Obstetric Anaesthesia PDF

Made with Xodo PDF Reader and Editor Anesthesiology Lec:-3 (13/10/2024) Obstetric Anaesthesia  Physiological Changes During Pregnancy Changes in pregnancy are largely due to increases in hormones (i.e., progesterone and estrogen) to mee...

Made with Xodo PDF Reader and Editor Anesthesiology Lec:-3 (13/10/2024) Obstetric Anaesthesia  Physiological Changes During Pregnancy Changes in pregnancy are largely due to increases in hormones (i.e., progesterone and estrogen) to meet the increased metabolic demands of the fetus, placenta, and uterus ( O2 consumption) in addition to increase size uterus and fetus. Physiological and Pharmacological Changes During PG A. Cardiovascular Effects Cardiac output and blood volume increase to meet accelerated maternal and fetal metabolic demands.(Table below)  Made with Xodo PDF Reader and Editor 1. Cardiac Output Cardiac output (HR × SV)(70beats /m × 70 ml/beat ) )will increase up to 40% at term. Most of the increase occurs in the 1st and 2nd trimesters. 2. Blood Pressure (systole/diastol)(90-140mmHg/60-90 mmHg) Despite increases in the patient's cardiac output and blood volume, the patient’s blood pressure does not normally increase from pre- pregnancy levels unless there is an abnormality such as pregnancy- induced hypertension.  Approximately 5% of women at term develop the supine hypotension syndrome (aortocaval compression), which is characterized by hypotension, pallor, sweating, or nausea and vomiting. This because complete or near-complete occlusion of the inferior vena cava by the gravid uterus. And can readily produce fetal asphyxia.  Made with Xodo PDF Reader and Editor Turning the patient on her side restores venous return from the lower body and corrects the hypotension in such instances. This maneuver doing by placing a wedge (>15°) under the right hip. 3. Blood volume(70ml/Kg) At term, blood volume has increased by 1000–1500 mL in most women, allowing them to easily tolerate the blood loss associated with delivery; total blood volume reaches 90 mL/kg. This increase of blood volume consist of (55%) in plasma volume in excess of an increase in red cell mass (45%) produces Dilutional anemia (Relative anemia) and reduces blood viscosity. Average blood loss during vaginal delivery is 400–500 mL, compared with 800–1000 mL for a cesarean section. 4. Clotting Mechanism Clotting components of the patient’s blood also increase to enhance clotting, reducing excessive bleeding during delivery. These components include fibrinogen, and factors VII, X, and XI. B. Respiratory Effects All the pulmonary changes in the fallowing's tables are directed to meet the increase metabolic demands ( O2 consumption).  Made with Xodo PDF Reader and Editor The combination of decreased FRC ) ‫ﻛﻤﻴﻪ اﻟﻬﻮاء اﻟﻤﻮﺟﻮده ﻓﻲ اﻟﺤﻮﻳﺼﻼت‬ ‫ )اﻟﻌﺎﻣﻠﺔ‬and increased oxygen consumption promotes rapid oxygen desaturation (Hypoxia)(PaO2 < 50mmHg) during periods of apnea(‫)ﺗﻮﻗﻒ اﻟﺘﻨﻔﺲ‬. Preoxygenation (denitrogenation) prior to induction of general anesthesia is therefore mandatory (‫)ﺿﺮوري‬to avoid hypoxemia in pregnant patients.  Short neck, large breast and capillary engorgement of the respiratory mucosa during pregnancy predisposes to difficult intubation and upper airways to trauma, bleeding, obstruction and also desaturation. The obstetric population is more difficult to intubate compared to the non-pregnant population. A smaller-than-usual endotracheal tube may be required.  Made with Xodo PDF Reader and Editor Good preparation and gentle laryngoscopy and smaller endotracheal tubes (6–6.5 mm) should be employed during general anesthesia. C. Gastrointestinal Effects Mechanical and hormonal alterations result in several changes within the gastrointestinal system. As the uterus enlarges, pressure is placed on the stomach resulting in an incompetent lower esophageal sphincter. In addition, progesterone will reduce the competence of the lower esophageal sphincter. Placental gastrin causes an increased secretion of gastric acid. Gastroesophageal reflux and esophagitis are common during pregnancy. This factor place the parturient at high risk for regurgitation and pulmonary aspiration during anesthesia. Pregnant patients should be considered to have “full stomachs”, regardless of fasting.  Made with Xodo PDF Reader and Editor Management A. Prolong fasting period B. medications should be administered before anesthesia to reduce gastric acidity and volume. 1. A non-particulate antacid (i.e., sodium citrate), 2. Metoclopramide (Plasil) 10 mg IV should be administered 30-60 minutes before anesthesia to stimulate gastric emptying and increase lower esophageal sphincter tone. 3. The use of histamine H2 blockers 30-60 minutes before surgical intervention may help to reduce the acidity of stomach contents. C. Cricoid pressure should be applied and held until the patient is intubated. Cricoid pressure should not be released until it is confirmed that the endotracheal tube has been placed in the trachea. D. Do not routinely administer positive pressure ventilation (‫ﻧﻔﺦ اﻻ‬ ‫)وﻛﺴﺠﻴﻦ ﻟﻠﻤﺮﻳﺾ‬, with a mask, before intubation. D. Central nervous system changes Changes in hormones result in a decrease of up to 40% in minimal alveolar concentration (MAC)(‫)ﺟﺮﻋﺔ اﻟﻐﺎزات‬. By the 3rd-day post-delivery MAC levels return to normal.  Made with Xodo PDF Reader and Editor Hormonal changes and venous dilatation contribute to a 30% decrease in local anesthetic requirements for spinal and epidural anesthesia. Anatomical changes may create an epidural space that has positive pressure instead of negative pressure. Anesthetic considerations due to Central nervous system Changes in pregnancy: a) Reduces the dose of inhaled anesthetics by up to 40%. b) Reduces the dose of local anesthetics for spinal and epidural anesthesia by up to 30%. c) Positive pressure in the epidural space may make it slightly more difficult to identify the epidural space. Anesthesia Of Obstetrical Operations (Cesarean Section) ( CS) As any patient the approach should consist of a maternal health history, anesthesia and anesthesia-related obstetric history, vital signs ,airway assessment, and back examination for regional anesthesia and Lab. Investigations.  Made with Xodo PDF Reader and Editor With special care for the fallowing's points discuses below:- 1.. Regardless of the time of last oral intake, all patients are considered to have a full stomach and to be at risk for pulmonary aspiration. Prophylactic administration of a clear antacid (15–30 mL of 0.3 M sodium citrate orally) every 30 min prior to a cesarean section can help maintain gastric pH greater than 2.5 and may decrease the likelihood of severe aspiration pneumonitis. An H2 -blocking drug (ranitidine,100–150 mg orally or 50 mg intravenously) or Proton pump inhibitors (Omeprazol) or Antiemetic (metoclopramide, 10 mg orally or intravenously), 2.. The supine position should be avoided unless a left uterine displacement device (>15° wedge) is placed under the right hip. 3.. Good preparations for airway difficulties Common indications for cesarean section are listed below:-  Made with Xodo PDF Reader and Editor  The choice of anesthesia for cesarean section is determined by multiple factors, including the 1. Indication (‫)ﺳﺒﺐ اﻟﻌﻤﻠﻴﺔ اﻟﻘﻴﺼﺮﻳﻪ‬for operative delivery, 2. Its urgency(‫)ﻫﻞ اﻟﻘﻴﺼﺮﻳﺔ ﻃﺎرﺋﺔ ام ﺑﺎردة‬. 3. Patient and obstetrician preferences(‫)رﻏﺒﺔ اﻟﻤﺮﻳﺾ واﻟﺠﺮاح‬. 4. The skills of the anesthetist(‫)ﻣﻬﺎرة ﻃﺒﻴﺐ اﻟﺘﺨﺪﻳﺮ‬.  Regional anesthesia has become the preferred technique because general anesthesia has been associated with a greater risk of maternal morbidity and mortality.  Made with Xodo PDF Reader and Editor  Deaths associated with general anesthesia are generally related to airway problems, such as inability to intubate, inability to ventilate, or aspiration pneumonitis, whereas  Deaths associated with regional anesthesia are generally related to excessive dermatome spread of blockade or to local anesthetic toxicity.  Advantages of regional anesthesia include:- (1) less neonatal exposure to potentially depressant drugs. (2) A decreased risk of maternal pulmonary aspiration. (3) An awake mother at the birth of her child. (4) The option of using spinal opioids for postoperative pain relief. Advantage General anesthesia (1) Very rapid and reliable onset. (2) Control over the airway and ventilation. (3) Greater comfort for patient who have morbid fears of needles or surgery. (4) Potentially less hypotension than regional anesthesia. (5) Facilitates management in the event of severe hemorrhagic complications such as placenta accreta.  Made with Xodo PDF Reader and Editor  Disadvantages of GA are :- (1) The risk of pulmonary aspiration. (2) The potential inability to intubate or ventilate the patient. (3) Drug-induced fetal depression.