physiological changes in pregnancy PPT.pptx

physiological changes in pregnancy and how it affects anaesthesia

1. Physiological Changes in Pregnancy PRESENTER Dr Bulus Faith K MODERATOR DR Idris Mohammad El-Amin. 5/21/2024 1

2. OUTLINE INTRODUCTION CARDIOVASCULAR SYSTEM CHANGES RESPIRATORY SYSTEM CHANGES HAEMATOLOGICAL CHANGES GASTROINTESTINAL SYSTEM CHANGES RENAL SYSTEM CHANGES CENTRAL NERVOUS SYSTEM CHANGES ENDOCRINE SYSTEM CHANGES FACTORS AFFECTING PLACENTAL TRANSFER OF DRUGS ANAESTHETIC DRUGS CONCLUSION REFERENCES 5/21/2024 2

3. INTRODUCTION Pregnancy is associated with significant adaptive changes in most of the organ systems of the maternal body. The basis of most changes are hormonal, being in response to the marked changes in the hormones associated with pregnancy. Most of the changes are in place in the first trimester but may increase in intensity as pregnancy progresses. 5/21/2024 3

4. CARDIOVASCULAR SYSTEM CHANGES VARIABLE CHANGE % CHANGE Heart rate Increased 20 % Systolic blood pressure Decreased 5% Diastolic blood pressure Decreased 15% Stroke volume Increased 30% Cardiac output Increased Increases measurably by the 5 th week. Increases by approx. 40% by the end of 1 st trimester. 40 -50% by 3 rd trimester Systemic vascular resistance Decreased 20% Central Venous pressure unchanged Pulmonary Vascular resistance Decreased 30% 5/21/2024 4

5. ANAESTHETIC IMPLICATIONS CVS EXAM ANATOMY- The heart is displaced upward and to the left by the gravid uterus. Physical examination of the term pregnant woman may also be abnormal with the auscultation commonly revealing a wide, loud 1st heart sound , an S3 sound and soft systolic ejection murmur. So it is necessary to differentiate abnormal cardiac changes from Normal physiological changes of pregnancy Criteria to diagnose cardiac disease during pregnancy: 1 ) Presence of diastolic murmur 2 ) Systolic murmur of severe intensity (grade 3) 3 ) Presence of severe arrhythmias , atrial fibrillation or flutter 5/21/2024 5

6. CVS EXAM 2 Systemic vascular resistance(SVR) is decreased due to vasodilatory effect of progesterone and proliferation of low vascular resistance vascular beds in the intervillous spaces of placenta. BP is decreased due to decrease in SVR. ECG shows Left axis deviation, ST segment depression and T wave flattening due to cephalad movement of diaphragm. Blood flow- to uterus increases up to 700mls/min by term. - increases to kidney and skin - remains same to brain and liver 5/21/2024 6

7. ANAESTHETIC IMPLICATIONS CONTD   AORTOCAVAL Compression Enlarged uterus compresses IVC and Lower Aorta when the patient lies supine. Obstruction of IVC decreases v enous r eturn which then leads to decrease in cardiac output. It can occur as early as the 13 th week of pregnancy. When awake most women are capable of compensating for the decrease in stroke volume by increasing Sytemic Vascular Resistance and Heart rate. There are also alternative venous pathways : the paravertebral and azygos systems . During Anaesthesia compensatory mechanisms are reduced or abolished . Obstruction of lower aorta causes reduced blood flow to kidneys, uteroplacental unit and lower extremities. 5/21/2024 7

8.   SUPINE HYPOTENSION SYNDROME It is seen in 8 to 15% of pregnant women, they have Overt Caval Compression (supine hypotension syndrome) characterized by; Hypotension , Sweating , Bradycardia , Pallor , Nausea and Vomiting Prevention of SHS: Uterus should be displaced by placing a rigid wedge under the right hip or left lateral tilting of the operating table. 5/21/2024 8

9. RESPIRATORY SYSTEM CHANGES   Changes in the respiratory system during pregnancy involves the upper airway, minute ventilation, lung volume , oxygen consumption. Major changes occurs in the respiratory system during pregnancy, due to combination of both hormonal and mechanical factors. The maternal respiratory pattern changes as the uterus enlarges :- Diaphragm rises up by 4 cm , causes reduction in the Functional residual capacity by 20% patient prefers thoracic breathing over the Abdominal. Due to increased metabolic demands, Oxygen consumption and minute volume increases (40- 50%) progressively. 5/21/2024 9

10. RESPIRATORY PARAMETERS VARIABLE CHANGE % CHANGE VALUE Tidal volume Increased 30-40% 650ml Expiratory reserve volume Decreased 25% 500ml Functional residual capacity Decreased 20% 1300ml Residual volume Decreased 15% 800ml PaO2 Slight increase 10% 12.3kpa PaCo2 Decreased 15% 4.7kpa Respiratory rate Increased 15% 16 Inspiratory reserve volume Slightly increased 5% 3200ml Vital capacity Unchanged 2050ml Total lung capacity Decreased 5% 5/21/2024 10

11. ANAESTHETIC IMPLICATIONS Decreased FRC and Increased oxygen consumption promotes rapid oxygen desaturation during periods of apnea. This is more marked in obese patients and during anaesthesia . Preoxygenation prior to induction of general anesthesia is therefore mandatory to avoid hypoxemia in pregnant patients. 5/21/2024 11

12.   Factors increasing risk of hypoxaemia There is venous/capillary engorgement and edema of the upper airway down to the pharynx, false cords, glottis and arytenoids. The increase in chest diameter and enlarged breasts can make laryngoscopy difficult. There is reduced diaphragmatic movement. Failure to intubate the trachea is 7 times more common in the term parturient compared to non pregnant patients . A smaller diameter endotracheal tube may be required for intubation especially in cases of pre eclampsia . 5/21/2024 12

13. HAEMATOLOGICAL CHANGES VARIABLE CHANGE PERCENTAGE CHANGE Value Haemoglobin Decreased 20% 12g/dl Haematocrit Decreased 31-34% Red cell count Increased 20% 3.8 X 10 9/L White cell count Increased 9.0 X 10 9/L Erythrocyte sedimentation rate Increased 58 -68 Platelets Slight increase/normal 120 -400 X 10 9/L Plasma volume Increased By 40- 50% 5/21/2024 13

14. COAGULATION CHANGES   A state of hypercoagulability exists during pregnancy  This is probably, a protective adaptation to lessen the risk of acute haemorrhage that occurs at delivery . There is an increase in the majority of clotting factors, decrease in quantity of natural anticoagulants and a reduction in fibrinolytic activity. The platelet count remain remains unchanged throughout most of pregnancy, but it may get reduced in third trimester. Despite the changes Bleeding time, prothrombin time and partial thromboplastin time remain within normal limits. 5/21/2024 14

15. COAGULATION CHANGES VARIABLE CHANGE Fibrinogen Increased (from 2.5 to 4.6 -6.0g/l ) Factor II Unchanged Factor V Unchange d Factor VII Increased 10 fold Factor VIII Increased twice non-pregnant state Factor IX Increased Factor X Increased Factor XI Decreased by 60-70% Factor XII Increased by 30-40% Factor XIII Decreased by 40-50% Antithrombin III Decreased slightly Plasminogen unchanged Plasminogen activator Reduced Plasminogen inhibitor Increased Fibrinogen stabilizing factor Decreases gradually to 50% of non-pregnant value 5/21/2024 15

16. ANAESTHETIC IMPLICATIONS There is increased risk of epidural haematoma in preeclampsia due exponential fall in platelets. Thus, platelet count should done within 6 hours before placing epidural and removal of the catheter   Standard heparin(unfractionated ) preparation prophylaxis in low doses i.e. 5000 I.U. Subcutaneously can be used in pregnancy, as it does not cross the placenta. For performing the neuraxial block 4-6 hr gap after the last dose,should be given. 5/21/2024 16

17. ANAESTHETIC IMPLICATION (cont’d) In case of epidural anesthesia, catheter removal should be done 1 hr prior to the next dose or 3-4 hr after the dose. Neuraxial anesthesia should be avoided in patient on the I.V. heparin with increased Partial thromboplastin time. If the patient is started on heparin after placement of catheter, removal of catheter is to be done after evaluation of the coagulation profile. 5/21/2024 17

18.   Low molecular weight heparin - Neuraxial block should be performed after the minimum gap of 12 hr from the last dose (if receiving higher dose e.g. enoxaparin 1mg/kg neuraxial block should be performed after 24 hr gap). Platelet count should be obtained in the patient receiving LMWH to prevent heparin induced thrombocytopenia. Post-op LMWH can be started only after 12 hr from the spinal needle insertion. Use of oral anticoagulants is restricted as these agents can cross placenta. 5/21/2024 18

19. GASTROINTESTINAL(GI) SYSTEM CHANGES The changes in the GI stems from the effect of progesterone and mechanical changes. Upward & anterior displacement of the stomach by the uterus leads to increase in intragastric pressure and decrease in gastroesophageal angle . Reduction of lower esophageal sphincter pressure due to the effect of progesterone. Risk of Regurgitation and aspiration of gastric contents due to lower oesophageal sphincter pressure. This may occur in at least 80% of pregnant women. 5/21/2024 19

20. The onset of GI symptom is from 16-20 th week of gestation and by 24 th hr post delivery progesterone falls to non pregnant level while reflux usually resolves by 36 th hr. Increased placental gastrin secretion which can worsen gastric acidity. GI motility is decreased but gastric emptying is believed to not be delayed.Due to increase in transit time in small and large intestine, there might be constipation. 5/21/2024 20

21. LIVER FUNCTION CHANGES IN PREGNANCY PARAMETER CHANGE Albumin Decreased as early as 1 st trimester by up to 60% Alkaline Phophatase Increased , more than 3x the upper normal limit of the enzyme because is also produced by placenta ALT/AST No change but can be elevated in cases preeclampsia/ eclampsia , HELLP sydrome and AFLP Plasma cholinesterase Decreased by 25% 5/21/2024 21

22.   ANAESTHETIC IMPLICATIONS The parturient should be considered a full stomach patient during most of gestation. Prophylaxis in the form of H2 blocking drug and Prokinetic drugs should be given routinely to pregnant patients before surgery from 2nd trimester. During GA airway protection by means of cuffed ETT is mandatory; So is rapid sequence induction from 2nd trimester of pregnancy till 48hrs post partum . Extubation should be done when the patient is awake and on their side to reduce the risk of aspiration. The danger of aspiration is almost eliminated when regional anaethesia is used. 5/21/2024 22

23. RENAL SYSTEM CHANGES Renal vasodilatation increases renal blood flow by 40% during early pregnancy. • Increased Cardiac output leads to Increased GFR & Increased renal plasma flow by 50% which increases clearance of urea, uric acid and Creatinine. • Increased Renin & Aldosterone level promotes Na+ retention leading to volume overload, fall in serum creatinine and urea. • Decreased Renal tubular threshold for glucose & amino acids → mild glycosuria & proteinuria (< 300mg/d). • Progesterone mediated ureteric smooth muscle relaxation can lead to urinary stasis making pregnant women prone to urinary tract infections. 5/21/2024 23

24. CENTRAL NERVOUS SYSTEM CHANGES CBF is increased due to decreased Cerebrovascular resistance Permeability of BBB is increased There is an increase in threshold to pain at term and labour due increase level plasma endorphins and progesterone Engorged epidural plexus of veins will decrease the volume of the epidural and subarachnoid space. The CSF pressure is increased due to compression from the epidural veins in the epidural space. Exaggerated lumbar lordosis contribute to cephalad spread of the local anaesthetic . 5/21/2024 24

25. 25-40% decrease in minimum alveolar concentrations (MAC) secondary to increased levels of progesterone and β- endorphin levels which will lead to rapid induction with inhalation agents. The amount of local anaesthetic drug required in a pregnant woman is decreased by up to 30% (2/3 ) compared to the non pregnant state. Increased sensitivity to opiods , sedatives, and local anaesthetics when used for neuraxial anaesthesia . 5/21/2024 25

26. ENDOCRINE SYSTEM Preganancy is Diabetogenic as insulin steadily rises during pregnancy and the human placental lactogen (aka human chorionic Somatomamotropin ) causes relative insulin resistance. Pregnancy is biochemically a starving like state (blood glucose and amino acids are low and Free fatty acids , ketones and triglycerides are high) to promote the Foetal growth. Secretion of HCG and Elevated oestrogen levels promotes hypertrophy of the thyroid gland. There is increased in the production of thyroid globulin: although T3, T4 levels are elevated up to 50% but the free T3, T4 & TSH remain normal due to increase production THYROID BINDING GLOBULIN Level of PARATHYROID HORMONES and serum Ca ++ tend to fall during pregnancy but the level of ionized Ca ++ tend to remain constant due changes in serum albumin concentration 5/21/2024 26

27. There is 30% increase in oxytocin store in the pituitary which is released during labour There is hyperprolactinaemia due to placenta lactogen and dopamine during pregnancy GA can mask the signs and symptom of hypoglycaemia while neuraxial anaesthesia can worsen the haemodynamic instability due to autonomic dysfunction related to DM 5/21/2024 27

28. MUSCULOSKELETAL SYSTEM Exaggerated lumbar lordosis with flexion of the neck and downward movement of the shoulders Due to relaxin , progesterone and mechanical effects of pregnancy, joint laxity is increased to prepare for child birth Implication Lordosis can decrease the distance between the spinous processes and make neuraxial techniques difficult Widening of pelvis causes head down position in lateral decubitus and lead cephalad position of LA during SAB in lateral position A pillow placed under the dependent position can counteract this effect 5/21/2024 28

29. FACTORS AFFECTING PLACENTAL TRANSFER OF DRUGS Lipid Solubility:- The placental membrane is freely permeable to lipid soluble substances, higher the solubility higher is the drug transfer. Highly ionized substances have poor lipid solubility. Protein binding:- Protein bound drugs will not diffuse easily, only free drug would cross the placental barrier easily , reduced albumin levels will increases the unbound portion of drug in plasma.  Maternal drug concentration :- Directly proportional , Affected by the dose and route of administration. Others factors include: tissue binding, pH, pKa and blood flow 5/21/2024 29

30. ANAESTHETIC DRUGS   OPIODS – All opioids cross the placenta in significant amounts. They are weak bases, bound to α-glycoprotein. Pethidine – Longer half life is due to its active metabolite norpethidine , which may lead to respiratory depression in the neonate . Morphine – It is water soluble but readily crosses the placenta due to low protein binding . Fentanyl – It is highly lipid soluble and albumin bound, so crosses the placental barrier easily. IV Induction agents – Sodium thiopentone is highly lipid soluble, weakly acidic, 75% protein bound and less than 50% ionized at physiological pH. It crosses the placenta easily. Propofol – It is highly protein bound and lipophilic. 5/21/2024 30

31.   INHALATIONAL AGENTS- These agents are highly soluble with low molecular weights. All cross placenta Muscle relaxants – These are quaternary ammonium compounds and fully ionized with low lipid solubility, hence they do not cross the placenta. Local Anaesthetics – These drugs have low molecular weights and also are lipid soluble . The materno-foetal transfer is enhanced by foetal acidosis leading to ion trapping . Different drugs have different protein binding. 5/21/2024 31

32. CONCLUSION Pregnancy produces profound physiological changes that alter the usual responses to Anesthesia . Unique challenges - two patients are cared for simultaneously . Failure to take care can be disastrous for one or both of them . 5/21/2024 32

33. REFERENCES John F,David M,John W: Morgan and Mikhail’s Clinical anaesthesiology 5 th edition Alan R.A,Ian K.M,Jonathan P.T: Smith&Aitkenhead’s textbook of anaesthesia 6 th edition,2014 Peter K,Ian P: Principles of phyiology for the Amaesthetist,4 th edition Lee CY: Manual of Anaesthesia , MGH Education, 2006 Steve MY, Nicholas PH, James KI: Anaesthesia , Intensive Care And Perioperative Medicine (A-Z), 6 th edition 5/21/2024 33

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