A pressure regulator for the cuff of a tracheal tube

A regulator is described for the maintenance of a constant pressure difference above airway pressure during positive pressure ventilation in a cuffed tracheal tube. It comprises a tubular threshold valve which is powered by the anaesthetic gas supply source to a breathing system. The valve is interposed between the anaesthetic gas supply machine and the breathing system creating a pressure differential. The upstream pressure is transmitted to the pilot tube supplying the cuff of a tracheal tube via an upstream connection. The valve is suitable only for breathing systems that require a constant gas supply. The regulator was evaluated during anaesthesia, using a modified Mallinkrodt Hi-Lo jet ventilation tube to obtain simultaneous pressure measurements within the cuff and the lumen of the tracheal tube. A greater pressure was demonstrated in the cuff than in the airway and the two traces were approximately parallel throughout the respiratory cycle. The device should prevent excessive cuff inflation pressure and solves the problem of forgetting to let the cuff down before extubation.     

Biphasic positive airway pressure (BIPAP)--a new form of augmented ventilation

Two modes of combining spontaneous breathing and mechanical ventilation are already in use: periodic mechanical support always followed by a period of spontaneous breathing (intermittent mandatory ventilation; IMV) and mechanical support of each spontaneous breath (inspiratory assistance; IA). Biphasic positive airway pressure (BIPAP), in contrast, is based on neither of the above mentioned principles. It is rather a mixture of pressure controlled (PC) ventilation and spontaneous breathing, which is unrestricted in each phase of the respiratory cycle. The BIPAP circuit switches between a high (Phi) and a low (Plo) airway pressure level in an adjustable time sequence. At both pressure levels the patient can breathe spontaneously in a continuous positive airway pressure system (CPAP). The volume displacement caused by the difference between Phi and Plo and the BIPAP frequency (F) contribute the mechanical ventilation to total ventilation. Duration of the Phi and the Plo phases can be independently adjusted. Similar to the I:E ratio during controlled ventilation, the phase time ratio (PhTR) is calculated as the ratio between the durations of the two pressure phases. A PhTR greater than 1:1 is called IR-BIPAP. A BIPAP system can be set up either as a continuous flow system, or as a demand valve system. A continuous-flow BIPAP system consists of a high-flow CPAP system, a reservoir bag, and a pneumatically controlled membrane valve in the expiratory limb. A magnetic valve operated by an impulse generator switches between Phi and Plo, controlling the pop-off pressures of the expiratory valve.(ABSTRACT TRUNCATED AT 250 WORDS)     

A UNIVERSAL VALVE FOR ANAESTHETIC CIRCUITS

During intermittent positive pressure respiration, volume-controlledrather than pressure-controlled ventilation is preferred. Toaccomplish volume-controlled ventilation, a safe, efficient,universal valve has been designed. This valve has an adequatelylow opening pressure and an automatic exit closure when desired.     

Decreases in ventricular volume correlate with decreases in ventricular pressure in idiopathic normal pressure hydrocephalus patients who experienced clinical improvement after implantation with adjustable valve shunts

OBJECTIVE: This retrospective study examined whether changes in ventricular volume correspond with changes in adjustable valve pressure settings in a cohort of patients who received shunts to treat idiopathic normal pressure hydrocephalus. We also examined whether these pressure-volume curves and other patient variables would co-occur with a positive clinical response to shunting. METHODS: We selected 51 patients diagnosed with idiopathic normal pressure hydrocephalus who had undergone implantation of a Codman Hakim programmable valve (Medos S.A., Le Locle, Switzerland). Clinical data were gathered from the patients' records and clinical notes by an investigator blinded to patients' ventricular volumes. Ventricular volume was measured using 3D Slicer, an image analysis and interactive visualization software package developed and maintained at the Surgical Planning Laboratory at Brigham and Women's Hospital. RESULTS: Eighty-six percent of patients with gait disturbance at presentation showed improvement of this symptom, 70% experienced improvement in incontinence, and 69% experienced improvement in dementia. For the group showing 100% clinical improvement, the correlation coefficient of average changes in valve pressure over time (delta P/delta T) and average changes in ventricular volume over time (delta V/delta T) were high at 0.843 (P < 0.05). For the group experiencing no or only partial improvement, the correlation coefficient was 0.257 (P = 0.32), indicating no correlation between average delta V/delta T and average delta P/delta T for each patient. CONCLUSION: This was a carefully analyzed modeling study of idiopathic normal pressure hydrocephalus treatment made possible only by adjustable valve technology. With careful volumetric analysis, we found that changes in ventricular volume correlated with adjustments in valve pressure settings for those patients who improved clinically after shunting. This suggests that positive clinical responders retained parenchymal elasticity, emphasizing the importance of dynamic changes in this cohort.     

搏动辅助血泵专用的蝴蝶瓣离体性能测试

目的：对已设计制成的低成本搏动血泵专用瓣膜蝴蝶瓣（butterfly valve,B-Y)按ISO5840进行国际规范化的离体性能测试。方法：先对B－Y瓣进行物理性能测试,然后根据ISO5840的要求用特殊仪器对3枚B－Y瓣作静态及动脉性能测试,其均值与进行同样测试的2种美国进口植入型瓣膜Bjork-Shiley(B-S)瓣和Medtronic-Hall(M-H)瓣作比较。结果：B－Y瓣的物理性能符合临床要求,在静态测试中2枚B－Y瓣膜片过薄,在12mmHg（1kPa=7.5mmHg)水压下有下凹内翻产生较多静止泄漏量。动态测试方面无搏动流中B－Y瓣的跨瓣压力落差及搏动流时跨瓣正压压力阶差均较B－S瓣和M－H瓣膜略高,但其关闭回流量远较B－S瓣与M－H瓣为低,其舒张泄漏量与B－S瓣相仿,而明显低于M－H瓣。结论：B－Y瓣的水流阻力较进口瓣膜为高,但在临床允许范围以内。其总反流量（关闭回流量、舒张泄漏量）明显低于进口瓣膜,保证了瓣膜的效率和耐用性,潜在溶血程度亦因而轻微。B－Y瓣由于结构简单,成本低廉,却有与进口植入型瓣膜相仿的功能,是其主要特点,适合短期辅助循环的临床应用。     

Use of the Inspiron nebuliser during continuous positive airway pressure ventilation

The Inspiron Nebuliser 002305 with air entrainment was assessed as a gas delivery device in a continuous positive airway pressure system. Inspired oxygen concentrations, total gas flows and pressures within the system were measured over a range of settings, with and without positive and expiratory pressure. Inspired oxygen concentrations and total flows were completely disrupted when a positive and expiratory pressure valve was applied, and the system failed to generate continuous positive airway pressure. We would not therefore recommend the Inspiron nebuliser as a gas delivery system for continuous positive airway pressure.     

The mechanism of opening of the aortic valve.

The mechanism of opening of the aortic valve was investigated in dogs by attaching radiopaque markers to the commissures and the leaflets. Analysis of abnormal cardiac cycles demonstrated that, when the ventricular pressure first equalled the aortic pressure, the intercomissural distances increased 9 percent, and the valve opened with a stellate orifice without forward flow and without a rise in aortic pressure. Further opening of the aortic valve was dependent on forward flow over a narrow range. A new mechanism of aortic valve opening is proposed. This mechanism results in minimal flexion stresses on the leaflets and is important for the longevity of the normal aortic valve. It can occur only if the leaflets arise from an expansile aortic root.     

Influence of fixation conditions on the performance of glutaraldehyde-treated porcine aortic valves: towards a more scientific basis.

To maintain optimum mechanical properties in glutaraldehyde-treated heart-valve tissue the full collagen crimp geometry originally present in the relaxed fresh tissue should be retained. By varying the pressure at which glutaraldehyde fixation is carried out, considerable alterations to this crimp geometry can be achieved. The mechanical stiffness of the preserved tissue is consequently affected, and this in turn has a striking influence on both the opening behaviour of the valve and the degree of strain localisation in the leaflet tissue. A pressure of 100 mmHg eliminated the collagen crimp geometry entirely, and this resulted in the formation of sites of local strain or kinks in the valve leaflets during opening. It is expected that this strain localisation phenomenon will influence the long-term fatigue durability of the treated tissue. Pressures even as low as 4 mmHg result in significant reductions of crimp geometry. Fresh valves should therefore be fixed under a positive head of pressure sufficient only to ensure that the leaflets seal along their coapting free margins. A pressure of less than 1 mmHg was sufficient to achieve this. Leaflets of the commercially available Hancock valve show features similar to valves fixed in glutaraldehyde at about 100 mmHg pressure.     

Carbon dioxide retention associated with a humidifier defect

A case is presented which describes a patient who developed hypercarbia resulting from a defective humidifier. A Puritan-Bennett Cascade I humidifier was incorporated into a circle system between the inspiratory dome one way valve and the patient. A screw which supports the thermal well to the head of the humidifier was missing, thereby allowing an intermittent leak to develop in the system. The leak was present when the system pressure dropped to ambient level; however, at positive system pressure the leak sealed. This allowed exhaled gases into the inspiratory limb of the circuit unchecked by the inspiratory valve yet when the breathing circuit was occluded at the patient end and submitted to pressures of 20 and 40 cm H2O, no leaks were detected. Intraoperatively, PaCO2 was noted to be as high as 68 mmHg just prior to removing the humidifier from the circuit and corrected to 38 mmHg within 15 minutes of removal of the humidifier.     

The pneuPAC ventilator with new patient valve and air compressors

The pneuPAC Model 2-R pneumatic logic ventilator with a new air entrainment valve that offers the option of an FIO2 of 1.0 or 0.45 is described. Its robustness, portability, variable FIO2, choice of positive end expiratory pressure and pressure relief valves make it versatile and suitable for transporting critically ill patients, as well as for resuscitation use when adverse conditions may be encountered. Two new medical air compressors, one mains driven and the other battery powered, designed for use with the ventilator, are also described. The function of the ventilator with the new valve was assessed using a piped gas supply and then reassessed when powered by the compressors.     

Clinical experience with a new pressure-adjustable shunt valve

Summary The pressure-adjustable valve system Codman Medos allows valve pressure adjustment in 18 steps between 30 and 200 mm H₂O. A series of 90 patients, 15 children and 75 adults, who were shunted with this new programmable valve, is reported. Indication for shunt insertion were various types of hydrocephalus in 79 cases, malfunction of a medium pressure membrane valve shunt system in 9 cases and an arachnoid cyst and pseudotumour each in one case. The valve pressure was programmed prior to insertion to 200 mm H₂O in the adults and according to age in children and was modified postoperatively according to the clinical course.Underdrainage with subdural fluid collections appearing in 5 patients could be managed by valve pressure adjustment alone in 2 cases. One malfunctioning of the valve mechanism was due to mechanical obstruction. At the time of follow-up, 7 to 29 months after operation, outcome was excellent in 64 patients, good with marked improvement but residual symptoms in 19 patients and unchanged in 7 patients.The possibility of adjusting the valve pressure to the patient's demands was frequently used in children and adult normal pressure hydrocephalus patients with satisfying clinical results.     

Right atrial to left atrial shunt through foramen ovale during pneumoperitoneum for laparoscopic cholecystectomy

A 62-year old female patient in whom paradoxical right atrial to left atrial shunt flow through the foramen ovale was detected by transesophageal echocardiography during pneumoperitoneum for laparoscopic cholecystectomy was reported. This patient had a history of mitral valve replacement with residual tricuspid valve regurgitation. It was considered that the onset of paradoxical interatrial shunting through the foramen ovale might be caused not only by mechanical ventilation with positive end-expiratory pressure but also by pneumoperitoneum, especially in patients with heart disease, even if the intra-abdominal pressure was maintained at 12 mmHg.     

Anesthetic management of a patient with psoriasis arthropathica]

A 37-year-old woman with psoriasis arthropathica associated with aortic regurgitation underwent replacement of her aortic valve. The serum rheumatic factor was negative. HLA-B 27 was demonstrated in HLA analysis. She experienced a sudden onset of dyspnea and cardiac arrest in the hospital. She was hospitalized and found to have severe aortic regurgitation. She had her aortic valve replaced. We paid attention to management of blood pressure not to trigger cardiac ischemia and of skin lesion not to trigger infection and the worsening of skin condition. There are few reports of HLA-B 27 positive psoriasis arthropathica accompanied by aortic regurgitation. However, the present case may suggest that the cardiac study may be required for HLA-B 27 positive psoriasis arthropathica.     

Blunt cardiac injury and intraoperative hypoxaemia

A 28-yr-old man sustained blunt chest trauma in a motor vehicle accident. Severe intraoperative hypoxaemia occurred, unresponsive to oxygen and positive expiratory pressure therapy. Transoesophageal echocardiography revealed myocardial contusion and tricuspid valve rupture. Dobutamine improved left ventricular function and ejection fraction resulting in an immediate improvement in arterial oxygenation and saturation. Tricuspid injury and the diagnosis of myocardial contusion are discussed. The case highlights the importance of a non-pulmonary mechanism of hypoxaemia.     

Speed of collapse of the non-ventilated lung during single-lung ventilation for thoracoscopic surgery: the effect of transient increases in pleural pressure on the venting of gas from the non-ventilated lung

A study of 10 anaesthetised patients placed in the lateral position for thoracoscopic surgery assessed whether transient increases in pleural pressure on the side of the non-ventilated lung might increase the speed at which gas vents from that lung. The transient increases in pleural pressure were generated by the mediastinal displacement that occurs with each inspiratory phase of positive pressure ventilation of the dependent lung. When combined with a unidirectional valve allowing gas to flow out of the non-ventilated lung, and a second valve allowing ambient airflow into, but not out of, the thoracic cavity via an initial thoracoscopy access site, this mediastinal displacement could conceivably serve to 'pump' gas out of the non-ventilated lung. Using the four different combinations of valve inclusion or omission, the volume of gas that vented from the non-ventilated lung into a measuring spirometer was recorded during a 120-s measurement sequence. It was found that the speed of venting was not increased by the transient increases in pleural pressure, and that in all but one of a total of 34 measurement sequences, venting had ceased by the end of the sequence. Gas venting was a mean (SD) of 85.5 (11.9)% complete in 25 s (five breaths), and 96.6 (6.1)% complete in 60 s. This prompt partial lung collapse very likely reflected the passive elastic recoil of the lung, while the failure of transient increases in pleural pressure to result in ongoing venting of gas was probably a consequence of airways closure as the lung collapsed. It is concluded that techniques that aim to speed lung collapse by increasing pleural pressure are unlikely to be effective.     

Inverted valve after initially successful transfemoral aortic valve implantation

A 73-year-old woman with severe aortic stenosis was accepted for transcatheter aortic valve implantation. There was minimal paravalvular leakage after the implantation, and the patient was stable. Twelve minutes after the implantation, the arterial pressure suddenly dropped. Transesophageal echocardiography showed severe left ventricular dysfunction. Cardiopulmonary resuscitation was started, and initially was successful with a systolic blood pressure of 90 mm Hg. However, despite initiation of extracorporeal circulation support, the patient deteriorated, pulmonary edema developed, and she died. Autopsy revealed an inverted aortic valve. The reasons why the patient had cardiac arrest and an inverted transfemoral aortic valve remain unclear.     

Aortic root remodeling for root aneurysm with a uni-commissural aortic valve: report of a case.

A 23-year-old man was admitted for an aortic root aneurysm with mild aortic valve regurgitation (AR) and a small pressure gradient. At surgery, findings of aortic valve, one normal left posterior commissure and very rudimentary right anterior commissure, was compatible with the uni-commisural aortic valve. Aortic root replacement with valve-sparing technique was performed. Four years later no residual AR was observed.     

Prolonged "Phantom" Square Wave Capnograph Tracing after Patient Disconnection or Extubation: Potential Hazard Associated with the Siemens Servo 900c Ventilator

Background: The authors report on the appearance of misleading square wave "phantom" capnograph tracings for approximately 3 min after disconnection from the Siemens Servo 900c ventilator. A series of experiments are described to examine the mechanism of this phenomenon.

Methods: Patients were ventilated using the Siemens Servo 900c ventilator with the following settings: minute volume, 5 l/min; respiratory rate, 8 breaths/min; PEEP, 0 cm H2 O; trigger sensitivity, 20 cm H2 O. The ventilator was connected to the Siemens Servo Evac 180 evacuation system (25 l/min on evacuation flowmeter). Airway pressure and capnography were recorded at the Y piece during ventilation and after disconnection. A back-up ventilator was used to support the patient during disconnection of the ventilator being studied.

Results: Initially, the "phantom" capnograph tracing closely resembled the square wave capnograph tracing before disconnection, but the amplitude and shape of the waveform gradually decayed. Based on experiments described in this article, the authors show that the carbon dioxide for the "phantom" capnograph tracing comes from the gas exhaled by the patient in the last breaths before disconnection and which is present in both the expiratory tubing and in the evacuation system. The small pressure gradient between the exhaust reservoir and the atmosphere causes reverse flow of expired gas after disconnection, when both the nonreturn flap valve at the exhaust outlet is open (due to minimal valve incompetence) and when the expiratory servo valve is open (in the absence of positive end-expiratory pressure). This continuous reverse flow is detected by the capnograph but is interrupted intermittently by each attempted positive pressure ventilation, thereby creating a "phantom" capnograph.     

Percutaneous venoarterial extracorporeal membrane oxygenation as a bridge to double valve implantation in acute biventricular heart failure with profound cardiogenic shock

A 71‐year‐old woman was admitted with acute hypoxic and hypercapnic respiratory failure and cardiogenic shock, secondary to acute on chronic biventricular systolic and diastolic congestive heart failure and severe aortic and mitral valve stenosis. She further presented with pulmonary hypertension and moderate‐to‐severe tricuspid regurgitation requiring high and increasing doses of vasopressors. The patient was percutaneously cannulated for venoarterial extracorporeal membrane oxygenation (VA‐ECMO) and stabilized on ECMO, with a urine output of 17.3 L within the following 8 days. Balloon valvuloplasty and/or transcatheter aortic valve replacement were discussed but ruled out by the multidisciplinary team considering the mitral valve could not be fully addressed. Though lung function was not fully optimized, a window of opportunity was identified and used for double valve replacement on day 8 of VA‐ECMO support. After a 24‐hour vasoplegic period, the patient was extubated to continuous positive airway pressure and further transitioned to nasal cannula, following which she recovered well.     

Two cases of failure of a programmable pressure valve]

Two cases of a programmable pressure valve trouble are reported. Case #1 was that of a 49-year-old male who had received a ventriculoperitoneal shunt (VPS) using a Sophy programmable pressure valve (Model S3) after the removal of the fourth ventricle ependymoma. After the VPS, the patient went through several episodes of complaining of headache due to the spontaneous movement of the rotor from the high pressure position to the medium or low pressure position. The symptom had disappeared after exchanging the valve for a new one and by setting the valve pressure at high. Examination of the removed valve revealed that the bending-degree of the spring tip was insufficient, and that the opening pressures at the medium and high pressure positions were both lower than the desired range. Case #2 was that of a 62-year-old female who had received a VPS for normal pressure hydrocephalus using a Sophy programmable pressure valve (Model S3) with the valve pressure set a high. However, her symptoms did not improve, so an attempt was made to change the valve pressure from the high pressure position to the medium pressure position with a ring magnet. But the rotor could not be moved. The valve was exchanged and the valve pressure was set at medium, and the symptoms of the patient improved postoperatively. Examination of the removed valve revealed that the movement of the rotor with a ring magnet was not able to be carried out smoothly.(ABSTRACT TRUNCATED AT 250 WORDS)