title: Intrinsic positive end-expiratory pressure during ventilation through small endotracheal tubes during general anesthesia: incidence, mechanism, and predictive factors.
abstract: OBJECTIVE
  To assess the safety of mechanical ventilation and effectiveness of extrinsic positive end-expiratory pressure (PEEP) (PEEPe) in improving peripheral oxygen saturation (SpO2) during direct microlaryngeal laser surgery; to assess the incidence, amount, and nature (dynamic hyperinflation or airflow obstruction) of ensuing intrinsic PEEP (PEEPi); and to find a surrogate PEEPi indicator.
  
  
  METHODS
  Quasiexperimental.
  
  
  METHODS
  S. Raffaele Hospital (Milano), November 2009 to December 2010.
  
  
  METHODS
  Fifty-two adults scheduled for direct microlaryngeal laser surgery. Exclusion criterion is pregnancy.
  
  
  METHODS
  Twenty-one percent O2 mechanical ventilation through 4.5- to 5.5-mm internal diameter endotracheal tubes; in 29 patients, after measurement of PEEPi, an identical amount of PEEPe was added; and PEEPi.
  
  
  METHODS
  SpO2, peak (Pawpeak) and plateau (Pawplateau) airway pressure, and end-expiratory carbon dioxide were measured every 5 minutes. Respiratory compliance (Crs) was computed. PEEPi was measured (end-expiratory occlusion method).
  
  
  RESULTS
  PEEPi ≥5 cm H2O occurred in 14 patients (27%) after intubation, in 16 (30%) at the beginning, and in 14 (27.3%) at the end of surgery. Thirty-one patients (59.4%) exhibited PEEPi ≥5 cm H2O on at least 1 time point. PEEPi at the beginning of surgery was positively correlated with Pawplateau, Crs, tidal volume, and body mass index. Body mass index was the only predictor for the occurrence of PEEPi ≥5 cm H2O. At the beginning of surgery, the Pawplateau receiver operating characteristic curve predicting PEEPi ≥5 cm H2O had area under the receiver operating characteristic curve of 0.85; best cutoff value of 15.5 cm H2O (sensitivity, 88.9%; specificity, 75%; correctly classified cases, 86.1%). When PEEPe was applied, in 23 cases (82.1%), total PEEP equaled PEEPe+ PEEPi; in 3 (10.7%), it was lower; and in 2 (7.1%), it was higher. Application of PEEPe increased SpO2 (P< .05) and Crs (P< .05).
  
  
  CONCLUSIONS
  During ventilation through small endotracheal tubes, PEEPi (mostly due to dynamic hyperinflation) is common. Hemodynamic complications, barotrauma, and O2 desaturation (reversible with PEEPe) are rare. Pawplateau provided by ventilators is useful in suspecting and monitoring the occurrence of PEEPi and allows detection of lung overdistension as PEEPe is applied.
authors.affiliation: Anesthesia and Intensive Care, Department of Anesthesiology, San Raffaele Scientific Institute, via Olgettina 60, 20132 Milan, Italy. Electronic address: gemma.marco@hsr.it.
authors.forename: Marco
authors.initials: M
authors.lastname: Gemma
authors.affiliation: Anesthesia and Intensive Care, Department of Anesthesiology, San Raffaele Scientific Institute, via Olgettina 60, 20132 Milan, Italy. Electronic address: nicelli.elisa@hsr.it.
authors.forename: Elisa
authors.initials: E
authors.lastname: Nicelli
authors.affiliation: Anesthesia and Intensive Care, Department of Anesthesiology, San Raffaele Scientific Institute, via Olgettina 60, 20132 Milan, Italy. Electronic address: corti.daniele@hsr.it.
authors.forename: Daniele
authors.initials: D
authors.lastname: Corti
authors.affiliation: Anesthesia and Intensive Care, Department of Anesthesiology, San Raffaele Scientific Institute, via Olgettina 60, 20132 Milan, Italy. Electronic address: devitis.assunta@hsr.it.
authors.forename: Assunta
authors.initials: A
authors.lastname: De Vitis
authors.affiliation: Anesthesia and Intensive Care, Department of Experimental Medicine, University of Milan-Bicocca, via Pergolesi 33, 20052 Monza, Italy. Electronic address: nicolo.patroniti@unimib.it.
authors.forename: Nicolò
authors.initials: N
authors.lastname: Patroniti
authors.affiliation: Anesthesia and Intensive Care, Department of Anesthesiology, Alessandro Manzoni Hospital, via dell'Eremo 9, 23900 Lecco, Italy. Electronic address: g.foti@ospedale.lecco.it.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Foti
authors.affiliation: Anesthesia and Intensive Care, Department of Anesthesiology, San Raffaele Scientific Institute, via Olgettina 60, 20132 Milan, Italy. Electronic address: calvi.mariarosa@hsr.it.
authors.forename: Maria Rosa
authors.initials: MR
authors.lastname: Calvi
authors.affiliation: Anesthesia and Intensive Care, Department of Anesthesiology, San Raffaele Scientific Institute, via Olgettina 60, 20132 Milan, Italy. Electronic address: beretta.luigi@hsr.it.
authors.forename: Luigi
authors.initials: L
authors.lastname: Beretta
mesh_terms: D000768:Anesthesia, General; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D018467:Positive-Pressure Respiration, Intrinsic / Q000453:epidemiology*; D012121:Respiration, Artificial / Q000295:instrumentation*; D012307:Risk Factors
keywords: Airflow obstruction; Barotauma; Intrinsic PEEP; Mechanical ventilation; Pulmonary dynamic hyperinflation