Effect of high-frequency jet ventilation on oxygenation during one-lung ventilation in patients undergoing thoracic aneurysm surgery

Purpose To evaluate the effect of high-frequency jet ventilation (HFJV) and continuous positive airway pressure (CPAP) on oxygenation and the shunt fraction (Qs/Qt) during one-lung ventilation (OLV). Methods Twenty-five patients who were undergoing resection of a descending aortic aneurysm were studied. Arterial oxygenation, Qs/Qt, and hemodynamics were evaluated just before the initiation of OLV (T₁), 15 min after OLV (T₂), and 15 min (T₃) and 30 min (T₄) after the application of HFJV or CPAP to the nondependent lung. Results There were no significant changes in the mean arterial blood pressure (MAP), heart rate (HR), central venous pressure (CVP), or mixed venous partial pressure of oxygen throughout this study. The arterial partial pressure of oxygen (Pa_O2) values after the application of HFJV or CPAP increased significantly, from 173.8 ± 39.6 mmHg (T₂) to 344.1 ± 87.9 mmHg (T₃) and 359.9 ± 82.4 mmHg (T₄) in the HFJV group (P < 0.05), and from 153 ± 38.5 mmHg (T₂) to 243 ± 48.5 mmHg (T₃) and 249.7 ± 55.0 mmHg (T₄) in the CPAP group (P < 0.05). The shunt fraction decreased significantly after the initiation of HFJV or CPAP, from 38.7% ± 8.9% (T₂) to 27.0% ± 8.0% (T₃) and 25.9% ± 8.7% (T₄) in the HFJV group (P < 0.05), and from 44.6% ± 8.6% (T₂) to 34.3% ± 10.2% (T₃) and 32.6% ± 8.5% (T₄) in the CPAP group (P < 0.05). The arterial saturation of oxygen (Sa_O2) increased significantly after the application of either HFJV or CPAP (P < 0.05). Conclusions Both HFJV and CPAP can improve oxygenation during OLV.     

Improvement of arterial oxygenation by selective infusion of prostaglandin E1 to ventilated lung during one-lung ventilation

Background:One-lung anesthesia provides a better surgical field for thoracic procedures but also impairs the arterial oxygenation and venous admixture. During one-lung ventilation, pulmonary vasoconstriction is assumed to be present within both ventilated and collapsed lungs. We propose that arterial oxygenation could be optimized by offsetting the vasoconstriction within the microcirculation of ventilated lung. Method:In an anesthetized dog model, incremental doses of prostaglandin E₁ (PGE₁) were selectively infused into the main trunk of the pulmonary artery of the ventilated lung after one-lung ventilation for 60 min (PGE₁ group, n=9). Arterial oxygenation and calculated venous admixture (Qs/Qt) was also assessed in a time-course control group (Control group, n =5). During two-lung ventilation (FIO₂: 0.66), arterial PO₂ and venous admixture was 44.22 ± 3.5 kPa and 10.7±2.3%, respectively. One-lung ventilation (FIO₂: 0.66) with left lung collapsed reduced arterial PO₂ to 11.6±1.7 kPa and increased venous admixture to 40.7±5.8% (P<0.001). Venous O₂ tension also decreased from 6.3±0.7 kPa to 5.0±0.6 kPa with a slight increase in mean pulmonary artery pressure and pulmonary vascular resistance (P <0.05). Results: During selective infusion of PGE₁ at a dose of 0.04 to 0.2 μg kg^-1 min^-1, there was a dose-dependent improvement in arterial PO₂ with a parallel reduction of venous admixture during one-lung ventilation. Arterial PO₂ increased to a maximum of 23.0±4.3 kPa, and the venous admixture decreased significantly to a minimum of 27.4±4.2% by PGE₁ at a dose of 0.04-0.4 μg kg^-1 min^-1 (P<0.01). PGE₁ resulted in a small increase in cardiac output and decreases of pulmonary pressure and pulmonary vascular resistance at a relatively high dose of 0.4 μg kg^-1 min^-1 during selective infusion (P<0.05). Conclusion: These results suggest that a selective pulmonary artery infusion of PGE₁ to the ventilated lung within the dose range of 0.04-0.4 μg kg^-1 min^-1 is practical and effective to improve arterial oxygenation and reduce venous admixture during one-lung ventilation.     

Effect of Boussignac continuous positive airway pressure ventilation on Pao2 and Pao2/Fio2 ratio immediately after extubation in morbidly obese patients undergoing bariatric surgery: a randomized controlled trial

Study ObjectivePathophysiological changes after laparoscopic Roux-en-Y gastric bypass may increase the risk of pulmonary complications in morbidly obese patients. The purpose of the study was to assess the impact of immediate postextubation use of Boussignac continuous positive airway pressure (CPAP) on arterial oxygenation in morbidly obese patients undergoing laparoscopic Roux-en-Y gastric bypass. The hypothesis is that the use of CPAP may improve oxygenation in the postoperative period when compared to Venturi mask.DesignRandomized controlled study.SettingA tertiary referral hospital.PatientsRecruited morbidly obese adult patients undergoing laparoscopic Roux-en-Y gastric bypass.InterventionsBoussignac CPAP or Venturi mask was randomly applied immediately after extubation in the operating room and was maintained during the first 2 hours in the recovery room.MeasurementsPao₂ and Pao₂/fraction of inspired oxygen (Fio₂) ratio values were measured preoperatively and at 1 (T1), 2 (T2), and 24 hours (T24) after extubation, through arterial blood samples. Secondary outcomes (spirometric parameters) were measured at the same periods. For comparison between groups, Student t test, Mann-Whitney U nonparametric test, and χ² test were used. Statistical significance is at P < .05.Main ResultsTwenty-four patients were included, 12 in each group. There were no differences in preoperative evaluation. There were significant differences between groups in Pao₂ and Pao₂/Fio₂ mean values at T1, T2, and T24, being superior in the Boussignac group. During the 24 hours postextubation, 9% of patients in the Boussignac group and 50% in the Venturi group had a Pao₂ less than 60 mm Hg in at least 1 of the evaluations. After extubation, a Pao₂/Fio₂ ratio value less than 300 was observed in all patients in the Venturi group and in 55% in Boussignac group in at least 1 of the evaluations. There were no differences in spirometric parameters between groups at T1, T2, and T24.ConclusionsApplication of Boussignac CPAP for 2 hours after extubation improved oxygenation but did not improve forced expiratory volume at 1 second and forced vital capacity.     

Effects of hypothermia in hypercapnia and hypercapnic hypoxemia

Anesthetized, paralyzed and mechanically ventilated pigs were hypoventilated to extrene hypercapnia (Paco₂?20 kPa) at Fio₂ 0.5, and allotted to a hypothermic group (31.5 ±0.l°C, n = 6) or a control group (39.6±0.2°C, n = 6). Compared with the controls, the hypothermic animals had higher Pao₂ (19.2 vs 15.6 kPa, P>0.05), Sao₂ (97.2 vs 89.3%), Sv?o₂ (78.7 vs 68.2%), end-tidal 0₂ (34.5 vs 24.8 kPa) and arterial pH (7.01 vs 6.91), (P>0.01), but lower Pv?o₂ (7.0 vs. 10.2 kPa) and Paco₂ (13.2 vs 23.5 kPa), (P>0.01). Hypothermia reduced O₂ delivery (Do₂), O₂ consumption (Vo₂) and CO₂ production by 40–45% (P> 0.05), but O₂ extraction ratio, i.e. VO₂, Do₂-¹. 100 (%), did not differ between groups. Hypothermic animals had lower heart rate (127 vs 223 beats.min-¹, P>0.05) and cardiac output (2.5 vs 3.9 l.min-¹, P>0.01). Subsequently, the inspired oxygen fraction (Fio₂) was decreased stepwise (0.3, 0.25, 0.21, 0.15, 0.10) at 30- min intervals. At Fio₂ 0.3, the hypothermic group had higher Pao₂ (10.0 vs 5.7 kPa), Sao₂ (91.3 vs 28.5%), Pv?o, (5.8 vs 3.4 kPa), Sv?o₂ (70.7 vs 10.3%), end-tidal O₂ (16.7 vs 8.5 kPa), O₂ delivery (344 vs 155 ml.min-¹), arterial pH (7.02 vs 6.94) and systemic vascular resistance (3850 vs 1652 dyn.s. cm-⁵(38500 vs 16520 μN. s. c m-⁵)) compared with the controls (P>0.01), while Paco₂ was lower (12.4 vs 22.7 kPa), as well as O₂ extraction ratio (23 vs 63%) and O₂ half saturation tension (4.3 vs 8.0 kPa) (P>0.01). Except for Pao₂, all differences between groups remained significant at Fio₂ 0.25. The control animals died during Fio₂ 0.25 and 0.21, while all hypothermic animals remained circulatorily stable. One hypothermic animal died after 12 min at Fio₂ 0.15 and the remainder after 6–39 min (mean 22 min) at Fio₂ 0.10. We conclude that hypothermia markedly improves whole-body oxygen balance, cardiovascular stability and survival in hypercapnic hypoxemia.     

Unilateral high-frequency jet ventilation during one-lung ventilation for thoracotomy

One-lung ventilation is indicated during thoracic operations for bronchopleural fistula, pulmonary abscess, and pulmonary hemorrhage in spite of the possibility of the development of severe hypoxemia. To evaluate methods for improving oxygen transport during one-lung ventilation, we applied high-frequency jet ventilation (HFJV) and continuous positive airway pressure (CPAP) to the nondependent lung following deflation to atmospheric pressure in each procedure, and measured the effects on cardiac output and arterial oxygenation. In each case, the dependent lung was ventilated with conventional intermittent positive pressure ventilation (IPPV).

Eight patients were studied during posterolateral thoracotomy using double-lumen endobronchial tubes. HFJV or CPAP to the nondependent lung improved arterial oxygenation significantly during both closed and open stages of the surgical procedures (p < 0.008). When the chest was open, HFJV maintained satisfactory cardiac output, whereas CPAP usually decreased cardiac output (p < 0.008). There were no significant differences in mean partial pressure of arterial carbon dioxide between HFJV, CPAP, and deflation to atmospheric pressure.

In conclusion, HFJV to the nondependent lung provides not only satisfactory oxygenation but also good cardiac output, thereby maintaining better oxygen transport than CPAP or deflation to atmospheric pressure, while the dependent lung is ventilated with IPPV during one-lung ventilation for thoracotomy.     

Effect of high-frequency jet ventilation on heart rate variability

We investigated the effects of high-frequency jet ventilation (HFJV) on heart rate variability in nine patients during fentanyl (10μg·kg⁻¹) anesthesia using power spectral density analysis. ECG and arterial pressure were recorded during intermittent positive pressure ventilation (IPPV) (tidal volume 8 ml·kg⁻¹, respiratory rate 0.25 Hz) and during HFJV [5 Hz, 2.5 kg·(cm²)⁻¹]. The R-R interval time series obtained were analyzed by the autoregressive method, and low-frequency (LF) (0.05–0.15 Hz) power and high-frequency (HF) (0.20–0.50 Hz) power from R-R interval spectra were used for statistical comparison. LF power did not change during IPPV and HFJV (108.8±41.6 ms² vs 105.8±22.4 ms², mean±SE). HF power was detected during IPPV (65.1±14.3 ms²); however, it was not detected during HFJV. Plasma levels of norepinephrine and epinephrine were significantly higher during HFJV than during IPPV. The mean R-R interval, arterial pressure, and arterial blood gas data did not differ between IPPV and HFJV. These data indicate that, during fentanyl anesthesia, HFJV influences mainly the respiratory frequency fluctuation of heart rate variability, and they suggest that alteration of breathing patterns caused by HFJV might be involved, as well as elevated sympathetic neural outflow to the heart.     

Unilateral high-frequency jet ventilation during one-lung ventilation for thoracotomy

One-lung ventilation is indicated during thoracic operations for bronchopleural fistula, pulmonary abscess, and pulmonary hemorrhage in spite of the possibility of the development of severe hypoxemia. To evaluate methods for improving oxygen transport during one-lung ventilation, we applied high-frequency jet ventilation (HFJV) and continuous positive airway pressure (CPAP) to the nondependent lung following deflation to atmospheric pressure in each procedure, and measured the effects on cardiac output and arterial oxygenation. In each case, the dependent lung was ventilated with conventional intermittent positive pressure ventilation (IPPV). Eight patients were studied during posterolateral thoracotomy using double-lumen endobronchial tubes. HFJV or CPAP to the nondependent lung improved arterial oxygenation significantly during both closed and open stages of the surgical procedures (p less than 0.008). When the chest was open, HFJV maintained satisfactory cardiac output, whereas CPAP usually decreased cardiac output (p less than 0.008). There were no significant differences in mean partial pressure of arterial carbon dioxide between HFJV, CPAP, and deflation to atmospheric pressure. In conclusion, HFJV to the nondependent lung provides not only satisfactory oxygenation but also good cardiac output, thereby maintaining better oxygen transport than CPAP or deflation to atmospheric pressure, while the dependent lung is ventilated with IPPV during one-lung ventilation for thoracotomy.     

Protective ventilation to reduce inflammatory injury from one lung ventilation in a piglet model

Objectives: To test the hypothesis that protective ventilation strategy (PVS) as defined by the use of low stretch ventilation (tidal volume of 5 ml·kg^?1 and employing 5 cm of positive end expiratory pressure (PEEP) during one lung ventilation (OLV) in piglets would result in reduced injury compared to a control group of piglets who received the conventional ventilation (tidal volume of 10 ml·kg^?1 and no PEEP). Background: PVS has been found to be beneficial in adults to minimize injury from OLV. We designed the current study to test the beneficial effects of PVS in a piglet model of OLV. Methods: Ten piglets each were assigned to either ‘Control’ group (tidal volume of 10 ml·kg^?1 and no PEEP) or ‘PVS’ group (tidal volume of 5 ml·kg^?1 during the OLV phase and PEEP of 5 cm of H₂O throughout the study). Experiment consisted of 30 min of baseline ventilation, 3 h of OLV, and again 30 min of bilateral ventilation. Respiratory parameters and proinflammatory markers were measured as outcome. Results: There was no difference in PaO₂ between groups. PaCO₂ (P < 0.01) and ventilatory rate (P < 0.01) were higher at 1.5 h OLV and at the end point in the PVS group. Peak inflating pressure (PIP) and pulmonary resistance were higher (P < 0.05) in the control group at 1.5 h OLV. tumor necrosis factor‐alpha (P < 0.04) and IL‐8 were less (P < 0.001) in the plasma from the PVS group, while IL‐6 and IL‐8 were less (P < 0.04) in the lung tissue from ventilated lungs in the PVS group. Conclusions: Based on this model, PVS decreases inflammatory injury both systemically and in the lung tissue with no adverse effect on oxygenation, ventilation, or lung function.     

Continuous Flow Apneic Ventilation

A study was designed to evaluate the adequacy of gas exchange during continuous flow apneic ventilation (CFAV) in dogs. Seventeen dogs (average weight 22.9 kg) were divided into three experimental groups. Group I (n = 7) was anesthetized, paralyzed and ventilated with air using intermittent positive pressure ventilation (IPPV) through a tracheal tube. The tube was removed and each main stem bronchus was cannulated with a 2.5 mm i.d., 4 mm o.d. polyethylene catheter using a fiberoptic bronchoscope. The tracheal tube was replaced to hold the catheters in place. Heated, humidified air was continuously delivered equally to each catheter. Total flows ranged from 8 to 28 1/min (0.4—1.4 1 + kg^-1 min-^-1). Airway pressure (P_aw) in the trachea did not exceed 2 mmHg (0.27 kPa). Adequate gas exchange in terms of arterial oxygen and arterial carbon dioxide tension (Pao₂ and Paco₂) was found after 30 min at flows greater than 16 l · min_-1. Group II (n = 7) was managed similarly to the first group, insufflating endobronchial air using the optimal flow of 1.0 1 · kg ¹ · min^-1 obtained from Group I. CFAV continued for 5 h in all animals. Blood gas samples and measurements of systemic blood pressure, heart rate (HR), pulmonary artery blood pressure, pulmonary artery wedge pressure, cardiac output (Qt), and temperature were taken every 30 min. Group III (n = 3) was anesthetized similarly to the other groups. Pulmonary gas distribution was evaluated in relation to catheter placement using Xe¹³³. Results showed significant differences between Paoj values during CFAV and IPPV; however, all animals were adequately oxygenated. During 5 h of CFAV, adequate CO₂ elimination was achieved in all animals. There was no difference in PaO₂, Paco₂ and shunt fraction (Qs/C}t) with CFAV at 30 min and 5 h. Differences in HR, Qt, and systemic vascular resistance at 30 min and 5 h were related to the hypothermia during the developing course of experimentation. With the catheters above the carina, gas distribution studies demonstrated gas limited to the large airways with no peripheral distribution, resulting in low Pao₂ levels and elevated Paco₂ levels. Endobronchial catheters permitted gas distribution to the peripheral airways, and oxygenation and ventilation were normal.     

Physiological effects of a lung-recruiting strategy applied during one-lung ventilation

Background: One‐lung ventilation (OLV) affects respiratory mechanics and ventilation/perfusion matching, reducing functional residual capacity of the ventilated lung. While the application of a lung‐recruiting manoeuvre (RM) on the ventilated lung has been shown to improve oxygenation, data regarding the impact of RM on respiratory mechanics are not available. Methods: Thirteen patients undergoing lung resection in lateral decubitus were studied. During OLV, a lung‐recruiting strategy consisting in a RM lasting 1 min followed by the application of positive end‐expiratory pressure 5 cmH₂O was applied to the ventilated lung. Haemodynamics, gas exchange and respiratory mechanics parameters were recorded on two‐lung ventilation (TLV_baseline), OLV before and 20 min after the RM (OLV_pre‐RM, OLV_post‐RM, respectively) and TLV_end. Haemodynamics parameters were also recorded during the RM. Results: The PaO₂/FiO₂ ratio was 358±126 on TLV_baseline; it decreased to 235±113 on OLV_pre‐RM (P<0.01) increased to 351±120 on OLV_post‐RM (P<0.01 vs. OLV_pre‐RM), and remain stable thereafter. During the RM, CI decreased from 3.04±0.7 l/m² OLV_pre‐RM to 2.4±0.6 l/m² (P<0.05), and returned to baseline on OLV_post‐RM (3.1±0.7 l/m², NS vs. OLV_pre‐RM). The RM resulted in alveolar recruitment and caused a significant decrease in static elastance of the dependent lung (16.6±8.9 cmH₂O/ml OLV_post‐RM vs. 22.3±8.1 cmH₂O/ml OLV_pre‐RM) (P<0.01). Conclusions: During OLV in lateral decubitus for thoracic surgery, application to the dependent lung a recruiting strategy significantly recruits the dependent lung, improving arterial oxygenation and respiratory mechanics until the end of surgery. However, the transient haemodynamic derangement occurring during the RM should be taken into account.     

Automatic jet ventilation in children anaesthetized by the T-piece circuit

Investigation was carried out in ten children aged between one month and six years, who were anaesthetized by the T-piece circuit. The volume of the reservoir tubing of the T-piece was 250 ml. Ventilation was controlled automatically by oxygen jets which were delivered via an injector attached to the reservoir tubing. The oxygen jets were regulated by an electronically-controlled solenoid valve. The children were ventilated by a tidal volume about 12 ml±kg^?1 at a rate of 12-20 per min depending on their age, while the FGF varied between 3 and 6 l min^?1 depending on their body weight. The resulting FIO₂ ranged between 0.32 and 0.34 which was expected from the oxygen:nitrous oxide mixture (1:2), denoting no mixing of the oxygen jets with the anaesthetic mixture. The PA_co2 was ventilation-dependent, and ranged between 4±6-5±3 kPa (35-41 mmHg). The results suggest that automatic jet ventilation facilitates controlled ventilation in children anaesthetized by the T-piece circuit, while maintaining the original simplicity of the T-piece.;     

Age and Sex Predict Pao2/Fio2 Ratio in Brain-Dead Donor Lungs

Objectives

To define the prevalence of various ranges of the ratio of partial arterial oxygen tension to fraction of inspired oxygen (Pao₂/Fio₂) and to determine correlative and predictive variables of donor lung Pao₂/Fio₂.

Material and Methods

From the brain death database of Masih Daneshvari Hospital Organ Procurement Center, we extracted demographic data, cause of injury, patient clinical condition, and laboratory findings as independent data. Donor lung suitability was determined with an oxygen challenge test, with results of 400 mm Hg considered ideal; 300 to 399 mm Hg, good; 200 to 299 mm Hg, borderline; and less than 200 mm Hg, not acceptable.

Results

Using the Pao₂/Fio₂ cutoff points, 6.7% of donor lungs were considered ideal; 26.7%, good; 40%, borderline; and 26.7%, unacceptable. Mean (SD; range) Pao₂/Fio₂ was 266.6 (85.6; 110-460). The Pao₂/Fio₂ was significantly correlated with age (r = −0.35; P = .02). After entering the study variables into a linear regression model, age (−2.3; P = .008) and sex (51.5; P = .04) were significant predictors of donor lung suitability (R² = 0.95; P < .001).

Conclusion

Results of oxygen challenge tests demonstrated better suitability of lungs from male and younger brain-dead donors. This finding is independent of other variables including cause of brain death and clinical and paraclinical data.     

Negative pressure ventilation vs. spontaneous assisted ventilation during rigid bronchoscopy: A controlled randomised trial

Background: Ventilation during interventional rigid bronchoscopy (IRB) under general anaesthesia (jet ventilation, positive pressure ventilation and spontaneous assisted ventilation) may offer some difficulties. This study compares the effectiveness during IRB of intermittent negative pressure ventilation (INPV) and spontaneous assisted ventilation (SAV). Methods: Thirty-eight patients submitted to IRB were randomised into two groups: SAV or INPV. All patients received a total intravenous anaesthesia; INPV patients were paralysed. Pre-and intra-operative arterial blood gases and O₂ flow through a rigid bronchoscope were assessed. The endoscopist applying a subjective score evaluated the operating conditions. Results: Patients of the INPV group, as compared to the SAV group, required a lower dosage of fentanyl (2.6 ± 1.8 (μg · kg^?1· h^?1 vs. 6.6 ± 4.8 μg · kg^?1· h^?1), a lower O₂ supply (3.3 ± 2.8 1/min vs. 11.6 ± 3.4 1/min), a shorter recovery time (5.4 ± 2.9 min vs. 9.8 ± 7.1 min) and no manually assisted ventilation (0 ± 0 vs. 1 ± 1.1 nd?/procedure). Intraoperative PaCO₂ was higher in the SAV (8.1 ± 1.3 kPa) than in the INPV group (5.0 ± 1.6 kPa) and intraoperative pH differed in the two groups (7.26 ± 0.05, SAV vs. 7.47 ± 0.08, INPV). Operating conditions, as assessed by a subjective score, were considered better with INPV than with SAV (4.9 vs. 4.3). Conclusions: As compared to SAV, INPV in paralysed patients during IRB reduces administration of opioids, shortens recovery time, prevents respiratory acidosis, excludes the need for manually assisted ventilation, reduces 02 need and affords optimal surgical conditions. INPV appears a safe, non-invasive and effective ventilatory management during IRB.     

Tubeless combined high-frequency jet ventilation for laryngotracheal laser surgery in paediatric anaesthesia

BACKGROUND: High-frequency jet ventilation (HFJV) is an alternative ventilatory approach in airway surgery and for facilitating gas exchange in patients with pulmonary insufficiency. We have developed a new technique of combined HFJV utilising two superimposed jet streams. In this study we describe the application of tubeless supralaryngeal HFJV during laryngotracheal laser surgery in infants and children. METHODS: Tubeless combined HFJV characterised by the simultaneous supralaryngeal application of a low-frequency (LF) and a high-frequency (HF) jet stream was evaluated in a clinical study in 10 children undergoing elective laryngotracheal CO2 laser surgery. Additionally, pressure and flow characteristics were determined with the use of a paediatric test lung. HFJV was applied by means of a modified Kleinsasser laryngoscope with integrated metal injectors. In addition to pulse oximetry, monitoring of ECG, heart rate and blood pressure, supraglottic airway pressure was measured and arterial blood gases were analysed. RESULTS: Tubeless combined HFJV was used in 10 infants and children (mean age 4.6 yr, range 2 months-10 years) undergoing 17 consecutive endoscopic procedures with CO2 laser microsurgery of the larynx or the trachea under general anaesthesia.The mean duration of supralaryngeal HFJV was 46 min (range 15-75 min). Mean driving pressures of the HF and the LF jet streams were 0.75 bar and 0.95 bar, respectively. Inspiratory oxygen ratios were in the range 0.4-1.0. HFJV resulted in mean PaO2 and PaCO2 values of 19.7 kPa and 6.1 kPa, respectively. No complications during HFJV were observed. In the test lung, combined HFJV applied with driving pressures of 0.7-1.0 bar and 0.9-1.2 bar for HF and LF jet ventilation, respectively, resulted in maximum peak and baseline distal airway pressures of 17.6 cm H2O and 5.4 cm H2O, respectively. CONCLUSION: The application of the combined double frequency HFJV was effective in maintaining gas exchange in the presence of laryngeal or tracheal stenoses. It provided good visibility of anatomical structures and offered space for surgical manipulation, avoiding the use of combustible material inside the larynx or trachea.     

The effect of combined high frequency ventilation with and without continuous positive airway pressure in experimental lung injury

Combined high frequency ventilation (CHFV) with 8 mmHg (1.0 kPa) continuous positive airway pressure (CPAP) and without CPAP (CHFV0) were compared to each other, and to continuous positive pressure ventilation (CPPV) with 8 mmHg (1.0 kPa) CPAP in pigs with oleic acid induced lung injury. The respiratory rate was 15 min-1 and the high frequency (HF) rate 360 min-1. Arterial carbon dioxide tension (PaCO2) was adjusted to 5 kPa and 25% oxygen was used. After CHFV, CPAP was briefly discontinued to allow the establishment of CHFV0 in order to examine the cardiovascular and pulmonary effects of combined high frequency ventilation alone. Mean arterial oxygen tension (PaO2) was 15.8 +/- 3.9 kPa during CPPV, 15.5 + 3.2 kPa during CHFV and 13.2 +/- 5.1 kPa during CHFV0 (ns). The peak airway pressure and the pericardiac pressure were lowest during CHFV0. CHFV provoked significant cardiovascular depression (mean arterial pressure, stroke index, left and right ventricle stroke work index). When compared to CPPV, a non-significant trend towards improved cardiovascular function was found during CHFV0. With similar mean airway pressures (during CHFV0) or the same CPAP (during CHFV) as during CPPV, no further improvement in oxygenation due to HF waves was found. Airway pressure was the major factor causing alterations in cardiovascular function, not the ventilation technique.     

Effects of buffering in hypercapnia and hypercapnic hypoxemia

Anesthetized, paralyzed and mechanically ventilated pigs were exposed to extreme hypercapnia (Paco_2-20 kPa) at Fio₂ 0.4 for 480 min, with (n = 6) or without (n = 6) continuous infusion of isotonic buffers (bicarbonate and trometamol). Arterial pH was higher in buffered animals than controls, 7.21 ±0.01 vs 7.01±0.01 (mean ± s.e.mean, P < 0.01). Serum osmolality and Paco₂ did not differ between groups throughout the experiment. The hemodynamic response to hypercapnia was attenuated in the buffered group, who had lower heart rate, 133 ± 6 vs 189±12 min^-1 (P < 0.01), mean arterial pressure (MAP) 109 ± 4 vs 124 ± 4 mmHg (14.5 ± 0.5 vs 16.5 ± 0.5 kPa) (P < 0.05), mean pulmonary arterial pressure 16±1 vs 23 ± 1 mmHg (2.1 ±0.1 vs 3.1 ±0.1 kPa) (P < 0.01), and pulmonary vascular resistance (PVR) 249 ± 21 vs 343 ± 20 dyn s-cm^-5 (2490±210 vs 3430±200 μN-s-cm^-5) (P < 0.01), compared with the control group. Subsequently, both groups were exposed to hypercapnic hypoxemia by stepwise increases in Fio₂ (0.15, 0.10, 0.05) at 30-min intervals, while Fico₂ was kept at 0.2. PVR increased in both groups (P < 0.05) but, except for heart rate, all hemodynamic differences between the groups disappeared during hypoxia. At Fio₂ 0.15, buffered animals had higher arterial oxygen saturation (73 ± 5%) than the controls (55 ± 5%), (P < 0.05). The control animals died after 1–29 min (mean 14 min) at Fio₂ 0.10, while all buffered animals survived Fio₂ 0.10 with stable MAP (122 ± 14 mmHg (16.3 ± 1.9 kPa). The buffered animals died after 4–22 min (mean 15 min) at Fio₂ 0.05. We conclude that buffering to a pH of 7.21 attenuates the observed hemodynamic response in extreme hypercapnia and improves survival in hypercapnic hypoxemia.     

Low dose methylprednisolone prophylaxis to reduce inflammation during one-lung ventilation

Background: The specific aim of this study was to examine the efficacy of a low dose of methylprednisolone in minimizing inflammatory response in juvenile piglets when given 45–60 min prior to onset of one‐lung ventilation. Methods: Twenty piglets aged 3 weeks were assigned to either the control group (n = 10) or methylprednisolone group (n = 10). The animals were anesthetized and after 30 min of ventilation, they had their left lung blocked. Ventilation was continued via right lung for 3 h. The left lung was then unblocked. Following another 30 min of bilateral ventilation, the animals were euthanized and both lungs were harvested. The methylprednisolone group had a single dose (2 mg·kg^?1) of methylprednisolone given i.v. 45–60 min prior to onset of one‐lung ventilation. Physiological parameters (PaO₂, resistance, and compliance) and markers of inflammation (tumor necrosis factor [TNF]‐α, interleukin [IL]‐1β, IL‐6, and IL‐8) were measured at baseline and every 30 min thereafter. Lung tissue homogenates from both collapsed and ventilated lungs were analyzed for TNF‐α, IL‐1β, IL‐6, and IL‐8. Results: The methylprednisolone group had higher partial pressure of oxygen (P = 0.01), lower plasma levels of TNF‐α (P = 0.03) and IL‐6 (P = 0.001) when compared with control group. Lung tissue homogenate in the methylprednisolone group had lower levels of TNF‐α (P < 0.05), IL‐1β (P < 0.05), and IL‐8 (P < 0.05) in both the collapsed and the ventilated lungs. Conclusions: In a piglet model of one‐lung ventilation, use of prophylactic methylprednisolone prior to collapse of the lung improves lung function and decreases systemic pro‐inflammatory response. In addition, in the piglets who received methylprednisolone, there were reduced levels of inflammatory mediators in both the collapsed and ventilated lungs.     

Endotracheal tube versus face mask with and without continuous positive airway pressure (CPAP)

Various ways of delivering continuous positive airway pressure (CPAP) have been extensively studied, with little attention, however, being paid to the effects of an intubation tube compared with breathing through a face mask, with or without CPAP. Pulmonary and cardiovascular variables were measured while 12 patients recovering from coronary artery bypass grafting were spontaneously breathing at ambient airway pressure, then at 7.4 mmHg (1 kPa) CPAP, and again at ambient pressure just before extubation. The same stages were repeated immediately after extubation, with patients breathing through a tight-fitting face mask. Arterial oxygen tension (Pao₂, mean ± s.d.) was better when the patients were breathing at ambient pressure through a face mask (11.7±2.8 kPa) than when they were intubated (10.6±2.4 kPa, P < 0.05). Compared with ambient pressure, CPAP (7.4 mmHg) (1 kPa) increased Pao₂ in both modes (13.4 ± 3.5 kPa with mask, and 12.6 ± 3.5 kPa when intubated, n.s.). The best arterial oxygen saturation was measured during CPAP with a face mask (96± 1%). Cardiac output remained unchanged in all the breathing modes. After coronary artery bypass grafting, spontaneous breathing with a face mask resulted in better Pao₂ than breathing through an endotracheal tube, both with and without 7.4 mmHg (1 kPa) CPAP. This study indicates that unnecessary delay in extubation should be avoided.     

Lung protective ventilation during pulmonary resection in children: a prospective,single-centre,randomised controlled trial

Background

Perioperative ventilatory strategies for lung protection in children are underexplored. This study evaluated the effects of lung protective ventilation (LPV) on postoperative clinical outcomes in children requiring one-lung ventilation (OLV) for pulmonary resection.

Intermittent capnography during high-frequency jet ventilation for prolonged rigid bronchoscopy

BACKGROUND: Gas exchange during high-frequency jet ventilation (HFJV) for prolonged rigid bronchoscopy (RBS) is usually monitored by arterial blood gas analysis. Capnography of expired gases during brief HFJV discontinuation may be a reliable and noninvasive supplemental method. Capnography can be performed either for single breaths or with respiratory rate (RR) reduced to 10 x min(-1). The aim of this study was to demonstrate that capnography during short periods of HFJV discontinuation represents a reliable measure of PaCO2 during prolonged RBS. METHODS: We prospectively investigated 100 consecutive patients (75 male and 25 female) undergoing HFJV for RBS. HFJV was delivered through the rigid bronchoscope at the following settings: working pressure 1.2 bar, rate 100 x min(-1), FIO2 0.99, t(i)/t(tot)0.6. The light guiding channel ending at the distal tip of the rigid bronchoscope was used for gas sampling. Capnograms were assessed at 5 min intervals and compared to PaCO2 from arterial blood samples drawn simultaneously. The accuracy of single breath CO2 sampling was compared with sampling at RR=10 x min(-1). RESULTS: Mean duration of RBS was 30+/-21 min. A significant correlation between capnography (PetCO2) and arterial blood gas analysis (PaCO2) was observed, being r=0.90 for the RR= 10 x min(-1) method and r=0.91 for the single breath method. Mean difference between PaCO2 and PetCO2 was 0.37+/-0.2 kPa throughout the entire study period. No significant differences between single breath sampling or sampling at RR=10 x min(-1) were observed. CONCLUSION: Capnography performed during short periods of HFJV discontinuation reliably and noninvasively reflects PaCO2 during prolonged endoscopic procedures. Capnography during HFJV for RBS may reduce the frequency of arterial blood gas sampling, the duration of unmonitored intervals and costs.