Department of Anaesthesia University of Cape Town Anaesthesia Overview Anaesthetists are responsible for the peri-operative care of a surgical patient. This implies that they should be involved in the pre-, intra- and post- operative management of patients; in consultation with other clinicians, e.g. surgeons, physicians, intensivists, the primary care physician etc. Outline of an anaesthetic Each anaesthetic is divided into 3 distinct periods. First is the pre-operative visit where you meet the patient and make a plan and prepare for the anaesthetic. Second is the anaesthetic itself, which is further subdivided into induction, maintenance and reversal of anaesthesia. Last, and never least, is the postoperative or recovery period where the patient returns to full physiological functioning. Anaesthesia does no good to anybody! Anaesthesia facilitates surgery, i.e. renders the patient pain and movement free, allowing the surgeon to operate. Anaesthesia may severely effect normal physiological functioning. Anaesthetists are the patient’s guardian during this period, and must endeavour to maintain normal physiological functioning whilst administering the anaesthetic. 1. Pre-operative visit The pre-operative assessment is the subject of a separate tutorial. However, it is important to note that following a pertinent history, examination and perusal of the special investigations; the patient must be fully informed of the attendant anaesthetic risks and given an outline of the journey through the surgical period. This visit includes the premedication orders. 2. Anaesthetic period A) Pre-induction This comprises the machine, monitoring and equipment check, identifying the presence of emergency equipment and drugs and drawing-up the drugs to be used. The patient is prepared for anaesthesia, e.g. by establishing venous access and administering pre-induction drugs. B) Induction There are many methods to take a patient from wakefulness to anaesthesia, and the technique used is dependent on patient-, medical- or surgical- factors; as well as the knowledge and technical skills of the anaesthetic team. This is a high-risk period. The risks of induction come from equipment and monitor malfunctions, failure to recognise airway problems and untoward reactions to administered drugs; emphasising the importance of the pre-operative visit, meticulous preparation and the equipment check. C) Maintenance Once the patient has the chosen anaesthetic, be it regional (local) or general anaesthesia; it must be administered adequately to the appropriate level, and maintained until the surgery is complete. The anaesthetist must pay careful attention to the patient and monitor the patient on: (i) Clinical grounds - colour, feel, temperature, pulse volume, auscultation (ii) Non-invasive and invasive monitoring devices and (iii) “Point-of-Care” blood tests. Problems that may arise include peri-operative fluid shifts, blood loss and aggravation of pre- existing medical or surgical conditions. D) Emergence or reversal The patient is allowed to “lighten”, regain spontaneous ventilation and the ability to maintain their own airway and protective reflexes. This may simply mean removing the maintenance drugs, or administering antidotes. Postoperative placement of the patient is important and this may be to: (i) A recovery area or post anaesthesia care unit prior to returning to the ward (or home) (ii) A high care unit for more intensive monitoring or pain / fluid management or (iii) the intensive care unit (ICU) for further invasive monitoring and organ support. 3. Postoperative period No anaesthetic is complete until the patient is fully recovered from the effects of the anaesthetic drugs. Patients must be monitored until able to cope with all basic physiological functions. Pain management is crucial for relieving the patient from discomfort, both physical and psychological. Anaesthesia overview Aims of anaesthesia In order to render safe anaesthesia to patients, anaesthetists have developed drugs and techniques to the extent that there are few areas of the human body to which surgeons cannot have access. For general anaesthesia there are three main objectives, and treating each angle of this triad with specific drugs allows a lower total dose of each drug due to synergism and therefore less chance of severe side effects. This is called the TRIAD of ANAESTHESIA. Each point represents a separate issue as follows: HYPNOSIS ANALGESIA MUSCLE RELAXATION The TRIAD of ANAESTHESIA 1) Patients want to be awareness free = HYPNOSIS 2) Surgeons want patients to be movement free = MUSCLE RELAXATION 3) Anaesthetist wants the patient to be reflex free = ANALGESIA 1) Hypnosis (a) Psychological Hypnosis Time-consuming Unreliable (only 10 - 30 % of patients can tolerate surgery) Expertise not available (b) Chemical Hypnosis General anaesthesia: Intravenous anaesthesia - One dose – Induction agent - Continuous – Total intravenous anaesthesia (TIVA) Inhalational anaesthesia Sedation: Non-anaesthetic agents - All general CNS depressants may cause unconsciousness - Benzodiazepines, alcohol, phenothiazines, barbiturates Neuroleptic anaesthesia - Partial sedation whereby consciousness is altered enough to lose comprehension or resistance to procedure Ketamine Butyrophenones (droperidol or haloperidol) 2) Muscle relaxation (a) Restraints Some patients, once rendered unconscious, are physically restrained to assist the surgeon's view. Be aware of patients' neurovascular bundles to prevent injury. (b) Deep general anaesthesia This can be used alone to prevent movement, but this may result in high doses of drugs causing side effects. (c) Neuromuscular blocking drugs These drugs work on the neuromuscular junction and are divided into two groups: (a) Depolarising (b) Non-depolarising (d) Local anaesthetics In the correct place and at the correct strength, local anaesthetics are sufficient to cause motor nerve blockade with adequate muscle relaxation for surgery. 2 Anaesthesia overview 3) Analgesia It is preferable to use a multimodal approach to analgesia, combining several methods of pain relief: (a) Simple analgesics, e.g. paracetamol per os, per rectum or intra-venous (Perfalgan®) (b) Non-steroidal anti-inflammatories (NSAIDs) for surgical inflammatory pain, e.g. diclofenac (c) Opiates reduce pain inputs, i.e. inhibit the nociceptive pathway, e.g. morphine. Many routes of delivery, e.g. oral, intramuscular, subcutaneous, transcutaneous, epidural or spinal (d) Local anaesthetics block pain pathways (e) Serotonin and / or Noradrenaline agonists, e.g. tramadol The final aspect, perhaps the fourth angle of an anaesthetic quadrad, is monitoring of the patient. HYPNOSIS ANALGESIA MUSCLE RELAXATION MONITORING 4) Monitoring of the anaesthetised patient Central nervous system Clinical Monitors (1) Wakefulness / Verbal response (1) EEG and processed EEG (2) Pupil signs (i) BIS, Entropy (3) Respiration, if spontaneous (ii) Sensory evoked potentials (4) Autonomic activity, i.e. pulse and blood (2) Carotid blood flow pressure (BP) response to surgery (3) Jugular bulb blood flow (5) Motor response to surgery if not paralysed (4) Intracranial pressure Cardiovascular system Clinical Monitors (1) Pulse rate, rhythm, and character (1) ECG – s-T segment analysis (2) Capillary filling and colour (2) Pulse oximeter (O2 saturation and HR) (3) BP, jugular venous pressure. (3) Capnography (end-tidal CO2) (4) Auscultation (4) BP, invasive (intra-arterial) or non-invasive (5) CVP and / or Swan-Ganz (CVP, PAP, PAWP, CO) (6) Colour flow and / or 2-dimensional doppler (7) Trans-oesophageal echocardiography (TOE) Respiratory system Clinical Monitors (1) Respiratory rate, volume of breaths (1) Airway pressure (2) Inspection (2) Tidal volume (3) Auscultation (3) Respiratory rate (4) Palpation (4) Capnography (CO2 output) (5) Inspired Oxygen concentration (6) Oxygen saturation (pulse oximetry) (7) Arterial blood gases Metabolic / Renal Clinical Monitors (1) Hydration (1) Glucose (2) Temperature (2) Temperature (3) Urine output (3) Electrolytes (4) Arterial blood gases (5) Haematocrit / haemoglobin Peri-operative fluids (1) Expected fluid deficit (2) Maintenance fluids (3) Unusual losses, i.e. gastro-intestinal (GIT), blood, sweat (4) Third space losses. That volume lost to evaporation and sequestration at site of surgery 3 Anaesthesia overview Anaesthesia as a specialty Anaesthetists are peri-operative physicians, who have the task of examining; optimising; conducting the anaesthesia; recovering, and finally managing the postoperative analgesia and monitoring of a surgical patient. It must be re-emphasised that anaesthesia is not curative, has no inherent benefits (with some exceptions) and merely allows another clinician to perform the cure (the surgeon usually!). This, plus the fact that we remove all protective reflexes and substitute the normal oxygen supply for an artificial one, makes it particularly important that we do no harm. Safety of anaesthesia is paramount! “Primum non nocere” – Firstly, do no harm To perform this function, the anaesthetist needs to have certain skills and knowledge over and above the usual clinical and medical skills: Pharmacology is an important subject, as no other clinician uses the number of potentially lethal drugs as quickly and via the intravenous route as does an anaesthetist Physiology, particularly neurological-, cardiovascular-, respiratory-, renal- and hepatic- physiology are important; as we derange the normal homeostasis with the potent agents at our disposal A knowledge