title: Plasma magnesium should be monitored perioperatively in patients undergoing colorectal resection.
abstract: OBJECTIVE
  Hypomagnesemia has been shown to have several clinically important sequelae. The aims of this study were: to assess the impact of bowel preparation, with sodium picosulphate (Picolax), on plasma electrolytes, with particular regard to plasma magnesium, in patients undergoing bowel preparation for colonoscopy and colorectal resection and to evaluate the influence of perioperative magnesium levels on postoperative cardiac dysrhythmias.
  
  
  METHODS
  Sixty-one patients receiving sodium picosulphate (Picolax) bowel preparation were studied in two groups: Colonoscopy (31 patients) and Colorectal resection (30 patients). Plasma sodium, potassium, magnesium, calcium, urea, creatinine and blood haematocrit were measured in all patients prior to commencement of bowel preparation, at the time of colonoscopy or colorectal resection and 24 h postoperatively (surgery group only). Mean electrolyte and haematocrit levels were then compared. Postoperative cardiac dysrhythmias were recorded and analysed.
  
  
  RESULTS
  No significant changes following bowel preparation were observed in plasma sodium, potassium, calcium or creatinine. Plasma urea fell following bowel preparation (colonoscopy P < 0.001, resection P = 0.004) and rose following resection (P = 0.002). Magnesium levels increased following bowel preparation in both groups (colonoscopy P < 0.001, resection P = 0.007) and fell following resection (P < 0.001). Thirty-four per cent (21/60 patients) were hypermagnesemic following bowel preparation and 20% (6/30 patients) became hypomagnesemic following surgery. Postoperative cardiac dysrhythmias were associated with lower magnesium levels at induction and postoperatively (P = 0.022 and P = 0.033).
  
  
  CONCLUSIONS
  Bowel preparation with Picolax does not appear to cause significant electrolyte disturbance, except in elevating plasma magnesium. Postcolorectal resection plasma magnesium dropped significantly suggesting perioperative monitoring and replacement should be routine following colorectal surgery.
authors.affiliation: Department of Surgery, Princess of Wales Hospital, Bridgend, UK.
authors.forename: M D
authors.initials: MD
authors.lastname: Evans
authors.forename: K
authors.initials: K
authors.lastname: Barton
authors.forename: G A
authors.initials: GA
authors.lastname: Pritchard
authors.forename: E J
authors.initials: EJ
authors.lastname: Williams
authors.forename: S S
authors.initials: SS
authors.lastname: Karandikar
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001281:Atrial Fibrillation / Q000209:etiology*; D002400:Cathartics / Q000009:adverse effects*; D002951:Citrates; D003106:Colon / Q000601:surgery*; D003113:Colonoscopy; D005260:Female; D006801:Humans; D008274:Magnesium / Q000097:blood*; D008297:Male; D008875:Middle Aged; D009942:Organometallic Compounds; D010847:Picolines / Q000009:adverse effects*; D011182:Postoperative Care; D011300:Preoperative Care / Q000009:adverse effects*; D011446:Prospective Studies; D014883:Water-Electrolyte Imbalance / Q000097:blood / Q000139:chemically induced
chemical_list: D002400:Cathartics; D002951:Citrates; D009942:Organometallic Compounds; D010847:Picolines; D008274:Magnesium; C005701:picosulfate sodium