Supraglottic jet oxygenation and ventilation-assisted fibre-optic bronchoscope intubation in patients with difficult airways.

A difficult airway may lead to hypoxia and brain damage. The WEI Nasal Jet Tube (WNJ) is a new nasal pharyngeal tube that applies supraglottic jet oxygenation and ventilation (SJOV) for patients during tracheal intubation without the need for mask ventilation. We evaluated the effectiveness and safety of SJOV-assisted fibre-optic bronchoscopy (FOB) using the WNJ in the management of difficult tracheal intubations. A total of 50 adult patients with Cormack-Lehane grade ≥3 and general anesthesia with tracheal intubation were randomly assigned to either the laryngeal mask airway (LMA) or WNJ groups. The primary outcome was the percentage of patients with SpO2 values lower than 94 % during intubation. The proportion of successful intubations, total time of intubation, and associated complications were also recorded. The percentage of patients with SpO2 values lower than 94 % during intubation was significantly higher in the LMA group (25 % in the LMA vs. 0 % in the WNJ, P = 0.01). Although there were no statistically significant differences in the total success rates of intubation, the first-attempt success rate was significantly higher in the WNJ group (100 vs. 79.2 %, P = 0.02). The total time required for intubation with the WNJ was shorter than that of the LMA (73.4 vs. 99.5 s, P < 0.001), although the duration of fibre-optic intubation was similar. The incidence of complications was similar between the two groups. SJOV-assisted FOB using the WNJ improved oxygenation and successful tracheal intubation in the management of difficult airways. This technique can be used as an alternative approach to improve success and minimize hypoxia during difficult airway management.

Jet ventilation for surgical interventions in the upper airway.

The clinical applications of jet ventilation (JV) in ear, nose, and throat surgery can be best understood by the characteristics that distinguish this form of ventilation from conventional positive pressure ventilation. By definition, JV is based on the application of gas portions under high pressure through an unblocked catheter into the airway, which is open to the ambient air. Beneficial opportunities arise in JV, which otherwise are not available in regular ventilation.

Pressures available for transtracheal jet ventilation from anesthesia machines and wall-mounted oxygen flowmeters.

BACKGROUND: Oxygen supplies capable of supporting transtracheal jet ventilators can be lifesaving. There is not much information about which oxygen sources (readily available inside and outside operating rooms) have sufficient driving pressure for transtracheal jet ventilation. METHODS: We measured driving pressures (upstream or residual oxygen pressure) in a specially designed jet ventilation test system with a 2.25-mm (14-gauge) i.v. catheter. High-pressure oxygen sources evaluated included wall-mounted (Puritan, Allied Health, Precision, and Datex-Ohmeda) and anesthesia machine auxiliary oxygen flowmeters and oxygen flush valves from anesthesia machines (Draeger Narkomed 2B, Narkomed 4, Datex-Ohmeda Excel, and Datex-Ohmeda Modulus). RESULTS: All 4 types of wall-mounted oxygen flowmeters, opened past their highest scale settings (15 L/min), delivered sufficient working pressures (range, 103-282 kPa; 16-41 psi). Working pressures from auxiliary oxygen flowmeters mounted on Datex-Ohmeda machines were adequate to support jet ventilation (range, 189-248 kPa; 27-36 psi), whereas those on tested Draeger machines did not supply sufficient pressure for jet ventilation: Narkomed 2B, 14-28 kPa (2-4 psi); Narkomed 4, 24-28 kPa (3-4 psi). Working pressures delivered by oxygen flush valves on tested Draeger machines were adequate to support jet ventilation, ranging from 96 to 117 kPa (14-17 psi), whereas pressures generated by tested Datex-Ohmeda flush valves were not (ranging from 50 to 62 kPa, 7-9 psi). CONCLUSION: Oxygen sources other than dedicated jet ventilator connectors to high-pressure pipeline oxygen may supply adequate working pressure, but each type of oxygen source needs testing to ensure that it supplies adequate working pressure.

The quality of the surgical field during functional endoscopic sinus surgery--the effect of the mode of ventilation--a randomized, prospective, double-blind study.

OBJECTIVES/HYPOTHESIS: The outcome of functional endoscopic sinus surgery (FESS) depends on a clean surgical field achieved by minimizing intraoperative bleeding. High frequency jet ventilation (HFJV), due to lower airway pressures, offers the benefit of improved venous return, less bleeding, and improved operating conditions. HFJV was compared to intermittent positive pressure ventilation (IPPV) by assessment of surgical conditions and measurement of intraoperative blood loss. STUDY DESIGN: Prospective, randomized, double-blind study. METHODS: A total of 22 patients undergoing FESS were randomly assigned to be ventilated during surgery under general anesthesia by either HFJV or IPPV. The quality of the surgical field was assessed and the total blood loss was measured. RESULTS: The mean airway pressure was significantly lower in the HFJV group than in the IPPV group (2.42 +/- 1.17 and 7.11 +/- 0.72, respectively, P < .0001). The total mean loss of blood in the HFJV group was 170 cc and in the IPPV group was 318.18 cc (P = .017). The quality of the surgical field as estimated by the surgeon was significantly better in the HFJV group. The mean point values on the Boezaart et al. scale for the IPPV and HFJV groups were 2.72 +/- 0.77 and 1.80 +/- 0.686, respectively (P = .012). CONCLUSIONS: HFJV significantly reduced the amount of intraoperative bleeding and thus significantly improved the quality of the surgical field. It is suggested that increased venous return due to lower intrathoracic pressures resulted in less bleeding and improved operating conditions. HFJV can be effectively used for FESS in order to improve endoscopic view with no adverse effects.

Measurement of changes in respiratory mechanics during partial liquid ventilation using jet pulses.

OBJECTIVE: To compare the changes in respiratory mechanics within the breathing cycle in healthy lungs between gas ventilation and partial liquid ventilation using a special forced-oscillation technique. DESIGN: Prospective animal trial. SETTINGS: Animal laboratory in a university setting. SUBJECTS: A total of 12 newborn piglets (age, <12 hrs; mean weight, 725 g). INTERVENTIONS: After intubation and instrumentation, lung mechanics of the anesthetized piglets were measured by forced-oscillation technique at the end of inspiration and the end of expiration. The measurements were performed during gas ventilation and 80 mins after instillation of 30 mL/kg perfluorocarbon PF 5080. MEASUREMENTS AND MAIN RESULTS: Brief flow pulses (width, 10 msec; peak flow, 16 L/min) were generated by a jet generator to measure the end-inspiratory and the end-expiratory respiratory input impedance in the frequency range of 4-32 Hz. The mechanical variables resistance, inertance, and compliance were determined by model fitting, using the method of least squares. At least in the lower frequency range, respiratory mechanics could be described adequately by an RIC single-compartment model in all piglets. During gas ventilation, the respiratory variables resistance and inertance did not differ significantly between end-inspiratory and end-expiratory measurements (mean [sd]: 4.2 [0.7] vs. 4.1 [0.6] kPa x L(-1) x sec, 30.0 [3.2] vs. 30.7 [3.1] Pa x L(-1) x sec2, respectively), whereas compliance decreased during inspiration from 14.8 (2.0) to 10.2 (2.4) mL x kPa(-1) x kg(-1) due to a slight lung overdistension. During partial liquid ventilation, the end-inspiratory respiratory mechanics was not different from the end-inspiratory respiratory mechanics measured during gas ventilation. However, in contrast to gas ventilation during partial liquid ventilation, compliance rose from 8.2 (1.0) to 13.0 (3.0) mL x kPa(-1) x kg(-1) during inspiration. During expiration, when perfluorocarbon came into the upper airways, both resistance and inertance increased considerably (mean with 95% confidence interval) by 34.3% (23.1%-45.8%) and 104.1% (96.0%-112.1%), respectively. CONCLUSIONS: The changes in the respiratory mechanics within the breathing cycle are considerably higher during partial liquid ventilation compared with gas ventilation. This dependence of lung mechanics from the pulmonary gas volume hampers the comparability of dynamic measurements during partial liquid ventilation, and the magnitude of these changes cannot be detected by conventional respiratory-mechanical analysis using time-averaged variables.

Comparison of high-frequency flow interruption ventilation and hyperventilation in persistent pulmonary hypertension of the newborn.

INTRODUCTION: Because of the high mortality, potential limitations, and inherent adverse effects associated with conventional therapies, as well as extracorporeal membrane oxygenation, for persistent pulmonary hypertension of the newborn (PPHN), alternative modes of ventilatory support have been researched. There is anecdotal evidence that high-frequency flow interruption ventilation (HFFI) benefits neonates with severe air leak and lung diseases unresponsive to conventional ventilation, so we conducted a study to compare the hospital course, survival rate, and incidence of chronic lung disease of neonates with PPHN treated with hyperventilation (HV) and HFFI. METHODS: Enrolled in the study were 36 neonates who (1) were treated with HV and a fraction of inspired oxygen of 1.0 for PPHN, (2) had arterial partial pressure of oxygen (P(aO2)) values or= 120 mm Hg; (3) shorter mean time to P(aO2) >or= 120 mm Hg (13.5 vs 50.2 h, p = 0.001); (4) shorter mean time to reduced fraction of inspired oxygen (16 vs 84 h, p < 0.001); (5) shorter mean time to fraction of inspired oxygen 0.70 (53 vs 187 h, p < 0.001); (6) shorter mean time to extubation (8.1 vs 18.7 d, p = 0.033); (7) shorter length of hospitalization (22.7 vs 50.6 d, p = 0.025); and (8) fewer neonates with chronic lung disease (1 vs 5, p = 0.018). CONCLUSIONS: HFFI with the ventilation strategy we describe accomplishes sustained hyperoxygenation without hypocarbia and alkalosis, and response to HFFI can predict outcomes. HFFI does not significantly reduce mortality, but it does reduce the length of mechanical ventilation, the length of hospitalization, and the incidence of chronic lung disease in neonates with PPHN. The nonrandomized design of our study precludes firm conclusions about the potential benefits of HFFI. The results may be biased by practice variations. Additional randomized controlled trials are warranted to determine the efficacy of HFFI in neonates with PPHN.

A cart to provide high frequency jet ventilation during transport of neonates.

UNLABELLED: We report the evaluation of a cart we created to provide high frequency jet ventilation (HFJV) to neonates during intrahospital or interhospital transport. DESCRIPTION: The cart carries a conventional ventilator, jet ventilator (JV), incubator, gas blender, 3 E cylinders of oxygen and 2 of air, uninterruptible electric power supply (UPS), 2 syringe infusion pumps, cardiac monitor, and oximeter. EVALUATION METHODS: To determine the available operating time of the ventilators, we ran tests with 60% and 100% oxygen, high and low ventilator settings, 2.5-mm and 3.5-mm endotracheal tubes, and lung simulator set for low and high time constants. With five different combinations of these variables, the system was run to exhaustion of its gas supply. To determine the operating time limit of the UPS, we used it to operate the JV until the low-battery alarm sounded. RESULTS: The UPS always provided electrical power for at least 2 hours. In no case did a single cylinder of oxygen fail to power the system for less than 20 min. Because the cart carries 3 cylinders of oxygen and 2 of air, under the conditions tested a minimum of 60 min of continuous operation, using 100% oxygen, should be available during those portions of transports when the system is away from hospital and ambulance bulk power sources and is dependent on its own UPS and E cylinders of gas. EXPERIENCE: We have used the cart on two occasions to transport a 30-week gestational age, 1-kg, HFJV-dependent infant, first from ICU to surgery, then to another hospital for cardiac catheterization. Total transport time was 3 hours; there were no problems. The cart has also been used to transport three patients between hospitals during ECMO, without HFJV. CONCLUSIONS: Our HFJV transport system is adequate to transport an HFJV-dependent infant during the 30 to 60 minutes that may elapse when the cart is away from ambulance or hospital sources of electricity and gas. Available operating time with an HFJV transport system should be estimated conservatively; when an infant is dependent on HFJV, it would be well to have aircraft backup in case of ambulance breakdown or other contingencies.

An experimental randomized study of five different ventilatory modes in a piglet model of severe respiratory distress.

OBJECTIVES: To characterize different modes of pressure- or volume-controlled mechanical ventilation with respect to their short-term effects on oxygen delivery (DO2). Furthermore to investigate whether such differences are caused by differences in pulmonary gas exchange or by airway-pressure-mediated effects on the central hemodynamics. DESIGN: After inducing severe respiratory distress in piglets by removing surfactant, 5 ventilatory modes were randomly and sequentially applied to each animal. SETTING: Experimental laboratory of a university department of Anesthesiology and Intensive Care. ANIMALS: 15 piglets after repeated bronchoalveolar lavage. INTERVENTIONS: Volume-controlled intermittent positive-pressure ventilation (IPPV) with either 8 or 15 cmH2O PEEP; pressure-controlled inverse ratio ventilation (IRV); pressure-controlled high-frequency positive-pressure ventilation (HFPPV) and pressure-controlled high frequency ventilation with inspiratory pulses superimposed (combined high frequency ventilation, CHFV). The prefix (L) indicates that lavage has been performed. MEASUREMENTS AND RESULTS: Measurements of gas exchange, airway pressures, hemodynamics, functional residual capacity (using the SF6 method), intrathoracic fluid volumes (using a double-indicator dilution technique) and metabolism were performed during ventilatory and hemodynamic steady state. The peak inspiratory pressures (PIP) were significantly higher in the volume-controlled low frequency modes (43 cmH2O for L-IPPV-8 and L-IPPV-15) than in the pressure-controlled modes (39 cmH2O for L-IRV, 35 cmH2O for L-HFPPV and 33 cmH2O for L-CHFV, with PIP in the high-frequency modes being significantly lower than in inverse ratio ventilation). The mean airway pressure (MPAW) after lavage was highest with L-IRV (26 cmH2O). In the ventilatory modes with a PEEP > 8 cmH2O PaO2 did not differ significantly and beyond this "opening threshold" MPAW did not further improve PaO2. Central hemodynamics were depressed by increasing airway pressures. This is especially true for L-IRV in which we found the highest MPAW and at the same time the lowest stroke index (74% of IPPV). CONCLUSIONS: In this model, as far as oxygenation is concerned, it does not matter in which specific way the airway pressures are produced. As far as oxygen transport is concerned, i.e. aiming at increasing DO2, we conclude that optimizing the circulatory status must take into account the circulatory influence of different modes of positive pressure ventilation.

High frequency oscillatory ventilation in neonates with respiratory distress.

High frequency oscillatory ventilation (HFOV) was attempted in ten infants with severe respiratory failure not responding to conventional ventilation (CV); it was, therefore, used as a rescue measure. HFOV was successful in improving the respiratory status of seven infants, all with hyaline membrane disease (HMD). Five of these infants survived, of the remaining two, one died of massive peri/intra-ventricular haemorrhage and the other of cholestasis associated with total parenteral nutrition. It was unsuccessful in three infants, one with meconium aspiration, the second died within two hours commencing HFOV and the third with severe depression and hypotonia.

An experimental randomized study of six different ventilatory modes in a piglet model with normal lungs.

A randomized study of 6 ventilatory modes was made in 7 piglets with normal lungs. Using a Servo HFV 970 (prototype system) and a Servo ventilator 900 C the ventilatory modes examined were as follows: SV-20V, i.e. volume-controlled intermittent positive-pressure ventilation (IPPV); SV-20VIosc, i.e. volume-controlled ventilation (IPPV) with superimposed inspiratory oscillations; and SV-20VEf, i.e. volume-controlled ventilation (IPPV) with expiratory flush of fresh gas; HFV-60 denotes low-compressive high-frequency positive-pressure ventilation (HFPPV) and HVF-20 denotes low-compressive volume-controlled intermittent positive-pressure ventilation; and SV-20P denotes pressure-controlled intermittent positive-pressure ventilation. With all modes of ventilation a PEEP of 7.5 cm H2O was used. In the abbreviations used, the number denotes the ventilatory frequency in breaths per minute (bpm). HFV indicates that all gas was delivered via the HFV 970 unit. The ventilatory modes described above were applied randomly for at least 30 min, aiming for a normoventilatory steady state. The HFV-60 and the HFV-20 modes gave lower peak airway pressures, 12-13 cm H2O compared to approximately 17 cm H2O for the other ventilatory modes. Also the mean airway pressures were lower with the HFV modes 8-9 cm H2O compared to 11-14 cm H2O for the other modes. The gas distribution was evaluated by N2 wash-out and a modified lung clearance index. All modes showed N2 wash-out according to a two-compartment model. The SV-20P mode had the fastest wash-out, but the HFV-60 and HFV-20 ventilatory modes also showed a faster N2 wash-out than the others.(ABSTRACT TRUNCATED AT 250 WORDS)

High frequency jet ventilation in experimental pulmonary emphysema.

The effects of high frequency jet ventilation (HFJV, f = 2 Hz and 8 Hz, I:E = 0.43, FiO2 = 0.4) were studied and compared with intermittent positive pressure ventilation (IPPV, f = 10-14 breaths/min, VT = 15 ml/kg, I:E = 0.5, FiO2 = 0.4) in 8 dogs before and after induction of panlobular emphysema (PLE). PLE increased alveolar-arterial PO2 difference (PA-aO2) during all modes of ventilation, whereas PaCO2 did not change significantly. In both periods of the study, HFJV8 Hz was less effective in terms of CO2-elimination and oxygenation. In the control-period, functional residual capacity (FRC) was 937 +/- 212 ml. The increase during HFJV (HFJV2 Hz: 1156 +/- 508 ml, HFJV8 Hz: 1153 +/- 433 ml) did not reach significance (P = 0.09). Closing volume (CV) increased from 1.5 +/- 4.3% of vital capacity (%VC) (IPPV) to 6.3 +/- 7.1%VC (HFJV2 Hz) and 10.8 +/- 9.8% VC (HFJV8 Hz), respectively. In the PLE-period, FRC and CV increased significantly to 1107 +/- 207 ml and 14.1 +/- 7.0% VC respectively during IPPV (P less than 0.05). Application of HFJV neither increased FRC (HFJV2 Hz: 1153 +/- 433 ml, HFJV8 Hz: 1005 +/- 344 nor CV 14.8 +/- 6.0% VC and 13.9 +/- 8.1% VC, respectively). It is concluded that HFJV induces no alveolar overdistension in dogs with emphysematous lungs.

High-frequency oscillatory ventilation compared with conventional intermittent mechanical ventilation in the treatment of respiratory failure in preterm infants: neurodevelopmental status at 16 to 24 months of postterm age. The HIFI Study Group.

The High-Frequency Intervention Trial was a 10-center randomized clinical trial to test the efficacy and safety of high-frequency oscillatory ventilation (HFO) in the treatment of neonates weighing 750 to 2000 gm; 327 infants were assigned to HFO and 346 to conventional intermittent mechanical ventilation (IMV). Survival and lung morbidity rates were the same in the two groups. Bayley psychometric evaluations and CNS examination were performed at 16 to 24 months of postterm age in 77% of the survivors (185 HFO and 201 IMV). There was no difference in growth or respiratory status at follow-up. Cerebral palsy was diagnosed in 19 (10%) HFO-treated infants and 23 (11%) IMV-treated infants. There was no difference in severity between the two groups. A significantly higher incidence of hydrocephalus (12% vs 6%) was present in the HFO group (p less than 0.05). Bayley index scores greater than 83 were scored in 57% of HFO-treated infants compared with 66% of IMV-treated infants. The proportion of children at follow-up with a normal neuro-developmental status (i.e., Bayley score greater than 83 and no major CNS defect) was significantly less in the HFO than in the IMV group (54 vs 65%; p less than 0.05). Both treatment groups showed a strong association between the presence of grade 3 or 4 intraventricular hemorrhage and the development of major CNS or cognitive defects. No significant long-term beneficial or deleterious effects were demonstrated in the use of HFO versus IMV for the treatment of respiratory failure in low birth weight premature infants, except that there were slightly more neurologic deficits in the HFO group related to the higher proportion of survivors with major intraventricular hemorrhage.

Factors influencing humidification in high-frequency jet ventilation.

A new method of water nebulization for high-frequency jet ventilation (HFJV) using a coaxial saline infusion is described. A bench study was performed to investigate how alteration of the HFJV variables affects humidity using this method of humidification. The variables examined included the water flow rate (0.1, 0.25, 0.5, and 1.0 ml/min), cannula OD 2.1 mm (14 ga) and 1.4 mm (17 ga), ventilation rate (60, 80, 100, and 120 beat/min), inspiratory/expiratory (I/E) ratio (0.25, 0.67, and 1.5), and driving pressure (600, 900, 1200, and 1500 torr). Increasing water flow rate increased humidity. Humidity decreased with increased driving pressure, I/E ratio, and cannula OD. Humidity is not much affected by ventilation rate.