Mech Vent the ED - Englebrecht

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CME March 2007 Vol.25 No.3

An increasing number o critically ill patients need to be managedin emergency departments worldwide. Numerous theories haveattempted to explain the growing number o critically ill patientspresenting to emergency departments, including the complexmedical problems o an expanding elderly population in countriessuch as the USA.1Te situation in South Arica is exacerbated byHIV and trauma epidemics.

Critically ill patients who require intubation and mechanicalventilation ofen need to be treated or extended periods inemergency departments. It is thereore no longer acceptable toapply a single strategy o ventilation or all such patients. Tisis especially true with increasing awareness o the complicationso mechanical ventilation, such as barotrauma, volutrauma andbiotrauma.

In this new and challenging environment the emergency physicianis expected to be amiliar with the mechanical ventilators in his/her unit and to be able to select an appropriate strategy or eachcritically ill patient requiring mechanical ventilation. In this article,key aspects are addressed that highlight the essential skills requiredto ventilate patients saely and appropriately (able I).

Incis r hc li(Tl II)It is important to remember that the indications or endotrachealintubation and mechanical ventilation in the emergency departmentare not necessarily the same. Some patients are intubated simply orairway protection, while others are intubated owing to respiratoryailure. Where the indication or intubation is simply to protectthe airway, patients may be allowed to breathe spontaneously withsupplemental oxygen via a -tube. Indications or intubation andventilation can be divided into 2 categories: (i) ventilatory ailure,in which the neuromuscular mechanisms o breathing cannotmaintain adequate ventilation in the presence o normal lungs; and(ii) oxygenation ailure, which usually occurs with disease o the

airway or lung parenchyma.

Mde o liPositive pressure breaths may be delivered to the airways o patientsreceiving mechanical ventilation in two ways, namely mandatory(ventilator breathes or the patient and perorms all the work obreathing), or assisted (patient-triggered breath with support romthe ventilator).

Furthermore, each breath is preset to deliver either a targettidal volume or inspiratory pressure (depending on the mode oventilation). Te most commonly used mode o ventilation is thatwhich is volume targeted (i.e. a preset tidal volume is delivered at apredetermined requency and flow rate). Alternatively, a pressure-targeted mode may be selected (i.e. preset inspiratory pressuredelivered to the airways).2Tese modes, with examples o each, aresummarised in Fig. 1.

Mhc li mrgncydprm

Intubation and mechanical ventilation are ofen needed in emergency

treatment.

A ENGELBRECHT,MB ChB, MMed (Fam Med), Dip PEC, DAHead, Emergency Medicine Unit, University o Pretoria Medical School and Pretoria Academic Hospital

Andreas Engelbrecht is Head of the Emergency Unit at Pretoria Academic Hospital. He has a special interest in airway management and in the provisionof critical care in the emergency department.

G R TINTINGER,MB ChB, MMed (Int)Head, Medical ICU, Department o Internal Medicine, Pretoria Academic Hospital and University o Pretoria

Greg intinger has a keen interest in critical care medicine and pulmonology.

Fig. 1. Modes of ventilation.

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It is vital to be amiliar with the basicmodes o ventilation that can be used in theemergency unit. Rather be expert in ewerventilation modes and with the ventilatorscommonly used in your unit, as this willbe sufficient or most circumstancesencountered.

Sdr tngsA sound working knowledge o themechanical ventilators used in your hospitalpermits ventilator parameters to be setconfidently without undue delay.3Te basicparameters to be set differ slightly accordingto the mode o ventilation, but usuallyinclude the parameters or volume andpressure-targeted modes set out in able III.

Note: Peak airway pressures are dependenton lung and chest wall compliance as well asairway resistance and may vary rom patientto patient in volume-driven modes.Similarly, the tidal volume delivered to

the patient is not guaranteed when usingpressure-driven modes.

Gs o liTe primary goal o mechanical ventilationis adequate oxygenation. Tis should beconfirmed by serial arterial blood gas

determinations o PaO2 and saturationafer initiation o mechanical ventilation.

Te traditional approach has been to aim ornormoxia, normocarbia and a normal pH.4In patients with primary lung pathology,aiming or these goals can lead to highairway pressures (barotrauma), large tidalvolumes (volutrauma) and high inspiredoxygen concentrations (oxygen toxicity).Tereore, or patients with ARDS permissivehypercapnoea (PaCO2 50 cm H2O) andmoderate acidosis (pH 7.25 - 7.40) may beallowed in order to protect the lungs. In

patients without underlying lung diseasethe traditional approach can be ollowed.

Te second important goal o ventilationis to reduce the work o breathing o thepatient to prevent atigue o the respiratorymuscles. Tis will lower the oxygendemand on the respiratory muscles andconserve oxygen or vital organs.

Te third goal is that o a comortablepatient on the ventilator. Tis is achieved

by selecting the correct mode o ventilationand by providing sufficient sedation andanalgesia.

Goals of mechanical ventilation

Oxygenation (most important).

Protect lungs rom barotrauma andvolutrauma.

Reduce work o breathing o patient.

Patient must be comortable on ventilator.

Correct acid-base balance.

Sl i o lirgyTe ventilation strategy reers to theventilator settings appropriate or thespecific condition o the patient.5 Treegroups o patients can be identified basedon clinical and radiological findings.

Firstly, those with normal lungs in whomstandard settings may be used.

Secondly, those with lung infiltratesdue to pneumonia, ARDS, aspiration

or cardiogenic pulmonary oedema andaccumulation o fluid in the alveoli, whichdecrease lung compliance. Tis leadsto hypoxia and high airway pressureswhen standard settings are used. Inthese patients application o PEEP is themost effective way to recruit collapsedalveoli and improve oxygenation. Othermethods include inverse ratio ventilationwhere the I:E ratio is increased to 1:1, orprone positioning which may be difficultto perorm in the emergency department.Smaller tidal volumes should be selectedto maintain plateau pressures below 35 cm

H2O and peak airway pressures 45 cmH2O.

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Tirdly, or patients with severe airflowobstruction due to asthma and COPD, theset rate should be lowered to allow longerexpiratory times and I:E ratios o 1:3 or 1:4.Volumes should be reduced with higherinspiratory flows, which allow a greaterportion o the ventilatory cycle to be spentin expiration. Because intrinsic PEEP maybe increased in asthma and COPD, theuse o applied (extrinsic) PEEP should belimited (< 5 cm H2O) (see the algorithm

or selection o a ventilation strategy).7

Table II. Indications for mechanical ventilation

Failure to breathe (normal lungs) CNS pathology, e.g. severe head injury or decreased cerebral perusion due to shock Drugs and poisons, e.g. heroin overdose Neuromuscular disease, e.g. myasthenia gravis or Guillain Barr syndrome

Poor gas exchange (sick lungs) Localised or diffuse lung infiltrates, e.g. acute respiratory distress syndrome (ARDS),

severe cardiogenic pulmonary oedema, pneumonia and aspiration Severe airflow obstruction, e.g. asthma/chronic obstructive pulmonary disease

(COPD)

Table I. Key questions to ask before and during the mechanical venti-

lation of a critically ill patient in the emergency department

What are the indications or mechanical ventilation?

Which mode o ventilation should I select?

What are the standard settings or ventilated patients?

What are the goals o ventilation? Which strategy o ventilation is appropriate or the specific clinical condition?

When should I use positive end-expiratory pressure (PEEP)?

How should I respond when a ventilator alarm is triggered?

What are potential complications o mechanical ventilation?

How should mechanical ventilation be discontinued?

Table III. Parameters to be set (suggested values for patients withnormal lungs)

Volume-targeted mode Pressure-targeted mode

Oxygen concentration (FiO2) (< 60%) FiO2(< 60%)

Rate/min (10 - 20) Rate/min (10 - 20)

idal volume (8 -10 ml/kg) Inspiratory pressure (10 - 30 cmH2O)

Inspiratory flow rate (50 - 70 l/min) Inspiratory:expiratory ratio(determines inspiratory time) (I:E = 1:3)

PEEP (3 - 5 cm H2O) PEEP (3 - 5 cm H2O) Alarm limits Alarm limits

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Vlr lrsVentilator alarms are used to alert nursesand clinicians that a set limit (pressure,volume, rate, FiO2) has been reached,which may have deleterious consequencesor the patient. Te ollowing steps shouldbe taken when a ventilator alarm sounds.

1. Check patients oxygenation and

peripheral saturation.2. Make sure that the ventilator circuit is

intact, with the endotracheal tube inthe correct position.

3. Confirm breath sounds in both lungs.

4. Determine the reason or the alarm alertand treat according to the underlyingcause, e.g. high peak airway pressuresmay be caused by airway secretions,biting on tube, kinked tubing,bronchospasm or pneumothorax.

5. Chest X-ray or arterial blood gas may

be needed as part o the assessment.6. Never ignore an alarm alert it is

usually or a good reason.

Ccis ohc li Complications o endotracheal

intubation, e.g. endotracheal tube inoesophagus or right main bronchus ortracheal tear.

Pneumothorax and tension pneumo-thorax (Fig. 4).

Oxygen toxicity.

Lung injury due to volutrauma,

barotrauma and atelectotrauma.

Hyperventilation and hypoventilation.

Inection.

Hypotension.

Acute myocardial inarction.

Stress ulceration.

Dscui ohc li(ng)Mechanical ventilation can usually bediscontinued when the ollowing criteriaare met:

good oxygenation (PaO2 > 70 mmHg,saturation 92%) on FiO2 o 40% andPEEP = 5 cm H2O

the condition necessitating ventilationhas been reversed (e.g. patient regainsconsciousness)

patient is haemodynamically stablewithout significant cardiac arrhythmiasor impending organ ailure

patients level o consciousness allowsspontaneous breathing and adequateprotection o airway (without excessivesedation).

Numerous methods or the discontinuation oventilation have been advocated (e.g. IMV,pressure support) with ew significantadvantages o any particular one othese being ound during randomised

controlled trials. Te principle behindeach one is to allow patients to increasetheir own work o breathing whilereducing the contribution o the ventilatorwithout unnecessary delay. Tereore, assoon as a patient meets the above criteria,measure the rapid shallow breathing index(RSBI) (respiratory rate/tidal volume)afer spontaneous breathing or 1 min,and i RSBI < 105 institute a spontaneousbreathing trial (SB). Te SB should lastabout 30 - 90 min with careul monitoringo peripheral saturation, respiratory rate,pulse rate, blood pressure, mental status

and pattern o breathing. Te SB shouldbe terminated i patients develop signs orespiratory muscle atigue (respiratory

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Setting positive end-expiratory pressure

(PEEP)

PEEP reers to a level o positive pressuremaintained during the expiratoryphase o ventilation, which acilitatesrecruitment o non-unctioning regionso the lung.

PEEP is applied to minimise alveolarcollapse (atelectasis) associated withconditions such as ARDS, aspiration,multilobar pneumonia and cardiogenicpulmonary oedema. With high levelso PEEP, patients should be closelymonitored or adverse effects such as

hypotension resulting rom diminishedcardiac preload and cardiac output orbarotrauma.

Fig. 2. Bilateral infiltrates typical of ARDS.

Fig. 4. Tis patient developed a pneumo-thorax during mechanical ventilation.

Fig. 3. Hyperinflated lungs typical of COPD.

Table IV. Ventilation strategies for lung infiltrates and airflowobstruction

Lung infiltrates Airflow obstruc-tion

(ARDS, pneumonia) (asthma, COPD)X-ray image Fig. 2 Fig. 3Ventilator settings

FiO2 100% until condition is 100% until condistabilised, then < 60% tion is stabilised,

then < 60%

idal volume 6 - 8 ml/kg to keep airway 6 - 8 ml/kg topressures low minimise exhaled

volumes Respiratory rate 16 - 24/min 6 - 10/min PEEP 8 - 15 cm H2O 0 - 4 cm H2O I:E ratio 1:2, consider inverse ratio 1:1 1:3 to 1:4 to allow

only i SO2< 90% despite longer time oradequate PEEP expiration

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I An increasing number o patients need to be managed in emergency departments worldwide.

Te situation in South Arica is exacerbated by HIV and trauma epidemics.

Mechanical ventilation is an important acet o critical care provided in emergency departments.

Indications or mechanical ventilation include ailure to breathe in spite o normal lungs and poor gas exchange due to sick lungs.

Each physician should be amiliar with the basic modes o ventilation that can be used in emergency units.

Te goals o ventilation include oxygenation, lung protection, reduced work o breathing, acid-base balance and that the patient shouldbe comortable on the ventilator.

Separate ventilation strategies exist or patients with normal lungs, patients with outflow obstruction such as COPD and asthma, andpatients with lung infiltrates such as ARDS and pneumonia.

Never ignore a ventilator alarm sounding it exists or a good reason.

Mechanical ventilation can be discontinued when the patient is stable and the condition necessitating ventilation has been reversed.

rate > 30/min or abdominal paradox),marked anxiety or significant alterations invital signs rom baseline values. Extubationcan proceed afer completion o a successulSB.

References

1. Goldstein RS. Management o the critically illpatient in the emergency department: ocus on

saety issues. Critical Care Clin 2005; 21: 81-89.

2. Gali B, Deepi GG. Positive pressure mechanicalventilation. Emerg Med Clin N Am 2003; 21:453-473.

3. Orebaugh Sl. Initiation o mechanical ventilationin the emergency department. Am J Emerg Med1996; 14: 59-69.

4. Bhangwanjee S. Teory and practical issuesin ventilatory support o the trauma victim.rauma and Emergency Medicine1999; 16: 35-

39.

5. Spritzer CJ. Unravelling the mysteries omechanical ventilation: a helpul step-by-stepguide. J Emerg Nurs2003; 29: 29-36.

6. Ware LB, Matthay MA. Medical progress: theacute respiratory distress syndrome. NEJM2000; 342: 1334-1349.

7. Phipps P, Garrard CS. Te pulmonary physicianin critical care: Acute severe asthma in theintensive care unit. Torax2003; 58: 81-88.

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ngl rPersistent otitis media and development

A new study, published in the New England Journal of Medicine, suggests that persistent otitis media in young children does not causedevelopmental problems later in lie. In the trial, which started in 1991, researchers ollowed a cohort o 241 children with otitis media.Tey ound that early treatment with tympanostomy tubes made no difference to cognitive, academic or social development o childrenup to the age o 11 when compared with 6 months o watchul waiting. Te final results were consistent with previous findings rom thesame children at the ages o 3, 4 and 6 years. Te trial started when there were serious concerns in the USA but no real evidence thatpersistent middle-ear effusion could cause irreversible damage to a childs ability to learn. Placement o tympanostomy tubes became

the second most common operation in the USA, afer neonatal circumcision.

Paradise JL, et al. N Engl J M2007; 356: 300-302.

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Mech Vent the ED - Englebrecht