Normal swallowing and cough allow for airway protection and the prevention of aspiration. Swallowing consists of three phases: the oral phase, the pharyngeal phase and the esophageal phase.14 The pharyngeal phase is most involved in airway protection and preventing aspiration.15 The tongue base moves solids or liquids toward the pharynx by moving posteriorly while the larynx moves up and forward under the tongue base, pulling open the upper esophageal sphincter.14 Other airway protective mechanisms occur during this phase to avoid aspiration: the soft palate rises and the nasopharynx closes, pushing material down into the esophagus;14 the true and false vocal folds adduct to close the larynx;14,15 and the epiglottis moves backward to cover the trachea.15
Aspiration can occur before, during or after swallowing. When it occurs, the normal reflex is to cough.15 Aspiration that occurs during swallowing can be seen in patients with an impaired voluntary cough.16 The ability to cough is particularly impaired in neuropathic and neuromuscular disorders such as myasthenic crisis or Guillain-Barré Syndrome (see below). Dysphagia from stroke can be seen with both brainstem and cortical lesions.17 Lesions to the anterior insula demonstrate a delay in pharyngeal swallowing and supraglottic aspiration.18 Right-sided strokes additionally have delay at each stage of pharyngeal swallowing, leading to an increase in aspiration.19
When aspiration does occur, aspiration pneumonitis or pneumonia can develop. Aspiration pneumonitis is caused by sterile, acidic stomach contents entering the airway, resulting in a chemical inflammatory injury to the lungs; aspiration pneumonia is caused by oropharyngeal secretions colonized with bacteria entering the airway, resulting in infection.20 The use of medications for ulcer prophylaxis can cause gastric contents to become colonized with bacteria by increasing the pH of the stomach.21 Enteral feedings are also associated with colonization of the stomach with Enterobacteriaceae.22 Feeding a patient via nasogastric tube versus percutaneous endoscopic gastrostomy (PEG) tube has shown similar rates of aspiration, though over the long-term a PEG tube is more comfortable for a patient.20 Feeding patients via a post-pyloric tube has not shown to decrease the incidence of pneumonia compared to gastric enteral feeds.23
Patients admitted to a NCCU must be carefully assessed. Small changes with quick provider notification and intervention may be highly influential to a patient’s long term outcome. Assessment skills must be keen to all body systems, with specific attention to neurological and respiratory status.
Though a thorough neurological exam must be completed with great frequency, specific components that affect the respiratory system include assessment of cranial nerves V, VII, IX, and XII, cough and gag reflexes, motor strength in patients with spinal cord injuries above the level of T10 or neuromuscular disorders, and level of consciousness. See Table 2 for additional assessment details. Abnormal findings in any of these areas may prompt additional assessment or early intervention, including placement of an artificial airway to prevent respiratory arrest.
Table 2 – Nursing Neurological Assessment related to Ventilation and Respiration29,30
Table 3 – Abnormal Respiratory Patterns33
Indications for Intubation
There are five common reasons for which a patient may need to be intubated:34
- Hypoxic respiratory failure – low arterial oxygen saturation by pulse oximetry or arterial blood gas
- Hypercarbic respiratory failure – a failure to ventilate indicated by hypercapnia or by inadequate breaths on physical exam
- Airway protection – in patients who have a decreased level of consciousness (Glasgow Coma Scale ≤ 8) or bulbar dysfunction
- Expected neurological or cardiopulmonary deterioration
- Planned surgical or endovascular interventions
The incidence of endotracheal intubation in the NCCU ranges from 25-39%. Over two-thirds of patients need to be intubated for airway protection.35,36 Over a quarter need to be intubated for anesthesia. The remainder (<10%) are intubated for primary respiratory failure.35
Patients requiring intubation should be assessed for a difficult airway and for ability to bag-mask ventilate (BMV).34
First, one can determine if a patient might have a difficult airway using the “LEMON” mnemonic.37
L = Look externally
E = Evaluate the mouth opening and airway position
M = Mallampati score
O = Obstruction
N = Neck mobility
Figure 1 – Mallampati Classifications
The “OBESE” mnemonic can be used to evaluate for the capacity to BMV.38
O = Obese (BMI > 26 kg/m2)
B = Bearded
E = Elderly (Age > 55 years old)
S = Snoring history
E = Edentulous
Consideration can be given to calling for anesthesia back-up or having assist devices such as fiberoptic devices or a laryngeal mask airway in patients who are at risk for a difficult airway or inability to BMV.34
Table 4 – Potential for a difficult airway in the neurocritical care unit
Pre-Intubation Neurological Assessment
A focused and succint neurological exam is important for estabilishing a baseline prior to sedation and intubation.34
Exam elements should include the following:
- Level of consciousness
- Pupil reflex
- Corneal reflex
- Face symmetry
- Gag reflex
- Cough reflex
- Motor response in each extremity
- Presence or absence of seizure activity or other abnormal movements
Rapid sequence intubation is an effective method of emergently intubating patients at risk for aspiration of stomach contents.39 The patient is pre-oxygenated with 100% oxygen. Typically, a nonrebreathing bag reservoir facemask is used. However, since this must be interrupted during intubation, a high-flow nasal cannula can be used to decrease hypoxia and allow for apneic oxygenation.40 An induction agent and neuromuscular blocking agent are then administered. The patient is intubated once loss of consciousness and paralysis has occurred.39 Traditionally, cricoid pressure is applied prior to intubation to decrease the risk of aspiration. However, there is little evidence that this maneuver is helpful in reducing the incidence of aspiration.41
Special considerations are frequently necessary in the neurocritically ill population. Patients with elevated intracranial pressure (ICP) or at risk for elevated ICP should be intubated by the most experienced clinician on the team to avoid unnecessary airway manipulation.34 Both the reflex sympathetic response (RSR) and the direct laryngeal reflex can cause a rise in ICP. The RSR is both increased heart rate and increased blood pressure, leading to increased ICP, and the direct laryngeal reflex can raise ICP independently.42-44 In addition to ICP, the clinician must all be aware of the patient’s cerebral perfusion pressure (CPP). CPP is dependent on both ICP and mean arterial pressure (MAP), the latter often being reduced by induction drugs.
CPP = MAP – ICP
CPP is a surrogate for cerebral blood flow. Thus, hypotension should be avoided so that CPP is maintained. Assuming that ICP is less than 20 mm Hg, the MAP should be maintained at 80 mm Hg to avoid a CPP less than 60 mm Hg throughout the procedure.34
In patients with a cervical spine injury, extreme care must be taken to guarantee spine stabilization. A second clinician has to manually stabilize the head and neck, ensuring inline immobilization.45
Nursing Interventions - Intubation
During intubation, great caution should be used while intubating a patient with increased intracranial pressure.34 As both hypotension related to the use of induction agents as well as hypertension related to the RSR are possible, a pre-intubation plan should be discussed with the interprofessional team prior to RSI.42,43 Additional equipment that should be ready to use includes suction, colorimetric EtCO2 detector or EtCO2 monitor, and video laryngoscope or bronchoscope if the airway has any potential to be difficult.46 An advanced airway surgical tray should be available especially in cases of traumatic injury. In patients with neurological injury, adequate oxygenation throughout intubation must be maintained as cerebral tissues may be hypoxic and at risk for ischemia.47 Close monitoring by the nurse during intubation can cue the provider to halt an attempt, administer oxygen via BVM, and attempt again after oxygen saturation returns to adequate levels.
Patient positioning during intubation is usually supine to allow the proceduralist to visualize the vocal cords. However, this position is contraindicated in patients with increased intracranial pressure.48 Once the airway is secure and normotension has been achieved, the patient’s position should be quickly returned to head of bed 30° to improve venous jugular drainage. In trauma patients, hyperextension of the neck is contraindicated and a jaw thrust maneuver should be used to visualize the vocal cords and prevent any further cervical spinal cord injury.45
The general principles of mechanical ventilation are to ventilate, avoiding hypo- or hypercapnia, and to oxygenate with the least amount of oxygen needed. In addition, mechanical ventilation can decrease a patient’s work of breathing. The exact ventilator settings will be patient dependent, though the clinician should avoid lung injury by giving volumes that are 6-8 mL/kg ideal body weight and avoiding high plateau pressures (≥ 30 mm H20).49,50
Table 5 – Frequently used ventilator settings
In patients with brain ischemia from any cause, hyperventilation should be avoided except in cases of emergency treatment of intracranial hypertension, since hypocarbia may lead to cerebral vasoconstriction. Patients with traumatic brain injury who underwent hyperventilation had increased volumes of hypoperfused brain and a total decrease in cerebral blood flow despite improved CPP and ICP measurements.51 Not uncommonly, patients exhibit centrally driven hyperventilation, which can be mediated by both pontine lesions or by cortical brain injury, leading to respiratory alkalosis and hypocapnea.8 There is no clear data that patients should be sedated to blunt this response.
Table 6 – Commonly encountered problems with mechanical ventilation
The best method to wean a patient in the NCCU from mechanical ventilation is not known. Coma alone is not a reason to delay weaning. Spontaneous awakening trials (SATs) and spontaneous breathing trials (SBTs) have been recommended in the general critical care population because of associations with fewer number of ventilator days, decreased incidence of delirium and improved functional outcomes.52 However, patients in the NCCU have special considerations. Pauses in sedation can lead to increased ICP and possible decreases in CPP.53 Thus, abrupt weaning methods may not be safe in patients with intracranial hypertension or those who need analgesia and sedation to manage ICP. In one prospective observational study, the trial of interrupted sedation had to be aborted in one-third of comatose patients because of ICP crisis.54 A risk-benefit analysis must be considered in these patients prior to weaning.
Nursing Interventions – Spontaneous Awakening Trials
Though our patient populations may be challenging, there may be some benefit to a daily sedation vacation when executed safely. SATs should be completed on patients that have an advanced airway, are mechanically ventilated, and are receiving continuous infusion sedation/analgesia. When the SATs are paired with an SBT, a synergistic effect is seen with patients more likely to pass their breathing trials and get successfully extubated.55 However, adequate screening of the safety of an SAT/SBT is vitally important in the neurocritical care unit. Contraindications to tapering or discontinuing sedation can be seen in table 7. Additional considerations should be given to patients during end of life care, as analgesia and sedation may be used differently for this population prior to extubation.
If patients do not meet any of the exclusion criteria for an SAT, sedation can be discontinued, with signs and symptoms of SAT intolerance also listed in Table 7. During an SAT, patients are at high risk for unplanned extubation and may require direct supervision by a nurse to prevent harm. Endotracheal tubes should be firmly secured and restraints may be applied, though their use remains somewhat controversial.56,57
Intermittent boluses of intravenous analgesia may be used at this time if pain is present, but should not be used for sedation.58 If patients exhibit SAT failure, sedation should be reinitiated at half the previous dose and titrated up until goal parameters are achieved.58 In patients who cannot tolerate an SAT due to agitation, consideration can be given to using dexmedetomidine, which does not depress the respiratory drive.59 Once agitation has been successfully treated, an SAT may be reattempted.
Several non-NCCU studied protocols indicate that a patient passes their SAT or progresses from SAT to SBT when they are able to follow simple commands.58,60 In the NCCU patient, this may be difficult because of their underlying neurological injury. More evidence is needed in this population in order to make any strong recommendations.61
Table 7 – Spontaneous Awakening Trials58
Bpm, breaths per minute; SpO2, peripheral capillary oxygenation saturation; pbtO2, partial pressure of brain tissue oxygenation
Table 8 – Patient readiness for a spontaneous breathing trial
ICP, intracranial pressure; RASS, Richmond Agitation-Sedation Scale; SpO2, peripheral capillary oxygen saturation; PaO2, partial pressure of oxygen; FiO2, fraction of inspired oxygen; PaCO2, partial pressure of carbon dioxide; PEEP, positive end-expiratory pressure; RR, respiratory rate; VT, tidal volume; NIF, negative inspiratory force; HR, heart rate; MAP, mean arterial pressure
Table 9 – Indications for stopping a spontaneous breathing trial
RSBI, rapid shallow breathing index; RR, respiratory rate; VT, tidal volume; PaCO2, partial pressure of carbon dioxide; SpO2, peripheral capillary oxygen saturation; PaO2, partial pressure of oxygen; HR, heart rate; SBP, systolic blood pressure
When to extubate a neurocritically ill patient is not always a simple decision. Many times these patients meet respiratory criteria for extubation, but they are still at risk for not protecting their airways.62 Extubation failure rates in patients with primary brain injury can range from 15-35%63-66 and can be higher (30-40%) in patients with neuromuscular disease.67 Delaying extubation also has risk. Patients can develop ventilator associated pneumonia and have an increased length of stay in the intensive care unit.68 Patients with two of the following have been found to have a likelihood ratio of 3.8 for extubation failure: weak cough, secretions and inability to follow commands. However, the inability to follow commands should not preclude a patient from a trial of extubation. In addition, inability to tolerate an SBT due to agitation does not exclude a patient from a trial of extubation if the patient otherwise meets extubation readiness.69
Many studies have attempted to predefine a GCS that will predict extubation success, with varied results. Patients with GCS scores as low as 3 and 4 have been extubated safely,68 whereas others have shown that a GCS score > 7 and ability to follow commands predicts extubation success.64,70 Other scales, such as the FOUR Score have also not been necessarily predictive of who will tolerate extubation.62 Most recently, a GCS > 10 has been demonstrated to predict extubation success. In addition, patients who were successfully extubated all opened their eyes spontaneously and followed commands, and visual pursuit and swallowing attempts in a multivariate analysis were associated with extubation success.71
Table 10 – Factors indicating possible extubation success
Patients who cannot be extubated safely must undergo a tracheostomy. The incidence of tracheostomy placement in neurocritically ill patients ranges from 14-35%,36,63 compared to 7-13% in non-neurologically injured patients.63,72 After undergoing a tracheostomy, neurocritical care patients are faster to wean from the ventilator than general ICU patients.72 Given that many of these patients underwent tracheostomy for airway protection and not because of primary lung pathology, it is not surprising that they can be liberated from the ventilator more quickly. The best timing for placement of a tracheostomy is not known. A randomized trial of early (up to day 3 from intubation) vs. late (days 7-14 from intubation) tracheostomy in stroke patients did not demonstrate improved outcomes with early tracheostomy.73 They did, however, show that early tracheostomy is safe and feasible and may decrease the need for sedation in the NCCU. Patients should proceed to tracheostomy after failing extubation or once it is recognized that a trial of extubation is not reasonable, assuming that this is consistent with a patient’s goals of care. Tracheostomy placement can be associated with transient intracranial hypertension. To avoid elevations in ICP and lowering of CPP, the head of bed may be kept at 30 degrees, hypotension during the procedure should be avoided, bronchoscopy should be minimized or thin bronchoscopes used to avoid hypoventilation, and hypoxia and adequate analgesia should be given for the procedure.74
Tracheostomy can be performed via percutaneous dilatation or a traditional surgical technique. The overall complication rate of percutaneous dilatational tracheostomy (PDT) is lower (3%) than surgical tracheostomy (12%), including lower rates of bleeding and infection when PDT is performed with bronchoscopy.75 Additionally, PDT allows for the procedure to be performed at the bedside in the ICU. Granulation tissue forms after tracheostomy, though only 3-12% will have complications from tracheal stenosis. Other rare (<1%) late complications that can occur are tracheo-innominate artery and tracho-esophageal fistulas.76
Nursing Management of Mechanical Ventilation
The threshold for intubating a patient with a neurological injury is low in many clinicians’ minds. Because of this, many nurses in NCCUs care for patients requiring mechanical ventilation. There are several considerations specific to this population.
- Suctioning should not be completed on a regular basis but as needed. Frequent suctioning may lead to hypertensive episodes as well as bouts of increased intracranial pressure leading to decreased cerebral perfusion pressure. Lidocaine administered via the endotracheal tube may help alleviate the intracranial hypertension related to suctioning, but more evidence is needed to make this a mainstay of treatment.77
- Ventilator settings should be titrated to achieve normocapnea and normal peripheral capillary oxygen saturation (SpO2). However, during times of intracranial hypertension, hyperventilation can be used as a rescue therapy. While this therapy may lower intracranial pressure, it also decreases cerebral blood flow and can lead to ischemia.1 Because of this, hyperventilation should only be maintained for a short period of time. Additionally, FiO2 should be titrated to maintain adequate oxygen levels but avoid oxygen toxicity.78
- Many patients with sudden neurological injuries have an increased risk for acute respiratory distress syndrome (ARDS).79,80 While managing ventilator settings for patients that progress to ARDS, increasing PEEP settings will be needed to maintain oxygen saturations and improve alveoli recruitment. This increased PEEP can cause an increase in intrathoracic pressure, leading to decreased ventricular filling and subsequent decreased cardiac output.81 The increased intrathoracic pressure can also decrease jugular drainage from the cranial vasculature, leading to worsening ICP and cerebral edema.
ARDS management may also include certain novel treatments like proning, high frequency jet oscillation, or extracorporeal membrane oxygenation. Severe neurological injury and intracranial hypertension is a common contraindication to these more radical interventions.82,83 The interdisciplinary team should carefully consider the patient’s status and prognosis prior to moving forward with any advanced treatments with family involvement in the plan of care discussion.