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Background We aimed to determine whether high-flow nasal oxygen could reduce the incidence of decreased peripheral oxygen saturation (SpO2) compared with standard oxygen in patients at risk of hypoxaemia undergoing gastrointestinal endoscopy under deep sedation. Methods This was a multicentre, randomised controlled trial with blinded assessment of the primary outcome evaluating high-flow nasal oxygen (gas flow 70 L min−1, inspired oxygen fraction 0.50) or standard oxygen delivered via nasal cannula or face mask (6 L min−1) or nasopharyngeal tube (5 L min−1) in patients at risk of hypoxaemia (i.e. >60 yr old, or with underlying cardiac or respiratory disease, or with ASA physical status >1, or with obesity or sleep apnoea syndrome) undergoing gastrointestinal endoscopy. The primary endpoint was the incidence of SpO2 ≤92%. Secondary outcomes included prolonged or severe desaturations, need for manoeuvres to maintain free upper airways, and other adverse events. Results In 379 patients, a decrease in SpO2 ≤92% occurred in 9.4% (18/191) for the high-flow nasal oxygen group, and 33.5% (63/188) for the standard oxygen groups (adjusted absolute risk difference, –23.4% [95% confidence interval (CI), –28.9 to –16.7]; P 1 min) and manoeuvres to maintain free upper airways were less frequent in the high-flow nasal oxygen group than in the standard oxygen group (7.3% vs 14.9%, P=.02, and 11.1% vs 32.4%, P Conclusions In patients at risk of hypoxaemia undergoing gastrointestinal endoscopy under deep sedation, use of high-flow nasal oxygen significantly reduced the incidence of peripheral oxygen desaturation. Clinical trial registration NCT03829293.

Background During induction of general anaesthesia a ‘cannot intubate, cannot oxygenate' (CICO) situation can arise, leading to severe hypoxaemia. Evidence is scarce to guide ventilation strategies for small-bore emergency front of neck airways that ensure effective oxygenation without risking lung damage and cardiovascular depression. Methods Fifty virtual subjects were configured using a high-fidelity computational model of the cardiovascular and pulmonary systems. Each subject breathed 100% oxygen for 3 min and then became apnoeic, with an obstructed upper airway. When arterial haemoglobin oxygen saturation reached 40%, front of neck airway access was simulated with various configurations. We examined the effect of several ventilation strategies on re-oxygenation, pulmonary pressures, cardiovascular function, and oxygen delivery. Results Re-oxygenation was achieved in all ventilation strategies. Smaller airway configurations led to dynamic hyperinflation for a wide range of ventilation strategies. This effect was absent in airways with larger internal diameter (≥3 mm). Intrapulmonary pressures increased quickly to supra-physiological values with the smallest airways, resulting in pronounced cardio-circulatory depression (cardiac output Conclusions Dynamic hyperinflation can be demonstrated for a wide range of front of neck airway cannulae when the upper airway is obstructed. When using small-bore cannulae in a CICO situation, ventilation strategies should be chosen that prevent gas trapping to prevent severe adverse events including cardio-circulatory depression.

Background Atelectasis after cardiac surgery is common and promotes ventilation/perfusion mismatch, infection, and delayed discharge from critical care. Recruitment manoeuvres are often performed to reduce atelectasis. In severe respiratory failure, recruitment manoeuvres in the prone position may increase oxygenation, survival, or both. We compared the effects of recruitment manoeuvres in the prone vs supine position on lung aeration and oxygenation in cardiac surgical patients. Methods Subjects were randomised to recruitment manoeuvres (40 cm H2O peak inspiratory pressure and 20 cm H2O PEEP for 30 s) in either the prone or supine position after uncomplicated cardiac surgery. The co-primary endpoints were lung aeration (end-expiratory lung volume measured by electrical impedance tomography (arbitrary units [a.u.]) and lung oxygenation (ratio of arterial oxygen partial pressure to fractional inspired oxygen [Pao2/FiO2 ratio]). Secondary outcomes included postoperative oxygen requirement and adverse events. Results Thirty subjects (27% female; age, 48–81 yr) were recruited. Dorsal lung tidal volume was higher after prone recruitment manoeuvres (363 a.u.; 95% confidence intervals [CI], 283–443; n=15) after extubation, compared with supine recruitment manoeuvres (212 a.u.; 95% CI, 170–254; n=15; P Conclusions Recruitment manoeuvres in the prone position after cardiac surgery improve lung aeration and oxygenation. Clinical trial registration NCT03009331.

Background The role of prone positioning in intubated subjects with acute respiratory distress syndrome caused by coronavirus disease 2019 (COVID-19) remains unclear. Methods We conducted an observational cohort study of intubated patients admitted to our academic medical centre intensive care unit with COVID-19 between March 18-31 2020. Exclusion criteria were pregnancy, reintubation and previous prone positioning at a referring hospital. Patients that were placed in the prone position were followed up until hospital discharge. The primary outcome was oxygenation assessed by arterial oxygen tension/fraction of inspired oxygen ratio (PaO2/FIO2). Secondary outcomes included PaO2/FIO2 ratio improvement ≥20%. Treatment failure of prone positioning was defined as death or requirement for extracorporeal membrane oxygenation (ECMO). Results Forty-two subjects (29 males; mean age:58.5 [12.7] years) were eligible for analysis. Nine subjects were placed in the prone position only once, with 25 requiring prone positioning on ≥3 occasions. 31/42 (74%) subjects survived to discharge, with 5 requiring ECMO; 11/42 (26.2%) subjects died. Following the first prone positioning session, mean (SD) PaO2/FIO2 ratio increased from 17.9kPa (7.2) to 28.2kPa (12.2) (p

Background Global and intra-renal perfusion and oxygenation may be affected by the choice of anaesthetic. We compared the effects of isoflurane with those of propofol and fentanyl on renal blood flow (RBF) and intra-renal perfusion and oxygenation, and assessed how these were associated with renal sympathetic nerve activity (RSNA). Methods A renal artery flow probe and laser Doppler and oxygen-sensing probes were surgically implanted in the renal medulla and cortex in 20 Merino ewes. RSNA was measured in 12 additional ewes. We compared the effects of volatile or i.v. anaesthesia on global RBF, renal oxygen delivery (RDO2), intra-renal perfusion, and RSNA with the non-anaesthetised state on postoperative day 3 as control reference. Results Compared with a non-anaesthetised state, volatile anaesthesia reduced global RBF [–76 (82–68)%], RDO2 [−76 (83–71)%], and cortical [–68 (74–54)%] and medullary [–76 (84–72)%] perfusion. I.V. anaesthesia reduced RBF [–55 (67–38)%], RDO2 [–55 (65–44)%], and cortical [–27 (45–6)%] and medullary [–35 (48–30)%] perfusion, but to a lesser extent than volatile anaesthesia. Renal PO2 was not influenced by anaesthesia, whilst RSNA was elevated during volatile, but not during i.v. anaesthesia. Conclusions Volatile and i.v. general anaesthesia markedly reduced global RBF, RDO2, and regional kidney perfusion. These effects were greater with volatile anaesthesia, and were paralleled by an increase in RSNA. Our findings suggest a neurogenic modulatory effect of anaesthetics on renal perfusion and oxygenation.

Background Oxygenation via a high-flow nasal cannula (HFNC) can be an alternative to tracheal intubation during short apnoeic procedures. This randomised, non-inferiority study assessed the efficacy of HFNC compared with tracheal intubation in laryngeal microsurgery. Methods Patients (≥20 yr old) undergoing laryngeal microsurgery under general anaesthesia and neuromuscular blockade were randomised to either the HFNC or tracheal intubation groups. The primary endpoint was lowest pulse oxygen saturation (SpO2) during the first 30 min of surgery. Secondary endpoints included incidence of desaturation (SpO2 Results Amongst 130 patients randomised, 118 were included in the analysis. The lowest SpO2 was 100 (98–100)% in the HFNC group (n=56) and 100 (100–100)% in the tracheal intubation group (n=62), with a mean difference of –1.4% (95% confidence interval: –2.4% and –0.3%), failing to confirm non-inferiority with a non-inferiority margin of 2%. The peak transcutaneous CO2 and end-tidal CO2 at the end of surgery were higher in the HFNC group compared with the tracheal intubation group. Incidences of desaturation, hypercarbia, and rescue intervention were more frequent in patients receiving HFNC compared with tracheal intubation. Conclusions HFNC oxygenation was not non-inferior to tracheal intubation for maintaining oxygen saturation during laryngeal microsurgery. Considering more frequent desaturation, hypercarbia, and requirement for rescue intervention compared with tracheal intubation, HFNC should be used with cautious monitoring even for short duration airway surgery. Clinical trial registration NCT03629353.

BACKGROUND: During induction of general anaesthesia, patients frequently experience apnoea, which can lead to dangerous hypoxaemia. An obstructed upper airway can impede attempts to provide ventilation. Although unrelieved apnoea is rare, it continues to cause deaths. Clinical investigation of management strategies for such scenarios is effectively impossible because of ethical and practical considerations. METHODS: A population-representative cohort of 100 virtual (in silico) subjects was configured using a high-fidelity computational model of the pulmonary and cardiovascular systems. Each subject breathed 100% oxygen for 3 min and then became apnoeic, with an obstructed upper airway, during induction of general anaesthesia. Apnoea continued throughout the protocol. When arterial oxygen saturation (Sao(2)) reached 20%, 40%, or 60%, airway obstruction was relieved. We examined the effect of varying supraglottic oxygen fraction (Fo(2)) on the degree of passive re-oxygenation occurring without tidal ventilation. RESULTS: Relief of airway obstruction during apnoea produced a single, passive inhalation (caused by intrathoracic hypobaric pressure) in all cases. The degree of re-oxygenation after airway opening was markedly influenced by the supraglottic Fo(2), with a supraglottic Fo(2) of 100% providing significant and sustained re-oxygenation (post-rescue Pao(2) 42.3 [4.4] kPa, when the airway rescue occurred after desaturation to Sao(2) 60%). CONCLUSIONS: Supraglottic oxygen supplementation before relieving upper airway obstruction improves the effectiveness of simulated airway rescue. Management strategies should be implemented to assure a substantially increased pharyngeal Fo(2) during difficult airway management.

Background Anaesthesia-induced changes in renal perfusion are dependent on the choice of anaesthetic agent. However, the effects of varying inspired oxygen fraction (FiO2) on renal perfusion and oxygenation during TIVA (propofol + fentanyl) or volatile anaesthesia (VA; isoflurane) are unknown. Methods In 16 Merino ewes, we surgically implanted a renal artery flow probe and laser-Doppler and oxygen-sensing probes in the renal medulla and cortex. We compared the systemic and renal effects of graded alterations in FiO2 (0.21, 0.40, 0.60, and 1.0) during TIVA or VA and compared the changes with those in the non-anaesthetised state. Results Compared with the non-anaesthetised state, TIVA and VA decreased renal blood flow (−50% vs −75%), renal oxygen delivery (−50% vs −80%), and renal cortical (−40% vs −60%) and medullary perfusion (−50% vs −75%). At an FiO2 of 0.21, both anaesthetic regimens induced similar reductions in cortical (−58 vs −65%) and medullary (−37% vs −38%) oxygenation. At higher concentrations of FiO2, renal blood flow and renal tissue perfusion were not changed, but intrarenal oxygenation improved similarly under TIVA and VA. In particular, at an FiO2 of ≥0.40 and ≤0.60, cortical and medullary oxygen tension were similar to the non-anaesthetised state. Conclusions Irrespective of FiO2, TIVA decreased renal and intrarenal perfusion less than VA, but at low FiO2 concentrations both led to equivalent reductions in renal cortical and medullary oxygenation. However, with FiO2 between 0.40 and 0.60 during TIVA or VA, both cortical and medullary oxygenation was maintained at normal physiological levels.

Background Near infrared spectroscopy (NIRS) is widely used to monitor regional cerebral tissue oxygenation (rScO2). We compared rScO2 values during cardiac surgery in patients with or without new cerebral ischaemic lesions on diffusion weighted magnetic resonance imaging (DWI). We hypothesised patients with new cerebral lesions would have impaired tissue oxygenation reflected in their rScO2 values. Methods NIRS and DWI data were collected in 152 elective cardiac surgery patients. Absolute rScO2 values, duration of desaturation below thresholds (baseline, 10%, and 20%), and accumulated cerebral desaturation load were compared between patients with or without new cerebral lesions on DWI. Primary outcome was time below 10% from rScO2 baseline. Results The time below 10% from rScO2 baseline was significantly longer for patients with new cerebral lesions than for patients without [median (inter-quartile range): 11.0 (0.4; 37.5) min vs 1.8 inter-quartile range: (0.05; 20.9) min, P=0.02]. Furthermore, they had a higher accumulated desaturation load below baseline (P=0.02) and 10% below baseline (P=0.02). Finally, their absolute minimum rScO2 value was significantly lower (P=0.01). However, the frequency of patients with desaturation below 10% and 20% was comparable between patients with and without new cerebral lesions. Receiver-operating characteristic curve analysis did not identify a clear-cut critical threshold among the investigated rScO2 variables. Conclusions Use of NIRS identified significant group differences in rScO2 values between patients with or without new ischaemic lesions. However, a critical threshold could not be identified because of a high variation in NIRS values across both groups. Clinical trial registration NCT 02185885.

Background Transnasal humidified rapid insufflation ventilatory exchange (THRIVE) comprises the administration of heated, humidified, and blended air/oxygen mixtures via nasal cannula at rates of ≥2 litres kg−1 min−1. The aim of this randomized controlled study was to evaluate the length of the safe apnoea time using THRIVE with two different oxygen concentrations (100% vs 30% oxygen) compared with standard low-flow 100% oxygen administration. Methods Sixty patients, aged 1–6 yr, weighing 10–20 kg, undergoing general anaesthesia for elective surgery, were randomly allocated to receive one of the following oxygen administration methods during apnoea: 1) low-flow 100% oxygen at 0.2 litres kg−1 min−1; 2) THRIVE 100% oxygen at 2 litres kg−1 min−1; and 3) THRIVE 30% oxygen at 2 litres kg−1 min−1. Primary outcome was time to desaturation to 95%. Termination criteria included SpO2 decreased to 95%, transcutaneous CO2 increased to 65 mmHg, or apnoea time of 10 min. Results The median (interquartile range) [range] apnoea time was 6.9 (5.7–7.8) [2.8–10.0] min for low-flow 100% oxygen, 7.6 (6.2–9.1) [5.2–10.0] min for THRIVE 100% oxygen, and 3.0 (2.4–3.7) [0.2–5.3] min for THRIVE 30% oxygen. No significant difference was detected between apnoea times with low-flow and THRIVE 100% oxygen administration (P=0.15). THRIVE with 30% oxygen demonstrated significantly shorter apnoea times (P Conclusions High-flow 100% oxygen (2 litres kg−1 min−1) administered via nasal cannulas did not extend the safe apnoea time for children weighing 10–20 kg compared with low-flow nasal cannula oxygen (0.2 litres kg−1 min−1). No ventilatory effect was observed with THRIVE at 2.0 litres kg−1 min−1. Clinical trial registration NCT02979067.

Compromised tissue oxygenation is one of the root causes of dysfunction of various organs and postoperative complications. Oxygenation of different tissue beds may follow different patterns of change during physiological derangement.Patients undergoing elective major posterior spine surgery participated in this prospective observational study. Cerebral tissue oxygen saturation (SctO 2 ) was monitored on the upper forehead and muscular tissue oxygen saturation (SmtO 2 ) on the lower leg. The associations of various oxygenation indices with postoperative composite complications and length of hospital stay (LOH) were investigated.The number of composite complications per patient was 3 (2) while the LOH was 6 (3) days (n = 102). Multiple SmtO 2 indices (maximum, minimum, mean, median, and area under curve (AUC)) were associated with composite complications (univariate analysis, P 0.05). No SctO 2 indices were associated with complications. Multiple SmtO 2 indices (maximum, mean, median, and AUC) showed differences ( P 0.05) between patients with composite complications ≤3 and 3, respectively. SmtO 2 standard deviation, AUC, and AUC weighted, and SctO 2 standard deviation, were associated with LOH (univariate analysis, P 0.05). Two SmtO 2 indices (AUC and AUC weighted), showed differences ( P 0.05) between the patients with an LOH ≤6 and 6 days, respectively. SmtO 2 , but not SctO 2 , indices improved the adjusted R 2 for composite complications (+54.0%, P = 0.0001) and LOH (+19.0%, P = 0.02) based on multiple linear models.Muscular tissue oxygenation has a stronger association with postoperative complications and length of hospital stay than cerebral tissue oxygenation after major spine surgery.

Background The mechanisms by which hypertonic sodium lactate (HSL) solution act in injured brain are unclear. We investigated the effects of HSL on brain metabolism, oxygenation, and perfusion in a rodent model of diffuse traumatic brain injury (TBI). Methods Thirty minutes after trauma, anaesthetised adult rats were randomly assigned to receive a 3 h infusion of either a saline solution (TBI–saline group) or HSL (TBI–HSL group). The sham–saline and sham–HSL groups received no insult. Three series of experiments were conducted up to 4 h after TBI (or equivalent) to investigate: 1) brain oedema using diffusion-weighted magnetic resonance imaging and brain metabolism using localized 1 H-magnetic resonance spectroscopy ( n = 10 rats per group). The respiratory control ratio was then determined using oxygraphic analysis of extracted mitochondria, 2) brain oxygenation and perfusion using quantitative blood-oxygenation-level-dependent magnetic resonance approach ( n = 10 rats per group), and 3) mitochondrial ultrastructural changes ( n = 1 rat per group). Results Compared with the TBI–saline group, the TBI–HSL and the sham-operated groups had reduced brain oedema. Concomitantly, the TBI–HSL group had lower intracellular lactate/creatine ratio [0.049 (0.047–0.098) vs 0.097 (0.079–0.157); P vs 66% (55–73); P vs 38.4 (31.0–47.5) nm; P Conclusions These findings indicate that the hypertonic sodium lactate solution can reverse brain oxygenation and metabolism dysfunction after traumatic brain injury through vasodilatory, mitochondrial, and anti-oedema effects.

Background High inspiratory oxygen fraction ( F I O 2 ) may improve tissue oxygenation but also impair pulmonary function. We aimed to assess whether the use of high intraoperative F I O 2 increases the risk of major respiratory complications. Methods We studied patients undergoing non-cardiothoracic surgery involving mechanical ventilation in this hospital-based registry study. The cases were divided into five groups based on the median F I O 2 between intubation and extubation. The primary outcome was a composite of major respiratory complications (re-intubation, respiratory failure, pulmonary oedema, and pneumonia) developed within 7 days after surgery. Secondary outcomes included 30-day mortality. Several predefined covariates were included in a multivariate logistic regression model. Results The primary analysis included 73 922 cases, of whom 3035 (4.1%) developed a major respiratory complication within 7 days of surgery. For patients in the high- and low-oxygen groups, the median F I O 2 was 0.79 [range 0.64–1.00] and 0.31 [0.16–0.34], respectively. Multivariate logistic regression analysis revealed that the median F I O 2 was associated in a dose-dependent manner with increased risk of respiratory complications (adjusted odds ratio for high vs low F I O 2 1.99, 95% confidence interval [1.72–2.31], P -value for trend

Hypoventilation is the main reason for hypoxia during upper gastrointestinal endoscopy procedures with sedation. The key to preventing hypoxia is to maintain normal ventilation during the procedure. We introduced supraglottic jet oxygenation and ventilation (SJOV) through a new Wei nasal jet tube (WNJ) to reduce the incidence of hypoxia in patients sedated with propofol during upper gastrointestinal endoscopy procedures.In a multicentre, prospective randomized single-blinded study, 1781 outpatients undergoing routine upper gastrointestinal endoscopy who were sedated with propofol by an anaesthetist were randomized into the following three groups: the supplementary oxygen via nasal cannula group [nasal cannula oxygen: O 2 (2 litres min -1 ) was administered via a nasal cannula]; the supplementary oxygen via WNJ group [WNJ oxygen: O 2 (2 litres min -1 ) was administered through a WNJ]; and the SJOV via WNJ group (WNJ SJOV: SJOV was administered via WNJ) at three centres from March 2015 to July 2016. The primary outcome of interest was the incidence of hypoxia (peripheral oxygen saturation of 75-89%). Other adverse events were also recorded.Supraglottic jet oxygenation and ventilation decreased the incidence of hypoxia from 9 to 3% ( P0.0001). No severe hypoxia occurred in the WNJ SJOV group, one instance occurred in the WNJ oxygen group, and two instances were observed in the nasal cannula oxygen supply control group. Supraglottic jet oxygenation and ventilation-related minor adverse events increased significantly within 1 min after the procedure but decreased 30 min later.The use of SJOV during upper gastrointestinal endoscopy for patients who are sedated with propofol reduces the incidence of hypoxia, with minor and tolerable adverse events. Supraglottic jet oxygenation and ventilation has a favourable risk-to-benefit ratio and may improve patient safety.NCT02436018.

Background Superimposed high-frequency jet ventilation (SHFJV) has proved to be safe and effective in clinical practice. However, it is unclear which frequency range optimizes ventilation and gas exchange. The aim of this study was to systematically compare high-frequency jet ventilation (HFJV) with HFJV by assessing chest wall volume variations (ΔEEV CW ) and gas exchange in relation to variable high frequency. Methods SHFJV or HFJV were used alternatively to ventilate the lungs of 10 anaesthetized pigs (21–25 kg). The low-frequency component was kept at 16 min −1 in SHFJV. In both modes, high frequencies ranging from 100 to 1000 min −1 were applied in random order and ventilation was maintained for 5 min in all modalities. Chest wall volume variations were obtained using opto-electronic plethysmography. Airway pressures and arterial blood gases were measured repeatedly. Results SHFJV increased ΔEEV CW compared with HFJV; the difference ranged from 43 to 68 ml. Tidal volume ( V T ) was always >240 ml during SHFJV whereas during HFJV ranged from 92 ml at the ventilation frequency of 100 min −1 to negligible values at frequencies >300 min −1 . We observed similar patterns for P a O 2 and P a CO 2 . SHFJV provided generally higher, frequency-independent oxygenation ( P a O 2 at least 32.0 kPa) and CO 2 removal ( P a CO 2 ∼5.5 kPa), whereas HFJV led to hypoxia and hypercarbia at higher rates ( P a O 2 10 kPa at f HF >300 min −1 ). Conclusions In a porcine model, SHFJV was more effective in increasing end-expiratory volume than single-frequency HFJV, but both modes may provide adequate ventilation in the absence of airway obstruction and respiratory disease, except for HFJV at frequencies ≥300 min −1 .

Background High-flow nasal oxygen (HFNO) has been shown to benefit oxygenation, ventilation and upper airway patency in a range of clinical scenarios, however its use in spontaneously breathing patients during general anaesthesia has not been described. Spontaneous respiration using i.v. anaesthesia is the primary technique used at our institution for tubeless airway surgery. We hypothesized that the addition of HFNO would increase our margin of safety, particularly during management of an obstructed airway. Methods A retrospective observational study was conducted using a SponTaneous Respiration using IntraVEnous anaesthesia and High-flow nasal oxygen (STRIVE Hi) technique to manage 30 adult patients undergoing elective laryngotracheal surgery. Results Twenty-six patients (87%) presented with significant airway and/or respiratory compromise (16 were stridulous, 10 were dyspnoeic). No episodes of apnoea or complete airway obstruction occurred during the induction of anaesthesia using STRIVE Hi. The median [IQR (range)] lowest oxygen saturation during the induction period was 100 [99–100 (97–100)] %. The median [IQR (range)] overall duration of spontaneous ventilation was 44 [40–49.5 (18–100)] min. The median [IQR (range)] end-tidal carbon dioxide (ETCO2) level at the end of the spontaneous ventilation period was 6.8 [6.4–7.1 (4.8–8.9)] kPa. The mean rate of increase in ETCO2 was 0.03 kPa min−1. Conclusions STRIVE Hi succeeded in preserving adequate oxygen saturation, end-tidal carbon dioxide and airway patency. We suggest that the upper and lower airway benefits attributed to HFNO, are ideally suited to a spontaneous respiration induction, increasing its margin of safety. STRIVE Hi is a modern alternative to the traditional inhalation induction.

Background It is no longer safe to use large tidal volumes ( V T ) (>8 ml kg −1 ) for one-lung ventilation (OLV), and limiting plateau pressure should be a major objective. Due to the specificity of OLV, the use of positive end-expiratory pressure (PEEP) remains controversial. This study determined whether at the same low plateau pressure, reducing V T and increasing PEEP were not inferior to larger V T and lower PEEP ventilation in terms of oxygenation. Methods This prospective, randomized, non-inferiority, cross-over trial included 88 patients undergoing open thoracotomy who received two successive ventilatory strategies in random order: V T (8 ml kg −1 of ideal body weight) with low PEEP (5 cm H 2 O), or low V T (5 ml kg −1 ) with a high PEEP. Respiratory rate and PEEP were, respectively, adjusted to maintain constant ventilation and plateau pressure. The primary endpoint was the P a O 2 / F I O 2 ratio under each ventilatory strategy. Results The non-inferiority of low- V T ventilation could not be established. The mean adjusted P a O 2 / F I O 2 ratio was lower overall during low- V T ventilation, and differences between the two ventilatory modes varied significantly according to baseline (T0) P a O 2 / F I O 2 . Decreased oxygenation during low V T was smaller when baseline values were low. Systolic arterial pressure was not lower during low- V T ventilation. Conclusion During OLV, lowering V T and increasing PEEP, with the same low plateau pressure, reduced oxygenation compared with larger V T and lower PEEP. This strategy may reduce the risk of lung injury, but needs to be investigated further.

This study was conducted to determine whether an alveolar recruitment strategy (ARS) applied during two-lung ventilation (TLV) just before starting one-lung ventilation (OLV) improves ventilatory efficiency. Subjects were randomly allocated to two groups: (i) control group: ventilation with tidal volume (VT) of 8 or 6 ml kg(1) for TLV and OLV, respectively, and (ii) ARS group: same ventilatory pattern with ARS consisting of 10 consecutive breaths at a plateau pressure of 40 and 20 cm H2O PEEP applied immediately before and after OLV. Volumetric capnography and arterial blood samples were recorded 5 min (baseline) and 20 min into TLV, at 20 and 40 min during OLV, and finally 10 min after re-establishing TLV. Twenty subjects were included in each group. In all subjects, the airway component of dead space remained constant during the study. Compared with baseline, the alveolar dead space ratio (VDalv/VTalv) increased throughout the protocol in the control but decreased in the ARS group. Differences in VDalv/VTalv between groups were significant (P0.001). Except for baseline, all Pa-O2 values in kPa (SD) were higher in the ARS than in the control group (P, 0.001), respectively [70 (7) and 55 (9); 33 (9) and 24 (10); 33 (8) and 22 (10); 70 (7) and 55 (10)]. Conclusions. Recruitment of both lungs before instituting OLV not only decreased alveolar dead space but also improved arterial oxygenation and the efficiency of ventilation.

† In this study of patients after cardiac surgery, HFNC increased end-expiratory lung impedance, suggesting increased lung volumes and functional residual capacity. † Oxygenation improved and the benefits were greatest in patients with high BMIs. † Further data are required to assess the clinical significance of these data. Background. High-flow nasal cannulae (HFNCs) create positive oropharyngeal airway pressure, but it is unclear how their use affects lung volume. Electrical impedance tomography allows the assessment of changes in lung volume by measuring changes in lung impedance. Primary objectives were to investigate the effects of HFNC on airway pressure (Paw) and end-expiratory lung volume (EELV) and to identify any correlation between the two. Secondary objectives were to investigate the effects of HFNC on respiratory rate, dyspnoea, tidal volume, and oxygenation; and the interaction between BMI and EELV. Methods. Twenty patients prescribed HFNC post-cardiac surgery were investigated. Impedance measures, Paw, Pao2 /FIo2 ratio, respiratory rate, and modified Borg scores were recorded first on low-flow oxygen and then on HFNC. Results. A strong and significant correlation existed between Paw and end-expiratory lung impedance (EELI) (r¼0.7, P,0.001). Compared with low-flow oxygen, HFNC significantly increased EELI by 25.6% [95% confidence interval (CI) 24.3, 26.9] and Paw by 3.0 cm H2O (95% CI 2.4, 3.7). Respiratory rate reduced by 3.4 bpm (95% CI 1.7, 5.2) with HFNC use, tidal impedance variation increased by 10.5% (95% CI 6.1, 18.3), and Pao2 /FIo2 ratio improved by 30.6 mm Hg (95% CI 17.9, 43.3). A trend towards HFNC improving subjective dyspnoea scoring (P¼0.023) was found. Increases in EELI were significantly influenced by BMI, with larger increases associated with higher BMIs (P,0.001). Conclusions.ThisstudysuggeststhatHFNCsreducerespiratoryrateandimproveoxygenation byincreasingbothEELVandtidalvolumeandaremostbeneficialinpatientswithhigherBMIs.

† This study investigates the effects of propofol-induced changes in bispectral index (BIS) on cerebral microcirculation and oxygenation during craniotomies. † In 2 mm cerebral depth, an increase in propofol dosage resulted in increased oxygen saturation (srvO2 )w ithout reduction of capillary venous blood flow (rvCBF). † Difference in oxygen content (avDO2) and approximated cerebralmetabolicrateofoxygen (aCMRO2) decreased with an increase in propofol dosage in 2 mm cerebral depth. † Alterations in BIS showed no effect on rvCBF, srvO2 ,a nd haemoglobin amount (rvHb) or on avDO2 or aCMRO2 in 8 mm cerebral depth. † These findings suggest that the CBF/CMRO2 ratio is altered by propofol in a regionally specific fashion. Background. Propofol reduces cerebral blood flow (CBF) secondary to cerebral metabolic depression. However, in vitro and in vivo studies demonstrate that propofol directly dilates the vascular smooth muscle. This study investigates the effects of propofolinduced changes in bispectral index (BIS) on cerebral microcirculation and oxygenation during craniotomies. Methods. In 21 craniotomy patients undergoing routine craniotomy, anaesthesia was maintained with propofol 4‐10 mg kg 21 h 21 and remifentanil 0.1‐0.4 m gk g 21 min 21 . Propofol concentration was adjusted to achieve higher BIS (target 40) or lower BIS (target 20). Regional measurements of capillary venous blood flow (rvCBF), oxygen saturation (srvO2), and haemoglobin amount (rvHb) at 2 mm (grey matter) and 8 mm (white matter) cerebral depth were randomly performed at higher and lower BIS by combined laser-Doppler flowmetry and spectroscopy. Calculations: approximated arteriovenous difference in oxygen content (avDO2) and cerebral metabolic rate of oxygen (aCMRO2). Results: mean values (SD). Statistics: Mann‐Whitney test (*P,0.05).

† Phenylephrine, but not ephedrine, decreased cardiac output (CO) and brain oxygenation. † This study highlights the importance of CO in preserving brain oxygenation during management of intraoperative hypotension. Background. How phenylephrine and ephedrine treatments affect global and regional haemodynamics is of major clinical relevance. Cerebral tissue oxygen saturation (SctO2 )-guided management may improve postoperative outcome. The physiological variables responsible for SctO2 changes induced by phenylephrine and ephedrine bolus treatment in anaesthetized patients need to be defined. Methods. A randomized two-treatment cross-over trial was conducted: one bolus dose of phenylephrine (100‐200 mg) and one bolus dose of ephedrine (5‐20 mg) were given to 29 ASA I‐III patients anaesthetized with propofol and remifentanil. SctO2, mean arterial pressure (MAP), cardiac output (CO), and other physiological variables were recorded before and after treatments. The associations of changes were analysed using linear-mixed models. Results. The COdecreased significantlyafter phenylephrine treatment [△CO¼ 22.1 (1.4) litre min 21 , P,0.001], but was preserved after ephedrine treatment [△CO¼0.5 (1.4) litre min 21 , P.0.05]. The SctO2 was significantly decreased after phenylephrine treatment [△SctO2 ¼ 23.2 (3.0)%, P,0.01] but preserved after ephedrine treatment [△SctO2 ¼0.04 (1.9)%, P.0.05]. CO was identified to have the most significant association with SctO2 (P,0.001). After taking CO into consideration, the other physiological variables, including MAP, were not significantly associated with SctO2 (P.0.05). Conclusions. Associated with changes in CO, SctO2 decreased after phenylephrine treatment, but remained unchanged after ephedrine treatment. The significant correlation between CO and SctO2 implies a cause‐effect relationship between global and regional haemodynamics.

We compared pressure and volume-controlled ventilation (PCV and VCV) in morbidly obese patients undergoing laparoscopic gastric banding surgery.Thirty-six patients, BMI35 kg m(-2), no major obstructive or restrictive respiratory disorder, and Pa(CO(2))6.0 kPa, were randomized to receive either VCV or PCV during the surgery. Ventilation settings followed two distinct algorithms aiming to maintain end-tidal CO(2) (E'(CO(2))) between 4.40 and 4.66 kPa and plateau pressure (P(plateau)) as low as possible. Primary outcome variable was peroperative P(plateau). Secondary outcomes were Pa(O(2)) (Fi(O(2)) at 0.6 in each group) and Pa(CO(2)) during surgery and 2 h after extubation. Pressure, flow, and volume time curves were recorded.There were no significant differences in patient characteristics and co-morbidity in the two groups. Mean pH, Pa(O(2)), Sa(O(2)), and the Pa(O(2))/Fi(O(2)) ratio were higher in the PCV group, whereas Pa(CO(2)) and the E'(CO(2))-Pa(CO(2)) gradient were lower (all P0.05). Ventilation variables, including plateau and mean airway pressures, anaesthesia-related variables, and postoperative cardiovascular variables, blood gases, and morphine requirements after the operation were similar.The changes in oxygenation can only be explained by an improvement in the lungs ventilation/perfusion ratio. The decelerating inspiratory flow used in PCV generates higher instantaneous flow peaks and may allow a better alveolar recruitment. PCV improves oxygenation without any side-effects.

Background Improved postoperative outcome has been demonstrated by perioperative maximization of cardiac stroke volume (SV) with fluid challenges, so-called goal-directed therapy. Oesophageal Doppler (OD) has been the most common technique for goal-directed therapy, but other flow-related techniques and parameters are available and they are potentially easier to apply in clinical practice. The objective of this investigation was therefore to use OD for preoperative SV maximization and compare the findings with a Modelflow determined SV, with an OD estimated corrected flow time (FTc), with central venous oxygenation ( S v O 2 ) and with muscle and brain oxygenation assessed with near infrared spectroscopy (NIRS). Methods Twelve patients scheduled for radical prostatectomy were anaesthetized before optimization of SV estimated by OD. A fluid challenge of 200 ml colloid was provided and repeated if at least a 10% increment in OD SV was obtained. Values were compared with simultaneously measured values of Modelflow SV, FTc, S v O 2 and muscle and cerebral oxygenation estimated by NIRS. Results Based upon OD assessment, optimization of SV was achieved after the administration of 400–800 ml (mean 483 ml) of colloid. The hypothetical volumes administered for optimization based upon Modelflow and S v O 2 differed from OD in 10 and 11 patients, respectively. Changes in FTc and NIRS were inconsistent with OD guided optimization. Conclusion Preoperative SV optimization guided by OD for goal-directed therapy is preferable compared with Modelflow SV, FTc, NIRS and S v O 2 until outcome studies for the latter are available.

Background In the present randomized study, we evaluated the differential effects of a colloid and a crystalloid fluid on renal oxygen delivery ( R D O 2 ), glomerular filtration (GFR), renal oxygen consumption ( R V ˙ O 2 ), and the renal oxygen supply–demand relationship (i.e. renal oxygenation) after cardiac surgery with cardiopulmonary bypass. Methods Thirty patients with normal preoperative renal function, undergoing uncomplicated cardiac surgery, were studied in the intensive care unit in the early postoperative period. Patients were randomized to receive a bolus dose of either a crystalloid (Ringers-acetate® 20 ml kg−1, n=15) or a colloid solution (Venofundin® 10 ml kg−1, n=15). Systemic haemodynamics were measured via a pulmonary artery catheter. Renal blood flow and GFR were measured by the renal vein retrograde thermodilution technique and by renal extraction of 51Cr-EDTA (=filtration fraction). Arterial and renal vein blood samples were obtained for measurements of renal oxygen delivery ( R D O 2 ) and R V ˙ O 2 . Renal oxygenation was estimated from the renal oxygen extraction. Results Despite an increase in cardiac index and renal blood flow with both fluids, neither of the fluids improved R D O 2 , because they both induced haemodilution. The GFR increased in the crystalloid (28%) but not in the colloid group. The crystalloid increased the filtration fraction (24%) and renal oxygen extraction (23%), indicating that the increase in GFR, the major determinant of R V ˙ O 2 , was not matched by a proportional increase in R D O 2 . Conclusions Neither the colloid nor the crystalloid improved R D O 2 when used for postoperative plasma volume expansion. The crystalloid-induced increase in GFR was associated with impaired renal oxygenation, which was not seen with the colloid. Clinical trial registration NCT01729364.

Background Awake fibre-optic intubation is a widely practised technique for anticipated difficult airway management. Despite the administration of supplemental oxygen during the procedure, patients are still at risk of hypoxia because of the effects of sedation, local anaesthesia, procedural complications, and the presence of co-morbidities. Traditionally used oxygen-delivery devices are low flow, and most do not have a sufficient reservoir or allow adequate fresh gas flow to meet the patient's peak inspiratory flow rate, nor provide an adequate fractional inspired oxygen concentration to prevent desaturation should complications arise. Methods A prospective observational study was conducted using a high-flow humidified transnasal oxygen-delivery system during awake fibre-optic intubation in 50 patients with anticipated difficult airways. Results There were no episodes of desaturation or hypercapnia using the high-flow system, and in all patients the oxygen saturation improved above baseline values, despite one instance of apnoea resulting from over-sedation. All patients reported a comfortable experience using the device. Conclusions The high-flow nasal oxygen-delivery system improves oxygenation saturation, decreases the risk of desaturation during the procedure, and potentially, optimizes conditions for awake fibre-optic intubation. The soft nasal cannulae uniquely allow continuous oxygenation and simultaneous passage of the fibrescope and tracheal tube. The safety of the procedure may be increased, because any obstruction, hypoventilation, or periods of apnoea that may arise may be tolerated for longer, allowing more time to achieve ventilation in an optimally oxygenated patient.

Background Transtracheal access and subsequent jet ventilation are among the last options in a ‘cannot intubate–cannot oxygenate' scenario. These interventions may lead to hypercapnia, barotrauma, and haemodynamic failure in the event of an obstructed upper airway. The aim of the present study was to evaluate the efficacy and the haemodynamic effects of the Ventrain, a manually operated ventilation device that provides expiratory ventilation assistance. Transtracheal ventilation was carried out with the Ventrain in different airway scenarios in live pigs, and its performance was compared with a conventional jet ventilator. Methods Pigs with open, partly obstructed, or completely closed upper airways were transtracheally ventilated either with the Ventrain or by conventional jet ventilation. Airway pressures, haemodynamic parameters, and blood gases obtained in the different settings were compared. Results Mean (sd) alveolar minute ventilation as reflected by arterial partial pressure of CO2 was superior with the Ventrain in partly obstructed airways after 6 min in comparison with traditional manual jet ventilation [4.7 (0.19) compared with 7.1 (0.37) kPa], and this was also the case in all simulated airway conditions. At the same time, peak airway pressures were significantly lower and haemodynamic parameters were altered to a lesser extent with the Ventrain. Conclusions The results of this study suggest that the Ventrain device can ensure sufficient oxygenation and ventilation through a small-bore transtracheal catheter when the airway is open, partly obstructed, or completely closed. Minute ventilation and avoidance of high airway pressures were superior in comparison with traditional hand-triggered jet ventilation, particularly in the event of complete upper airway obstruction.