Obstetric Anesthesia Flashcards
(19 cards)
Cardiovascular changes in in pregnancy?
- Physiological anemia of pregnancy due to
- Hypercoagulability state after first trimester
- Increased cardiac output (50% increase) with decreased vascular resistance
- AP= CO(HR X SV) X SVR - The heart is physiologically dilated and dis- placed in both cephalad and lateral directions
- A normal pregnancy ECG may have left axis deviation and T waves may be inverted in lateral leads and lead III mimicking left ventricular hypertrophy and other structural disease - Aorto-caval compression
Physiological anemia of pregnancy is due to?
- Increase in red cell mass by 10-20%
- While the increase in plasma volume is in the region of 40 – 50% its maximal at 30-32 weeks
Causes of hypercoagulability?
All clotting factors except XI and XIII increase; there is a decrease in fibrinolytic activities
- Risk of DVT (Pre-op ask about LMWH/Warfarin usage)
Aortal-caval compression in pregnancy?
- 20 weeks in a singleton pregnancy.
- Compensation – sympathetic activation and shunting.
MRS TILT?
Pregnant woman should be in lateral decubitus position
- Tilt the bed
- Wedge beneath the patient
Respiratory changes in pregnancy?
- difficult airway
- high risk of hypoxemia despite preoxygenation
- respiratory alkalosis
- increased rate of uptake of inhalation agents
Causes of difficult airway in pregnancy?
- Interstitial oedema of the upper airway –capillary engorgement
- Enlarged breasts
- Obesity
- Mallampati 3 and 4 in 2nd and 3rd trimester
Cause of hypoxemia in pregnancy?
- Increased oxygen consumption from 200-250ml/min to 500mls/min
- Reduced FRC and RV -upward displacement of the diaphragm
Causes of respiratory alkalosis?
- Hyperventilation
- Increase in TV and minimal increase in RR - Shift of oxyhaemoglobin curve to the left – bad for the featus!!
- Compensation - renal sodium bicarb excretion
Cause of increased rate of uptake of inhalation agent?
- Increased Minute Ventilation
- Reduced FRC
Oxyhemoglobin dissociation curve - left shift?
increase O2 affinity + decrease O2 unloading
1. decrease in CO2, H+, temp, DPG
2. increase pH
Oxyhemoglobin dissociation curve?
decrease O2 affinity + increase O2 unloading
1. increase in CO2, H+, temp, DPG
2. decrease pH
CNS changes in pregnancy?
- Enhanced neural susceptibility to local anesthetic
- Increased susceptibility to drugs acting on the central nervous system
Causes of enhanced neural susceptibility to local anaesthetic?
25% reduction in the dose requirement for spinal and epidural anaesthesia
1. epidural plexus becomes engorged due gravid uterus
2. a compensatory decrease in cerebrospinal fluid volume
3. higher apical level of the thoracic kyphosis
Causes of increased susceptibility to drugs acting on the CNS?
a decrease in MAC of 30% of inhalation anesthetic agents.
Renal system changes in pregnancy?
- Increase in renal size and a raised glomerular filtration rate
- There is an increase in renal blood flow of 50% and GFR rate from 100 to 150 ml/min
- Increased clearance of urea, creatinine, and drugs. (Drop in serum urea and creatinine) - Enhanced action of aldosterone
- Leading to increased water absorption, causing an increase in the volume of distribution and increased elimination half-life of certain drugs e.g thiopental.
GIT changes in pregnancy?
Increased risk of aspiration (Mendelson’s syndrome)
1. Slow gastric emptying
2. Stomach is increasingly displaced upwards by the gravid uterus leading to altered axis and increased intragastric pressure
3. Decreased esophageal sphincter tone
Mitigation of GIT changes in pregnancy?
- from 16 weeks gestational age, antacid premedication should be considered.
- Histamine H2-receptor antagonists used in combination with sodium citrate.
- If general anesthesia is necessary, after preoxygenation, a rapid sequence induction technique with cricoid pressure should be used and the airway secured with a cuffed tracheal tube.
- Gastrointestinal effects return to the pre-pregnancy state 24–48 h post-partum
