The ability to safely secure and manage a definitive airway on the cardiothoracic intensive care unit is an essential and challenging skill. Patients are frequently haemodynamically compromised with reduced cardiorespiratory reserve, resulting in poor tolerance of suboptimal ventilation.
Important airway competencies within cardiothoracic intensive care include endotracheal intubation and tracheostomy forming techniques, as well as a good working knowledge of how to rescue the airway should initial attempts fail.
Tracheal Intubation
The presence of a cuffed tube within the trachea represents a secure airway, providing protection from aspiration and facilitating positive pressure ventilation. Endotracheal tubes are made from polyvinyl chloride and are sized based on their internal diameter in millimetres. Since the internal diameter is inversely proportional to airflow resistance, it is appropriate to use the largest size that can be easily accommodated (usually 8–9 mm for males and 7–8 mm for females).
Many patients following cardiac surgery already have an endotracheal tube in place when admitted to the critical care unit. In these patients a period of haemodynamic stability may be required before preparations are made for discontinuation of sedation and extubation. It is important to document the endotracheal tube position, laryngoscopic grade and whether there were any difficulties with facemask ventilation and/or intubation following induction.
In contrast, the postoperative management of patients following thoracic surgery tends to focus on early extubation and the avoidance of positive pressure mechanical ventilation where possible. This is to avoid positive pressure stress on suture and staple sites, which may increase the risk of postoperative complications including persistent air leaks.
Patients who are breathing unsupported or receiving non-invasive ventilation may require intubation for a number of reasons (Table 8.1).
Table 8.1 Indications for tracheal intubation on the critical care unit
| Hypoxia |
| Hypercarbia |
| Reduced conscious level |
| Increased work of breathing |
| Cardiac arrest |
| Airway obstruction |
| To facilitate transfer |
Airway Assessment
When planning any intubation, it is important to perform an initial airway assessment to gauge whether there may be any potential difficulties with facemask ventilation or laryngoscopy. A key finding from the 4th National Audit Project on major airway events in the UK found that poor airway assessment contributed to poor airway outcomes. The degree of harm from airway incidents was also found to be highest in intensive care patients.
Recognised predictors of difficult intubation are listed in Table 8.2. An absence of these signs however does not guarantee straightforward airway management.
Performing Endotracheal Intubation
The intubating environment on the intensive care unit can be very different from that of the elective operating room. Critically ill patients have less physiological reserve and often require intubation urgently to address cardiorespiratory collapse. They may not be fasted and often experience delayed gastric emptying, so a rapid sequence induction with cricoid pressure is often performed.
Preparation
Prior to intubation, it is necessary to prepare the patient, drugs, equipment and intubating team. Roles should be applied to appropriately skilled personnel and a backup plan for a failed intubation should be in place. Essential equipment required for emergency intubation, along with rescue equipment in case of difficulty, should be immediately available in the intensive care unit and moved to the patient’s bedspace. A ‘difficult airway’ trolley containing basic and advanced equipment is an ideal way to organise this.
Patient
Critically ill patients requiring intubation should have standard monitoring (non-invasive blood pressure, electrocardiography, pulse oximetry) and working intravenous access as a minimum. Capnography to confirm correct tube position after intubation should be immediately available.
Head position should be gently manipulated (if it is safe to do so) into the ‘sniffing the morning air position’ which includes a mild amount of cervical flexion (a pillow is usually necessary behind the head to provide this) and mild atlanto-occipital extension in order to optimise direct laryngoscopic view. In obese patients extra pillows may be necessary behind the shoulders in order to allow atlanto-occipital extension.
Equipment
Basic airway equipment includes: a self-inflating bag, gum-elastic bougie, oropharyngeal airway, functioning laryngoscope (with a spare in case of failure) and at least two options of appropriately sized endotracheal tubes. A supraglottic airway device (laryngeal mask airway, LMA) should also be present in case of intubation difficulty, in order to assist with rescue oxygenation. A suitable device for emergency cricothyrotomy should also be available in case of failure to intubate or oxygenate.
It is necessary to be able to tilt the patient’s bed in a head-down position in case of regurgitation during airway manipulation and to have working suction available. It is also prudent to ensure the ventilator to be used after intubation is fully operational and attached to a reliable oxygen source.
Occasionally it may be necessary to site a double-lumen endotracheal tube rather than a single-lumen tube, either to facilitate protection of one lung from soiling by secretions or blood from the other lung, or to enable differential ventilation of the lungs. Double-lumen tube placement requires additional experience and specific training.
Drugs
Rapid sequence induction involves the administration of a predetermined dose of intravenous induction agent followed immediately by a neuromuscular blocking drug to achieve rapid loss of consciousness and optimal intubating conditions with minimal patient apnoea time.
The haemodynamic side effects of the common induction agents at dosages used in anaesthetic practice are such that their administration in critically ill patients can cause catastrophic cardiovascular collapse. To reduce the amount of induction agent needed, operators often coadminister opioids and benzodiazepines. Despite coinduction, vasopressors are still frequently needed following induction and should be immediately available.
Suxamethonium has been the traditional neuromuscular blocking agent used to achieve paralysis due to its speed of onset and offset. Rocuronium is now an alternative option, since the recently developed sugammadex allows immediate block reversal in case of emergency.
Table 8.2 Predictors of difficult intubation
| Receding chin |
| Short neck |
| Thick neck |
| Limited neck extension/flexion |
| Long upper incisors |
| Prominent overbite |
| Inability to extend mandibular incisors anterior to the maxillary incisors |
| Less than 3 cm interincisor distance |
| High arched palate |
| Less than 3 finger breadth thyromental distance |
| Mallampati score greater than II |
| Non-compliant mandibular space |
The choice of drugs used should be tailored to the individual critical care patient based on an assessment of aspiration risk, physiological reserve and indication for intubation (Table 8.3).
Table 8.3 Commonly used intubating drugs
| Drug | Comments |
|---|---|
| Thiopentone | Fastest speed of onset |
| Cardiovascular suppression | |
| Potential harm from extravasation | |
| Propofol | Rapid speed of onset |
| Suppresses laryngeal reflexes | |
| Cardiovascular suppression | |
| Ketamine | Slower onset time |
| Cardiovascular stability | |
| Bronchodilation | |
| Etomidate | Rapid speed of onset |
| Cardiovascular stability | |
| Possible adrenal suppression | |
| Midazolam | Slower onset time |
| Prolonged duration of action | |
| Reduces anaesthetic dose requirements | |
| Opioids | Unreliable amnesic |
| Limits sympathetic response to intubation | |
| Reduces anaesthetic dose requirements | |
| Suxamethonium | Rapid onset and offset of paralysis |
| Hyperkalaemia | |
| Risk of malignant hyperthermia | |
| Rocuronium | Rapid onset of neuromuscular block |
| Rapid reversal with sugammadex |
Team
Clear roles matched to the skillset within the team need to be allocated prior to induction. The team leader is responsible for the overall running of the intubating process and ideally should not be performing any other tasks. The first intubator performs preoxygenation, laryngoscopy and intubation, with a second intubator on standby in case of failure. One team member is responsible for administering drugs and another should be competent at performing cricoid pressure.
Endotracheal Intubation: Sequence of Events
The salient sequence of events during an uncomplicated tracheal intubation on the intensive care unit is preoxygenation, cricoid pressure, anaesthetic induction, paralysis, laryngoscopy and confirmed endotracheal intubation.
Preoxygenation
Preoxygenation describes the process of replacing nitrogen with oxygen in the functional residual capacity (FRC) of the lungs to maximise oxygen stores. This allows for a longer apnoeic time to secure the airway before desaturation occurs, and should be performed where possible. Effective preoxygenation is performed by encouraging the patient to take tidal volume breaths of 100% oxygen through a tight fitting mask (to prevent entrainment of air) at flows above 10 l (to minimise rebreathing) for 3–5 minutes. Since FRC is lower in the supine position, adopting a head-up position can improve oxygen storage capacity. An expired oxygen concentration of 90% signifies effective preoxygenation. These ideal conditions for preoxygenation are not always possible, particularly in patients requiring intubation for respiratory failure who are deteriorating despite non-invasive respiratory support, or who are not able to cooperate with instructions. In these patients a careful attempt at preoxygenation can often be made, but care must be taken not to cause stomach inflation, which increases the risk of regurgitation and aspiration.
Cricoid
Cricoid pressure is a manoeuvre intended to reduce the risk of aspiration during induction. The circumferential cricoid cartilage is the most inferior laryngeal structure and can be pressed against the body of the fifth cervical vertebrae to compress the oesophageal lumen. The thumb and index finger are placed either side of the cartilage and a posterior force of 10 N is applied before induction, which is increased to 30 N following loss of consciousness. The assistant applying cricoid pressure needs to be experienced since incorrect technique can result in airway obstruction and a poor view on laryngoscopy.
Laryngoscopy
Laryngoscopy is most commonly performed with a curved Macintosh laryngoscope blade (sizes 3–5) to allow visualisation of the glottis and enable intubation under direct vision. The laryngoscope is held in the left hand and the blade is inserted into the oral cavity to the right side of the midline, which allows distraction of the tongue to the left. The tip is then slowly advanced over the base of the tongue and into the valecula, where an anterior vector force is applied to remove the tongue from the line of sight. The laryngeal view is graded according to the Cormack and Lehane classification (Table 8.4). Poor views can often be improved by external laryngeal manipulation (BURP; backwards, upwards and rightward pressure on the thyroid cartilage) or a reduction in cricoid pressure. With grade 3 and 4 views, the glottic aperture is not visualised and advanced airway equipment such as videolaryngoscopes and fibreoptic scopes may be required to aid intubation.
Table 8.4 Cormack and Lehane classification of laryngoscopy view
| Grade 1 | Full view of vocal cords/glottis |
| Grade 2 | Only posterior commissure/arytenoid cartilages visible |
| Grade 3 | Only epiglottis visible |
| Grade 4 | No glottic structure visible |
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