Tuesday, 26 May 2015

An unusual case of implantable cardioverter-defibrillator inhibition. MJA April 2015.

A case report in which a magnet in a maternity bra was found to be the culprit in interfering with an ICD. Magnetic fields of >10 gauss is sufficient to inhibit the device and the magnet in question exhibited field strengths of up to 800 gauss. This case highlights the danger of using magnets in clothing as they are a hidden source of electromagnetic interference.

Trial of early, goal-directed resuscitation for septic shock. NJEM April 2015.

Since 2002 the Surviving Sepsis Campaign has promoted best practice for the management of sepsis, including early recognition, source control, appropriate and timely antibiotic administration and resuscitation with intravenous fluids and vasoactive drugs. These recommendations are mainly based on a single centre landmark study by Rivers et al in 2001.

This randomised trial compared early, goal-directed therapy (EGDT, a 6 hour protocol) or usual care in 1260 patients with septic shock across 56 hospitals in England. There was no significant different in the primary outcome of mortality at 90 days among those receiving 6 hours of EGDT and those receiving usual resuscitation. Treatment intensity was greater in the EGDT group, including increased use of central venous catheters, intravenous fluids, vasoactive drugs and red-cell transfusion. This group also has significantly worse organ-failure scores and spent more days in ICU. There were no significant differences in any secondary outcomes including health-related quality of life or rates of serious adverse events. The use of EGDT also increased costs. This finding may be attributed to the short intervention phase of 6 hours or that techniques used in usual resuscitation have significantly improved over the last 15 years.

High-flow oxygen through nasal cannula in acute hypoxemic respiratory failure. NEJM May 2015.

High flow oxygen through nasal cannula has been widely used in the past decade (including in Westmead Hospital) despite the lack of evidence to support its use. This method provides a high concentration of heated and humidified oxygen through a nasal cannula, with flow rates from 40 to 60 litres per minute that generate low levels of PEEP. It is thought to be more comfortable for the patient and it also increase excretion of carbon dioxide.  This multicentre randomised trial is the first of its kind to demonstrate the effectiveness of high-flow oxygen therapy. 310 patients with acute nonhypercapnic hypoxemic respiratory failure were randomised to receive high-flow oxygen therapy, standard oxygen therapy through face mask or non-invasive positive-pressure ventilation. The primary outcome, the rate of endotracheal intubation, was lower among patients treated with high-flow oxygen than among those who received standard oxygen therapy or noninvasive ventilation, but the rates did not differ significantly (38% vs. 47% and 50%, respectively) (P = 0.18). However, in a post hoc adjusted analysis that included the 238 patients with severe initial hypoxemia (Pao2 :Fio2, ≤200 mm Hg), the intubation rate was significantly lower among patients who received highflow oxygen than among patients in the other two groups (P = 0.009). In the entire cohort of 310 patients, the highflow delivery mode significantly increased the number of ventilator-free days and also reduced 90-day mortality, as compared with standard oxygen therapy alone (P = 0.046) or noninvasive ventilation (P = 0.006). An editorial emphasising the significance of this finding is also available in this issue of NEJM.

The effects of continuous positive airway pressure on postoperative outcomes in obstructive sleep apnea patients undergoing surgery: A systematic review and meta-analysis. Anesthesia Anaglesia May 2015.

The objective of this review was to investigate the effectiveness of continuous positive airway pressure (CPAP) in reducing the risk of postoperative adverse events in patients with OSA undergoing surgery, the perioperative Apnea-Hypopnea Index (AHI), and the hospital length of stay (LOS). This systematic review/meta-analysis is the first to examine the effectiveness of CPAP therapy on postoperative adverse events, postoperative AHI, and LOS in OSA patients under- going surgery.

6 studies (with 904 patients in total) (3 observational, 2 RCTs and 1 case series) were eligible. There was no significant difference in the postoperative adverse events between the 2 groups (CPAP vs non – CPAP). The preoperative baseline AHI with- out CPAP was reduced significantly with postoperative use of CPAP (preoperative AHI versus postoperative AHI, 37 ± 19 vs 12 ± 16 events per hour, P < 0.001). However only 2 studies investigated this in their trial. LOS showed a trend toward significance in the CPAP group versus the no-CPAP group (4.0 ± 4 vs 4.4 ± 8 days, P = 0.05).

The main reasons for the seeming lack of benefit may be because of the low compliance in the preoperative and postoperative period (only 33% used CPAP for >4h post op).

Another important issue highlighted by the study is the lacks of RCTs to provide quality information regarding the use of preoperative and/or postoperative CPAP in OSA patients. The RCTs in this meta-analysis were also small studies. The impact of reduction in AHI, shortened LOS, and the efficacy of CPAP in postoperative adverse events need further investigation.


Peripheral regional anaesthesia and outcome: Lessons learned from the last 10 years. BJA February 2015.

This is a narrative review looking at the published data on efficacy and safety of the most common upper limb, lower limb and trunk peripheral nerve blocks over the last 10 years.

The paper sets out to collate all recent studies on the short and long term risks and benefits of regional blocks when compared to GA alone. This is a narrative review rather than a systematic review so there is no meta-analysis. The justification for this is the heterogeneity in techniques and outcome measures.

The description of improved outcome measures are pretty vague because they haven’t tried to collate the data from the RCTs but it is still a useful summary and helpful in terms of providing information for your patients when discussing risks and benefits for particular blocks. Also a good source of references for block related RCTs.

Notable points include:

  • Significant improvement in early recovery, opiate use, patient satisfaction and PONV for all regional techniques.
  • No recent publications supporting longer term benefits (day 14 onwards)
  • Higher than anticipated rated of neurological complications from axillary blocks
  • Improved recovery and post-op opiate use following TAP blocks for patients undergoing simple day surgery laparoscopic procedures.

Administration of parenteral prophylactic beta lactam antibiotics in 2014: a review. Anesthesia & Analgesia April 2015.

Perhaps this is a good time to review our antibiotic dosing given the recent Antibiotic Audit. Key points:

1. Dosing of antibiotics
Prophylactic antibiotics are given to minimise incidence of surgical site infections. The time from skin incision to a few hours after skin closure is a “decisive period” during which infection is established. Prophylactic antibiotics are most effective when given during this period, however they need to be given at a sufficient dose and frequency so that maximum tissue concentration occurs at the time of incision and tissue concentration exceeds the MIC (minimum inhibitory concentration) of potential microbial pathogens for the duration of this period.  Beta lactams (as well as clindamycin) are time dependent antibiotics, i.e. the fraction of time the drug concentration exceeds MIC is the primary determinant of effectiveness and it does not have any post antibiotic effect. Gentamicin is concentration dependent and has significant post antibiotic effect.

2. Timing
Antimicrobials need to reach the operative site before contamination occurs, and the tissue concentration exceeds MIC for the probable pathogen. Consensus seems to be 30-45min prior to skin incision, especially for obese patients (there is more tissue for the drug to travel).

3. Redosing
Cefazolin has plasma half life of 1.2-2.2h and should be redosed every 2 half lives thus every 4 hours; ampicillin redosed every 2h. Many suggest a continuous infusion after the initial prophylactic bolus injection is more effective in preventing plasma concentration falling below MIC.

4. Dose amount
Cephazolin: 1g <70kg; 2g >70kg and 3g if >120kg; the article does have a more complex dosing calculator.

5. Use of a tourniquet
First dose 15-45min prior to tourniquet application and then another dose after tourniquet release for joint replacements; continuous infusion is not logical.

6. In patients with penicillin allergy, the article suggests that the patient needs to have had a serious adverse reaction to dismiss cephazolin.

The April issue of Anesthesia and Analgesia is all about anaesthetists making a difference in hospital acquired infections. In fact bacterial transmission within the anaesthesia work area as the root cause of 30day postoperative infections occuring in up to 16% of patients undergoing surgery! A multi-modal approach is required to reduce the risk of “within patient” and “between patient” pathogen transmission and post-operative infection. This multimodal approach targets decontaminating the patients’ bacterial reservoirs and the anaesthetic working space, better IV access handling and stricter hand hygiene. Double gloving during intubation significantly reduces workspace contamination, analogous to surgeons double gloving during surgical draping. Speaking of IV access ports, a small studys showed that more bacteria was grown from stop cocks in patient who had propofol as part of their anaesthesia than those who didn’t. By 48h, the stop cocks with propofol had >100 times CFU! If propofol is used and the IV line is to remain in place, should we change the infusion sets or at least the stopcocks before the patients leave PACU? Knowing that we recently changed our practice to not change IV extension tubing in PACU prior to going to the ward…


Age of transfused blood in critically ill adults. NEJM April 2015.

This large multicenter RCT compared the transfusion of fresh red cells (stored for less than 8 days) with standard-issue red cells (the oldest compatible units available in the blood bank, up to 42 days) in patients admitted to ICU. It found no significant difference in the primary outcome of 90-day mortality, and also no significant differences in secondary outcomes of major illness, duration of respiratory haemodynamic or renal support, length of stay in hospital, transfusion reactions. This differs from the finding of a systematic review (Wang 2012) of 18 observational studies of 409840 patients and 3 RCTs of 126 patients which suggest transfusion of older red cells, as compared with new red cells was associated with a 16% increase in the risk of death.

Efficacy and safety of paracetamol for spinal pain and osteoarthritis: systematic review and meta-analysis of randomized placebo controlled trials. MJA February 2015.

This systematic review and meta-analysis of 13 RCTs (10 for  osteoarthritis, 3 for back pain) concluded that paracetamol is ineffective in the treatment of low back pain and provides minimal short term benefit for people with osteoarthritis of hips or knees. It also found that patients taking paracetamol are nearly 4 times more likely to have abnormal LFTs results but the clinical importance of this effect is uncertain. Is it time to reconsider the use of paracetamol in back pain and osteoarthritis?

Limitations of ultrasound-guided central venous cannulation & A quicker and more reliable method of excluding inadvertent arterial puncture during central venous line insertion (letters). Anaesthesia & Intensive care March 2015.

These 2 interesting letters remind us of the perils of central line placements using ultrasound. Practitioners must be aware of the anatomy, be skilled at cannulation, have ultrasound skills and be able to verify correct vessel placement. These letters discuss methods to minimise harm, and that the “use of ultrasound is only one element, and not a panacea” in central venous access.

On taking notice – learning mindfulness from (Boston) Brahmins. NEJM March 2015.

If you think "mindfulness" is a very relevant concept and at least a partial antidote in the mad world of modern medicine, this article is for you. Relax, get yourself a drink, sit back and enjoy a well written article that articulates beautifully how thinking "in the moment" can be a wonderful source of connection and reassurance for patients otherwise stressed by a busy system. All of us have many opportunities every day to enact this sort of behaviour, yes even in anaesthetic practice...

If you think "mindfulness" is a touchy feely concept for new age namby pambies, this article is also for you. You're just going to have to suppress that judgment for about 7 minutes until you've finished reading it. 7 minutes because you'll need 5 minutes of uninterrupted time to read the article and another 2 uninterrupted minutes afterwards to just sit, take it in, and look honestly for the relevant aspects to your clinical or personal life. If, after 7 minutes, your original point of view comes back, then give up trying to relax, you're beyond help... Give it a go.