICU team for assistance

Radionale

A common failure to assess in this situation is searching for other causes of hypotension. Eg. Sepsis, hypovolemic, weak contractility, etc.

A common failure to recognize in this situation is the endgame. The patient is likely hypotensive from IV sedation and analgesia however she is reliant on these medications to help her oxygenate and ventilate, which is her primary problem.

A failure to communicate would be not communicating the hypotension to the ICU team once a problem has been recognized.

A failure to escalate in this situation would be an intervention suggested by the ICU team but the patient does not improve from the intervention. Eg. Fluid bolus.


44 year old is admitted to critical care for hypoxemia secondary to COVID-19. The patient is intubated and mechanically ventilated.

His blood pressure is 70/40, MAP of 50, HR 120, Temp 39.9, urine output 10 ml/hr x 3 hours. He is on IV sedation and analgesia to assist ventilator tolerance.

How do you assess hemodynamics?

Build a POP

Find Problems

  • Hypotension NYD – MAP 50
  • Tachycardia NYD
  • Decreased urinary output
  • ?Undifferentiated shock

Identify Objectives

  • MAP >65
  • SBP >100
  • Urinary output >30 ml/hr
  • Creatinine within normal limits
  • Rule in/out shock states
  • Lactate <4
  • pH 7.35-7.45

Build a Plan

  • Vasopressors (eg. Norepinephrine)
  • Cautious 250 ml IV fluid bolus (tank/preload)
  • Insert arterial line
  • Blood gas
  • Check lactate
  • Check renal function
  • Ask for bedside ultrasound to assess the pump and tank (contractility and preload)
  • Calculate ins/outs (preload)
  • Consider checking blood tests for pulmonary embolism (pipes)

Rationale

A failure to assess in this situation is searching for other causes of hypotension. Eg. Sepsis, hypovolemic, weak contractility, etc.

A common failure to recognize in this situation is having inadequate objectives to achieve in critical illness; the sum is greater than its parts!
In addition, it is a failure to recognize in this situation is the severity of critical illness and needing early communication and escalation of care.

A failure to communicate would be not communicating the overall critical illness to the ICU team.

A failure to escalate in this situation would be implementing interventions suggested by the ICU team but the patient does not improve from the intervention. Eg. Fluid bolus.

References

1. Ernstl / CC BY-SA

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