An excellent blog from Oman! Cases and topics for anaesthetists. Click here.
Beware of conus injuries from needling the spinal cord during spinal anaesthesia. It can lead to lifelong disability and pain. Once you insert your spinal needle more than one space above a line joining the iliac crests then the risks start to escalate.
Maintain adequate levels of blood pressure during anaesthesia. Hypotension under anaesthesia continues to be associated with increased morbidity and mortality. Patient age and co-morbidities should influence the minimum acceptable blood pressure.
The recommended dose of morphine for an IV PCA should not be greater than 1 mg with a 5 minute lockout, except in opiate dependent patients.
There is no point giving a test dose of antibiotic IV unless you perform minute dilutions into one litre of crystalloid and run it into the patient slowly.
Blood needs to be carefully checked to ensure the correct patient is receiving the correct blood. Errors continue to occur. Mismatched blood transfusion carries a high mortality rate.
When injecting significant amounts of LA it is recommended to have patients awake and communicative to reduce the likelihood of LA toxicity
Aspiration prior to injection does not rule out being intravascular (the side of the vessel wall can be sucked against the bevel of the needle).
Slow injection of LA is essential while maintaining communication with the patient: “Tell me if you are experiencing anything unusual”.
Longer acting LA’s such as bupivacaine and ropivacaine have a higher incidence of LA toxicity than shorter acting ones such as lignocaine or prilocaine.
LA toxicity with mortality and major morbidity continues to occur.
Laryngeal tumours can create major airway difficulties for anaesthesia with airway obstruction and bleeding
Patients with laryngeal tumours ideally should have an MRI prior to anaesthesia.
Beware of gas trapping with IPPV in patients with respiratory conditions such as asthma and cystic fibrosis. This can lead to cardiovascular collapse. Such patients require reduced respiratory rates and longer I:E ratios to allow sufficient time for gas to be exhaled.
In patients with gastric outlet obstruction be prepared for regurgitation of large volumes of gastric fluid or blood.
Naloxone can precipitate massive sympathetic response with pulmonary oedema. Giving divided doses may diminish this effect.
Take care not to have malleable stylets protruding out the end of ETTs as they can also cause tracheal damage.
Jet ventilation must be used with considerable caution as surgical emphysema and pneumothoraces have been frequently reported. Care must be taken to ensure the upper airway is not obstructed. Gas needs to be able to get out as well as get in.
TIVA continues to be associated with awareness under anaesthesia.
Gas insufflation at laparoscopy can cause asystole or profound bradycardia. Careful monitoring is required. Treatment may require allowing the gas to escape rapidly.
Negative pressure pulmonary oedema may occur following emergence from anaesthesia in younger patients. CPAP or IPPV will usually be required.
Syringe swap continues to cause problems. Take extra care with muscle relaxants and vasopressors.
If your patient is hypotensive consider anaphylaxis, particularly if you have given muscle relaxants or antibiotics. There are many case reports of patients receiving significant doses of metaraminol and ephedrine prior to anaesthetists starting definitive treatment of anaphylaxis with adrenaline.
Nitrous Oxide in Anaesthetic
Practice
(This talk given in October 2008)
I’m Dr Rod Tayler, a VMO anaesthetist at the Alfred Hospital in Melbourne and I’m talking with Professor Paul Myles. Paul is Professor and Director of the Department of Anaesthesia and Peri-operative Medicine at the Alfred Hospital and Monash University. We are discussing nitrous oxide in anaesthetic practice, particularly in relation to evidence based medicine.
Paul, what triggered your interest in N2O?
I have had a long standing interest in evidence-based anaesthetic practice.
I like to question what is seen as routine anaesthetic practice. N2O is at the top of that list. It has been around for more than 160 years. We do know from a variety of editorials and review papers that it has a longstanding and safe history.
Despite that there have never been definitive randomized control trials to test its overall safety or effectiveness. This issue was raised recently in an editorial in the Acta Anaesthesiologica Scandinavica journal, and that is really what stimulated my interest in this area.
So I went back and reviewed all that is known or had been written about N2O and concluded from that that we really don’t know whether or not it is an effective and safe drug for use in practice today.
What are the known benefits of N20?
The fact that we’ve got a drug that we’ve been using for now for 160 years, underpins the likely safe and simple to use characteristics of this anaesthetic drug. We are all trained to use it. For most anaesthetists it has been part of their routine daily practice. It is easy to use. It appears to be very effective as an adjunctive anaesthetic and helps smoothing out anaesthesia and perhaps speeding up recovery time. Given that it is so simple to use, it forms a basis for what we would normally give for most general anaesthetics. I guess it is a part of our makeup. It is a bit like the potatoes in a roast dinner or the pasta, part of our staple diet.
What are the known or suspected risks of N2O?
Well we’ve known really since the 1950’s that prolonged exposure, particularly in the ICU setting, can lead to symptoms and signs of vitamin B 12 deficiency. That is subacute combined degeneration of the spinal cord and also megaloblastic anaemia. I think most anaesthetic trainees learn that very early on, it is a part of many exams. What probably is not appreciated is that even short term repeat exposure in normal surgical practice has lead to some reports of these serious consequences. It is for that reason that I think we need to question its use in contemporary practice. So that is I guess what the average textbook would talk about and what the average exam candidate would know. But what is probably not appreciated is that the same metabolic pathway that involves methionine synthetase in DNA synthesis actually uses homocysteine as one of the substrates. In cardiovascular medicine particularly over the last 10 years it has become appreciated that elevated homocysteine levels are a risk factor for both coronary artery disease, stroke and probably dementia. In the anaesthetic setting of course we have a lot of patients who are at risk of coronary artery disease and it could be that elevated homocysteine levels after N2O anaesthesia is a new and possibly unappreciated risk factor.
You’ve been involved in a large trial looking at N2O, the ENIGMA trial. What did the ENIGMA trial show?
The ENIGMA trial was a large multi-centred multi-national randomized controlled trial that involved over 2,000 patients in around about 30 hospitals around the world. Particularly in Australia, New Zealand, South East Asia and Europe. The details of the study were published in the journal Anesthesiology in August 2007.
We set up the ENIGMA trial to test the overall safety and effectiveness, or if you like the added benefit of using N2O in routine practice. It involved a wide variety of patients having all types of surgery.
We asked anaesthetists to give their normal anaesthetic with or without N2O according to the randomized design. Our understanding of the effects of methionine synthetase and therefore RNA and DNA synthesis led us to suspect that there could be a number of unexpected side effects of N2O, in particular wound infection or immune suppression as well as the known effects on nerve function, red cell function, nausea and vomiting and possibly cardiovascular effects. So we measured each of these outcomes in the ENIGMA trial.
Firstly and most importantly, we found there was no beneficial effect of N2O. Specifically there was no improvement in the recovery time, there was no improvement in pain scores after surgery and in fact overall patients were less likely to be discharged from the recovery room in a reasonable period of time.
So in other words we could find no net benefit or gain. We also looked for adverse effects. In each area we found marked and clinically significant reductions in these side effects when N2O was avoided in the anaesthetic gas mixture. In particular there was a halving of the rate of severe nausea and vomiting up to and including 24 hours after surgery. We found significant reductions in wound infections, atelectasis and pneumonia when N2O was avoided.
We also found some trends which weren’t statistically significant but were worrying in that there appeared to be a possible increased rate of myocardial infarction and death in the N2O group. Now the simple interpretation of this study is that the removal of nitrous oxide led to better outcomes after surgery, and that could be the case.
Some commentators have argued that the inclusion of additional inspired O2 in the N2O free group of itself could have led to better outcomes and that is a theoretical explanation.
But we could find no evidence to suggest that this was the cause in our study. So we attribute it most likely to adverse effects of nitrous oxide.
However I do acknowledge there are some question marks about the full interpretation of the study and therefore what we need to be considering in our clinical practice now.
What further research is currently being done on these N2O issues?
Well I think the ENIGMA trial raised some very important questions. First of all, could the effects be explained away by supplemental O2. For that reason we are now controlling for that in a large follow up study which we have called ENIGMA 2. This is a 7,000 patient study. Secondly we are focusing on the cardiovascular side effects because of the known effects of.homocysteine on coronary artery disease.
Hence this large trial is looking at post-operative cardiovascular complications and deaths up to 30 days after surgery. And we will take the opportunity to confirm our earlier findings from ENIGMA 1.
So in the light of our current knowledge about N2O, how should we as anaesthetists be currently practicing?
ENIGMA 1 could not identify any positive or
beneficial effects of N2O so there appears to be no real reason for
it to be included. At the same time there are some possible real or
at least suspected serious complications that we can attribute to
N2O. So on balance I think it is clear that N2O should not be a
part of routine anaesthetic practice, and its use
should be questioned. This was the conclusion of our study
As patients are at greater risk of complications I think generally
it should be avoided. That particularly includes elderly patients,
those having more major surgery, those at a greater risk of wound
infection and those with a history of post-operative nausea and
vomiting.
There are other circumstances that we didn’t include in our study such as paediatric practice, or labour ward practice or perhaps young healthy males having more minor surgery where it is probably reasonable to continue to use N2O. Overall I think there is probably still a role for it. However we need to await the results of our larger ENIGMA 2 trial.
Paul, thank you for these perspectives on N2O in anaesthetic practice.
This study showed that beta blockers (metoprolol) given 2 – 4 hours prior to surgery and continued for 30 days led to a reduction in non fatal myocardial infarction (3.6% vs 5.1%). However this benefit was offset by an increase in stroke rate (1.0% vs 0.5%). Also total mortality in the metoprolol group was higher (3.1% vs 2.3%).
Commentators on this paper are suggesting that commencing beta-blockers peri-operatively for noncardiac surgery to prevent cardiovascular events (in at-risk patients) may lead to more harm than benefit.
Here follows an edited transcript of a presentation given by Prof Paul Myles, one of the POISE trial investigators.
This is also available as a podcast (10 minutes) Click here
I’m Dr Rod Tayler, a VMO Anaesthetist at the Alfred Hospital in Melbourne. I’m talking with Professor Paul Myles, Professor and Director of the Department of Anaesthesia and Peri-operative Medicine at the Alfred Hospital and Monash University. We are discussing the POISE trial. That is the Peri-Operative ISchaemic Evaluation trial, which was published in the Lancet in May 2008.
Paul, what was the trial looking into?
The purpose of the trial was to test whether or not complete peri-operative beta blockade in patients at risk of coronary or cardiac events, could lead to a reduction in adverse outcomes. The purpose was to design the study in a routine peri-operative or anaesthetic setting. And it aimed to represent a broad range of patients in numerous hospitals at many sites around the world. That is, designed to be very much a practical or pragmatic trial.
Paul, what was the thinking in the anaesthetic world about routinely starting high risk patients on beta blockers prior to the POISE results being published?
This has been a controversial area and is really illustrated by the fact that if you asked colleagues around the country and around the world you would find marked variation in practice. There had been a couple of small but influential trials published back in the mid to late 1990s suggesting that peri-operative beta blockers – atenolol or bisoprolol, could potentially improve outcomes and survival in this setting. But there were also some other studies that were negative and these didn’t receive the same level of exposure or press that the two influential studies did. The two studies I’m referring to are the Mangano study published in the New England Journal in 1996 and the Polderman’s study from the Netherlands looking at bisoprolol in vascular surgery. This was published in the New England Journal in 1999. Both of these studies showed a marked reduction in mortality, short term and long term with beta blockers. It was these two studies that I think heavily influenced practice guidelines. These guidelines were consensus statements put out by the American Heart Association and the American College of Cardiologists that recommended peri- operative beta blockers, particularly in patients who had risk factors for coronary artery disease or were undergoing vascular surgery. These consensus guidelines together with those influential trials were considered by some groups to be so important that peri-operative beta blockers became a standard of care or a mark of quality of hospital care, at least in some parts of North America. Other anaesthetists, myself included, were never convinced by the weight of evidence, and considered that in fact the data was conflicting and there needed to be a more comprehensive large scale study before there should be recommendations to change practice. That is essentially why the POISE study was set up.
And what did the POISE trial show?
The POISE trial is a most interesting study. It does require careful consideration and debate before we fully understand what it shows and what its implications are. One thing I think is clear is that there is a reduction in myocardial infarction. That is one clear end point. This replicates what was demonstrated in those earlier studies. I think it is now beyond dispute that beta blockers in the cardiac and non cardiac surgical settings, and also in non surgical settings such as medical patients, are an important and effective intervention that should be used in many circumstances.
But the trial showed some other findings that I think are at least if not more important, and I think are particularly relevant of those of us looking after surgical patients. This is where it differs from the medical (ie non surgical) situation. We know as anaesthetists that peri-operative beta blockers increase the risk of bradycardia during surgery and in the intensive care setting afterwards there is a higher incidence of hypotension. We know that. And therefore in this setting with patients with known coronary artery disease they are also at risk of other complications – organ failure, and in particular stroke. This is where I think the POISE study is very important. The POISE study demonstrates that overall there is an increased mortality and a higher incidence of stroke with peri-operative beta blockers. Therefore we have to weigh up the potential benefits to reduce myocardial infarction with the now demonstrated increase risks of stroke and death. And that’s were we are now.
The dose of metoprolol used in the trial has been criticized by some commentators.
Yes I think this is an unfair criticism If the POISE study had been a negative study , the first point that would of been made by any commentators would have been that not enough beta blocker had been given. That is you didn’t properly beta block the patients. We know from both medical studies and the smaller trials in the surgical settings in the past that many patients who have been put on beta blockers are not adequately beta blocked. And many experts in the world strongly recommended that the target heart rate should be around about 60 beats per minute. Certainly less than 75 beats per minute. And in fact if you read the previous guidelines from the American Heart Association and the American College of Cardiologists, if you read the detail of those documents both in 2002 and updated as recently as December last year, they once again make that point , that you have to target a heart rate of around about 60. Now to do that you need to give quite a lot of beta blocker.
It’s different in the medical world because the average physician will up-titrate beta blocker therapy in a new patient. Slowly and carefully introducing the new therapy. We haven’t got that luxury in a peri-operative setting, because patients arrive often on the day of surgery or perhaps in the days earlier, or perhaps in a semi-urgent or urgent situation and we have to beta block them acutely. If you accept the guidelines then the dose was the correct dose to use in the trial.
Now it needs to be appreciated that the trial protocol allowed practitioners to stop the beta blocker on any particular day or to halve the beta blocker dose if the patient had unwanted bradycardia or hypotension. In fact only a relative small proportion of the 8000 patients needed that to be done. So in fact the dose used was probably the correct dose, it did allow for a dose reduction if there was unwanted bradiacardia or hypotension, and it did I think adhere to the guidelines.
One of the other things which has been criticized about the trial is the timing of the initial dose. What are your thoughts on that?
Well again, this is where I guess an ideal setting might differ from the real world. The medical experience of beta blockade is different from the surgical peri-operative situation that we are familiar with. In our setting we don’t have the luxury of these patients being seen in the weeks before surgery and having a slow titration of beta blockade.
The Mangano study was the pivotal study back in 1996. They beta blocked patients with atenolol an hour or so before surgery and that was really replicated in the POISE study . So I think it was a practical, realistic, and representative technique of peri-operative beta blockade.
Is there a need for more clinical trials with regard to this issue?
Well I think there is. I think the peri-operative beta blocker story is a very good example of many interventions in anaesthesia in peri-operative medicine. That is how we change our practice and what evidence is required before we change our practice. There now have been many excellent beta blocker studies and now the definitive POISE trial. Even so, we have some unanswered questions. As anaesthetists we need to understand there’s rarely a single landmark study that answers all questions once and for all. I think this study, the POISE trial, raises a few new questions. That is, could a lower dose of beta blockers be used more safely so you gain all the benefits of avoiding myocardial infarction but also avoid the risks of severe hypotension, stroke and increased mortality.
It also raises a question about patients who are all ready on beta blockers. The current recommendations by experts are still stating that the POISE results don’t apply to people who are already on beta blockers. In my own practice I am now more cautious about maintaining peri operative beta blockade, certainly at higher doses and certainly in patients who are at greater risk of major blood loss or fluid shifts or a stormy post operative course. So these are the studies that need to be done: lower doses, titrated doses, more targeted studies in patients who are in fact at very low risk of stroke or hypotension but at higher risk of unstable coronary syndromes.
Thanks Paul for your comments on the POISE trial and the peri-operative use of beta blockers.
How much information should be given to patients prior to anaesthesia. Some of our colleagues give a lengthy list of potential complications (including death) to low risk patients having minor procedures.......
Thanks to "Squiz" for the comment below.
As supraglottic airways gain greater acceptance, have they all but eliminated the need for intubation?
�What questions do you routinely ask an obese 60 yo male about sleep apnoea prior to major bowel surgery?
Here is one contribution:
OSA PATIENT
(Have a low threshold for sleep studies if anaesthetising in a hospital without an HDU).