Chapter 13

As a junior doctor, you will be expected to perform procedures on your patients safely. As you become more senior, the complexity of the procedures will increase and the supervision will decrease. Just remember that practice makes perfect and the more procedures you do the more confident you will become.

This section is aimed to guide you through most procedures you will encounter as a foundation doctor. Becoming competent, safe and skilful in undertaking interventions to help patients is one of the great joys of medicine.

General hints

  • Obtain consent from the patient – often, verbal consent will suffice, but if in doubt, be sure to at least document that you have discussed the procedure and risks and that the patient agreed.
  • Never perform a procedure on your own unless you have been supervised at least once.
  • Never undertake a procedure where you cannot deal with all potential complications unless there is someone available who can. If you think there is a realistic potential for needing support it is better to prewarn them before embarking on the procedure.
  • Being methodical and having space and a spare pair of hands make procedures much easier. Before starting, get everything you need ready on a trolley. Mentally run through the procedure and check you have the necessary equipment at each stage. Take a sharps bin to where you are working or have a kidney dish ready. Make sure you have enough local anaesthetic, needles and gloves. If possible take extra equipment in case you fail first time round.
  • Consider taking the patient to a side room for the procedure, rather than performing it at the bedside which can be embarrassing for the patient and others on the ward. Always draw the curtains round.
  • A warm, confident approach is useful even if you are nervous. Try to avoid negative comments before a procedure: ‘you look like you have difficult veins, this may be a struggle’; this will simply heighten the patient’s anxiety and will diminish their confidence in you. It is, however, acceptable (and – in the case of a ‘difficult’ patient – advisable) to warn them that there is no guarantee that you will be successful the first time. Never promise you will get it first time – even the best miss sometimes!
  • Never be afraid to ask for help.
  • Wear gloves for all procedures. Remember that the most unlikely people have hepatitis B.
  • Nurses can help in positioning and reassuring the patient. They can also be those useful extra pair of hands when you are doing fiddly procedures.
  • Use local anaesthetic for all but the smallest procedures – it is a good habit to have.
  • Remember that you always have more time than you think, even during emergencies. If necessary, hand your bleep to a nursing or medical colleague.
  • Use every single opportunity to be assessed. Bring a supervisor and have them complete the assessment documentation immediately if at all possible.

Arteries in order of preference

  1. Radial – check collateral blood supply from the ulnar artery by asking the patient to make a tight fist and applying pressure over the radial artery. Ask the patient to relax the hand. If it remains white after 10 seconds, try the other arm (this is Allen’s test).
  2. Femoral – however, it is easy to hit the vein. You need to apply strong pressure to the puncture site for at least 5 minutes after taking blood.
  3. Brachial – use this as a last resort. Use a 20–22G needle. The problem with this artery is that it is an end artery and collaterals may be insufficient if it occludes.

Have ready

  1. Lidocaine 1% without adrenaline
  2. One 3 ml syringe
  3. One 23G (blue) and 25G (orange) needle (alternatively a 1 ml insulin needle with pre-attached syringe can work excellently and is even less painful than a 25G)
  4. Heparinized ABG syringe
  5. Alcohol swabs
  6. Sterile swabs/cotton wool balls
  7. Plastic bag or carton with a few ice cubes at the bottom

In lots of hospitals, two to four come made up in an ABG packet.

The procedure

(See Figs. 13.1 and 13.2.)

  1. Ask your colleagues where the blood gas machine is before taking an ABG sample (it is often in intensive therapy unit, accident and emergency (A&E) or the respiratory ward).
  2. Most ABG syringes come with heparin already in them. Expel the heparin completely – classical teaching states that excess heparin will cause an erroneous acidosis; however, in reality this is minimal and most effects are dilutional with a rise in PaCO2 and a fall in PaO2. You only need a few molecules of heparin to prevent the blood from clotting.
  3. Clean the skin and infiltrate superficially with a small bleb of local anaesthetic if there is no emergency.
  4. Hold the syringe at a 60–90° angle to the skin and slowly advance the needle. Keep very still and the syringe will usually fill due to arterial pressure with 1–2 ml of bright red blood. If this is not forthcoming, you can gently aspirate 1–2 ml; however, this often indicates a venous puncture that will be confirmed by the results.
  5. Withdraw and apply pressure for at least 3 minutes (5 minutes if the patient is anticoagulated).
  6. Expel all air from the syringe. Cap the syringe, gently roll between your hands and either take to the ABG machine immediately (within a maximum of 15 minutes) or place on ice and read as soon as possible (1 hour).
  7. Note the oxygen concentration that the patient is on. This is important for interpretation. Take the blood gas from the patient at least 10 minutes after a change in oxygen concentration. It is not acceptable to take a hypoxic patient off oxygen for a ‘baseline’ blood gas.

Figure 13.1 Radial arterial puncture.


Figure 13.2 Femoral arterial puncture: inguinal canal anatomy may be remembered using the mnemonic ‘NAVY’ – nerve, artery, vein and Y-fronts (!).

If you fail

  • Withdraw the needle to a point near the skin, redirect the needle, and try again. The artery is usually only a few millimetres under the skin; it is not unusual to transect the artery. Try aiming the needle at a shallower angle. This allows a steadier approach. Try not to remove the needle completely, as the two most painful parts are piercing the skin and then the artery. The artery is often more medial than you may think so re-angle the needle in this direction and you will be likely to be successful.
  • Try to avoid bones and tendons. If you hit a bone, withdraw whilst gently aspirating.


  • It is important to expel all the air from the sample to prevent erroneous readings of false oxygenation. Once this is done, ice only serves to slow cellular use of O2 which is negligible over 60 minutes.
  • Do not expect immediate ABG changes after adjusting someone’s O2 supply. It takes up to 20 minutes for the ABGs to equilibrate to a change in inspired O2 concentration, although 10 minutes is usually enough. If a reading looks suspiciously high or low, repeat it.
  • You can tell the difference between arterial and venous blood by its percentage saturation: 50% or less suggests venous blood, whilst 80% or above is certainly arterial – unless they have an arteriovenous shunt!

Interpreting ABGs

Normal ABG values are shown in Table 13.1.

Table 13.1 Normal ABG values.

pH 7.35–7.45
PCO2 4.3–6.0 kPa
Base excess ±2 mmol/l
PO2 10.5–14.0 kPa
Serum HCO3 22–26 mmol/l
O2 saturation 95–100%

Points to consider when interpreting ABGs

PO2 and PaCO2

First ask yourself: does the patient have abnormally low O2 for them? What is their baseline PaO2 value? Many patients with chronic respiratory disease live quite happily with a PaO2 of 7.5 kPa. Check the results of previous ABGs when the patient was well to see how much they have decompensated.

Next check if the patient is retaining CO2. This will determine the amount of O2 therapy you can give and will guide you to the degree that a respiratory component is determining their blood gas. The body never overcompensates; so if the PaCO2 is high, the patient is not ventilating adequately. The pH will tell you if the acidosis is of respiratory origin or if it is compensatory (if there is a metabolic alkalosis and the patient is hypoventilating to try and compensate for this).

Remember that the O2 saturation curve for haemoglobin (Hb) is a steep sigmoid curve that starts to plateau around a PaO2 of 9.1 kPa (70 mmHg). This means a patient may have a PaO2 of 8.5 kPa and still have better than 90% O2 saturation. However, in the steep part of the curve (PaO2 of 6–8 kPa), small changes in PaO2 dramatically affect O2 saturation and are clinically significant.


Check to see if the pH is normal or if there is an acidosis (pH <7.35) or an alkalosis (pH >7.45). If either exists, decide if it is metabolic or respiratory and whether or not it is compensated (see Table 13.2).

Table 13.2 Interpreting acid–base disorders.

Reproduced from Zilva J.F., Pannall P.R., Mayne P. (1989) Clinical Chemistry in Diagnosis and Treatment. Lloyd-Luke (Medical Books) Ltd, London.


Metabolic – early Normal Usually ↑
Metabolic – compensated Normal Normal or ↓
Respiratory – early Normal or ↑
Respiratory – compensated Normal ↑↑

Metabolic – early Normal
Metabolic – compensated Normal ↑↑
Respiratory – early Normal or ↓
Respiratory – compensated Normal ↓↓ Normal or ↑

A compensated acid–base disorder suggests chronic disease, over days to weeks, whilst an uncompensated acidosis or alkalosis suggests a more acute problem. In general, the body compensates for changes in pH by altering the respiratory rate (e.g. in metabolic acidosis, CO2 is ‘blown off’) and regulating renal excretion of HCO3. Respiratory compensation occurs much quicker (minutes) than renal compensation (hours to days).

Serum electrolytes (Na+, Cl and HCO3)

If the patient is acidotic, you will need to calculate the anion gap ([Na + K] − [Cl + HCO3]) in order to refine the differential diagnosis. A raised anion gap is due to the addition of unmeasured acid to the system, for example, methanol, urea, diabetes (ketones), paraldehyde, isoniazid, lactic acid (in anaerobic metabolism), ethanol and salicylic acid. A good mnemonic for this is ‘MUD PILES’.

A normal anion gap acidosis is usually due to loss of base, for example, from use of acetazolamide or other carbonic anhydrase inhibitors, diarrhoea and renal tubular acidosis.


  • A patient with a mixed picture or who is well compensated may have a normal pH. Check all the parameters of the ABG analysis, not just the pH and PO2.

    • If the results of the ABG analysis are very poor, you may have sampled venous blood.
    • ABGs will also give you results of several electrolytes such as K, Na, Ca, Cl as well as Hb. These are relatively accurate if the machine has been calibrated, so if they are grossly abnormal you should act to correct them. Always remember to send a formal set of bloods to the lab at the same time.

  • Patients with decompensated organ failure (e.g. cirrhosis, congestive cardiac failure, respiratory or renal insufficiency) may have developed acid–base and electrolyte disturbances over weeks. Do not be tempted to correct them in a day.

Respiratory disease and ABGs interpretation

Type 1 respiratory failure:

  • PaO2 less than 8.0 kPa (60 mmHg)
  • PaCO2 less than 6.0 kPa (45 mmHg)

If stable, their ABGs will reveal a compensated respiratory alkalosis.

Type 2 respiratory failure:

  • PaO2 less than 8.0 kPa (60 mmHg)
  • PaCO2 greater than 6.0 kPa (45 mmHg)

If stable, their ABGs will reveal a compensated respiratory acidosis. They will often have a very high bicarbonate.

Patients with type 1 failure progress to type 2 as they tire.

Bladder catheterization

Female nurses usually (but not always) catheterize women; you will certainly end up catheterizing men (whether you are a man or a woman).


Have ready

  1. Catheterization pack – kidney bowl, gauze swabs, sterile towels, etc.
  2. Sterile gloves – two sets.
  3. Cleaning solution, either normal saline or sterile water.
  4. Sterile tube of lidocaine jelly.
  5. 10 ml syringe and 10 ml sterile water (this often comes with the catheter).
  6. Several Foley catheters. For the first attempt, 14 F is the usual size. If you cannot pass a 14 F due to a large prostate, try a bigger size to circumnavigate benign prostatic hypertrophy.
  7. Urine bag and stand.

The procedure

  1. Get a clean trolley that has been swabbed with an alcohol wipe and place the catheter pack on it.
  2. Wash your hands thoroughly.
  3. Fully expose the patient’s penis. Make sure there are no bedclothes in the way that might dirty the working area. Urinary tract infections are easy to induce with catheterization.
  4. Tell the patient what you are about to do and why you are doing it.
  5. Open the catheter pack, and put sterile gloves, tube of lidocaine jelly, syringe, water and catheter onto the trolley in a sterile fashion. Pour the cleaning solution into a receptacle.
  6. Put on gloves.
  7. Drape the sterile towels to leave only the patient’s penis exposed.
  8. Gently retract the foreskin and clean the urethral opening with cleaning solution.
  9. Gently squeeze the contents of the tube of lidocaine jelly into the urethra. Give this 5 minutes to work and use the time to change your gloves to ensure you are as sterile as possible.
  10. Open the catheter wrapping at the tip end only and insert the catheter into the urethra, withdrawing the plastic covering in stages as you go. This is the trickiest part of the procedure. Make sure the end is in the kidney bowl to collect urine. You should get some urine back when you reach the bladder from all but the most dehydrated patients.
  11. If you feel resistance, gently pull the shaft of the penis upwards. Never use force.
  12. Once fully inserted, inflate the catheter balloon with 5–10 ml of sterile water by placing the syringe directly over the proximal opening (no needle) and pushing hard. Stop immediately if the patient experiences pain, as the balloon may be in the urethra. Once inflated, gently pull the catheter until you feel resistance of the balloon, indicating it is stable in the bladder.
  13. Always remember to gently replace the foreskin over the penis tip and document this in the notes. If you cannot, gently try again. If the foreskin genuinely gets stuck and starts to swell, get senior help immediately. Paraphimosis is a surgical emergency.
  14. Connect the end of the catheter to the bag and mount on a catheter stand.
  15. Document in the notes and record the residual volume.
  16. Send a sample of urine for microscopy, culture and sensitivity (MC&S).
  17. If the patient is septic, consider giving a stat dose of gentamicin IV/IM. Consult your local microbiology policy or discuss with your microbiologist if this is appropriate.

If you fail

  • The catheter may be blocked with jelly. Aspirate the catheter with the syringe or gently massage the bladder above the pubic bone to encourage urine flow.
  • The patient may have a large prostate or penile stricture. For strictures, a smaller size catheter should be used – proceed with care and be ready to abandon the procedure! For large prostates, larger catheters are useful, particularly stiff, silastic ones.
  • If after several attempts with different size catheters you cannot access the bladder, call for help. Even the most senior urologists have trouble sometimes and can show you tricks for really difficult urethras.

    Suprapubic catheterization is a useful last resort. It is useful to perform a bladder scan to get an idea of the bladder volume before such a procedure.


Have ready

Same equipment as for the men

The procedure

  1. Position the patient as for a vaginal examination. Ask her to lie flat on her back, knees bent, feet together and to allow her knees to fall down in full abduction.
  2. Part the labia minora and clean the area with cleaning solution.
  3. Locate the urethral opening just posterior to the clitoris and introduce a well-lubricated catheter tip. Female catheterization is usually much less problematic because they have no prostate and a short urethra.

Be aware of underlying causes for problems in catheterization such as tumours. If concerned, do a PV and call for help.

Blood cultures

If you are going to the trouble of doing blood cultures, it is better to do two sets from different sites, particularly if accurate diagnosis is important. Three sets for infective endocarditis are the gold standard.

Have ready

  1. One or two sets of culture bottles
  2. Two 20 ml syringes and needles or a vacutainer system
  3. Lots of alcohol swabs

The procedure

  1. Select a vein.
  2. Clean the skin with alcohol, from the centre out. Allow to dry for at least 30 seconds.
  3. Without relocating the vein, cannulate and withdraw at least 10 ml of blood for each set of cultures.
  4. Inject at least 5 ml into each bottle.
  5. Place in incubator as soon as possible.


  • It is not necessary to change needles between taking blood and inserting it into the culture bottles. There is increased risk of needlestick injury and little increase in contamination.
  • It is also unnecessary to clean flip-cap culture bottle tops. Try to avoid getting air in the anaerobic bottle.
  • The above technique is fine for easy veins. If not, keep your gloves sterile, as this will allow you to palpate for veins.


Have ready

  1. Tourniquet
  2. Needles (green or blue)
  3. Syringe(s) of adequate size for the bloods you need to take
  4. Alcohol swab(s)
  5. Cotton wool ball or small plaster
  6. Blood tubes
  7. A sharps container

Vacutainers are much quicker to use than needles and syringes but have no ‘flashback’ to let you know when you have entered the vein.

The procedure

  1. Put on gloves.
  2. Tell the patient what you are doing and why.
  3. Choose the preferred arm – not a drip arm; tighten the tourniquet above the elbow and find a vein.
  4. Alcohol swab the insertion area.
  5. Put the needle on the syringe. Holding the patient’s skin taut around the vein (tether it distally), gently advance the needle into the vein. After breaching the skin with the bevel up, make sure the needle is very shallow. With practice you feel the vein give way when you are through. You should get a small ‘flashback’ in the base of the syringe.
  6. Draw back the plunger until you have enough blood.
  7. Undo the tourniquet before withdrawing the needle.
  8. Apply pressure to the puncture site with cotton wool.
  9. Taking care not to needlestick yourself, insert the needle into the blood tubes and allow the vacuum to withdraw the blood. Some labs recommend that you remove the needle from the syringe, uncap the tube and gently squirt the blood directly into the tube. This prevents needlestick injuries. Never squirt blood into the tube through small needles as this risks haemolysis and false readings. The main benefit of vacutainer systems is avoiding this high-risk transfer of blood.
  10. Tidy up, especially sharps.
  11. Send blood to the lab.

Choosing a vein

Ask the patient for their preferred arm. Obvious forearm or cubital fossa veins are good. In dialysis patients, never use their arteriovenous (AV) fistula arm. Likewise, never use an arm with lymphoedema or one that has had its lymph nodes removed or irradiated.

If you can’t find a vein

  1. Hang the arm over the edge of the bed, ‘milking’ it or tapping the back of the hand. Hitting the skin releases histamine and brings up the veins.
  2. Use a sphygmomanometer; it is better than a tourniquet. Pump it up to diastolic pressure; you are aiming for the artery to fill the limb in systole but prevent venous drainage. Also, ask the patient to pump their hand. An experienced assistant who squeezes the arm may be equally effective.
  3. Immerse the arm or hand in a bowl of warm water for 2 minutes; pump the sphygmomanometer up with the arm in the water; dry the arm and quickly look for veins.
  4. If all else fails, a femoral stab can be much less painful than repeated failed venepuncture attempts. It is a useful skill to have and in periarrest or arrest situations is often the only way you will get blood.


  • Don’t overfill heparinized tubes – they will clot.
  • Paediatric tubes, which only require a few drops of blood, can be used for patients with very difficult veins (though your lab-based colleagues may disagree and question you when they note the date of birth!).
  • Find out from the labs how much blood is really necessary for standard tests at your hospital. Often you need very little, particularly for biochemistry. Clotting is usually the exception and requires a full bottle.

Cannulation (Venflon/line insertion)

(See Fig. 13.3)


Figure 13.3 Cannulating a vein.

Cannulation often worries junior doctors as it is something that they are routinely required to do and is initially a difficult skill to acquire. Anyone who tells you that they never had trouble cannulating is lying! That said, it is a skill that anyone can acquire but practice really is the only way to be good at this. Here we outline the basic procedure but the best way to learn is to get someone with good technique to show you.

Have ready

  1. Tourniquet
  2. Appropriate size cannula (see Table 13.3)
  3. Cannula dressing (wing shaped)
  4. 5–10 ml syringe
  5. Saline flush
  6. Alcohol swab(s)
  7. Cotton wool ball/small plaster
  8. Bandage and tape

Table 13.3 Cannula sizes.

Colour Size Use
Yellow 24G Paediatric or oncology patients and intravenous (IV) drug users
Blue 22G Small, fragile veins
Pink 20G Regular IV drugs and fluid administration
Green 18G Blood transfusions and fluids
White 17G As above – rarely available
Grey 16G Rapid fluid administration, GI bleeds
Brown/orange 14G Major bleeds, usually placed prophylactically in theatre

The basic procedure

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