Anaesthesia Notes

AIRWAY ASSESSMENT Introduction Before anaesthetizing or sedating any patient it is important to examine the airway because the airway may obstruct and you may have to treat the obstruction. Sometimes the airway can be anatomically difficult to manage and such cases need to be identified. Failure to adequately treat airway obstruction can lead to hypoxia and death, which accounts for up to 30% of peri-operative deaths due entirely to anesthesia.

Factors that make airway management difficult: 1.

Pathological condition of face and oral cavity

2.

Trauma, burns and radiation to the head and face

3.

Cervical spinal injuries and immobility

4.

Beards, lack of teeth, obesity

Anatomical causes: Difficulty airway for anatomic reasons (3 key components): 1. The relationship between the size of the tongue and the pharynx 2. The mobility of atlanta-occipital joint 3. The size of the mandible and space for sublingual structures

Three bedside examinations to assess these three factors exist. The first two are most commonly used. 1. Mallampati Classification (alone not entirely predictive of intubation difficulty) The size of the tongue in relation to the size of the oral cavity is graded by how much the pharynx is obscured by the tongue. The patient is examined sitting. The head is neutral or slightly extended. The patient opens his mouth as wide as possible. The tongue is protruded as far as possible. Phonation may help. The assessor classifies the airway according to which oropharyngeal structures he can see: Class I

Soft palate, fauces, entire uvula, tonsillar pillars

Class II

Soft palate, fauces, uvula

Class III

Soft palate, base of uvula

Class IV

Soft palate only (uvula not seen)

There is a well recognized relationship between the ability to view faucial pillars, soft palate, uvula and the ease of laryngoscopy. Patients with a Class I airway will also have a Grade I laryngoscopic view almost 100% of the time and those with a Class IV airway will have a Grade III or Grade IV laryngoscopic view almost 100% of the time.

Above: Mallampati classification of the upper airway based on tongue size & pharyngeal structures seen on mouth opening. Below: The four grades of laryngoscopicview of the laryngeal aperture.

Limitations of Mallampati Airway Classification: 1. Does not consider cervical spine mobility 2. Does not evaluate mandibular space size 3. Significant inter-observer variability

Atlanto-Occipital (AO) Joint Extension Successful exposure of the glottic opening requires alignment of the oral, pharyngeal and laryngeal axes (the "sniff' position) and this is most easily achieved when the neck is moderately flexed on the chest and the head is well extended on the neck. Normal AOJ extension > 35o.

The patient is asked to extend the neck in the sitting position. Inability to extend the neck sufficiently suggests that intubation will be difficult.

Figure: shows the head in sniffing poison with the AO joint extended. Provided the head is sufficiently flexed at the AO joint and the posterior tongue can be displaced anterior by the laryngoscope, then the glottis should be visualized.

Mandibular Space This is the space within of arch of mandible, and forms the floor of the mouth. During laryngoscopy the tongue is pushed into the space by the blade. If the mandible is too small, there will be insufficient room for the tongue to be displaced forward and the post tongue and epiglottis will obstruct the laryngoscopic view of the glottis.

The size of mandibular space can be estimated by measuring the distance between the thyroid cartilage (or hyoid bone) and the inside of the chin (mentum). If the thyroid-mental distance of less than 6 cm (or hyoid-mentum distance of less than 3 cm) then laryngoscopy will be difficult.

The Dental Exam Teeth can be damaged by the laryngoscope. The anaesthetist should be aware the condition of the patients teeth. There may be loose, missing or damaged/chipped teeth. Dental prosthesis may also be present, such as crowns, bridges, dentures and braces. It is important to note if any problem with dentition exists ahead of time, since if it is discovered later, you will not know if occurred at the time of intubation. Many patients is Hong Kong have severe periodontal disease with poorly secured loose teeth.

Previous Airway History The patient’s medical record should be carefully examined for a history of previous difficulty with airway management. Make note of previous findings with mask ventilation and with laryngoscopy.

AIRWAY MANAGEMENT The patient is intubated using a size 7.0 for female, or 8.0 for male, plastic cuffed endotracheal tube, which is tapped to the face and connected to breathing system (usually a circuit with CO2 absorber).

Endotracheal tube with pink hitch-hiker. Note the cuff (deflated) and pilot balloon (blue). The syringe is used to inflate the cuff. The tube is disposable and make of non-allergenic plastic. The double black lines denote the level of the vocal cords.

Short procedures An endotracheal tube is often unnecessary and the airway can be maintained by (a) holding a face mask or (b) inserting a laryngeal mask airway. In such cases mechanical ventilation of the lung is often unnecessary.

Figure: Hand-held clear plastic anaesthetic face mask. Anaesthetist wears protective gloves. Mask is connected to the anaesthetic breathing system via a filter (blue).

Figure: Classical LMA or laryngeal mask airway (adult size 4). The cuff is inflated and sits in the patient's pharynx over the laryngeal opening. The classical LMA has been succeeded by a newer LMA, the ProSeal. The ProSeal has an improved cuff and drain tube (bougie in-situ) to prevent gastric aspiration.

Rapid sequence intubation During general anaesthesia the patient is unconscious and losses the protective laryngeal reflexes that prevent food entering the trachea and lungs (aspiration). In elective cases the patient is starved (nil by mouth) pre-operatively to make sure that there is no food in the stomach that can be regurgitated and aspirated.

The normal guidelines are ‘2,6,8 rule’ for adults and ‘2,4,6,8 rule’ for children. 2,6,8 rule

2,4,6,8 rule

2 hours for clear fluid

2 hours for clear fluid

(* carbohydrate drinks help e.g. orange juice)

4 hours for breast milk

6 hours for non-fatty food (e.g. toast with jam)

6 hours for formula milk

8 hours for food with fat (e.g. steak)

8 hours for solid food

Some patients arrive in theatre for anaesthesia with potentially fully stomachs (i.e. emergency surgical cases, bowel obstruction or pregnancy) or are at higher risk of regurgitation (i.e. hiatus hernia or obesity). In these cases precautions need to be taken to prevent regurgitation and aspiration. The standard approach when inducing anaesthesia in such cases is to perform a rapid sequence induction and intubation with the patient lying supine.

Steps 1.

Pre oxygenation of the patient for 3-minutes: The air in the lungs is replaced with oxygen. If intubation proves difficult the anaesthetist now has more time to solve the problem before the onset of hypoxia. His time is increased to 5 minutes. (*SpO2 = 100%)

2.

Application of cricoid pressure: An assistant locates the cricoid ring situated just below the thyroid cartilage. Firm pressure downwards is applied with the first 3 fingers to the cricoid to occlude the oesophagus. This prevents regurgitation.

3.

Induction of anaesthesia using rapidly acting drugs: An induction agent (propofol) followed by suxamethonium are injected. Sleep and muscle paralysis (heralded by muscle fasciculation) occur within 60 seconds. Non-depolarizing muscle relaxants tend not to be used because of their slower onset of action.

4.

Efficient placement of the endotracheal tube with cuff protection: A cuffed endotracheal tube should be inserted without undue delay. The inflated cuff prevents subsequent aspiration.

5.

Verifying correct placement before releasing the cricoid pressure: - Verify that the endotracheal is placed in the treachea, not the bronchus/oesophagus (fatal) 1.

Direct vision

2.

See chest movement

3.

Auscultating bilateral axilla for breath sounds à instead of chest to prevent transmitted sound from collataeral chest leaving bronchial intubation undiagnosed (One lung collapse + V-Q mismatch: 要 lateral lie the patient)

4. Observe end tidal CO2 for 5 expiratory peaks (esophageal intubation could bring 2 peaks) Acid aspiration prophylaxis Pregnancy and labour are associated with high levels of acid in the stomach. If this acid is aspirated during induction of general anaesthesia it can lead to acid aspiration syndrome (Mendelson's syndrome). The lungs are a severely damaged by the acid and become oedematous. The patient will require intensive care treatment and may die. To reduce the risk anaesthesia is induced using a rapid sequence technique. Furthermore, the acid in the stomach is neutralized before inducing anaesthesia. At the Prince of Wales maternity unit 30 ml of 0.3Molar sodium citrate is routinely give to all women just prior to Caesarean section. Other antacid medications are prescribed at the discression of the anaesthetist. (+/- ranitidine)

Difficult intubation Patients anatomically difficult to be intubated can be identified by examining the airway pre-operatively. The vocal cords are difficult, or impossible, to visualize at laryngoscopy. A number of techniques exist to overcome the problem. 1. Bougies Most difficult to intubate patients can be intubated by use of a bougie which is passed into the larynx first and then the endotracheal is guided over the bougie into the trachea. * S.Tang: bend bougie within ET tube and don’t get through it [↓trauma to airway]

2. Laryngoscope A number of variations on the standard adult MacIntosh laryngoscope are available to help in the difficult patient.

Designs of laryngoscope used for intubating in difficult circumstances: Far left: classical straight bladed Magill laryngoscope (one of oldest designs) Centre: McCoy laryngoscope - has a lever & movable tip displace the epiglottis. Far right: shortened handle of a scope used in obstetrics where pendulous (large) breasts often make it difficult to position a regular scope. Also note the right handed MacIntosh blade.

3. Fibre-optic intubation The availability of fibre-optic scopes and video equipment has revolutionized the anaesthetic approach to difficult intubation. Awake or asleep, the patient can be intubated either orally or nasally by passing a scope under camera vision through the vocal cords and then guiding an endotracheal tube over the scope into the trachea. In difficult cases it is best to have the patient awake so that airway obstruction and hypoxia during the procedure is avoided. The airway of the patient will need to be anaesthetized with local anaesthetic in order that the patient will tolerate the procedure.

Figure shows a fibre-optic bronchoscope passing through the manikin's nose and into the trachea. Video picture of the carina and two main bronchi is displayed. In the real-life situation the nasal passage and upper airway would be anaesthetized with local anaesthetic. The scope would be passed through an endotracheal tube that could later be guided into the trachea.

Alternatives to intubation When difficulty with laryngoscopy arises it is not essential to have the patient intubated. For short procedures a face mask or laryngeal mask airway can be used to maintain the airway and administer anaesthesia. In more problematic cases one can perform a tracheostomy under local anaesthesia.

ANAESTHETIC DRUGS Induction: Propofol [or thiopentone], fentanyl and muscle relaxant [suxamethonium, atracurium or rocuronium] Maintenance: Nitrous oxide [or air], volatile anaesthetic agent [isoflurane or sevoflurane] and increments of opiate and muscle relaxants. Note that when muscle relaxants are used the patient needs to be ventilated. Reversal: The anaesthetic gases are turned off. Muscle relaxation is reversed using neostigmine and atropine. When spontaneous ventilation returns the patient is extubated. * Louis Mok: Neostigmine is cholinesterase inhibitor acting on all NMJ but Ach’s S/E includes bradycardia, so atropine is competitive antagonist of muscarinic cholinergic receptors (in myocardiocytes!!) to maintain heart rate (but it has faster onset than neostigmine so patient in reversal first↑HR than↓back to normal)

From left-to-right: Induction agents / Thiopentone and Propofol. Muscle relaxants / Suxamethonium, Atracurium and Rocuronium. Opiates / Fentanyl and Morphine. Reversal agents / Neostigmine and Atropine.

Additional information Thiopentone is thio-barbituate that was first used in the 1930s. It was the first intravenous anaesthetic induction agent to be used. It is a powder that needs to be dissolved in water. It is injected into a vein and sleep occurs with 1-2 minutes. Induction with thiopentone is very pleasant, has few side effects and its main disadvantage is a post anaesthetic hangover (compare to alcohol). Propofol is a recently introduced intravenous anaesthetic induction agent and has replaced thiopentone. It comes dissolved in intralipid which accounts for its white or milk like appearance. Unlike thiopentone, it causes little post anaesthetic hangover. It is also used as an infusion for anaesthetic maintenance (i.e. TIVA or total intravenous anaesthesia).

Suxamethonium is a short acting depolarizing muscle relaxant. It needs to be kept in the fridge to prevent degradation. Its rapid onset of paralysis makes it useful when rapid paralysis is needed, such as rapid sequence intubations (i.e. when the patient is at risk of gastric aspiration). Suxamethonium has many undesirable side effects which restrict its use. It causes muscle fasciculations on injection, muscle pains after use and may cause a number of life threatening conditions such as hyperkalaemia, prolonged (scoline) apnoea and malignant hyperpyrexia.

Atracurium is a new short acting non-depolarizing muscle relaxant. It needs to be kept in the fridge to prevent degradation. It has a novel method of deactivation (Hoffman elimination) that does not rely on hepatic or renal elimination. Rocuronium is also a new short acting non-depolarizing muscle relaxant. It also needs to be kept in the fridge to prevent degradation. One of the features of a new muscle relaxant drug that the anaesthetist desires is minimal respiratory (bronchospasm) and cardiovascular (hypotension) side effects. This was a problem with the older drugs like curare, alcuronium and pancuronium. Rocuronium has minimal side effects and thus its has become very popular.

Fentanyl is a short acting and potent opiate. It acts on "mu" receptors. It is a potent respiratory depressant and should not be used in the ward setting without proper patient monitoring and supervision. Morphine is the active ingredient of opium. It is very cheap and provides good analgesia for several hours. It is still the main drug used to treat severe pain.

Neostigmine is a cholinergic drug used to reverse non-depolarising neuromuscular block. It is the most potent cholinergic agent available. Cholinergic drugs are also used to treat myasthenia. Neostigmine has a number of unwanted cholinergic effects which include bradycardia and excessive salivation. Therefore, neostigmine is usually administered with atropine. The atropine blocks these secondary effects. Ideally neuromuscular block should be monitored using a nerve stimulator. Train of four (TOF) is a modality most commonly used. Four repeated maximal stimuli, at 0.5 s intervals, are given to assess the degree of motor block. If muscle relaxation is not fully reversed breathing will be inadequate and airway obstruction and aspiration may occur post operatively.

Nitrous oxide is an inorganic gas. It is a good analgesia as well anaesthetic in higher concentrations (above 70%). It is delivered by pipeline or cylinder. It is used with oxygen during general anaesthesia. In obstetrics mixtures of 50:50 nitrous oxide and oxygen (Entonox) are used to provide pain relief during labour.

Figure: Cylinders of oxygen (black and white) and nitrous oxide (blue). Normally the anaesthetic machine operates on piped gases. Gas pipelines seen far left (similar colour coding). The cylinders act as a secondary gas supply. The anaesthetist should check that the cylinders are full before each new patient.

Isoflurane and sevoflurane are potent anaesthetic vapours. 1-2% is sufficient to induce anaesthesia. At room temperature they are liquids easily vaporize with low boiling points (about 50oC). These agents have replaced Ether, chloroform and halothane. The two vaporizers contain Sevoflurane (left) and Isoflurane (right). Oxygen and nitrous oxide / air are passed through the vaporizer and the liquid anaesthetic vaporizes and enriches the anaesthetic mixture.

Motor block monitor (Train-of-four): -

electrodes attached to orbicularis oculi

-

stimuli at 60mA for 4 times, could be visualized / felt by palm put on muscle

-

in neurosurgery should suppressed to 0 contraction in 4 firings

-

in hepatectomy could tolerate 2 contractions

ANAESTHETIC PLANNING 1. Long operations The anaesthetist must consider the duration of the operation, although this can be difficult to predict. Extent and duration of surgery plays a major part in determining the type of anaesthetic technique chosen. Remember that the anaesthetist is not only responsible for providing anaesthesia but is also responsible for the patient's physiological wellbeing. During longer operations patients become cold, develop fluid and electrolyte deficit, accumulate drugs and develop pressure areas, all of which need attention.

2. Poor access to the patient It is very important that the anaesthetist has good access to the airway, intravenous lines and monitoring sites. Usually, this involves the head, neck and arms. Sometimes, the operation involves the upper part of the body, such thyroid, eye and dental surgery. In these types of surgery, the anaesthetist's access to the airway and upper limbs is restricted by the surgeons and sterile field. Hence, he/s must take precautions to secure the endotracheal tube, intravenous lines and patient monitoring because they may be dislodged during the operation. Re-inserting an endotracheal tube or re-sitting IV lines and patient monitoring during the operation can be very inconvenient, difficult and hazardous to patients in these types of surgery. Figure A: Eye operation. The anaesthetic machine, anaesthetist, tubes and monitoring have to be set-up at the foot end of the operating table. The surgeons sit around the patient's head and use the microscope. Figure B: Bleeding from the airway. The anaesthetist has to share the airway with the surgeon who is operating inside the mouth. Anaesthetic access to the patient is limited.

3. Blood loss The anaesthetist must evaluate potential blood loss during surgery. In addition to blood grouping the patient, he/s may also have to order blood in case the need to transfuse arises. The blood bank cannot issue blood products without typing and cross-matching the patient. The anaesthetist should consider the blood supply of the organs involved and their potential to bleed. When heavy blood loss is likely (>2 litres) coagulation will be effected as platelets and clotting factors are reduced. Stored blood is deficient in platelets and clotting factors. Therefore, platelets (4 units) and fresh frozen plasma (4 units) are also ordered. Figure: Unit of packed cells (upper left), unit of platelets (upper right) and units of fresh frozen plasma (frozen - lower left & thawed - defrosted right).

4. Distention of body cavities with gas Laparoscopic surgery involves the insufflation of gas (carbon dioxide) into a body cavity, usually the abdominal cavity. The gas distends the cavity and improves the view of internal organs. However, abdominal distention adversely effects the circulation and lung ventilation. These effects become a concern in very fragile (babies & the elderly) and sick patients.

5. Post operative respiratory failure Operations that involve the upper abdomen and the thorax result in injury to the muscles of respiration (i.e. abdominal, intercostal & diaphragm) and sometimes the lungs. This results in post operative pain and inhibits respiratory muscle movement. If lung function is already limited due to pre-existing lung disease, there is a high risk of post operative complications including infection and respiratory failure. The anaesthetist should be aware of the possibility and take appropriate measures. In moderate risk cases good quality pain relief (i.e. IV PCA or epidural infusion) and close attention to post operative respiratory function (i.e. chest physiotherapy) should be sufficient. However, in high risk cases admission to the intensive care unit with a period of post operative ventilation is needed.

6. Renal failure For any major surgical procedure acute renal failure is always a risk, especially if pre-existing renal impairment is present. Therefore, renal function should be assessed preoperatively and urine output measured hourly intra-operatively. The patient should be catheterized. Patients are at high risk of renal failure if their surgery is associated with prolonged hypotension, interference with the renal blood supply (aortic surgery) or circulating toxins (sepsis, bilirubin, free haemoglobin and some antibiotics).

7. Temperature regulation The development of hypothermia is of concern during any long operation. Hypothermia delays recovery and causes stress as energy stores are depleted to generate heat. This may lead to hypoglycaemia, particularly in babies, as liver glycogen stores are easily exhausted. Some groups of patients are at high risk of developing hypothermia, such as babies, the elderly and those with large areas of moist exposed skin (burns) or viscera. Example: Operation to remove the uterus and ovaries. The intestines (viscera) are exposed to cold and evaporation. This resulted in the patient's temperature decreasing intra-operatively for 37.0 to 34.5 °C.

Special equipment Some types of operation require specialized equipment, such as microscopes, X-ray machines, operating robots and specialized operating tables. This equipment can be bulky and place additional space limitations on the anaesthetist and his/her access to the patient. Figure: The operating robot in theatre 10. The patient is a small child who is hidden under the green-brown surgical drape. Note the positions of the operating table (left) and the anaesthetic machine (right). The anaesthetist has to cope with the presence of this sizable piece of operating equipment (far left: stand and multiple arms). Access to the patient is reduced. Advanced planning of the anaesthetic set up is needed to prevent mistakes.

ANAESTHETIST PATIENT INTERVIEW Introduction The pre-operative anaesthetic interview provides an opportunity for the anaesthetist to build up a professional relationship with the patient, the importance of which should not be underestimated.

Specific risks It is important medico-legally that the patient is informed about the common complication that may arise during the anaesthetic such as damage to teeth and exposure to blood transfusion. These are covered in by the anaesthetic consent form. Additional risks related to the medical condition may also need to be discussed.

Intensive care Following major surgery patients are often sent to the intensive care unit. This can be a frightening experience especially if the patient wakes up to find that he/she is unexpectedly intubated and ventilated. Therefore, one should warn the patient in advance of such experiences.

Choice technique Certain operations (i.e. Caesarean section and transurethral resection of prostate) can be performed under both regional and general anaesthesia. The anaesthetist should discuss the merits of each method with the patient.

Explanations Occasionally the anaesthetic involves a new or unusual procedure such as anaesthetizing the nose for awake fibre-optic intubation or injecting into the axilla or shoulder for a brachial plexus block. The patient may be surprised by such procedures. The anaesthetist may also need the patient's co-operation. One should discuss the procedure with the patient.

Fears and worries Many patients have concerns about the anaesthetic. They may have a friend or relative that has died or been aware during a previous anaesthetic. Such fears need to be talked through with the patient and the patient reassured.

Figure: Section F provides a summary of what the patient should be told about the anaesthetic and its risks.

ASA CLASSIFICATION ASA status refers to the American Society of Anesthesiologists physical status classification. It is a score of 1 to 4 that provides a general appraisal of physical health and anaesthetic risk. It provides a universally accept method of classifying anaesthetic risk.

*DC Chung: The classification is not very predictive to anaesthetic risk but reflects that the anaesthetist had completely appraised patient’s medical history.

ASA Physical Status Classification System ASA 1 A normal healthy patient ASA 2 A patient with mild systemic disease ASA 3 A patient with severe systemic disease ASA 4 A patient with severe systemic disease that is a constant threat to life ASA 5* A moribund patient who is not expected to survive without the operation ASA 6* A declared brain-dead patient whose organs are being removed for donor purposes * Additional categories added since June 2005 # Add an ‘E’ behind the class to indicate emergency, e.g. ASA class 1E

Examples of different ASA scores: ASA 1

A final year medical student with past good health admitted for a knee arthroscopy following an injury whilst playing football. A 35-year old secretary with past good health admitted for an emergency laparoscopic appendectomy. She has a two day history of abdominal pain.

ASA 2

A 45-year old school teacher admitted for a total abdominal hysterectomy for uterine fibroids. She is a type 2 diabetic controlled by oral hypoglycaemic drugs and diet. She has been a diabetic for several years and has no major complications from her disease. A 27-year old business man admitted for removal of nasal polyps. He has allergic rhinitis and bronchial asthma, for which he takes regular beconase (steroid) and ventolin inhalers.

ASA 3

A 75-year old man admitted for a transurethral resection (TURP) following an episode of acute retention of urine, due to benign prostatic hypertrophy (BPH). He has severe chronic bronchitis and is limited to walking only 100 yards on the flat before he has to stop to regain his breath. He has had numerous hospital admissions for his chest. A middle-aged insulin dependant diabetic admitted for an eye operation procedure. The patient is known to have significant renal dysfunction with high creatinine levels and she is CAPD.

ASA 4

A 60 year old woman needs a laparotomy of acute lower abdomen pain. She has known mitral valve disease and here exercise tolerance is limited to walk a few yards on the flat. She is on multiple heart medications and regularly attends the outpatient clinic. On examination she is visibly short of breath and her legs up to the ankles are swollen.

ASA 5

92-year old demented woman is admitted with a ruptured aortic aneurysm. She is hypotensive and struggling to breathe.

ASSESSMENT OF CLOTTING MECHANISMS Described simply, the clotting mechanism is triggered by injury to blood vessels which releases tissue factor. Tissue factor activates platelets which adhere to the injured vessel wall. Platelets aggregate to form a plug that stops the bleeding. Tissue factor also triggers the clotting cascade. There are two pathways. The intrinsic pathway triggered by surface contact and the extrinsic pathway triggered by vascular injury. Both pathways feed into a common pathway (prothrombin & fibrinogen) which forms fibrin and a more permanent blood clot. Finally there are mechanisms that modulate clot formation (natural inhibitors) and breakdown clots (fibrinolysis and plasmin).

The integrity of this clotting process is vitally important during surgery, as impaired clotting leads to excessive intra-operative blood loss and post-operative haematoma formation with poor wound healing. Good surgical haemostasis depends on both platelets and clotting factors. Haemostais can be deranged for several reasons. Pre-operatively, the patient may have a low platelet count (2L or 4 units packed cells).

The most common reasons for anticoagulating a patient are (1)prosthetic heart valves, (2)non-rheumatic atrial fibrillation and (3)venous thromboembolism. Coumarins or warfarin are generally used. Warfarin inhibits vitamin K and the synthesis of the extrinsic pathway clotting factors II, VII, IX and X. The integrity of this pathway is assessed by measuring the prothrombin time (PT). As results form different laboratories vary, a normalized valve is use, the INR (International normalized ratio). The normal INR is approximately 1.0. The aim of warfarin therapy is to maintain the INR between 2.0 to 3.0. (An INR above 5.0 is dangerously high and may lead to haemorrhagic stroke or internal bleeding). During surgery the INR needs to be lower, less than 1.5. Regional anaesthetic techniques such as spinal, epidural and brachial block are contra-indicated in the anticoagulated patient because of the risk of haematoma formation at the site of needle puncture.

In most anticoagulated patients the warfarin can be stopped for 4-5 days before surgery and the INR will decrease to a safe level (