Hemodynamics & Shock States Overview

Hemodynamics & Shock States

• Hemodynamics is the study of blood flow in the body
• Shock is acute circulatory failure, insufficient oxygen supply to tissues

Supplemental Materials

• Hoffman EW, Basics of cardiovascular hemodynamic monitoring, Clin Pharm 1982;16(9):657-64.
• Moranville MP, Mieure KD, Santayana EM, Evaluation and management of shock states, J Pharm Pract 2011;24(1):44-60.
• MedCram 16-minute review of cardiogenic, hypovolemic, & distributive shock: https://youtu.be/CbM4UihE1TQ

Note

• PCWP is used in place of LVEDP
• JVP is used instead of CVP

Hemodynamics

• Normal hemodynamics are crucial for understanding disease states
• Blood pressure, cardiac output, and stroke volume are key parameters influencing arterial blood pressure

Learning Objectives

• Define the hemodynamic parameters that influence arterial blood pressure, cardiac output, and stroke volume.
• Describe relationships between hemodynamic parameters using Frank Starling Curves.

Cardiac Output (CO)

• Amount of blood ejected from the left ventricle per minute
• Normal range: 4-7 L/min
• Cardiac Index (CI): CO normalized to body surface area
• Normal range: 2.8-3.6 L/min/m²

If CO = 4.2 L/min...

• 27-year-old male (6'2", 85 kg, BSA 2.11): CI = 1.99 L/min/m²
• 27-year-old female (5'2", 45 kg, BSA 1.42): CI = 2.96 L/min/m²

Cardiac Output Factors

• Heart rate (HR): influences cardiac output
• Stroke volume (SV): influenced by preload, afterload, and contractility
• Preload: stretch of the myocardium before contraction
• Afterload: resistance the heart must overcome to eject blood
• Contractility: intrinsic strength of myocardium during systole

Preload

• Stretch of the myocardium prior to contraction
• Increases with total blood volume, venous return
• Decreases with poor ventricular or venous compliance, tachycardia, or blood loss
• Represents a patient's volume status (e.g., left ventricular end-diastolic pressure (LVEDP))

Afterload

• The "load" the heart must overcome to eject blood
• Increased with systemic vascular resistance (SVR), aortic pressure, and aortic valve stenosis

Systemic Vascular Resistance (SVR)

• Resistance to blood flow caused by systemic vasculature
• Controlled by autonomic nervous system
• Normal range: 800-1200 dyne-sec/cm³
• Cooler skin temperature with ↑SVR

Arterial Blood Pressure

• Systolic pressure: maximal aortic pressure during ejection (systole)
• Diastolic pressure: lowest aortic pressure during relaxation (diastole)
• Normal range: reported in mmHg

Mean Arterial Pressure (MAP)

• Average arterial pressure during one cardiac cycle
• Normal range: 80-100 mmHg

Central Venous Pressure (CVP)

• Pressure in the superior and inferior vena cava near right atrium
• Right atrial pressure (RAP) ≈ CVP
• Normal range: 2-6 mmHg (12-16 mmHg if ventilated)

Normal Ranges

• Cardiac Output (CO): 4-7 L/min
• Cardiac Index (CI): 2.8-3.6 L/min/m²
• Systemic Vascular Resistance (SVR): 800-1200 dyne-sec/cm³
• Systolic Blood Pressure (SBP): 110-130 mmHg
• Mean Arterial Pressure (MAP): 80-100 mmHg
• Central Venous Pressure (CVP): 2-6 mmHg

Stroke Volume (SV) and Variation (SVV)

• Volume of blood ejected from the ventricle during contraction
• Stroke volume index (SVI): SV/BSA, range 33-47 ml/beat/m²
• SVV: indicates preload responsiveness (in mechanically ventilated patients) • SVV < 10% = Not fluid responsive • SVV > 10-15% = Fluid responsive

Contractility

• Intrinsic strength of myocardium during systole (inotropy)
• Not directly measured

Frank Starling Curve

• Relationship between preload and stroke volume
• Increase in preload will result in a proportional increase in stroke volume, to a point

Hemodynamic Monitoring

• Comparing non-invasive methods (heart rate, blood pressure, skin temperature, urine output) to invasive methods (arterial lines, Swan-Ganz catheters, FloTrac, or LIDCO)
• Arterial pulse pressure waveform analysis aids in shock classification

Invasive- Arterial Line (“A-line”)

• Continuous measurement of SBP, DBP, and MAP for increased accuracy during shock

Arterial Pulse Pressure Waveform Analysis (FloTrac or LIDCO)

• Continuous measurements of hemodynamics (CO, CI, SVV, and SVR) to assist in shock classification

Swan Ganz

• Pulmonary artery catheter (PAC) measures right heart pressures
• Pulmonary wedge pressure (PCWP): indirect estimate of LVEDP
• Normal range: 6-12 mmHg

Mixed Venous Oxygen Saturation (SvO2)

• Percent of O2 returning to right side of the heart after tissue extraction
• Normal range: 60-75%
• <60% = Cardiogenic shock

• 75% = Distributive shock

Shock Subsets

• Hypovolemic: reduced blood volume (blood loss, dehydration)
• Cardiogenic: impaired heart function (massive MI, aortic stenosis)
• Distributive: widespread vasodilation (septic shock, anaphylaxis, neurogenic shock)
• Obstructive: physical obstruction to blood flow (cardiac tamponade, massive pulmonary embolus)

Management of Shock

• Predicting how hemodynamic parameters will change with therapeutic interventions, including isotonic crystalloids, inotropes, vasodilators, diuretics, and vasopressors
• Designing individualized treatment plans based on the specific shock subset

Patient Case Examples

• Case-specific data for patient assessment and diagnosis of shock and required interventions and management

Non-hemorrhagic Hypovolemic Shock Summary

• Multifactorial plasma loss from burns, pancreatitis, peritonitis, vomiting or diarrhea
• IV fluids needed, isotonic crystalloids (Lactated Ringer's) first line
• Resuscitation recommendations vary

Fluid Compartments

• Total body water (TBW): 2/3 intracellular fluid, 1/3 extracellular
• Extracellular fluid (ECF): 1/3 interstitial fluid, 1/4 intravascular fluid

Fluid Tonicity

• Table showing various fluids, their tonicity, and associated electrolyte/osmolality values

Practice Fluid Compartments

• Illustration demonstrating the division of total body water into intracellular and extracellular compartments, and further division into interstitial and intravascular compartments, with approximated volumes
• Table indicating the different percentages for each fluid compartment

Case Details for Patient #2, #3, and #4

• Subsets (warm and wet, cold and dry, cold and wet) and interventions based on hemodynamic data

Distributive Shock

• Clinical presentations including low SVR
• Treating underlying cause and supplementing blood volume

Inotropic Therapy (Subset III and IV)

• Indicated for patients experiencing hypoperfusion despite adequate fluid volume (low MAP and/or SBP)
• Additional symptoms including altered mental status and worsening renal function

Vasodilators

• Used as an adjunct for managing dyspnea, specifically subsets II, III, IV; includes nitroglycerin, sodium nitroprusside, and hydralazine

Diuretics (Subset II)

• Used to reduce preload (right/CVP, left/LVEDP) and hence unload the heart
• Example: furosemide, bumetanide

Cardiogenic Shock

• Persistent hypotension despite fluid administration
• Reflects poor cardiac output or perfusion of tissue
• Elevation of LVEDP and CVP

Forrester Classification of Cardiogenic Shock

• Categorization of subsets (I-IV) includes hemodynamic parameters (CI, PCWP) and clinical status (warm/dry, warm/wet, cold/dry, cold/wet)