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Welsh Anaesthetic Trainees Journal Club

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January 2018

Journal Club: 30th January 2018

Assessing the accuracy of algorithm-derived cardiorespiratory fitness in surgical patients: a prospective cohort study. Canadian Journal of Anesthesiology 2017;64:361–369 doi: 10.1007/s12630-017-0812-5

Presented by:  Dr Owen Lewis

Background 

  • Widely appreciated that assessing cardiorespiratory fitness pre operatively is useful for estimating perioperative risk
  • Cardiopulmonary exercise testing (CPEX) is seen as gold standard test of cardiorespiratory fitness; however, it’s not practical for all patients to undergo CPEX testing.
  • The authors postulate that an algorithm which calculates a patients MET value based on: height, weight, waist circumference, resting HR, smoking status, and self reported fitness level will provide similar results to MET values calculated from the same patients 6 minute walk test (6MWT) and Duke Activity Status Index (DASI) and therefore be a more accurate way of quantifying cardiorespiratory fitness than simply asking how many flights of stairs they can climb

Design & Setting

  • Prospective cohort study
  • Two Tertiary hospitals in Alberta Canada

Subjects

  • Patients undergoing major elective surgery between May and September 2015 at above 2 hospitals.
  • Exclusion criteria:
    • ASA 1 or 2
    • Age <45
    • Blood pressure >180/110
    • Unstable angina
    • MI within last month
    • Heart rate >120
    • Taking B blockers
    • Going to be admitted to ITU post operatively
    • Physical or mental disability such that could not perform 6MWT

Intervention

  • All patients meeting inclusion criteria had there MET value calculated using the trial algorithm, 6MWT and DASI questionnaire.

Outcomes

  1. Correlation between trial algorithm MET score and 6MWT MET score
  2. Correlation between trial algorithm MET score and DASI MET score
  3. Correlation between trial algorithm MET score and 6MWT distance covered

Results

  • Trial algorithm and 6MWT MET score were highly correlated (Pearson R = 0.870, P <0.001)
  • Trial algorithm and DASI MET score were loosely correlated (Pearson R = 0.252, P <0.001)
  • Trial algorithm and distance walked in 6MWT were moderately correlated (Pearson R = 0.420, P<0.001)

Conclusions

  • Strong correlation between trial algorithm and 6MWT and as such could be considered as an alternative.
  • The fact that they excluded patients on B blockers meant low prevalence of heart disease in sample, limiting genralisability of results.
  • Their data suggests that DASI may over estimate cardiorespiratory fitness in those with a low 6MWT, but the number of patients with a low 6MWT in this study was very small and previous bigger studies have shown good correlation
  • There was no attempt in this paper to correlate calculated MET values with post operative outcomes
  • Further evaluation of this algorithm is warranted

Strengths

  • Attempts to answer a useful question
  • Prospective design
  • Seems adequately powered to demonstrate their outcome measure

Weaknesses

  • Effectively a single site study
  • Exclusion criteria significantly limit generalizability particularly excluding patients on B blockers
  • Half of those that met inclusion criteria declined to be in study, is this because they didn’t want a 6MWT and were less fit?
  • Didn’t compare their algorithm to CPEX (gold standard) and also didn’t compare to “current practice” i.e. just asking about flights of stairs or similar

Implications

  • Cannot apply study result to average set of patients seen preoperatively in the UK
  • No evidence as yet that MET score calculated this way is as accurate as CPEX or that it correlates to post operative outcomes and as such aids post op planning.

Potential for impact

Very limited impact at present but could be further evaluated in studies

 

 

 

Journal Club: 16th January 2018

Age-dependent decrease in desflurane concentration for maintaining bispectral index below 50. 
Acta Anaesthesiologica Scandinavica 60 (2016) 177–182 doi: 10.1111/aas.12642

Presented by: Dr S Hale

Background

Particularly since NAP5, the potential for awareness under anaesthesia is frequently discussed, and more anaesthetic departments are investing in depth of anaesthesia monitors. At the same time, more evidence now suggests an association between increased depth of anaesthesia and post-operative adverse neurological complications.

Design & Setting

The study hypothesised that the MACBIS50 would decrease with advancing age. Sixty patients requiring elective orthopaedic of GI surgery were enrolled into the trial. The investigators specifically looked at the MACBIS50 during the resting state, prior to knife to skin. Within each of the three age groups, they induced anaesthesia and intubated each patient with remifentanil and propofol (as desflurane is a respiratory irritant). A BIS monitor was attached prior to induction, and EEG measured for a set period. Desflurane was then started at a preset value once the BIS rose >60, using 8L/min driving gas.

After 10 minutes, a blinded observer monitored the BIS each minute. Within each age group, the starting Desflurane concentration was 4%. This was based on their unpublished preliminary study which showed that the MACBIS50/MAC ratio for sevoflurane was 0.6 for middle ages subjects. They applied the same ratio to the MAC of 6 for desflurane. If the patient had an average BIS < 50, they reduced the desflurane concentration by 0.5% for the next patient in that age group, or if it was >50%, then increased it by 0.5%.

The study was performed in Osaka City General Hospital, Japan.

Subjects

Twenty subjects for each group: Young (20-30 years), middle aged (31-65 years) and elderly (65-80 years). All were ASA I or II. Patients with asthma, arrhythmias, psychiatric illness, neuromuscular disease, ischaemic heart disease, LVEF <40%, Blood pressure <80mmHg, or serum Na ≤135 of ≥148mEq/l were excluded.

All patients were of a similar height and weight. Other demographics such as smoking status and ethnicity were not mentioned.

Intervention

The concentration of inspired desflurane was altered for each patient as described above. They then calculated the average desflurane used for each age group, using an up-down method and further logistical regression analysis. The two methods correlated relatively well.

Outcomes

The MACBIS50 did decrease with advancing age. The results were significantly significant using the up-down method. The MACBIS50 for the young was 4.25, middle ages 3.58, and elderly 2.75.

Results

The authors state that the statistics within this study do provide the necessary information to prevent awareness under anaesthesia when using desflurane. However, given the study was performed during the resting state, it does not provide information regarding probability of movement in response to surgical stimulation. During our discussion, the group concluded that it would neither predict BIS values once surgical stimulation is applied, and can therefore the conclusions cannot necessarily be relied upon to avoid awareness.

Conclusions

The MACBIS50  during resting state did decrease with advancing age.

Strengths

All of the 60 patients recruited completed the study. A preliminary study ensured adequate power of this study.

No patients reported awareness on questioning one day post operatively.

Weaknesses

There are a number of weaknesses within the trial. By excluding patients with a range of common medical conditions, their study population does not necessarily reflect the average NHS cohort of patients. They did not fully justify why they used MACBIS50. We still don’t really know what BIS50 means, and it likely to be different between individuals. We don’t know at what BIS value an individual can be predicted to lose or regain consciousness. BIS values do not predict movement to stimulus, and the degree to which commonly used opioids effect BIS are unpredictable.

The study used average BIS, rather than highest and lowest values.

Implications & potential for impact

We know that MAC50 decreases by 6% for each decade of life and many modern anaesthetic machines will display MAC values adjusted for age.

Although this study supports current evidence, a knowledge of the values for MACBIS50 for three wide ranging age groups of patients not being surgically stimulated, is unlikely to change every day clinical practice.

Journal Club: 9th January 2018

Does preoperative mechanical prophylaxis have additional effectiveness in preventing postoperative venous thromboembolism in elderly patients with hip fracture? – Retrospective case controlled study. PLoS ONE 12(11):e0187337 doi:10.1371/journal.prone.0187337

Presented by: Dr. Sebastian Willis          

Background

Elderly patients who undergo surgery following a hip fracture are at high risk of postoperative venous thromboembolism. This study set out to establish if pre-operative mechanical thromboprophlaxis conferred any additional benefit over an existing regimen of post-operative mechanical and chemical thromboprophlaxis in the prevention of symptomatic venous thromboembolism.

Design & Setting

Retrospective review of records for 614 consecutive patients undergoing surgery for femoral neck or intertrochanteric fracture between January 2012 and June 2016 at a university hospital in the Republic of Korea. The incidence of symptomatic, CT angiogram confirmed venous thromboembolism was recorded.

Subjects

614 consecutive patients over the age of 70 with femoral neck or intertrochanteric fracture. 75 patients were excluded. The remaining 539 patients fell into two cohorts;

  1. Those undergoing surgery from January 2012 to December 2014 received standard treatment (control group)
  2. Those undergoing surgery from Jan 2015 to June 2016 received study intervention (study group).

There was no process for matching subjects.

Intervention

  • Patients in the control group received a standard protocol of post operative mechanical and chemical thromboprophylaxis with tinzaprain.
  • Those in the intervention group received graduated compression stockings and intermittent pneumatic compression device pre-operatively and the same standardised protocol for VTE prophylaxis post operatively.

Outcomes

The incidence of symptomatic, CT angiogram confirmed DVT and PE occurring within 30 days of surgery.

Results

  • After multivariate analysis and adjustment for ASA grade, cardiovascular disease, neurological disease, and anticoagulant medication the incidence of symptomatic DVT was lower in the study group (7.4% vs 2.2%, OR 0.28 [0.08-0.95], P = 0.042).
  • The incidence of symptomatic PE was lower in the study group, though this difference was not statistically significant (3.7% vs 1.5%, OR 0.39 [0.09-1.77], P = 0.223).
  • The mean length of stay for the study group was significantly shorter than the control group (17.4 +/-8.5 vs 22.7+/-12.4, P = 0.043).
  • The study group had a significantly higher proportion of ASA III-IV patients (94% vs 84%, P=0.025).
  • The study group were significantly more likely to take anticoagulant or anti-platelet medication prior to admission (39% vs 28%, P=0.025)

Conclusions

Preoperative mechanical prophylaxis may confer additional benefits in preventing symptomatic VTE. More evidence in the form of randomised controlled trials is needed to confirm benefit and exclude confounding variables as the cause for the observed effect.

Strengths

  • This is the first study to suggest possible benefits of preoperative mechanical prophylaxis in hip fracture patients.
  • The study population was representative of the typical demographic of patients presenting with hip fractures as it retrospectively recruited all patients over 70 undergoing surgery for hip fractures.
  • There were relatively few exclusion criteria.
  • The study only presented data on symptomatic and therefore clinically significant VTE.

Weaknesses

  • This is an observational study, therefore there was no randomisation.
  • The authors described this study as a case control study. In fact it is an observational cohort study.
  • There was no patient matching between cohorts.
  • The two cohorts have significant demographic differences as described in the results, though some of these were adjusted for.
  • A further potential confounding factor not described in the paper is the influence of changing practice over time.
  • The two groups were temporally consecutive cohorts, so changes in management not recorded might affect outcomes. For example, recent emphasis on early mobilisation and rehab could influence VTE rates and was not accounted for in the study.
  • There was no mention of adverse events or undesirable side effects associated with mechanical prophylaxis, E.g. patient discomfort, barrier to mobility.
  • Exclusion criteria are not justified in the paper and seem to have been arbitrarily chosen. Example: Patients on warfarin are excluded but those on LMWH are not. Patients who are bed ridden and those who have a history of VTE are excluded despite these patients being at high risk of VTE.

Implications

The weaknesses of this study greatly limit the conclusions that can be drawn as confounding variables could explain the difference in rates of VTE.

Application

At this stage application is limited due to weakness of the study. Changes in practice will require further evidence of efficacy and safety before firm recommendations can be made.

Potential for impact

VTE is a significant complication of hip fractures and if further evidence supported the use of mechanical prophylaxis preoperatively there is potential to reduce a significant burden of disease.

 

 

 

January 2018

Written by Dr C. Williams

Sexual harassment in medicine – #MeToo. Jagsi R. New England Journal of Medicine 2017 doi:10.1056/NEJMp1715962

This is a short but highly interesting article looking at the phenomenon of sexual harassment in medicine. Currently it seems that not a week passes without the media filled with news of celebrities engaged in sexual misconduct. This article is written by a medical academic who has led a study of workplace sexual harassment in medicine. She describes the numerous incidents reported to her of sexual harassment in medicine and how victims often do not report incidents and the ones that do experience marginalisation, retaliation, stigmatisation and worse. Despite the #MeToo movement, reporting such behaviour is still not straightforward.

But what is sexual harassment. Working in an operating theatre still seems to be a male dominated environment and often an environment where lewd ‘locker-room’ humour dominates. But at what point does this humour cross the line into sexual harassment? One only has to have a few conversations with other healthcare professionals to start to hear stories, often told in jest, of incidences that clearly cross this line. I too have multiple stories which when looking at them objectively are clearly examples of unacceptable behaviour. I was relating one such experience to a colleague as a humorous story (which it was – although not so much at the time). I was asked to formally report the event……..but I didn’t, for several reasons, not least the concern that it would effectively be career suicide. This is also touched upon in the article.

This article concentrates on females being subjected to sexual harassment. But females aren’t the only ones affected. I have witnessed a male colleague being harassed by a bay of 80-plus year old female patients. If the situation had been reversed then I suspect there may have been a different attitude to the event by the female nursing witnesses.

The article mentions an interesting concept devised by academic astronomers. They recognised that mandatory reporting dissuades people so developed a rescue system, or a list of ‘astronomy allies’. These are senior female astronomers who wear prominent buttons at national society meetings and make themselves available to remove colleagues from problematic situations (www.astronomyallies.com). The aim is to provide ‘judgement-free’ help if someone believes it is needed. As the author points out, it raises questions about our society and how sexual harassment is viewed that such a system is required in a professional setting. Maybe such a system is needed in medicine. Much work is clearly still needed on this but the fact we are now openly talking about is a start.

Risk of epilepsy in surgical patients undergoing general or regional anaesthesia. Chang HC, Liao CC, Chang CC et al. Anaesthesia 2017 doi:10.1111/anae.14099

This study looks at the rates of new-onset epilepsy occurring in patients after surgery where they have had either a general or a neuraxial anaesthetic. It is well known that patients who have epilepsy, especially poorly-controlled epilepsy, are at risk, as are patients undergoing brain surgery, open-heart surgery or liver transplantation. But new-onset epilepsy is not something generally that many anaesthetists would consider although both stress and anaesthetic medication have been associated with epilepsy. Previous studies looking at this issue have had many limitations. This nationwide retrospective cohort study of patients in Taiwan sought to evaluate the one-year risk of epilepsy after surgery in patients receiving general or neuraxial anaesthesia.

The Taiwan National Health Insurance Research Database was used to identify patients. Over 200,000 patients were included in each group (general or neuraxial anaesthesia). During the one-year follow-up period the incidence of postoperative epilepsy after general anaesthesia was 0.41 per 1000 and after neuraxial anaesthesia 0.32 per 1000 persons. Compared with patients who had neuraxial anaesthesia, the risk of postoperative epilepsy significantly increased in patients with general anaesthesia when co-existing medical conditions and postoperative complications were included.

This study raises questions about the epileptogenic effects of various anaesthetic agents. But it has limitations. Information about blood biochemistry, lifestyle factors, genetic susceptibility, drug use and the anaesthetic agents used is not available on the database and these could have significant impact on the risk of developing seizures post-operatively. Further clinical studies are needed to be able to draw and firm conclusions.

Doppler-guided goal-directed fluid therapy does not affect intestinal cell damage but increases global gastrointestinal perfusion in colorectal surgery: a randomised controlled trial. Resigner KW, Willigers HM, Jansen J et al. Colorectal disease 2017;19(12):1081-1091 doi:10.1111/codi.13923

Fluid management for colorectal surgery has been much debated recently – should we aim for a restrictive fluid regimen or more liberal fluid treatment? It has been suggested that both restrictive and liberal fluid regimens induce hypo perfusion, the former due to local tissue oedema and the latter due to hypovolaemia. It is also now thought that fluid management in the first hours following surgery may be as important as intra-operative fluid management in improving tissue perfusion and oxygenation. Goal directed fluid therapy (GDFT) has been proposed as a way to reduce complicaations, mortality and length of hospital stay after major colorectal surgery. This study hypothesised that oesophageal doppler guided GDFT as opposed to standard fluid therapy decreased intestinal injury and improved gastrointestinal perfusion during surgery and in the first few hours after surgery.

Patients having elective colorectal cancer surgery with a primary anastomosis were enrolled either to have doppler guided GDFT or standard fluid therapy. All patients had an oesophageal doppler probe inserted and this was kept in situ for a maximum of six hours postoperatively or until the patient could no longer tolerate the probe.

Intestinal damage was determined by measuring intestinal fatty acid binding protein (I-FABP) plasma levels with increasing levels said to correlate with gut-hypoperfusion. Gastric tonometry measuring the intramuscosal carbon dioxide pressure was used to detect gastrointestinal hypoperfusion with the gastric tonometry catheter also left in place for six hours postoperatively.

Interestingly the amount of fluid given did not differ between the intervention and the control groups. The results also showed no difference between the I-FABP levels although the gastric tonometry results indicated better global gastrointestinal fluid perfusion in the intervention group. The clinical outcomes were not statistically analysed but there seems to be relatively little difference between the two groups, although the patients in the intervention group stayed a median of 11 days in hospital as compared to the control groups median of 8 day stay!

Unfortunately this study fails to shed any more light on the best way to manage fluid therapy during major colorectal surgery. Although the authors state that the gastric tonometry results indicated better global gastrointestinal perfusion it is not actually known whether gastric tonometry correlates with colonic perfusion. It is unlikely that these findings will affect current clinical practice anytime soon.

Sugammadex and oral contraceptives: is it time for a revision of the anaesthesia informed consent? Cora DM, Robards CB. Anesthesia & Analgesia 2017 doi:10.1213/ANE.0000000000002677 

This is an interesting letter to the editors raising concerns abut potential issues for women on oral contraceptives who receive sugammadex in the perioperative period. Sugammadex administration can cause certain drugs, including oral contraceptives, to becomes less effective due to lowering of the free plasma concentration. The letter goes on to point out that the drug information that comes with sugammadex states that ‘in vitro binding studies indicate that Bridion may bind to progestogen………the administration of Bridion is considered equivalent to missing dose(s) of oral contraceptives containing oestrogen or progestogen’. The makers of sugammadex recommend that is the patient is taking oral contraceptives and receives a dose of sugammadex then they should be advised to use an additional non-hormonal contraceptive method for the next 7 days.

Sugammadex is not the only drug administered in the perioperative period that could affect oral contraceptives. Many of the routinely used antibiotics can have a similar effect. Currently, there is little emphasis on discussion and counselling patients about these potential drug interactions. The authors suggest that a revision of the anaesthetic consent should contain a general statement to make patients aware that certain medications given during the anaesthetic may interfere with the effectiveness of oral contraceptives. Maybe this is needed but a good starting place would be raising awareness of the issue amongst anaesthetists – in my questioning of a cross-section of anaesthetic colleagues about this issue, no one was aware that sugammadex may interfere with oral contraceptives.

Surgery and discontinuation of angiotensin converting enzyme inhibitors: current perspectives. Bardic N, Povsic-Cevra Z. Current Opinion in Anesthesiology 2017 doi:10.1097/ACO.0000000000000553 

Angiotensin-converting enzyme inhibitor (ACEIs) have been used since the 1970s to treat hypertension with angiotensin II receptors blockers (ARBs) introduced in the 1990s. These medications, collectively known as renin-angiotensin system or RAS antagonists) are thought to work be four different mechanisms:

  1. Cardiovascular protection via reduction of ischaemia
  2. Improvement in cardiac function and short-term survival after myocardial infarction
  3. Antihypertensive effects
  4. Delay in nephropathic progression in diabetic patients

Their use in the perioperative period continues to be a subject of debate. Although the general consensus amongst many anaesthetists is that these drugs should be omitted during the perioperative period in the context intraoperative vasoplegia, previous studies and review articles fail to make any clear recommendations. Multiple studies suggest that patients who take ACEIs or ARBs to treat hypertension are at increased risk of developing severe prolonged hypotension intraoperatively, commonly immediately after induction of anaesthesia.

A large multicentre study published in 2017 (as part of the VISION study) compared patients given ACEIs or ARBs on the day of surgery versus withholding them for 24 hours preoperatively. Their findings suggest that withholding RAS antagonists before major non-cardiac surgery was associated with less risk for complications or death. However, the data from this study had various limitations and it is important to note that withdrawal of ACEIs after surgery is associated with a significant risk of fatal and nonfatal complications postoperatively.

Overall, this article gives a good summary of the recent evidence surrounding RAS antagonists during the perioperative period but still does not provide an answer to the question of whether these drugs should be withheld before surgery or not. It does makes some sensible suggestions as to how to manage these patients:

  • The decision to discontinue RAS antagonists should take into account the original indications for their use, the patient’s clinical status, variability in the patient’s blood pressure and the type of surgery
  • Special attention is needed in surgery with presumed larger blood loss or haemodynamic instability
  • If ACEIs or ARBs are discontinued, they should be restarted as soon as the patient’s condition allows.

Postoperative nausea and vomiting after unrestricted clear fluids before day surgery: a retrospective analysis. McCracken GC, Montgomery J. European Journal of Anaesthesiology 2017 doi:10.1097/EJA.0000000000000760 

Nil by mouth timing remains a contentious issue and a topic that continues to be discussed to great extent in the literature. Current European guidelines encourage the intake of oral fluids until up to two hours before induction of general anaesthesia. The reality is that many patients continue to be starved from the early hours of the morning before surgery and that it is difficult to give patients a true two hour cut-off time for clear fluids.

This study was carried out at Torbay Hospital Day Surgery Unit with a change in the day surgery policy permitting unrestricted clear oral fluids up until the time of transfer to theatre. The aim was to assess the incidence of postoperative nausea and vomiting (PONV) before and after the change to unrestricted pre-operative clear oral fluids.

A total of 11500 patients who received either sedation, general anaesthesia, regional anaesthesia or a combination were included. The results showed a reduction in PONV from 5.2% in patients who could not drink within 2 hours or surgery to 3.8% in patients who had unrestricted clear oral fluids. This suggests that the liberal consumption of clear fluids before the induction of day case anaesthesia reduces PONV.

During the time of the study there were no recorded adverse events of pulmonary aspiration of gastric content requiring patient admission. Since the conclusion of the study a further 10487 patients have undergone surgery on the ‘new’ day surgery pathway which continues to include liberal preoperative clear fluid consumption. During this time there was one episode of aspiration by a patient breathing via a supraglottic airway – the review of the case would suggest that possibly a supraglottic airway was not the most suitable choice for this patient!

This study does seem to present a strong argument that allowing clear oral fluids up until the time of transfer to theatre in day surgery patients is safe, reduces PONV, is not associated with increased episodes of aspiration and gives an improvement in patient satisfaction.

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