Tips for Anaesthesia Attachments- understand the importance of and perform under supervision appropriate safety checks;
- practise the skills of:
insertion of an IV cannula;
creating and maintaining an airway in an unconscious patient;
ventilating a patient using the anaesthetic breathing system;
insertion of a supraglottic airway, for example an LMA, i-gel;
laryngoscopy and tracheal intubation;- discuss the principles of anaesthesia:
induction;
maintenance;
analgesia;
neuromuscular blockade;
emergence;- learn how to manage the intraoperative fluid requirements of surgical patients;
- discuss signs of adequacy and depth of anaesthesia.
There should be a smooth, controlled sequence of preplanned events from the time patients arrive in the anaesthetic room until they leave. This chapter aims to outline how, by applying the knowledge and skills from the previous chapters, the anaesthetist achieves this, thereby minimizing the risks of both anaesthesia and surgery. The descriptions given follow as closely as possible the sequence of events as they might be expected to occur during a normal anaesthetic.
Preoperative Checks
Checking the Anaesthetic Machine
It is the responsibility of every anaesthetist to check that the anaesthetic machine, monitors, breathing system and any ancillary equipment will function in the manner expected at the beginning of each operating session. The main danger is that the anaesthetic machine appears to perform normally but in fact is delivering a hypoxic mixture to the patient. Most modern integrated anaesthesia machines perform a ‘self-test’ when first switched on and do not need to be retested by the user. A check of the gas supply, patency and lack of gas leaks in the breathing system is essential. The function, calibration and alarm settings on the monitors should also be checked. The AAGBI publish a document entitled Checking Anaesthetic Equipment that gives more comprehensive details. A record should be kept of each check of the anaesthetic machine and equipment. Appropriate procedures must also be in place to deal safely with any machine failure.
Checking the Patient
Anaesthesia and surgery are not without risk. The World Health Organisation (WHO) has reported that in the industrialized countries, major complications occur in 3–16% of inpatient surgical procedures and permanent disability or death in 0.4–0.8%. To try and reduce this degree of harm, the ‘Safe Surgery Saves Lives’ project was introduced. One of the key components of this is the use of a ‘Surgical Safety Checklist’, which is completed in three stages:
- before the induction of anaesthesia (‘sign in’);
- before the start of the surgical intervention (skin incision or equivalent) (‘time out’);
- before the team leaves the operating theatre (or at skin closure or its equivalent) (‘sign out’).
Sign in
Preparation for Anaesthesia
Several things now happen, often simultaneously:
- monitoring equipment is attached to the patient;
- IV access is obtained;
- the patient is preoxygenated.
Once all of these have been achieved satisfactorily, the patient is anaesthetised.
Monitoring the Patient
This should commence before the induction of anaesthesia and continue until the patient has recovered from the effects of anaesthesia, and the information generated should be recorded in the patient’s notes. The type and number of monitors used depend upon a variety of factors including:
- type of operation and operative technique;
- anaesthetic technique used;
- present and previous health of the patient;
- equipment available and the anaesthetist’s ability to use it;
- preferences of the anaesthetist;
- any research being undertaken.
The AAGBI recommends certain monitoring devices as essential for the safe conduct of anaesthesia. These are ECG, non-invasive blood pressure (NIBP), pulse oximeter, capnography, and vapour concentration analysis. Clearly the latter two are only used after general anaesthesia has commenced. In addition, a peripheral nerve stimulator should be immediately available. Finally, additional equipment will be required in certain cases, to monitor, for example invasive blood pressure, urine output, CVP, and various haemodynamic parameters.
Recent recommendations from NICE are that all patients should have their temperature measured before induction of anaesthesia, and surgery should not be started (unless there is a critical need) if it is below 36 °C. Subsequently the patient’s temperature should be measured every 30 min. Active warming should be used as described below.
There is good evidence that monitoring reduces the risks of adverse incidents and accidents. The combination of pulse oximetry, capnography, and blood pressure monitoring will detect the majority of serious incidents before there has been serious harm to the patient. Ultimately, monitoring supplements clinical observation; there is no substitute for the presence of a trained and experienced anaesthetist throughout the entire operative procedure.
Monitoring is not without its own potential hazards:
- faulty equipment may endanger the patient, for example from electrocution secondary to faulty earthing;
- the anaesthetist may act on faulty data, instituting inappropriate treatment;
- the patient may be harmed by the complications of the technique to establish invasive monitoring, for example pneumothorax following central venous catheterization.
Ultimately, too many monitors may distract the anaesthetist from recognizing problems occurring in other areas.
Intravenous Access
The superficial veins on the back of the hand (dorsal metacarpal veins) and forearm (cephalic and basilic veins) are most commonly used for IV access. Veins in the antecubital fossa tend to be used either in an emergency situation or when attempts to cannulate peripheral veins have failed. It must be remembered that the brachial artery, the median nerve, and branches of the medial and lateral cutaneous nerves of the arm are in close proximity to the antecubital veins and easily damaged by needles or extravasated drugs. A cannula must not be sited in a patient’s arm on the side where the patient has undergone clearance of axillary lymph nodes for malignant disease unless there is no alternative because of the risk of exacerbating lymphoedema. The size of cannula inserted will depend upon its purpose: large-diameter cannulas are required for giving fluid rapidly; smaller ones are adequate for giving drugs and maintenance fluids. Peripheral venous cannulation is an essential skill, best learnt under the supervision of an anaesthetist, rather than reading about it! Complications of peripheral venous cannulation are shown in Table 4.1.
Table 4.1 Complications of peripheral venous cannulation
| • Failure: attempt cannulation distally in a limb and work proximally. If multiple attempts are required, fluid or drugs will not leak from previous puncture sites. |
| • Haematoma: usually secondary to the above with inadequate pressure applied over the puncture site to prevent bleeding, and made worse by forgetting to remove the tourniquet! |
| • Extravasation of fluid or drugs: failing to recognize that the cannula is not within the vein before use. May cause damage to the surrounding tissues. |
| • Damage to local structures: secondary to poor technique and lack of knowledge of the local anatomy. |
| • Air embolus: most likely following cannulation of a central vein (see below). |
| • Shearing of the cannula: usually a result of trying to reintroduce the needle after it has been withdrawn. The safest action is to withdraw the whole cannula and attempt again at another site. |
| • Thrombophlebitis: related to the length of time the vein is in use and irritation caused by the substances flowing through it. High concentrations of drugs and fluids with extremes of pH or high osmolality are the main causes, e.g. antibiotics, calcium chloride, sodium bicarbonate. Once a vein shows signs of thrombophlebitis (i.e. tender, red and deteriorating flow) the cannula must be removed to prevent subsequent infection or thrombosis. |
A small amount of local anaesthetic (0.2 mL lignocaine 1%) should be infiltrated into the skin at the site chosen for venepuncture using a 25 g (0.5 mm) needle, particularly if a large (>18 g, 1.2 mm) cannula is used. This reduces pain and makes the patient less likely to move and less resistant to further attempts.
As with any procedure where there is a risk of contact with body fluids, gloves must be worn by the operator.
Central Venous Cannulation
This usually takes place after the patient has been anaesthetised to allow monitoring of the cardiovascular system or to give certain drugs (for example, inotropes). Rarely, it is required before the anaesthetic is given because of lack of or inadequate peripheral venous access (for example in a patient who has a history of IV drug abuse). It is included at this point for completeness. There are many different types of equipment and approaches to the central veins, and the following is intended as an outline. It is now recommended that an ultrasound scanner is used to detect central veins and guide the insertion of the needle into the vein (Fig. 4.1).
Figure 4.1 (a) CVP catheter being inserted using ultrasound guidance. (b) Ultrasound screen showing relative positions of the internal jugular vein (IJV) and carotid artery (CA).
The Internal Jugular Vein
This approach is associated with the highest incidence of success (95%), and a low rate of complications (Table 4.2). The right internal jugular offers certain advantages: there is a ‘straight line’ to the heart, the apical pleura does not rise as high on this side, and the main thoracic duct is on the left.
Table 4.2 Complications of internal jugular vein cannulation
| • arterial puncture and bleeding causing haematoma or haemothorax |
| • air embolus |
| • venous thrombosis |
| • pneumothorax |
| • thoracic duct injury (left side) and chylothorax |
| • hydrothorax if the catheter is intrapleural and fluid given |
| • bacteraemia |
| • septicaemia |
| • soft tissue infection at puncture site |
| • injury to nerves: |
 brachial plexus |
 recurrent laryngeal |
 phrenic |
Subclavian Vein
This can be approached by both the supra- and infraclavicular routes. Both are technically more difficult than the internal jugular route and there is a significant incidence of causing a pneumothorax (approximately 2%). The main advantages of this route are comfort for the patient and low risk of infection during long-term use.
Bilateral attempts at central venous cannulation must not be made because of the risk of airway obstruction due to haematoma formation in the neck or bilateral pneumothoraces.
Equipment for Central Venous Catheterization
The techniques commonly used for percutaneous cannulation of the central veins are:
- Catheter over needle. Similar to a peripheral IV cannula, the main difference is that it is longer so that it reaches from the site of insertion to the superior vena cava.
- Seldinger technique. The vein is punctured initially percutaneously using a small-diameter needle. A flexible guidewire is then passed through the needle into the vein and the needle carefully withdrawn, leaving the wire behind. The catheter is now passed over the wire into the vein, sometimes preceded by a dilator. The advantage of this method is that the initial use of a small needle increases the chance of successful venepuncture and reduces the risk of damage to the vein.
Arterial Cannulation
This can be performed under local anaesthesia before the patient is anaesthetised or once the patient has been anaesthetised. The radial artery is most commonly used (femoral and brachial are also used) as it is superficial, compressible and there is usually good collateral circulation to the hand via the ulnar artery. It has been advocated that Allen’s test to check the adequacy of the ulnar circulation is performed before radial artery cannulation.
Technique of Cannulation
The wrist is fully supinated and dorsiflexed about 60°, often over a small support. The skin is cleansed appropriately and the position of the radial artery identified by palpation at the level of the proximal wrist skin crease. If local anaesthetic is used, a small volume (0.2 ml) is injected using a 25 g needle over and to either side of the artery. Two techniques are used to cannulate the artery:
- Direct puncture using a catheter over needle, either a non-ported IV cannula or a specifically designed arterial cannula with a built-in on/off switch. The skin is punctured at an angle of 20–30° and the needle point advanced toward as the artery. As the artery is punctured, arterial blood fills the flashback chamber. The needle should then be lowered to about 10° and advanced a further 1–2 mm to ensure the tip of the cannula lies within the artery. The cannula is then advanced off the needle into the artery.
- Seldinger technique. The artery is punctured directly with the needle as described above. Successful puncture is confirmed by getting pulsatile blood from the hub of the needle. The guidewire is advanced through the needle and the needle carefully withdrawn, leaving the wire behind. The catheter is now passed over the wire into the artery.
Once the cannula is in place, it is usually sutured to reduce the risk of accidental removal and covered with a transparent, sterile dressing.
Complications of arterial cannulation include bleeding, infection, thrombosis and aneurysm formation.
Preoxygenation
At the end of expiration, the lungs contain a significant volume of air that acts as a reservoir (the functional residual capacity, FRC). Amongst other things, this prevents hypoxaemia during brief periods of breath-holding. However, breathing room air the vast majority of the FRC is nitrogen. The purpose of preoxygenation is to replace the nitrogen with oxygen, thereby significantly increasing the length of time a patient can be apnoeic (or not ventilated), without becoming hypoxic; effectively ‘buying time’ for both the patient and anaesthetist in case of difficulty. Preoxygenation is usually achieved by getting the patient to breathe 100% oxygen via a close-fitting facemask for about 3 minutes or until the oxygen concentration in expired gas exceeds 85%. In an emergency situation a reasonable degree of preoxygenation can be achieved by asking a cooperative patient to take four vital capacity breaths of 100% oxygen via an anaesthetic circuit with a tight-sealing facemask.
Induction of Anaesthesia
Intravenous drugs are the most frequently used method of inducing anaesthesia. The drug dose is calculated, taking into account the patient’s age and any comorbidities, and then given over 20–30 s. This method is generally preferred by both the patient, as consciousness is lost rapidly, and by the anaesthetist because pharyngeal reflexes are depressed allowing the insertion of an airway device. There are a number of potential disadvantages:
- Patients often become apnoeic. This may necessitate manual ventilation until spontaneous ventilation resumes.
- There will be a varying degree of hypotension. This will depend on the drug, dose used, speed given, and ‘fitness’ of the patient.
- There may be loss of airway patency. This can usually be overcome by a combination of basic airway opening manoeuvres, insertion of an oropharyngeal airway or supraglottic airway device.
Inhalational induction of anaesthesia is an alternative. It is achieved by the patient breathing a gradually increasing concentration of an inhalational drug in oxygen or a mixture of oxygen and nitrous oxide. Its advantages are that it can be used in:
- Patients with a lack of suitable veins. Rather than subject the patient to repeated attempts at venepuncture, anaesthesia is induced and, as most drugs are vasodilators, venepuncture is then possible.
- An uncooperative child, or patients with a needle phobia. Venous access can be obtained after induction.
- Patients with airway compromise, in which an IV drug may cause apnoea and loss of airway patency. Ventilation and oxygenation become impossible, with catastrophic results. Inhalation induction preserves spontaneous ventilation and if airway patency is threatened, further uptake of anaesthetic is prevented, limiting the problem.
Potential disadvantages include:
- Unconsciousness occurs more slowly than with an IV drug.
- Most inhalational drugs are unpleasant to breathe. Currently, sevoflurane is the most popular anaesthetic used for this technique.
- Hypotension and a fall in cardiac output occur with increasing concentrations. This may be difficult to treat until IV access is obtained.
- The combination of hypercapnia, as a result of respiratory depression and the vasodilator effect of these drugs lead to increased cerebral blood flow, making this technique unsuitable in patients with raised intracranial pressure.
As the concentration of inhalational drug increases, there is progressive reduction in the ventilatory activity of the intercostal muscles, muscle tone generally is also reduced and laryngeal reflexes are lost. The pupils start by becoming dilated, then slightly constricted and finally gradually dilate. This point is referred to as ‘surgical anaesthesia’. Any further increase in depth of anaesthesia will result in diaphragmatic paralysis and cardiovascular collapse.
As well as the above, the anaesthetic will have effects on all of the other body systems, which will need appropriate monitoring.
Maintaining the Airway
General anaesthesia frequently causes the patient’s airway to become obstructed following loss of tone in the muscles of the tongue and pharynx (Fig. 4.2). The easiest way to restore patency is through basic airway manoeuvres; a combination of the head tilt, chin lift (Fig. 4.3) and jaw thrust (Fig. 4.4), in conjunction with an oro- or naso- pharyngeal airway. Although a patent airway can be maintained in the majority of patients in this manner it is increasingly uncommon as it severely restricts any further activity by the anaesthetist. This problem has been overcome by the use of a supraglottic airway device. The best method of providing and securing a clear airway in patients is tracheal intubation, but this is not appropriate in all patients.
Figure 4.2 Sagittal section of the head and neck showing how the tongue contributes to airway obstruction.
Figure 4.4 Jaw thrust. The application of pressure is behind the angles of the mandible. The thumbs can be used to open the mouth.
Oropharyngeal Airway
Estimate the size required by comparing the airway length with the vertical distance between the patient’s incisor teeth (or if edentulous, the front of the mouth) and the angle of the jaw. Then insert, the airway initially ‘upside down’, as far as the back of the hard palate before rotating it 180° and fully inserting until the flange lies in front of the teeth, (or gums in an edentulous patient) (Fig. 4.5a–d).
Nasopharyngeal Airway
Choose an appropriately sized airway, 7 mm for women, 8 mm for men, check the patency of the nostril to be used (usually the right) and lubricate the airway. The airway is then inserted along the floor of the nose, with the bevel facing medially to avoid catching the turbinates (Fig. 4.6a–c). A safety pin may be inserted through the flange to prevent inhalation of the airway. If obstruction is encountered, do not use force as severe bleeding may be provoked. Instead, try the other nostril.
Problems with Airways
- Although the techniques described so far will create and maintain a patent airway, they offer no protection against aspiration of regurgitated gastric contents.
- Failure to maintain a patent airway: snoring, indrawing of the supraclavicular, suprasternal and intercostal spaces, use of the accessory muscles, or paradoxical respiratory movement (see-saw respiration) suggest obstruction.
- Inability to maintain a good seal between the patient’s face and the mask, particularly in those without teeth.
- Fatigue, when holding the mask for prolonged periods.
- The anaesthetist not being free to deal with any other problems that may arise.
A supraglottic airway or tracheal intubation may be used to overcome these problems.
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