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, where he is Deputy Director (Education). He is a Clinical Adjunct Associate Professor at Monash University, the Lead for the Clinician Educator Incubator programme, and a CICM First Part Examiner.
He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives. He was one of the founders of the FOAM movement (Free Open-Access Medical education) has been recognised for his contributions to education with awards from ANZICS, ANZAHPE, and ACEM.
His one great achievement is being the father of three amazing children.
On Bluesky, he is @precordialthump.bsky.social and on the site that Elon has screwed up, he is @precordialthump.
| INTENSIVE | RAGE | Resuscitology | SMACC