Obstetric General Anaesthesia

Hello. My name’s Nuala Lucas, and I’m a consultant anaesthetist in Northwick Park Hospital in London. I’ve got a special interest in obstetric anaesthesia. And I’m here with Rosie May, who’s our obstetric anaesthetic fellow. We’re shortly going to be considering some aspects of the provision of general anaesthesia in obstetric patients. But before we do that, we just want to discuss some of the particular challenges for these patients. So Rosie, thinking back to when you were starting work on the labour ward as an anaesthetic trainee, I’d like you to just tell us about some of your experiences at this time.

OK, I think when I started, particular I started covering on calls on the labour wards, it felt like quite a step up in terms of autonomy and responsibility from my previous obstetric anaesthetic experience. Although I did have some prior experience, it was just in terms of getting my basic obstetric competencies. I was also quite– or was always in quite heavily supervised environment. An environment which, we know, in most hospitals is quite remote from the rest of the theatre suite and the main theatre suite. And so if I was to run into difficulty out of hours or on night shifts, then I needed help from my colleagues. I knew that it wouldn’t always be immediately readily available.

And it may take a few minutes for them to come over and help. On top of that, I knew that the situation when you have to give a general anaesthetic on the labour ward, is usually in quite a time-pressured environment. We had to either do them for category 1 Caesarean sections where the risk to the mother or the foetus whose life is felt to be present. Or in a situation where we’re converting from a regional technique to a general technique on the table, perhaps because of an inadequate effect of the regional technique.

And in both of these situations, understandably, there’s going to be an anxious mother and also an anxious team surrounding you while you’re doing what we consider to be a reasonably high risk general anaesthetic. Practically, as well, we know that the obstetric airway poses a variety of challenges for us. So we know that they have a higher incidence of a difficult airway. We know that an aspiration risk is higher, and even though that’s rare, it can have pretty catastrophic consequences. And we know that it’s a patient population that desaturates quite quickly. And so we feel that time is precious.

And on top of that, in the back of your mind, you’re always thinking about the risk of accidental awareness, and how to mitigate that. It’s something that we know is higher in our statute population of the back of the NAP5 studies. Thanks, Rosie. So you’ve made some useful points. And I think if we summarise it, I think first of all, it’s an isolated setting. We know that labour wards are frequently remote from main theatre environments. So you may have a more junior anaesthetist working alone, often out of hours. We know that, in these particular situations, we’re working in very high pressure situation, and we know that stress can affect an individual anaesthetist’s performance.

And lastly, we know that this particular patient group do have very specific challenges associated with ensuring safe management for them. Yes.

We’ve heard about some of the challenges associated with the provision of general anaesthesia in obstetrics. What can we do to mitigate these risks and ensure safe care for our women and babies? Managing risk associated with emergency general anaesthesia for Caesarean section starts even before the decision has been made. Anticipation and preparation are crucial. Know your labour ward. Attend multidisciplinary ward rounds. Identify women who are at risk of having a Caesarean section. If they have an epidural for labour analgesia, is it working well? Could it be extended to provide anaesthesia in the event of emergency Caesarean section, and therefore avoid the need for general anaesthesia? Secondly, know your theatre environment. What airway kit is available to assist you?

Are you familiar with this kit?

If a woman needs a category 1 Caesarean section, the most clinically urgent type of Caesarean section, and you intend to do a general anaesthetic, planning and preparation remain essential even in this time-critical situation. This is emphasised in the obstetric anaesthetist association, and difficult airway society guidelines for the management of difficult and failed endotracheal intubation and obstetrics, which has three algorithms to support practise.

The first algorithm includes advice about pre-induction planning and preparation. It can be challenging to remember everything in a time-pressured, stressful environment. The use of a rapid-sequence induction checklist can be a helpful way to organise your thoughts and ensure no critical steps are forgotten.

There are several checklists available which emphasise preparation of the patient. For example, optimization of patient position. Preparation of equipment. For example, ensuring your laryngoscope is working. And lastly, preparing for difficulty. Who will you call in the event of difficult or failed tracheal intubation?

We know that obstetric patients are more vulnerable to desaturation, so how should we pre-oxygenate our patients to minimise this risk? A wide variety of techniques have been described to achieve optimal pre-oxygenation, and each has its own relative merits. Many anaesthetists prefer a period of tidal breathing, as it enables checklist to be undertaken, as well as a time to provide calm reassurance to the woman. There is significant current interest in the role of high-flow nasal oxygenation.

Two recently published studies that have investigated the role of high-flow nasal oxygenation in pre-oxygenation in obstetric patients. Perhaps disappointingly, neither study demonstrated a benefit with this technique. High-flow nasal oxygen did not reliably achieve an entitled oxygen concentration of greater than 90%, compared with standard flow rate facemask oxygen. This leads us to the question, does the role of high-flow nasal oxygenation in obstetrics lie with apnoeic oxygenation rather than pre-oxygenation?

Currently there are no clinical studies looking at the time to de-saturation in the obstetric patient. However, in a computational model, the positive effect of increasing oxygen concentration at the open glottis on oxygen saturation during apnea in the average term parturient has been demonstrated. A fraction-aspired oxygen of greater than 0.6 delayed de-saturation by almost 15 minutes, with a fraction aspired oxygen of 1.0 increasing this time to more than 70 minutes. Additionally, there are an increasing number of case reports highlighting the benefits of high-flow nasal oxygenation in the management of the difficult obstetric airway.

The OAA and DAS guidelines recommend that an anaesthetist should consider attaching nasal cannula with five litres per minute of oxygen flow before starting pre-oxygenation to maintain bulk flow of oxygen during apnea and intubation attempts.

Obstetric patients are at increased risk of failed tracheal intubation. The advent of videolaryngoscopy has been a major evolution in airway management. But what role does it have in obstetrics? A Cochrane review was published in 2017 examining viceolaryngoscopy versus direct laryngoscopy for intubation in adult patients. The review evaluated 64 studies, but only one of these specifically examines obstetric patients. There are a small number of observation and retrospective studies and case reports that do support the use of viceolaryngoscopy in obstetrics.

What further evidence is there to support the use of videolaryngoscopy in obstetrics? This paper used previously published investigations in a decision-tree analysis to quantify the time taken to establish anaesthesia and the probability of failure of three possible anaesthetic techniques in a woman with an anticipated difficult airway who required a category 1 Caesarean section. The success rate of all three techniques was similar, but videolaryngoscopy was markedly faster.

If you elect to videolaryngoscopy for intubation and obstetrics, it is preferable to ensure you are familiar with the laryngoscope blade that it comes with. For most anaesthetists, this would be the Macintosh blade.

One consideration with videolaryngoscopy is that there is currently no short-handled laryngoscopt escape available. Short-handled laryngoscopes are often helpful in obstetrics, as the hand position of cricoid pressure in obstetrics frequently makes placement of laryngoscope handle difficult, particularly with upward displacement of a woman’s breasts when supine.

The UK Royal College of Anaesthetists fifth national audit project identified general anaesthesia in obstetrics as being at higher risk of accidental awareness during general anaesthesia. This can be associated with significant psychological sequelae for a woman. The project identified a number of risk factors, including emergency surgery, obesity and difficult airway management, all of which can be encountered in obstetric patients.

Nap 5 made many recommendations to minimise the risk of accidental awareness during general anaesthesia. These include an additional syringe of intravenous agent should be immediately available to maintain anaesthesia in the event of airway difficulties when it is in the mother’s interests to continue with delivery rather than allow return of consciousness. A second relevant consideration relates to the fact that, in contrast to many other types of surgery, there may be a short time between anaesthetic induction and the start of surgery. This may lead to a gap in effect of anaesthesia, when the induction agent has worn off but the volatile maintenance agent has not yet reached acceptable levels.

After induction, it is crucial that adequate end tidal volatile levels are rapidly attained. In summary, there are many challenges associated with the provision of general anaesthesia in obstetrics. However, there are many strategies that can be used to improve practise in general anaesthesia in obstetrics and ensure safe outcomes for women and their babies. These include adequate preparation and the use of checklists, maximising oxygenation by utilising high-flow nasal oxygen during the apneoic period. Videolaryngoscopy to support tracheal intubation. And lastly, adoption of measures to minimise the risk of accidental awareness during general anaesthesia. Thank you for listening to this MOOC.