Preserved oxygenation in obese patients receiving protective ventilation during laparoscopic surgery: a randomized controlled study.

BACKGROUND: Venous admixture from atelectasis and airway closure impedes oxygenation during general anaesthesia. We tested the hypothesis that continuous positive airway pressure (CPAP) during pre-oxygenation and reduced fraction of inspiratory oxygen (FIO2 ) during emergence from anaesthesia can improve oxygenation in patients with obesity undergoing laparoscopic surgery. METHODS: In the intervention group (n = 20, median BMI 41.9), a CPAP of 10 cmH2 O was used during pre-oxygenation and induction of anaesthesia, but no CPAP was used in the control group (n = 20, median BMI 38.1). During anaesthesia, all patients were ventilated in volume-controlled mode with an FIO2 of 0.4 and a positive end-expiratory pressure (PEEP) of 10 cmH2 O. During emergence, before extubation, the control group was given an FIO2 of 1.0 and the intervention group was divided into two subgroups, which were given an FIO2 of 1.0 or 0.31. Oxygenation was assessed perioperatively by the estimated venous admixture (EVA). RESULTS: The median EVA before pre-oxygenation was about 8% in both groups. During anaesthesia after intubation, the median EVA was 8.2% in the intervention vs. 13.2% in the control group (P = 0.048). After CO2 pneumoperitoneum, the median EVA was 8.4% in the intervention vs. 9.9% in the control group (P > 0.05). One hour post-operatively, oxygenation had deteriorated in patients given an FIO2 of 1.0 during emergence but not in patients given an FIO2 of 0.31. CONCLUSIONS: A CPAP of 10 cmH2 O during pre-oxygenation and induction, followed by PEEP after intubation, seemed to preserve oxygenation during anaesthesia. Post-operative oxygenation depended on the FIO2 used during emergence.

Post-operative atelectasis - a randomised trial investigating a ventilatory strategy and low oxygen fraction during recovery.

BACKGROUND: Atelectasis is common during and after general anaesthesia. We hypothesized that a ventilation strategy with a combination of 1) continuous positive airway pressure (CPAP) or positive end-expiratory pressure (PEEP) and 2) a reduced end-expiratory oxygen concentration during recovery would reduce post-operative atelectasis. METHODS: Sixty patients were randomized into two groups. During anaesthesia induction, inspiratory oxygen fraction (FIO2) was 1.0, and depending on weight, CPAP 6, 7 or 8 cmH2O was applied in both groups via facemask. During maintenance of anaesthesia, a laryngeal mask airway (LMA) was used, and PEEP was 6-8 cmH2O in both groups. Before removal of the LMA, FIO2 was set to 0.3 in the intervention group and 1.0 in the control group. Atelectasis was studied by computed tomography (CT) approximately 14 min post-operatively. RESULTS: In one patient in the group given an FIO2 of 0.3 before removal of the LMA a CT scan could not be performed so the patient was excluded. The area of atelectasis was 5.5, 0-16.9 cm(2) (median and range), and 6.8, 0-27.5 cm(2) in the groups given FIO2 0.3 or FIO2 1.0 before removal of the LMA, a difference that was not statistically significant (P = 0.48). Post-hoc analysis showed dependence of atelectasis on smoking (despite all were clinically lung healthy) and American Society of Anesthesiologists class (P = 0.038 and 0.015, respectively). CONCLUSION: Inducing anaesthesia with CPAP/PEEP and FIO2 1.0 and deliberately reducing FIO2 during recovery before removal of the LMA did not reduce post-operative atelectasis compared with FIO2 1.0 before removal of the LMA.

Oxygen concentration and characteristics of progressive atelectasis formation during anaesthesia.

BACKGROUND: atelectasis is a common consequence of pre-oxygenation with 100% oxygen during induction of anaesthesia. Lowering the oxygen level during pre-oxygenation reduces atelectasis. Whether this effect is maintained during anaesthesia is unknown. METHODS: during and after pre-oxygenation and induction of anaesthesia with 60%, 80% or 100% oxygen concentration, followed by anaesthesia with mechanical ventilation with 40% oxygen in nitrogen and positive end-expiratory pressure of 3 cmH(2) O, we used repeated computed tomography (CT) to investigate the early (0-14 min) vs. the later time course (14-45 min) of atelectasis formation. RESULTS: in the early time course, atelectasis was studied awake, 4, 7 and 14 min after start of pre-oxygenation with 60%, 80% or 100% oxygen concentration. The differences in the area of atelectasis formation between awake and 7 min and between 7 and 14 min were significant, irrespective of oxygen concentration (P<0.05). During the late time course, studied after pre-oxygenation with 80% oxygen, the differences in the area of atelectasis formation between awake and 14 min, between 14 and 21 min, between 21 and 28 min and finally between 21 and 45 min were all significant (P<0.05). CONCLUSION: formation of atelectasis after pre-oxygenation and induction of anaesthesia is oxygen and time dependent. The benefit of using 80% oxygen during induction of anaesthesia in order to reduce atelectasis diminished gradually with time.

Ceasing routine use of nitrous oxide-a follow up.

BACKGROUND: The role of nitrous oxide in modern anaesthesia is questioned. The routine use of nitrous oxide was almost completely stopped in our department after November 1, 2000, and we now report some consequences. METHODS: Staff completed a questionnaire after 6 months, and we analysed the use of hypnotics and opioids after 12 months. The cost of drugs for the year after stopping nitrous oxide was compared with the cost 2 yr before. RESULTS: Less than half of the 55 staff members who answered the questionnaire used nitrous oxide in the 6 months after the stop, and they did so on only a few occasions. Half of the staff members thought the benefit of nitrous oxide was small. Most supported the change. The use of opioids was stable during the study period, and there was an annual increase of 12-14% in the use of hypnotics during the 3 yr. CONCLUSIONS: The staff questionnaire showed a strong acceptance of the new policy, and the use of other anaesthetic agents did not increase as expected. Has the value of nitrous oxide been overestimated?

Time to reconsider the pre-oxygenation during induction of anaesthesia.

Atelectasis is a frequent finding in paralysed and mechanically ventilated patients. Atelectasis, causing shunt, impairs oxygenation and could contribute to postoperative pulmonary complications. Pre-oxygenation used during anaesthesia induction causes atelectasis. A lowering of oxygen fraction from 100% to 80% does not shorten the safety time of apnoea period, particularly useful for a difficult intubation, but it reduces drastically the atelectasis incidence.

Low frequency of adenylate kinase release into cerebrospinal fluid during balanced, normotensive anaesthesia and a non-orthognathic surgical procedure.

Activity of strictly intracellular enzymes in the cerebrospinal fluid (CSF) may indicate leakage from dysfunctional brain cells. Increased activity of adenylate kinase (AK) in the CSF is indicative of brain cell injury arising from several sources, among them orthognathic surgery. The mechanism in the latter case is obscure, but the use of an oscillating saw which generates vibrations, and the site of surgery close to the brain may be contributing factors. Anaesthesia may also play a role. In the present study, CSF-AK activity was measured after hysterectomy and was compared with activity after orthognathic surgery in two other studies. Four of 19 patients (21%) in the present study expressed pathological activity, compared with 34 of 47 (72%) orthognathic patients in the two other studies. No firm conclusion may be drawn from historical comparisons, and the difference in activity seen between the two types of surgery might not necessarily be the result of surgical factors. Until this is investigated further, however, we conclude that there may be a difference in postoperative CSF-AK activity between orthognathic and lower abdominal surgery.