الفهرس 
PHYSIOLOGICAL CHANGES DURING PREGNANCYOnly 14 pages are availabe for public view
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Abstract
The prevalence of significant obesity continues to
rise in both developed and developing countries.
As a result, the anesthetist can expect to be presented frequently with obese patients in the operating theatre.
An individual is considered obese when the amount of fat tissue is increased to such an extent that physical and mental health are affected.
Pregnancy leads to physiological changes in multiple organ systems, these changes include:
1. Cardiovascular changes:
- Increased cardiac output mainly due to increased heart rate.
- Increased blood volume and plasma volume.
2. Respiratory changes:
- Expiratory reserve volume, residual volume and functional residual capacity are progressively decreased.
- A progressive increase in minute ventilation due to a rise in tidal volume and a rise in respiratory rate
(2-3 breaths/minute).
3. Hematological changes:
- Increase in red blood cell (RBC) mass. However, the increase of 15% to 20% in RBC mass is disproportionate to the 30% to 50% increase in blood volume. As a result, the hematocrit decreases, resulting in the ”physiological hemodilutional anemia of pregnancy”.
- Levels of several coagulation factors are increased, especially fibrinogen and factor VIII.
4. Gastrointestinal changes:
- Increased intragastric pressure and relaxation of the lower esophageal sphincter, both tend toward greater esophageal reflux.
Many of the effects of obesity and pregnancy are additive, and lead to significant functional impairment, and increased obstetric and anesthetic risks in the morbidly obese pregnant women:
• Obesity and pregnancy both increase risk for difficult
intubation and decrease lung volumes and ventilation.
Women with obesity are more likely to have OSA which is characterized by frequent episodes of apnea or hypopnea during sleep, leading to hypoxemia and hypercapnia.
• Both obesity and pregnancy are associated with
increased circulating blood volume, stroke volume, and cardiac output. Long-standing morbid obesity is associated with dilated cardiomyopathy and systolic dysfunction that seems to develop if left ventricular hypertrophy is insufficient to meet increased demand for cardiac output.
Obese parturients are at risk to develop profound supine hypotensive syndrome. The weight of the uterus and abdominal adipose tissue can compress the inferior vena cava and decrease cardiac preload, which result in decreased cardiac output and reflex tachycardia.
• In obese pregnant females, the combination of
increased intra-abdominal pressure, high volume and low PH of gastric contents, delayed gastric emptying and increased incidence of hiatus hernia and gastro-esophageal reflux, increases risk of aspiration pneumonitis.
• The risk of deep-vein thrombosis in an obese
parturient is almost the double. This results from prolonged immobilization leading to venous stasis, increased abdominal pressure with increased pressure in the deep venous channels of the lower limb, cardiac failure and decreased fibrinolytic activity with increased fibrinogen concentrations.
As regards anesthetic management, aspiration prophylaxis, thromboembolism prophylaxis, and antibiotic prophylaxis must be done, regardless the type of surgery.
In vaginal delivery, epidural analgesia is the preferred method for labor analgesia in morbidly obese women.
To improve initial success rate of the epidural placement, the sitting position is recommended.
Occasionally, a long epidural needle is needed to reach the epidural space. If attempts at lumbar epidural placement are not successful, ultrasound guidance may be helpful.
In caesarean section, the anesthetic options include epidural anesthesia, spinal anesthesia, combined spinal epidural, infiltration anesthesia, or general anesthesia.
Epidural anesthesia is preferred if a catheter is already in place, or if the surgery is likely to take more than 2 hours.
Spinal anesthesia is recommended if the obstetricians expect to complete the surgery in less than 90 minutes.
If general anesthesia is mandatory, rapid sequence induction after good preoxygenation is done, with the essential airway equipment available at hand.
To maintain oxygenation under anesthesia, we can increase the tidal volume and the fraction of oxygen delivered.
Delay extubation until the patient is completely awake, sitting upright, and able to breath spontaneously with satisfactory tidal volume. Administer supplemental oxygen in recovery.
In cases of nonobstetric surgery, the anesthetic management involves two unique patients, thus several unique concerns should be addressed when creating an anesthetic plan:
- Maintenance of uterine perfusion combined with adequate maternal oxygenation.
- Discuss perioperative tocolysis with the patient’s obstetrician. Indomethacin (oral or suppository) and magnesium sulfate (by infusion) are the most commonly used perioperative tocolytics.
- Teratogenic effects of anesthetics are probably minimal and have never been conclusively demonstrated in humans.
- If it will not interfere with the surgical field, intermittent or continuous fetal monitoring may be performed to ensure the intrauterine environment is optimized.
- Fetal monitoring should continue postoperatively