Modifications of lung microbiota structure in traumatic brain injury ventilated patients according to time and enteral feeding formulas: a prospective randomized study.

BACKGROUND: Specialized diets enriched with immune nutrients could be an important supplement in patients (pts) with acute traumatic brain injury (TBI). Omega-3 and arginine may interact with immune response and microbiota. No data are available about the role of the specialized diets in modulating the lung microbiota, and little is known about the influence of lung microbiota structure in development of ventilator-associated pneumonia (VAP) in TBI pts. The aims of this study are to evaluate the impact of specific nutrients on the lung microbiota and the variation of lung microbiota in TBI pts developing VAP. METHODS: A cohort of 31 TBI pts requiring mechanical ventilation in ICU was randomized for treatment with specialized (16pts) or standard nutrition (15pts). Alpha and beta diversity of lung microbiota were analyzed from bronco Alveolar Lavage (BAL) samples collected at admission and 7 days post-ICU admission in both groups. A further analysis was carried out on the same samples retrospectively grouped in VAP or no VAP pts. RESULTS: None developed VAP in the first week. Thereafter, ten out of thirty-one pts developed VAP. The BAL microbiota on VAP group showed significant differences in beta diversity and Staphylococcus and Acinetobacter Genera were high. The specialized nutrition had influence on beta diversity that reached statistical significance only in Bray-Curtis distance. CONCLUSION: Our data suggest that TBI patients who developed VAP during ICU stay have different structures of BAL microbiota either at admission and at 7 days post-ICU admission, while no correlation has been observed between different enteral formulas and microbiota composition in terms of richness and evenness. These findings suggest that targeting the lung microbiota may be a promising approach for preventing infections in critically ill patients.

Effect of Intraoperative High Positive End-Expiratory Pressure (PEEP) With Recruitment Maneuvers vs Low PEEP on Postoperative Pulmonary Complications in Obese Patients: A Randomized Clinical Trial.

Importance: An intraoperative higher level of positive end-expiratory positive pressure (PEEP) with alveolar recruitment maneuvers improves respiratory function in obese patients undergoing surgery, but the effect on clinical outcomes is uncertain. Objective: To determine whether a higher level of PEEP with alveolar recruitment maneuvers decreases postoperative pulmonary complications in obese patients undergoing surgery compared with a lower level of PEEP. Design, Setting, and Participants: Randomized clinical trial of 2013 adults with body mass indices of 35 or greater and substantial risk for postoperative pulmonary complications who were undergoing noncardiac, nonneurological surgery under general anesthesia. The trial was conducted at 77 sites in 23 countries from July 2014-February 2018; final follow-up: May 2018. Interventions: Patients were randomized to the high level of PEEP group (n = 989), consisting of a PEEP level of 12 cm H2O with alveolar recruitment maneuvers (a stepwise increase of tidal volume and eventually PEEP) or to the low level of PEEP group (n = 987), consisting of a PEEP level of 4 cm H2O. All patients received volume-controlled ventilation with a tidal volume of 7 mL/kg of predicted body weight. Main Outcomes and Measures: The primary outcome was a composite of pulmonary complications within the first 5 postoperative days, including respiratory failure, acute respiratory distress syndrome, bronchospasm, new pulmonary infiltrates, pulmonary infection, aspiration pneumonitis, pleural effusion, atelectasis, cardiopulmonary edema, and pneumothorax. Among the 9 prespecified secondary outcomes, 3 were intraoperative complications, including hypoxemia (oxygen desaturation with Spo2 ≤92% for >1 minute). Results: Among 2013 adults who were randomized, 1976 (98.2%) completed the trial (mean age, 48.8 years; 1381 [69.9%] women; 1778 [90.1%] underwent abdominal operations). In the intention-to-treat analysis, the primary outcome occurred in 211 of 989 patients (21.3%) in the high level of PEEP group compared with 233 of 987 patients (23.6%) in the low level of PEEP group (difference, -2.3% [95% CI, -5.9% to 1.4%]; risk ratio, 0.93 [95% CI, 0.83 to 1.04]; P = .23). Among the 9 prespecified secondary outcomes, 6 were not significantly different between the high and low level of PEEP groups, and 3 were significantly different, including fewer patients with hypoxemia (5.0% in the high level of PEEP group vs 13.6% in the low level of PEEP group; difference, -8.6% [95% CI, -11.1% to 6.1%]; P < .001). Conclusions and Relevance: Among obese patients undergoing surgery under general anesthesia, an intraoperative mechanical ventilation strategy with a higher level of PEEP and alveolar recruitment maneuvers, compared with a strategy with a lower level of PEEP, did not reduce postoperative pulmonary complications. Trial Registration: ClinicalTrials.gov Identifier: NCT02148692.

Correction to: Protective ventilation with high versus low positive end-expiratory pressure during one-lung ventilation for thoracic surgery (PROTHOR): study protocol for a randomized controlled trial.

After publication of the original article [1], the authors have notified us that two of the collaborator first and last names have been inverted in the "PROTHOR Investigators" table.

Protective ventilation with high versus low positive end-expiratory pressure during one-lung ventilation for thoracic surgery (PROTHOR): study protocol for a randomized controlled trial.

BACKGROUND: Postoperative pulmonary complications (PPC) may result in longer duration of in-hospital stay and even mortality. Both thoracic surgery and intraoperative mechanical ventilation settings add considerably to the risk of PPC. It is unclear if one-lung ventilation (OLV) for thoracic surgery with a strategy of intraoperative high positive end-expiratory pressure (PEEP) and recruitment maneuvers (RM) reduces PPC, compared to low PEEP without RM. METHODS: PROTHOR is an international, multicenter, randomized, controlled, assessor-blinded, two-arm trial initiated by investigators of the PROtective VEntilation NETwork. In total, 2378 patients will be randomly assigned to one of two different intraoperative mechanical ventilation strategies. Investigators screen patients aged 18 years or older, scheduled for open thoracic or video-assisted thoracoscopic surgery under general anesthesia requiring OLV, with a maximal body mass index of 35 kg/m2, and a planned duration of surgery of more than 60 min. Further, the expected duration of OLV shall be longer than two-lung ventilation, and lung separation is planned with a double lumen tube. Patients will be randomly assigned to PEEP of 10 cmH2O with lung RM, or PEEP of 5 cmH2O without RM. During two-lung ventilation tidal volume is set at 7 mL/kg predicted body weight and, during OLV, it will be decreased to 5 mL/kg. The occurrence of PPC will be recorded as a collapsed composite of single adverse pulmonary events and represents the primary endpoint. DISCUSSION: PROTHOR is the first randomized controlled trial in patients undergoing thoracic surgery with OLV that is adequately powered to compare the effects of intraoperative high PEEP with RM versus low PEEP without RM on PPC. The results of the PROTHOR trial will support anesthesiologists in their decision to set intraoperative PEEP during protective ventilation for OLV in thoracic surgery. TRIAL REGISTRATION: The trial was registered in clinicaltrials.gov ( NCT02963025 ) on 15 November 2016.

Protective intraoperative ventilation with higher versus lower levels of positive end-expiratory pressure in obese patients (PROBESE): study protocol for a randomized controlled trial.

BACKGROUND: Postoperative pulmonary complications (PPCs) increase the morbidity and mortality of surgery in obese patients. High levels of positive end-expiratory pressure (PEEP) with lung recruitment maneuvers may improve intraoperative respiratory function, but they can also compromise hemodynamics, and the effects on PPCs are uncertain. We hypothesized that intraoperative mechanical ventilation using high PEEP with periodic recruitment maneuvers, as compared with low PEEP without recruitment maneuvers, prevents PPCs in obese patients. METHODS/DESIGN: The PRotective Ventilation with Higher versus Lower PEEP during General Anesthesia for Surgery in OBESE Patients (PROBESE) study is a multicenter, two-arm, international randomized controlled trial. In total, 2013 obese patients with body mass index ≥35 kg/m2 scheduled for at least 2 h of surgery under general anesthesia and at intermediate to high risk for PPCs will be included. Patients are ventilated intraoperatively with a low tidal volume of 7 ml/kg (predicted body weight) and randomly assigned to PEEP of 12 cmH2O with lung recruitment maneuvers (high PEEP) or PEEP of 4 cmH2O without recruitment maneuvers (low PEEP). The occurrence of PPCs will be recorded as collapsed composite of single adverse pulmonary events and represents the primary endpoint. DISCUSSION: To our knowledge, the PROBESE trial is the first multicenter, international randomized controlled trial to compare the effects of two different levels of intraoperative PEEP during protective low tidal volume ventilation on PPCs in obese patients. The results of the PROBESE trial will support anesthesiologists in their decision to choose a certain PEEP level during general anesthesia for surgery in obese patients in an attempt to prevent PPCs. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT02148692. Registered on 23 May 2014; last updated 7 June 2016.

The anaesthetic and recovery profile of two concentrations (0.25% and 0.50%), of intrathecal isobaric levobupivacaine for combined spinal-epidural (CSE) anaesthesia in patients undergoing modified Stark method caesarean delivery: a double blinded randomized trial.

BACKGROUND: In spinal anaesthesia for a Caesarean delivery, it is important to limit anaesthesia only at the surgical area, and to resolve fast motor block. We compared the intraoperative effectiveness, hemodynamic effects, anaesthetic recovery times and patients satisfaction after isobaric levobupivacaine (L) 0.25% versus L0.50% spinal anaesthesia during elective Caesarean deliveries performed with the Stark technique. PATIENTS AND METHODS: In this double-blinded prospective study, seventy women undergoing elective caesarean delivery were randomized to receive either intrathecal 7.5 mg Levobupivacaine 0.25% plus sufentanil 2.5 µg (Group L0.25), or intrathecal 7.5 mg L 0.50% plus sufentanil 2.5 µg (GroupControl). The onset time, duration of anaesthesia, analgesia and sensory and motor block and hemodynamic parameters were measured from the beginning of spinal anaesthesia until four hours after spinal anaesthesia (T240). RESULTS: Onset time, duration of anaesthesia and haemodynamic variations were similar in the two groups. No patients required general anesthesia to complete surgery. Motor block vanished faster in Group L0.25 as compared with GroupControl (p < .01). The cephalad spread of the 0.50% solution was higher than that of the 0.25% solution: no patient in Group L0.25 experienced paresthesia of the upper limbs vs 14% in GroupControl (p < .05). In GroupControl anaesthesia reached the dermatome T1 in 15% of cases. Maternal and surgeon satisfaction was good in every patient. CONCLUSIONS: Levobupivacaine 7.5 milligrams at 0.25% may be used as a suitable alternative to L 0.50% for spinal anaesthesia for caesarean deliveris with the Stark technique with good maternal satisfaction. In Group L0.25 a lower appearance of nausea and hypotension were observed and motor and sensitive block developed and diminished faster while no clinically significant differences in hemodynamic behavior was observed between groups.

Implementation of epidural analgesia for labor: is the standard of effective analgesia reachable in all women? An audit of two years.

BACKGROUND: Social and cultural factors combined with little information may prevent the diffusion of epidural analgesia for pain relief during childbirth. The present study was launched contemporarily to the implementation of analgesia for labor in our Department in order to perform a 2 years audit on its use. The goal is to evaluate the epidural acceptance and penetration into hospital practice by women and care givers and safety and efficacy during childbirth. PATIENTS AND METHODS: This audit cycle measured epidural analgesia performance against 4 standards: (1) Implementation of epidural analgesia for labor to all patients; (2) Acceptance and good satisfaction level reported by patients and caregivers. (3) Effectiveness of labor analgesia; (4) No maternal or fetal side effects. RESULTS: During the audit period epidural analgesia increased from 15.5% of all labors in the first trimester of the study to 51% in the last trimester (p < 0.005). Satisfaction levels reported by patients and care givers were good. A hierarchical clustering analysis identified two clusters based on VAS (Visual Analogue Scale) time course: in 226 patients (cluster 1) VAS decreased from 8.5±1.4 before to 4.1±1.3 after epidural analgesia; in 1002 patients (cluster 2) VAS decreased from 8.12±1.7 before (NS vs cluster 1), to 0.76±0.79 after (p < 0.001 vs before and vs cluster 2 after). No other differences between clusters were observed. CONCLUSIONS: Present audit shows that the process of implementation of labor analgesia was quick, successful and safe, notwithstanding the identification of one cluster of women with suboptimal response to epidural analgesia that need to be further studies, overall pregnant womens'adhesion to labor analgesia was satisfactory.

Micro opioid receptor A118G polymorphism and post-operative pain: opioids' effects on heterozygous patients.

The single-nucleotide-polymorphism (SNP) 118A>G in the micro-1 opioid receptor gene (OPRM1) is associated with a decrease in the analgesic effects of opioids. The aim of this study is to assess whether 118A >G polymorphism could influence the analgesic response to opioid-based postoperative pain (POP) therapy. The study consisted of two parts: section alpha, observational, included 199 subjects undergoing scheduled surgical procedures with pain management standardized on surgery invasiveness and on expected level of postoperative pain; section beta, randomized, included 41 women undergoing scheduled caesarean delivery with continuous intra-operative epidural anesthesia and post-operative analgesia (CEA). In both sections, POP was measured over 48 h (T6h-T24h-T48h) by the visual analogue scale (VAS). In section beta we also tested the responsiveness of hypothalamic-pituitary-adrenal axis (HPA) expressed by cortisol levels. In section alpha, with cluster analysis, subjects were analyzed according to their genotype: a group (no. 1) of 34 patients reporting VAS score >3 at every time lapse was identified and included only A118G carriers, while wild-type (A118A - absence of 118A>G polymorphism) patients were unevenly distributed between those with cluster no. 2 (VAS score <3 at every study steps) and those with cluster no. 3 (VAS score progressively reducing from T6h). In section beta, A118G carriers receiving epidural sufentanil had the lowest VAS scores at T24h; also in these patients, cortisol levels remained more stable, with a mild decrease at T6h. This study shows that the OPRM1 118A>G polymorphism affects postoperative pain response in heterozygous patients: they have a different postoperative pain response than patients with wild-type genes, which may affect the efficacy of the analgesic therapy.

Physiological effects of a lung-recruiting strategy applied during one-lung ventilation.

BACKGROUND: One-lung ventilation (OLV) affects respiratory mechanics and ventilation/perfusion matching, reducing functional residual capacity of the ventilated lung. While the application of a lung-recruiting manoeuvre (RM) on the ventilated lung has been shown to improve oxygenation, data regarding the impact of RM on respiratory mechanics are not available. METHODS: Thirteen patients undergoing lung resection in lateral decubitus were studied. During OLV, a lung-recruiting strategy consisting in a RM lasting 1 min followed by the application of positive end-expiratory pressure 5 cmH(2)O was applied to the ventilated lung. Haemodynamics, gas exchange and respiratory mechanics parameters were recorded on two-lung ventilation (TLV(baseline)), OLV before and 20 min after the RM (OLV(pre-RM), OLV(post-RM), respectively) and TLV(end). Haemodynamics parameters were also recorded during the RM. RESULTS: The PaO(2)/FiO(2) ratio was 358+/-126 on TLV(baseline); it decreased to 235+/-113 on OLV(pre-RM) (P<0.01) increased to 351+/-120 on OLV(post-RM) (P<0.01 vs. OLV(pre-RM)), and remain stable thereafter. During the RM, CI decreased from 3.04+/-0.7 l/m(2) OLV(pre-RM) to 2.4+/-0.6 l/m(2) (P<0.05), and returned to baseline on OLV(post-RM) (3.1+/-0.7 l/m(2), NS vs. OLV(pre-RM)). The RM resulted in alveolar recruitment and caused a significant decrease in static elastance of the dependent lung (16.6+/-8.9 cmH(2)O/ml OLV(post-RM) vs. 22.3+/-8.1 cmH(2)O/ml OLV(pre-RM)) (P<0.01). CONCLUSIONS: During OLV in lateral decubitus for thoracic surgery, application to the dependent lung a recruiting strategy significantly recruits the dependent lung, improving arterial oxygenation and respiratory mechanics until the end of surgery. However, the transient haemodynamic derangement occurring during the RM should be taken into account.

Effect of Propofol, Sevoflurane and Desflurane on systemic redox balance.

We studied the effects of Propofol, Desflurane, and Sevoflurane on the systemic redox balance in patients undergoing laparohysterectomy. We measured blood concentration of glutathione (GSH), plasma antioxidant capacity (Trolox Equivalent Antioxidant Capacity-TEAC), and lipid peroxidation products (malondialdehyde (aMDA) and 4-hydroxynonenal (aHNE) protein adducts). Sixty patients were randomly placed into three groups of twenty people each. In Group P anesthesia was induced with Propofol 2 mg/kg and maintained with 12-10-8 mg/kg/min; in Groups S and D anesthesia was induced with 3 mg/kg Sodium Thiopental and maintained with 2 percent Sevoflurane and 6 percent Desflurane, respectively. Blood samples were collected prior to induction (T0 bas), 60min and 24h postoperatively (T1 60 and T2 24 h). In Group P, GSH increased on T1 60 and returned to baseline on T24h, while TEAC remained unmodified; in Groups S, GSH and TEAC decreased on T1 60 in Group D, on T1 60 there was a slight decrease of GSH and TEAC. The levels of aMDA slightly decreased throughout the study periods in Group P, increased in Group D, and remained stable in Group S. Propofol showed antioxidant properties, while Sevoflurane and Desflurane seemed to shift the redox balance towards oxidation, yet without inducing overt oxidative damage.

Abdominal hypertension and liver dysfunction in intensive care unit patients: an "on-off" phenomenon?

Intra-abdominal hypertension (IAH) can affect liver hemodynamics but it is not known if has a significant clinical impact on liver function. The aim of this study was to investigate the relationship between IAH and liver function. A prospective study was performed in 110 adult intensive care unit (ICU) patients. Intra-abdominal pressure (IAP) was measured on admission and every other day, and liver sequential organ failure assessment (SOFA) score was collected whenever IAP was measured. IAH was defined by a IAP >or= 10 mm Hg, and liver dysfunction was defined by a hepatic SOFA score >or= 2. An overall IAH incidence of 56.3% was found (n = 62). Thirty-three patients presented a liver SOFA score >or= 2, with an overall incidence of 30%. Liver SOFA score of the group of patients with abdominal hypertension was higher than in group of patients without abdominal hypertension. (0.8 +/- 1.05 vs 0.4 +/- 0.7; P < .05), but IAH and liver dysfunction were not significantly associated (chi2 = 2.03; P = .15). When the whole sample was divided according to the worst IAP score (IAP < 10, IAP between 10 and 15, and IAP > 15), the corresponding liver dysfunction scores in the three groups were 0.35 +/- 0.6, 0.74 +/- 1, and 1.2 +/- 1.3, respectively (P = .01). A strict association between IAH and liver dysfunction was not found. Most likely, low levels of IAH, although able to reduce liver blood flow, are not per se sufficient to produce a real dysfunction; however, a correlation between the degree of IAH and the degree of hyperbilirubinemia exists. IAH does not seem to be an "on-off" phenomenon, but produces liver alterations for increasing levels of its severity.

Airways humidification during mechanical ventilation. Effects on tracheobronchial ciliated cells morphology.

AIM: Airways humidification during mechanical ventilation (MV) can be performed by means of heat and moisture exchangers (HME). Good performance of selected hygroscopic HME was shown in terms of tracheal temperature and humidity control and low tube obstruction rates. However, few data are available on their effects on tracheobronchial ciliated cells. The purpose of this study was to evaluate the effects of 2 different HME on ciliated cell during MV. METHODS: Twenty consecutive patients undergoing elective surgery lasting <4 h were randomly assigned to be treated with Rusch (Group 1) or Mediflux (Group 2) hygroscopic HME. The morphology of tracheobronchial ciliated cells was evaluated from cytologic smears of endotracheal aspirate. Smears were prepared by using the thin-prep processor, stained using the Papanicolau method and examined in triplicate: recognizable respiratory cells were graded on a six-point scale, according to the normal appearance of cilia, cytoplasm and nucleus. RESULTS: In Group 1, 178.3+37 cells were retrieved from aspirates and , 155.6+58 in Group 2 (NS). The score was 739+241 in Group 1 and 617+329 in Group 2 (NS). Cilia and end plate were undamaged in 80+17% and 81+20% cells respectively in Group 1 and in 56+23% and 62+22% cells respectively in Group 2 (P<0.01 and <0.05). CONCLUSIONS: During MV epithelial tracheobronchial cells can be affected by the humidification device used. Our findings suggest that the 2 HME tested in the present study have a different impact on ciliated cells structure.

[Hemodynamic and respiratory changes during hip and knee arthroplasty. An echocardiographic study]. / Modificazioni emodinamiche e respiratorie in corso di protesi di anca e di ginocchio. Studio ecocardiografico.

BACKGROUND: The "bone cement implantation syndrome" is a rare but severe complication observed especially during the insertion of cemented prostheses in hip and knee replacement surgery. Several mechanisms are involved: effects of methylmethacrilate, embolism of fat, air and bone marrow, and release of tissue thromboplastin during acetabular and femoral reaming. Aim of this study was to detect embolic events, right heart impairment, hemodynamic and respiratory changes during hip and knee replacement surgery. DESIGN: Prospective study, between February-May 2001. ENVIRONMENT: Orthopedic Operative room. PATIENTS: Twenty-one patients who underwent total hip or knee arthroplasty under general anesthesia. Patients were divided in methylmethacrylate cemented prostheses groups (CEM, n=10) and totally uncemented prostheses (NON CEM, n=11). DATA COLLECTION: Standard anesthesia monitoring and omniplane TEE were performed. TEE probe was positioned in order to obtain "inflow-outflow" views of right heart. Measurements were obtained after anesthesia induction (T1), during femoral realing (T2) at prostheses insertion (T3), and at the end of surgery (T4). RESULTS: Hemodynamic and respiratory parameters measured in different phases of surgical procedures were not different within groups and between groups. Fourtheen patients had TEE evidence of emboli, and the phenomenon was more evident in CEM group (Z= -347; p<0.001). During prostheses insertion, a slight, not significant increase in right ventricular dimensions was observed in both groups, without any right ventricular wall kinetic abnormality. No difference was observed between groups. No adverse cardiac or cerebrovascular events in intra- and postoperatory period were observed. CONCLUSIONS: In normal patients total hip or knee arthroplasty is associated with embolic phenomena, without any significant change in systemic and right heart hemodynamics. Insertion of cemented prostheses does not modify hemodynamic profile. It remains to be elucidated if the occurrence of emboli has a critical role in patients with cardiorespiratory disease.

Independent lung ventilation in patients with unilateral pulmonary contusion. Monitoring with compliance and EtCO(2).

OBJECTIVE: a) to describe a non-barotraumatic ventilatory setting for independent lung ventilation (ILV); b) to determine the utility of single lung end-tidal CO(2) (EtCO(2)) monitoring to evaluate the ventilation to perfusion (V/Q) matching in each lung during ILV and for ILV weaning. DESIGN: prospective study. SETTING: general intensive care unit in a university teaching hospital. PATIENTS: twelve patients with unilateral thoracic trauma needing ILV. INTERVENTIONS AND RESULTS: ILV was started with each lung ventilated with the same tidal volume (Vt): plateau airway pressure (Pplat) was 34.2+/-3.2 cmH2O in diseased lungs (DL) and 18.1+/-1.9 cmH2O in normal lungs (NL) ( P<0.01). Static compliance (Cst) was 9.9+/-1.1 ml/cmH(2)O in DL and 19.3+/-1.7 ml/cmH(2)O in NL ( P<0.01). EtCO2 was 22.5+/-2.2 mmHg in DL and 36.6+/-1.9 mmHg in NL ( P<0.01). PaO(2)/FiO(2) was at 151+/-20. PEEP was applied on the DL and each lung was ventilated with a Vt that developed Pplat < or =26 cmH2O. With this setting, Vt given to the NL was unchanged, whereas it was reduced in the DL (238+/-30 ml vs 350+/-31 ml; P<0.01). Cst and EtCO2 were still significantly lower in the DL ( P<0.01, respectively), while the PaO(2)/FiO(2) ratio remained unchanged. Vt was then progressively increased in the DL as Pplat decreased, but remained unchanged in the NL. ILV was discontinued when Vt, Cst and EtCO(2) were the same in each lung. PaO(2)/FiO(2) ratio had then increased to 295+/-18. CONCLUSIONS: a) during ILV, adequate oxygenation and a reduction in V/Q mismatch can be obtained by setting Vt and PEEP to keep Pplat below a safe threshold for barotrauma; b) measurement of single lung EtCO2 can be useful to evaluate progressive V/Q matching.

Gradual reduction of endotracheal tube diameter during mechanical ventilation via different humidification devices.

BACKGROUND: Limited data suggest that increased resistance to flow within endotracheal tubes (ETT) may occur in patients whose lungs are mechanically ventilated for more than 48 h, especially when airway humidification is inadequate. This could lead to sudden ETT obstruction or induce excessive loading during spontaneous breathing. METHODS: Twenty-three such patients were randomly assigned to three types of airway humidifier based on three different working principles: a Fisher Paykell hot water system (n = 7), a Pall BB2215 heat and moisture exchanger (HME) hydrophobic filter (n = 8), and a Dar Hygrobac 35254111 HME hygroscopic filter (n = 8). The decrease in internal pressure along the ETT and the flow rate were measured in each patient every 2 days. An "effective inner diameter" was derived from these measurements and allowed the inner ETT configuration to be monitored. RESULTS: On the first day of intubation, the mean diameter was similar in the three groups, and was slightly smaller than the in vitro diameter (mean +/- SD: 7.6 +/- 0.6 mm for Fisher-Paykell, 7.7 +/- 0.4 for Pall, and 7.5 +/- 0.4 for Dar). The mean diameter tended to decrease from day to day. At the end of the study, the overall reduction in mean diameter was significantly greater with the hydrophobic HME (Pall) than with the two other systems (Pall: -6.5 +/- 4% vs. 2.5 +/- 2.5% for Dar and 1.5 +/- 3% for Fisher-Paykell; P < 0.01 with analysis of variance). The same was true of the mean reduction in effective inner ETT diameter expressed per day of ventilation (-1.6 +/- 1.5% per day for Pall vs. -0.5 +/- 0.4% for Dar and -0.2 +/- 0.4% for Fisher-Paykell; P < 0.01). In four patients, the ETT became obstructed and emergency repeated tracheal intubation was required. The Pall HME and the Fisher-Paykell system were being used in three and one patient, respectively. Before obstruction, the reduction in ETT diameter was significantly greater for these four patients than for the remaining 23 patients (7.8 +/- 1.4% vs. 3.1 +/- 4.1%; P < 0.01). CONCLUSIONS: During prolonged mechanical ventilation, significant alterations in inner ETT configuration occur frequently and are influenced by the type of humidification device used. In vivo monitoring of ETT mechanical properties might be clinically useful.