Presentation on theme: "ANEMIA IN PREGNANCY AND ITS ANAESTHETIC IMPLICATIONS"— Presentation transcript:
ANEMIA IN PREGNANCY AND ITS ANAESTHETIC IMPLICATIONS
Anemia Definition: Quantitative or qualitative reduction of Hb or circulating RBC’s or both. Definition: Quantitative or qualitative reduction of Hb or circulating RBC’s or both. As per WHO, Hb conc. Of <11 gm/dl or Hct < 0.33 in 1st & 3rd trimester. In developing countries, limit brought down to 10 gm/dl. As per WHO, Hb conc. Of <11 gm/dl or Hct < 0.33 in 1st & 3rd trimester. In developing countries, limit brought down to 10 gm/dl. Incidence = 40 to 60 % Incidence = 40 to 60 %
Normal Level Of Hb/Hct Normal Level Of Hb/Hct AGE Newborn Newborn 1 month 3 month 12 months 12 months Adult male Adult male Adult female Adult female Hb/Hct 16/55 16/5512/3810/3012/3814/4512/36 Levels vary with age and gender
WHO definition for Chronic Anemia AGE Hb gm% AGE Hb gm% 6/ yrs <10 6/ yrs < yrs < yrs <12 Adult male <13 Adult male <13 Non pregnant female <12 Non pregnant female <12 Pregnant female <11/ Hct <33 Pregnant female <11/ Hct <33 1 st trimester <11 1 st trimester <11 2 nd trimester < nd trimester <10.5
Severity of Anemia ICMR CATEGORIES ICMR CATEGORIES Category Severity Hb levels gm % Category Severity Hb levels gm % 1 Mild 10 – Mild 10 – Moderate 7 – Moderate 7 – Severe <7.0 3 Severe <7.0 4 Very severe <4.0 4 Very severe <4.0
Physiological anemia of pregnancy ↑ in RBC mass ↑ demand for iron ↑ demand for iron ↓in total body iron stores ↓in total body iron stores ↓in serum ferritin levels (28-32 weeks of ↓in serum ferritin levels (28-32 weeks of pregnancy) pregnancy)
Criteria for Physiological anemia Hb = 10 gm% RBC = 3.2 million/mm 3 PCV = 30% Peripheral smear showing normal morphology of RBC with central pallor.
Regulation of Iron Transfer to fetus Maternal circulation ↓ Serum transferrin carries Fe ↓ Serum transferrin carries Fe Transferrin receptors located on apical surface of placental synctiotrophoblast ↓ Holotransferrin is endocytosed ↓ Fe is released & apotransferrin ↓ Free Fe binds to ferritin in placental cells ↓ Transferred to apotransferrin which enters from foetal side of placenta & exits into fetal circulation. of placenta & exits into fetal circulation.
Pathophysiology Oxygen Hemoglobin dissociation curve: O2 released to the tissues is affected by the shape & position of ODC which can move either to right or left. Shift is described in terms of P 50 – O 2 tension (Po 2 ) at which Hb is 50% which Hb is 50% saturated with O 2, saturated with O 2, corresponds to 27 corresponds to 27 mm Hg. mm Hg..
Normal values of oxygen in arterial and Venous blood Normal values of oxygen in arterial and Venous blood Oxygen content: Volume of oxygen carried in 100ml of blood. Arterial O2 content – CaO 2 = (1.34 x Hb x SaO 2 ) + (0.003 x PaO 2 ) CaO 2 = (1.34 x Hb x SaO 2 ) + (0.003 x PaO 2 ) Venous O2 content – CvO 2 = (1.34 x Hb x SvO 2 ) + (0.003 x PvO 2 ) CvO 2 = (1.34 x Hb x SvO 2 ) + (0.003 x PvO 2 ). Parameters Arterial bloood Venous Blood Po 2 (mm Hg) O 2 carried by Hb/100ml blood(ml) O 2 in solution/100ml of blood(ml)
Oxygen flux: Amount of oxygen leaving the left ventricle per minute in the arterial blood. per minute in the arterial blood. CO x arterial O 2 sat x Hb conc. X 1.31 CO x arterial O 2 sat x Hb conc. X 1.31 Oxygen delivery: Amount of oxygen that reaches the systemic capillaries each min. systemic capillaries each min. Do 2 = Q x CaO 2 x 10 (Q = Cardiac output) Do 2 = Q x CaO 2 x 10 (Q = Cardiac output) Oxygen uptake: Volume of oxygen that leaves the capillary blood and moves into the tissues capillary blood and moves into the tissues each min. each min. Measure of oxygen consumption of Measure of oxygen consumption of tissues. tissues. Vo 2 = Q X (CaO 2 – CvO 2 ) X 10 Vo 2 = Q X (CaO 2 – CvO 2 ) X 10
Oxygen extraction ratio: Fraction of oxygen delivered to the capillaries that is taken up into to the capillaries that is taken up into the tissues. the tissues. Index of efficiency of oxygen. Index of efficiency of oxygen. O 2 ER = VO 2 / DO 2 O 2 ER = VO 2 / DO 2 Parameters Absolute Range Cardiac output 5 – 6 L/min O 2 delivery 900 – 1100ml/min O 2 uptake 200 – 270ml/min O 2 extraction ratio 0.20 – 0.30 Normal range for oxygen transport parameters
Acute Anemia Blood loss > 20% of blood volume Hypovolemia & hemodynamic instability. Signs & symptoms of acute Blood loss Signs & symptoms of acute Blood loss Blood loss % Volume, ml SymptomsSigns <20<1000Restlessness Mild Tachycardia Anxiety Tachycardia on exertion & ↓ pulse pressure Syncope on sitting or standing Tachycardia at rest, ↑RR, Syst. Hypoten. >40>2000 Confusion, shortness of breath Marked tachycardia, Shock
Compensatory mechanism: Stimulation of adrenergic nervous system & release of vasoactive hormones. Sympathetic stimulation leading to ↑ CO & HR. Systemic vasoconstriction, ↑ VR and ↑ SV. Redistribution of blood volume to vital organs. Anerobic metabolism, acidosis, hyperventilation. Renal conservation of water & electrolytes. Factors affecting Compensation: Cardiopulmonary disease Left ventricular dysfunction. Magnitude of loss, oxygen consumption Anaesthesia
Anaesthetic considerations: Management of patient is judged by magnitude of hemorrhage and adequacy of volume replacement. Management of patient is judged by magnitude of hemorrhage and adequacy of volume replacement. Thiopentone - suitable induction agent for normovolemic patients who sustained acute blood loss. Ketamine or Etomidate - hypovolemic patients. Decrease conc. of volatile anaesthetic or infusion rate of agents administered i/v. Regional anaesthesia – not a good option. Small doses of midazolam can be given.
Anaesthetic management: Secure 2 large bore cannulas. Monitor SpO2,ETCO2,NIBP,temp,UO,CVP,ECG. GA with RSI. Fluid resuscitation, oxygen by mask, aspiration prophylaxis. Send blood for CBC, cross matching, coagulation profile Arrange adequate blood. Ensure left uterine placement. Transfuse blood if Hb < 7gm % with ongoing blood loss. If coagulation disorder present, give ml/kg. Prepare for intraop cell salvage if indicated. Regional not indicated.
Guidelines for Blood Transfusion (By National Institutes of Health Consensus Conference): Hb > 10gm/dl – transfusion rarely indicated. Hb < 6gm/dl – transfusion almost always indicated. Hb 6 to10gm/dl – decision to transfuse is determined by patient’s risk for complications of decreased tissue oxygenation ( pt. with IHD ). Preoperative autologous donation in selected patients. Intraoperative blood salvage when appropriate. Acute normovolemic hemodilution when appropriate.
Chronic Anemia Includes Iron Deficiency Anemia, Thalassemia, sickle cell anemia. Symptoms: No symptom (unless RBC count is very low). Fatigue, dyspnoea on exertion, palpitation. Nausea, loss of appetite, constipation, indigestion. Postural hypotension, vertigo, light headedness. Angina, heart failure, confusion. H/O bleeding (DUB, malena, hematuria). Signs: Vitals - ↑ HR,RR GPE - Pallor of skin & mucous membranes, JVP ↑, pedal edema, generalised anasarca, pedal edema, generalised anasarca, glossitis, stomatitis, Koilonychia, mouth soreness. glossitis, stomatitis, Koilonychia, mouth soreness. Resp. system - Tachypnoea - Basal crepts, if LVF. - Basal crepts, if LVF.
CVS - Tachycardia, strong peripheral pulses with wide pulse pressure. pulse pressure. - Functional cardiac murmur (Ejection murmur). - Functional cardiac murmur (Ejection murmur). - Evidence of cardiomegaly, CHF. - Evidence of cardiomegaly, CHF. Abd. - Jaundice, hepatosplenomegaly. CNS - altered sensorium. - Mental disturbances (B 12 def). - Mental disturbances (B 12 def). Edema (Renal failure). Lower leg ulcers (Sickle cell Anemia). Compensatory Mechanisms: ↑ 2,3 DPG shift of O 2 Hb dissociation curve to right. ↑ Oxygen Extraction ratio. Circulatory adjustments - ↑ CO by increasing SV. - myocardial hypertrophy. - myocardial hypertrophy. Release of erythropoietin which stimulates erythroid precursors in bone marrow to produce RBC’s.
Respiratory adjustments - ↓ physiological shunting in lungs. lungs. - ↓ respiratory reserve. - ↓ respiratory reserve. - tachypnoea, - tachypnoea, hyperventilation. hyperventilation. GIT - reduced splanchnic blood flow. Lab Investigations: 1. Complete blood count a) RBC count – Hb, Hct. a) RBC count – Hb, Hct. b) RBC indices – MCV,MCH,MCHC, RDW. b) RBC indices – MCV,MCH,MCHC, RDW. c) WBC count c) WBC count - Cell differential - Cell differential - Nuclear segmentation of neutrophils. - Nuclear segmentation of neutrophils.
Iron Deficiency Anemia Most common cause of anemia in pregnancy. Stored as S.ferritin & Hemosiderin. Adult male Adult female Adult male Adult female Stores 1000mg 300 – 500mg Stores 1000mg 300 – 500mg Losses 1mg/day 2mg/day Losses 1mg/day 2mg/day 3mg/day(Pregnancy) 3mg/day(Pregnancy) Daily iron requirement 2.5mg – early pregnancy. 2.5mg – early pregnancy. 5.5mg – from 20 to 22 wks 5.5mg – from 20 to 22 wks 6 to 8mg – 32 wks onwards 6 to 8mg – 32 wks onwards
Basal Iron 280mg Basal Iron 280mg Transfer to fetus mg Transfer to fetus mg For placenta mg For placenta mg Blood loss at delievery mg Blood loss at delievery mg Expansion of red cell mass 570mg Expansion of red cell mass 570mg Iron conserved by Amenorrhea mg Iron conserved by Amenorrhea mg TOTAL REQUIREMENT mg(4-6mg/d) TOTAL REQUIREMENT mg(4-6mg/d)Causes: Increased iron demand Diminished intake of iron Disturbed metabolism Pre-pregnancy health status Excess demand
Haematological parameters: IDA Normal values IDA Normal values Plasma iron < ug/dl S.Ferritin < ug/l TIBC > ug/dl Transferrin saturation <15% 30-50% MCV < fl MCH < pg MCHC < g/dl RBC Protoporphyhrin > ug/dl
Complications: During Pregnancy - Pre eclampsia (due to malnutrition or hypoproteinemia) hypoproteinemia) - Intercurrent infection (infection impairs - Intercurrent infection (infection impairs erythropoiesis by BM depression) erythropoiesis by BM depression) - heart failure (at 30-32wks or preg) - heart failure (at 30-32wks or preg) - Preterm labour - Preterm labour During labour - Uterine inertia - PPH - PPH - Cardiac failure - Cardiac failure - shock - shock
Puerperium - Puerperal sepsis - Subinvolution - Subinvolution - Failing lactation - Failing lactation - Puerperal venous thrombosis - Puerperal venous thrombosis - Pulmonary embolism - Pulmonary embolism Effects on baby - Amount of Fe transferred to fetus is Amount of Fe transferred to fetus is uneffected even if mother suffers from IDA. uneffected even if mother suffers from IDA. - increased incidence of low birth. - increased incidence of low birth. - IUD due to severe maternal anoxemia. - IUD due to severe maternal anoxemia.
Folic acid Deficiency FA is cofactor in nucleic acid synthesis and has imp. role in cell division. Stores are limited (6-10mg). Daily requirement is mg. Def. causes Megaloblastic anemia. High incidence in multigravida, twin pregnancy, hyperemesis gravidarum, alcohol consumption, smoking, malabsorption, antiepileptic drugs. Effects on mother: Incidence of abortion high. Effects on Fetus: Premature birth, Neural tube defects, cleft palate. cleft palate.
Management Prevention: Avoidance of frequent child birth. Supplementary Fe therapy (60mg elemental Iron three times a day). Dietary prescription. Adequate treatment for any infection. Early detection of falling Hb level, levels should be estimated at 1 st A/N visit, 30 th & finally 36 th week.
Pregnancy <30wks Pregnancy 30-36wks Pregnancy >36wks IDA FA def. Oral iron Oral FA Intolerance or Non-compliance I/M iron I/V iron IDA FA def. Parenteral Oral FA I/M iron I/V iron Blood transfusion PROTOCOL OF SEVERE ANEMIA IN PREGNANCY
Curative: 1. ORAL THERAPY - 200mg (60mg elemental iron) X 3 times a day. 200mg (60mg elemental iron) X 3 times a day. WHO – 60mg elemental iron + 250ug FA OD/BD. WHO – 60mg elemental iron + 250ug FA OD/BD. Govt. of India Regimen – Govt. of India Regimen – 100mg Fe + 500ug FA during 2 nd half of 100mg Fe + 500ug FA during 2 nd half of pregnancy X 100 days. pregnancy X 100 days.Drawbacks: - Intolerance - Intolerance - Unpredictable absorption rate. - Unpredictable absorption rate. - Non Compliant patient. - Non Compliant patient. - Long time for 0.3-1gm/100ml/wk. - Long time for 0.3-1gm/100ml/wk.
Response to therapy: - Sense of well being. - Sense of well being. - Increased appetite. - Increased appetite. - Increase in Hb. - Increase in Hb. - Reticulocytosis with in 5-10 days. - Reticulocytosis with in 5-10 days. 2. PARENTERAL THERAPY- Indications: - Failure to iron therapy. - Failure to iron therapy. - Non compliant patient. - Non compliant patient. - Case seen for the 1 st time during last 8-10 wks - Case seen for the 1 st time during last 8-10 wks with severe anemia. with severe anemia.
Advantages: - Certainity of admission. - Certainity of admission. - Hb - Hb I/V Route: Iron Dextran (1ml contains 50mg elemental iron & one Iron Dextran (1ml contains 50mg elemental iron & one ampoule contains 2ml). ampoule contains 2ml). Total dose infusion – Deficit of iron calculated & total amount required to correct deficit is amount required to correct deficit is administered in single setting I/V administered in single setting I/V infusion. infusion. Elemental Iron Needed (mg) = (Normal Hb - Patients Hb) X Wt(kg) X (Normal Hb - Patients Hb) X Wt(kg) X
drops/min X 30 mins (diluted in normal saline or 5% dextrose). saline or 5% dextrose). If no reaction, ↑ to 40 drops/min. If no reaction, ↑ to 40 drops/min. Side effects: - Anaphylactoid reaction. - Anaphylactoid reaction. - Chest pain, rigors, chills, fall in BP, dyspnoea, - Chest pain, rigors, chills, fall in BP, dyspnoea, hemolysis. hemolysis. Treatment: Stop infusion. Treatment: Stop infusion. Give antihistaminics, corticosteroids & Give antihistaminics, corticosteroids & epinephrine. epinephrine. I/M Route: Iron Sorbitol Citrate (Jactofer) Iron Sorbitol Citrate (Jactofer) Iron Dextran (imferon) Iron Dextran (imferon) Oral iron should be suspended at least 24 hrs prior to therapy to avoid reaction.
Drawbacks: - Painful injection (less with jactofer). - Painful injection (less with jactofer). - Chances of abcess formation & discolouration of skin - Chances of abcess formation & discolouration of skin over injection site. over injection site.
3. BLOOD TRANSFUSION - Transfusion triggers: Task force 1996, 2006 – No uniform transfusion Task force 1996, 2006 – No uniform transfusion trigger trigger Patient factors Type of surgery Patient factors Type of surgery Preg Preg Elective Emergency 36wks C/S C/S 36wks C/S C/S -Hb ≤ 5gm% - Hb ≤ 6gm% - with H/O -Always Without CHF without CHF APH,PPH, arrange -Hb 5-7gm%,if -Hb 6-8gm%,if previous blood. CHF,hypoxia, CHF,hypoxia, LSCS. Infections. Infections. Hb <8gm%,2 units blood should be arranged. Hb <8gm%,2 units blood should be arranged.
Guidelines for transfusion: Prefer fresh Packed cells. Do not repeat tranfusion within 24 hrs. Effects of Transfusion: ↑ O2 carrying capacity of blood. Viscosity increases by 33%. Hb increases by 1gm/unit. Heart rate decreases by 7%. Supplies natural constituents of blood. Improvement with in 3 days. Drawbacks: Premature labour (blood reaction). CHF Transfusion rexn. Infections: HIV, Hep B etc.
Anaesthetic Considerations: Etiology & Chronicity of anemia Pt. overall condition Pt. ability to compensate for ↓ O 2 delievery. Operative procedure. Anticipated blood loss. Minimize factors interfering with O 2 delivery - low myocardial contractility, CO (careful with - low myocardial contractility, CO (careful with volatile anesthetic agents volatile anesthetic agents - left shift of ODC (hyperventilation, - left shift of ODC (hyperventilation, hypothermia, alkalosis) hypothermia, alkalosis) Prevent increase in O2 consumption (reduce postop pain, fever, shivering).
Anaesthetic technique: Regional anaesthesia – Spinal or epidural can be given Preloading fall in hct by 20% (2lt). Exacerbate anemia Exacerbate anemia Heart failure. Heart failure. General anaesthesia – Principle: a) Avoid hypoxia. b) Maintain cardiovascular stability. c) Minimize factors which produce unwanted shift of O2 dissociation curve.
Secure 2 large bore cannulas. Monitor SpO2,ETCO2,NIBP,temp,UO,CVP,ECG. Induction: a) Adequate preoxygenation. b) I/V agents administered slowly. Maintenance: a) Ventilation should be maintained to provide normocapnia. b) Possibility of awareness is to be kept in mind as O conc. is increased. b) Possibility of awareness is to be kept in mind as O 2 conc. is increased. c) Mild tachycardia & wide pulse pressure may be physiological obtunded by anaesthetic agents. d) Tissue perfusion judged by blanching ear lobes, nose. e) Change posture cautiously ↓ BP & CO.
Postoperative: 1. Extubate relaxant effect worn off. 2. Monitor vitals, fluid intake/output & respiratory parameters for 12 – 24 hrs. 3. Oxygen enriched air given by mask. 4. Prevent shivering. 5. Hb should be checked postoperatively & transfusion accordingly.
Management during labour Adequate oxygenation. Avoid sympathetic stimulation and hyperventilation; prevent rightward shift of ODC. Decreased blood loss. Avoid maternal stress, patient can go into CHF. Improved uterine blood flow. PPH should be emergently treated.
Sickle cell Anemia Valine substituted for glutamic acid at 6 th position on ß chain of Hb molecule. Common variants - SS ( sickle cell anemia). - SA ( sickle cell trait). - SA ( sickle cell trait). - SC ( sickle cell disease). - SC ( sickle cell disease). Hb SS Hb SA Hb SC Cell trait HomozygousHeterozygous Double heterozygous HbS 70 – 90%, rest HbF. 10 – 40%, % HbA. Very low Hb (g/dl) Life expectancy 30 yrs normal Slightly ↓ Propensity for sickling (O 2 falls < 40%) ++
Signs & symtoms of sickle cell disease: 1. Vaso-occlusive complications a) Painful episodes a) Painful episodes b) Acute chest syndrome b) Acute chest syndrome c) Strokes c) Strokes d) Renal insufficieny d) Renal insufficieny e) Splenic sequestration e) Splenic sequestration f) Proliferative retinopathy f) Proliferative retinopathy g) Priapism g) Priapism h) Spontaneous abortion h) Spontaneous abortion i) Bone pains, leg ulcers, Osteonecrosis i) Bone pains, leg ulcers, Osteonecrosis 2. Complications related to hemolysis a) Anemia (Hct 15 – 30%) a) Anemia (Hct 15 – 30%) b) Cholelithiasis b) Cholelithiasis c) Acute aplastic episodes c) Acute aplastic episodes
3. Infectious complications a) Streptococcus pneumonia sepsis a) Streptococcus pneumonia sepsis b) E.coli sepsis b) E.coli sepsis c) Osteomyelitis c) Osteomyelitis Factors favouring Sickling: Hypoxia Hypoxia Acidosis Acidosis Decrease in body temperature Decrease in body temperature Dehydration Dehydration Circulatory stasis Circulatory stasisInvestigations: Hb, Hct, Reticulocyte count Hb, Hct, Reticulocyte count Blood film Blood film Hb electrophoresis Hb electrophoresis Sickle cell test (Na metabisulphite) Sickle cell test (Na metabisulphite)
Anaesthetic Management: Goals - Avoidance of acidosis due to hypoventilation of lungs. Maintenance of optimal oxygenation. Prevention of circulatory stasis (improper body positioning, use of tourniquets). Maintenance of normal body temperature. Preoperative period - a) Admit to hospital 12 – 24 hrs before surgery to a) Admit to hospital 12 – 24 hrs before surgery to permit optimal hydration with I/V fluids. permit optimal hydration with I/V fluids. b) Correction of any coexisting infection. b) Correction of any coexisting infection. c) Transfuse RBC’s if needed ( keep Hb b/w 9-12 c) Transfuse RBC’s if needed ( keep Hb b/w 9-12 gm% & Hct of about 35%, with 60-70% HbA). gm% & Hct of about 35%, with 60-70% HbA). Intraoperative period - a) Monitor SpO 2,ETCO 2,NIBP,temp,UO,CVP,ECG a) Monitor SpO 2,ETCO 2,NIBP,temp,UO,CVP,ECG
b) Maintain arterial oxygenation b) Maintain arterial oxygenation c) Hydration. c) Hydration. d) Body temperature. d) Body temperature. e) Replace blood loss when necessary. e) Replace blood loss when necessary. General anaesthesia: Preoxygenate for 5 mins before induction to make HbS as Preoxygenate for 5 mins before induction to make HbS as possible is in oxy form. possible is in oxy form. After airway is established, give 30 – 50% inspired oxygen. After airway is established, give 30 – 50% inspired oxygen. Regional anaesthesia: Maintain oxygenation, ventilation, hypotension. Maintain oxygenation, ventilation, hypotension. Prevent stasis of blood flow. Prevent stasis of blood flow.
Postoperative period – a) Maintain oxygenation, hydration a) Maintain oxygenation, hydration b) Avoid acidosis & hypothermia. b) Avoid acidosis & hypothermia. c) Adequate analgesia. c) Adequate analgesia. d) Incentive spirometry. d) Incentive spirometry.
Thalassaemia Quantitative abnormalities of polypeptide globin chain synthesis. TypeHb Hb electrophoresis Clinical syndrome α-thalassaemia 1.Hydrops foetalis (deletion of 4 α- genes) 3-10g/dl Hb Barts(100%) Fatal in utero or in early infancy 2.HbH disease (deletion of 3 α- genes) 2-12g/dl HbH (2%), rest HbA,HbA,HbF HbH (2%), rest HbA,HbA 2,HbF Hemolytic anemia 3.α-thalassaemia trait (deletion of 2 α-genes) 10-14g/dlnormal Microcytic hypochromic bloood picture but no anemia
TypeHb Hb- electrophoresis Clinical syndrome ß- thallassaemias 1. ß- thallassaemias Major (Cooley’s anemia) <5g/dlHbA(0-50%)HbF(50-98) Severe cong. Hemolytic anemia,requ BT 2. ß- thallassaemias Intermedia5-10g/dlVariable Severe anemia but no regular BT 3. ß- thallassaemias minor10-12g/dl HbA(4-9%) HbA 2 (4-9%)HbF(1-5) Usually asymptomatic
Anaesthetic management: Management depends on severity of Anemia. Preoperative evaluation of cardiac & hepatic function in transfusion dependent patients as a risk of Fe toxicity in transfusion dependent patients as a risk of Fe toxicity or haemochromatosis. or haemochromatosis. Extramedullary haematopoiesis Hyperplasia of facial bones difficult intubation. Spinal cord compression & massive haemothorax also caused by extramedullary haematopoiesis.
Oxygen Cascade Dry atmospheric air PO = 159 mmHg PO= PB x FiO, Dry atmospheric air PO 2 = 159 mmHg PO 2 = PB x FiO 2, 760 x.21 = x.21 = 159 In Humidified air PiO = 149 mmHg PiO = (PB – 47) x FiO2 In Humidified air PiO 2 = 149 mmHg PiO 2 = (PB – 47) x FiO2 Alveolar air PAO= 100 mmHg PAO = PiO – PACO/RQ Alveolar air PAO 2 = 100 mmHg PAO 2 = PiO 2 – PACO 2 /RQ Arterial blood PaO = 97 mmHg PaO = 102 – Age/3 Arterial blood PaO 2 = 97 mmHg PaO 2 = 102 – Age/3 Mixed venous blood PVO = 40 mmHg Mixed venous blood PVO 2 = 40 mmHg Cell PO= 5 to 40 mmHg Cell PO 2 = 5 to 40 mmHg Mitochondria PO = 1 to 2 mmHg Mitochondria PO 2 = 1 to 2 mmHg
PreoxygenationDenitrogenation. Replacement of the nitrogen volume of the lung (upwards of 69% of the FRC) with oxygen to provide a reservoir for diffusion into alveolar capillary blood after the onset of apnoea. reservoir for diffusion into alveolar capillary blood after the onset of apnoea. Three Methods: 100% O via tight fitting mask for 5 mins in a 100% O 2 via tight fitting mask for 5 mins in a spontaneously breathing patient spontaneously breathing patient 10 mins of oxygen reserve 10 mins of oxygen reserve 4 vital capacity breaths of 100% O over a 30 secs. 4 vital capacity breaths of 100% O 2 over a 30 secs. 8 deep breaths in a 60 sec period.
Oxygen Stores Normal Oxygen Stores in adults ml. (Oremaining in lungs + bound to Hb + dissolved in body fluids) (O 2 remaining in lungs + bound to Hb + dissolved in body fluids) Hemoglobin’s high affinity and very limited quantity in solution restricts the availibility of these stores. The oxygen contained within the lungs at FRC becomes the most important source of oxygen during the period of apnea, of which 80% is used only.
Clinical Importance Apnea in a patient breathing room air Oxygen content= fiO(.21) X FRC(2300 ml)=480 ml Oxygen content= fiO 2 (.21) X FRC(2300 ml)=480 ml Metabolic activity =V O =250ml/min Metabolic activity =V O 2 =250ml/min Severe hypoxemia in 90 sec. Severe hypoxemia in 90 sec. Apnea in a patient breathing 100% O2 Oxygen content= fiO(1) X FRC(2300 ml)=2300 ml Oxygen content= fiO 2 (1) X FRC(2300 ml)=2300 ml Metabolic activity =V O =250ml/min Metabolic activity =V O 2 =250ml/min Severe hypoxemia in 7-8 Min. Severe hypoxemia in 7-8 Min.
Pregnant patients- Pregnant patients- ↓FRC (15-20%) +↑O2 Consumption(20-40%) ↓FRC (15-20%) +↑O2 Consumption(20-40%) Rapid desaturation during period of apnea Rapid desaturation during period of apnea Preoxygenation for Min. Preoxygenation for Min.
References 1. Obstetric Anesthesia- Principles and practice David H Chestnut 3 rd edition Chestnut 3 rd edition 2. Anaesthesia & Co-existing diseases-Stoelting. 3. Miller’s Anesthesia- Ronald D. Miller 6 th edition. 4. Short Practice of Anaesthesia – Churchill Davidson. 5. Textbook of obstetrics- DC Dutta. 6. The ICU book – Paul. L. Marino. 7. Text book of Pathology – Robbins.