Tomoyo Nishida

Performance of Heated Humidifiers with a Heated Wire According to Ventilatory Settings

Delivering warm, humidified gas to patients is important during mechanical ventilation. Heated humidifiers are effective and popular. The humidifying efficiency is influenced not only by performance and settings of the devices but the settings of ventilator. We compared the efficiency of humidifying devices with a heated wire and servo-controlled function under a variety of ventilator settings. A bench study was done with a TTL model lung. The study took place in the laboratory of the University Hospital, Osaka, Japan. Four devices (MR290 with MR730, MR310 with MR730; both Fisher & Paykel, ConchaTherm IV; Hudson RCI, and HummaxII; METRAN) were tested. Hummax II has been developed recently, and it consists of a heated wire and polyethylene microporous hollow fiber. Both wire and fiber were put inside of an inspiratory circuit, and water vapor is delivered throughout the circuit. The Servo 300 was connected to the TTL with a standard ventilator circuit. The ventilator settings were as follows; minute ventilation (V(E)) 5, 10, and 15 L/min, a respiratory rate of 10 breaths/min, I:E ratio 1:1, 1:2, and 1:4, and no applied PEEP. Humidifying devices were set to maintain the temperature of airway opening at 32 degrees C and 37 degrees C. The greater V(E) the lower the humidity with all devices except Hummax II. Hummax II delivered 100% relative humidity at all ventilator and humidifier settings. When airway temperature control of the devices was set at 32 degrees C, the ConchaTherm IV did not deliver 30 mg/L of vapor, which is the value recommended by American National Standards at all V(E) settings. At 10 and 15 L/min of V(E) settings MR310 with MR730 did not deliver recommended vapor, either. In conclusion, airway temperature setting of the humidifying devices influenced the humidity of inspiratory gas greatly. Ventilatory settings also influenced the humidity of inspiratory gas. The Hummax II delivered sufficient water vapor under a variety of minute ventilation.

Effects of reduced rebreathing time, in spontaneously breathing patients, on respiratory effort and accuracy in cardiac output measurement when using a partial carbon dioxide rebreathing technique: a prospective observational study

IntroductionNew technology using partial carbon dioxide rebreathing has been developed to measure cardiac output. Because rebreathing increases respiratory effort, we investigated whether a newly developed system with 35 s rebreathing causes a lesser increase in respiratory effort under partial ventilatory support than does the conventional system with 50 s rebreathing. We also investigated whether the shorter rebreathing period affects the accuracy of cardiac output measurement.MethodOnce a total of 13 consecutive post-cardiac-surgery patients had recovered spontaneous breathing under pressure support ventilation, we applied a partial carbon dioxide rebreathing technique with rebreathing of 35 s and 50 s in a random order. We measured minute ventilation, and arterial and mixed venous carbon dioxide tension at the end of the normal breathing period and at the end of the rebreathing periods. We then measured cardiac output using the partial carbon dioxide rebreathing technique with the two rebreathing periods and using thermodilution.ResultsWith both rebreathing systems, minute ventilation increased during rebreathing, as did arterial and mixed venous carbon dioxide tensions. The increases in minute ventilation and arterial carbon dioxide tension were less with 35 s rebreathing than with 50 s rebreathing. The cardiac output measures with both systems correlated acceptably with values obtained with thermodilution.ConclusionWhen patients breathe spontaneously the partial carbon dioxide rebreathing technique increases minute ventilation and arterial carbon dioxide tension, but the effect is less with a shorter rebreathing period. The 35 s rebreathing period yielded cardiac output measurements similar in accuracy to those with 50 s rebreathing.

Steroids Improve Hemodynamics in Infants With Adrenal Insufficiency After Cardiac Surgery

OBJECTIVE To investigate whether steroid replacement therapy improved hemodynamics in infants after surgery for congenital heart disease only when they develop adrenal insufficiency. The authors retrospectively investigated adrenal function and evaluated hemodynamic responses to steroid replacement therapy in infants after surgery for congenital heart disease. DESIGN Retrospective, cohort study. SETTING Intensive care unit in the National Cerebral and Cardiovascular Center Hospital in Japan. PATIENTS Thirty-two neonates and infants<3 months old who underwent cardiovascular surgery. INTERVENTIONS The patients were divided into 2 groups based on corticotropin stimulation test results: group AI with adrenal insufficiency (baseline cortisol<15 µg/dL or incremental increase after testing of<9 µg/dL, with baseline cortisol of 15-34 µg/dL); and group N with normal adrenal function. The corticotropin stimulation test was performed by injecting 3.5 µg/kg of tetracosactide acetate. Hydrocortisone (1 mg/kg) was administered every 6 hours, and hemodynamics were compared before and after steroid administration between the groups. MEASUREMENTS AND MAIN RESULTS Seven patients were classified into group AI, and demonstrated a mean blood pressure increase from 53±8 mmHg before treatment to 68±9 mmHg 18 hours after steroid administration (p<0.01). Urine output also increased, from 2.7±1.0 mL/kg/h to 4.8±1.9 mL/kg/h (p<0.05). In group N, neither mean blood pressure nor urine output increased after steroid administration. CONCLUSIONS After surgery for congenital heart disease, one-fifth of infants developed adrenal insufficiency. Steroid replacement therapy improved hemodynamics only in the subgroup with adrenal insufficiency.

Survey of acute renal failure in patients after cardiovascular surgery

Acute renal failure (ARF) is one of the major complications after cardiovascular surgery. To investigate the incidence and prognosis of ARF after cardiac surgery, we performed a retrospective study. Our hypothesis is that ARF is more common in patients who underwent surgery for great vessel diseases than in those who underwent coronary or valve surgery.

Artificial ventilation-induced diffuse alveolar damage in rabbits: preliminary study of early detection on expiratory high-resolution computed tomography.

Honda O, Nishimura M, Tomiyama N, et al. Artificial ventilation–induced diffuse alveolar damage in rabbits: Preliminary study of early detection on expiratory high-resolution computed tomography. Invest Radiol 2000;35:534–538. RATIONALE AND OBJECTIVES.To investigate whether expiratory high-resolution computed tomography (HRCT) is more useful than inspiratory HRCT for the detection of early-phase diffuse alveolar damage. METHODS.Eleven anesthetized rabbits were scanned with both inspiratory and expiratory HRCT every 30 minutes during mechanical ventilation. Ten rabbits were killed after the detection of pulmonary abnormalities on both inspiratory and expiratory HRCT. The remaining rabbit was killed when the pulmonary abnormalities appeared only on expiratory HRCT. RESULTS.In four cases (36%), the abnormal findings were detected earlier on expiratory HRCT than on inspiratory HRCT. In seven cases (64%), the abnormalities appeared simultaneously on inspiratory and expiratory HRCT. In all 11 cases, the histopathological changes of areas with abnormal CT findings corresponded to the exudative or proliferative phase of diffuse alveolar damage. CONCLUSIONS.Expiratory HRCT has the potential to detect the abnormalities of diffuse alveolar damage earlier than inspiratory HRCT.