Reducing Atelectasis during General Anaesthesia – the Importance of Oxygen Concentration, End-Expiratory Pressure and Patient Factors : A Clinical Study Exploring the Prevention of Atelectasis in Adults

Background: The use of pure oxygen during preoxygenation and induction of general anaesthesia is a major cause of atelectasis. The interaction between reduced lung volume, resulting in airway closure, and varying inspiratory fractions of oxygen (FIO2) in determining the risk of developing atelectasis is still obscure. Methods: In this thesis, computed tomography (in studies I and II during anaesthesia, in studies III and IV postoperatively) was used to investigate the area of atelectasis in relation to FIO2 and varying levels of continuous positive airway pressure (CPAP) or positive end-expiratory pressure (PEEP). Study I investigated the short-term influence of reducing FIO2 during preoxygenation and induction of general anaesthesia, and the time to hypoxia during apnoea. Study II focused on the long-term effect of an FIO2 of 0.8 for preoxygenation. Study III applied CPAP/PEEP with an FIO2 of 1.0 or 0.8 for pre- and postoxygenation until extubation. After extubation, CPAP with an FIO2 of 0.3 was applied before the end of mask ventilation. Study IV compared two groups given CPAP/PEEP during anaesthesia and an FIO2 of 1.0 or 0.3 during postoxygenation, but without CPAP after extubation. Results: Study I showed a reduction in atelectasis with an FIO2 of 0.8 or 0.6, compared with 1.0, but the time to hypoxia decreased. In study II, atelectasis evolved gradually after preoxygenation. In study III, atelectasis was reduced with an FIO2 of 1.0 and CPAP/PEEP compared with an FIO2 of 1.0 without CPAP/PEEP. The intervention failed in the group given an FIO2 of 0.8, this group had more smokers. Atelectasis and age were correlated. In study IV, no difference was found between the groups. Post hoc analysis showed that smoking and ASA class increased the risk for atelectasis. Conclusion, the effect of reducing FIO2 during preoxygenation to prevent atelectasis might be short-lived. A lower FIO2 shortened the time to the appearance of hypoxia. Increasing lung volume by using CPAP/PEEP also decreased the risk of atelectasis, but the method might fail; for example in patients who are heavy smokers. In older patients care must be taken to reduce a high FIO2 before ending CPAP

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 cmH(2)O 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

Using trigger tools to identify triage errors by ambulance dispatch nurses in Sweden : an observational study

Objectives: This study aimed to assess whether trigger tools were useful identifying triage errors among patients referred to non-emergency care by emergency medical dispatch nurses, and to describe the characteristics of these patients. Design: An observational study of patients referred by dispatch nurses to non-emergency care. Setting: Dispatch centres in two Swedish regions. Participants: A total of 1089 adult patients directed to non-emergency care by dispatch nurses between October 2016 and February 2017. 53% were female and the median age was 61 years. Primary and secondary outcome measures: The primary outcome was a visit to an emergency department within 7 days of contact with the dispatch centre. Secondary outcomes were (1) visits related to the primary contact with the dispatch centre, (2) provision of care above the primary level (ie, interventions not available at a typical local primary care centre) and (3) admission to hospital in-patient care. Results: Of 1089 included patients, 260 (24%) visited an emergency department within 7 days. Of these, 209 (80%) were related to the dispatch centre contact, 143 (55%) received interventions above the primary care level and 99 (38%) were admitted to in-patient care. Elderly (65+) patients (OR 1.45, 95% CI 1.05 to 1.98) and patients referred onwards to other healthcare providers (OR 1.58, 95% CI 1.15 to 2.19) had higher likelihoods of visiting an emergency department. Six avoidable patient harms were identified, none of which were captured by existing incident reporting systems, and all of which would have received an ambulance if the decision support system had been strictly adhered to. Conclusion: The use of these patient outcomes in the framework of a Global Trigger Tool-based review can identify patient harms missed by incident reporting systems in the context of emergency medical dispatching. Increased compliance with the decision support system has the potential to improve patient safety

Oxygenation Impairment during Anesthesia: Influence of Age and Body Weight

WHAT WE ALREADY KNOW ABOUT THIS TOPIC: During anesthesia oxygenation is impaired, especially in the elderly or obese, but the mechanisms are uncertain. WHAT THIS ARTICLE TELLS US THAT IS NEW: Pooled data were examined from 80 patients studied with multiple inert gas elimination technique and computed tomography. Oxygenation was impaired by anesthesia, more so with greater age or body mass index. The key contributors were low ventilation/perfusion ratio (likely airway closure) in the elderly and shunt (atelectasis) in the obese. BACKGROUND: Anesthesia is increasingly common in elderly and overweight patients and prompted the current study to explore mechanisms of age- and weight-dependent worsening of arterial oxygen tension (PaO2). METHODS: This is a primary analysis of pooled data in patients with (1) American Society of Anesthesiologists (ASA) classification of 1; (2) normal forced vital capacity; (3) preoxygenation with an inspired oxygen fraction (FIO2) more than 0.8 and ventilated with FIO2 0.3 to 0.4; (4) measurements done during anesthesia before surgery. Eighty patients (21 women and 59 men, aged 19 to 69 yr, body mass index up to 30 kg/m) were studied with multiple inert gas elimination technique to assess shunt and perfusion of poorly ventilated regions (low ventilation/perfusion ratio [VA/Q]) and computed tomography to assess atelectasis. RESULTS: PaO2/FIO2 was lower during anesthesia than awake (368; 291 to 470 [median; quartiles] vs. 441; 397 to 462 mm Hg; P = 0.003) and fell with increasing age and body mass index. Log shunt was best related to a quadratic function of age with largest shunt at 45 yr (r =0.17, P = 0.001). Log shunt was linearly related to body mass index (r = 0.15, P < 0.001). A multiple regression analysis including age, age, and body mass index strengthened the association further (r = 0.27). Shunt was highly associated to atelectasis (r = 0.58, P < 0.001). Log low VA/Q showed a linear relation to age (r = 0.14, P = 0.001). CONCLUSIONS: PaO2/FIO2 ratio was impaired during anesthesia, and the impairment increased with age and body mass index. Shunt was related to atelectasis and was a more important cause of oxygenation impairment in middle-aged patients, whereas low VA/Q, likely caused by airway closure, was more important in elderly patients. Shunt but not low VA/Q increased with increasing body mass index. Thus, increasing age and body mass index impaired gas exchange by different mechanisms during anesthesia

Positive end-expiratory pressure during induction of general anesthesia increases duration of nonhypoxic apnea in morbidly obese patients.

Positive end-expiratory pressure (PEEP) applied during induction of anesthesia prevents atelectasis formation and increases the duration of nonhypoxic apnea in nonobese patients. PEEP also prevents atelectasis formation in morbidly obese patients. Because morbidly obese patients have difficult airway management more often and because arterial desaturation develops rapidly, we studied the clinical benefit of PEEP applied during anesthesia induction. Thirty morbidly obese patients were randomly allocated to one of two groups. In the PEEP group, patients breathed 100% O(2) through a continuous positive airway pressure device (10 cm H(2)O) for 5 min. After induction of anesthesia, they were mechanically ventilated with PEEP (10 cm H(2)O) for another 5 min until tracheal intubation. In the control group, the sequence was the same but without any continuous positive airway pressure or PEEP. We measured apnea duration until Spo(2) reached 90% and we performed arterial blood gases analyses just before apnea and at 92% Spo(2). Nonhypoxic apnea duration was longer in the PEEP group compared with the control group (188 +/- 46 versus 127 +/- 43 s; P = 0.002). Pao(2) was higher before apnea in the PEEP group (P = 0.038). Application of positive airway pressure during induction of general anesthesia in morbidly obese patients increases nonhypoxic apnea duration by 50%

Prevention of atelectasis formation during the induction of general anesthesia in morbidly obese patients

Atelectasis caused by general anesthesia is increased in morbidly obese patients. We have shown that application of positive end-expiratory pressure (PEEP) during the induction of anesthesia prevents atelectasis formation in nonobese patients. We therefore studied the efficacy of PEEP in morbidly obese patients to prevent atelectasis. Twenty-three adult morbidly obese patients (body mass index >35 kg/m(2)) were randomly assigned to one of two groups. In the PEEP group, patients breathed 100% oxygen (5 min) with a continuous positive airway pressure of 10 cm H(2)O and, after the induction, mechanical ventilation via a face mask with a PEEP of 10 cm H(2)O. In the control group, the same induction was applied but without continuous positive airway pressure or PEEP. Atelectasis, determined by computed tomography, and blood gas analysis were measured twice: before the induction and directly after intubation. After endotracheal intubation, patients of the control group showed an increase in the amount of atelectasis, which was much larger than in the PEEP group (10.4% +/- 4.8% in control group versus 1.7% +/- 1.3% in PEEP group; P < 0.001). After intubation with a fraction of inspired oxygen of 1.0, PaO(2) was significantly higher in the PEEP group compared with the control group (457 +/- 130 mm Hg versus 315 +/- 100 mm Hg, respectively; P = 0.035) We conclude that in morbidly obese patients, atelectasis formation is largely prevented by PEEP applied during the anesthetic induction and is associated with a better oxygenation. IMPLICATIONS: Application of positive end-expiratory pressure during induction of general anesthesia in morbidly obese patients prevents atelectasis formation and improves oxygenation. Therefore, this technique should be considered for anesthesia induction in morbidly obese patients