Tuesday 25 July, 2006

How to stop warfarin for surgery

Posted in General Practice, Medicine, Michael Tam, Surgery, Wards at 20:14 by Michael Tam

Index: Anticoagulation :: Printer friendly

Original article by: Michael Tam

One would think that there would be guidelines on how, when or if warfarin should be ceased before surgery but the reality is that this is often not the case. I remember working as a surgical resident in the pre-operative clinic and having to make this decision on the fly. I can only hope that the anaesthetic registrar who conducted the (parallel) anaesthetic clinic knew what he or she was doing.

In a nutshell:

Low thromboembolic risk:

  • stop warfarin 5 days pre-op;
  • restart warfarin post-op as soon as oral fluids are tolerated.

High thromboembolic risk:

  • stop warfarin 4 days pre-op and start low molecular weight heparin (LMWH) at therapeutic dose;
  • stop the LMWH 12-18 pre-op;
  • restart LMWH 6 hours post-op (assuming haemostasis achieved);
  • restart warfarin when oral fluids are tolerated;
  • stop LMWH when INR = 2.0.

See below for details

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Monday 19 June, 2006

Anticoagulation for prevention of venous thromboembolism

Posted in Medicine, Michael Tam, Surgery, Wards at 12:19 by Michael Tam

Index: Anticoagulation :: Printer friendly

Original article by: Michael Tam

Note: updated in June 2009 with the eighth edition (from the seventh) evidence-based clinical practice guidelines from the American College of Chest Physicians.

Prophylaxis against deep venous thrombosis (DVT) and venous thromboembolic (VTE) disease is an important part of modern medical and surgical treatment for the unwell or bed bound patient. There is high quality research with high grade evidence for many recommendations.

For the majority of patients, the following is usually appropriate:

heparin 5000 units subcutaneously bd (tds for high risk)

or

enoxaparin 40 mg subcutaneously daily

+/-

graduated compression stockings

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Sunday 11 June, 2006

How to use local anaesthetic

Posted in Emergency Dept., General Practice, Michael Tam, Procedures, Surgery, Wards at 16:12 by Michael Tam

Original article by: Michael Tam :: Printer friendly

Local anaesthetic is one of the best inventions in medicine. It is difficult to imagine doing minor surgery, debridement, incision and drainage, repair of laceration, excisions, etc., without it, though we have only had infiltration local anaesthetics for about a century (with the creation of synthetic cocaine in 1891).

My first regular experience with infiltration local anaesthetics was in the emergency department. There was always a steady flow of people presenting with lacerations. At that time, I had always used whatever was available. However, there are some tricks to using “local”.

Where available and not contraindicated, use lignocaine 2% + 1:80,000 adrenaline

Simply, lignocaine 2% works better than lignocaine 1%. Adrenaline causes local tissue vasoconstriction, leading again to better and longer anaesthesia, and a less bloody field. Furthermore, as the adrenaline keeps the lignocaine in the local tissues longer, you are less likely to have systemic side-effects (meaning you can use more local anaesthetic).

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Saturday 10 June, 2006

Beware of serotonin syndrome

Posted in May Su, Medicine, Psychiatry, Surgery, Wards at 10:40 by May Su

Original article by: May Su :: Printer friendly

Serotonin syndrome is a medical emergency. It usually occurs when several serotonergic agents are used simultaneously or concurrently and is due to excess serotonin in the central nervous system.

Serotonin syndrome is a clinical diagnosis and a high index of suspicion is required:

Clinical features of serotonin syndrome (1)

Cognitive

  • confusion
  • agitation
  • hypomania
  • hyperactivity
  • restlessness

Autonomic

  • hyperthermia
  • sweating
  • tachycardia
  • hypertension
  • mydriasis
  • flushing
  • shivering

Neuromuscular

  • clonus
  • hyperreflexia
  • hypertonia
  • ataxia
  • tremor

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Sunday 14 May, 2006

IV fluid therapy in post-operative oliguria

Posted in Medicine, Michael Tam, Surgery, Wards at 20:54 by Michael Tam

Index: Intravenous fluid therapy :: Printer friendly

Original article by: Michael Tam

This is a common problem seen on overtime.

First step is to ensure that it is true oliguria. That is, make sure that the indwelling urinary catheter isn’t blocked or that there isn’t a post-operative urinary obstruction/retention (by physical examination of the abdomen and a ward bladder scan optimally).

“Low urine output” in a non-catheterised patient in the middle of the night is usually a furphy. My “urine output” is usually zero as well. Any patient with suspected oliguria needs an indwelling catheter and hourly urine output measurements.

Secondly, ensure that the patient doesn’t have pre-existing renal failure to explain the oliguria (look up the pre-op UECs).

Any urine output below 30 mL/h should be considered acute renal failure, but that doesn’t mean that a urine output of 40 mL/h is “okay”. Optimally, you should aim for a urine output of at least 1 mL/kg/hr.

Your target post-operative urine output is > 1 mL/kg/hr

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IV fluid therapy in post-obstruction polyuria

Posted in Medicine, Michael Tam, Surgery, Wards at 20:21 by Michael Tam

Index: Intravenous fluid therapy :: Printer friendly

Original article by: Michael Tam

Foley catheter

Urine output in these patients can be hundreds of millilitres per hour. This can lasts for a few days. Most commonly, these patients are post-operative urology patients.

The polyuria in these patients is partly physiological due to the expansion of the extracellular fluid during obstruction. A brief diuresis may not compromise fluid status as long as it is brief. The diuresis is generally electrolyte rich.

Nevertheless, there can be a substantial and huge loss of fluid leading to shock. These patients can literally lose their intravascular volume in a matter of hours. Given this is the case, these patients must have an indwelling urinary catheter and urine output measured on an hourly basis. Daily blood tests for electrolytes, urea and creatinine as well as serum calcium, magnesium and phosphate are a must.

Fluid choice: 0.9% NaCl (“normal saline”)

Rate: IV fluid rate (mL/h) = urine output of the past hour

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Friday 12 May, 2006

Standard post-operative fluid management in adults

Posted in Medicine, Michael Tam, Surgery, Wards at 17:07 by Michael Tam

Index: Intravenous fluid therapy :: Printer friendly

Original article by: Michael Tam

Not enough fluids?

Update (19 June 2011): This article is not consistent with current best evidence.  Please see the following comment. [Michael Tam]

Despite getting plenty of fluids intraoperatively, most patients are usually dehydrated after an operation. There are several reasons for this:

  1. Poor oral intake prior to fasting for theatre (e.g., due to anxiety)
  2. Prolonged fasting period pre-operatively (e.g., operating theatre delayed)
  3. Fluid and blood loss intra-operatively
    • direct blood loss
    • exposure of large internal surfaces to the heat and light of the theatre lights
    • fluid loss from respiration while intubated
  4. Post-operative ileus with third space losses of fluid into the bowel (especially after intra-abdominal and bowel surgery)
  5. Post-operative intravenous fluid therapy insuffient for maintenance and replacement.

Depending on the type and length of the operation, it is not uncommon for patients to be several litres “dry” in the post-operative period. In fact, unless you have specific knowledge otherwise, it is probably safe to assume that the patient is around 1-2 litres dehydrated. These patients would usually be otherwise asymptomatic. The aim is to rehydrate the patient to euvolaemia over a 24 hour period.

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Monday 1 May, 2006

“Maintenance” IV fluids in euvolaemic adults

Posted in Emergency Dept., Medicine, Michael Tam, Surgery, Wards at 17:37 by Michael Tam

Index: Intravenous fluid therapy :: Printer friendly

Original article by: Michael Tam

Bag of IV fluids

Bag of IV fluids

The easy (autopilot) way:

Assumptions:

  1. That the patient is relatively “normal
    • normal size
    • relatively well
    • no kidney failure
    • no heart failure
    • no electrolyte disturbance
    • no particular abnormal losses
  2. patient is “nil-by-mouth” (i.e., they have no other sources of hydration)
  3. patient is euvolaemic – i.e., not dehydrated or fluid overloaded.

If any of the assumptions are false, then you should seriously consider working it out properly. If they are all true, then you can use the following regimens (assuming standard 1L IV fluid bags):

Regimen One

  • Bag 1: 0.9% NaCl (“normal saline”) + 30 mmoL KCl (use premixed if available) then
  • Bag 2: 5% dextrose + 30 mmoL KCl then
  • Bag 3: 5% dextrose then back to Bag 1.

Regimen Two

  • Bag 1: 0.18% NaCl + 4% dextrose (“4% and a fifth”) + 30 mmoL KCl (use premixed if available) then
  • Bag 2: 0.18% NaCl + 4% dextrose + 30 mmoL KCl then
  • Bag 3: 0.18% NaCl + 4% dextrose then back to Bag 1.

Intravenous fluid infusion rate

  • Usual sized person: 125 mL/h (or “q8h”)
  • Smaller or older person: 100 mL/h (or “q10h”)
  • Tiny, old and frail person: 84 mL/h (or “q12h”) – though you shouldn’t be writing fluids on “autopilot” for the tiny, old and fail person.

You are hereby warned that imprudent use of “autopilot” therapy with intravenous fluids can (though rarely) harm your patients.

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