Non-invasive cardiac monitoring during anaesthesia

1. Electrocardiography (ECG)
   • Continuous ECG display is mandatory.
   • Measures heart rate, rhythm, conduction abnormalities, and ST-T changes suggesting myocardial ischaemia.
   • Lead II is useful for arrhythmia detection; V5 is sensitive for ischaemia detection.
2. Non-invasive blood pressure (NIBP)
   • Automated oscillometric cuff measures systolic, diastolic, and mean arterial pressure.
   • Select an appropriately sized cuff and place it at heart level.
   • Record BP at least every 5 minutes, or more often in unstable patients.
   • Limitations: inaccurate with arrhythmias, severe hypotension, vasoconstriction, movement, or improper cuff size.
3. Pulse oximetry with plethysmographic waveform
   • Gives pulse rate and a continuous pulse waveform in addition to arterial oxygen saturation.
   • A falling or poor-quality waveform may indicate reduced peripheral perfusion, hypovolaemia, hypotension, or vasoconstriction.
   • It does not directly measure cardiac output or blood pressure.
4. Clinical pulse monitoring
   • Palpation of peripheral pulse and/or auscultation of heart sounds helps confirm mechanical cardiac activity.
   • Useful to correlate with ECG, especially if ECG artefact or pulseless electrical activity is suspected.
5. Non-invasive cardiac output monitors, where indicated
   • Devices based on thoracic electrical bioimpedance/bioreactance, pulse-wave transit time, or Doppler techniques may estimate cardiac output and stroke volume.
   • Mainly used in selected high-risk surgery or haemodynamically unstable patients; accuracy can be affected by arrhythmias and altered vascular tone.

Apnoeic oxygenation

• During apnoea, oxygen continues to be taken up from alveoli into the blood.
• Carbon dioxide production is lower than oxygen uptake because much CO₂ is buffered in blood and tissues.
• This produces a net inward movement of gas from the upper airway to alveoli if the airway is patent, allowing oxygen to diffuse into alveoli.
• It maintains oxygenation but does not provide ventilation. CO₂ continues to rise and acidosis may develop.

1. Optimise preoxygenation first, preferably in a head-up position when appropriate.
2. Keep a nasal cannula in place during induction and laryngoscopy.
3. Administer oxygen through nasal cannula, commonly 10-15 L/min in adults, while attempting intubation.
4. Alternatives include high-flow nasal oxygen/THRIVE, which delivers warmed, humidified oxygen at high flow rates.

• Anticipated difficult laryngoscopy or prolonged intubation.
• Obesity, pregnancy, paediatric patients, severe respiratory disease, and low oxygen reserve.
• Rapid-sequence induction, particularly in patients at risk of rapid desaturation.

• Requires a reasonably patent upper airway. It may be ineffective in complete airway obstruction.
• Does not replace bag-mask ventilation or a rescue oxygenation plan.
• Monitor SpO₂ continuously and stop attempts early if desaturation occurs.
• High-flow oxygen can cause nasal dryness; gastric insufflation is possible with some techniques.

Techniques to provide apnoeic oxygenation

1. Standard nasal cannula (nasal prongs)
   • Leave nasal prongs in place during induction and intubation.
   • Deliver 100% oxygen at approximately 10-15 L/min in adults.
   • Simple, readily available, and does not obstruct laryngoscopy.
2. Nasopharyngeal catheter
   • A soft catheter is passed through the nostril into the nasopharynx.
   • Oxygen is insufflated at about 3-10 L/min.
   • It places oxygen closer to the laryngeal inlet and may be useful when longer apnoea is anticipated.
   • Insert gently and avoid in suspected basal skull fracture or significant nasal trauma.
3. Oropharyngeal oxygen insufflation
   • Oxygen is delivered into the mouth or pharynx through a catheter, suction tubing, or an oropharyngeal airway connected to oxygen.
   • Particularly useful if the nasal route is unavailable or obstructed.
   • Care is needed to prevent trauma and gas insufflation into the stomach.
4. High-flow nasal oxygen (HFNO) / THRIVE
   • Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE) provides warmed, humidified oxygen through nasal cannula at high flow, commonly 40-70 L/min.
   • Used for preoxygenation and continued during apnoea.
   • Useful in anticipated difficult airway, obesity, airway surgery, and tubeless laryngeal procedures.
   • It prolongs safe apnoea time, but does not reliably prevent CO₂ accumulation.
5. Oxygen through a supraglottic airway or endotracheal tube
   • If a supraglottic airway or tracheal tube has been placed, oxygen may be insufflated through it during a brief apnoeic period.
   • This is generally a rescue or procedural method rather than routine oxygenation during laryngoscopy.

Methods to obtund stress response to laryngoscopy and intubation

1. Adequate depth of anaesthesia
   • Ensure sufficient induction agent and adequate analgesia before laryngoscopy.
   • Propofol or a volatile anaesthetic at adequate concentration reduces the pressor response.
   • Avoid light anaesthesia and avoid repeated or prolonged laryngoscopy.
2. Opioids
   • Fentanyl 1-3 micrograms/kg IV, remifentanil, or alfentanil before laryngoscopy attenuates sympathetic response.
   • Remifentanil infusion is useful when a short, titratable effect is desired.
   • Watch for respiratory depression, bradycardia, and hypotension.
3. Intravenous lidocaine
   • Lidocaine 1-1.5 mg/kg IV, given about 1-3 minutes before laryngoscopy, may blunt airway reflexes, coughing, and haemodynamic response.
   • Airway topicalisation with lidocaine, superior laryngeal block, and transtracheal block are useful for awake intubation.
4. Beta-blockers
   • Esmolol 0.5-1.5 mg/kg IV or a titrated small-dose infusion effectively limits tachycardia and hypertension.
   • Avoid or use cautiously in bradycardia, heart block, bronchospasm, or decompensated cardiac failure.
5. Alpha-2 agonists
   • Dexmedetomidine or clonidine reduces central sympathetic outflow and attenuates tachycardia and hypertension.
   • They can cause bradycardia and hypotension, especially with a rapid loading dose.
6. Vasodilators and calcium-channel blockers
   • Nitroglycerin, sodium nitroprusside, or nicardipine may be used in selected severely hypertensive patients.
   • They predominantly control hypertension, so a beta-blocker may be needed to prevent reflex tachycardia.
7. Non-pharmacological measures
   • Gentle, skilled laryngoscopy with minimum duration, ideally under 15 seconds.
   • Use videolaryngoscopy where it improves first-pass success and reduces repeated airway stimulation.
   • Ensure complete neuromuscular relaxation and treat anxiety with appropriate premedication.