1 Laryngoscopy: time to change our view. Editorial -Anaesthesia. 2009 Apr;64(4):351-4.
This excellent editorial discusses the current dilemma when considering equipment available for advanced airway management. The recent introduction of many new devices, specifically video & optical laryngoscopes, has presented a large choice of potential (expensive) devices. All of these devices aim to reduce some of the limitations of the Macintosh laryngoscope, however unfortunately each intubation tool has not yet been evaluated in a large enough numbers of patients to conclusively determine whether it is as good as, or ideally better than the Macintosh in routine practice, let alone the difficult airway.
Take home message: The current gold standard laryngoscope (Macintosh) fails as often as 1 in 75 cases, with potentially life-threatening consequences, so level 1 evidence indicating superior performance for clinically relevant endpoints in an alternative device/devices would be very welcome.
For further reading about this topic this month: 1 Tracheal tube exchange: feasibility of continuous glottic viewing with advanced laryngoscopy assistance. Anesth Analg. 2009 Apr;108(4):1228-31 2 Use of the Pentax-AWS in 293 patients with difficult airways. Anesthesiology. 2009 Apr;110(4):898-904. 3 Expected difficult tracheal intubation: a prospective comparison of direct laryngoscopy and video laryngoscopy in 200 patients. Br J Anaesth. 2009 Apr;102(4):546-50.
2 Early exposure to anesthesia and learning disabilities in a population-based birth cohort. Anesthesiology. 2009 Apr;110(4):796-804. [Article]
Update on neonatal anesthetic neurotoxicity: insight into molecular mechanisms and relevance to humans. Editorial - Anesthesiology. 2009 Apr;110(4):703-8 [Editorial]
This population based retrospective birth cohort study (n=5,357) investigated the association between anaesthetic exposure before the age of 4 yrs and the development of learning disabilities (LD), namely language, verbal and math skills. The cohort was selected from a single state in the US and was originally created to study the incidence of learning disabilities in a population. Efforts were made to control for potential confounding factors including sex, gestational age and birth weight. The cumulative incidence of LD diagnosed by age 19 yr among those with repeated anaesthetic exposures (n=144) was almost twice as high (35.1%) compared with children not exposed to anaesthesia (20%; n=4764) or exposed to a single anaesthetic (20.4%; n=449). A further strength of the findings is evidence of a dose-response relationship and almost complete data for the subjects included in the study. Limitations of the study include a loss of the original study subjects due to emigration or death (n=2,830) and withdrawal of parental consent (n=342). Other potential confounding factors such as genetic, family and socioeconomic factors can be difficult to control for.
Further research is required to determine whether the anaesthesia itself contributes to LD or the need for anaesthesia is a marker for unidentified factors that contribute to LD i.e. burden of illness, stress response to surgical injury. The editorial refers to this study and other recent clinical and animal research that suggest anaesthetic agents are toxic to the developing brain and may be associated with long-term impairment of cognitive function and emphasizes the preliminary but provocative nature of this work. It also highlights the relevance of the ongoing trial comparing neonatal GA/spinal anaesthesia that was the subject of a recent editorial by local authors (Davidson, Anesthesiology, Dec, 2008).
Take home message: In this population based birth cohort, exposure to anaesthesia before the age of 4 yrs was a risk factor for the development of LD (Learning Disabilities) in children receiving multiple but not single anaesthetics. However, there is insufficient evidence to imply that multiple episodes of anaesthesia play a causative role in the development of LD.
For further reading about this topic this month: Behavior and development in children and age at the time of first anesthetic exposure. Anesthesiology. 2009 Apr;110(4):805-12.
3 Prediction and outcomes of impossible mask ventilation: a review of 50,000 anesthetics. Anesthesiology. 2009 Apr;110(4):891-7. [Article]
This is study should be compulsory reading for any ‘airway expert’ who is keen to avoid the dreaded CICV situation (hopefully all of us!). The author reports results from a large observational study (n=53,041), which aimed to identify predictors of impossible (not difficult) mask ventilation. Incidence of impossible mask ventilation was 1 in 690 and five independent predictors were identified: neck radiation changes, male sex, OSA, Mallampati III/IV and presence of a beard. Notably, 25% of impossible to ventilate patients were also difficult to intubate. Some traditional risk factors were not found to be significant in this study i.e. obesity, older age & lack of teeth. Limitations of the study included some junior anaesthesia providers and exclusion of patients who underwent awake FOB for predicted airway difficulty. It is also a shame that the analysis did not capture the presence or absence of muscle relaxant in the cases of impossible ventilation.
Take home questions:
1 Given that the presence of a beard is the only modifiable predictor for impossible mask ventilation identified in this study, if a patient has multiple risk factors for difficult mask ventilation, is it reasonable to ask them to remove their beard?
2 In view of the many differing versions of facemasks available in our workplaces, does any testing to ensure equivalent performance ever occur, and are anaesthetists involved in the purchasing decisions for this piece of equipment that can form such a crucial part of our airway crisis armamentarium?
4 Mortality related to anaesthesia in France: analysis of deaths related to airway complications. Anaesthesia. 2009 Apr;64(4):366-70. [Abstract]
Although the methodology of this article is not beyond reproach, it reveals information most anaesthetists will find compelling. The ‘airway deaths’ examined were identified from death certificates and the authors ‘calculated’ a decrease in perioperative ‘airway death’ from 1 in 7960 in 1978-82 to 1 in 48, 200 in 1999, although the methods for identification were completely different in the two time periods & denominators were estimated. It is fascinating to note that 83/131 of the respiratory deaths were associated with aspiration whilst only 16/131 deaths were attributed to initial difficult tracheal intubation. All but two of the deaths associated with difficult intubation were emergency cases. Other causes of death were late respiratory depression & intraoperative bronchospasm. The author emphasizes that inadequate preoperative airway evaluation played a role in some of the deaths especially when the case involved major ENT surgery. There was one death associated with initial LMA use, but is worth remembering this data is now 10 years old, and use of the LMA was less common during this time. Likewise, there was limited evidence of use of LMA for ‘airway rescue’.
Take home message: It is vital to use the evidence from studies which analyse the devastating anaesthetic complication of an ‘airway death’ to optimize our own airway expertise in an attempt to hopefully avoid such complications in our own practice.
5 Arterial pressure management and carotid endarterectomy. Br J Anaesth. 2009 Apr;102(4):442-52
This article is a review of the somewhat limited evidence for perioperative blood pressure management and CEA. It details the pathophysiology of hypertension in association with carotid disease, effects of cross-clamping/shunting and potential complications related to post-operative hypertension including wound haematoma formation & cerebral hyperperfusion syndrome. The potential influence of regional vs GA on blood pressure control is also mentioned but unfortunately there is only fleeting mention of the GALA trial (NEJM, 12/08). The author discusses the paradox anaesthetists are faced with when trying to avoid perioperative hypertension whilst being cognizant of the fact that over-vigorous antihypertensive treatment can predispose to cerebral ischaemia. The author gives practical (and occasionally evidence based) aims for pre-operative, intra-operative and post-operative blood pressure control and emphasizes the importance of communicating these aims to other staff involved in the ongoing care and monitoring of the patient.
Take home message: Poor arterial pressure control is associated with increased morbidity and mortality after CEA, but good control of arterial pressure is often difficult to achieve in practice because of the underlying pathophysiology of vascular and specifically carotid disease.
6 NICE-SUGAR: Intensive versus conventional glucose control in critically ill patients. N Engl J Med. 2009 Mar 26;360(13):1283-97 (Abstract)
Glucose control in the ICU--how tight is too tight? N Engl J Med. 2009 Mar 26;360(13):1346-9
This landmark large, multicenter trial, predominantly conducted in Australia & NZ, will have a major impact on glucose control in critical care. The results of the trial have been eagerly anticipated due to the current international controversy relating to inpatient glycaemic control and conflicting results of previous published research, which began in earnest with publication of the Leuven trial in 2001. Intensive and conventional glycaemic control were compared in a randomized, unblinded fashion in 6104 patients in the ICU, involving the use of intravenous insulin to achieve a blood glucose level of 4.5-6 mmol/l (n=3054) or a level of 8-10 mmol/l (n=3050), respectively. The study found an absolute increase of 2.6 percentage points in the rate of the primary end point, death at 90 days, with intensive glucose control (25.5% vs 24.9% with conventional glucose control; NNH 38). The odds ratio was 1.14 however it is worth noting the lower limit of the confidence interval approached 1: 1.02-1.28. Also worth noting is that the odds ratio for any cause of death at 28 days (a tertiary outcome) did not reach statistical significance and there was no significant differences found in the lengths of stay in the ICU or hospital or in organ-dysfunction rates between the two groups, despite higher mortality in the intensive group. An interesting feature of the patient selection was that only those expected to require treatment in the ICU on 3 or more consecutive days were eligible (excludes most step-down elective surgical patients, including routine cardiac patients). This selection criteria, presumably based on the 2006 medical ICU Van den Berghe study, obviously selects sicker patients for inclusion in this trial and relies on a subjective judgment on behalf of the treating doctors for eligibility. Most patients in both arms of the study received insulin: 97.2% of the intensive group received insulin vs 69% of the conventional group. The time weighted blood glucose from randomization to cessation of study treatment in the intensive group was 6.4+/-1 mmol/l vs 8+/-1.3 mmol/l in the conventional group to give an average glycaemic separation of only 1.6 mmol/l, in part due to failure to achieve target glucose in the intensive group. However more remarkable statistically significant differences between intensive and conventional groups include: the daily dose of insulin 50.2 vs 16.9 IU respectively, corticosteroid treatment 34.6% vs 31.7% respectively, episodes of severe hypoglycaemia (<2.2 mmol/l-potentially associated with neuroglycopenia) 6.8% vs 0.5% respectively. The scale of this study and the robust methodology is impressive but an obvious limitation of this trial was that 10% of the intensive group had the study treatment discontinued prematurely which effectively resulted in crossover to the conventional group however, study analysis was based on an intention to treat protocol. It is not possible to be sure whether the harm evident in the intensive group is due to reduced blood glucose level, increased administration of insulin, occurrence of hypoglycaemia, larger steroid dose or other specific methodologic factors or even the study protocol distracting from other aspects of patient care. The accompanying editorial commends the investigators & presents a perspective that, just because tight glycaemic control may not be good, the conclusion shouldn’t be that uncontrolled hyperglycaemia is good.
Take home message: The NICE-SUGAR trial suggests that a goal of normoglycaemia for glucose control (4.5-6 mmol/l) does not necessarily benefit critically unwell medical & surgical patients who are expected to require ICU for 3 or more days, and may actually be harmful compared to conventional treatment (8-10 mmol/l). However, the results of this study may not be generalizable to the perioperative setting and the study must be interpreted with the knowledge that there is ample evidence to suggest uncontrolled hyperglycaemia (>10 mmol/l) is associated with increased morbidity and mortality in a wide range of clinical settings.
7 Recurrence of cardiotoxicity after lipid rescue from bupivacaine-induced cardiac arrest. Anesth Analg. 2009 Apr;108(4):1344-6.
Editorial - Limits to lipid in the literature and lab: what we know, what we don't know. Anesth Analg. 2009 Apr;108(4):1062-4.
This case report details the neurotoxicity and cardiotoxicity resulting from a presumed intravascular injection of bupivacaine and subsequent resuscitation including lipid rescue. The outstanding feature of this case was the recurrence of cardiovascular instability 40 mins after completion of Intralipid in recommended doses. Unfortunately, the available stock of intralipid in the institution (500 ml) had already been used, leaving the team to rely on amiodarone to treat the ventricular arrhythmias encountered. The accompanying editorial discusses the emerging safety concerns & limitations of lipid therapy but strongly advocates its use within published guidelines (ie. AAGBI guidelines: www.aagbi.org/publications/guidelines/docs/latoxicity07.pdf).
Take home message: This case lends support to the AAGBI recommendation that at least 1000 mL of 20% lipid emulsion should be available in any institution where regional anaesthesia is practiced.
8 A preliminary report on the prognostic significance of preoperative brain natriuretic peptide and postoperative cardiac troponin in patients undergoing major vascular surgery. Anesth Analg. 2009 Apr;108(4):1069-75.
This study was a prospectively prespecified secondary analysis of data examining major adverse cardiac event (MACE) rates from patients undergoing aortic of infrainguinal peripheral vascular surgery (n=133). The initial trial evaluated the impact of the drug moxoidine in reduction of MACE and death. Moxoidine did not reduce event rate compared to placebo. The secondary analysis reported in this paper found a strong and additive prognostic value of preoperative BNP when combined with postoperative troponin for prediction of MACE (adjusted HR: 25.2 95% CI: 5-128.4) and all-cause mortality (adjusted HR: 18.7, 95% CI: 3.1-112.5) within 1 year of surgery.
Take home message: Further prospective evaluation is required to determine whether preoperative measurement of BNP will become a useful intervention in stratifying patients for cardiac risk and potentially indicating a high risk group who may benefit from postoperative measurement of troponin and appropriate medical intervention.
9 Patient safety incidents associated with airway devices in critical care: a review of reports to the UK National Patient Safety Agency. Anaesthesia. 2009 Apr;64(4):358-65. [Abstract]
Editorial - Airway incidents in critical care, the NPSA, medical training and capnography. Anaesthesia. 2009 Apr;64(4):354-7.
This paper presents an audit of airway-associated patient safety incidents submitted to the UK National Patient Safety Agency from critical care units in a 24-month period. Of note, many more incidents were post-airway management problems rather than intubation or tracheostomy insertion complications, although intubation problems were often associated with significant harm. Partial displacement of tubes resulted in more than temporary harm to the patient more frequently than complete tube displacement. Inadequacies identified included equipment failures and lack of suitably trained staff. Under-reporting is an obvious limitation of this study and the reported incidents will only have represented a convenience sample of all of the incidents that occurred in the time-frame. The accompanying editorial makes recommendations for the minimum training for those managing the airway in ICU as well as presenting evidence for a tracheal intubation protocols. The 4th national audit of the RCoA, which is evaluating major complications of airway management and is due for completion in late 2009, should reveal more.
Take home message: Lack of capnography in any critical care setting which cares for ventilated patients is unjustifiable and not having staff with adequate airway skills and the provision of adequate (functioning) equipment is likewise inexcusable.
10 The Hunsaker Mon-Jet tube with jet ventilation is effective for microlaryngeal surgery. Can J Anaesth. 2009 Apr;56(4):284-290
This paper reports results of a 10-year audit of patients undergoing microlaryngeal surgery with a Hunsaker Mon-Jet tube (n=552). The Hunsaker is a subglottic tube used in combination with an automated jet ventilator and advantages of its use include ability to monitor expired CO2, its laser safety and the fact it allows the surgeon a relatively unobstructed view of the larynx. The Hunsaker was exchanged for a laser-safe ETT in 15 cases (3%) because of actual or impending hypoxia, hypercarbia or both. The discussion includes tips for use of the Mon-jet tube & mention of the potential danger of barotrauma with the use of manual subglottic ventilation. The main limitations of the study are non-randomised, retrospective design and significant amounts of missing data.
Take home message: This observational study suggests subglottic ventilation via the Hunsaker Mon-Jet tube with an automated jet ventilator may be considered an effective, safe and versatile technique for the anaesthetic management of microlaryngeal surgery.
11 A meta-analysis of clinical screening tests for obstructive sleep apnea. Anesthesiology. 2009 Apr;110(4):928-39.
This metanalysis suggests that even the best validated screening tests for OSA can only be expected to reliably predict the diagnosis of OSA in patients with severe sleep apnoea (AHI 25-30). Only the Kushida index (morphometry: neck & oral cavity measurements; BMI) reproducibly performed as an excellent predictor in multiple validated studies with a false negative rate of 0-6.2%. Other tests that performed well were the Berlin questionnaire (false negative rate 8.1-38.2%), the Sleep Disorders questionnaire (FN 10.5-22.2%) and the clinical-cephalometry model (Battagel-requires skull X-ray). The tests that are easiest to use and useful for screening the diagnosis of severe OSA were STOP-BANG (FN 0-16.4%) and Berlin questionnaire. The STOP-BANG requires 4 questions: Snoring Tiredness (daytime) Observed apnoeas Pressure (HPT) & 4 ‘measurements’: BMI Age Neck circumference Gender. The Berlin Questionnaire is 10 item checklist consisting of 5 questions on snoring, 2 on excessive daytime sleepiness, 1 on sleepiness with driving and 1 about hypertension; the patient’s height & weight are also recorded.
Take home message: The ASA guidelines regarding perioperative management for OSA recommend careful assessment preoperatively to identify patients at high risk postoperatively. There is evidence that several OSA screening tests are likely to detect the patients with severe OSA who potentially present the highest perioperative risk for respiratory complications.
For further reading about this topic this month:
Identification of patients at risk for postoperative respiratory complications using a preoperative obstructive sleep apnea screening tool and postanesthesia care assessment. Anesthesiology. 2009 Apr;110(4):869-77.
Intermittent hypoxia and the practice of anesthesia. Anesthesiology. 2009 Apr;110(4):922-7.
Obstructive sleep apnea of obese adults: pathophysiology and perioperative airway management. Anesthesiology. 2009 Apr;110(4):908-21.
12 Epidemiology of anesthesia-related mortality in the United States, 1999-2005. Anesthesiology. 2009 Apr;110(4):759-65.
Innocent prattle. Anesthesiology. 2009 Apr;110(4):698-9. (Editorial)
This study relies on a complex process of identifying anaesthesia related deaths from US data files for the years 1999-2005 (n=2211). The identification of cases was based on the ICD coding of the death from the hospital records/death certificate, which could be seen as a major limitation of the study because they capture only a limited number of codes. There is also an attempt to estimate death rates from census & discharge data. The authors attribute anaesthesia as the main cause of death in 10.9% of the cases studied (n=241). The coding of the death led to classifications of anaesthesia related death that are not particularly clinically relevant ie. 46.6% were attributable to overdose of anaesthetics; 42.5% were attributable to adverse effects of anaesthetics in therapeutic use; 3.6% were attributable to obstetric anaesthesia complications and 7.3% were attributable to other complications. However, the most contentious claim of the article is that, based on the investigator’s calculations, the US has experienced a 97% decrease in anesthesia related death since 1940’s. The accompanying editorial is critical of the investigators using the new data to draw such conclusions because the methodology bears no resemblance to previous studies cited.
Take home message: The lack of a comprehensive data system monitoring anaesthesia exposure is a problem that has hindered research efforts in the US and other countries for many years, and greatly limits the accuracy of estimates relating to the risk of anaesthesia and anaesthesia death rates.
Other April articles of specific interest:
Choosing a lung isolation device for thoracic surgery: a randomized trial of three bronchial blockers versus double-lumen tubes. Anesth Analg. 2009 Apr;108(4):1097-101.
Non-cardiac implantable electrical devices: brief review and implications for anesthesiologists. Can J Anaesth. 2009 Apr;56(4):320-326
Upper extremity regional anesthesia: essentials of our current understanding, 2008. Reg Anesth Pain Med. 2009 Mar-Apr;34(2):134-70.
Does anaesthetic management affect early outcomes after lung transplant? An exploratory analysis. Br J Anaesth. 2009 Apr;102(4):506-14. NB: Expatriate author!