Physiological changes in pregnancy ppt tmu-1.pptx

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1. PHYSIOLOGICAL CHANGES IN PREGNANCY Presented by :Dr Niketa Jain Moderator: Dr M. Niranjan Reddy No of slide : 30

2. PHYSIOLOGICAL CHANGES Pregnancy produces profound physiological changes(adaptive to stress)that become more significant as pregnancy progress. This changes can be to: Hormonal alteration. Mechanical effect of gravid uterus. Increased oxygen and metabolic requirement. Haemodynamical alteration.

3. VOLUME HOMEOSTASIS Fluid retention is the most fundamental systemic change of normal pregnancy. The total plasma volume is increased during pregnancy 45%. Factors contributing:- Increase sodium retention (RAAS) Decrease in thirst threshold Decrease in plasma oncotic pressure

4. VOLUME HOMEOSTASIS At term, maternal blood volume has increased by 1000-1500ml in most women, allowing them to easily tolerate the blood loss associated with delivery. Normal delivery=400-500ml blood loss Cesarean section=800-1000ml blood loss Blood volume does not return to normal until 1-2 weeks after delivery.

5. CARDIAC OUTPUT EFFECTS Cardiac output (40%)increase to meet accelerated maternal and fetal metabolic demands .This increase is mostly due to an increase in stroke volume(30%) as heart rate increases only slightly(about 15%). Heart rate elevation occurs in response to increased oxygen demand. CO ↑40% by 12weeks 50% for rest of pregnancy 60%-100% during labor & after delivery CO highest right after delivery(release of aorto-caval compression) due to uterine contraction.

6. CARDIOVASCULAR EFFECTS Peripheral vascular resistance(VR)decreases due to the vaso-dilatory effects of progesterone and the proliferation of low resistance vascular beds in the inter-villous spaces of the placenta. Because of the decrease in peripheral vascular resistance (inspite of increased CO),arterial blood pressure does not significantly change or may show a slight fall in a uncomplicated pregnancy.

7. OTHERS CHANGES Despite the increase in blood volume , there is no change in the central venous pressure(CVP) during pregnancy ,this is likely due to dilated systemic and pulmonary circulations. Cardiac chambers enlarge and myocardial hypertrophy is often noted on echocardiography.(eccentric due to activation of RAAS). Also show variable ECG,ECHO,CXR changes .

8. Effect of pregnancy on cardiovascular investigations Investigation Chest radiography ECG Findings Apparent cardiomegaly Enlarged left atrium(lateral view) Increased vascular markings Straightening of left sided heart border Postpartum pleural effusion Right axis deviation Right bundle branch block St-segment depression on left precordial leads Q wave in lead III T wave inversion in leads III,V2,V3

9. CVS:- ITS ANAESTHETIC IMPLICATIONS Aorto-caval compression Compression of lower aorta ↓Blood flow to kidneys ,utero-placental circulation & lower extremities Fetal Hypoxia Compression of IVC by the gravid uterus ↓CO by 24% at term Supine hypotension syndrome (Hypotension associated with pallor ,sweating or nausea and vomiting) Decreases in cardiac output can occur in the supine position after the 28thweek of pregnancy

10. Women with a 28-week or longer gestation should not be placed in supine without left uterine displacement Can be done by:- Left Lateral decubitus Tilting the table left side down Rigid wedge(>15degree)under the right hip Fluid preloading before neuro -axial anesthesia It does not completely avoid maternal hypotension but it ↑ maternal CO →preserve utero-placental blood flow.

11. Physical examination of the term pregnant woman may also be abnormal with auscultation commonly revealing a wide loud , split first heart sound, an s3 sound , and a soft systolic ejection murmur . Hence essential to differentiate abnormal cardiovascular changes from normal physiological changes of pregnancy.

12. CRITERIA TO DIAGNOSE CARDIAC DISEASE DURING PREGNANCY: Presence of diastolic murmur Systolic murmur of severe intensity Unequivocal enlargement of heart(x-ray) Presence of severe arrhythmias , atrial fibrillation or flutter

13. RESPIRATORY CHANGES Due to increased metabolic demands, oxygen consumption(+20% to +50%) and minute ventilation(+40%) progressively increase during pregnancy The pregnant woman thus takes larger tidal volumes(40-50%) to eliminate carbon dioxide. PaCO2 decreases to (28 to 32mmHg);significantly respiratory alkalosis is prevented by a compensatory decreased in plasma HCO3 concentration .

14. RESPIRATORY CHANGES Hyperventilation may also increases PaCO2. Elevated levels of 2,3-diphosphoglycerate offset the effect of hyperventilation The combination of increased 2,3-DPG with increase in cardiac output enhances oxygen delivery to tissues .

15. ANAESTHETIC IMPLICATIONS Decreased FRC and Increased oxygen consumption promotes rapid oxygen desaturation during periods of apnea. This is more marked in obese patients. The reduced FRC causes airway ciosure in 50 % of parturients at term in the supine position making pre- oxygenation less effective. Regional bloc k further diminishes FRC which leads to rapid development of Hypoxemia. Preoxygenatio n prior to induction of general anesthesia is therefore mandatory to avoid hypoxemia in pregnant patients.

16. FACTORS AFFECTING SMOOTH INTUBATION There is 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 l aryngoscopy difficult. 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 eclampsi a . Blood flow to th e nasal mucosa is increased so Oropharynge al intubation is preferred over Nasal intubation.

17. GIT CHANGES The parturient should be considered a full stomach patient during most of gestation because – Upward &anterior displacement of the stomach by the uterus leads to increase in intragastric pressure and decrease in gastro esophageal angle. Reduction of lower esophageal sphincter pressure due to increased progesterone levels Risk of regurgitation and aspiration of gastric contents. Increased placental gastrin secretion which worsen gastric acidity.

18. ANESTHETIC IMPLICATION Prophylaxis in the form of H2 blocking drug and prokinetic drugs to all pregnant patients for surgery from 2 nd trimester onwards is a must. During GA airway protection by means of cuffed ETT is mandatory so is rapid sequence induction from 2 nd trimester of pregnancy till 48hrs postpartum. Extubation should be done when the patient is awake and on their side to reduce the risk of aspiration.

19. CNS CHANGES &ITS IMPLICATION The amount of local anesthetic drug required in a pregnant woman is less compared to the non pregnant state . Exaggerated lumber lordosis contribute to cephalad spread of the local anesthetic. 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.

20. RENAL CHANGES Renal vasodilatation increases renal blood flow early during pregnancy. ↑ Cardiac output leads to ↑ GFR & i ncreased renal plasma flow by 50% which increases clearance of urea, uric acid and Creatinine. ↑ Renin & Aldosteron e level promotes Na+ retention leading to volume overload. ↓ Renal tubular threshold for glucose & amino acids mild glycosuria & proteinuria (< 30 mg/d ) . Progesterone mediated urete ric smooth muscle relaxation can lead to urinary stasis making pregnant women prone to urinary tract infections.

21. HEPATIC CHANGES Hepatic function and blood flow are unchanged. A mild decrease in serum albumin is due to an expanded plasma volume. Thus, the free fraction of albumin- bound medications is increased. A 2 5-3 0% decrease in serum pseudocholinesterase activity is also present at term,but it rarely produces significant prolongation of SC h action. Increased cho lesterol gall stone formation(pro gesterone) .

22. HEMATOLOGICAL CHANGES Increase blood volume(up to 90ml/kg) Increase by 1000-1500ml at term. ↑plasma volume(45%)>↑RBC mass(30%) Dilutional anemia &↓blood viscosity Facilitates maternal & fetal ↓ impact of maternal blood loss at exchange of respiratory gases delivery ,nutrients& metabolites

23. HEMATOLOGICAL CHANGES Pregnancy leads to a hypercoagulable state , due to, ↑ factors VII,VIII,X,XII,IX(only factor XI↓) ↑ fibrinogen and FDP’s ↓ fibrinolytic activity - ↓ levels of plasminogen activators ↓ antithrombin III

24. MUSCULO-SKELETAL CHANGES Increased level of Relaxin – softening cervix - relax symphysis pubis - pelvis joint Increased risk of back pain (lax ligament)

25. FACTORS AFFECTING PLACENTAL TRANSFER OF DRUGS Lipid solubility — The placental membrane is freely permeable to lipid soiuble substances, which undergo flow dependent transfer. Higher the lipid solubility , higher the transfer of drugs. Molecular weight — Drugs with smaller molecular weight diffuse easily (<600da) Degree of ionization — Ionized form will not cross the barrier easily. The degree of ionization of acidic drugs is greater on the maternal side and lower on the fetal side. Protein binding — protein bound drugs will not diffuse easily, only free drug would cross the placental barrier easily. Acidosis reduces the protein binding of local anaesthetic . Reduced albumin concentration increases the proportion of unbound drug

26. ANAESTHETIC DRUGS Opioids - ------ All opioids cross the placenta in significant amounts. They are weak bases, bound to a- glycoprotein. Pethidine - Longer half life is due to its active metabolite norpethidine, which may lead to respiratory depression in the neonate. Morphine - It is poorly lipid soluble but readily crosses the placenta due to low protein binding. Fentanyl - It is highIy 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.

27. Inhalational Agents — These agents are highly soluble with low molecular weights. Muscle relaxants — These are quaternary ammonium compounds and fully ionized. These drugs are fully ionized as well as have low lipid solubility, hence they do not cross the placenta. Local Anaesthetics — These drugs have low molecular weights and also are lipid soluble. Different drugs have different protein binding. Propofo l - It is highly protein bound and lipophilic.

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