Non-invasive Mechanical Ventilation
in Acute Hypoxemic Lung Injury(AHLI).
Immediate effects analysis.
Dr. Lasdica Sergio (2),
Dr. Fainstein Daniel (1), Dr. Casas Pablo (2),
Dr. Frizza Ignacio(2),
Dr. Sierra Fernando (2), Dr.Ontivero Marcelo (2), Dr. Giussani Juan .
Chief Medical Physician.
Intensive Care Unit. Hospital Privado del Sur. Bahía Blanca. Argentina
Duty Physicians. Intensive
Care Unit. Hospital Privado del Sur. Bahía Blanca. Argentina.
Address
for correspondence:
Dr. Sergio Lasdica
Unidad de Cuidados Intensivos.
Hospital Privado del
Sur.
Las Heras 164.
8000 Bahía Blanca.
Argentina.
Tel: (#54)-(0)291- 455-0270
Fax: (#54)-(0)291- 453-9516
e-mail: slasdica@ topmail.com.ar
Acute lung injury (ALI)
is one of the most frequently attended pathologies in Intensive Care Units
(ICU). This is caused by distinct medical and surgical complications, which
directly provoke pulmonary damage, disturbing the gaseous interchange and
the pulmonary compliance leading to respiratory muscular fatigue. Mechanical
muscular assistance is a vital component in the treatment of this affection.
In most cases orotracheal intubation (OTI) or tracheostomy is required.
Various complications can occur and these are associated with the intubation
procedure, during the mechanical ventilation (MV) or even after the weaning
of the patient (1,2).
A new option for the treatment
of ALI has appeared through the use of non-invasive mechanical ventilation
(NIMV), which is used firstly for patients with neuromuscular disorders,
being applied either by means of negative external pressure or by oscillation
of the thoracic wall (3). However, the use of ventilatory support pressure
(PSV) administered with facial or nasal masks achieved a more physiological
and comfortable method to improve ventilation, obtaining mayor benefits
from gas interchange and respiratory works with a decline in the incidence
of OTI, mortality and time in the Intensive Care Unit (4,5). As the OTI
is not required, the benefits over the conventional MV are important: the
defence mechanisms of the larynge, speech and deglutition are maintained
with mayor comfort to the patient. Nevertheless, the NIMV also has its
limitations such as the necessity for the collaboration of the patient,
the absence of direct access to the airway to extract secretions, the occasioning
of facial lesions discomfort from the mask and a potential respiratory
deterioration if the patient suffers dissynchronization with the ventilator
(6). The benefits were proved by various studies (7,8), principally of
acute hypercapnic respiratory failure. There is insufficient evidence,
at this moment, to demonstrate the effectiveness of the NIMV in acute hypoxemic
lung injury (AHLI) exclusively (9). It is for this reason that we carried
out this prospective study, with the object of evaluating the immediate
effects of the NIMV on OTI necessity, gaseous interchange, mortality rate
and the time spent in intensive care on AHLI patients who did not present
cronic obstruction pulmonary disease (COPD) or asthma antecedents, and
who under standard conditions, out of protocol, would require immediate
intubation and initiation of the conventional MV.
Material
and Methods
Selection of Patients
AHLI patients, who did
not have COPD or asthma antecedents, were included in the study immediately
on being admitted to the Intensive Care Unit of the Hospital Privado del
Sur in Bahía Blanca in order to better their clinical condition.
The protocol was approved by the Teaching and Investigation Committee of
the hospital.
On being admitted their
APACHE II (10) and acute lung injuries (11) score were analysed. The AHLI
diagnosis was carried out based on the following clinical and gasometric
criteria:
Severe dyspnea, with utilization
of the accessory inspiratory muscles.
Respiratory frequency of
more than 30 per minute.
Arterial oxygen pressure
(PaO2) less than 60 mmHg.
Arterial oxygen saturation
inferior to 90%.
A PaO2/FiO2
relation of less than 300.
The intensive medical management
consisted of oxygen therapy applied immediately on being admitted to intensive
care, administered through Venturi system masks with an inspired oxygen
fraction (FiO2) of 50%, together with the appropriate hemodynamic
support and antibiotic therapy if needed.
The criteria for exclusion
from the study were:
Patients with COPD and asthma
antecedents
Arterial pressure of less
than 90 mmHg or the use of large doses of inotropic drugs or vasopresors.
The presence of unstable
angina or a recent acute myocardium infarction (less than 3 months).
The presence of grave arrhythmia.
The necessity for orotracheal
intubation to protect the airway (patients in coma or with convulsions.
Bad management of secretions.
Non-invasive
Ventilatory Strategy
When a patient entered
the Intensive Care Unit with the criteria necessary to enter in the study,
the treatment was initiated by administering an inspired oxygen fraction
(FiO2) of 50%, using a Venturi mask, the analysis of sanguineous
arterial gases, and registering, at the same time, the respiratory and
cardiac frequencies. If the condition of the patient did not improve under
conventional treatment the VMNI with PSV was initiated adding positive
end expiratory pressure (Peep) through facial masks. This was fixed in
place using rubber harnesses which minimized the escape of air and possible
facial lesions. An analysis of arterial gases was carried out, [pH, arterial
carbon-dioxide pressure (Paco2), arterial oxygen pressure (Pao2), and arterial
saturation], in order to calculate the Pa/FiO2 ratio as gaseous
interchange parameters, the respiratory and cardiac frequencies as clinical
parameters, and PSV and Peep as parameters ventilatory, at base time, after
sixty minutes and after 6 hours on NIMV. When the process was well tolerated
and the clinical condition improved the decision was taken to continue,
uninterrupted, the ventilatory process.
If the NIMV was ineffective
or the condition of the patient did not improve, intubation orotracheal
and conventional MV was carried out. The VSP and Peep were administered
using Bird 6400 ST commercial ventilators connected to a standard circuit
with a facial mask. The sensitivity of the trigger was adjusted minimally
so that the patient had to make only the least effort in order to trip
the respirator, avoiding the autocycle. The levels of the PSV, Peep and
FiO2 were adjusted so as to attain a respiratory frequency of
less than 30 cycles per minute and arterial oxygen saturations and pressures
(PaO2) greater than 90% and 60 Torr respectively. The FiO2
was progressively reduced until it reached an inferior level, whilst maintaining
greater than 90% saturations. When the patient showed a lack of co-operation
through excessive respiratory exertion, mask compression, or air leaks
through the mask, the facial mask or the level of PSV was adjusted. The
situation was controlled for a period of no more than 10 minutes in order
to try to revert the situation. After overcoming the initial acute phase
and after 6 hours of favourable results, the doctor could decide to withdraw
the transitory NIMV and administer oxygen through the Venturi mask at the
same concentration as prior to the withdrawal of the NIMV. For the rest
of the time that the patient was assisted, the gaseous interchange controls
were carried out through additional blood analyses of arterial gases. The
observance of oxygen saturation was carried out through the same process
or by pulse oxymetry.
Statistical
Analysis
Where appropriate the
variance analysis for repeated samples (ANOVA) or the Kruskal-Wallis test
was used, where a p inferior to 0.05 was considered significant.
Results
Twenty-nine patients,
who could tolerate NIMV and who did not present transitory hemodynamics,
were admitted into the study. The demographic characteristics of the patients
is shown in Table 1. The causes of AHLI are detailed in Fig.1.
The mean duration of NIMV
was 1.62 ± 0.86 days. Fig.2 describes the general levels of PSV
and Peep used and the differences between patients included in and those
excluded from the trials. Seven patients who did not improve their clinical-gasometrical
status when controlled after 6 hours had to be intubed. The reasons for
intubation were: excessive muscular exertion (3 patients), failure to achieve
a significant gaseous interchange improvement (2 patients) and intolerance
to the mask (2 patient). Of the 27 patients who were entered into the study
7 died (26%). The clinical data and the gaseous interchange of the patients
who required intubation and who died are detailed in Table 2.
The major significant
benefits were obtained via the reduction in respiratory rate (RR), the
increase in the Pa/FiO2 ratio and the reduction of the cardiac
rate (CR) with relation to the state at admission and after the first 6
hours from starting the assistance. Fig.3.
Between the patients without
and with intubation there was found to be a statistically significant improvement
of the RR and CR, provoking an improvement in the Pa/FiO2 ratio.
Fig.4.
Significant differences
were obtained between the pulmonary injury scores of the patients with
and without intubation.(2.0 ± 0.4 vs 2.5 ± 0.36 p = 0.01),
which did not occur when the APACHE scores were compared between the two
groups. Internment in the Intensive Care Unit was less for patients without
intubation (4.7 ± 3.3 vs 9.9 ± 7.8 p = 0.02) than for those
with intubation.
The subjective tolerance
to the mask was very good and there was no necessity to exclude patients
from the study for this reason. There were three cases (10,3%) of nasal
skin lesions but no other complications were observed. The application
of PSV and Peep diminished the inspiratory effort, and a reduction in the
use of accessory muscles, principally the sternocleidomastoid, was observed.
After 48 hours under the protocol and on suspending the NIMV, the patients
maintained their spontaneous respiration without clinical or gasometric
changes.
Discussion
The results of this study
demonstrated that NIMV applied through a facial mask could reduce the need
for intubation by 75,9% and also internment in the Intensive Care Unit
for patients with AHLI. (12).
On applying NIMV with
PSV, the patient increased the actual spontaneous respiratory volume, maintaining
her respiratory pattern (RR and the inspiration-exhalation ratio). When
the PSV was increased it proportioned higher flow and mayor volume at the
same time and for the same inspiratory effort. (13). The patient adapted
her respiratory pattern and improved the alveolar ventilation producing
a reduction in the respiratory rate which augmented the respiratory time.
The PSV reduced respiratory effort and the consumption of oxygen by the
respiratory muscles in proportion to the level of PSV used, a situation
which also occurs when it is administered in a non-invasive form, (14).
The addition of Peep generated
the opening and conscripting of collapsed alveoli, redistributing the interstitial
liquids and proportioning an increase in the gaseous interchange surface,
improving the residual functional capacity and the pulmonary compliance.(15).
Thus, the PSV, by reducing respiratory effort and augmenting alveolar ventilation,
and the Peep, by increasing the residual functional capacity and the gaseous
interchange surface, improved the ventilatory and general condition of
the patient. Brochard et al., (4) used a PSV system which operated
by on-demand valves which were activated by the patient’s efforts and which
reduced the effort necessary to trigger the respirator. This study, as
in other studies (5.16), used commercial ventilators homologous with the
systems used by Brochard, which, moreover, are widely used in distinct
Intensive Care Units.
In spite of the differences
in design, quality and quantity of the patients, and taking principally
into account the type of respiratory failure, the results, obtained on
comparing the OTI, interment time and mortality rates, are comparable with
those described in other publications (5, 17, 18). Although the incidence
of intubation and the rate could be considered higher than those in other
studies (7, 12, 19) it is believed that this difference is due to the fact
that the patients treated were, exclusively, those with acute hypoxemic
respiratory failure, as the patients who received intubation, in spite
of an improvement in the gaseous interchange, required a greater PSV, Peep
in order to maintain saturations and oxygenation in accordance with the
established objectives, making one presume that the predominant alveolar
compromise on the ventilation, and as the shunt was the predominant physiopathelogical
mechanism in these patients, thus one
reflects, also, that the
pulmonary injury score presented by the patients who had to be intubed,
would have been greater in the same.
It was observed that the
rapid improvement was not only at the gaseous interchange level, but also
at a clinical level. This could not be only due to the use of PSV, but
also through the addition of distinct levels of Peep, which improved the
general condition of the patients.
The tolerance to the apparatus
was excellent in the majority of the cases, without encountering resistance
on the part of the patients during the realization of the procedure. This
was due to two factors, the ventilators and the masks used in this study.
The former proportion a PSV with a high respiratory flow which compensates
the demand from the inspiratory effort necessary to trigger the respirator.
The latter had the advantage of proportioning greater comfort to the patient,
permitting the ingestion of aliments, liquids and inclusively it alleviated
the sensation of claustrophobia described by several (6). However, according
to several publications, facial masks would be more efficient for administering
ventilatory support (7, 20). This study used facial masks due to the fact
that the majority of the patients with severe AHLI had dyspnea and thus
breathed through an open mouth, which situation would cause a loss of ventilatory
efficiency if nasal masks were used. The increase in dead space produced
through the use of facial masks was compensated for through the contribution
of an adequate PSV (5). These masks caused only rarely caused lesions to
the nasal wall (3 patients), which were believed to have been caused exclusively
by the pressure used to maintain the masks over the nasal zone, and which
were alleviated and corrected by the collocation of dressings over the
major pressure points. There were no patients who presented abdominal distension.
It was concluded that
NIMV using facial masks is a safe and reliable method for the alleviation
of dyspnea in patients with AHLI who are willing to co-operate, improving
the alveolar ventilation and the clinical-gasometrical state of these patients,
without occasioning excessive adverse effects, and permitting the maintenance
of spontaneous ventilation whilst carrying out medical treatment. Also
it was able to reduce costs through the shorter interment time in the Intensive
Care Unit.
Bibliography
Fagon J, Chastre J, Hance
A. Nosocomial pneumonia in ventilated patients: A cohort study evaluating
attributable mortality and hospital stay. Am J Med 1993; 94: 281-88
Stauffer J, Olson D, Petty
T. Complications and consequences of endotracheal intubation and tracheotomy.
Am J Med 1981; 70: 65-76.
Fasano L, Fabbri M, Sturani
C. Acute ventilatory effects of extrathoracic negative pressure ventilation
in stable COPD: Iron lung (IL) vs pneumowrap (PW). Am Rev Respir Dis 1991;
143: A686 (abstract).
Brochard L, Isabey D, Piquet
J. Reversal of acute exacerbations of chronic obstructive lung disease
by inspiratory assistance with a face mask. N Engl J Med 1990; 323: 1523-30.
Fernandez R, Blanch Ll, Vallés
J. Pressure support ventilation via face mask in acute respiratory failure
in hypercapnic COPD patients. Intensive Care Med 1993; 19: 456-61.
Conti G, Antonelli M, Gasparetto
A. Non-Invasive Ventilation 1997; 495-504. In Yearbook of Intensive Care
and Emergency Medicine. Vincent JL Eds. Springer-Verlag. Berlín
1997.
Brochard L, Mancebo J, Wysocki
M. Noninvasive ventilation for acute exacerbations of chronic obstructive
pulmonary disease. N Engl J Med 1995; 333: 817-22.
Meduri GU, Turner R, Abou-Shala
N. Noninvasive positive pressure ventilation via face mask. Chest 1996;
109: 179-93.
Keenan S, Brake D. An evidence-based
approach to noninvasive ventilation in acute respiratory failure. Crit
Care Clin 1998; 14 (3): 359-71.
Knaus W, Draper E, Wagner
D. APACHE II: A severity of disease classification system. Crit Care Med
1985; 13: 818-29.
Murray J, Matthay M, Luce
J. An expanded definition of the adult respiratory distress sydrome. Am
Rev Respir Dis 1988; 138: 720-23
Antonelli M, Conti G, Rocco
M. A comparison of noninvasive positive-pressure ventilation and conventional
mechanical ventilation in patients with acute respiratory failure. N Engl
J Med 1998; 339: 429-35.
Brochard L, Pluskwa F, Lemaire
F. Improved efficacy of spontaneous breathing with inspiratory pressure
support. Am Rev Respir Dis 1987; 136: 411-15.
Appendini L, Pasessio A,
Zanaboni S. Physiologic effects of positive end-expiratory pressure and
mask pressure support during exacerbations of chronic obstructive pulmonary
disease. Am J Respir Crit Care Med 1994; 149: 1069-76.
Marini JJ, Wheeler AP: Positive-end
expiratory Pressure. In: Critical Care Medicine: The Essentials. Second
Edition. Baltimore, Lippincott Williams and Wilkins, 1997, p 169.
Meduri GU. Noninvasive positive
pressure ventilation in patients with acute respiratory failure. Clin Chest
Med 1996; 17: 513-53
Bott J, Carroll M. Conway
J. Randomised controlled trial of nasal ventilation in acute ventilatory
failure due chronic obstructive airways disease. Lancet 1993; 341: 1555-57.
Kramer N, Meyer T, Meharg
J. Randomized, prospective trial of noninvasive positive pressure ventilation
in acute respiratory failure. Am J Respir Crit Care Med 1995; 151: 1799-806.
Keenan SP, Kernerman PD,
Cook DJ. The effect of noninvasive positive pressure ventilation on mortality
in patients admitted with acute respiratory failure: a meta-analysis. Crit
Care Med 1997; 25:1685-92.
Vitacca M, Rubini F, Foglio
K. Non-invasive modalities of positive pressure ventilation improve the
outcome of acute exacerbations in COLD patients. Intensive Care Med 1993;
19: 450-55.
Table 1
Demographic data of
patients with AHLI
M: male.
F: female.
I.P.: intrahospital
pneumonia.
E.P.: extrahospital
pneumonia.
Pop. Thorax: postoperatory
thorax surgery.
Pop. Abdomen: postoperatory
abdominal surgery.
ALIS : acute pulmonary
injury score.
RR1: respiratory rate
on entry to the ICU.
CR1: cardiac rate on
entry to the ICU.
Pafio1: artrial pressure
of oxygen inspired oxygen fraction frequency on entry to the ICU.
RR3: respiratory rate
after 6 hs. of NIMV assistance.
CR3: cardiac rate after
6 hs. of NIMV assistance..
Pafio3: artrial pressure
of oxygen inspired oxygen fraction frequency 6hs after entry to the ICU
Fig. 1
Causes of acute pulmonary
injury.
Fig.2
PSV values and Peep.
* Kruskall – Wallis –
p value for PSV in intubated patients (p = 0,005)
** Kruskall – Wallis –
p value for Peep in intubated patients (p = 0,005)
PSV: pressure support
ventilation (cm H2O)
Peep: positive
final exhalation pressure (cm H2O).
Fig. 3
Respiratory and cardiac
rates values requencies and the Pa/fiO2 ratio on intermente,
at one hour and after 6 hours of NIMV assistance.
RR: respiratory
rate. (p < 0,05)
CR: cardiac rate.
(p < 0,05)
Pa/fio2: arterial
oxygen pressure/inspired oxygen fraction ratio. (p < 0,05) (ANOVA)
Fig. 4
Respiratory and cardiac
rate values and the Pa/fiO2 ratio between intubed and non-intubed
patients.
RR3: respiratory
rate after 6 hs.
CR3: cardiac rate
after 6 hs.
Pafi3: arterial
oxygen pressure inspired oxygen fraction ratio after 6 hs.
(*) Kruskall-Wallis Test.