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Print version ISSN 0034-7094
Rev. Bras. Anestesiol. vol.59 no.2 Campinas Mar./Apr. 2009
Analysis of the effects of the alveolar recruitment maneuver on blood oxygenation during bariatric surgery*
Análisis de los efectos de la maniobra de reclutamiento alveolar en la oxigenación sanguínea durante el procedimiento bariátrico
Alda Paiva de SouzaI; Márcia BuschpigelII; Ligia Andrade Silva Telles Mathias, TSAIII; Carlos Alberto MalheirosIV; Vera Lucia dos Santos AlvesV
Respiratória do Departamento de Recuperação Pós-anestésica,
UTI do Departamento de Cirurgia e UTI - Neurocirurgia da ISCMSP; Mestre em Ciências
da Saúde - Faculdade de Ciências Médicas da Santa Casa de
São Paulo (FCMSCSP)
IIAnestesiologista do Hospital Central da ISCMSP
IIIDiretora do Serviço e Disciplina de Anestesiologia da ISCMSP e FCMSCSP; Responsável pelo CET/SBA da ISCMSP
IVMédico-Cirurgião; Diretor do Departamento de Cirurgia e Diretor da Disciplina de Área IV: Estômago, Duodeno e Obesidade da ISCMSP
VProfessora da FCMSCSP; Chefe do Serviço de Fisioterapia Respiratória do Hospital Santa Isabel; Doutora em Ciências da Saúde - FCMSCSP
METHDS: Alveolar recruitment maneuver (ARM) is indicated in the treatment
of intraoperative atelectasis. The objective of the present study was to compare
two techniques of ARM using the response of the PaO2/FiO2
ratio and [PaO2 + PaCO2] in patients with grade
METHODS: This was an open prospective study with adult patients with grade III obesity who underwent bariatric surgery under volume-controlled mechanical ventilation with positive end-expiratory pressure (PEEP) of 5 cmH2O, divided in three groups: GCONT: PEEP of 5 cmH2O; GARM10/15/20 after suture of the aponeurosis: progressive increase in PEEP to 10, 15, and 20 cmH2O with a 40-second pause and maintaining each level of PEEP for 2 minutes; and GARM30 after suture of the aponeurosis: sudden increase in PEEP to 30 cmH2O with a 40-second pause and maintaining a PEEP of 30 for 2 minutes. Heart rate, mean arterial pressure, systolic and diastolic blood pressure, mean (PAW) and plateau (PPLAT) airways pressure, partial pressure of oxygen (PaO2), partial pressure of carbon dioxide (PaCO2), PaO2/FiO2 ratio (inspired fraction of oxygen), and [PaO2 + PaCO2] were analyzed.
RESULTS: The following parameters showed statistically significant differences among the study groups: PPLAT, PAW, PaO2, PaO2/FiO2 ratio, and [PaO2 + PaCO2] (p < 0.0001). Comparing the groups two by two, the following parameters showed statistically significant differences: for PPLAT and PAW: GCONT x G2ARM10/15/20 and GCONT x GARM30; and for PaO2/FiO2 ratio and [PaO2 + PaCO2]: GCONT x GARM30.
CONCLUSIONS: Alveolar recruitment maneuver with sudden increase of PEEP to 30 cmH2O showed a better response of the PaO2/FiO2 ratio.
Key Words: COMPLICATIONS: atelectasis; SURGERY, Bariatric; VENTILATION: alveolar recruitment maneuver, positive end-expiratory pressure
Y OBJETIVOS: La maniobra de reclutamiento alveolar (MRA) se indica en el
tratamiento de atelectasias intraoperatorias. El objetivo del presente estudio
fue comparar dos técnicas de MRA por medio de la respuesta de la relación
PaO2/FiO2 y de la suma [PaO2+PaCO2],
en pacientes obesos con grado III.
MÉTODO: Estudio prospectivo abierto en pacientes adultos, obesos grado III, sometidos a procedimiento quirúrgico bariátrico en ventilación controlada a volumen, presión positiva al final de la expiración (PEEP) de 5 cmH2O y divididos en tres grupos: GCONTROL: PEEP de 5 cmH2O; GMRA10/15/20 después de la sutura de la aponeurosis: aumento progresivo de la PEEP para 10,15 y 20 cmH2O, pausa de 40 segundos y mantenimiento de cada valor de la PEEP por 2 minutos; GMRA30: después de la sutura de la aponeurosis: aumento súbito de la PEEP para 30 cmH2O, 40 segundos de pausa y mantenimiento de la PEEP en 30 cmH2O por dos minutos. Se analizaron las variables frecuencia cardíaca, presión arterial promedio, sistólica, diastólica, presión promedio de las vías aéreas (PMVA) y de meseta (PPLAT), presión arterial de oxígeno (PaO2), presión arterial de CO2 (PaCO2), relación PaO2/FiO2 (fracción inspiratoria de oxígeno) y suma [PaO2+PaCO2].
RESULTADOS: Las variables que presentaron una diferencia estadística significativa entre los tres grupos fueron: PPLAT, PMVA, PaO2, relación PaO2/FiO2 y suma [PaO2+PaCO2] (p < 0,0001). En la comparación de los grupos dos a dos, se verificó una diferencia estadística significativa para las variables PPLAT y PMVA: GCONTROL X GMRA10/15/20 y GCONTROL X GMRA30 y para las variables relación PaO2/FiO2 y suma [PaO2+PaCO2]: GCONTROL X GMRA30.
CONCLUSIONES: La técnica de MRA con aumento súbito de la PEEP para 30 cm H2O mostró la mejor respuesta de la relación PaO2/FiO2.
The development of atelectasis is common during general anesthesia due to the reduction in residual functional capacity (RFC) 1,2. This situation tends to be worse in patients with grade III obesity since their RFC is already reduced during spontaneous breathing 3.
Alveolar recruitment maneuver (ARM) consists of sustained insufflations, mainly with the use of positive end-expiratory pressure (PEEP). The use of ARM is indicated in the presence of atelectasis or alveolar hypoventilation, in the initial stages of pulmonary lesion and acute respiratory distress syndrome, and in patients with alveolar instability 4-6. In open bariatric surgery, the use of PEEP to prevent the development of areas of atelectasis has been suggested, although the levels have not been established, which motivated this study.
The objective of the present study was to compare two techniques of ARM using the response of the ratio between the partial pressure of oxygen and the inspired fraction of oxygen (PaO2/FiO2) and the sum of the partial pressure of oxygen with the partial pressure of carbon dioxide [PaO2 +PaCO2] in patients with grade III obesity undergoing open bariatric surgery.
After approval by the Ethics Committee of the Irmandade da Santa Casa de Misericórdia de São Paulo, patients from the Department of Surgery of the Stomach, Duodenum and Obesity Division with the diagnosis of grade III obesity undergoing sylastic ring gastric bypass with Y-en-Roux anastomosis, from March 2004 to June 2005, were enrolled in this open, prospective study.
Patients underwent preoperative evaluation by a multidisciplinary team, all necessary explanations were given, and an informed consent was signed.
Patients were randomly divided in three groups:
- Control group (GCONT): ventilation with PEEP of 5 cmH2O;
- ARM 10/15/20 group (GARM10/15/20): progressive ARM with PEEP of 10, 15, and 20 cmH2O;
- ARM 30 group (GARM30): conventional ARM, according to the American-European Consensus, using PEEP of 30 cmH2O and plateau pressure (PPLAT) of 35 cmH2O 5,6.
Inclusion criteria were as follows: BMI > 40 kg.m-2; and normal pulmonary function tests or with mild abnormalities. Patients with history of spontaneous pneumothorax and laparoscopic gastroplasty were excluded.
The sequence of care of patients in all three groups was identical. In the operating room, a peripheral vein was cannulated with an 18G catheter and hydration with Ringer's lactate was initiated.
Patients were placed in dorsal decubitus with discrete head-up tilt. The following parameters were monitored: heart rate (HR); electrocardiogram (ECG); non-invasive systolic (SBP) and diastolic (DBP) blood pressure; and peripheral hemoglobin saturation (SpO2).
Ventilation was initiated with 100% O2 with a face mask, followed by anesthetic induction with the sequential administration of intravenous midazolam (5 to 10 mg), alfentanil (300 µg), propofol (2 to 3 mg.kg-1), and atracurium (50 mg). Anesthesia was maintained with propofol, 0.075 to 0.1 mg.kg-1. min-1, and alfentanil, 0.75 to 1.0 µg.kg-1.min-1 .
After tracheal intubation, patients were maintained with volume-controlled mechanical ventilation using the anesthesia equipment in a semi-closed circular system (model LINEA A Intermed1® Brazil), with tidal volume (VT) of 8 to 10 mL.kg-1 of ideal weight, limiting pressure to 45 cmH2O, inspired fraction of O2 (FiO2) of 0.5, respiratory rate of 12 to 14, and PEEP of 5 cmH2O.
- GCONT: ventilation with PEEP of 5 cmH2O until the end of the surgery (Figure 1).
In the other two groups, ARM was done after suture of the aponeurosis as follows (Figure 1):
- progressive increase of PEEP to 10 cmH2O; 40-second pause; PEEP of 10 cmH2O maintained for 120 seconds;
- progressive increase of PEEP to 15 cmH2O; 40-second pause; PEEP of 15 cmH2O maintained for 120 seconds;
- progressive increase of PEEP to 20 cmH2O; 40-second pause; PEEP of 20 cmH2O maintained for 120 seconds; and
- gradual reduction in PEEP to the initial level of 5 cmH2O every 5 ipm.
- sudden increase of PEEP from 5 to 30 cmH2O; 40-second pause; PEEP of 30 cmH2O maintained for 120 seconds;
- gradual reduction in PEEP to the initial level by 5 cmH2O every 5 ipm.
Parameters analyzed included: age, gender, weight, height, and BMI; length of surgery; HR, SBP, and DBP; SpO2, PaO2, PaCO2, PaO2/FiO2 ratio, [PaO2 + PaCO2], plateau pressure (PPLAT), and mean airways pressure (PMAV); and intraoperative complications.
Heart rate, SBP, DBP, and SpO2 were analyzed before induction and every 5 minutes until the end of the procedure. Partial pressure of oxygen, PaCO2, PaO2/PaCO2 ratio, [PaO2 + PaCO2], plateau pressure (PPALT), and mean airways pressure (PAW) were analyzed immediately after suture of the aponeurosis (before ARM) and at the end of ARM.
ANOVA was used to compare quantitative parameters in relation to the three groups, and the Kruskal-Wallis test and the Tukey method were used for multiple comparisons. The chi-square test was used to compare qualitative parameters. The level of significance adopted was 5%.
The software SPSS (Statistical Package for the Social Sciences) for Windows 10.01 and the Epi Info version 3.2.2 were used for the statistical analysis.
The final sample was composed of 47 patients, 14 in GCONT, 17 in GARM10/15/20, and 16 in GARM30. Demographic data, length of surgery, and initial hemodynamic parameters and SpO2 did not show statistically significant differences (Table I).
Hemodynamic parameters and SpO2 did not show statistically significant differences throughout the study.
Immediately before ARM, PaO2, PaCO2, PaO2/FiO2 ratio, [PaO2 + PaCO2], PPLAT, and PAW did not show statistically significant differences among the three groups (Table III).
At the time of ARM (Table III), a statistically significant difference was observed among the three groups for: PaO2, PaO2/FiO2 ratio, [PaO2 + PaCO2], PPLAT, and PAW. Subsequently, the Tukey test was used to analyze those parameters, which showed statistically significant differences between GCONT and GARM30 (p < 0.05) for PaO2, PaO2/FiO2 ratio, and [PaO2 + PaCO2]. For PPLAT and PAW, Tukey test showed statistically significant differences in all groups when compared two by two (GCONT x GARM10/15/20, p < 0.001; GCONT x GARM30, p < 0.001; GARM10/15/20 x GARM30, p < 0.01), except when GPLAT was compared with GARM10/15/20 and GARM30 (p > 0.05).
Intraoperative complications were not observed.
Perioperative pulmonary complications represent a significant cause of morbidity and mortality 8, and atelectasis affect almost 90% of the patients undergoing general anesthesia, with a positive correlation with the perioperative values of pulmonary shunts 1,8-12; this explains why the moment of the surgery and respiratory monitoring were chosen to evaluate the ventilation/perfusion imbalance.
Immediately after general anesthesia, atelectasis, which are responsible for the perioperative changes in oxygenation, develop in dependent areas of the pulmonary parenchyma; PEEP, maintained at 5 cmH2O throughout the surgery, led to the opening and maintenance of alveolar permeability 10, which was confirmed by the analysis of the levels of hyperoxia demonstrated by SpO2 and PaO2 in all three groups before and after alveolar recruitment maneuver (ARM), in which PaO2 was elevated in every phase. It was possible to demonstrate it even when obese patients were ventilated with lower levels of VT (between 10 and 11 mL.kg-1) and FiO2 (0.4) 7.
Maintenance of the tidal volume is also debated in the literature and, when above 12 mL.kg-1 it is associated with alveolar hyperinflation, compression of the adjacent pulmonary capillary, and inadequate gas exchange. Hedenstierna 13 stated that the main causes of alveolar collapse include the loss of muscular tone and high inspired fractions of oxygen (FiO2). In the present study, the orientation of the Brazilian consensus on mechanical ventilation, maintaining constant VT at 10 mL.kg-1 and FiO2 of 0.5, was followed, leading to results similar to those of Coussa et al. 2 and Pelosi et al. 14, in which obese patients ventilated with a VT of 10 mL.kg-1 showed a significant improvement in PaO2, since the BMI is related with the reduction of RFC.
The use of PEEP is typically associated with an increase of PAW, which was constant in all three groups from the beginning of the surgery on, with a proportional increase with increasing levels of PEEP 32.
The elevated PAW suggests greater mechanical pulmonary vulnerability, because the increase in PEEP increased PPLAT significantly. The resistance exerted by the adipose tissue in the thoracic region of the patients in this study could also have contributed to the significant change in PAW in all phases of changes in PEEP 1,7,15.
The relationship between BMI and FRC has been reported by several authors who study the changes in gas exchange in obese individuals 7,15-19. The reduction in FRC is also common after the institution of mechanical ventilation, as reported by Pelosi et al. 9, who proposed the inverse relationship between the reduction in oxygenation and pulmonary volume and the BMI.
In view of what was explained above, the alveolar recruitment maneuver (ARM) is a technique that leads to the opening of collapsed alveolar units through the sustained increase in airways pressure, increasing the pulmonary area available for gas exchange and, consequently, arterial oxygenation 20.
The response of acute pulmonary lesion (APL) and acute respiratory distress syndrome (ARDS) to ARM with pressures of 45 cmH2O in non-obese patients can present different pulmonary profiles, which are classified as: difficult to recruit, reasonably recruitable, or potentially recruitable 18. Obese patients can also be classified, in a similar fashion, by the elevated BMI as compromised thoracic cage, increased resistance, and decreased complacence. This can hinder comparison of the results obtained for alveolar recruitment, as reported by several studies 8,9,15.
The PaO2/FiO2 ratio and [PaO2 + PaCO2] in the three study groups increased progressively, but without changes among the groups and [PaO2 + PCO2], demonstrating the absence of pulmonary lesion (normal level: e 400 mmHg with FiO2 = 1.0). However, patients in GARM30 showed better response of the PaO2/FiO2 ratio and [PaO2 + PaCO2], but this last index is not commonly used during studies on the response to ARM in patients with APL and ARDS.
Borges et al. 24, analyzing patients with acute pulmonary lesion associated with early hypoxemia, demonstrated that APL can be reverted when elevated pressures are used in the airways (above 60 cmH2O). However, the harmful effects (barotrauma, hyperinsufflation, decreased cardiac index, and disrupted hemodynamics) are more commonly seen when the same levels of inspiratory pressure are used for prolonged times 25.
The alveolar recruitment maneuver with PEEP of 30 cmH2O used in GARM30 was idealized according to the American-European Consensus, and showed better response of the PaO2/FiO2 ratio and [PaO2 + PaCO2] 26.
According to the literature, CPAP (continuous positive airways pressure), with pressure levels ranging from 30 to 40 cmH2O for 30 to 90 seconds in patients with ARDS, is the method used more often by authors to sustain airways pressure 20,27,28.
In other studies 6,29, this level of pressure was maintained for 15 seconds and the area of recruitment was followed-up by CT scan during ARM. The authors noticed that, after seven seconds of recruitment, PaO2 improved significantly and the areas of atelectasis reduced. The lower incidence of reduced cardiac output and blood pressure is the main advantage of the shorter ARM 9; however, the study population is small, being classified as a level D scientific evidence recommendation. In the present study, increased PEEP levels were maintained for two minutes, which did not change the hemodynamic parameters of the patients.
Under the conditions of the present study, the best response of the PaO2/FiO2 ratio was seen with the alveolar recruitment maneuver with PEEP of 30 cmH2O for two minutes.
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Correspondence to: Submitted em 2
de agosto de 2007 *
Received from do Departamento de Cirurgia da Irmandade da Santa Casa de Misericórdia
de São Paulo (ISCMSP), São Paulo, SP
Dra. Ligia AST Mathias
Alameda Campinas 139/41
01404-000 São Paulo, SP
Accepted para publicação em 10 de dezembro de 2008
Submitted em 2
de agosto de 2007
* Received from do Departamento de Cirurgia da Irmandade da Santa Casa de Misericórdia de São Paulo (ISCMSP), São Paulo, SP