Suppression of spontaneous breathing during high-frequency jet ventilation

The effect of ventilatory frequency of high-frequency jet ventilation (HFJV) from 1 to 5 Hz, apart from changes in thoracic volume, on spontaneous breathing activity was studied in Yorkshire piglets under pentobarbital anesthesia. The highest P_aCO₂ at which the animals did not breathe against the ventilator (apnea point) was established either by changing minute volume of ventilation or by adding CO₂ to the respiratory gas. The higher the apnea point, the higher the suppression of spontaneous breathing activity was assumed to be. If the apnea point was searched for by changing minute volume a progressive increase of suppression of spontaneous respiratory activity was found at ventilatory rates of 3 Hz or more, concomitantly with a rise in end-expiratory pressure (P_EE). In case the tidal volume was kept constant, increase of ventilatory rate resulted in a tremendous increase of lung volume, together with considerably higher levels of P_EE. When under these conditions the apnea point was searched for by adding CO₂ to the respiratory gas a much higher CO₂-drive was needed for spontaneous breathing and therefore a much stronger inhibition of spontaneous breathing was concluded. By placing the animals in a body box in which pressure could be varied, thoracic volume could be kept constant during HFJV. When thoracic volume was kept constant in this way a constant tidal volume at increasing jet frequencies resulted in only a slight increase in suppression of spontaneous breathing.We conclude that the increase in lung volume is a major factor in suppressing central respiratory activity during HFJV. Jet frequency by itself might be an additional suppressive factor. Airway CO₂ did not seem to have an important effect.     

Alveolar pressure during high-frequency jet ventilation

We studied the influence of ventilatory frequency (1–5 Hz), tidal volume, lung volume and body position on the end-expiratory alveolar-to-tracheal pressure difference during high-frequency jet ventilation (HFJV) in Yorkshire piglets. The animals were anesthetized and paralysed. Alveolar pressure was estimated with the clamp off method, which was performed by a computer controlled ventilator and which had been extensively tested on its feasibility. The alveolar-to-tracheal pressure difference increased with increasing frequency and with increasing tidal volume, the common determinant appearing to be the mean expiratory flow. The effects in prone and in supine position were similar. Increasing thoracic volume decreased the alveolar-to-tracheal pressure difference indicating a dependence of this pressure difference on airway resistance. We concluded that the main factors determining the alveolar-to-tracheal pressure difference (P) during HFJV are expiratory flow (V_E) and airway resistance (R), PV_E×R.     

Assessment of lung volume and alveolar pressure during combined high-frequency jet ventilation in a child with adult respiratory distress syndrome

Lung volume and alveolar pressure were assessed using inductance plethysmography, airway occlusion and pneumotachography in a child with severe adult respiratory distress syndrome during both conventional mechanical and combined high-frequency ventilation (HFJV). The results suggest that improved oxygenation during combined HFJV is associated with higher end-expiratory lung volume and lower peak and mean lung volume and alveolar pressure.This work was presented in part at the 5th International Symposium on Pediatric, Surgical and Neonatal Intensive Care, Madrid, Spain 8–11 November 1991     

Determinants of ventilation during high-frequency jet ventilation

To better define the variables unrelated to ventilator frequency that affect gas transport during high-frequency jet ventilation (HFJV), we performed experiments in anesthetized paralyzed dogs (n = 8). The independent effects of changing driving pressure (300, 200, 150 kPa), catheter used for HFJV delivery (14-gauge and jet port of endotracheal tube), inspiratory time (30%, 50%, and 70%), and injector cannula diameter (12-gauge, 14-gauge, and 16-gauge) on minute volume (VE ), gas exchange, and cardiac output were studied at a ventilatory frequency of 100 min⁻¹. V_E increased with increasing driving pressure and inspiratory time. Entrainment decreased with increasing inspiratory time or when HFJV was delivered either via the jet port of the endotracheal tube, or via a jet cannula with distal side holes. Arterial PCO₂ varied inversely with V_E. Arterial oxygenation increased with hypocarbia, whereas venous admixture and cardiac output were unchanged. Several factors affect the ventilator-delivered and entrained volumes during HFJV, which in turn affect gas exchange. The determinants of gas exchange during HFJV appear to be similar to those described for conventional low-frequency positive-pressure ventilation.     

Arterial to end-tidal CO2 gradients during spontaneous breathing, intermittent positive-pressure ventilation and jet ventilation

Arterial to end-tidal CO2 tension gradients were measured in 18 dogs during spontaneous breathing (SB), intermittent positive-pressure ventilation (IPPV), and both low-frequency and high-frequency jet ventilation (LFJV and HFJV). The dogs were anesthetized with nembutal and permitted to breathe spontaneously through an 8-mm internal diameter endotracheal tube; blood gas tensions, cardiac output, and end-tidal CO2 partial pressure (PetCO2) were measured. IPPV, LFJV, and HFJV were then instituted in a random sequence and measurements repeated. PaO2, PaCO2 and cardiac output were similar during all four ventilatory modes. The mean PaCO2 differed significantly (p less than .001) from PetCO2 during IPPV, LFJV, and HFJV but not during SB. The mean PaCO2-PetCO2 gradient was 3.7 +/- 1 (SD), 12.6 +/- 5.0, and 24.3 +/- 8 torr during IPPV, LFJV and HFJV, respectively. The large gradients during LFJV and HFJV were not produced by dilution of tracheal CO2 by entrained air or by oxygen delivered by the jet. These results suggest that both LFJV and HFJV may be associated with a large PaCO2-PetCO2 gradient.     

急性呼吸窘迫综合征机械通气中的自主呼吸：兴利除弊

急性呼吸窘迫综合征（ARDS）是重症医学科（ICU）常见危重症。尽管人们不断地探索其诊疗方法,但病死率仍高达40%。肺保护性通气策略指导的机械通气仍是ARDS治疗的基石。ARDS患者接受机械通气时保留适度的自主呼吸有助于塌陷肺泡的复张、改善氧合、预防膈肌功能障碍等。联合有效的监测技术,设置恰当的机械通气模式及参数等措施使患者保持耐受性良好的自主呼吸状态,预防患者自身诱发性肺损伤（P-SILI）,可能是肺保护性通气策略的又一重要组成部分。     

The impact of spontaneous breathing during mechanical ventilation

PURPOSE OF REVIEW: In patients with acute respiratory distress syndrome, controlled mechanical ventilation is generally used in the initial phase to ensure adequate alveolar ventilation, arterial oxygenation, and to reduce work of breathing without causing further damage to the lungs. Although introduced as weaning techniques, partial ventilator support modes have become standard techniques for primary mechanical ventilator support. This review evaluates the physiological and clinical effects of persisting spontaneous breathing during ventilator support in patients with acute respiratory distress syndrome. RECENT FINDINGS: The improvements in pulmonary gas exchange, systemic blood flow and oxygen supply to the tissue which have been observed when spontaneous breathing has been maintained during mechanical ventilation are reflected in the clinical improvement in the patient's condition. Computer tomography observations demonstrated that spontaneous breathing improves gas exchange by redistribution of ventilation and end-expiratory gas to dependent, juxtadiaphragmatic lung regions and thereby promotes alveolar recruitment. Thus, spontaneous breathing during ventilator support counters the undesirable cyclic alveolar collapse in dependent lung regions. In addition, spontaneous breathing during ventilator support may prevent increase in sedation beyond a level of comfort to adapt the patient to mechanical ventilation which decreases duration of mechanical ventilator support, length of stay in the intensive care unit, and overall costs of care giving. SUMMARY: In view of the recently available data, it can be concluded that maintained spontaneous breathing during mechanical ventilation should not be suppressed even in patients with severe pulmonary functional disorders.     

The role of spontaneous breathing during mechanical ventilation

The tremendous progress in microprocessor-driven ventilator technology over the last years has facilitated the introduction of a broad variety of different ventilatory modes into the clinical practice of mechanical ventilation. Many of these newer modalities are designed for partial ventilatory support, which might reflect the complexity of the issue of patient ventilator interactions when spontaneous breathing activity is present compared to controlled mechanical ventilation. There are reasons to believe that allowing some degree of spontaneous breathing activity during mechanical ventilation is useful not only to gradually withdraw ventilatory assistance in the process of weaning but also to avoid some of the adverse effects of mechanical ventilation in the early phase of acute respiratory failure when classically controlled modes of ventilation are used. It is the aim of this article to review the effects of preserved spontaneous breathing activity during mechanical ventilation with different ventilatory modalities in acute respiratory failure patients.     

Clinical applications of high-frequency jet ventilation

Six patients with acute respiratory failure were treated with high-frequency jet ventilation (HFJV): 3 because they developed barotrauma while on conventional mechanical ventilation (CMV), 2 because of sedative- or PEEP-induced hypotension on CMV, and 1 because of bronchopleural fistula. In all patients, except the one with bronchopleural fistula, who was treated from the start with HFJV, gas exchange before (while on CMV) and after institution of HFJV could be compared. In these five patients, including the two with acute respiratory failure not complicated by barotrauma, gas exchange was better during HFJV than during CMV for the same levels of F_IO₂ and PEEP. HFJV therefore seems the method of choice for ventilatory support, not only in patients with bronchopulmonary disruption, but also in patients with hemodynamic embarrassment during CMV.     

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, V_T=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 (P_A-aO₂) during all modes of ventilation, whereas PaCO₂ did not change significantly. In both periods of the study, HFJV_8Hz 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 (HFJV_2Hz:1156±508 ml, HFJV_8Hz: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 (HFJV_2Hz) and 10.8±9.8% VC (HFJV_8Hz), respectively. In the PLE-period, FRC and CV increased significantly to 1107±207 ml and 14.1±7.0% VC respectively during IPPV (P<0.05). Application of HFJV neither increased FRC (HFJV_2Hz: 1153±433 ml, HFJV_8Hz: 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.     

Assessment of spontaneous breathing during pressure controlled ventilation with superimposed spontaneous breathing using respiratory flow signal analysis

Journal of Clinical Monitoring and Computing - Integrating spontaneous breathing into mechanical ventilation (MV) can speed up liberation from it and reduce its invasiveness. On the other hand,...     

Life threatening complication of high-frequency jet ventilation

High-frequency jet ventilation is being increasingly used as an alternative to conventional methods of ventilation in both anaesthesia and intensive care. We report a case of severe respiratory obstruction as a complication of high-frequency jet ventilation. Patients with bleeding diathesis, including patients on haemodialysis, may particularly be at risk.     

Imposed work of breathing during high-frequency oscillatory ventilation: a bench study

Introduction  

The ventilator and the endotracheal tube impose additional workload in mechanically ventilated patients breathing spontaneously. The total work of breathing (WOB) includes elastic and resistive work. In a bench test we assessed the imposed WOB using 3100 A/3100 B SensorMedics high-frequency oscillatory ventilators.     

Unloading work of breathing during high-frequency oscillatory ventilation: a bench study

Introduction  

With the 3100B high-frequency oscillatory ventilator (SensorMedics, Yorba Linda, CA, USA), patients' spontaneous breathing efforts result in a high level of imposed work of breathing (WOB). Therefore, spontaneous breathing often has to be suppressed during high-frequency oscillatory ventilation (HFOV). A demand-flow system was designed to reduce imposed WOB.     

Efficacy of a heat and moisture exchange device during high-frequency jet ventilation

A hygroscopic condensor humidifier has been tested during high-frequency jet ventilation, in an experimental set up. The influence of various ventilator settings on relative humidity, temperature and water content of the inspiratory and expiratory gases was investigated. The device provides adequate conditioning of the inspired gases with regard to relative humidity, temperature and water content at various ventilator settings.     

Airway pressure as a measure of gas exchange during high-frequency jet ventilation

Airway pressure during high-frequency jet ventilation (HFJV) reflects safety, ventilator performance, and gas exchange. The value of airway pressure as a monitoring and control variable for predicting the effectiveness of gas exchange was examined in 2 studies using healthy dogs. In the first study, HFJV was delivered to the airway via an extra lumen in the wall of an endotracheal tube, at a frequency of 150 cycle/min and 30% inspiratory time. Airway pressures (peak, mean, trough) were measured at various locations, from 5 cm below to 30 cm above the jet port. Pressures measured above the jet were misleading, but the proper measurement distance below the jet remains uncertain. The second study used the same ventilator settings but varied the airway pressure difference between peak and end-expiratory pressures (2, 4, or 6 cm H2O), and either the mean airway pressure (6 or 10 cm H2O) or the positive end-expiratory pressure (0, 5, 10, or 15 cm H2O). The airway pressure difference correlated strongly with efficiency of gas exchange for both CO2 elimination and oxygenation. Mean and end-expiratory pressures showed little influence over moderate ranges, but use of 15 cm H2O of PEEP decreased efficiency of both CO2 elimination and oxygenation, presumably due to increased dead space because of lung overdistension. We conclude that the airway pressure difference, measured as far distal in the airway as is safe and practical, can be useful for monitoring and controlling HFJV.     

Technical and psychological complications of high-frequency jet ventilation

The type and the incidence of complications during treatment with high-frequency jet ventilation were evaluated in 10 critically ill patients with acute respiratory failure. HFJV was used for 2 to 34 days for management of bronchopleural fistulae, tracheal rupture, laryngeal trauma or voluminous lung abscesses. The most significant technical problems observed were disconnection or kinking of the jet catheter, hypothermia and CO₂ retention. Insufficient humidification could induce severe complications such as viscous bronchial secretions, desiccation of the tracheobronchial mucosa or total obturation of the endotracheal tube. Psychological tolerance of high-frequency jet ventilation was generally satisfactory but the ventilator noise was sometimes hardly tolerated. Patients could develop a psychological dependence to high-frequency jet ventilation, leading to weaning problems. Solutions are suggested to decrease the incidence and severity of the technical and psychological complications.