Review of the physiological rationale for and development of high-frequency positive-pressure ventilation--HFPPV

Comparing the effectiveness of single-lumen high-frequency positive pressure ventilation with double-lumen endobronchial tube for the anesthesia management of endoscopic thoracic sympathetic blockade surgery

OBJECTIVES

In this trial, we aimed to compare anesthetic effectiveness of single lumen tube (SLT) for tracheal intubation with high-frequency positive pressure ventilation (HFPPV) versus classic double lumen tube (DLT) for tracheal intubation in endoscopic thoracic sympathetic blockade surgery.

DESIGN

This was a prospective randomized controlled clinical study.

SETTING

The study was single-centered and conducted in a university hospital.

PARTICIPANTS

There were 135 endoscopic thoracic sympathetic blockade patients in this study.

INTERVENTIONS

The patients were randomly allocated either to DLT (n = 67) or SLT (n = 68) groups. In SLT group, the ventilator setting was kept with frequencies that range from 1 to 1.8 Hz (60-110/min). Data regarding anesthesia duration, surgery duration, difficult intraoperative lung deflation, postoperative atelectasis, postoperative pain, postoperative pneumothorax were recorded and compared. All patients were operated by a single experienced surgeon under general anesthesia provided by the same anesthesia team.

MEASUREMENTS AND MAIN RESULTS

Both groups were age and gender matched. Among all recorded variables, only anesthesia time was found to be close to statistical significance (P = .059, favoring single lumen). All other parameters were found to be similar between groups. (P < .05).

CONCLUSION

We reported that DLT and single lumen tracheal intubation were equally effective for lung deflation during surgery, and SLT with HFPPV ventilation mode during endoscopic thoracic sympathetic blockade surgery provided the surgeon with an adequate and clean workspace with shorter onset of anesthesia. We may suggest the HFPPV technique for uncomplicated surgery groups or where sufficient conditions for DLT cannot be provided in the operating room.

Post-operative hypertension during early recovery following liver tumour ablation: A retrospective study

BACKGROUND

High-frequency jet ventilation is necessary to reduce organ movements during stereotactic liver ablation. However, post-operative hypertensive episodes especially following irreversible electroporation ablation compared with microwave ablation initiated this study. The hypothesis was that hypertensive episodes could be related to ventilation or ablation method.

METHODS

The aim of this retrospective study was to assess the proportion of patients with hypertensive events during recovery following liver ablation under general anaesthesia and to analyse the relation to ventilation and ablation technique. A medical chart review of 134 patients undergoing either high-frequency jet ventilation and microwave ablation (n = 45), high-frequency jet ventilation and irreversible electroporation (n = 44), or conventional ventilation and microwave ablation (n = 45) was performed. The proportion of patients with at least one episode of systolic arterial pressure 140-160, 160-180 or >180 mmHg during early recovery and the impact of ventilation method was studied.

RESULTS

Out of 134 patients, 100, 75 and 34 patients had at least one episode of mild, moderate and severe hypertension. Microwave ablation, as well as high frequency jet ventilation, was associated with an increased odds ratio for post-operative hypertension. The proportion of patients with at least one severe hypertensive event was 18/45, 9/44 and 7/45, respectively.

CONCLUSION

Both ventilation and ablation technique had an impact on post-operative hypertensive episodes. The microwave ablation/high-frequency jet ventilation combination increased the risk as compared with irreversible electroporation/high-frequency jet ventilation and microwave ablation/conventional ventilation.

Reducing kidney motion: optimizing anesthesia and combining respiratory support for retrograde intrarenal surgery: a pilot study

BACKGROUND

One of the greatest challenges presented with RIRS is the potential for movement of the stone within the operative field associated with diaphragm and chest respiratory excursions due to mechanical ventilation. To overcome this challenge, we propose in this pilot study a new general anesthesia technique combining high frequency jet ventilation (HFJV) with small volume mechanical ventilation (SVMV). Data regarding safety, feasibility and surgeons' impression was assessed.

METHODS

Patients undergoing RIRS for kidney stones from November 2017 to May 2018 were prospectively recruited to participate in the study. In each case after the beginning of general anesthesia (GA) with mechanical ventilation (MV) surgeons were asked to assess the mobility of the operative field and conditions for laser lithotripsy according to the developed questionnaire scale. The questionnaire consisted of 5 degrees of assessment of kidney mobility and each question was scored from 1 to 5, 1 being very mobile (extremely poor conditions for dusting) and 5 completely immobile (Ideal conditions for dusting). After the assessment GA was modified with combined respiratory support (CRS), reducing tidal volume and respiratory rate (small volume mechanical ventilation, SVMV) and applying in the same time transcatheter high frequency jet ventilation (HFJV) inside the closed circuit. After beginning of CRS, surgeons were once again asked to assess the mobility of the operative field and the conditions for laser lithotripsy. Main ventilation parameters were recorded and compared in both regimens.

RESULTS

A total of 38 patients were included in the study. The mean age was 49 (range 45-53) with a mean stone size of 10 mm (range 10-14) and Hounsfield unit of 1060 (range 930-1190). All patients underwent successful RIRS and no intraoperative complications occurred throughout the duration of the study. A statistically significant difference between ventilation parameters prior to and after CRS institution was detected in all cases, however their clinical impact was negligible. Despite this, assessment via the questionnaire scale point values varied significantly before and after the application of CRS and were 2.3 (2.1; 2.6) and 3.8 (3.7; 4.0) respectively (p < 0.001).

CONCLUSIONS

The novel combined respiratory approach consisting of HFJV and SVMV appears to provide better conditions for stone dusting through reduced respiratory kidney motion and is not associated with adverse health effects or complications.

TRIAL REGISTRATION

NCT03999255 , date of registration: 25th June 2019 (retrospectively registered).

High frequency jet ventilation for motion management during ablation procedures, a narrative review

BACKGROUND

High frequency jet ventilation (HFJV) is a method of ventilation that has gained renewed interest over the recent years as it can reduce organ movement to near static conditions, thus enhancing surgical precision in minimal invasive procedures, for example, ablation procedures for atrial fibrillation and solid organ tumours. The aim of this review was to create a summary of the current evidence concerning the clinical use of HFJV for ablative procedures.

METHOD

PubMed was searched for the key words high frequency ventilation and ablation January 1990-December 2016.

RESULT

The search initially identified 34 papers, 14 met the inclusion criteria. Articles in other languages than English (n = 1), comments regarding other articles (n = 4) and articles that did not include HFJV or ablative procedures (n = 15) were excluded. Two articles were added from references in papers included from the primary search. Sixteen studies were finally included in the review; four updates/reviews and 12 papers with results from studies of HFJV on humans, with a total of 889 patients; 498 patients ventilated with HFJV and 391 controls. There were no randomised studies. The overall scientific quality of the studies was low.

CONCLUSION

There is a lack of well-designed studies evaluating HFJV during ablation procedures. The available information, while sparse, supports the effect of less tissue movement, resulting in better surgical precision and outcome; such as shorter procedural time, fewer shock waves (ESWL) and less recurrence of atrial fibrillation. Randomised controlled studies are needed in this promising area of research to prove its superiority to standard ventilation.

High-Frequency Ventilation in Newborn Infants

In the past mechanical ventilation always mimicked the tidal volumes and ventilatory frequencies of normal breathing. Recently, there has been great interest in techniques that use rapid rates (60 to 3,000 per minute) and tidal volumes approximating dead space. These techniques are known collectively as high-frequency ventilation, although they differ in circuit design, use, potential complications, and mechanism of gas transport. High-frequency ventilation can be divided into four categories: (1) high-frequency positive pressure ventilation, (2) high-frequency jet ventilation, (3) high-frequency oscillatory ventilation and high-frequency flow interruption, and (4) high-frequency chest wall oscillation. In this review we discuss the similarities and differences of these high-frequency techniques, their clinical applications, and some physiological mechanisms involved in gas transport.

Clinical Use of Nonconventional Modes of Ventilator Support

High-frequency oscillatory ventilation (HFOV) is now a mainstay of respiratory care for the neonatal patient. In this chapter, we will define HFOV as those ventilators with a “true” active expiratory phase created by a piston or diaphragm. Jet ventilation and flow interrupters are discussed elsewhere in this book.

La eterna promesa de la ventilación de alta frecuencia

High frequency oscillatory ventilation (HFOV) is based on the application of continuous pressure in the respiratory system, which assures oxygenation, on which a small oscillation that permits ventilation is added. Although this ventilation form seems to comply with the requirements necessary to minimize the pulmonary lesion associated to mechanical ventilator-induced lung injury in acute lung injury, as several experimental studies suggest, its advantages in the clinical practice must still be demonstrated. Part of this lack of evidence is due to methodological problems of the studies published. However, the major limitation is that it has not been compared against a conventional ventilation strategy with low volumes/pressures. At present, it seems that high frequency ventilation is limited to cases refractory to conventional ventilation. A more extensive knowledge on how to optimize high frequency ventilation is needed before proposing clinical trials having greater scope.

High-frequency oscillation in children after Fontan operation

OBJECTIVE: The increase in intrathoracic pressure produced by positive-pressure ventilation has been shown to have an adverse effect on pulmonary blood flow after Fontan operations. OBJECTIVE: The main objective was to compare the hemodynamic effect of high-frequency oscillation ventilation (HFOV) with intermittent positive-pressure ventilation (IPPV) in children after Fontan operations. DESIGN: Prospective study. SETTING: Department of pediatric critical care in a tertiary care, university-based children's hospital. PATIENTS: Five children (age, 2.3 +/- 0.3 yrs) in the early period after Fontan operations. INTERVENTION: After a short period of stabilization after surgery using conventional IPPV, baseline data were collected and patients were converted to HFOV. After a short period of stabilization using HFOV, a second series of measurements were performed and patients were reconnected to IPPV, after which a third series of measurements were made. Paco(2) and pH were kept unchanged throughout the study. MEASUREMENTS AND MAIN RESULTS: Hemodynamic and respiratory variables were obtained at each time point (IPPV1, HFOV, and IPPV2). The mean cardiac index at baseline (IPPV1) was 3.1 +/- 1.1 L/min/m(2); during HFOV, it was 3.2 +/- 1.2 L/min/m(2) (p =.46); and during IPPV2, it was 3.1 +/- 1.1 L/min/m(2). The mean pulmonary vascular resistance values using IPPV1, HFOV, and IPPV2 were 3.0 +/- 1.1, 2.7 +/- 1.3 (p =.21), and 2.6 +/- 1.1 Woods units/m(2), respectively. CONCLUSION: HFOV had no effect on the cardiac output or the pulmonary vascular resistance in a small group of stable patients after Fontan operations.

Transesophageal echocardiographic assessment of pulmonary arterial and venous flow during high-frequency jet ventilation

STUDY OBJECTIVE

To evaluate high-frequency jet ventilation (HFJV) effects on pulmonary arterial and venous flow compared to those of intermittent positive-pressure ventilation (IPPV) by using pulsed Doppler transesophageal echocardiography.

DESIGN

Prospective clinical study.

SETTING

University-affiliated hospital operating room.

PATIENTS

13 ASA physical status I and II patients undergoing lower abdominal or lower extremity surgery.

INTERVENTIONS

PATIENTS had total IV anesthesia with propofol and fentanyl. After anesthesia induction, a transesophageal echocardiography probe was inserted into the esophagus. IPPV (TV, 8-10 mL/kg; respiratory rate, 10-12 cycles/min; I/E ratio, 1:2; FIO(2), 1.0) and HFJV (driving pressure, 0.5-0.6 kgf/cm(2); frequency,3 Hz; I/E ratio, 1:1; FIO(2), 1.0) were performed under hemodynamically stable conditions.

MEASUREMENTS

Pulmonary-arterial-flow velocity, pulmonary-venous-flow velocity, left ventricular short-axis view, and airway-pressure curve were recorded simultaneously. Parameters measured were: hemodynamic variables, arterial blood gases, inspiratory airway pressure; [from pulmonary-arterial-flow velocity] pre-ejection period (PEP), acceleration time (AT), right ventricular ejection time (RVET), and their ratios (PEP/AT, AT/RVET); [from pulmonary-venous-flow velocity] time-velocity integral of the first systolic wave (S1), second systolic wave (S2), and diastolic wave (D), and systolic fraction (integral S1 + S2/S1+ S2 + D); [from M-mode] left-ventricular-end systolic volume, left-ventricular-end diastolic volume (LVEDV), stroke volume, cardiac output, and ejection fraction, using Teichholz's method.

MAIN RESULTS

Peak inspiratory airway pressure during HFJV was significantly lower than that during IPPV. HFJV significantly decreased PEP/AT, correlating positively with pulmonary arterial pressure, and significantly increased AT and AT/RVET, correlating negatively with pulmonary arterial pressure. Systolic fraction, correlating negatively with left atrial pressure, increased significantly during HFJV, as did LVEDV, stroke volume, cardiac output, and ejection fraction.

CONCLUSIONS

Our results suggest that, in comparison to IPPV, HFJV significantly decreases pulmonary arterial pressure and left atrial pressure, resulting in significant increases in cardiac output and ejection fraction in healthy anesthetized adults.

Non-conventional respiratory support modalities applicable in the older child. High frequency ventilation and liquid ventilation

HFV, LV, and several other novel therapies offer promise to adults and children that the mortality associated with respiratory failure may be affected. Although there are several forms of HFV, HFOV is presently gaining favor in the treatment of severe respiratory failure and has generally supplanted HFJV in pediatric critical care. HFOV has the advantage of having an active expiratory phase, which helps to minimize air trapping and better modulate mean lung volume. Ventilators with sufficient power to perform HFOV in adults are currently under investigation, although there is a growing experience in using current ventilators in larger patients. To date, however, demonstration of lowered mortality with HFOV is lacking although intermediate outcome indicators are improved. PLV also offers promise in the treatment of ARF through its drastic ability to improve oxygenation, ventilation, and compliance in many lung injury models. Human trials are presently underway, but the optimal delivery of this novel therapy still necessitates extensive investigation. TLV is likely even more removed from general clinical application given the necessity of developing a new generation of ventilators for the delivery of liquid tidal volumes. How these and other modalities may piece together to improve the condition of our patients who have respiratory failure remains to be seen, but certainly, present and future investigation will be intriguing for years to come.

High-frequency pressure-control ventilation with high positive end-expiratory pressure in children with acute respiratory distress syndrome

OBJECTIVE

Animal models suggest that high-frequency ventilation with low tidal volumes and high positive end-expiratory pressure (PEEP) minimize secondary injury to the lung. We hypothesized that using a high-frequency pressure-control mode of ventilation with high PEEP in children with severe acute respiratory distress syndrome (ARDS) would be associated with improved survival.

DESIGN

The study was a retrospective and prospective clinical study at a 24-bed tertiary care pediatric critical care unit. Fifty-three patients with severe ARDS were studied during a 37-month period, 30 prospectively and 23 retrospectively. Severe ARDS was defined as (1) rapid onset of severe bilateral infiltrates of noncardiac origin, (2) partial pressure of oxygen (arterial)/fraction of inspired oxygen less than 200 on PEEP of 6 cm H2O or more for 24 hours or longer, and (3) Murray disease severity score greater than 2.5. All patients meeting these criteria underwent ventilation in the pressure-control mode; the protocol for ventilation had the following general guidelines: (1) fraction of inspired oxygen limited to 0.5, (2) mean airway pressure titrated with PEEP to maintain arterial partial pressure of oxygen of 55 mm Hg or greater (7.3 kPa), (3) peak inspiratory pressure minimized to allow hypercapnia (arterial partial pressure of carbon dioxide, 45 to 60 mm Hg (6.0 to 8.0 kPa), and (4) ventilator rates of 40 to 120/min. Percutaneous thoracostomy and mediastinal tubes were placed for treatment of air leak.

RESULTS

The survival rate was 89% (47/53) in children with severe ARDS. Nonsurvivors had significantly higher peak inspiratory pressures (75 vs 40 cm H2O, p = 0.0006), PEEP (23 vs 17 cm H2O, p = 0.0004), mean airway pressure (40 vs 28 cm H2O, p = 0.04), alveolar-arterial oxygen gradient (579 vs 540 mm Hg, p = 0.03), and oxygenation index (43 vs 19, p = 0.0008) than survivors. Air leak was present in 51% of patients; there was no difference in the incidence of air leak between survivors and nonsurvivors (p = 0.42).

CONCLUSIONS

The high-frequency positive-pressure mode of ventilation was safe and was associated with an improved survival rate (89%) for children with severe ARDS. Limitation of both inspired oxygen and tidal volume, along with aggressive treatment of air leak, may have contributed to the improved survival rate.

New concepts in the treatment of children with acute respiratory distress syndrome

Recent advances in mechanical ventilation, accompanied with a better understanding of the pathophysiology of ARDS, have resulted in a brighter outlook for the child who acquires this still dreaded disease. A greater understanding of the pathophysiology of ARDS has led to a heightened awareness that the care of these patients should be more than just supportive. The potential for exacerbation of lung injury by mechanical ventilation is real. Many new therapies are being evaluated for the treatment of ARDS; all are intended to reduce ventilator-induced injury. With the recognition of "volutrauma" as a serious complication of mechanical ventilation in ARDS, the mode of ventilation used should minimize the potential for this complication in a child with signs of progressive lung disease requiring mechanical ventilation. Optimal integration of the many new techniques into the treatment of pediatric ARDS will require more research and experience. Surfactant replacement in ARDS as an adjunct to the basic care of these patients may be beneficial. Liquid ventilation is another exciting new ventilation technique that has a significant protective effect in animal models of ARDS. Other therapies, such as tracheal gas insufflation, or other new modes of ventilation may also improve outcome. Techniques of high-frequency ventilation and ECMO in the treatment of children already show potential for improved outcome. The decision between using ECMO or "nonconventional" forms of mechanical ventilation should be considered carefully, after the morbidity of the procedures, the duration of therapy, and the cost have been weighed. Centers with experience using ECMO in the setting of pediatric ARDS have better results than those where ECMO is infrequently used for this purpose. It is imperative that future studies of both mechanical ventilation and ECMO describe ventilation strategy and prospectively identify protocols or algorithms for ventilator management. Coupled with severity scores, ventilator techniques and ECMO can then be systematically compared in children with ARDS.

High frequency jet ventilation in tracheobronchoplasty. An experimental study

An experimental study on dogs was performed to determine the optimal driving gas pressure and frequency in high-frequency jet ventilation (HFJV) during tracheobronchoplasty. Right thoracotomy, sleeve upper lobectomy and sleeve pneumonectomy were done with various HFJV settings and insufflation via a 3.0 mm catheter with 2.4 mm internal diameter. In sleeve lobectomy, HFJV to the reconstructed lung improved the peroperative ventilation. Driving gas pressure 0.5-1.0 kg/cm2 and frequency 6-10 Hz were the optimal settings for sleeve lobectomy. In sleeve pneumonectomy adequate ventilation and oxygenation were achieved with HFJV to the contralateral lung, and the optimal HFJV settings were 1.0-2.0 kg/cm2 driving gas pressure and 6-10 Hz frequency.

Evaluation of high-frequency jet ventilation in oxygenation through an artificial membrane lung

The membrane oxygenator often develops impaired gas exchange after prolonged use because plasma proteins adhere to the membrane's surface and leak through its micropores. This study was performed to examine the efficacy of high-frequency jet ventilation (HFJV) in minimizing these problems in a "flat plate" type of membrane oxygenator. We first vibrated the membrane of the oxygenator by HFJV from 1 to 10 Hz to find the frequency most effective for optimal gas exchange in animals with partial extracorporeal circulation. These studies suggested that 6 Hz HFJV was preferable in our model. We subsequently performed in vivo extracorporeal oxygenation in dogs for 8 h using the membrane oxygenator with or without 6 Hz HFJV. Although the gas exchange capacity within the first 8 h was similar in the two groups, after 6 h a significant decrease in the red blood cell count and in the hematocrit was found in the group not receiving HFJV. Scanning electron microscopic examination of the membranes after 8 h of use disclosed that the membrane from the group receiving HFJV had less plasma protein and fibrin adhesion than that from the group not receiving HFJV. Moreover, it appears that with prolonged extracorporeal oxygenation, 6 Hz HFJV also protects against a decrease in the hematocrit of the passed blood and might lead to enhanced gas exchange. Our data suggest that good gas exchange can be maintained for periods even longer than 8 h if HFJV is used in conjunction with the membrane oxygenator.

The pulmonary physician and critical care. 2. The injured lung: conventional and novel respiratory therapy

Several alternatives to conventional ventilation in acute lung injury are now available and have been investigated to a varying degree. The assessment of all such techniques is limited by difficulties in designing proper comparative studies and by the time needed to recruit a large number of appropriate patients with acute lung injury. A common theme of lung volume maintenance combined with strategies designed to limit the extent of ventilator induced lung damage has emerged and should encourage reassessment of the conventional approach. The results of several large prospective comparative studies are eagerly awaited. Meanwhile we may reasonably suggest that improvements in respiratory support, together with advances in microbiological and pharmacological treatment, have the potential for improving the persistently disappointing survival rate in acute lung injury.

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.

Extracorporeal carbon dioxide removal performed with surface-heparinized equipment in patients with ARDS

To avoid the drawbacks of systemic anticoagulation during prolonged extracorporeal circulation in patients with adult respiratory distress syndrome (ARDS) a heparinization technique has been developed by which partially degraded heparin can be covalently end-point attached to the surface of the equipment constituting the extracorporeal circuit (Carmeda Bio-Active Surface, CBAS) thereby localizing the anticoagulatory effect. Since 1986 we have used extracorporeal circuits and membrane lungs coated with the CBAS for extracorporeal lung assistance (ECLA) in 14 patients suffering from ARDS. The patients were on ECLA for 3 to 55 days with a survival rate of 43%. Our experience so far is that by using equipment coated with CBAS it is possible to perform long-term extracorporeal circulation with a minimum of intravenously administered heparin, thus avoiding the risk of major coagulation defects.

Comparison of tidal ventilation and high-frequency jet ventilation before and after cardiopulmonary bypass in dogs using two-dimensional transesophageal echocardiography

This study compared the use of high-frequency jet ventilation (HFJV) and tidal ventilation (TV) in a group of dogs with induced global myocardial ischemia before and after cardiopulmonary bypass. Transesophageal echocardiography was used to determine whether HFJV with its lower airway pressures could improve cardiac performance. The surgical procedure was separated into four study periods: closed chest before bypass, open chest before bypass, open chest after bypass, and closed chest after bypass. During each of these study periods, the dogs were randomly ventilated with alternate periods of TV and HFJV to maintain the PaCO2 at 34.3 +/- 3.3 mm Hg (mean +/- SEM). Cardiac output, stroke volume, systemic mean blood pressure, left ventricular ejection fraction, left ventricular end-diastolic volume, left ventricular dP/dt, left ventricular stroke work, and expiratory volumetric flows were higher during HFJV, whereas airway pressures and pulmonary vascular resistance were lower. Increases in cardiac output and stroke volume during HFJV were due to a combination of improved left ventricular contractility indicated by increased LV dP/dt and increased left ventricular end-diastolic volume accompanying decreased airway pressures. These data indicate that HFJV with its lower airway pressure is associated with significantly less impairment of cardiovascular function than TV in dogs with induced global myocardial ischemia.

An experimental study of different ventilatory modes in piglets in severe respiratory distress induced by surfactant depletion

In 19 anesthetized piglets 3 ventilatory modes were studied after inducing pulmonary insufficiency by bronchoalveolar lavage by the method of Lachmann. The lavage model was considered suitable for reproduction of severe respiratory distress. This model was reproducible and stable with respect to alveolar collapse, decrease in static chest-lung compliance and increase in extravascular lung water. The ventilatory modes studied were volume-controlled intermittent positive-pressure ventilation (IPPV), pressure-controlled inverse ratio ventilation (IRV), and pressure-controlled high-frequency positive-pressure ventilation (HFPPV). The 3 ventilatory modes were used in random sequence for at least 30 min to produce a ventilatory steady state. Ventilation with no PEEP, permitting alveolar collapse, was interposed between each experimental mode. The ability to open collapsed alveoli, i.e. alveolar recruitment, was different. The recruitment rate for IPPV was 74%, but for IRV and HFPPV it was 95%, respectively. Although IRV provided the best PaO2, this was at the expense of high airway pressures with circulatory interference and reduced oxygen transport. In contrast to this, HFPPV provided lower airway pressures, less circulatory interference and improved oxygen transport. In the clinical setting there might be negative effects on vital organs and functions unless the ventilatory modes are continuously and cautiously adapted to the individual requirements in different phases of severe respiratory distress. Therefore, one ventilatory strategy could be to "open the airways" with IRV, but then switch to HFPPV in an attempt to maintain the airways open with lesser risk of barotrauma and with improved oxygen transport.

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 oscillatory ventilation

The improved survival rate of premature infants with respiratory failure is attributable to advances in mechanical ventilation, although an adverse consequence has been an increased incidence of bronchopulmonary dysplasia (BPD) (1;32). Positive pressure ventilation with its attendant “barotrauma” is suspected in the causation of BPD. While many attempts to alter respirator variables, such as pressure and time components, have produced optimal patterns for gas exchange, evidence is lacking to support any one pattern that minimizes the incidence of chronic lung injury. The high incidence of BPD has promoted a search for alternative methods of ventilation that might reduce lung injury through a reduction in peak pressure applied to the lung. Additional motivation has come from the need for oxygenation when mechanical ventilation has failed or pulmonary interstitial emphysema has developed. Less compelling reasons have come from the desire to avoid high swings in thoracic pressure that might adversely affect cardiac output, venous return, and cerebral blood flow.

Modified jet ventilation during total laryngectomy: a prospective study using pulse oximetry and a pressure regulator

A method of jet ventilation during total laryngectomy is described. During the construction of the terminal tracheostomy, a small metal tube is used, instead of the traditional tracheostomy tube, to provide intermittent jet ventilation down the distal trachea. A pressure regulator is also employed to choose a driving pressure best suited to the chest and lung compliance of each patient. Excellent surgical access for tracheo-cutaneous anastomosis is achieved. Satisfactory ventilation during the jet period is also confirmed by unaltered PaCO2 and increased PaO2 levels. The use of pulse oximetry as a non-invasive and continuous monitor of arterial oxygenation is a simple alternative to arterial blood sampling.

In what respect does high frequency positive pressure ventilation differ from conventional ventilation?

The original rationale for HFPPV was that under certain conditions adequate alveolar ventilation could be achieved with high ventilatory frequencies and small tidal volumes. It was theorized further that increased ventilatory frequencies and low tidal volumes would decrease the airway pressures, barotrauma, and cardiovascular and other systemic consequences seen with conventional mechanical ventilation. The first clinical applications of HFPPV were in bronchoscopy and laryngoscopy for diagnostic and/or therapeutic purposes. Apart from these endoscopic applications, volume-controlled HFPPV has been compared with conventional ventilation in upper abdominal surgery and coronary artery bypass grafting. The possible advantages of HFPPV over conventional volume-controlled ventilation in the intensive care setting are still unclear. Provided that the mean lung volumes are similar, oxygenation in acute respiratory failure is similar with both ventilation methods. Although the role of HFPPV in the management of pulmonary diseases still remains to be clarified, it does provide effective ventilation in selected types of patients needing ventilatory support. New modes of pressure-controlled ventilation have not resolved all clinical problems in severe ARDS and/or acute respiratory failure. The search for means of optimal ventilatory support with minimal complications must continue, as conventional ventilation does not always offer the best treatment.

Effect of sternotomy and cardiopulmonary bypass on airway pressures and respiratory mechanics during high frequency ventilation

The airway pressures at ventilatory frequencies of 15, 60, 100, 120 and 150 breaths per minute were measured in eight adult patients undergoing coronary artery bypass grafting. Measurements were made perioperatively at four stages: precardiopulmonary bypass with the chest closed, precardiopulmonary bypass with the chest open, postcardiopulmonary bypass with the chest open and postcardiopulmonary bypass with the chest closed. In five patients thoracic compliance and airways resistance were also measured at these times. Neither sternotomy nor cardiopulmonary bypass made any significant difference to the airway pressures during normal and high frequency ventilation, nor were lung mechanics affected.

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.

High-frequency ventilation

Over the last six years high-frequency ventilation has been extensively evaluated both in the clinical and laboratory settings. It is now no longer the great mystery it once was, and it is now no longer believed (as many had hoped), that it will solve all the problems associated with mechanical pulmonary ventilation. Although the technique is safe and appears to cause no harm even in the long term, it has not yet been shown to offer any major advantages over conventional mechanical ventilation.

Trials of high frequency jet ventilation in preterm infants with severe respiratory disease

Nine preterm newborn infants were maintained on conventional mechanical ventilation for respiratory diseases were given high frequency jet ventilation in the same inspired FiO2 for short periods (10-120 min). Lower mean airway pressures were used in high frequency jet ventilation (0.70 +/- 0.2 kPa versus 0.96 +/- 0.2 kPa in intermittent positive pressure ventilation), and peak inspiratory pressures were reduced from 2.06 +/- 0.4 to 1.38 +/- 0.24 kPa. Respiratory and haemodynamic data were compared with those obtained in intermittent positive pressure ventilation, PaO2 and PCO2 were similar, while an increase in pH and reduction of central venous pressure were observed during high frequency jet ventilation. This preliminary study indicates that high frequency jet ventilation provides good ventilatory support, at least for short periods, with reduced airway pressures, and could be a promising technique for prevention of acute and chronic pulmonary barotrauma.

High frequency jet ventilation. A method for thoracic surgery

High frequency jet ventilation for thoracic surgery offers some practical advantages over intermittent pressure ventilation using bronchial tubes. Satisfactory blood gases were obtained in 50 patients and good operating conditions were provided.

Low-compression high frequency positive pressure ventilation (HFPPV): a review

HFPPV is not a jet technique, as it works without air entrainment. A low-compression ventilator, with a conventional rate of 20/min, provides efficient intrapulmonary gas mixing; however, with higher rates of 60-100/min the high inspiratory flow improves transfer/mixing of gas in the conducting airways. HFPPV for endoscopy is now established in clinical practice, and its use for treatment of bronchopleural fistulas in documented. In acute respiratory failure, volume-controlled HFPPV seems to be as efficient and as well accepted by the patients as conventional intermittent positive pressure ventilation. It is important to note that enhanced gas mixing and improved gas distribution during HFPPV in acute respiratory failure patients are accomplished with lower mean airway pressure, thereby reducing barotrauma. In the future, versatile low-compression ventilators for volume-controlled IPPV and HFPPV will hopefully improve safety, efficiency and patient acceptance of mechanical ventilation in acute respiratory failure.

One-lung high-frequency ventilation for tracheoplasty and bronchoplasty: a new technique

Major airway surgery requires the maintenance of adequate ventilation and oxygenation during the period of resection and reconstruction, as well as an unobstructed surgical field and optimal access to the airway's circumference. High-frequency positive-pressure ventilation (HFPPV) at a frequency of 1 Hz (60 breaths/min) or more, along with a small tidal volume (50 to 250 cc), provides adequate ventilation and oxygenation with minimal impairment of pulmonic and systemic circulatory functions. We have used HFPPV of one lung through a 2 mm internal diameter catheter in six patients (three undergoing right sleeve pneumonectomies, two having carinal tumor resections, and one having tracheal resection). High-frequency positive-pressure ventilation of the left lung provided continuous and adequate ventilation and oxygenation during the period of resection and reconstruction of the airways, while the small catheter permitted unimpaired visualization and adequate access to the operative site.

High-frequency jet ventilation: theoretical considerations and clinical observations

High-frequency jet ventilation (HFJV) described a technique of mechanical respiratory support based on the delivery of gases under conditions of constant flow and low pressure. Among the benefits ascribed to HFJV are lessened interference with hemodynamic function and reduced danger of barotrauma. The theoretical and technical aspects of HFJV are discussed and the clinical experience with 39 patients in respiratory failure reported. Synchronization of HFMV with heart rate was attempted in three patients. Cardiac output and ejection fraction increased in all of them. At present, results suggest that HFJV may be the ideal form of support for patients with major airway disruption. The available data also indicated that extensive clinical trials are warranted to define advantages and limits of this form of ventilation.

Tidal volume and frequency dependence of carbon dioxide elimination by high-frequency ventilation

Six patients with chronic respiratory failure received mechanical ventilation with tidal volumes less than or equal to the dead-space volume, at frequencies of 30 to 900 breaths per minute. The rate of elimination of carbon dioxide from the ventilator system during a brief trial of high-frequency ventilation accurately predicted the long-term effectiveness of a given combination of frequency and tidal volume. Below frequencies of about 200 breaths per minute, the volume of carbon dioxide eliminated from these patients was most strongly related to the product of frequency and tidal volume; at higher frequencies, carbon dioxide elimination was determined by the tidal volume and was independent of frequency. These results suggest that although the effectiveness of high-frequency ventilation is primarily a function of the product of tidal volume and frequency, above a critical frequency the mechanical characteristics of the lung reduce gas transport by limiting the volume transmitted to the periphery of the lung.

Effects of frequency, tidal volume, and lung volume on CO2 elimination in dogs by high frequency (2-30 Hz), low tidal volume ventilation

Recent studies have shown that effective pulmonary ventilation is possible with tidal volumes (VT) less than the anatomic dead-space if the oscillatory frequency (f) is sufficiently large. We systematically studied the effect on pulmonary CO2 elimination (VCO2) of varying f (2-30 Hz) and VT (1-7 ml/kg) as well as lung volume (VL) in 13 anesthetized, paralyzed dogs in order to examine the contribution of those variables that are thought to be important in determining gas exchange by high frequency ventilation. All experiments were performed when the alveolar PCO2 was 40 +/- 1.5 mm Hg. In all studies, VCO2 increased monotonically with f at constant VT. We quantitated the effects of f and VT on VCO2 by using the dimensionless equation VCO2/VOSC = a(VT/VTo)b(f/fo)c where: VOSC = f X VT, VTo = mean VT, fo = mean f and a, b, c, are constants obtained by multiple regression. The mean values of a, b, and c for all dogs were 2.12 X 10(-3), 0.49, and 0.08, respectively. The most important variable in determining VCO2 was VOSC; however, there was considerable variability among dogs in the independent effect of VT and f on VCO2, with a doubling of VT at a constant VOSC causing changes in VCO2 ranging from -13 to +110% (mean = +35%). Increasing VL from functional residual capacity (FRC) to the lung volume at an airway opening minus body surface pressure of 25 cm H2O had no significant effect on VCO2.

High-frequency jet ventilation during the treatment of acute fulminant pulmonary edema

High-frequency jet ventilation (HFJV) was used during the treatment of fulminant pulmonary edema in a 45-year-old man so that toxic levels of oxygen could be avoided when conventional methods of ventilation in combination with high levels of PEEP (20 cm H2O) were unsuccessful in raising PaO2. On each of four occasions, HFJV resulted in improved arterial oxygenation when compared with conventional modes.

Prospective clinical comparison of two methods for mechanical ventilation of neonates: rapid rate and short inspiratory time versus slow rate and long inspiratory time

A prospective comparison was made of the clinical courses of two groups of neonates ventilated according to different protocols: one group at rates of 20 to 40/minute with a one-second IT, and the other at a rate of 60/minute and 0.5 second IT. Other ventilator settings were adjusted within protocol limits to maintain desired blood gas values. Mean starting and highest PIP were lower in the rapid rate group. The results showed no difference in mortality, failure to remain within protocol limits, time requiring respiratory treatment or FiO2 more than 0.6, and incidence of PDA or chronic lung disease. There was a difference (P = 0.011) in number of infants developing pneumothoraces (14% in the rapid group vs 35% in the slow group). Rapid rate ventilation can be used to decrease the incidence of pneumothorax, reserving long IT and higher PIP for infants who cannot be oxygenated or ventilated without them.

New parachute cuff and positive end-expiratory pressure to minimize tracheal injury and prevent aspiration

A new parachute cuff has been tested in combination with a positive end-expiratory pressure (PEEP) on mongrel dogs. During positive-pressure ventilation the intracuff and intratracheal pressures showed synchronous, identical pressure variations, and therefore theoretically with this type of cuff the pressure against the tracheal wall would be minimal. The cuff provided a seal against gas leakage from the lungs throughout the entire test period, i.e., for up to 7 h. To avoid aspiration of mouth contents during the passive exhalation phase, different amounts of PEEP were tested. A PEEP of 4.0--8.0 cm H2O always produced a seal against a column of fluid in the mouth exerting a hydrostatic pressure of 5.4--8.8 cm H2O against the cuff. This seal was maintained during the whole test period. No difference in sealing capacity was found when the cuff was used with a normal respiratory frequency (20/min) and with high-frequency positive-pressure ventilation (60/min). When the PEEP is eliminated, e.g., when the respirator is disconnected for suction of the endotracheal tube, the sealing effect will be abolished. As the cuff extends up into the larynx there will be no pooling of fluid above the cuff. The risk of aspiration can therefore be diminished by suction of oral cavity before disconnecting the respirator. With the use of the pneumatic valve principle together with high-frequency positive-pressure ventilation, an open respirator system can produce a continuous PEEP, thereby preventing aspiration even during suctioning of the tracheal tube.