Outline the factors that determine central venous pressure and explain how it is measured.

Master answer

CVP

• Central venous pressure (CVP) is mean vena caval or right atrial pressure
• In the absence of tricuspid stenosis, equals right ventricular end-diastolic pressure.
• expressed in mmHg or cmH2O (1.36 cm water = 1.0 mm Hg)
• Normal 0-6mmHg in spontaneously breathing non-ventilated patient

• Venous Return, VR = (MSFP – RAP or CVP) / Resistance to venous return
• CVP is a major determinant of RV filling pressure (RV Preload)
  • This regulates stroke volume through Frank-Starling mechanism
• CVP increased in disorders that increase Rt sided diastolic pressures
  • left heart disease, lung disease, primary pulmonary hypertension, and pulmonic stenosis
• CVP is determined by an interplay of various factors
  • Mainly influenced by volume of blood and compliance of central compartment

Factors affecting the measured CVP:

• Central venous blood volume (Inc volume à inc flow à inc CVP)
  • Venous return/cardiac output
    • Vena cava compression (Obesity/Valsalva/pregnancy/inc IAbd pressure – dec VR à dec CVP)
  • Total blood volume
  • Regional vascular tone
• Compliance of central compartment (inc Comp à inc return and venous pressure)
  • Vascular tone
  • Right ventricular compliance
  • Myocardial disease
  • Pericardial disease
  • Tamponade
• Tricuspid valve disease
  • Stenosis (inc mean CVP)
  • Regurgitation (transient inc CVP)
• Cardiac rhythm (dec CVP with no atrial contraction, inc CVP when RA contracting against closed TV)
  • Junctional rhythm
  • AF
  • A-V dissociation
• Reference level of transducer (inc or dec)
  • Positioning of patient
• Intrathoracic pressure (inc pressure à inc CVP)
  • Respiration (Inspiration makes intrathoracic pressure more negativeà increases CVP)
  • Intermittent positive pressure ventilation (IPPV)
  • Positive end-expiratory pressure (PEEP)
  • Tension pneumothorax

Measurement

• Invasive:
  • by inserting central venous catheter into Internal Jugular or Subclavian Vein
• Non-Invasive:
  • Height of JVP provides visual estimate
  • peripheral vein collapse on the dorsum of the hand or antecubital fossae
  • Bedside ECHO and doppler techniques: IJV, Hepatic veins, IVC assessment

Invasive Measurement:

Complications of CVP Monitoring

• Mechanical complications:
  • Arterial puncture and cannulation, Hematoma, Hemothorax, Surrounding nerve injuries, Pneumothorax, Embolization of broken catheter or guide wire, Air embolus, Arrhythmias, Lymphatic system injury
• Infectious complications:
  • Sepsis, Endocarditis
• Thrombotic complications:
  • Venous thrombosis, Pulmonary embolism

CVP Waveform

(not required for this answer)

Changes in waveform:

AF	a wave lost, c wave more prominent. If coarse AF, fibrillation waves may be visible
A-V dissociation / Junctional rhythm	tall canon a waves (due to atrial contraction against closed Tricuspid valve)
TR	large fused c-v wave (due to blood ejected back during ventricular systole)
TS	attenuated a-wave and y-descent (increased pressure required to overcome TS)
RV compliance decreased	a wave accentuated
Pericardial constriction	short steep y-descent
Cardiac tamponade	CVP monophasic with a single x-descent

Sources:
Daniel Saddawi-Konefka, Critical Care Secrets
Shay McGuinness Cardiothoracic Critical Care 2007
Richard E. Klabunde, CVphysiology.com
T. Smith, Central Venous Pressure: Uses and Limitations

JC 2019

Answer by JC