Conventional and high-frequency ventilation in dogs with bronchopleural fistula

Seven anesthetized dogs with bronchopleural fistulas were subjected to a sequence of continuous positive-pressure ventilation (CPPV), volume-controlled high-frequency positive-pressure ventilation (HFPPV), and high-frequency vibratory ventilation (HFVV). Adequate short-term ventilation and oxygenation were possible with all three ventilatory modes. During HFPPV and HFVV, PaCO2 was unchanged, but hypercarbia developed during CPPV. PaO2 decreased during each mode of ventilation, but HFPPV maintained PaO2 at a sufficient and constant level during the 30-min test period. HFPPV was the most efficient technique with respect to delivery of minute ventilation, the relation between fistula flow and delivered ventilation, and maintenance of both ventilation and oxygenation.     

Comparison of high-frequency oscillation and tracheal gas insufflation versus standard high-frequency oscillation at two levels of tracheal pressure

Purpose  

In acute respiratory distress syndrome (ARDS), combined high-frequency oscillation (HFO) and tracheal gas insufflation (TGI) may improve oxygenation through a TGI-induced increase in mean tracheal pressure (P _tr). We compared standard HFO and HFO-TGI matched for P _tr, in order to determine whether TGI affects gas exchange independently from P _tr.     

Oxygenation during ventilation by high-frequency oscillation in dogs with acute lung injury

The effect of ventilation by high-frequency oscillation (HFO) on gas exchange in the abnormal lung is not well defined. In this study the efficiency of oxygenation by HFO (stroke volume 2.5 to 3.5 ml/kg, frequency 15 to 30 Hz) and by conventional mechanical ventilation (CMV) (tidal volume 15 to 20 ml/kg, frequency 8 to 15 breath/min) was compared in dogs with acute lung injury. Sixteen normal animals were studied under general anesthesia (halothane) on day 0 (control) and then injected intraperitoneally with 10 mg/kg of paraquat in divided doses over 3 consecutive days. Eight dogs were restudied on day 4 (moderate lung injury) and the other eight dogs on day 8 (more severe lung injury). With acute lung injury there was a progressive decrease in total lung capacity, decrease in lung compliance, and hypoxemia. In the moderate lung injury group, at equal alveolar ventilation, HFO resulted in a significant improvement in oxygenation (PaO2 95 to 104 torr) with a corresponding increase in mean lung volume when compared with CMV. In the severe lung injury animals, there were no significant differences in oxygenation or in mean lung volume between HFO and CMV.     

Collateral ventilation of obstructed lung during high-frequency oscillation in dogs and pigs

To determine if collateral ventilation (CV) occurs in pigs and dogs during intermittent positive-pressure ventilation (IPPV) and high-frequency oscillation (HFO), seven pigs and seven dogs were studied by measuring Xenon 133 washout (XeW) from an occluded subsegmental bronchus. The rate constant/min (K) for Xe blood uptake (KXeb) was derived, and when subtracted from K for XeW (KXeW) gave K for removal of Xe by CV (KXecv). Pig XeW were single exponentials with mean KXew = 0.25/min during IPPV and 0.12/min with HFO. In pigs, mean K of XeW was no different from KXeb so that all XeW occurred by blood uptake and none by CV. XeW in dogs had two exponentials. Dogs had over 11 times greater mean KXeW than pigs during IPPV and over 24 times greater during HFO. In dogs, on average, 79% (IPPV) and 87% (HFO) of XeW occurred by CV. CV is a means of gas exchange during HFO and IPPV in dogs but not in pigs.     

Synchronous versus nonsynchronous high-frequency jet ventilation: effects on cardiorespiratory variables and airway pressures in postoperative patients

In order to compare the differences of high-frequency jet ventilation (HFJV) synchronized with the cardiac cycle (sync) to that nonsynchronized with the cardiac cycle (async), ten stable postoperative ICU patients, without heart failure, in sinus rhythm were ventilated randomly in either mode. The async mode was HFJV at 100 cycle/min, while the sync mode was HFJV triggered by the R-wave of the ECG tracing. The heart rate ranged between 64 and 127 beat/min. Synchronization was studied at one of two periods, sync 0 and sync 60. Sync 0 consisted of inspiration triggered by the R-wave, with jet ventilation occurring early in systole; sync 60 represented a 60% delay of the time between the succeeding R-waves, with jet ventilation occurring in mid-diastole. There was no significant difference in the cardiorespiratory data when async was compared to either sync 0 or sync 60. Therefore, in these patients without heart failure, the selection of async vs. either sync mode appeared to have neither adverse nor beneficial hemodynamic effects.     

High-frequency ventilation and conventional mechanical ventilation in newborn babies with respiratory distress syndrome: A prospective,randomized trial

Objective Morbidity and mortality remain high amongst babies ventilated for a respiratory distress syndrome (RDS). Whether newly developed ventilators allowing high frequency ventilation such as high frequency flow interrupted ventilation (HFFIV) could decrease the morbidity and the mortality was investigated in a randomized study.Design Preterm babies weighing 1800g suffering from RDS and ventilated by conventional mechanical ventilation (CMV) were randomized to be further ventilated either by CMV (group CMV) or by HFFIV (group HFFIV) when peak inspiratory pressure (PIP) on CMV was 20cmH₂O.Setting The study was undertaken in the neonatal intensive care unit of the Erasmus Hospital.Patients 24 patients entered into the investigation and were randomized but 2 patients were removed from the study because the switch over to HFFIV failed. Eight of the 12 CMV patients and 5 of the 10 HFFIV patients completed the study.Measurements and results Clinical variables, blood gas analysis and ventilatory variables were looked at. There were no differences in mortality, in incidence of air leaks and pulmonary complications or in blood gas analysis. Bronchopulmonary dysplasia was not decreased by the use of HFFIV.Conclusion It is concluded that HFFIV is safe although it offers no concrete advantages over CMV when applied as we did in a low pressure approach.     

无创高频振荡通气对早产儿呼吸窘迫综合征的临床疗效

目的探讨无创高频振荡通气（nHFOV）对早产儿呼吸窘迫综合征（RDS）的临床疗效。 方法将2017年3月至2020年3月诊断为RDS的200例早产儿分为研究组和对照组,每组各100例。研究组给予nHFOV进行治疗,对照组给予经鼻持续气道正压通气（nCPAP）治疗。对比两组患儿治疗后的疗效、初始治疗失败率、早产儿支气管肺发育不良（BPD）发生率、不良事件发生率、血气分析相关指标、振幅整合脑电图（aEEG）评分及血清高迁移族蛋白B1（HMGB1）水平。 结果研究组患儿治疗后的疗效显著优于对照组患儿[93.00%（93/100）vs. 63.0%（63/100）,χ² = 68.923,P < 0.001],且研究组患儿初始治疗失败率[6.00%（6/100）vs. 15.00%（15/100）,χ² = 4.310,P = 0.038]及BPD发生率[1.00%（1/100）vs. 9.00%（9/100）,χ² = 6.737,P = 0.009]均显著低于对照组,而两组患儿气胸/气漏、消化道穿孔、早产儿坏死性小肠结肠炎、早产儿视网膜病、颅内出血、鼻损伤、死亡的发生率比较,差异均无统计学意义（χ² = 2.083、2.909、0.977、1.332、1.047、0.521、2.750,P均> 0.05）。同时,与对照组患儿比较,治疗后研究组患儿的氧分压[（89 ± 28）mmHg vs.（80 ± 29）mmHg,t = 2.151,P = 0.033]、二氧化碳分压[（37 ± 7）mmHg vs.（41 ± 10）mmHg,t = 3.386,P<0.001]及血氧饱和度水平[（97.4 ± 2.1）% vs.（90.6 ± 6.4）%,t = 10.049,P < 0.001]均显著改善,aEEG评分显著升高[（8.5 ± 1.5）分vs.（5.2 ± 1.9）分,t = 13.319,P<0.001],血清HMGB1水平显著降低[（578 ± 71）ng/L vs.（628 ± 72）ng/L,t = 5.071,P<0.001]。 结论nHFOV可有效改善RDS早产儿的脑功能、血气分析及呼吸支持相关指标,降低血清HMGB1水平,提升整体临床疗效。     

Comparison of high-frequency negative-pressure oscillation with conventional mechanical ventilation in normal and saline-lavaged cats

We modified a negative-pressure respirator to produce high-frequency, subatmospheric pressure oscillations around the chest. The effects of negative-pressure oscillation (NPO) on gas exchange, lung volume, compliance and cardiovascular variables were compared to those of conventional intermittent positive-pressure ventilation (IPPV) at 30 breath/min, using cats with normal and surfactant-depleted lungs. For frequencies in both normal lungs (1, 3, 4, 5, and 7 Hz) and saline-lavaged lungs (3, 5, and 7 Hz), peak inflating pressures were lower during NPO. Oxygenation was similar for both modes of ventilation. In cats with normal lungs, PaCO2 was significantly lower during NPO at 3 and 4 Hz (mean 24 torr) than during IPPV (mean 30 torr); normocapnia was maintained at the other frequencies. In damaged lungs, NPO and IPPV at 3 and 5 Hz resulted in similar CO2 removal, but PaCO2 was significantly higher during NPO at 7 Hz. Oscillatory tidal volumes decreased with increasing frequencies: in normal lungs, mean oscillatory tidal volume was 4.4 ml/kg at 1 Hz and 2.3 ml/kg at 7 Hz; in damaged lungs it was 6.5 ml/kg at 3 Hz and 3.2 ml/kg at 7 Hz. At 3 Hz and above, NPO was associated with a larger functional residual capacity than during sequences of IPPV matched for end-expiratory transthoracic pressure. There were no significant differences in respiratory system compliance, cardiac output, and pulmonary vascular resistance between both modes of ventilation. Further studies are warranted to investigate the potential clinical usefulness of NPO.     

Inhaled nitric oxide in persistent pulmonary hypertension of the newborn refractory to high-frequency ventilation

BACKGROUND: This study was designed to evaluate the effect of nitric oxide (NO) on the management of neonates with severe persistent pulmonary hypertension refractory to high-frequency oscillatory ventilation. METHODS: The birth weight and the gestational age of infants were 3125.5 +/- 794 g (mean +/- SD) and 39 +/- 2.4 weeks, respectively. All neonates were ventilated for an average of 137.5 min (range 90-180 min) prior to NO therapy. The mean oxygenation index (OI) of all neonates prior to NO was 46.3 +/- 5 (mean +/- SEM). NO was initially administered at 20 parts per million (ppm) for at least 2 h and increased gradually by 2 ppm to a maximum of 80 ppm. RESULTS: Eighteen infants (75%) responded and six (25%) did not respond to the treatment. Three neonates died in the responding group, while all the non-responders died (P = 0.0001). The survival rate was 62.5% among all neonates. NO significantly decreased OI (P < 0.0001) and improved the arterial/alveolar (a/A) oxygen ratio (P < 0.0001) within the first 2 h of NO therapy in 61.1% of the responders. However, the OI and the a/A oxygen ratio remained almost the same throughout the treatment in the non-responders and the non-survivors. CONCLUSION: Inhaled NO at 20 ppm, following adequate ventilation for 2 h without significant response, could be used to identify the majority of the non-responders in order to seek other alternatives.     

Hemodynamic effects of positive end-expiratory pressure during high-frequency ventilation

We studied the intrapleural and hemodynamic effects of positive end-expiratory pressure (PEEP) during high-frequency ventilation (HFV) with a Venturi high-frequency ventilator (Bird). Ten healthy mongrel dogs were anesthetized with sodium pentobarbital, catheterized with intrapleural and thermodilution pulmonary artery lines, and subjected to oleic acid-induced pulmonary edema. A mean PEEP of 16 +/- 6 (SD) cm H2O restored venous admixture to baseline in nine animals. Both mean airway pressure (Paw) and mean intrapleural pressure (Ppl) increased significantly with each increment of PEEP during HFV. Approximately 50% of Paw was transmitted to the intrapleural space. Cardiac index (CI) decreased with increments of PEEP in spite of constant transmural central venous and pulmonary capillary wedge pressures, so that oxygen delivery decreased despite increased PaO2. Possible mechanisms of PEEP-induced depression of CI during HFV are discussed. We conclude that both hemodynamic and intrapleural effects of PEEP during HFV are similar to those during conventional mechanical ventilation.     

Hemodynamic effects of high-frequency oscillatory ventilation in severe pediatric respiratory failure

Objective To assess the hemodynamic effects of high mean proximal airway pressures (Paw) during high-frequency oscillatory ventilation (HFOV) in non-neonatal pediatrics patients with severe respiratory failure.Design Prospective and retrospective study.Setting Pediatric ICU in a university-affiliated hospital.Patients 8 non-neonatal pediatric patients with severe respiratory failure ventilated with HFOV at our institution between July 1991 and February 1994. All patients had a pulmonary artery catheter.Interventions HFOV.Measurements and results Higher Paw was required during HFOV to obtain adequate lung expansion during the first 24 h (median 20.9 cmH₂O, range 16.9–30.0 cmH₂O in CMV, versus median 30.0 cmH₂O, range 21.0–33.0 cmH₂O in HFOV,p=0.008), resulting in improved oxygenation as evaluated by alveolar-arterial oxygen difference (median of 557.2 mmHg, range 360.4–607.8 mmHg in CMV, versus median of 410.5 mmHg, range 282.9–550.2 mmHg after 24 h of HFOV,p=0.03). The only observed effect on the cardiovascular system was a decrease in heart rate (median of 162, range 129–178 in CMV, versus median of 142, range 104–195 after 24 h of HFOV,p=0.03). Oxygen delivery, cardiac index, mean systemic arterial blood pressure, and pulmonary and systemic vascular resistances did not change significantly before and after HFOV in the patients as a group, although in one case a decrease in cardiac index and oxygen delivery was observed.Conclusions High-Paw HFOV must be used cautiously, but seems to have no discernible adverse effects on the cardiovascular system in most patients.     

Nociception in newborn and premature babies

BACKGROUND: The somatosensory system of preterms and newborns differs substantially from adults. These differences are of considerable preclinical and clinical interest. Maturation of A- and C-fibre synaptic connections in the dorsal horn and development of descending inhibition from the brainstem all take place postnatally in the rat. In early stages of development there is no definite spatial separation in the dorsal horn between the nociceptive and the non-nociceptive system. In preterms but not in adults non-noxious stimuli can induce central sensitization. Many neurotransmitters and signalling molecules involved in pain pathways are expressed early in the developing nervous system but do not reach adult levels for a considerable period. More important, receptors are frequently transiently overexpressed or expressed in areas during development where they are not seen in the adult and may have a different functional profile. The descending pain inhibitory system that provides an important protection against central sensitization develops later than the ascending nociceptive system. Thus, during a critical period of time the immature nociceptive system is highly vulnerable. For example, neonatal circumcision in the absence of analgesia results in increased pain responses during subsequent routine vaccination months later. CONCLUSIONS: In view of the changing nature of neonatal somatosensory and pain pathways and the vulnerability of the developing nervous system to alterations in sensory stimulation it is important that preterms and newborns need the care of a specialist for prevention and treatment of pain to avoid suffer and long-term changes in the nervous system.     

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.     

The hemodynamic effects of prolonged respiratory alkalosis in anesthetized newborn piglets

Objective: To test the hypothesis that prolonged alkalosis decreases cardiac output and, furthermore, exacerbates hypoxic pulmonary vasoconstriction, as respiratory alkalosis is frequently induced as a therapy for persistent pulmonary hypertension of the newborn despite a lack of controlled evidence of improved outcomes. Potential adverse effects of prolonged alkalosis have been demonstrated.¶Method: Two groups (control, n = 6, and hypocapnic alkalosis, n = 6) of 1–3 day old fentanyl-anesthetized, vecuronium-paralyzed piglets were instrumented to measure cardiac index (CI) and mean systemic (MAP) and pulmonary (PAP) arterial pressures. Baseline values were recorded. Alveolar hypoxia was then induced to achieve an arterial oxygen saturation of between 50 and 60 % for 15 min. Respiratory alkalosis was then induced, by increasing ventilation to achieve a pH between 7.55–7.60, and was continued for 240 min. Inspired carbon dioxide was used with hyperventilation in the control group to maintain pressure of arterial carbon dioxide (PaCO₂) at 35–45 mmHg and pH of 7.35–7.45. Hypoxia was induced again at 15 and 240 min. Pulmonary and systemic vascular resistances (PVR and SVR) were calculated.¶Results: Prolonged alkalosis led to a significant and progressive fall in mean MAP from 61 (SD 7) mmHg at the start of the study falling to 50 (SD 6.9, p = 0.043), with no effect on CI. Calculated SVR decreased (0.45 SD 0.03 vs 0.36 SD 0.05). There were no statistically significant changes in any of the variables in the control group. Neither acute nor prolonged respiratory alkalosis had a significant effect on hypoxic pulmonary vasoconstriction.¶Conclusions: Prolonged hyperventilation leads to systemic hypotension, however it does not exacerbate hypoxic pulmonary vasoconstriction.     

Adverse hemodynamic effects of lateral rotation during mechanical ventilation.

Turning critically ill, mechanically ventilated patients every 2 hours is a fundamental nursing intervention to reduce the negative impact of prolonged immobility from preventable pulmonary complications such as ventilator-associated pneumonia and atelectasis. Unfortunately, when coupled with positive pressure ventilation, the benefits of turning may come at the expense of cardiovascular function. Clinicians should closely monitor the hemodynamic response to turning mechanically ventilated patients, and if compromise is observed, the degree and duration of compromise may provide guidance to the appropriate intervention.     

Beat frequencies in high-frequency positive-pressure ventilation

Amplitude modulation of the waveforms of several cardiovascular variables was investigated during high-frequency (1.3 to 3.3 Hz) positive-pressure ventilation (HFPPV). The amplitude modulation of the pulmonary artery pressure wave was most prominent and its beat frequency (BF) was equal to the difference between the heart rate and the ventilation rate. Spectral analysis of the pulmonary artery pressure demonstrated well-defined peaks associated with the BF. No significant physiologic changes in either cardiovascular or pulmonary function were attributable to the presence of the beat phenomenon.