1.3: PREMEDICATION

Premedication is the administration of any medication before anaesthesia. With the advent of modern inhalation and intravenous anaesthetic agents, that have faster onset and fewer side effects, the once routine practice of prescribing premedication with strong sedatives and antisialogogue is now obsolete. Premedications should be specific to the individual patent, anaesthetic technique and procedure. The goals of premedication include producing anxiolysis, sedation, amnesia, analgesia and sympatholysis, and reducing salivation, gastritic volume and acidity, post-operative nausea and vomiting (PONV), and vagal induced bradycardia in children.

Aspiration prevention.

Pulmonary aspiration of gastritic contents is associated with significant perioperative morbidity and mortality especially if there is aspiration of solid particulate matter, a volume of aspirate greater than 0.8 ml/kg or a pH less than 2.5. All patents should be informed of fasting requirements and the reason for them. Compliance with fasting should be verified preoperatively. With adequate preoperative fasting the routine preoperative administration of aspiration prophylaxis is not recommended. The following drugs should only be preoperatively administered to patients at increased risk of pulmonary aspiration. Risks of pulmonary aspiration include inadequate fasting, emergency surgery, acute and chronic upper gastrointestinal pathology, delayed gastric emptying, pregnancy and opioid medication.

Gastrointestinal stimulants, histamine-2 receptor antagonists and proton pump inhibitors are all effective in reducing gastric volume and acidity. Non-particulate antacids are effective in increasing gastric pH. Colloid antacid suspensions are more effective than non-particulate agents however if aspirated produce significant and persistent pulmonary damage and should not be used. There is in sufficient evidence to support the administration of antiemetics or anticholinergics for aspiration prophylaxis. Patentis scheduled for a caesarean section should be administered a histamine-2 antagonist the night before and morning of surgery plus 30 ml sodium citrate 0.3 mol/l immediately prior to surgery. Currently, the validity and clinical utility of point of care gastric ultrasound to assess gastric volume is being validated.

 

Drug	Routine	Dose	Preoperative timing (minutes)
Ranitidine	Oral I.V	150 - 300 mg 50 mg	120 -180 60
Cimetidine	Oral I.V	300 mg 300 mg	120 -180 60
Omeprazole	Oral I.V	40 - 80 mg 40 mg	120 - 180 30
Metoclopramide	Oral I.V	10 - 20 mg 10 - 20 mg	30 - 60 15 – 30
Sodium Citrate 0.3 mol/l	Oral	30 m	15

 

Anxiolytics

Non-drug therapies are important in reducing preoperative anxiety. All patients and patients carers should have a non-time-pressured informative and interactive preoperative consultation where specific concerns are recognized, and the anaesthetic technique adapted to reduce these.Prescripton of preoperative anxiolytic drugs in adults is no longer routine. Benzodiazepines are the most commonly prescribed class of anxiolytics however clonidine is an effective alternative and may reduce PONV, analgesic consumption and post operative shivering.

Drug	Route	Dose	Preoperative timing (minutes)	Notes
Temazepam	Oral	0.3 mg/kg	60
Diazepam	Oral I.M	0.25mg/kg	120	Duration of action can be prolonged and unpredictable. Not recommended in children
Midazolam	Oral Nasal	0.5 mg/kg max. 20mg0.3 mg/kg	60	Bitter taste, needs to be disguised in a drink
Clonidine	Oral	4 μg/kg max. 150 μg	45 - 60
Ketamine	Oral	6 mg/k	30	Oral ketamine 3 -5 mg/kg +clonidine 3 μg/kg

 

Analgesics

All of the patient’s usual analgesics should be continued preoperatively, the exception being buprenorphine patches which should be ceased 7 days prior to scheduled surgery and replaced with an alternative. These have weak opioid action, but a high receptor affinity so can be problematic with post operative pain control. Oral paracetamol and nonsteroidal anti-inflammatory drugs are cheaper than and as effective intraoperative parenteral preparations.

Anticholinergics

As copious respiratory tract secretions do not occur with modern inhalation anesthetics,the use of preoperative anticholinergics is not routine. Scopolamine is a more potent antisialagogue than atropine, is less likely to increase heart rate and more likely to produce sedation. Glycopyrrolate is also a more potent antisialagogue than atropine but as is is a quaternary amine, it does not cross the blood brain barrier and therefore does not cause sedation. Intravenous atropine is a more potent vagolytic than glycopyrrolate or scopolamine. The vagolytic action of anticholinergic drugs is useful in preventing reflex bradycardia during surgery; however as the timing of reflex bradycardia stimulus during surgery is unpredictable, atropine or glycopyrrolate are best administered intravenously immediately before the stimulus.

Antibiotics

The goal of preoperative anabiotics is to prevent surgical site infection (SSI). Antimicrobial selection depends on desired anti microbial activity, safety, cost and pharmacokinetic profile. The antibiotic needs to be administered to achieve adequate serum and tissue levels for the entire duration of surgery. Cephazolin 2g IV (3g if > 120 kg) is often the drug of choice with an appropriate spectrum of action against streptococci, methicillin-sensitive staphylococci and many gram-negative bacteria. For patients with significant beta-lactam allergies or with a MRSA colonization or at high-risk of MRSA, vancomycin 15 mg/kg IV over 60 minutes (within 120 minutes before surgery) is an alternative. Patients having Gastrointestinal surgery should be administered metronidazole 500 mg IV in addition to Cephazolin. Antibiotics should be administered between 30–60 minutes before surgical incision. Repeat dosing is required when operating time exceeds two half lifes of the antibiotic (> 4 duration for Cephazolin) or if there is excessive blood loss.

In general antibiotic prophylaxis is required for:

Clean contaminated  (involve uncontaminated respiratory, alimentary, genital and urinary tract) Contaminated (open fresh accidental non-purulent wounds)Clean were infection would be catastrophic (prosthesis or implant)Prophylaxis for bacterial endocarditis or prevent infection in immunocompromised  patients

Usually, prophylaxis is not continued alter surgery but if continued should not exceed 24 hours. Pre-existing infections at surgical sites must be managed with an appropriate perioperative treatment regimen, not just prophylaxis before the procedure. Patients with burns may require prophylaxis against a wider range of bacteria including Staphylococcus aureus, Streptococcus pyogenes, Pseudomonas aeruginosa and aerobic Gram-negative bacilli. Antibiotic choice should be guided by the results of culture and sensitivity testing and local epidemiology.

Bacterial endocarditis prophylaxis

Prophylaxis is only recommended for patients with cardiac conditions that have the highest risk of infective endocarditis. This includes patients with prosthetic heart valves, prosthetic material used for cardiac valve repair, prior history of infective endocarditis, unrepaired cyanotic congenital heart disease, cardiac transplantation with subsequent cardiac valvuloplasty and some specific repaired congenital heart defects. Anabiotics may be required for dental work (amoxicillin), respiratory tract procedures, procedures on infected skin, skin structures or musculoskeletal tissue and cardiac procedures with prosthetic material.

 

Recommendation

Patients who are not in pain and not at increased risk of aspiration receive no premedication or only a sedative.

Patients at increased risk of aspiration receive histamine-2 receptor antagonist (e.g. cimetidine or ranitidine orally) one hour preoperatively and a non-particulate antacid before surgery.

Surgical antibiotic prophylaxis should be considered in all patients however only used if there is significant risk of infection.

There will be some patients that will need special premedication e.g. diabetics,asthmatics and those patients taking steroid treatment or anticoagulant treatment.