Open Journal of Nursing, 2012, 2, 336-340 OJN Published Online November 2012 (
Respiratory evaluation of patients requiring
ventilator support due to acute respiratory failure
Carmen Silvia Valente Barbas, Giovana Caroline Lopes, Débora Feijó Vieira, Lara Poletto Couto,
Letícia Kawano Dourado, Eliana Caser
University of São Paulo, São Paulo, Brazil
Received 16 September 2012; revised 19 October 2012; accepted 28 October 2012
This review, based on relevant published evidence
and the authors’ clinical experience, presents how to
evaluate a patient with acute respiratory failure re-
quiring ventilatory support. This patient must be care-
fully evaluated by nurses, physiotherapists, respira-
tory care practitioners and physicians regarding the
elucidation of the cause of the acute episode of respi-
ratory failure by means of physical examination with
the measurement of respiratory parameters and as-
sessment of arterial blood gases analysis to make a
correct respiratory diagnosis. After the initial evalua-
tion, the patient must quickly receive adequate oxy-
gen and ventilatory support that has to be carefully
monitored until its discontinuation. When available, a
noninvasive ventilation trial must be done in patients
presenting desaturation during oxygen mask and or
PaCO2 retention, especially in cases of cardiogenic
pulmonary edema and severe exacerbation of chronic
obstructive pulmonary disease. In cases of noninva-
sive ventilation trial-failure, endotracheal intubation
and invasive protective mechanical ventilation must
be promptly initiated. In severe ARDS patients, low
tidal ventilation, higher PEEP levels, prone position-
ing and recruitment maneuvers with adequate PEEP
titration should be used. Recently, new modes of ven-
tilation should allow a better patient-ventilator inter-
action or synchrony permitting a sufficient unloading
of respiratory muscles and increase patient comfort.
Patients with chronic obstructive pulmonary disease
may be considered for a trial for early extubation to
noninvasive positive pressure ventilation in centers
with extensive experience in noninvasive positive pres-
sure ventilation.
Keywords: Respiratory Failure; Noninvasive Ventilation;
Endotracheal Int ubat i on; I nvasive Mechanic al
Ventilation; Patient-Ventilator Synchrony
Acute respiratory failure is a condition in which the res-
piratory system fails to keep an adequate arterial blood
oxygenation or carbon dioxide concentration. The main
causes that lead to an acute insufficient oxygenation (less
than 60 mmHg while breathing room air) or a PaCO2
elevation (more than 50 mmHg with a concomitant de-
crease in arterial pH) are: 1) Pulmonary parenchyma dis-
ease; 2) Cardiovascular disease (left ventricular failure,
pulmonary embolism); 3) Airway disease, 4) Neuro-mus-
cular disease; and 5) Respiratory drive alterations. It is
crucial to assess the cause of the acute respiratory failure
episode in order to give the patient the best treatment
option allowing its reversion [1].
During the acute episode of respiratory failure, it is ne-
cessary to verify the level of consciousness, respiratory
frequency, tidal volume and peripheral oxygen saturation
(SpO2) and PaCO2 levels. If the patient is hypoxemic an
oxygen mask must be coupled to his/her face and pulse
oximetry should be monitored to obtain a peripheral
oxygen saturation above 90%. Use of high flow nasal
cannula oxygen (HFNC) is increasingly popular in adult
ICUs for patients with acute hypoxemic respiratory fail-
ure. This is the result of the successful long-term use of
HFNC in the neonatal field and recent clinical data in
adults indicating beneficial effects of HFNC over con-
ventional facemask oxygen therapy. HFNC rapidly alle-
viates symptoms of respiratory distress and improves
oxygenation by several mechanisms, including dead-
space washout, reduction in oxygen dilution and in in-
spiratory nasopharyngeal resistance, a moderate positive
airway pressure effect that may generate alveolar re-
cruitment and an overall greater tolerance and comfort
with the interface and the heated and humidified inspired
gases. Indications of HFNC are broad, encompassing
most if not all causes of acute hypoxemic respiratory
C. S. V. Barbas et al. / Open Journal of Nursing 2 (2012) 336-340 337
failure [2].
If the patient is obtunded with irregular respirations, a
bag-mask ventilation with a as high as possible dose of
oxygen must be coupled to the patient’s face and an en-
dotracheal intubation and mechanical ventilation must be
initiated. Respiratory arrest, mental deterioration, and pro-
gressive exhaustion of respiratory muscles are also indi-
cations for endotracheal intubatio n
In patients already coupled to an oxygen mask that
present desaturation or have an arterial CO2 above 50
mmHg with a concomitant decrease in arterial pH a trial
of noninvasive ventilation may be initiated [3-5]. Pa-
tients with acute respiratory distress syndrome or hypo-
xemia, either in the postoperative setting or in the pres-
ence of immunosuppression, may also be considered for
a trial of noninvasive positive pressure ventilation. A
comfort interface with a shape and size that adequately
fits the patient’s face avoiding air-leaks is crucial for the
noninvasive ventilation trial success determining the pa-
tient’s compliance and the best synchrony between the
patient and the machine. A variety of interfaces for non-
invasive ventilation can be used in the acute care setting.
Nevertheless, prevention and monitoring of interfaces
related side-effects and evaluation of patient’s tolerance
are crucial to avoid noninvasive ventilation failure [3,4].
Assessing the success/failure of the noninvasive
ventilation trial:
After 30 minutes to 2 hours of the noninvasive venti-
lation trial initiation the patients must present:
1) A better level of consciousness and airway protec-
2) Being comfortable with the mask;
3) Decreased/normalization of respiratory rate;
4) Increased tidal volume compared to the beginning
of the trial;
5) Improved PaO2;
6) Lower PaCO2;
7) Hemodynamic stability
8) Not having a large abdominal distension.
If the patient responds well to the noninvasive me-
chanical ventilation trial, this ventilatory support moda-
lity must be continued while clinical treatment is con-
comitantly administered until the patient recovers from
the acute episode of respiratory failure allowing the dis-
continuation of noninvasive ventilation and the reinstitu-
tion of oxygen mask or room air ventilation [5].
If the patient does not respond well to the noninvasive
mechanical ventilation trial, keeping low tidal volume
ventilation, high respiratory rate, limited oxygen satura-
tion (less than 92% with FIO2 higher than 50%), pH less
than 7.2 and PaCO2 higher than 60 mmHg, endotracheal
intubation and invasive mechanical ventilation must be
promptly instituted in order to avoid complications and
guarantee a secure intubation [6-8]. After intubation, the
adequate positioning of the endotracheal tube must be
checked with a capnography or Chest-X-ray and the tube
cuff-pressure checked with a manometer and kept around
20 - 25 mmHg.
A capnography is usually used in Intensive Care to
monitor ventilation, mainly in neurologic patients. Car-
bon dioxide levels are frequently monitored during car-
diopulmonary resuscitation to aid in determining the
proper placement of an endotracheal tube and to assess
the effectiveness of resuscitation efforts. Although pulse
oximetry is useful in the assessment of oxygenation,
capnography provides more direct information on the
ventilatory status of a patient. This is particularly true
when patients are receiving supplemental oxygen, during
which oxygen saturation may be normal despite the
presence of marked hypoventilation. Conversely, capno-
graphy does not monitor oxygenation; hypoxemia may
be present even when a capnography tracing is normal.
There are two types of capnographs. Mainstream capno-
graphs use sensors that are placed directly into the
breathing circuit of a ventilator. Sidestream capnographs
draw a sample of gas away from the breathing circuit to a
separate gas sensor (The response of a sidestream device
to changes in carbon dioxide concentration is delayed by
a few seconds, since the gas must travel through the
sampling line before it can be analyzed. However, side-
stream capnographs can be used conveniently in a patient
who is not intubated if the patient is fitted with a face
mask or nasal cannula to monitor respiration. Nasal can-
nulas and face masks that feature integrated carbon di-
oxide sampling lines are commercially available. You can
modify standard face masks by attaching the sampling
line directly to the orifice of a mask or by securing the
sampling line inside the mask. A normal capnogram
shows a regular, nearly square waveform that oscillates
at the same frequency as the patient’s respiratory rate.
During inspiration, the capnogram should be at zero as
the patient breathes in fresh gas. When the patient starts
to exhale, th e first gas exhaled will be from the anatomi-
cal dead space and will contain little or no carbon diox-
ide. However, the concentration of carbon dioxide in the
exhaled gas will rise rapidly and plateau as the alveoli
begin to empty. As exhalation proceeds, the concentra-
tion of carbon dioxide remains high and increases sligh-
tly. The peak concentration reached at the end of exhala-
tion is the ETCO2. As the patient begins to inhale again,
the capnogram falls rapidly to zero, indicating the ab-
sence of carbon dioxide in the inspired gas. Capno-
Copyright © 2012 SciRes. OPEN ACCESS
C. S. V. Barbas et al. / Open Journal of Nursing 2 (2012) 336-340
grams must always be interpreted in conjunction with
other physiological variables, and clinical judgment is
important. Loss of the capnographic waveform may oc-
cur in several circumstances. These include apnea, the
disconnection of a ventilator circuit, the occlusion or
dislodgment of an endotracheal tube, or the occlusion or
disconnection of the sampling catheter. Waveforms that
do not return to zero during inspiration indicate re-
breathing of carbon dioxide, which can occur if the car-
bon dioxide absorber in an anesthesia machine is chemi-
cally exhausted, if a valve in the ventilator circuit is not
functioning properly, or if the flow of fresh gas is insuf-
ficient. An elevated baseline can also be seen if the de-
vice is calibrated incorrectly. Decreases in ETCO2 can
result from hyperventilation, pulmonary embolism, car-
diac arrest, sudden hypotension, hypovolemia, hypother-
mia, leaks in the sampling system, or a partial airway
obstruction [4]. Increases in ETCO2 may be caused by
hypoventilation, rising body temperature, bronchospasm,
adrenergic discharge, release of a tourniquet on an arm or
leg, or ventilation of a previously unventilated lung. Shal-
low breathing causes transient lowering of ETCO2 be-
cause of dead-space ventilation, but the ETCO2 rises
again after a deep inspiration when full gas exchange
A gradient exists between the PaCO2 and the ETCO2;
this gradient increases as the dead-space volume in-
creases. In disease states characterized by increased dead
space and ventilation-perfusion mismatch, such as em-
physema, an arterial blood gas analysis is necessary to
obtain an accurate determination of the PaCO2 [9].
Several recent studies have advanced our understand-
ing of dead-space ventilation in patients with acute lung
injury/acute respiratory distress syndrome (ALI/ARDS).
They have demonstrated the utility of measuring physi-
ologic dead-space-to-tidal volume ratio (VD/VT) and re-
lated variables in assessing outcomes as well as thera-
peutic interventions. These studies have included the
evaluation of mortality risk, pulmonary perfusion, as
well as the effectiveness of drug therapy, prone position-
ing, positive end-expiratory pressure (PEEP) titration,
and inspiratory pattern in improving gas exchange. In
patients with ALI/ARDS managed with lung-protective
ventilation a significant relationship between elevated
VD/VT and increased mortality continues to be reported
in both early and intermediate phases of ALI/ARDS.
Some clinical evidence now supports the suggestion that
elevated VD/VT in part reflects the severity of pulmo-
nary vascular endothelial damage. Monitoring VD/VT
also appears useful in assessing alveolar recruitment
when titrating PEEP and may be a particularly expedient
method for assessing the effectiveness of prone position-
ing. It also has revealed how subtle manipulations of
inspiratory time and pattern can improve CO2 excretion.
Much of this has been accomplished using volumetric
capnography. This allows for more sophisticated meas-
urements of pulmonary gas exchange function including:
alveolar VD/VT, the volume of CO2 excretion and the
slope of the alveolar plateau which reflects ventilation:
perfusion heterogeneity. Many of these measurements
now can be made non-invasively which should only in-
crease the research and clinical utility of volumetric
capnography in studying and managing patients with
ALI/ ARDS [10].
Assist-controlled modes are often used after sedation and
sometimes curarization for endo tracheal intubation. Usu-
ally a FIO2 of 100% is set to allo w an ad equate oxygen a-
tion until an arterial blood gas analysis is obtained. A
respiratory rate from 12 to 20 breaths per minute is often
adequate in most cases, preferably being lower in ob-
structive patients and higher in restrictive ones. Tidal
volume must be set between 5 - 7 mL/predicted body
weight, the lower values being the most suited in severe
cases with extremely low compliances and high resis-
tances [6-8]. To have the fatigued respiratory muscles
rest in these patients, 24 - 48 hours of full ventilatory
support may be needed, with sedation to su ppress the pa-
tients’ respiratory effort. In severe ARDS patients (PaO2/
FIO2 less than 120), a randomized controlled trial com-
paring cisatracurium to placebo for 48 hours showed an
improved adjusted 90-day survival rate and increased
ventilator free days in the cisatracurium group without a
significant increase in muscleweakness. Short-term pa-
ralysis may facilitate patient-ventilator synchrony in the
setting of lung protective ventilation. Short-term paraly-
sis would eliminate patient triggering and expiratory mu-
scle activity. In combination, these effects may serve to
limit regional overdistension and cyclic alveolar col-
lapse. Paralysis may also act to lower metabolism and
overall ventilatory demand [11].
In ARDS patients, protective lung ventilation strate-
gies with tidal volumes equal or less than 6 mL/kg of
predicted body weight have been associated with lower
mortality when compared with 12 mL/kg of predicted
body weight [12,13]. Use of PEEP titrated by the lower
inflection point of the inspiratory pressure-volume curve
has been associated with lower mortality in two random-
ized, prospective and randomized trial [14,15]. Recent
meta-analysis suggest survival benefits of higher PEEP
levels [16] and prone position in ARDS patients (PaO2/
FIO2 < 200) [17]. Early high pressure lung recruitment
maneuvers and application of sufficient PEEP levels to
maintain an open lung can be used in severe cases of
Copyright © 2012 SciRes. OPEN ACCESS
C. S. V. Barbas et al. / Open Journal of Nursing 2 (2012) 336-340 339
ARDS [18,19].
Controlled hypoventilation appears to improve the
clinical outcome of patients who have status asthmaticus.
Low tidal volume ventilation, acceptance of higher levels
of PaCO2 (till 80 mmHg), pH equal or higher than 7.2
and auto-PEEP monitoring to keep it less than 15 cm
H20 appears to decrease barotrauma occurrence [20].
In chronic obstructive pulmonary disease patients that
require invasive mechanical ventilation, an equilibrium
point among low tidal volume, high inspiratory flow rate
and prolonged expiratory time must be reached to avoid
excessive auto-PEEP or dynamic hyperinflation [19,20].
After 24 - 48 hours of respiratory muscles rest, as-
sisted or pressure support ventilation must be initiated in
order to preserve respiratory muscle activity and avoid
respiratory muscle dystroph y [20,21]. Patients with chro -
nic obstructive pulmonary disease may be considered for
a trial for early extubation to noninvasive positive pres-
sure ventilation in centers with extensive experience to
decrease mechanical ventilation duration [5,22].
Recently, new modes of ventilation such as neutrally
adjust ventilation (NAVA), proportional assist ventilation
plus (PAV-PLUS) and adaptative support ventilation (ASV)
are introduced in order to increase the patient control of
the ventilator and to increase information about lung
mechanics and respiratory drive. These new modes of
ventilation should allow a better patient-ventilator inter-
action or synchrony permitting a sufficient unloading of
respiratory muscles and increase patient comfort [23].
The evaluation of a patient in respirator y failure is a mul-
tidisciplinary task. It should be accomplished in a timely
manner, monitoring the patient, sequentially evaluating
physical signs and symptoms, laboratory data and timing
of noninvasive ventilation trial; endotracheal intubation.
After noninvasive ventilation or mechanical ventilation
is instituted, care should be taken to evaluate patient
comfort, synchrony and success of ventilatory support
which is a dynamic process demanding frequent re-
evaluations until the patient is ready to the spontaneous
breathing trial (SBT) and to the extubation process.
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