physiological changes and implications for anaesthesia

Question 1

OB 1.1

cardiovascular changes

?? effect on anasethesia (add)

Answer 1

• uterus and fetus need extra blood flow
• CO increases 30-50% 1st and 2nd trimester
  o Increased blood volume, 10% by week 6, 50% by end of 3rd
  • Estrogen mediated activation of renin-angiotensin-aldosterone to increase Na and H2O retention
  o Increased stroke volume in first half only
  o In 3rd trim CO only sustained by increased HR (increase 10-20/min
• MAP falls despite this
  o Decreased SVR due to low resistance uterine circulation, espec late in pregnancy
  o Also hormonal dilation of resistance vessels
  o Diastolic falls more than systolic – increased pulse pressure (cos stroke volume higher)
• Exercise
  o Rest CO high so less capacity to increase further
  o IVC compression decreases VR and SV espec in 3rd