The effect of increased FIO(2) before tracheal extubation on postoperative atelectasis

[Emergency treatment of thoracic trauma]

Thoracic trauma, most often associated with other serious injuries, is the main cause of death in the first 45 years of life. The percentage of chest injuries in multiple trauma, mainly from blunt impact, has remained relatively constant at 80% during the last 30 years. Isolated thoracic injuries comprise only 25% of all trauma cases, 90% of chest injuries are due to blunt impact, while penetrating injuries make up 5-10%. Since 25% of deaths from trauma are attributable to chest injuries, they determine the survival rate in multiple trauma to a significant extent. The pattern of chest injuries is variable, frequently in different combinations comprising rib cage and diaphragm, lung parenchyma, airway and mediastinal organs. This article details the immediate simultaneous diagnostic and therapeutic procedures in the prehospital phase, management in the emergency room, the relative importance of computed tomography, ultrasound examination and endoscopy in the primary diagnostic evaluation and the principles of anaesthetic management of thoracic trauma.

Influence of intraoperative opioid on postoperative pain and pulmonary function after laparoscopic gastric banding: remifentanil TCI vs sufentanil TCI in morbid obesity

BACKGROUND

Choice of opioid may influence postoperative pain, recovery, and respiratory homeostasis in morbid obesity. The aim of this study was to compare the effects of target-controlled infusions (TCIs) of remifentanil or sufentanil on postoperative analgesia, recovery, and pulmonary function after laparoscopic gastric banding.

METHODS

Forty morbidly obese patients undergoing laparoscopic gastric banding received BIS-guided desflurane anaesthesia combined with remifentanil TCI (Group R) or sufentanil TCI (Group S). Intraoperative haemodynamic stability, BIS controllability, and immediate recovery in the operating room were measured. Pulmonary function, modified Aldrete score, modified Observers Assessment of Alertness and Sedation score, blood gas analysis, and visual analogue score for pain and postoperative nausea and vomiting were measured on admission to the post-anaesthesia care unit and 30, 60, 120 min afterwards. After operation, patients received patient-controlled analgesia with morphine.

RESULTS

During the first two postoperative hours, cumulative morphine consumption was higher in the remifentanil group compared with the sufentanil group, but was equal values after that time. Recovery profiles and spirometry showed no significant differences. During maintenance, remifentanil gave a better haemodynamic stability.

CONCLUSIONS

As few differences occurred in the postoperative period, the theoretical advantage of remifentanil over the longer acting sufentanil can be questioned when using TCI technology.

The carrier gas in anaesthesia: nitrous oxide/oxygen, medical air/oxygen and pure oxygen

PURPOSE OF REVIEW

The gas passing the module for the delivery of inhalation anaesthetics and carrying vapourized anaesthetics into the breathing system is called the carrier gas. Oxygen is the absolutely indispensable component of the carrier gas. Additive gaseous components can be medical air (nitrogen), nitrous oxide, cyclopropane, or xenon, the latter three being anaesthetic gases themselves. Cyclopropane is not used any more and xenon is not approved as a medical gas yet, leaving medical air and nitrous oxide as the only currently available adjuncts to oxygen.

RECENT FINDINGS

As review articles on nitrous oxide recommend unequivocally not using this gas routinely, and many anaesthetists already consistently omit any use of this gas, the alternative carrier gases are either a mixture of medical air and oxygen or pure oxygen. A nitrogen/oxygen mixture is absolutely inert with respect to metabolism or environment; there are no contraindications or shortcomings at all. The use of pure oxygen will result in high oxygen concentrations, improving the patients' safety by increasing the pulmonary oxygen reservoir and rendering impossible the development of hypoxic gas mixtures within the breathing system. Whether the incidence of postoperative wound infections or postoperative nausea and vomiting is reduced by perioperative hyperoxia is still under scientific discussion. In general, the use of high oxygen concentrations over a period of 6-8 h is not harmful for the patient, assuming the performance of recruitment manoeuvres, consistent use of positive end-expiratory pressure, and thorough observance of the contraindications that can result from the increased vulnerability of tissues to hyperoxia.

SUMMARY

Nitrous oxide should not be used routinely as a component of the carrier gas any more. A mixture of medical air and oxygen must be acknowledged to be the gold standard. Pure oxygen may be used as a carrier gas if medical air or properly performing flow controls for medical air are not available.

[Right-to-left shunt determination in dog lungs under inhalation anesthesia with rebreathing and non-rebreathing system]

PURPOSE

To investigatge right-to-left shunt determination in dog lungs under inhalantion anesthesia with non-rebreathing and rebreathing systems and fraction of inspired oxygen (F I O2) of 0.9 and 0.4, respectively.

METHODS

Two groups of 10 dogs each under inhalation anesthesia with sevoflurane: GI in which it was utilized non-rebreathing semiclosed system and F I O2 = 0.9, and GII in which it was utilized rebreathing semiclosed system and F I O2 = 0.4. The study parameters were: heart rate, medium arterial pressure, right-to-left intrapulmonary shunt, hematocrit, hemoglobin, arterial partial pressure of oxygen, mixed venous partial pressure of oxygen, mixed venous oxygen saturation, arterial partial pressure of carbon dioxide, partial pressure of water in the alveoli.

RESULTS

Shunt results were significantly different between the two groups - GI data were higher than GII in all the evaluated moments. Hence, the group with nonrebreathing (GI) developed a superior grade of intrapulmonary shunt when compared with the rebreathing group (GII). The partial pressure of water in the alveoli was significantly higher in GII.

CONCLUSION

The inhalation anesthesia with non-rebreathing system and F I O2 = 0.9 developed a higher grade of intrapulmonary right-to-left shunt when compared with the rebreathing system and F I O2 = 0.4. The higher humidity in GII contributed to the result.

Respiratory transition in infants delivered by cesarean section

One of the biggest challenges a newborn faces after birth is the task of making a smooth transition to air breathing. This task is complicated by the fact that fetal lungs are full of fluid which must be cleared rapidly to allow for gas exchange. Respiratory morbidity as a result of failure to clear fetal lung fluid is not uncommon, and can be particularly problematic in some infants delivered by elective cesarean delivery (ECS). Given the high rates of cesarean deliveries in the USA and worldwide, the public health and economic impact of morbidity in this subgroup is considerable. Whereas the occurrence of birth asphyxia, trauma, and meconium aspiration is reduced by elective Cesarean delivery, the risk of respiratory distress secondary to transient tachypnea of the newborn, surfactant deficiency, and pulmonary hypertension is increased. It is clear that physiologic events in the last few weeks of pregnancy coupled with the onset of spontaneous labor are accompanied by changes in the hormonal milieu of the fetus and its mother, resulting in preparation of the fetus for neonatal transition. Rapid clearance of fetal lung fluid is a key part of these changes, and is mediated in large part by transepithelial Na reabsorption through amiloride-sensitive Na channels in the alveolar epithelial cells, with only a limited contribution from mechanical factors and Starling forces. This chapter discusses the physiologic mechanisms underlying fetal lung fluid absorption and explores potential strategies for facilitating neonatal transition when infants are delivered by ECS before the onset of spontaneous labor.

Effect of Lung Ventilation With 50% Oxygen in Air or Nitrous Oxide Versus 100% Oxygen on Oxygenation Index After Cardiopulmonary Bypass

OBJECTIVE

This study was designed to assess the use of 100% oxygen or 50% oxygen in air or nitrous oxide after cardiopulmonary bypass (CPB) on atelectasis, as evidenced by the oxygenation index (PaO2/F(I)O2), after coronary artery bypass graft (CABG) surgery.

DESIGN

Prospective, randomized clinical study.

SETTING

University teaching hospital.

PARTICIPANT

Thirty-six adult patients undergoing CABG surgery.

INTERVENTIONS

Patients either received 50% O2 in air (50% O2 group), 50% O2 in N2O (50% N2O group), or 100% O2 (100% O2 group) after CPB.

MEASUREMENTS AND MAIN RESULTS

Apart from demographic and perioperative clinical data, extubation time, mediastinal drainage, and pulmonary complications were also recorded. After CPB, arterial blood gases done at various time points until 3 hours postextubation and oxygenation index were calculated. No significant differences were noted in demographic and perioperative data except preoperative hemoglobin and fluid use. Significant deterioration in arterial oxygenation was noted in the 100% O2 group from the baseline value, whereas significant improvement was seen in the 50% O2 group at 4 time points from baseline value and at all time points from the 100% O2 group. After initial deterioration in oxygenation, no further change was evident in the 50% N2O group. Furthermore, there was a greater increase in the oxygenation index as compared with the 100% O2 group. Time to extubation was also longer in the 100% O2 group than the 50% O2 group.

CONCLUSION

Significant deterioration in arterial oxygenation and an increase in the extubation time occurred with the use of 100% O2 after CPB, whereas better oxygenation was evident with the use of 50% O2 in air.

High inspired oxygen concentrations increase intrapulmonary shunt in anaesthetized horses

OBJECTIVES

To compare pulmonary function and gas exchange in anaesthetized horses during and after breathing either O2-rich gas mixtures or air.

ANIMALS

Six healthy standard bred trotters (age range 3-12 years; mass range 423-520 kg), four geldings and two mares. Study design Randomized, cross-over experimental study.

METHODS

Horses were anaesthetized on two occasions with tiletamine-zolazepam after pre-anaesthetic medication with acepromazine, romifidine and butorphanol. After endotracheal intubation and positioning in left lateral recumbency, animals were allowed to breathe spontaneously. One of two, randomly allocated inspired gas treatments was provided: either i) room air (fractional concentration of inspired O2 [FIO2] = 0.21) provided throughout anaesthesia; or ii) an O2-rich gas mixture (FIO2 = >0.95) for 15 minutes, followed by room air. The alternative treatment was delivered at the second anaesthetic. Respiratory and haemodynamic variables and the distribution of ventilation-perfusion (VA/Q) ratios (using the multiple inert gas elimination technique) were determined in the standing conscious horse (baseline) after sedation and during anaesthesia.

RESULTS

Breathing O2-rich gas was associated with a decreased respiratory rate (p = 0.015) increased PaCO2 (p < 0.001) and increased PaO2 (p = 0.004) compared with breathing air. All horses developed intrapulmonary shunt during anaesthesia, but shunt was significantly greater (13 +/- 5%) when O2-rich gas was delivered compared with air breathing (5 +/- 2%; p = 0.013). Ten minutes after O2-rich gas was replaced by air, shunt remained larger in horses that had initially received oxygen compared with those breathing air (p = 0.042). Mixed venous oxygen tensions were significantly lower during sedation than at baseline (p < 0.001) and during anaesthesia (p < 0.001).

CONCLUSIONS

During dissociative anaesthesia, arterial oxygenation was greater when horses breathed gas containing more than 95% oxygen, compared with when they breathed air. However, breathing O2-rich gas increased intrapulmonary shunt and caused hypoventilation. The intrapulmonary shunt created during anaesthesia by high inspired O2 concentrations remained larger when FIO2 was reduced to 0.21, indicating that absorption atelectasis produced during O2-rich gas breathing persisted throughout anaesthesia.

CLINICAL RELEVANCE

In healthy horses undergoing short-term dissociative anaesthesia, air breathing ensures a level of oxygen delivery that meets tissue demand. There is no benefit to horses in breathing O2-rich gas after the gas supply is discontinued. On the contrary, the degree of shunt induced by breathing O2-rich gas persists. The clinical relevance of this during recovery requires investigation.

Both lung recruitment maneuver and PEEP are needed to increase oxygenation and lung volume after cardiac surgery

BACKGROUND

Patients ventilated after cardiac surgery commonly have impaired oxygenation, mainly due to lung collapse. We have previously found that PaO2 and end-expiratory lung volume (EELV) were increased by a lung recruitment maneuver (LRM) followed by positive end-expiratory pressure (PEEP). The aim of this study was to evaluate whether only PEEP or only a LRM could give similar effects.

METHODS

Thirty circulatory stable patients (aged 55-79 years) mechanically ventilated after cardiac surgery were randomized to receive LRM (four 10-s insufflations to an airway pressure of 45 cmH2O) and zero end-expiratory pressure (LRM-group), PEEP 12 cmH2O (PEEP-group) or LRM in combination with PEEP 12 cmH2O (LRM + PEEP-group). The set end-expiratory pressure was kept for 75 min. Before, during and after the intervention, EELV (SF6 washout technique) and blood gases were measured.

RESULTS

Initial EELV and PaO2 were similar in all groups. In the LRM-group, PaO2 and EELV increased transiently (P < 0.0001), but returned at 5 min to the initial values. In the PEEP-group, PaO2 did not change but EELV increased to 155 +/- 27% of the initial value (P < 0.0001). In the LRM+PEEP-group, PaO2 and EELV increased to 212 +/- 66% and 178 +/- 31% of the initial values (P < 0.0001), respectively, and were maintained during PEEP application.

CONCLUSION

In patients ventilated after cardiac surgery: (1) PEEP increased lung volume but not PaO2, (2) a lung recruitment maneuver without subsequent PEEP had no sustained effect, and (3) both a lung recruitment maneuver and PEEP were needed to increase and maintain the increased lung volume and PaO2.

Administration of 100% Oxygen Before Removal of the Laryngeal Mask Airway Does Not Affect Postanesthetic Arterial Partial Pressure of Oxygen

Breathing 100% oxygen at the end of general anesthesia has been shown to worsen postoperative pulmonary gas exchange when an endotracheal tube is used. Counter measures, such as high positive end-expiratory pressure or the vital-capacity maneuver, may limit this effect. Such strategies, however, may be impracticable, or even contraindicated, when the laryngeal mask airway (LMA) is used. Because of the vast differences in design between the LMA and endotracheal tube, we examined postanesthetic blood gas tensions in patients after emergence from anesthesia breathing oxygen via LMA. Sixty-four ASA physical status I-II patients undergoing general anesthesia for 60 min with LMA were randomly assigned to receive either 100% or 30% oxygen during emergence from anesthesia and removal of LMA. Postoperative blood gas measurements were taken at 30 and 60 min after removal of the LMA. At either measurement, patients treated with 100% oxygen essentially had the same arterial partial pressure of oxygen (60-min measurement: 83 +/- 8 versus 85 +/- 7 mm Hg [mean +/- SD], P = 0.14) as those treated with 30% oxygen. We conclude that breathing 100% oxygen at the end of general anesthesia does not worsen postoperative pulmonary gas exchange when an LMA is used.

IMPLICATIONS

The endotracheal tube and laryngeal mask airway are substantially different artificial airways used to ventilate the lungs of anesthetized patients. Breathing 100% oxygen before removing the endotracheal tube results in lung function defects. This study shows that oxygen breathing before removing the laryngeal mask airway has no effect on pulmonary function.