Noninvasive ventilation techniques

Noninvasive techniques exist to support the asthmatic patient who has not made a full recovery. NIPPV is valuable in supporting patients with significant respiratory distress and may either delay or resolve the requirement for intubation. The patient must be alert with spontaneous breaths to receive non-invasive therapies. 

Administering NIPPV

NIPPV provides positive pressure ventilation via a mask adequately sealed to the face to support the spontaneously breathing individual. Devices cover the nose, the nose with the mouth, or the entire face. With bilevel settings, providers can control pressure received at both inspiration and expiration. 

The significant benefit of NIPPV is that patients may not require intubation, which has significant adverse effects. There is an associated reduction in morbidity, as well as mortality and difficulty in care and costs, are reduced. 

The steps of administering NIPPV are:

• Adequately secure the mask over the face
• Attach the ventilator and face mask. Both traditional mechanical ventilation device or a ventilation device-specific to NIPPV can be used
• Begin with a CPAP setting of 0 cm H20. Increase this to ensure PEEP even with spontaneous inspirations
• Positive pressure support (for inspiration) is set at 10 cm H20. Titrate as needed using ABG findings, but limit to under 25 cm H20
• Tidal volume should be 500mL
• The ventilatory rate should be under 25 breaths each minute
• Continue nebulized treatments via assisted ventilations.

Related Video: One Quick Question: How Does CPAP Work?

Who Benefits?

Patients must meet certain requirements to receive NIPPV:

• Alert with the ability to protect their airway
• Cooperative
• Spontaneously breathing

On the other hand, certain findings make patients ineligible for NIPPV: 

• Severe hypoxemia with PaO₂ under 60 mm Hg or SpO₂ under 90% with rebreathing mask
• PaCO₂ over 40 mm Hg (or rising)
• Falling pH
• Rapid or persistent clinical deterioration
• Altered mental state or inability to cooperate
• Hypotension (BP under 90 mm Hg)
• Ischemic cardiac disease
• Ventricular arrhythmias

Bilevel Positive Airway Pressure

The bi-level setting is more effective during an acute asthmatic episode. Its benefit is that it opposes the development of auto-PEEP and decreases breathing work more than other non-invasive techniques. It assists inspiratory effort while also decreasing the force needed in exhalation. The typical settings are inspiratory pressure between 8-10 cm H20 and expiratory pressure between 3-5 cm H20. 

Mechanical Ventilation in Asthma

The decision to proceed to advanced airway management is not to be taken lightly. This treatment does not manage the bronchoconstriction of small airways. It can actually worsen bronchoconstriction via complications of auto-PEEP as well as barotrauma. It is necessary, however, if the patient is clinically deteriorating despite maximal therapy.

A patient connected to a mechanical ventilator.

Who Benefits?

The patients who are candidates for advanced airway management include those: 

• Not improving on NIPPV;
• Deteriorating despite maximal therapy;
• With anaphylaxis;
• With alteration in mental status or confusion;
• With increasing PaCO₂ (over 40 mm Hg) or falling pH. This is especially true if there is associated alteration in mental status;
• With PaO₂ under 50 mm Hg with non-rebreather. This is especially true if there are indicators of hypoxemia such as confusion, agitation or fighting the mask;
• Showing signs of exhaustion or fatigue.

Rapid sequence Intubation

Asthmatic patients requiring intubation are at high risk for rapid desaturation even with adequate preoxygenation. Typically, these patients will need bac mask ventilation before and between intubation attempts. Be aware that patients may develop hypotension or cardiac arrest due to associated volume loss, sedative use, and trapped air. 

• The clinician should be skilled at intubation
• Continue bag-masking while preparing for intubation. Note this may be near impossible in patients with status asthmaticus
• Use a large ETT (8-9mm) to minimize airway resistance and allow an improved ability to suction
• Immediately confirm successful placement via clinical assessment and waveform capnography. A chest x-ray should be performed when the patient is stable. 

Premedications

Premedications for intubation include LOAD (lidocaine, opiates, atropine, and defasciculating agents)

• The most critical is lidocaine and should be given IV 1-2 mg/kg about 3 minutes before other medications. It decreases associated bronchospasm during the process of intubation.

Lidocaine Injection Preparation

Anesthesia and Sedation

Anesthetics are helpful as they often produce bronchodilation. Ketamine and propofol have increased efficacy in this regard.  

Ketamine 

It is a systemic anesthetic with dissociative properties that causes both dilation of the bronchial tree and increased bronchial secretions. Additionally, there is no associated vasodilation, hypotension, or cardiac depression. The dosage is 1-2 mg/kg. The effect is within 30-60 seconds and is ongoing for 10-20 minutes. It is often considered the preferred anesthetic for asthma patients requiring intubation. Atropine or glycopyrrolate can be given to minimize secretions.

Propofol

This sedative also provides bronchodilation and can be used for intubation as well as during treatment with mechanical ventilation. The dosage is 1-2 mg/kg. The effect is under 1 minute and is ongoing for 5-10 minutes. Note that there can be associated hypotension, especially in those who have had prolonged exacerbation and are volume depleted. 

Etomidate

This hypnotic can be used, but there is no associated bronchodilation or analgesic. It does cause less hemodynamic changes than propofol. The dosage is 0.2-0.4 mg/kg. The effect is under 1 minute and is ongoing for 5-10 minutes. 

Paralytics

• Succinylcholine is the standard paralytic used for intubation in asthmatic patients. the dosage is 1-1.5 mg/kg. 
• Rocuronium can also be used. It has a similar rapid effect and lasts for a longer time than succinylcholine. The dosage is 0.6-1.2 mg/kg. 
• Vecuronium is another choice. It has a slow onset of 1-3 minutes and lasts for a longer time than succinylcholine. The dosage is 0.1-0.2 mg/kg. 

Persistent Airway Obstruction

While intubation supports inadequate ventilation, it does not address the airway obstruction. The patient may have associated respiratory acidosis that persists even following intubation. The patient will need ongoing management of the obstructed airway. 

Inhaled beta 2 agonists: these are continued, and an additional dose of 2.5-5 mg albuterol is given via the ETT as this may improve the delivery of the medication. 

Slowly ventilate using 100% oxygen: note that there can still be obstructed airflow with the ETT in place.

The rate of ventilation should be between 6-10 breaths each minute with a tidal volume setting between 6-8 mL/kg. Additionally, short inspiratory time (rate of flow 80-100 L/min) with long expiratory time is recommended to achieve an inspiratory-respiratory ratio of 1:4 or 1:5. The combination of slowed rate and prolonged exhalation can help diminish auto PEPE and minimize the complications of pneumothorax or hypotension.

An acceptable strategy for intubation is as follows:

• Maintain the patient upright for patient comfort as needed
• IV 1.5-2mg/kg lidocaine (3 minutes before anesthesia)
• IV 2 mg/kg ketamine
• IV 1.5mg/kg succinylcholine (immediately after ketamine)
• Lay patient supine as anesthetic takes effect
• Place ETT via direct laryngoscopy. An 8-9 mm tube is preferred
• Confirm accurate placement via clinical signs and waveform capnography. 
• Begin mechanical ventilation
• Begin sedation (i.e., propofol, benzodiazepine) and paralytic medications (i.e., rocuronium, vecuronium) for maintenance for 4-6 hours
• Titrate parameters for optimal therapy
• Repeat ketamine if needed
• Bronchodilators via ETT
• Evaluate the patient response using airway pressures
• IV hydration as needed to manage hypotension associated with auto-PEEP.

Ventilation in Severe Asthma

Even following intubation, severe asthma requires close monitoring and management. 

Auto-PEEP

Asthmatics have obstruction of the airflow throughout the respiratory cycle, but the obstruction is at its greatest during expiration. As obstruction progresses, the air becomes trapped, leading to stacked breaths in which the inhaled air cannot be exhaled. 

Patients with severe asthma will have a longer expiration to attempt to exhale more air. If during mechanical ventilation, the exhaled time is too short, then auto-PEEP can result. The pressures at the end of exhalation become greater than mechanical PEEP settings, and the resulting increase in thoracic pressure occurs. The consequences are grave, with poor cardiac output, hemodynamic instability, and hypotension resulting. Patients may also suffer from barotrauma, including tension pneumothorax. 

To manage these complications, a slowed breath rate (between 6-10 breaths each minute), a small tidal volume (between 6-8 mL/kg), shorter inspiration time (rate of flow 80-100 L/min) with long expiratory time is recommended to achieve an inspiratory-respiratory ratio of 1:4 or 1:5. Start positive inspiratory pressure at 10 cm H₂0 and keep below 25 cm H₂0. Additionally, keep peak inspiration pressure below 40 cm H₂0 to limit barotrauma.

Auto-PEEP

Permissive Hypercapnia

While oxygenation can adequately be increased once mechanical ventilation is started, it may still be difficult to release carbon dioxide. Hypoventilation is actually encouraged as this minimizes auto-PEEP and complications of barotrauma. These patients should have mechanical settings that allow a mildly increased PaCO₂ to diminish adverse effects. 

In this case, ventilatory settings should minimize auto-PEEP, and this will cause a slow rise in PaCO₂ that can be as high as 70-90 mm Hg at 3-4 hours. Associated respiratory acidosis will occur with a pH that may go as low as 7.2-7.3; however, PaCO₂ can be managed to limit this. Note that in the next 24-48 hours, compensatory metabolic alkalosis will occur as the kidneys reabsorb bicarbonate, and the pH will return towards normal. 

Monitor patient response to acidosis before metabolic correction. Some patients may develop acidosis associated arrhythmia and will require a reduction in acidosis or slower elevation of hypercapnia. Note also that patients will need significant sedation with settings that limit auto-PEEP and lead to hypercapnia. 

Acute deterioration during ventilation

In the patient who deteriorates following intubation: 

• Ensure ETT placement
• Suction to relieve mucus plugging
• Assess for and treat (if found) a pneumothorax
• Evaluate the ventilation circuit to ensure it is working properly
  • Detach the circuit if there is excessive end expiration pressure to release PEEP during exhalation
• To correct auto-PEEP: decrease inspiratory time, decrease respirations by 2 per minute, and decrease tidal volume. 
• Continue albuterol management

The Difficult to Intubate Patient

Adequately assess the patient that is difficult to ventilate. While difficult to assess, there are four common causes of this situation, known as DOPE:

• ETT Displacement
• ETT Obstruction
• Pneumothorax
• Failure of Equipment

Intubation Procedure

The sequence of steps to manage the hard to ventilate include:

• Ensuring adequate sedation and paralysis, so the patient is not fighting the ventilator
• Ensure ETT is patent with no mucus plugs or kinks. Ensure the patient is not biting down. Suction the ETT
• Alter airflow to square wave patterning. This may require prolonging exhalation, shortening inhalation and increasing peak inspiratory pressures to allow adequate tidal volumes
• Reduce respirations to 6-8 each minute to minimize auto-PEEP to 15mm Hg or lower. 
• Reduce respirations to 3-5 each minute to minimize auto-PEEP to 15mm Hg or lower. 
• Raise peak flow to over 60 L/min to decrease inspiratory time further (and prolong expiratory time)

Poor Response Following Intubation

Following intubation, four reasons are commonly the cause of persisting hypotension or hypoxia. 

Poor ETT placement

Always reconfirm ETT placement if there is a change in exhaled CO2 or O2 saturation. Use clinical parameters to determine placement, rather than a chest x-ray, as that is too time-consuming. Waveform capnography is most reliable for determining displacement and can be used quickly to guide treatment. 

ETT obstruction

Evaluate for ETT patency if the patient is difficult to ventilate. Suction as needed to clear obstructions and rule out mucus plugs, biting, and kinking of the ETT.

Significant Auto-PEEP

Significant hypotension following intubation is most commonly secondary to profound auto-PEEP. Manage by briefly stopping ventilation. This will help release auto-PEEP. Closely monitor oxygenation ad restart the ventilation once auto-PEEP is released or if the patient becomes hypoxemic 

Tension pneumothorax

A tension pneumothorax is an emergency. Patients may have a poor expansion of the chest, reduced breath sounds, a tracheal shift away from the pneumothorax and subcutaneous emphysema. Management is with immediate needle thoracostomy. Use a 16 gauge needle with a cannula to pierce at the level of the 2nd intercostal space on the midclavicular line. The patient may require chest tube placement or other measures following the initial release.