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[Therese Huntly]

What a great place! This is what I have been looking for for years, hopefully to answer a long-standing question I have.

I was asked to give an anesthetic to a 28 year old well primip for an urgent Caesarian Section. The surgeon involved insisted on a GA because of fetal distress. As the woman was slim and had an easy airway, I had no objections.

After all usual monitors and a minute or two of pre-oxygenation, I induced her with thiopentone 300mg and sux 125mg. Intubation was easy and uneventful. However, within seconds, she began to desaturate. At first to 90% and then rapidly to 80% and 70% and 60%.

This was not a pulse oximeter problem - her skin color was blue--puple--grey.

I kept her on 100% O₂, ventilation was easy. Breath sounds were equal and obvious in both lungs. There was no wheeze or rash to indicate anaphylaxis, and here blood pressure remained normal throughout.

I told the surgeon that something very bad was happening and to get the baby out. The baby was delivered within 2 minutes and was well.

Meanwhile the mother was still hypoxic. I checked the tube. It was patent, I pulled it back to 20cm and there was nothing to aspirate when I inserted a suction catheter.

After about 5-7 minutes, she slowly improved, and by the time the operation was finished her saturations were back to normal. On waking up, she recalled nothing of the incident, and (by my estimation) was neurologically intact.

This was, and is, a great mystery to me. I am very confident this was not an aspiration. It was a very easy intubation, with no fluid in the pharynx visualized. Chest X-Ray post-op was completely normal, and she had no cough or fever afterwards.

Below is a printout of the record. I am keen to hear opinions as to the cause.

[George Miklos]

Sounds like an undiagnosed cardic defect such as a VSD or ASD with a right to left shunt. Did she have an echo afterwards?

[John Farnsworth]

I had a similar mysterious (and stressful) situation during my training. My very experienced obstetric anaesthetic collegue explained it thus: Some pregnant women have extremely twitchy pulmonary circulation which is very sensitive to intubation. That is, the act of intubating can trigger a catastrophic pulmonary hypertension which can cause this effect.

A went on to do a quick literature search which showed that most women, and especially pre-eclamptic women demonstrate a rise in pulmonary pressures during intubation which in the extreme case could cause severe hypoxia.

[Therese Huntly]

Thanks for the replies 

She was lost to followup. I doubt she had an echo, but she certainly was asymptomatic as far as cardiac function goes. There was no signs or symptoms of pre-eclampsia.

[Michael de Sousa]

If it looks like aspiration, smells like aspiration, sounds like aspiration, then its got to be.....?






 

[Bucky]

Sounds like a large shunt was induced along with the GA.  Not uncommon in pregnant women.

[Sandy Hancock]

Wow, that's quite a desaturation! Great you had an automated record....

I agree aspiration seems unlikely, especially as recovery was so complete after a relatively short period.

I'm sure some sort of severe shunt must have occured at intubation, but I wonder (and have been for some time) if your choice of induction technique may have contributed.

As we all know maternal oxygen consumption is very high at full term, especially if the mother is in labour and scared witless about an urgent section to "save her baby". We also know her FRC is down, and she's (supposedly) an aspiration risk; that's why a rapid sequence induction (RSI) is the way to go.

The problem is, preoxygenation is often not done long enough when an anxious obstetrician is breathing down our neck, and then a dose of suxamethonium makes every skeletal muscle in our patients body contract - significantly increasing oxygen consumption even further. Many of us were also taught to eschew opioids before the baby is out, so the hypertensive response to intubation probably makes it all worse (your record shows diastolics over 115 after intubation, and systolics off the scale). The net result of this type of RSI is often not very pretty. As an aside, I suspect a lot of failed intubations at caesarean section are more due to haste than anything intrinsically difficult about the paturient's airway.

I now start all GA sections with a modest dose of fentanyl (100-200mcg), then pre-oxygenate for at least three minutes (I use the BP cuff interval as a timer) while the opioid calms the patient down a little. If you are really paranoid about opioids I guess a dose of esmolol would do. I use rocuronium for the intubation. Just like any other GA I do. RSI should stand for "really smooth induction" - haste makes waste

[Therese Huntly]

Interesting comments, Sandy. I never thought about the metabolic consequences of sux before!

In terms of pre-oxygenation, I make sure I have a good seal, and wait until my monitor shows and ETO₂ of at least 75%. This takes less than 3 minutes usually, often 60 seconds. Getting it any higher than about 75%-80% takes too long and I doubt the extra 5% is worth it.

[hdesousa]

I doubt if increased metabolism from sux would decrease systemic arterial oxygenation, unless there was a pulmonary shunt present.
With an adequate FiO2, normal lungs are capable of fully oxygenating any desaturated venous blood.
I do not usually preoxgenate for an extended time.  High maternal arterial oxgen levels decreases utero-placental flow in order to protect the baby from premature closure of the ductus arteriosus, among other things.
Also, with lungs full of O2, pulse oximetry will not give an early warning of unrecognized esophageal intubation.  Important when working with trainees. I've seen a baby delivered by C-section before the SpO2 decreased, and the lungs were not being ventilated all that time! Why supress spontaneous ventilation with 100-200 mcg fentanyl before starting to de-nitrogenize the lungs?  You could probably accomplish the same amout of N2 washout in a fraction the time without fentanyl. And if delivery is delayed, narcotiization would have to be included in the differential diagnosis of a sluggish baby.  Rocuronium needs to be given in a fairly good size dose if tracheal intubation needs to be accomplished with a minimum of  'unprotected' time.  I wonder how much crosses the placenta, especially if the baby's acidotic?  Sux myalgias are rarely seen in parturients.

[ouraiby]

IT HAPENED ONCE TIME FOR ME AS SUCH PRESENTATION (DESATURATION AFTER ET INTUBATION) AND I HAVE CHECKED ALL WHAT YOU HAVE DID BUT  THE PROBLEB WAS  SOLVED WHEN I DISCOVERED THAT THE SIDE KNOB THAT SWITCH ON AND OFF THE FLOW OF FRESH GAS BETWEEN THE VENTILATOR (CV) AND THE ASSISTED VENTILATION (MANNUAL) WAS SWITCHED OFF THE FLOW OF THE VENTILATOR WHILE WE WERE WORKING ON CONTROLLED VENTILATION.
 
           DR.ALA OURAIBY               

[Dr.Rengarajan M.D]

?Endobronchial!

[sheeloopoonam]

This is definitely endobroncheal intubation it happens in laproscopic surgeries also when the co2 is insufflated.
suddenly the patient desaturates. I mean it can happen in any condition which pushes diaphragm upwards.

[amarkatira]

most likly endobronchial intubation

[lovebailey2000]

Well I doubt that it was an endobronchial intubation coz breathsounds were equal bilaterally!

[edwardjohnson2310]

I have my own experience of giving GA for all kinds of obsteterics elective and emergency cases up to 2500 cases.From my experience I think the following reasons 1)Not enough pre-oxygenation for 3 mts.Low FRC in pregnant women would have caused low Spo2. 2)Endobronchial intubation.3)Undiagnosed PPH(Primary Pulmonary Hypertension)Intubation would have caused increased Pul Art Pressure/Increased shunt fraction/desaturation.4)Increased intra abdominal pressure(polyhydromnios)-markedly reduced FRC/Inadequate pre oxygenation-all combined together-relieved once intra-abdominable pressure is relieved(after delivring the baby) and lungs are fully ventilated. 
                                                 Dr.J.Edward Johnson.