OB Crisis General Anesthesia

1. For an elective Cesarean Delivery we give metaclopramide, ranitidine, and sodium bicitrate before induction. Of these three drugs, which is the most important one to give bfore a general anesthetic for an emergent Cesarean Delivery?

Metaclopramide

Ranitidine

Sodium bicitrate

Answer: Sodium Bicitrate. Sodium bicitrate increases the pH of the stomach contents almost immediately. This may reduce morbidity if aspiration occurs. There is not very good evidence that giving sodium bicitrate actually does reduce morbidity and mortality, but it does raise gastric fluid pH. In the graph below, you can see that 15 ml of sodium citrate raised gastric acid pH over 3 in parturients for 14 minutes (O’Sullivan and Bullingham). BJOG. 1984; 91:973-978). Important take home message: Give the bicitra right before induction.

Aspiration remains one of the leading causes of death associated with general anesthesia for Cesarean delivery. From this graph taken from Hawkins et al. article on anesthetic related deaths in the U.S. from 1979 to 1990 you can see that aspiration is a significant cause of mortality (Anesthesiology: 86(2) 1997; 277-284):

Ranitidine is not useful in this circumstance because takes 30 to 60 minutes to start reducing stomach acidity. We actually give metaclopramide prior to spinal anesthesia to reduce nausea. In the case of a GETA for emergent Cesarean delivery, it is probably not very useful for emptying the stomach, but it does increase lower esophageal sphincter tone and this may be helpful in reducing reflux, but is probably not as useful as the sodium citrate or bicitra.

Explanation

Answer: Sodium Bicitrate. Sodium bicitrate increases the pH of the stomach contents almost immediately. This may reduce morbidity if aspiration occurs. There is not very good evidence that giving sodium bicitrate actually does reduce morbidity and mortality, but it does raise gastric fluid pH. In the graph below, you can see that 15 ml of sodium citrate raised gastric acid pH over 3 in parturients for 14 minutes (O’Sullivan and Bullingham). BJOG. 1984; 91:973-978). Important take home message: Give the bicitra right before induction.

Aspiration remains one of the leading causes of death associated with general anesthesia for Cesarean delivery. From this graph taken from Hawkins et al. article on anesthetic related deaths in the U.S. from 1979 to 1990 you can see that aspiration is a significant cause of mortality (Anesthesiology: 86(2) 1997; 277-284):

Ranitidine is not useful in this circumstance because takes 30 to 60 minutes to start reducing stomach acidity. We actually give metaclopramide prior to spinal anesthesia to reduce nausea. In the case of a GETA for emergent Cesarean delivery, it is probably not very useful for emptying the stomach, but it does increase lower esophageal sphincter tone and this may be helpful in reducing reflux, but is probably not as useful as the sodium citrate or bicitra.

2. Appropriate drugs and doses for induction of general anesthesia for Cesarean delivery in a stable patient include all the following except:

Propofol 2 mg/kg

Sodium thiopental 4 mg/kg

Propofol 3 mg/kg

Ketamine 2 mg/kg

Answer: Ketamine is appropriate to use in a hemorrhaging patient, but it may cause uterine hypertonus and should not be used in patients that are stable. The two propofol doses represent the lower and upper doses that are recommended. The thiopental dose is the average of the suggested ranges.

Explanation

Answer: Ketamine is appropriate to use in a hemorrhaging patient, but it may cause uterine hypertonus and should not be used in patients that are stable. The two propofol doses represent the lower and upper doses that are recommended. The thiopental dose is the average of the suggested ranges.

3. Pick the false statement: Cricoid pressure….

…has been shown to be efficacious and should be used without release during the intubation of a pregnant patient.

…is the standard of care and should be employed, but may be released to get a better view during intubation.

…should not be initiated before induction.

…should be released if the patient starts retching while obtunded.

Answer: Cricoid pressure has not been shown to prevent regurgitation and aspiration. In fact, if you look at a study from Malawi (IJOA: 2009; 18:106-10) with over 5000 general anesthetics, cricoid pressure was used 61% of the time. However, when regurgitation happened, cricoid pressure was used 82% of the time. The incidence of regurgitation was over 3 times a high when cricoid pressure was used.

Even though cricoid pressure has not proven to be efficacious, in this country it should still be used since it is still the standard of care and makes theoretical sense. Just be careful and do not initiate it before the patient is completely asleep so you don’t stimulate retching by applying cricoid pressure. If the patient starts retching, release the cricoid so that the patient does not burst her esophagus.

Explanation

Answer: Cricoid pressure has not been shown to prevent regurgitation and aspiration. In fact, if you look at a study from Malawi (IJOA: 2009; 18:106-10) with over 5000 general anesthetics, cricoid pressure was used 61% of the time. However, when regurgitation happened, cricoid pressure was used 82% of the time. The incidence of regurgitation was over 3 times a high when cricoid pressure was used.

Even though cricoid pressure has not proven to be efficacious, in this country it should still be used since it is still the standard of care and makes theoretical sense. Just be careful and do not initiate it before the patient is completely asleep so you don’t stimulate retching by applying cricoid pressure. If the patient starts retching, release the cricoid so that the patient does not burst her esophagus.

4. For pre-oxygenation is it important for a pregnant patient to have 3 full minutes of breathing 100% oxygen or are 4 vital capacity breaths more appropriate?

Use the 4 breath method it is much more efficacious.

Use the 4 breath method, it is faster and equally efficacious.

Use the full 3 minutes method that is significantly more efficacious.

Answer: The 4 breath method is faster and equally, not more, efficacious. Below is a graph showing the PaO2 of the maternal artery and umbilical vein and artery with the two different methods used for pre-oxygenation. There is no significant difference between the groups (Norris and Dewan. Anesthesiology. 1985 Jun; 62(6): 827-9).

Explanation

Answer: The 4 breath method is faster and equally, not more, efficacious. Below is a graph showing the PaO2 of the maternal artery and umbilical vein and artery with the two different methods used for pre-oxygenation. There is no significant difference between the groups (Norris and Dewan. Anesthesiology. 1985 Jun; 62(6): 827-9).

5. Pregnant patients desaturate faster than non-pregnant patients. In this study from the BJA (1974:46:358) patients were pre-oxygenated and then a minute after apnea a blood gas was drawn and compared to a gas drawn just before induction.

Pregnant women have a lower FRC

Pregnant women have bronchial swelling

Pregnant women have a faster metabolism

Aortocaval compression

Answer b. Pregnant women do have greater bronchial swelling, but that does not affect their oxygen saturation to any great degree. The other three reasons are all reasons why they desaturate more rapidly. The one people forget the most is aortocaval compression. Not only is this fact important for your boards, but also it is important to remember to use left uterine displacement even for general anesthesia. In this classic study by Crawford et al. (BJA 1972:44:477) you can see that even in cases of general anesthesia, left uterine displacement is important for preventing decreases in umbilical artery pH (umbilical artery pH reflects fetal oxygen delivery):

Explanation

Answer b. Pregnant women do have greater bronchial swelling, but that does not affect their oxygen saturation to any great degree. The other three reasons are all reasons why they desaturate more rapidly. The one people forget the most is aortocaval compression. Not only is this fact important for your boards, but also it is important to remember to use left uterine displacement even for general anesthesia. In this classic study by Crawford et al. (BJA 1972:44:477) you can see that even in cases of general anesthesia, left uterine displacement is important for preventing decreases in umbilical artery pH (umbilical artery pH reflects fetal oxygen delivery):

6. Pick the false statement.

The uterine vein:maternal vein ratio for succinylcholine is between 0.1 and 0.2.

Magnesium potentiates non-depolarizing neuromuscular blockers.

Succinylcholine is safe for the baby because of rapid metabolism.

Succinylcholine is highly ionized.

When using a succinylcholine infusion, doses up to 10 mg/kg are considered safe.

Answer: Succinylcholine is safe for the baby because it does not cross the placenta, not because it is metabolized fast. The reason it does not cross is that it is highly ionized and this gives it a low uterine vein:maternal vein ratio. Although out of fashion, sux drips were very good ways to maintain neuromuscular blockade during a short c-section and did not require reversal unless doses of 10 mg/kg were exceeded. Finally, be careful with giving neuromuscular blockers to patients on magnesium.

Explanation

Answer: Succinylcholine is safe for the baby because it does not cross the placenta, not because it is metabolized fast. The reason it does not cross is that it is highly ionized and this gives it a low uterine vein:maternal vein ratio. Although out of fashion, sux drips were very good ways to maintain neuromuscular blockade during a short c-section and did not require reversal unless doses of 10 mg/kg were exceeded. Finally, be careful with giving neuromuscular blockers to patients on magnesium.

7. Pick the false statement: With general anesthesia for cesarean delivery:

The risk of awareness is about 2%

About 50% of patients respond to verbal stimulation during a general anesthetic for cesarean delivery.

A laryngeal mask airway has been shown to be very safe in healthy, fasted patients.

Inhalational agents used at concentrations between 0.5 and 1.2 MAC increase the risk of bleeding significantly.

Blood loss is greater with general anesthesia compared to regional techniques in healthy patients.

Answer: The risk is actually significantly less than 1% (Paech et al. Int J Obstet Anesth. 2008;17(4):298-303). About 50% of patients respond to verbal stimuli, but this should not be confused with awareness ( CAN J ANAESTH 1995:42: 377-81). Laryngeal mask airways were safely used in over a thousand general anesthetics for Cesarean delivery when used on healthy, non-obese, fasted patients. Cricoid was applied until after delivery of the baby (Canadian Journal of Anesthesia. 2001;48:1117-1121). 

Explanation

Answer: The risk is actually significantly less than 1% (Paech et al. Int J Obstet Anesth. 2008;17(4):298-303). About 50% of patients respond to verbal stimuli, but this should not be confused with awareness ( CAN J ANAESTH 1995:42: 377-81). Laryngeal mask airways were safely used in over a thousand general anesthetics for Cesarean delivery when used on healthy, non-obese, fasted patients. Cricoid was applied until after delivery of the baby (Canadian Journal of Anesthesia. 2001;48:1117-1121). 

Ob Crisis General Anesthesia