Physiological changes in Pregnancy & its Anaesthetic implications Dr. Shailendra.V.L. MBBS, DA, MD. Specialist in Anaesthesia, Bukariya General Hospital.

Dr. Shailendra.V.L. MBBS, DA, MD.

Specialist in Anaesthesia,

Bukariya General Hospital.

Introduction Rapidly growing fetus Rising levels of progesterone, oestrogen, prostaglandin & HCG Increasing size of uterus All systems undergo changes Placenta

Rapidly growing fetus

Rising levels of progesterone, oestrogen, prostaglandin & HCG

Increasing size of uterus

All systems undergo changes

Placenta

Changes in the pregnant patient Changes due to uterine enlargement Changes to support the foetus

Changes due to uterine enlargement

Changes to support the foetus

Changes in the systems Cardiovascular System Respiratory System Haemopoietic System Hepatic System Renal System Gastro-intestinal System Metabolism & Nutrition Central Nervous System

Cardiovascular System

Respiratory System

Haemopoietic System

Hepatic System

Renal System

Gastro-intestinal System

Metabolism & Nutrition

Central Nervous System

Changes in uterus Uterine blood flow increases from 50 ml/ min to 700 – 800 ml /min Uterine weight increases from 30-60 g to 1000 g

Uterine blood flow increases from 50 ml/ min to 700 – 800 ml /min

Uterine weight increases from 30-60 g to 1000 g

Uterine blood flow Uterine Blood Flow - UBF: Uteroplacental vascular bed is passive capacitance bed Intervillous blood flow exhibits no auto regulation UBF dependent on mean arterial pressure, aorto-caval compression & cardiac output

Uterine Blood Flow - UBF:

Uteroplacental vascular bed is passive capacitance bed

Intervillous blood flow exhibits no auto regulation

UBF dependent on mean arterial pressure, aorto-caval compression & cardiac output

Cardiovascular system Changes in the cardiovascular system: Intravascular fluid volume: + 35% Plasma volume: + 45% Erythrocyte volume: + 20% Cardiac Output: + 40% Stroke volume: + 30% Heart rate: + 15% Peripheral Circulation: Systolic BP: no change Diastolic BP: - 15% Systemic Vascular Resistance: - 15% Femoral venous pressure: + 15%

Changes in the cardiovascular system:

Intravascular fluid volume: + 35%

Plasma volume: + 45%

Erythrocyte volume: + 20%

Cardiac Output: + 40%

Stroke volume: + 30%

Heart rate: + 15%

Peripheral Circulation:

Systolic BP: no change

Diastolic BP: - 15%

Systemic Vascular Resistance: - 15%

Femoral venous pressure: + 15%

Cardiovascular system Mean arterial pressure: MAP: -Inspite of increase of cardiac output, MAP is maintained due to concomitant decrease in peripheral resistance

Mean arterial pressure: MAP:

-Inspite of increase of cardiac output, MAP is maintained due to concomitant decrease in peripheral resistance

Cardiovascular system Compression of Inferior Venacava: IVC: In supine position the gravid uterus compresses the IVC and decreases the CO without fall in the blood pressure called as Concealed caval compression. Reasons for no fall in blood pressure are: Reflex vaso constriction Diversion of blood through paravertebral venous plexus

Compression of Inferior Venacava: IVC:

In supine position the gravid uterus compresses the IVC and decreases the CO without fall in the blood pressure called as Concealed caval compression.

Reasons for no fall in blood pressure are:

Reflex vaso constriction

Diversion of blood through paravertebral venous plexus

Cardiovascular system 8 to 15% of pregnant women have Overt Caval Compression (supine hypotensive syndrome) Hypotension Sweating Bradycardia Pallor Nausea Vomiting Prevention of SHS: (aim is to displace the uterus) Providing left lateral tilt 15 degrees Placing wedge under the right buttock

8 to 15% of pregnant women have Overt Caval Compression (supine hypotensive syndrome)

Hypotension

Sweating

Bradycardia

Pallor

Nausea

Vomiting

Prevention of SHS: (aim is to displace the uterus)

Providing left lateral tilt 15 degrees

Placing wedge under the right buttock

Cardiovascular system Poseiro Effect: Uterine artery is compressed during uterine contractions & by the presenting part of the fetus reducing the UBF

Poseiro Effect:

Uterine artery is compressed during

uterine contractions & by the presenting

part of the fetus reducing the UBF

Cardiovascular system Physiological Anaemia in Pregnancy: Total red cell mass increase by 30% (250-450ml) Plasma volume increase by 50% (about 1250ml) Overall increase of 40% blood volume with fall in haematocrit

Physiological Anaemia in Pregnancy:

Total red cell mass increase by 30% (250-450ml)

Plasma volume increase by 50% (about 1250ml)

Overall increase of 40% blood volume with fall in haematocrit

Cardiovascular system Heart rate: increases by about 15 beats /min Arterial pressure: minimal change noted Heart Size: Gravid uterus pushes the diaphragm cepahalad & displaces the heart. ECG shows false left axis deviation Chest X ray shows (false) cardiac dilatation

Heart rate: increases by about 15 beats /min

Arterial pressure: minimal change noted

Heart Size: Gravid uterus pushes the diaphragm cepahalad & displaces the heart.

ECG shows false left axis deviation

Chest X ray shows (false) cardiac dilatation

Respiratory system Changes in the respiratory system: Minute volume: + 50% Tidal volume: + 40% Breathing rate: + 10% FRC: - 20% Expiratory reserve volume: - 20% Residual volume: - 20% Oxygen consumption: + 20%

Changes in the respiratory system:

Minute volume: + 50%

Tidal volume: + 40%

Breathing rate: + 10%

FRC: - 20%

Expiratory reserve volume: - 20%

Residual volume: - 20%

Oxygen consumption: + 20%

Respiratory system Edematous mucosa of upper resp tract: Smaller Et tubes Gentle suctioning & larngoscopy Decreased FRC, ERV,RV: Increased O2 consumption: Pre-oxygenation prior to induced apnea Rate of fall in PaO2 per minute of apnea is 159mm hg in pregnant and 59 mm hg in non-pregnant state

Edematous mucosa of upper resp tract:

Smaller Et tubes

Gentle suctioning & larngoscopy

Decreased FRC, ERV,RV:

Increased O2 consumption:

Pre-oxygenation prior to induced apnea

Rate of fall in PaO2 per minute of apnea is 159mm hg in pregnant and 59 mm hg in non-pregnant state

Haemopoietic system Physiological anemia of pregnancy Fibrinogen, factors VII, VIII and X increased Makes the blood hypercoaguable & increases the risk of thromboembolism This hypercoaguability along with uterine inversion helps in reducing blood loss after delivery

Physiological anemia of pregnancy

Fibrinogen, factors VII, VIII and X increased

Makes the blood hypercoaguable & increases the risk of thromboembolism

This hypercoaguability along with uterine inversion helps in reducing blood loss after delivery

Gastro-intestinal system Decrease in lower oesophageal tone Delay in gastric emptying: Pylorus is pushed upwards & forwards making it non-dependent Relaxant effect on gastric smooth muscle Increased intragastric pressure

Decrease in lower oesophageal tone

Delay in gastric emptying:

Pylorus is pushed upwards & forwards making it non-dependent

Relaxant effect on gastric smooth muscle

Increased intragastric pressure

Hepatic system No alterations in the liver function Serum cholinesterase activity  Does not interfere with the suxamethonium (Scoline) R metabolism

No alterations in the liver function

Serum cholinesterase activity 

Does not interfere with the suxamethonium (Scoline) R metabolism

Renal system Renal plasma flow ↑ Glowmerular filtration rate ↑ Tubular reabsorbtion rate ↑ Blood Urea Nitrogen 40% 

Renal plasma flow ↑

Glowmerular filtration rate ↑

Tubular reabsorbtion rate ↑

Blood Urea Nitrogen 40% 

Metabolism & Nutrition Basal metabolic rate: ↑ by 15 to 20% Weight gain upto 11 kgs Serum protein concentration ↓ Albumin concentration ↓ Drugs are less bound to serum proteins thereby increasing the free drug availability

Basal metabolic rate: ↑ by 15 to 20%

Weight gain upto 11 kgs

Serum protein concentration ↓

Albumin concentration ↓

Drugs are less bound to serum proteins thereby increasing the free drug availability

Nervous system ↓ in minimum alveolar concentrations exaggerated lumbar lardosis contribute to cephalad spread of the local anaesthetic engorged epidural plexus of veins will decrease the amount of the local anaesthetic in epidural blocks engorged epidural veins will block the inter-vertebral foramina and prevent the escape of the local anaesthetic

↓ in minimum alveolar concentrations

exaggerated lumbar lardosis contribute to cephalad spread of the local anaesthetic

engorged epidural plexus of veins will decrease the amount of the local anaesthetic in epidural blocks

engorged epidural veins will block the inter-vertebral foramina and prevent the escape of the local anaesthetic

Placental functions Metabolism Endocrine secretion Human chorionic gonadotrophin Human chorionic somatotrophin Progesterone Estrogen Molecular transfer

Metabolism

Endocrine secretion

Human chorionic gonadotrophin

Human chorionic somatotrophin

Progesterone

Estrogen

Molecular transfer

Placental blood flow Placental Blood Flow = 500-700ml/min ( approximately 10% of the Cardiac output) Maternal blood pressure Maternal cardiac output Vasomotor tone of the uterine vessels Pathological changes of the placenta State of uterine contraction

Placental Blood Flow = 500-700ml/min

( approximately 10% of the Cardiac output)

Maternal blood pressure

Maternal cardiac output

Vasomotor tone of the uterine vessels

Pathological changes of the placenta

State of uterine contraction

Placental drug transfer Passive-diffusion is the mechanism Q/t = {k x A x (Cm-Cf)} / D Q: quantity of free drug (non ionized & non protein bound) crossing to placenta t : per unit of time k: diffusional coefficient of the drug A: total area available for transfer Cm-Cf: difference between maternal & fetal drug concentrations D: distance across the membrane

Passive-diffusion is the mechanism

Q/t = {k x A x (Cm-Cf)} / D

Q: quantity of free drug (non ionized & non protein bound) crossing to placenta

t : per unit of time

k: diffusional coefficient of the drug

A: total area available for transfer

Cm-Cf: difference between maternal & fetal drug concentrations

D: distance across the membrane

Placental transfer of drugs Diffusion Coefficient depends on: molecular weight spatial configuration degree of ionization lipid solubility Most anaesthesia drugs cross the placental barrier except the muscle relaxants because of their large size molecule (quaternary ammonia compounds)

Diffusion Coefficient depends on:

molecular weight

spatial configuration

degree of ionization

lipid solubility

Most anaesthesia drugs cross the placental barrier except the muscle relaxants because of their large size molecule (quaternary ammonia compounds)

Anaesthetic implications Pre-anaesthetic considerations: Starvation Respiratory infection Prophylaxis against pulmonary aspiration

Pre-anaesthetic considerations:

Starvation

Respiratory infection

Prophylaxis against pulmonary aspiration

Anaesthetic implications General Anaesthesia: Posture Tracheal Intubation Placental transfer of drugs Pre oxygenation

General Anaesthesia:

Posture

Tracheal Intubation

Placental transfer of drugs

Pre oxygenation

Anaesthetic implications Regional Anaesthesia: Posture Technique Vasopressors Oxygen supplementation

Regional Anaesthesia:

Posture

Technique

Vasopressors

Oxygen supplementation

Summary Cardiovascular changes Respiratory changes Gastro-intestinal changes Haemopoietic changes Placental transfer of drugs

Cardiovascular changes

Respiratory changes

Gastro-intestinal changes

Haemopoietic changes

Placental transfer of drugs

Bibliography Anaesthesia & Co-existing diseases-Stoelting Short Practice of Anaesthesia – Churchill Davidson Refresher Course Lectures, Manipal, ISA 1989

Anaesthesia & Co-existing diseases-Stoelting

Short Practice of Anaesthesia – Churchill Davidson

Refresher Course Lectures, Manipal, ISA 1989

Thank you

Thank you