Preload
OVERVIEW
- Preload = initial myocardial fibre length prior to contraction
DETERMINED BY
- anything that effects ventricular volume at the end of diastole
(1) Venous return – the quantity of blood blooding from the veins of the body into the right heart
VR = (MSFP – RAP)/SVR
VR is altered by:
- muscle pump
- thoracic pump (negative intrathoracic pressure -> inspiration (increased RV filling) and expiration (reduced RV filling)
- intrapericardial pressure
- venous tone
- posture
- blood volume
(2) HR – high HR reduces time for diastolic filling
(3) Atrial contraction -> ventricular filling
(4) Atrial and ventricular pressures during diastole (magnitude)
(5) Compliance of ventricles – hypertrophy, tamponade, fibrosis
MANIPULATION IN ICU
- fluid and blood product therapy: increase effective blood volume
- paralysis/sedation: abolish muscle pump
- positive pressure ventilation: abolish thoracic pump
- open chest/pericardiocentesis: relief of high intra-pericardial pressure
- supine position: encourages venous return
- prone position: ? effect on venous return
- anti-arrhytmics: optimise HR
- pacing: optimise HR
- inotropes: can not allow ventricular filling if volume status not optimal
Critical Care
Compendium
Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.
After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.
He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE. He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.
His one great achievement is being the father of three amazing children.
On Twitter, he is @precordialthump.
| INTENSIVE | RAGE | Resuscitology | SMACC