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vol.56 issue3Bioethics: issues regarding the anesthesiologistDr. Marcos Pedro Canassa - *29/06/1950 † 29/06/2005 author indexsubject indexarticles search
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Revista Brasileira de Anestesiologia

Print version ISSN 0034-7094

Rev. Bras. Anestesiol. vol.56 no.3 Campinas May/June 2006

http://dx.doi.org/10.1590/S0034-70942006000300012 

LETTER TO THE EDITOR

 

Aveolar recruitment maneuver in anesthetic practice: How, when and why it may be useful

 

 

Mrs. Editor,

It was with great interest that I read the above-mentioned article published by our respectful journal. I would like to congratulate the authors for the appreciable initiative. Concerned with explaining some aspects, I thought about making some observations:

1) Authors have attributed alveolar collapse to general anesthesia under mechanical ventilation associated to tidal volumes between 12 and 15 mL.kg-1. It is true that high tidal volumes may promote alveolar hyperinflation, adjacent pulmonary capillary compression and inadequate gas exchange, however this type of ventilation has been used for several years without evidences of problems to patient during surgery. Hedenstierna 1 calls the attention for the loss of muscle tone and the use of high oxygen inspired fractions (FiO2) as the major causes of alveolar collapse. Atelectasis is seen in 90% of all anesthetized patients, be it under spontaneous ventilation or after muscle paralysis, with and without nitrous oxide, and also under intravenous or inhalational general anesthesia 1.
2) CPAP (continuous positive airway pressure), referred by the authors as the most popular method in the literature, is only feasible for patients under spontaneous ventilation. Smith et al. 2 have used 12 ± 2 cmH2O in general anesthesia under spontaneous ventilation for breast oncologic surgery with increased PaO2 and decreased PaCO2 levels, contrasting with 30 to 40 cmH2O referred on the above-mentioned study. An option to patients to be submitted to muscle relaxation during surgery would be anesthetic induction with CPAP and anesthetic maintenance with low PEEP levels (positive end expiratory pressure) 3.
3) Authors advocated PaO2 and PaO2/FiO2 ratio to monitor pulmonary gas exchange and have also related inadequate ventilation to lack of PEEP. In a study with obese and non obese patients, Yoshino et al. 4 have shown that decreased PaO2/FiO2 ratio was only observed in obese and overweighed patients ventilated without alveolar recruitment maneuver (ARM) and without PEEP.
4) PEEP seems really to complement ARM action, however it is important to remember that after PEEP withdrawal there may be alveolar re-collapse and that this effect may already be observed one minute after PEEP discontinuation 1. With 40% FiO2 in nitrogen after ARM, atelectasis areas slowly reappear 1. Wetterslev et al. 5 state that it is not certain that ARM may decrease the incidence of late hypoxemia, pneumonia and other complications. Further studies are needed to define the optimal ARM time and its real role in the more favorable postoperative evolution of patients.
5) There are other methods to prevent alveolar collapse 1: PEEP alone, muscle tone maintenance and lower FiO2. PEEP levels between 5 and 10 cmH2O have been advocated by some authors as effective to recruit already collapsed areas 3,6. PEEP-induced pulmonary flow redistribution may limit its efficacy 1. Muscle tone should be maintained with ketamine and phrenic nerve electric stimulation 1. Ketamine protective effect is impaired with its association with muscle relaxants 1. There will be no alveolar collapse during anesthesia if anesthetic induction under mask with 100% oxygen is avoided 1. Nitrous oxide to decrease FiO2 does not prevent atelectasis by absorption 1 and animal studies have shown that its absorption in the mixture with oxygen is almost as fast as with 100% oxygen 4.

I wish to congratulate the authors for their elegant study which has called our attention for the possibility of optimizing our anesthetic technique to benefit patients.

Yours truly
Fabiano Timbó Barbosa, TSA, M.D.

 

REFERENCES

01. Hedenstierna G – Atelectasis and gas exchange during anaesthesia. Electromedica, 2003;71:70-73.

02. Smith RA, Bratzke EC, Miguel RV – Constant positive airway pressure reduces hypoventilation induced by inhalation anesthesia. J Clin Anesth, 2005;17:44-50.

03. Rusca M, Proietti S, Schnyder P et al – Prevention of atelectasis formation during induction of general anesthesia. Anesth Analg, 2003;97:1835-1839.

04. Yoshino J, Akata T, Takahashi S – Intraoperative changes in arterial oxygenation during volume-controlled mechanical ventilation in modestly obese patients undergoing laparotomies with general anesthesia. Acta Anaesthesiol Scand, 2003;47: 742-750.

05. Wetterslev J, Hansen EG, Roikjaer O et al – Optimizing preoperative compliance with PEEP during upper abdominal surgery: effects on perioperative oxygenation and complications in patients without preoperative cardiopulmonary dysfunction. Eur J Anaesth, 2001;18:358-365.

06. Coussa M, Proietti S, Schnyder P et al – Prevention of atelectasis formation during the induction of general anesthesia in morbidly obese patients. Anesth Analg, 2004;98:1491-1495.

 


 

Reply

 

 

Mrs. Editor,

I was happy to receive Dr. Fabiano's flattering letter. I thank for the praises and would like to add some comments:

  1. In fact, high tidal volumes promote cyclic alveolar hyperdistension and collapse as mentioned in our study. He is right when stating that there are no evidences of problems in anesthetized patients with high volumes, provided patients have no pulmonary disease; however it is known that such high volumes when used for a long time may promote volutrauma and should be avoided in any situation.
  2. In fact, CPAP can only be used in patients under spontaneous ventilation, so it could only be used in anesthetized patients being weaned from ventilatory prosthesis and close to extubation. It is possible that, in patients free from pulmonary disease, pressure levels for recruitment are lower than 30 to 40 cmH2O, as mentioned by Dr. Fabiano in the study by Smith et al. These pressure levels of 30 to 40 cmH2O mentioned by us were used in patients with ARDS, that is, patients with decreased pulmonary compliance 1,2.
  3. We advocate PaO2 or PaO2/FiO2 ratio evaluation to check alveolar recruitment efficacy because it is simpler and of lower cost as compared to the other method described in the literature, which is chest tomography. Yoshino et al.'s conclusion, after observing that obese and overweighed patients ventilated without recruitment maneuver or PEEP evolved with decreased PaO2/FiO2 ratio, is in line with the literature. When there are facts changing ventilatory mechanics or in the presence of pulmonary diseases, there is higher possibility of atelectasis and higher is the importance of adequate ventilation.
  4. Dr. Fabiano is right with regard to the fact that "further studies are needed to define the optimal ARM time and its real role in the more favorable evolution of patients" and is in line with our conclusions that routine recruitment maneuver in anesthesia cannot be recommended because it is not based on studies with high levels of evidence.
  5. PEEP and low FiO2 are undoubtedly effective methods to prevent alveolar collapse.

With this literature review we tried to bring to anesthesiologists intensive care practices which may help solving some anesthetic complications.

We greatly thank Dr. Fabiano for the opportunity to further discuss this subject.

Domingos Dias Cicarelli, TSA, M.D.

 

REFERENCES

01. Carvalho CRR – Ventilação Mecânica I. Clínicas Brasileiras de Medicina Intensiva, 1ª Ed, São Paulo, Atheneu, 2000.

02. Carvalho CRR – Ventilação Mecânica II. Clínicas Brasileiras de Medicina Intensiva, 1ª Ed, São Paulo, Atheneu, 2000.

01. Carvalho CRR – Ventilação Mecânica I. Clínicas Brasileiras de Medicina Intensiva, 1ª Ed, São Paulo, Atheneu, 2000.