1. Is the chance of aspiration higher in obstetric patients than in general patients?
Early in pregnancy, the tone of the lower esophageal sphincter is weakened in pregnant women (leading to acid reflux). The peristalsis of the esophagus slows down and food takes longer to pass through the intestine (leading to bloating). As pregnancy lengthens and the uterus enlarges, the stomach is pushed upward into a transverse position. These changes are all reasons why it was previously thought that pregnant women had a higher chance of aspiration by mistake than the general population. However, there are many reasons for aspiration, and the anatomical and physiological changes in pregnancy described above do not necessarily cause aspiration.
Pregnant women have more esophageal reflux than the general population, but the symptoms of acid reflux do not become apparent until mid to late pregnancy. The incidence of acid reflux increases with the duration of pregnancy. It is 14% before pregnancy, 22% in early pregnancy, 39% in mid-pregnancy, and 72% in late pregnancy. In the general population, 35% of Uyghurs have acid reflux, which is more factory than 28% of Han Chinese.
2.Does regurgitation lead to aspiration?
Gastric reflux and pulmonary aspiration are two different things. But regurgitation is a necessary condition for misaspiration, and gastric reflux is large enough for reflux to reflux to the throat in order for misaspiration to occur. The amount of gastric reflux is related to the amount of gastric residual (and pressure in the stomach).
3. How much gastric residual volume can cause aspiration under general anesthesia?
Animal studies have shown that 21 ml/kg body weight is required. Human trials have confirmed that a gastric residual volume of 200 ml can cause aspiration under general anesthesia, which is much larger than the 25 ml or 0.4 ml/kg of body weight traditionally taught. The gastric residual volume in normal subjects is 0.4-0.5 ml/kg body weight, which is also close to or greater than 25 ml. And the incidence of misaspiration is uncommon in the general patient, reported as 0.03% in 1993.
4. Are gastric residuals and gastric acidity in pregnant women the same as in normal non-pregnant women?
Studies show the same. An important factor affecting the amount of gastric residual is gastric emptying. If the gastric emptying time is slow, there will be more gastric contents. It also tends to reflux into the throat causing aspiration. Using resistance measurement or ultrasound measurement, several tests have confirmed that the gastric emptying time is the same for pregnant and non-pregnant women, and even for obese full-term pregnant women, the gastric emptying time is not prolonged. In other words, pregnant women in general are not at high risk for aspiration. The fasting requirement for pregnant women with elective cesarean delivery is the same as that for general patients.
5.Is the gastric residual of pregnant women the same as that of women in labor?
Once labor starts, the gastric emptying time of pregnant women is significantly longer. If a patient before the start of labor is called a pregnant woman and a patient after the start of labor is called a woman in labor, then a woman in labor is considered to have a full stomach and has a higher chance of aspiration than a normal patient or a pregnant woman.
6.Why is oral antacid given to the woman when epidural is used for emergency cesarean delivery?
Before emergency cesarean delivery, patients are usually given 30 ml of sodium citrate orally to neutralize stomach acid without increasing stomach volume. Others give gastric receptors, hydrogen pumps or H-2 receptor blockers at the same time, but these drugs take at least 30 minutes to take effect. General anesthesia needs to be changed if the epidural is not effective, if the anesthesia is unsatisfactory during surgery, or if other intraoperative accidents occur. The mother is at high risk of accidental aspiration, so antacids should be given before surgery to prevent chemical damage to lung tissue from stomach acid in case of accidental aspiration.
7.Why is the first thing a woman does when she passes to the operation bed is to put her right crotch up?
In the middle and late stages of pregnancy, the compression of the aorta by the pregnant uterus can cause “supine hypotension syndrome” in pregnant women, resulting in complications such as fetal hypoxia, placental abruption, lack of blood supply to the brain of pregnant women, decreased renal blood flow, and decreased urine output. In severe cases, it may cause maternal and fetal death. Clinical studies have confirmed that elevating the right crotch of pregnant women by more than 15 degrees to make the uterus tilt left effectively alleviates the mother’s symptoms and results in higher Arrhenius score and lower acidosis in the newborn. Therefore, pregnant women over 20 weeks of pregnancy should never lie flat on their backs. The left-leaning position of the uterus is the easiest and most effective way to alleviate “supine hypotension syndrome” and ensure the safety of mother and child.
8.What other problems can be caused by the compression of inferior vena cava?
When the inferior vena cava is compressed, the pressure is transmitted to the epidural space, causing the epidural plexus to dilate and fill with blood, thus making the epidural space smaller and spreading the local anesthetic drug widely. In other words, the injection of the same dose of local anesthetic will result in a higher plane of anesthetic analgesia in pregnant women than in non-pregnant women. Another problem, due to the dilated and congested epidural venous plexus, there is an increased chance of intravascular cannulation and injection during epidural puncture. Therefore, a test dose should be used to prevent the occurrence of intravascular injection of local anesthetic toxicity.
9.When general anesthesia is induced, why does the blood oxygen saturation of pregnant women drop faster than the general population after respiratory arrest?
This is a question of the relationship between oxygen reserve and oxygen consumption. As the tidal volume increases, the end-expiratory reserve decreases, and the pregnant uterus pushes up the diaphragm to squeeze the bottom of the lungs, making the functional residual air volume of pregnant women, that is, the oxygen reserve, decrease by 20%. Oxygen reserve is further reduced in obese patients or in the intraoperative head-down, foot-up position. At the same time, maternal oxygen consumption increases by 30% due to the high maternal metabolism, the enhanced work of the respiratory and circulatory system, and the metabolic needs of the fetus, uterus, and placenta during pregnancy. Oxygen reserve is reduced, oxygen consumption increases, and pregnant women are naturally prone to hypoxemia. Therefore, preoxygenation before induction of general anesthesia is crucial for pregnant women.
10.Why is the induction of general anesthesia faster in pregnant women than in the general population?
Theoretically, pregnant women can increase the alveolar concentration (or partial pressure of alveolar gas) of inhaled anesthetics because of alveolar hyperventilation, plus the reduced functional residual gas volume can make the inhaled gas balance with the gas concentration in the alveoli as soon as possible. These can quickly compensate for the absorption of anesthetic gases in the alveoli by the blood. Therefore, in inhalation induction of general anesthesia will be faster than the general population. When induced with intravenous, the clinical significance is not significant. However, this feature of pregnant women can easily make the amount of general anesthetic after induction excessive. In addition, the level of progesterone, which has a sedative effect during pregnancy, is 20 times higher than during non-pregnancy, and the beta endorphin also increases, so that the “minimum alveolar concentration” of inhaled anesthetics in pregnant women is reduced by 30%. These need to be considered during general anesthesia to avoid severe hypotension.
11.Why is regional anesthesia used as much as possible when pregnant women undergo surgery?
Regional anesthesia uses a single drug in a small dose, which has less effect on the fetus. For the mother, the main concern is to avoid possible difficult airway and misaspiration. The airway can be narrowed during pregnancy due to mucosal congestion of the airway and, moreover, easy bleeding. Therefore, transnasal tracheal intubation and transnasal gastric tube placement should be avoided as much as possible. The tracheal tube should be one size smaller than the average person, such as a 6 or 7 gauge tracheal tube.
Some studies have shown that Mallampati scores increase with increasing gestation and as labor progresses. Although the Mallampati score alone is not an accurate predictor of a difficult airway, the Mallampati score is a more valuable predictor of a difficult airway in the pregnant population than in the general population. In patients with vaginal delivery to cesarean section, this score gets worse, indicating that the edema of the upper airway becomes severe due to breath-holding, etc.
In addition. The enlargement of the breasts during pregnancy and the position of the breasts when lying down can affect the view of the tracheal tube. Therefore, regardless of whether regional or general anesthesia is used for cesarean delivery, the pregnant woman’s head should be in the best position to facilitate tracheal intubation, the olfactory position. If, intraoperatively, intubation cannot be encountered, the obstetric patient is characterized by the inability to revive the patient and then elective cesarean delivery or awake fiberoptic intubation. Every effort must be made to find a way to ventilate and ventilate the patient. General anesthesia cesarean delivery with a mask or laryngeal mask under cricoid cartilage pressure is feasible. Because the inability to intubate and ventilate remains the leading cause of anesthesia-related maternal death, preoperative airway assessment must be adequate and obstetrical operating rooms must be equipped with difficult airway equipment.
12. What is the difference between maternal non-intubation – non-ventilated emergencies and non-maternal?
For non-maternal surgery, unless it is an emergency, there is an option to wake up the patient and perform another elective surgery in case of non-intubation and non-ventilation. However, the mother is under general anesthesia, and in the event of such a life-threatening situation, there must be a set of contingency plans in place that meet local conditions. Otherwise, there is a risk of both mother and baby dying.