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On-line version ISSN 1806-907X
Rev. Bras. Anestesiol. vol.55 no.6 Campinas Nov./Dec. 2005
Alveolar recruitment maneuver in anesthetic practice: how, when and why it may be useful*
Maniobra de reclutamiento alveolar en anestesia: como, cuando y por qué utilizarla
Luciana Oliveira Gonçalves, M.D.I; Domingos Dias Cicarelli, TSA, M.D.II
Especialista em Terapia Intensiva
IIAnestesiologista; Especialista em Terapia Intensiva/AMIB
OBJECTIVES: Alveolar recruitment maneuver (ARM) is the reopening of lung
tissue collapsed by increased airway inspiratory pressure, primarily performed
in patients with acute respiratory distress syndrome. This study aimed at evaluating
ARM in anesthesia, how to do it and in which clinical situations.
METHODS: Literature review using MedLine database in the period 1993 to 2004.
RESULTS: Most common approach for recruitment maneuver is sustained inflation by CPAP with pressures varying from 30 to 40 cmH2O for 30 to 90 seconds. ARM was beneficial during laparoscopic procedures, single-lung ventilation surgeries and cardiac surgeries, and for obese and pediatric patients.
CONCLUSIONS: Recruitment maneuver may be useful for anesthetic practice, improving postoperative oxygenation and re-expanding atelectasis of anesthetized patients.
Key words: ANESTHESIA: General; COMPLICATIONS: atelectasis; MECHANICAL VENTILATION: alveolar recruitment maneuver, PEEP
Y OBJETIVOS: La maniobra de reclutamiento alveolar (MRA) consiste en la
reabertura de áreas pulmonares colapsadas a través del aumento de
la presión inspiratoria en la vía aérea, utilizada principalmente
en pacientes con Síndrome del Desaliento Respiratorio Agudo. Este estudio
tuvo como objetivo evaluar la aplicación de la MRA en anestesia, como realizarla
y en cuales situaciones clínicas.
MÉTODO: Revisión de la literatura a través de la base de datos MedLine, en el período transcurrido entre 1993 a 2004.
RESULTADOS: La forma más utilizada para realización de la MRA es la insuflación sostenida por el modo CPAP con presiones que varían de 30 a 40 cmH2O por 30 a 90 segundos. Las cirugías laparoscópicas, las cirugías con ventilación monopulmonar, cirugías cardíacas, pacientes obesos y pacientes pediátricos fueron las situaciones clínicas en que la MRA trajo beneficio a los pacientes.
CONCLUSIONES: La MRA puede ser útil en la práctica anestésica, mejorando la oxigenación postoperatoria y deshaciendo atelectasias de pacientes sometidos a anestesia general.
Mechanical ventilation (MV) has contributed to improve survival in different clinical situations, but notwithstanding its major advances, it may increase morbidity and mortality rate when inadequately used 1. MV may promote or perpetuate lung injury if there is cyclic alveolar hyperdistension and collapse at every breath. Some authors 2,3 consider ventilator-induced lung injury as undistinguishable from changes induced by acute respiratory distress syndrome (ARDS) and agree that inadequately applied MV increases ARDS mortality.
ARDS and acute lung injury (ALI) pathophysiology is the alveolar filling by inflammatory infiltrate, alveolar collapse and decreased aired lung volume. These changes alter ventilation-perfusion ratio with increased intrapulmonary shunt and worsening of arterial and tissue oxygenation 2. To improve survival of these patients, Amato et al. 4 have suggested ventilation as lung protecting strategy, consisting in low tidal volumes (4 to 6 mL.kg-1), maximum plateau pressure of 35 cmH2O and PEEP above the lower inflexion point of the VP curve.
General anesthesia with mechanical ventilation may cause cyclic alveolar hyperdistension and collapse, especially when high tidal volumes (12 to 15 mL.kg-1) are used without PEEP 5-7. In addition, decreased functional residual capacity (FRC) and atelectasis 8-11 (which appear 5 minutes after beginning of anesthesia 12) increase intrapulmonary shunt often leading to decreased postoperative arterial oxygenation. This fact may become more severe when surgical technique or patients' characteristics favor MV-induced changes. Laparoscopic surgeries (pneumoperitoneum inflation decreases FRC and predisposes to atelectasis), single-lung ventilation procedures (operated lung is not ventilated), cardiac surgeries (lungs are not ventilated during cardiopulmonary bypass), obese patients (they have decreased FRC) and pediatric patients (anesthetized with spontaneous ventilation) may further worsen postoperative arterial oxygenation 9,11,13-15.
Alveolar recruitment maneuver (ARM) is a technique using sustained airway pressure increase aiming at recruiting collapse alveoli, increasing lung area available for gases changes and consequently improving arterial oxygenation16. It is not only used in ARDS patients but also in clinical situation with the development of collapsed lung areas (atelectasis).
This study aimed at identifying, by literature review, the role of ARM in anesthesia and when and how to do it.
Literature review using MedLine database of the last 12 years (1993 to 2004). Articles published in English and Spanish were included by the crossing of keywords: anesthesia (anesthesia/anaesthesia) and recruitment maneuver (recruitment maneuver/maneuver) or alveolar recruitment (alveolar recruitment). Experimental studies were excluded. Studies were then evaluated and classified by their level of scientific evidence:
Level I: large
studies with randomized distribution and low risk of false positive (error a)
or false negative (error b).
Level II: small studies with randomized distribution, uncertain results and moderate or high risk of false positive and / or false negative.
Level III: recent, non randomized studies.
Level IV: old non-randomized studies with experts opinion.
Level V: series of uncontrolled cases with experts opinion.
Recommendations were classified by their power following Evidence-Based Medicine Working Group recommendations 17:
supported by at least two level I studies.
B: recommendation supported by at least one level I study.
C: recommendation supported by level II studies only.
D: recommendation supported by at least one level III study.
E: recommendation supported by level IV or V studies.
Our keywords found 46 studies. Three studies were excluded for being in different languages, 15 for being experimental and 3 for being published before 1993. A single study was found in Spanish, however we were only able to obtain its summary.
There are several ARM methods: sustained pressure for a single or multiple periods; intermittent sighs, progressive PEEP increase and low tidal volume (TV), increased PEEP without changing TV, simultaneous increase of TV and PEEP, intermittent and gradual PEEP increase with fixed controlled pressure value, spontaneous ventilation using the mode ventilation with airway pressure release, prone position and high frequency ventilation used in neonatology 1,6,8,10,18-20.
Table I summarizes the 20 most important studies, authors, publication year, number of patients included and type of alveolar recruitment.
According to the literature, most popular method among authors is sustained airway pressure by the CPAP method (continuous positive airway pressure), with pressure volumes varying from 30 to 40 cmH2O for 30 to 90 seconds in ARDS patients 4,13,16,21.
Rothen et al. 10 have studied the ARM in patients submitted to general anesthesia by increasing airways peak pressure to 40 cmH2O. In previous studies 6,22, this pressure value was maintained for 15 seconds until atelectasis areas were recruited. In this study, patients were controlled by CT scan during ARM. This way, authors have noticed that after 7 seconds there was significant PaO2 improvement and most atelectasis were already re-expanded. The advantage of shorter ARM is the lower incidence of side effects such as decreased cardiac output and blood pressure 10. This study is classified as level III since sample was small (12 cases) and there was no randomized distribution. So, author's conclusions should be classified as recommendations level D.
Pang et al. 9, have shown that ARM (manual ventilation until peak pressure of 40 cmH2O for 10 breaths or one minute and then PEEP of 5 cmH2O) improves intraoperative arterial oxygenation of healthy patients submitted to laparoscopic cholecystectomy, after pneumoperitoneum. This surgical technique is associated to 36% decrease in vital functional capacity two to four hours after surgery. Authors believe that alveolar recruitment may improve respiratory function during surgery by decreasing atelectasis and shunt, improving ventilation-perfusion ratio and consequently arterial oxygenation. This is a level II study (small sample, however with randomized distribution) and its conclusions are recommendations level C.
Tusman et al. 14 have shown satisfactory results by applying the maneuver during anesthesia with independent pulmonary ventilation, in thoracic surgeries and with patients in the lateral position (level III study with recommendations level D). During single lung ventilation, pulmonary shunt is15% to 40% increased due to total non-dependent lung collapse. However in other studies, the same author 9 concludes that 5 cm H2O or more PEEP may be needed to prevent alveolar de-recruitment 12 (level II study with recommendations level C). This author has extended his observations to pediatric patients below 7 years of age submitted to general anesthesia with spontaneous ventilation (Mapleson D) for MRI. One group was submitted to ARM (manual ventilation until peak pressure of 40 cmH2O for 10 breaths) with significant decrease of atelectasis as compared to the other two groups 15 (level II study with recommendations level C).
Recent studies report ARM after cardiac surgeries, during which authors believe that pulmonary function and oxygenation are decreased from 20 to 90 % with the use of cardiopulmonary bypass, probably as result of systemic inflammatory response and atelectasis formation 13. Cardiac surgery with cardiopulmonary bypass involves total lungs collapse. So, the maneuver improves oxygenation by opening collapsed lung areas 13,16,20 (level II study with recommendations level C).
To monitor ARM effects, most authors have evaluated arterial oxygenation improvement, a common method in the clinical practice, in which PaO2 values and PaO2/FiO2 ratio is analyzed 4,16,20,21,23. PaO2 values above 450 mmHg would indicate a recruited lung 14. Barbas 18 has evaluated the results of his maneuver by adding PaO2 and PaCO2, defining total recruitment as PaO2 + PaCO2 above 400 mmHg. Another described method to evaluate the effectiveness of alveolar recruitment is CT scan, able to quantify recruited lung tissue 24.
Bein et al. 25 and Moran et al. 2 have studied the impact of ARM on intracranial pressure (ICP) and brain metabolism in patients with brain trauma (BT) and respiratory failure. Authors have observed increased ICP at the end of the maneuver and decreased MBP, with consequent decrease in brain perfusion pressure which returned to normal values 10 minutes after (level III study with recommendations level D).
ARM aims at improving gases changes by maximum alveoli recruitment, providing more homogeneous pulmonary parenchyma ventilation. Although very popular to treat ARDS, literature has also shown good results when used in patients submitted to general anesthesia who develop atelectasis during the anesthetic procedure, with worsening of gases changes, increased pulmonary shunt and worsening of oxygenation 8-10,12,14,15,26. Authors agree with this fact, however the recommendation for routine ARM during anesthesia is still level C because it is supported only by studies with small number of cases.
Some authors recommend ARM after any mechanical ventilator disconnection as well as after tracheal aspirations 4,21 (recommendation level C). These indications could be extended to patients submitted to general anesthesia, both with MV or spontaneous ventilation. Many anesthetized patients are submitted to inadequate ventilation for the lack of simple ventilatory resources of anesthesia machines, such as PEEP. So, any anesthetized patient being inadequately ventilated could be submitted to ARM at the end of anesthesia, before extubation, to decrease the chances of postoperative respiratory complications (recommendation level C).
ARM aims at stabilizing alveolar patency which then should be maintained by adequate PEEP levels, that is, with lower pressures than those needed for recruitment. When successful, the benefit of each maneuver tends to disappear with time, unless a sufficient PEEP level is applied to prevent alveolar de-recruitment 9,12 when patients are to remain under mechanical ventilation.
Authors of reviewed studies have not described ARM counterindications, but their exclusion criteria are hemodynamic instability, pneumothorax, pneumomediastinum and subcutaneous emphysema, recent lung biopsy and resections 4,26. High inspiratory pressures may induce complications, such as hemodynamic changes and risk of barotrauma 1. Sustained airway pressure has hemodynamic repercussions (decreased venous return and increased left ventricle afterload during maneuver) and exposes lung to higher risk of barotrauma 19. Hypotension with fast improvement after maneuver interruption is more frequent in hypovolemic patients 19. PIC may increase during ARM.
ARM may be a major adjuvant during anesthesia, improving postoperative oxygenation and re-expanding atelectasis of patients submitted to general anesthesia. This would positively interfere with post-anesthetic recovery of patients who would need less postoperative oxygen supplementation with low risk of pulmonary complications. However, the routine use of ARM for anesthetized patients is not supported by high evidence level studies (A or B), so it cannot be recommended. Further studies on ARM for anesthetized patients are needed to define its real benefits and the situations in which it should be used.
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26. Tusman G, Bohm SH, Sipmann F et al - Lung recruitment improves the efficiency of ventilation and gas exchange during one-lung ventilation anesthesia. Anesth Analg, 2004;98: 1604-1609 [ Links ]
Dr. Domingos Dias Cicarelli
Address: Av. Piassanguaba, 2933/71 Planalto Paulista
ZIP: 04060-004 City: São Paulo, SP
Submitted for publication
January 26, 2005
Accepted for publication August 8, 2005
* Received from Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo (FMUSP), São Paulo, SP