NON-INVASIVE VENTILATION



NON-INVASIVE VENTILATION (NIV)

Respiratory failure can result in either hypoxia and/or hypercapnia, both of which are amenable to NIV. NIV improves lung mechanics by recruiting collapsed alveoli, improving pulmonary compliance and reducing the work of breathing.

NIV, however, can have a number of negative physiologic effects. Some patients may strain against the ventilator and increase the work of breathing. Increased intra-thoracic pressure can decrease venous return, and thus cardiac output, in those with marginal cardiac function. In some patients, the increased airway pressure may cause overdistension of the alveoli and produce barotrauma in acutely injured lungs.

The key to the successful application of NIV is in recognizing its capabilities and limitations. This also requires identification of the appropriate patient for the application of noninvasive ventilation.

Once patients that require immediate intubation and ventilation are identified, the remainder can be assessed as to whether NIV would be beneficial.

There are 3 ways Non-invasive Ventilation may be used:

1. To assist ventilation in patients at an earlier stage than that at which invasive ventilation would be considered. (ie. Attempt to avoid the need for intubation)

2. To improve the oxygenation of a patient while preparing for intubation. (Bridge to intubation)

3. As a ceiling of treatment in patients who are not candidates for intubation.

The decision about whether to progress to intubation if NIV fails should be made early for each patient in consultation with senior medical staff, the patient and family. This should be DOCUMENTED clearly in the notes.

Types of Non-invasive Ventilation

Whilst selection of appropriate patients for NIV is extremely important, so is the choice of which type of NIV. Choosing the initial mode of ventilation is based in part on past experience, the capability of ventilators available, and the condition being treated.

Continuous Positive Airway Pressure (CPAP)

CPAP is the most basic form of respiratory support as it delivers a continuous static airway pressure maintained throughout both the inspiratory and expiratory phases of respiration. CPAP is functionally equivalent to positive end expiratory pressure (PEEP) used in the intubated patient. It has been shown to improve oxygen exchange in patients with hypoxemia and acute respiratory failure.

To compensate for leaks, CPAP devices regulate airflow to maintain a set pressure. The amount of positive airway pressure can be adjusted to meet clinical needs. Generally, 5-10 cmH2O is the most common, and pressures above 15 cmH2O are rarely needed (or tolerated).

Start with low pressures (5 cmH2O) and increase in increments of 2 cmH2O as tolerated by the patient. Respiratory goals may include an exhaled tidal volume greater than 7 mL/kg, a respiratory rate of less than 25, oxygen saturation greater than 90%, and perhaps most importantly, patient comfort.

CPAP is most appropriate when the patient has hypoxemic respiratory failure or cardiogenic pulmonary oedema.

Bi-level Positive Airway Pressure (BiPAP)

BiPAP is the most commonly used mode of NIV. It also gives continuous positive airway pressure throughout the respiratory cycle, but this is at different levels of pressure during the inspiratory and expiratory phases. This extra inspiratory support is thought to further reduce the work of breathing.

BiPAP machines use a higher inhalation pressure (IPAP) and a lower exhalation pressure (EPAP). The difference between these is equivalent to the pressure support (PS) setting for an intubated patient. The EPAP is equivalent to the PEEP setting for an intubated patient. (IPAP = EPAP + PS) These two levels need to be clinically matched to patient demands. When the spontaneous mode of a BiPAP machine is used, it is essentially a flow-triggered pressure support ventilator.

IPAP setting may range from 5-24 cmH2O, while the EPAP setting may vary from 2-15cmH2O. Remember that the inspiratory pressure must be maintained higher than the expiratory pressure at all times to ensure bi-level flow. Flow must be synchronized with patient respiratory efforts.

Typical initial settings for BiPAP are levels of IPAP 8-10 cmH2O and EPAP 2-5 cmH2O. Lower settings tend to improve patient tolerance. If initial IPAP/EPAP settings do not produce tidal volumes of 5-7mL/kg, then increases should be made to achieve this. It is essential to monitor the tidal volumes to ensure they are adequate for gas exchange but not high enough to cause barotrauma.

Increasing the IPAP tends to increase the tidal volumes achieved by the patient. IPAP should be increased if there is persistent hypercapnoea on blood gases. Increasing the EPAP tends to improve hypoxemia.

BIPAP is the most appropriate for patients with hypercapnoeic respiratory failure in addition to hypoxemia.

Adjustments are constantly made to achieve these endpoints.

Initial settings focus on achieving adequate tidal volumes, usually in the range of 5-7 mL/kg.

Oxygen (FiO2) is adjusted to achieve adequate oxygenation, with a pulse oximetry goal of greater than 90%.

Serial arterial blood gas measurements are essential to monitor the response to therapy and to guide further adjustments in the ventilator.

Setting up the Ventilator for Non-invasive Ventilation

Patient Selection

Check that there are no immediate indications for intubation and no contraindications to the use of NIV.

Check baseline ABG and CXR to ensure no contraindications for NIV.

Check baseline observations to ensure haemodynamics will support the use of NIV.

Check GCS is adequate to support use of NIV.

Equipment Selection

* Mask

Choose a mask that is the appropriate size for the patient. There is a sizing chart in Resus that allows measurement of patients face and guides mask size selection. Typically, the smallest mask providing a proper fit is the most effective. Check the seal against the patient face before attaching to the machine. In ED the preference is for full face masks, although nasal masks are another alternative.

[pic][pic]

BiPAP Mask Mask Sizing Chart

Straps hold the mask in place, taking care to minimize excess pressure on the face or nose. Leaks make NIV less effective, but excess pressure applied by the straps increases the risk of pressure necrosis and skin breakdown. Straps should therefore be tight enough to prevent leaks, but with enough slack to allow passage of 1 or 2 fingers between the face and the straps.

* Ventilator

Most types of ventilator are capable of providing NIV. The Hamilton T1 ventilator is preferable to the OxyLog 3000 in this department due to a more appropriate range of settings and better patient tolerance. The Hamilton T1 should be the ventilator of choice for NIV unless it is unavailable.

[pic] [pic]

Hamilton T1 Oxylog 3000

Equipment Set-up & Safety Checks

Hamilton T1 Ventilator

Ensure ventilator is connected to wall oxygen outlet or oxygen transport cylinder.

Turn on ventilator (on/off button is on the top Right corner)

Run test of circuit if time permits. (This should be performed daily prior to use to ensure that circuit has no leak).

Attach mask to ventilator with filter in between ventilator and mask.

Ensure inspiratory and expiratory limbs of the tubing are connected to the side of the ventilator.

Set the mode of ventilation to NIV. This is the spontaneous mode used for non-invasive ventilation.

This is done by pressing the Modes button & choosing NIV from the menu.

(Do NOT choose SIMV, ASV or CMV as these modes are for intubated patients. NIV-ST is Non-invasive Spontaneous/Timed Ventilation Mode and is not recommended for use by the novice user.)

Confirm your selection of NIV mode by pressing the Confirm button twice and then checking that NIV appears in the top right hand corner as the selected mode of ventilation. (It is important to do this before attempting to set the settings as it will time out and revert to the previous mode if you take too long to confirm the settings.)

Once this is confirmed you can select your settings by pressing the Controls button, starting with Basic Controls.

Select Oxygen % (FiO2). Usually set at 100% and weaned down as soon as possible to maintain O2 sats > 90%.

Select your Pressure Settings

Psupport

PEEP/CPAP

PEEP/CPAP is the level of support given during expiration. (Also known as EPAP) This is usually set at 5-8cmH20 initially and titrated up if required.

Psupport (PS) is the additional support given on top of the PEEP during inspiration to provide the IPAP. This is usually set at 3-8cmH20.

REMEMBER: PS + PEEP = IPAP

Example: PS (5) + PEEP (5) = IPAP (10)

Please note that the default settings on this ventilator are actually PS (15) + PEEP (5) = IPAP (20). This is very high and could cause barotrauma and is unlikely to be tolerated by most patients. Seek help from a senior medical officer prior to commencing NIV if you are uncertain of what would be appropriate settings for your patient.

Leave the flow trigger set at 5.0L/min for most patients.

N.B If you wish to use just CPAP as the mode of non-invasive ventilation then the above set-up is the same, except that the Pressure Support (PS) is set to 0.

Set alarm limits.

Attach the mask to the patient and ensure good seal of mask.

Stand by the patient and watch for chest wall movement, tidal volume measurements, peak pressures and O2 sats.

Adjust the pressure settings until adequate tidal volumes are achieved (5-7mL/kg) and the patient appears to tolerate the settings.

If the patient deteriorates immediately after instituting NIV, take the mask off the patient, recheck your set-up and reassess your choice of settings.

Oxylog 3000

Whilst the Oxylog can be used for non-invasive ventilation this is not the ideal choice of ventilator and is usually poorly tolerated by patients. Please use the Hamilton T1 as preferred ventilator for NIV in this department.

Monitoring of Patients using NIV

Patients on NIV should receive 1:1 nursing at all times whilst in the ED.

Regular clinical assessments should be made and include:

• Chest wall movement

• Co-ordination of patient respiratory effort with the ventilator

• Accessory muscle use

• Patient comfort and conscious state

• Pressure areas on the skin beneath the mask, or air leaks around the mask

• Respiratory rate

• Oxygen saturations

• BP

• ABG (consider frequency based on clinical need)

Ongoing assessment of response to NIV is important in order to recognise those patients who are not improving. Limiting trials of NIV in patients whom it is unsuccessful is important so that the decision to move toward intubation & full ventilatory support is not delayed. After a trial of 1-2 hours of NIV, the absence of the above signs of improvement should alert the staff to the likelihood of failure of NIV.

Troubleshooting with Non-invasive Ventilation

* Persistent Hypercapnoea

Is the patient on too much oxygen? Adjust the FiO2 to maintain SaO2 ≥ 90%

Is the air leak excessive? Check mask fit and examine circuit for leaks.

Is re-breathing occurring? Check the patency of the expiratory port and consider an increase in EPAP to flush out more expired gas. The expiratory port should be as close to the mask as possible.

Is patient-ventilator dysynchrony a problem? Observe the chest wall movement and assess patient comfort.

Is the minute ventilation inadequate? Observe chest expansion and the measured tidal volume. Consider an increase in IPAP to achieve greater tidal volumes.

If the PaCO2 fails to improve despite BiPAP for 1-2 hours, invasive ventilation should be considered.

* Persistent Hypoxemia

Increase FiO2, aiming for O2 sats > 90%.

Consider an increase in EPAP.

* Excessive air leak

A small leak is acceptable as long as it does not blow towards the eyes.

If the leak is large, check mask fit and adjust as required. Insert any false teeth.

Check for circuit leaks.

Consider a reduction in pressure if the mask fits well and tidal volumes are adequate.

If tidal volumes are inadequate, and the mask fits well, then poor lung/chest compliance may be the problem.

* Hypotension in pre-load sensitive subjects

Ensure adequate intravascular volume before applying positive pressure ventilation.

Consider decreasing EPAP if hypoxaemia is improving as this will improve venous return.

If unable to volume load, or hypotension persists even after adequate volume loading, this is an indication that intubation & ventilation may be more appropriate.

* Decreasing level of consciousness

Check ABG for hypercapnoea.

Consider increasing IPAP to achieve greater tidal volumes if minute ventilation is low, so as to remove more CO2.

Consider other causes of ALOC including opiates, intracranial pathology.

NIV may no longer be appropriate if patient is too obtunded to protect their airway adequately.

* Increasing confusion/agitation

Check ABG for hypercapnoea and hypoxemia.

Consider increasing IPAP to achieve greater tidal volumes if minute ventilation is low, so as to remove more CO2. Consider increasing the FiO2 if persistent hypoxemia.

BiPAP may no longer be appropriate. If agitation is not due to the respiratory state and ABGs are improving (eg agitation due to claustrophobia), then a SMALL amount of sedation may be appropriate (eg morphine 2mg IV)

* Activation of abdominal muscles to terminate inspiratory flow

This is often patient-ventilator dysynchrony. Reduce the IPAP if tidal volumes are adequate, as lower pressures are often tolerated better by the patient.

If the problem is really due to a large leak causing prolonged inspiratory time, reduce the leak (see above) and consider setting time cycling (to reduce the inspiratory time)

* Nasal pressure areas

Check this area frequently and use Duoderm across the nose if there is persistent reddening.

Consider giving the patient a break from NIV if their clinical condition allows.

* Gastric distension (uncommon in adults)

Keep IPAP below the resting upper oesophageal sphincter pressure (33± 12mmHg). Insert a nasogastric tube if gastric distention occurs however this is likely to make the mask seal worse.

* Eye irritation

This might indicate excessive air leak from the top of the mask. Adjust the mask appropriately

* Barotrauma (uncommon)

Drain a pneumothorax urgently

References

Noninvasive Airway Management Techniques: How And When To Use Them

Emergency Medicine Practice July 2001: Volume 3 Number 7

BiPAP & Non-invasive Ventilation in Acute Respiratory Failure.

Wentworth Area Health Service

intensivecare.hsnet..au/five/doc/bipap_V_nepean.pdf

Non-invasive ventilation and continuous positive pressure ventilation in emergency departments: where are we now?

Bolton R, Bleetman A

Emerg Med J 2008;25:190-194 doi:10.1136/emj.2007.049072

iVent 201 Participant Guide: GE Healthcare

Hamilton T1 Ventilator Manual

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Advantages of NIV

• Improves pulmonary function

• Improves gas exchange

• Reduces venous return to the heart

• Increases functional residual capacity

• Reduces the work of breathing

• May increase or decrease cardiac output depending on underlying pathology

• Avoids the complications associated with intubation

Patients that may Benefit From Non-invasive Ventilation

• Acute exacerbation of COPD

• Obstructive sleep apnoea

• Cardiogenic pulmonary oedema without shock (CPAP)

• Asthma

• Pneumonia

• Near-drowning

• The patient with any of the above, who is not a candidate for intubation

Contraindications To Non-invasive Ventilation

Absolute Contraindications (These patients are better managed by intubation & ventilation)

• Apnoea

• Shock/Hypotension

• Inability to protect the airway

• Significantly altered mental status (eg. GCS < 10)

• Pneumothorax

• Recent gastric, laryngeal, or oesophageal surgery

• Significant facial fractures (especially involving cribiform plate)

• Inability to cooperate with fitting and wearing mask

• Rapid deterioration

• Copious secretions

• Profound hypoxemia (PaO2 < 60mmHg on FiO2 100%)

• Inadequate staff to closely monitor patient for deterioration

Relative Contraindications

• Nausea and vomiting

• Agitation

• Cardiac arrhythmias

• Cardiac ischemia or acute myocardial infarction (an absolute contraindication in some studies)

• Significant chest trauma

Disadvantages of NIV

• Reduces venous return to the left ventricle (this may also be an advantage)

• Potential for aspiration if patient vomits

Goals of NIV

• Adequate ventilation and oxygenation

• Correction of respiratory failure

• Adequate patient tolerance and comfort

Predictors of Success of NIV (after trial of 1-2 hrs)

• Decrease in PaCO2 greater than 8mmHg

• Improvement in pH of > 0.06

• Correction of respiratory acidosis

Common reasons for NIV failure

• Patient intolerance of mask

• Intermittent upper airway obstruction that is not overcome by the IPAP/EPAP settings

• Patient-ventilator dysynchrony

• Inadequate patient inspiratory effort fails to trigger IPAP

• Poor IPAP/EPAP selection

Complications of NIV

• Facial and nasal pressure injury and sores

• Gastric distension

• Dry mucous membranes and thick secretions

• Aspiration of gastric contents

• Barotrauma (less risk than with invasive ventilation)

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