The Hayek oscillator: a new method of ventilation in microlaryngeal surgery

Investigating the effect of materials and structures for negative pressure ventilators suitable for pandemic situation

The onset of the corona virus disease 2019 (COVID-19) pandemic caused shortages in mechanical ventilators (MVs) essential for the intensive care unit (ICU) in the hospitals. The increasing crisis prompted the investigation of ventilators which is low cost and offers lower health complications. Many researchers are revisiting the use of negative pressure ventilators (NPVs), due to the cost and complications of positive pressure ventilators (PPVs). This paper summarizes the evolution of the MVs, highlighting the limitations of popular positive and negative pressure ventilators and how NPV can be a cost-effective and lower health complication solution. This paper also provides a detailed investigation of the structure and material for the patient enclosure that can be used for a cost-effective NPV system using ANSYS simulations. The simulation results can confirm the selection and also help in developing a low cost while based on readily available materials. This can help the manufacturer to develop low-cost NPV and reduce the pressure on the healthcare system for any pandemic situation similar to COVID-19.

Novel Use of Biphasic Cuirass Ventilation During Definitive Radiation Therapy: A Technical Report

The use of biphasic cuirass ventilator supported radiation therapy has never been documented. We present the first technical report here. A 57-year-old man with obstructive sleep apnea presented with a T0N1M0 right sided, human papillomavirus related head and neck cancer diagnosed on excisional lymph node biopsy. On further workup, the cancer was found to have originated in the right tonsil and was staged as T1N1. The patient started definitive treatment with concurrent chemo-radiation therapy, but after 5 treatments was no longer able to lay in a supine position for treatment. Diagnostic imaging workup eventually revealed an idiopathic right sided hemi-diaphragm eventration. After consultation with cardiology, pulmonology, and head and neck surgery, recommendation was made for tracheostomy to tolerate supine radiotherapy position, but the patient refused. Instead, computed tomography simulation for radiotherapy replanning was performed using a combination of biphasic cuirass ventilation, home continuous positive airway pressure and oxygen. The patient then tolerated definitive treatment to a dose of 69.96 Gray in 33 fractions with concurrent chemotherapy and experienced no unexpected side effects. Although complex, daily treatment setup was consistent. Daily onboard imaging was precise and accurate. The patient continues to follow up with radiation oncology, medical oncology, and pulmonology. This is the first use of biphasic cuirass ventilator supported radiotherapy reported in the scientific literature. Although daily treatment setup is complex, its use could be considered in patients unable to tolerate radiation therapy treatment positioning as an alternative to tracheostomy.

Marked improvement of extensive atelectasis by unilateral application of the RTX respirator in elderly patients

The RTX respirator is a biphasic external cuirass-style ventilator that supports both inspiration and expiration at various cycle rates and pressures, as well as allowing application of the vibration and cough modes. With this respirator, the duration and pressure can be altered in both the inspiratory and expiratory phases, and it can promote the removal of secretions by switching between the vibration mode (which involves external high-frequency oscillation: EHFO) and the cough mode. We used this respirator to remove secretions in two elderly patients with extensive atelectasis. They were nursed in the lateral decubitus position with the cuirass attached to one side of the chest only. The vibration mode removed secretion to reduce the viscosity of secretions and loosen impacted bronchial secretions. The cough mode interrupts the vibration mode and forces secretions towards the pharynx. The lateral decubitus position was useful for postural drainage. The extensive atelectasis of both patients was improved by this procedure. The RTX respirator may be a useful tool for the management of elderly patients with sputum retention.

Biphasic extrathoracic cuirass ventilation for resuscitation

PURPOSES

The MRTX portable lightweight respirator (MRTX) provides noninvasive respiratory support using biphasic extrathoracic ventilation via a cuirass fitted around the patient's chest.

METHODS

MRTX was applied with or without full protective gear, on adult volunteers simulating nerve agent (NA) victims by nonmedical caregivers. Assessment was made based on scores for correct positioning of the cuirass, quality of seal, and rapidness.

RESULTS

For the unprotected and protected personnel, the respective median (+/-95% confidence interval) scores for correct positioning of the cuirass were 2 (1.4-1.9) and 1 (1.2-1.8) (n = 15 per group, P = NS); quality of seal scores were 2 (1.5-2.0) and 2 (1.3-1.8) ( P = NS); and mean (+/-SD) time required for instituting mechanical ventilation was 90.5 +/- 10.9 and 100.3 +/- 7.9 seconds ( P < .05). The respirator was activated at first attempt 11 times in the group of 15 without protective gear and 8 times in the group of 15 with protective gear ( P = NS).

DISCUSSION

Biphasic cuirass ventilation is an easily learned and rapidly applied method suitable for use by nonmedical personnel, even when wearing cumbersome protective gear.

Application of a cuirass and institution of biphasic extra-thoracic ventilation by gear-protected physicians

OBJECTIVES

To evaluate the speed by which cuirass application, followed by biphasic extra-thoracic ventilation, can be instituted by full anti-chemical protective gear-wearing physicians.

MATERIALS AND METHODS

Ten physicians of variable subspecialties applied a cuirass on an adult volunteer and instituted biphasic extra-thoracic ventilation, using the RTX respirator (Medivent, London, UK). Endotracheal (ET) intubation and manual ventilation of a mannequin and its ventilation was comparatively assessed. Performances were conducted in a prospective, crossover, randomized manner. Times to successful applications as well as failure rates were recorded.

RESULTS

Cuirass application was performed more rapidly (102 +/- 9 s, 177 +/- 31 s, respectively, P <.01) and with a slightly lower failure rate than ET intubation.

CONCLUSIONS

Physicians wearing full anti-chemical protective gear applied the cuirass and instituted biphasic extra-thoracic ventilation faster than ET intubation and manual positive pressure ventilation. Extra-thoracic ventilation should be further evaluated as an option for emergent respiratory support during toxic mass casualty events.

Combination of external chest wall oscillation with continuous positive airway pressure

We studied the effects of continuous positive airway pressure (CPAP) on pulmonary gas exchange during external chest wall oscillation (ECWO), and the relationship with obesity, in nine patients with normal body weight (group 'N') and 10 obese patients (group 'O'). During ECWO with CPAP 5, PaCO2 decreased in group 'O' (6.0 (SD 0.8) to 5.6 (0.5) kPa, P<0.05), whereas it increased in group 'N' at all levels (P<0.01). Arterial PO(2) (P<0.001) was greater and PaCO2 (P<0.01) less in group 'N' during CPPV and ECWO plus CPAP. We also compared the haemodynamic effects of ECWO plus CPAP with those of continuous positive pressure ventilation (CPPV). ECWO plus CPAP and CPPV were applied for 30 min to 6 ASA III patients. Cardiac output (CI 2.7 (0.5) vs 2.1 (0.2) litre x min(-1) x m(-2), P<0.05) and stroke volume (SVI 49 (9) vs 32 (6) ml x m(-2), P<0.05) were greater during ECWO plus CPAP than with CPPV. ECWO is less effective in obese individuals than in those with normal body weight, and the effect of CPAP in overweight individuals is small.

Negative pressure ventilation vs external high-frequency oscillation during rigid bronchoscopy. A controlled randomized trial

STUDY OBJECTIVES

To compare the effectiveness of two modalities of external ventilation during rigid bronchoscopy: intermittent negative pressure ventilation (INPV) and external high-frequency oscillation (EHFO).

DESIGN

Prospective, controlled, randomized, nonblinded study.

SETTING

University-affiliated hospital.

PATIENTS

Seventy patients undergoing interventional rigid bronchoscopy for tracheobronchial lesions were enrolled into the study.

INTERVENTIONS

Mechanical ventilation was performed by INPV or EHFO. When pulse oximetry was < 90%, manually assisted ventilation was delivered.

MEASUREMENTS AND RESULTS

Arterial blood gases were sampled preoperatively and intraoperatively. Most patients in both groups had normal intraoperative PaCO(2) (mean, 43. 6 +/- 11.8 mm Hg under EHFO and 37.4 +/- 8.2 mm Hg under INPV; p = 0.012), and acidemia occurred in 9 of 35 patients of EHFO group and in 2 of 35 patients of INPV group (p = 0.049). Hypercapnia (PaCO(2) > 50 mm Hg) was observed in 10 patients under EHFO and in 2 with INPV (p = 0.026). Intraoperative mean PaO(2) was similar (101.4 +/- 52.9 mm Hg with EHFO and 124.2 +/- 50.3 mm Hg with INPV; p = 0.07), but O(2) supply was different (3.5 +/- 2.3 L/min during INPV and 8.5 +/- 6.2 L/min during EHFO; p < 0.001). Intraoperative hypoxemia (PaO(2) < 60 mm Hg) occurred in five patients with EHFO and two with INPV (p = 0.426). Three EHFO patients required manually assisted ventilation (mean, 0.2 +/- 0.9), but no INPV patient did (p = 0.142).

CONCLUSIONS

External negative pressure ventilation appears to be a suitable choice during rigid bronchoscopy: both EHFO and INPV ensure effective ventilation and comfortable operating conditions in the majority of patients. Some patients may receive inadequate ventilation with EHFO, developing respiratory acidosis and requiring manually assisted ventilation. In comparison with INPV, EHFO requires a higher fraction of inspired oxygen.

Transesophageal echocardiographic evaluation during negative-pressure ventilation using the Hayek oscillator

OBJECTIVES

To evaluate the effects of negative-pressure ventilation (NPV) on hemodynamics using the Hayek oscillator (Breasy Medical Equipment, London, UK) and to determine whether the oscillation frequency can modify the hemodynamics, assessed by transesophageal echocardiography (TEE).

DESIGN

A prospective study.

SETTING

A university hospital.

PARTICIPANTS

Eleven American Society of Anesthesiologists class I patients undergoing orolaryngeal surgery.

INTERVENTIONS

The ultrasound probe was inserted under general anesthesia. After baseline measurements were determined during spontaneous breathing, the frequency was changed from 30 to 60 to 120 cycles/min, consecutively. The left ventricular end-diastolic area (LVEDA), end-systolic area (LVESA), fractional area change (LVFAC), and end-systolic wall stress (ESWS) were determined. The velocities of the pulmonary artery (PA) flow, pulmonary venous (PV) flow, and transmitral flow were measured by pulsed Doppler techniques.

MEASUREMENTS AND MAIN RESULTS

PaO2 increased and PaCO2 decreased significantly. NPV caused a significant increase in the LVEDA, whereas it did not significantly change the PA velocity. ESWS, an index of afterload, remained unchanged.

CONCLUSION

The authors conclude that NPV using the Hayek oscillator induces an increase in the LVEDA without any changes in PA velocity, suggesting increased transmural pressure rather than increased preload, and that the three different frequencies do not modify the effects on the hemodynamics.

Ventilation by external high-frequency oscillations improves cardiac function after coronary artery bypass grafting

OBJECTIVE

To compare the effects of ventilation with intermittent positive pressure and external high frequency oscillation by the Hayek Oscillator during the first 5 h after coronary artery bypass grafting.

METHODS

Eleven patients were randomized to intermittent positive pressure ventilation throughout the observation period (5 h), while 13 patients were initially ventilated with intermittent positive pressure ventilation, then by external high-frequency oscillations for 4 h, changing to positive pressure ventilation for the last hour.

RESULTS

Cardiac index, stroke volume index, right ventricular stroke work index, right ventricular end-diastolic volume index and mixed venous oxygen saturation were significantly increased during ventilation with external high-frequency oscillations, and arteriovenous oxygen content difference was significantly reduced. There were no significant inter- or intragroup differences in fluid accumulation, mean arterial blood pressure, arterial blood gases, pulmonary artery pressure, central venous pressure, pulmonary capillary wedge pressure, heart rate, systemic vascular resistance index, pulmonary vascular resistance index, intrapulmonary shunt fraction, right ventricular ejection fraction, right ventricular end-systolic volume index and left ventricular stroke work index.

CONCLUSIONS

Ventilation by external high-frequency oscillations increases cardiac index and improves tissue perfusion. The increased pumping of the heart is probably caused by changes of the intracardiac pressure-volume relationship. The Hayek Oscillator may have distinct cardiovascular benefits as ventilatory assistance in postoperative cardiac surgical patients.

External high frequency oscillation in normal subjects and in patients with acute respiratory failure

External high frequency oscillation was performed on 20 healthy volunteers using a cuirass-based system, the Hayek Oscillator. Five-min periods of oscillation were carried out on each subject at frequencies of 1, 2, 3, 4 and 5 Hz. Effective ventilation was measured in terms of the fall in alveolar partial pressure of carbon dioxide immediately after oscillation. The optimum frequency for oscillation was 1-3 Hz but most of the subjects were adequately ventilated over a wide range of frequencies. Thus, the Hayek Oscillator is capable of adequately ventilating normal subjects by means of chest wall oscillation. We also compared external high frequency oscillation with intermittent positive pressure ventilation in five patients with respiratory failure. Using the same inspired oxygen fraction, the external high frequency oscillation replaced intermittent positive pressure ventilation for a 30-min period. External high frequency oscillation improved oxygenation by 16% and reduced the arterial carbon dioxide by 6%. These preliminary findings suggest that normal subjects and intensive care unit patients can be adequately ventilated by means of external high frequency oscillation.

The use of the Hayek Oscillator during microlaryngeal surgery

An extremely mounted cuirass ventilator, the Hayek Oscillator, was used on 41 patients undergoing surgery to the larynx without the use of tracheal tube. Gas exchange and cardiovascular parameters remained satisfactory during the use of this technique, which offers a significant advance over existing tubeless methods of anaesthesia.

The Hayek oscillator. Nomograms for tidal volume and minute ventilation using external high frequency oscillation

The Hayek Oscillator is a recent development in external high frequency ventilation and is a useful mode of ventilatory support during anaesthesia, in chronic respiratory failure and weaning in intensive care. The Hayek Oscillator is new and its application is growing, as are the number of patients who have benefited from its use. However, there are no clear guidelines on how best to adjust the oscillator to achieve optimum ventilation. A simple method of predicting changes in tidal volume and minute ventilation following adjustment would make the oscillator more useful. We present nomograms for tidal volume, minute ventilation and effective alveolar ventilation when the three variables, oscillator frequency, mean chamber pressure and peak-to-trough pressure span were adjusted. The frequency-tidal volume relationship was unaffected by a mean chamber pressure of 0, -5, -10 cmH2O, but altered with changes in peak-to-trough pressure span. We have also determined the effect of increasing negative extrathoracic pressure on functional residual capacity. The relationship between tidal volume and frequency was non-linear and related to the peak-to-trough pressure span. Mean functional residual capacity significantly increased from 2.25 l (SEM 0.10) without the cuirass at rest to 2.61 l (SEM 0.14) at -10 cmH2O (p < 0.05; n = 5) and 2.47 (SEM 0.12) at -20 cmH2O of mean chamber pressure. Vital capacity was unchanged by increasing extrathoracic pressure as was total lung capacity.