Anaesthetics & the pregnant woman Flashcards
Cardiovascular system changes by 32 wks in pregnancy
CO up 40%, HR up 15%, SV up 35%, peripheral resistance down 35%, Heart displaced up & left, louder heart sounds with flow murmur, ECG inverted T in II, V1, V2. L axis deviation, some ST depression.
Aortocaval compression
- what is it
- compensation
- in context of epidural?
- aorta and IVC compressed by gravid uterus when woman lies prone
- tachycardia, vasoconstriction, diversion of blood through epidural & azygous system
- (decompensation) bradycardia, nausea, sweating, pallor, faining
Respiratory system changes by 35 wks in pregnancy
Tidal volume up 40%, RR up 15%, airways resistance down 35%, alveolar ventilation up 70%, FRC down 20%, some women CC>FRC, Diaphragm up 4cm, capillary & soft tissue engorgement upper airway
Haematological system by 35 wks in pregnancy
Total blood volume up 40%, plasma volume up 50%, RBC volume up 30%, Hb down to 120, Hct down 35%, platelets down 20%, clotting factors up 800%, plasminogen & anti-thrombin III down
Gastrointestinal system by 35wks in pregnancy
GIT tone and motility down, gastric emptying delayed, acid production up, LOS pressure down, reflux present in > 80%
Plasma proteins by 35wks in pregnancy
Total amount up, concentration of protein, albumin, globulin down, plasma oncotic pressure down 15%, plasma pseudocholinesterase levels down 28% before delivery, 35% for 3 days after
Urinary tract changes by 16 wks in pregnancy
Dilation of ureters and renal pelvices, RBF up 75%, GFR up 50%, renal threshold for glucose down, aldosterone up
Central nervous system by 16 wks in pregnancy
Sensitivity up to narcotics, local anaesthetics, GA gases; endorphins up
Effects of post delivery in the
- short term
- longer term
- loss placental shunt + auto-transfusion with uterine contraction = cardiovascular events
- reversal of changes over next 5 days = thrombo-embolism
Clinical implications of pregnancy on anaesthetics (systems are at end of reserve)
- risk of hypoxia (O2 consumption up 20%, FRC down, CC>FRC
- risk of failed intubation
- acid aspiration
- thromboembolism
Effect of pain in labour on
- resp system
- cardio system
- hyperventilation due to hypocarbia and alkalaemia (hypoventilate between contraction = maternal & fetal hypoxaemia and acidosis = uteroplacental & fetoplacental vasoconstriction = left shift of oxygen dissociation curve compromises O2 delivery to fetus); increased O2 consumption
- cardiovascular (increase stroke volume, heart rate = increase cardiac output)
Explain pain transmission in labour
- visceral
- somatic
- VISCERAL (paracervical region, through pelvis [inf, mid, sup hypogastric plexuses], lumbar sympathetics, T10-L1 synapses with interneurons in dorsal horn)
- SOMATIC (pudendal nerve (S2,3,4)+ilioinguinal+gentiofemoral+post.femoral cutaneous nerve
Pain in labour
- stage 1
- stage 2
- FIRST STAGE (dilatation of cervix, lower uterine segment contraction, T10-L1/2, referred to abdomen lower back upper thigh)
- SECOND STAGE (distension of outlet, vagina, vulva, perineum, S2-4 well localised
Labour pain relief - non pharmacological
- prepared (antenatal calsses)
- hypnosis
- acupuncture (infection, bleeding risks)
- TENS (high frequency low intensity current)
Labour pain relief -pharmacological
- nitrous oxide (rapid potent analgesic gas, ENTONOX, takes 50s, use before contraction starts)
- OPIOIDS (pethidine = most common, cheap, safe, easy, IM, but maternal N&V + dysphoria AND fetal effects)
(Fentanyl = shorter acting, highly lipophilic, IV, PCA)(Remifentanil = ultra short acting, narrow safety margin, PCA)
