Positive End-expiratory Pressure and Postoperative Atelectasis: A Randomized Controlled Trial.

BACKGROUND: Positive end-expiratory pressure (PEEP) increases lung volume and protects against alveolar collapse during anesthesia. During emergence, safety preoxygenation preparatory to extubation makes the lung susceptible to gas absorption and alveolar collapse, especially in dependent regions being kept open by PEEP. We hypothesized that withdrawing PEEP before starting emergence preoxygenation would limit postoperative atelectasis formation. METHODS: This was a randomized controlled evaluator-blinded trial in 30 healthy patients undergoing nonabdominal surgery under general anesthesia and mechanical ventilation with PEEP 7 or 9 cm H2O depending on body mass index. A computed tomography scan at the end of surgery assessed baseline atelectasis. The study subjects were thereafter allocated to either maintained PEEP (n = 16) or zero PEEP (n = 14) during emergence preoxygenation. The primary outcome was change in atelectasis area as evaluated by a second computed tomography scan 30 min after extubation. Oxygenation was assessed by arterial blood gases. RESULTS: Baseline atelectasis was small and increased modestly during awakening, with no statistically significant difference between groups. With PEEP applied during awakening, the increase in atelectasis area was median (range) 1.6 (-1.1 to 12.3) cm and without PEEP 2.3 (-1.6 to 7.8) cm. The difference was 0.7 cm (95% CI, -0.8 to 2.9 cm; P = 0.400). Postoperative atelectasis for all patients was median 5.2 cm (95% CI, 4.3 to 5.7 cm), corresponding to median 2.5% of the total lung area (95% CI, 2.0 to 3.0%). Postoperative oxygenation was unchanged in both groups when compared to oxygenation in the preoperative awake state. CONCLUSIONS: Withdrawing PEEP before emergence preoxygenation does not reduce atelectasis formation after nonabdominal surgery. Despite using 100% oxygen during awakening, postoperative atelectasis is small and does not affect oxygenation, possibly conditional on an open lung during anesthesia, as achieved by intraoperative PEEP.

Positive End-expiratory Pressure Alone Minimizes Atelectasis Formation in Nonabdominal Surgery: A Randomized Controlled Trial.

BACKGROUND: Various methods for protective ventilation are increasingly being recommended for patients undergoing general anesthesia. However, the importance of each individual component is still unclear. In particular, the perioperative use of positive end-expiratory pressure (PEEP) remains controversial. The authors tested the hypothesis that PEEP alone would be sufficient to limit atelectasis formation during nonabdominal surgery. METHODS: This was a randomized controlled evaluator-blinded study. Twenty-four healthy patients undergoing general anesthesia were randomized to receive either mechanical ventilation with PEEP 7 or 9 cm H2O depending on body mass index (n = 12) or zero PEEP (n = 12). No recruitment maneuvers were used. The primary outcome was atelectasis area as studied by computed tomography in a transverse scan near the diaphragm, at the end of surgery, before emergence. Oxygenation was evaluated by measuring blood gases and calculating the ratio of arterial oxygen partial pressure to inspired oxygen fraction (PaO2/FIO2 ratio). RESULTS: At the end of surgery, the median (range) atelectasis area, expressed as percentage of the total lung area, was 1.8 (0.3 to 9.9) in the PEEP group and 4.6 (1.0 to 10.2) in the zero PEEP group. The difference in medians was 2.8% (95% CI, 1.7 to 5.7%; P = 0.002). Oxygenation and carbon dioxide elimination were maintained in the PEEP group, but both deteriorated in the zero PEEP group. CONCLUSIONS: During nonabdominal surgery, adequate PEEP is sufficient to minimize atelectasis in healthy lungs and thereby maintain oxygenation. Thus, routine recruitment maneuvers seem unnecessary, and the authors suggest that they should only be utilized when clearly indicated. VISUAL ABSTRACT: An online visual overview is available for this article at http://links.lww.com/ALN/B728.

Minimizing atelectasis formation during general anaesthesia-oxygen washout is a non-essential supplement to PEEP.

BACKGROUND: Following preoxygenation and induction of anaesthesia, most patients develop atelectasis. We hypothesized that an immediate restoration to a low oxygen level in the alveoli would prevent atelectasis formation and improve oxygenation during the ensuing anaesthesia. METHODS: We randomly assigned 24 patients to either a control group (n = 12) or an intervention group (n = 12) receiving an oxygen washout procedure directly after intubation. Both groups were, depending on body mass index, ventilated with a positive end-expiratory pressure (PEEP) of 6-8 cmH2O during surgery. The atelectasis area was studied by computed tomography before emergence. Oxygenation levels were evaluated by measuring blood gases and calculating estimated venous admixture (EVA). RESULTS: The atelectasis areas expressed as percentages of the total lung area were 2.0 (1.5-2.7) (median [interquartile range]) and 1.8 (1.4-3.3) in the intervention and control groups, respectively. The difference was non-significant, and also oxygenation was similar between the two groups. Compared to oxygenation before the start of anaesthesia, oxygenation at the end of surgery was improved in the intervention group, mean (SD) EVA from 7.6% (6.6%) to 3.9% (2.9%) (P = .019) and preserved in the control group, mean (SD) EVA from 5.0% (5.3%) to 5.6% (7.1%) (P = .59). CONCLUSION: Although the oxygen washout restored a low pulmonary oxygen level within minutes, it did not further reduce atelectasis size. Both study groups had small atelectasis and good oxygenation. These results suggest that a moderate PEEP alone is sufficient to minimize atelectasis and maintain oxygenation in healthy patients.

Blood Lactate Is a Useful Indicator for the Medical Emergency Team.

Lactate has been thoroughly studied and found useful for stratification of patients with sepsis, in the Intensive Care Unit, and trauma care. However, little is known about lactate as a risk-stratification marker in the Medical Emergency Team- (MET-) call setting. We aimed to determine whether the arterial blood lactate level at the time of a MET-call is associated with increased 30-day mortality. This is an observational study on a prospectively gathered cohort at a regional secondary referral hospital. All MET-calls during the two-year study period were eligible. Beside blood lactate, age and vital signs were registered at the call. Among the 211 calls included, there were 64 deaths (30.3%). Median lactate concentration at the time of the MET-call was 1.82 mmol/L (IQR 1.16-2.7). We found differences between survivors and nonsurvivors for lactate and oxygen saturation, a trend for age, but no significant correlations between mortality and systolic blood pressure, respiratory rate, and heart rate. As compared to normal lactate (<2.44 mmol/L), OR for 30-day mortality was 3.54 (p < 0.0006) for lactate 2.44-5.0 mmol/L and 4.45 (p < 0.0016) for lactate > 5.0 mmol/L. The present results support that immediate measurement of blood lactate in MET call patients is a useful tool in the judgment of illness severity.

Seven Ventilators Challenged With Leaks During Neonatal Nasal CPAP: An Experimental Pilot Study.

BACKGROUND: Nasal CPAP is the most common respiratory support for neonates. Several factors are considered important for effective treatment, including leaks at the patient interface and the delivery of pressure-stable CPAP. Investigations of pressure stability during leaks should include both the change in the mean delivered CPAP and the pressure variation during each breath. The aim of this study was to examine the response of ventilators delivering nasal CPAP when challenged with leaks at the patient interface. METHODS: Seven ventilators providing nasal CPAP at 4 cm H2O were challenged with leaks during simulated neonatal breathing. Leak was applied for 15 consecutive breaths at a constant level (1-4 L/min). RESULTS: The 2 aspects of pressure stability were evaluated by measuring the mean delivered CPAP and the amplitude of pressure swings before, during, and after leaks. The ability to maintain the delivered CPAP and the amplitude of pressure swings varied greatly among the 7 ventilators before, during, and after leaks. Four of the ventilators tested have built-in leak compensation. CONCLUSIONS: There was no simple relationship between maintaining delivered CPAP during leaks and providing CPAP with low pressure swing amplitude. Maintaining the delivered CPAP and providing this without pressure swings are 2 separate aspects of pressure stability, and investigations concerning the clinical importance of pressure stability should address both aspects. This study also shows that compensation for leaks does not necessarily provide pressure-stable CPAP.

Prehospital analgesia using nasal administration of S-ketamine--a case series.

Pain is a problem that often has to be addressed in the prehospital setting. The delivery of analgesia may sometimes prove challenging due to problems establishing intravenous access or a harsh winter environment. To solve the problem of intravenous access, intranasal administration of drugs is used in some settings. In cases where vascular access was foreseen or proved hard to establish (one or two missed attempts) on the scene of the accident we use nasally administered S-Ketamine for prehospital analgesia. Here we describe the use of nasally administered S-Ketamine in 9 cases. The doses used were in the range of 0,45-1,25 mg/kg. 8 patients were treated in outdoor winter-conditions in Sweden. 1 patient was treated indoor. VAS-score decreased from a median of 10 (interquartile range 8-10) to 3 (interquartile range 2-4). Nasally administered S-Ketamine offers a possible last resource to be used in cases where establishing vascular access is difficult or impossible. Side-effects in these 9 cases were few and non serious. Nasally administered drugs offer a needleless approach that is advantageous for the patient as well as for health personnel in especially challenging selected cases. Nasal as opposed to intravenous analgesia may reduce the time spent on the scene of the accident and most likely reduces the need to expose the patient to the environment in especially challenging cases of prehospital analgesia. Nasal administration of S-ketamine is off label and as such we only use it as a last resource and propose that the effect and safety of the treatment should be further studied.

Comparison of nasal continuous positive airway pressure delivered by seven ventilators using simulated neonatal breathing.

OBJECTIVES: Nasal continuous positive airway pressure (NCPAP) is an established treatment for respiratory distress in neonates. Most modern ventilators are able to provide NCPAP. There have been no large studies examining the properties of NCPAP delivered by ventilators. The aim of this study was to compare pressure stability and imposed work of breathing (iWOB) for NCPAP delivered by ventilators using simulated neonatal breathing. DESIGN: Experimental in vitro study. SETTING: Research laboratory in Sweden. INTERVENTION: None. MEASUREMENTS AND MAIN RESULTS: Neonatal breathing was simulated using a mechanical lung simulator. Seven ventilators were tested at different CPAP levels using two breath profiles. Pressure stability and iWOB were determined. Results from three ventilators revealed that they provided a slight pressure support. For these ventilators, iWOB could not be calculated. There were large differences in pressure stability and iWOB between the tested ventilators. For simulations using the 3.4-kg breath profile, the pressure swings around the mean pressure were more than five times greater, and iWOB more than four times higher, for the system with the highest measured values compared with the system with the lowest. Overall, the Fabian ventilator was the most pressure stable system. Evita XL and SERVO-i were found more pressure stable than Fabian in some simulations. The results for iWOB were in accordance with pressure stability for systems that allowed determination of this variable. CONCLUSIONS: Some of the tested ventilators unexpectedly provided a minor degree of pressure support. In terms of pressure stability, we have not found any advantages of ventilators as a group compared with Bubble CPAP, Neopuff, and variable flow generators that were tested in our previous study. The variation between individual systems is great within both categories. The clinical importance of these findings needs further investigation.

Comparison of seven infant continuous positive airway pressure systems using simulated neonatal breathing.

OBJECTIVE: Continuous positive airway pressure is an established treatment for respiratory distress in neonates. Continuous positive airway pressure has been applied to infants using an array of devices. The aim of this experimental study was to investigate the characteristics of seven continuous positive airway pressure systems using simulated breath profiles from newborns. DESIGN: Experimental in vitro study. SETTING: Research laboratory in Sweden. INTERVENTION: None. MEASUREMENTS AND MAIN RESULTS: In vitro simulation of spontaneous neonatal breathing was achieved with a mechanical lung model. Simulation included two breath profiles, three levels of continuous positive airway pressure with and without short binasal prongs and different levels of constant leak. Pressure stability and imposed work of breathing were determined. Seven continuous positive airway pressure systems were tested. There were large differences in pressure stability and imposed work of breathing between tested continuous positive airway pressure systems. Neopuff and Medijet had the highest pressure instability and imposed work of breathing. Benveniste, Hamilton Universal (Arabella), and Bubble continuous positive airway pressure showed intermediate results. AirLife and Infant Flow had the lowest pressure instability and imposed work of breathing. AirLife and Infant Flow showed the least decrease in delivered pressure when challenged with constant leak. CONCLUSION: The seven tested continuous positive airway pressure systems showed large variations in pressure stability and imposed work of breathing. They also showed large differences in how well they maintain continuous positive airway pressure when exposed to leak. For most systems, imposed work of breathing increased with increasing continuous positive airway pressure level. The clinical importance of the difference in pressure stability is uncertain. Our results may facilitate the design of clinical studies examining the effect of pressure stability on outcome.

Local, regional, or general anaesthesia in groin hernia repair: multicentre randomised trial.

BACKGROUND: In specialised centres, local anaesthesia is almost always used in groin hernia surgery; whereas in routine surgical practice, regional or general anaesthesia are the methods of choice. In this three-arm multicentre randomised trial, we aimed to compare the three methods of anaesthesia and to determine the extent to which general surgeons can reproduce the excellent results obtained with local anaesthesia in specialised hernia centres. METHODS: Between January, 1999, and December, 2001, 616 patients at ten hospitals, were randomly assigned to have either local, regional, or general anaesthesia. Primary endpoints were early and late postoperative complications. Secondary endpoints were duration of surgery and anaesthesia, length of postoperative hospital stay, and time to normal activity. Analysis was by intention to treat. FINDINGS: Intraoperative tolerance for local anaesthesia was high. In the early postoperative period, local anaesthesia was superior to the other two types with respect to almost all endpoints. At 8 days' and 30 days' follow-up, there were no significant differences between the three groups. Although the mean duration of surgery was longer, the total anaesthesia time-ie, time from the start of anaesthesia until the patient left the operating room-was significantly shorter than it was for regional or general anaesthesia. INTERPRETATION: Local anaesthesia has substantial advantages compared with regional or general anaesthesia, such as shorter duration of admission, less postoperative pain, and fewer micturition difficulties. The favourable results obtained with local anaesthesia in specialised hernia centres can, to a great extent, be reproduced by general surgeons in routine surgical practice.