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PubMedDate not supplied

Mass spectrometry for innovative techniques of respirator care, ventilator weaning and differential ventilation in an intensive care unit.

The medical mass spectrometry as a monitoring instrument in a respiratory intensive care unit (RICU) is described. Its uses, both routine and as a tool for innovative techniques in respiratory care, are many. As an adjunct to traditional and intermittent mandatory ventilation (IMV) weaning techniques, monitoring of expired respiratory gases can hasten the safe removal of patients from mechanical ventilators. A specialized technique of dealing with ventilating the lungs differentially when their mechanical properties differ is described to illustrate the versatility of the instrument. In critical care areas, monitoring of patients with respiratory problems should include continuous monitoring of end-tidal or expired CO2.

Carbon Dioxide↗
PubMed1983

Instrumentation for the continuous measurement of gas exchange and ventilation of infants during assisted ventilation.

A system of instrumentation for continuous measurement of oxygen consumption (VO2), carbon dioxide production (VCO2) and minute ventilation (V1) in human newborns on assisted ventilation is described. VO2 and VCO2 are measured by open-circuit indirect calorimetry utilizing a Servomex OA 184 differential paramagnetic oxygen analyzer and a Beckman LB 2 infrared CO2 analyzer. Minute volume is measured with a body plethysmograph. Bench performance is described, limitations of the system are defined, and sample clinical data are presented. The instrumentation can measure safely, accurately, and continuously physiologic variables in sick infants on assisted ventilation.

Humans↗
PubMed1984

High-frequency jet ventilation versus conventional ventilation after surfactant displacement in dogs.

High-frequency jet ventilation (HFJV) was compared with conventional ventilation (CV) after surfactant displacement with diocytyl sodium sulfosuccinate (OT) via ultrasonic nebulization. After aerosol delivery, dogs were separated into 3 groups and followed for 2 h. Ventilator settings were not changed in group I (CV) and group II (HFJV) after OT delivery. In group III, drive pressure was increased to 40 psi. Adequacy of oxygenation varied directly with peak inspiratory pressure (PIP) rather than airway pressure (Paw) in both HFJV and CV. In all groups, immediately after OT administration PaO2 decreased and there was a slight increase in Paw; PIP was significantly elevated only in groups I and III. Two hours later, PaO2 had returned to baseline in groups I and III, but had not improved significantly in group II. Paw remained the same in all groups. These data demonstrate that in noncompliant lungs, oxygenation is not improved unless a high PIP is used to establish the critical opening pressures needed to rerecruit alveoli. In this noncompliant lung model, HFJV was not effective at low Paw values, and thus offered no apparent advantage over CV.

Animals↗
PubMed1984

High-frequency ventilation compared to conventional positive-pressure ventilation in the treatment of hyaline membrane disease in primates.

High-frequency ventilation (HFV) has been suggested as an alternative to conventional positive-pressure ventilation (PPV) in the treatment of infants with hyaline membrane disease (HMD). Using a previously validated primate model of HMD, 15 baboon fetuses were delivered at 75% of gestation and randomly assigned to 1 of 3 ventilator treatment groups: PPV, HFV delivered by an oscillator (HFO), or HFV delivered by a flow interrupter (HFFI). All animals had clinical and radiographic evidence of HMD. At 96 h of life, all animals were sacrificed and clinical and pathologic findings were analyzed. During the first 10 h of the experiment, the HFO animals required higher mean proximal airway pressures than either the HFFI or PPV groups. However, both the HFFI and HFO animals had higher PaO2/PAO2 ratios than the PPV controls, suggesting earlier saccular recruitment. Thus, HFV is as effective as PPV in the treatment of HMD in baboons. Whether it will decrease the risk of bronchopulmonary dysplasia is not known.

Animals↗
PubMed2002

Noninvasive proportional assist ventilation compared with noninvasive pressure support ventilation in hypercapnic acute respiratory failure.

OBJECTIVES: To compare short-term administration of noninvasive proportional assist ventilation (NIV-PAV) and pressure support ventilation (NIV-PSV). DESIGN: Prospective, crossover, randomized study. SETTING: Medicosurgical intensive care unit in a nonteaching hospital. PATIENTS: Twelve chronic obstructive pulmonary disease patients admitted for hypercapnic acute respiratory failure. INTERVENTION: NIV-PSV and NIV-PAV given in a randomized order after baseline evaluation in continuous positive airway pressure. Using a flow-triggering ventilator, NIV-PAV was adjusted using the runaway method and compared with NIV-PSV at similar peak inspiratory airway pressure. MEASUREMENTS AND MAIN RESULTS: Flow, airway pressure, and changes in esophageal pressure were measured and the tidal volume, the patient's inspiratory work of breathing, and the esophageal pressure--time product were calculated. Arterial pH and PaCO(2) were measured and breathing comfort was assessed using a visual analogic scale. Peak inspiratory airway pressure (17 +/- 3 cm H(2)O) and tidal volume were similarly increased with the two modalities with no change in respiratory rate. The change in esophageal pressure was similarly decreased (from 20 +/- 8 cm H(2)O in continuous positive airway pressure to 12 +/- 7 in NIV-PSV and 10 +/- 5 cm H(2)O in NIV-PAV) as well as inspiratory muscle effort indexes. Arterial pH and PaCO(2) were similarly improved. Breathing comfort was significantly improved in NIV-PAV (+38 +/- 38%) but not in NIV-PSV (+11 +/- 23%). The tidal volume was more variable in NIV-PAV (89 +/- 18%) than in NIV-PSV (15 +/- 8%) and changes in tidal volume variability were significantly correlated (p =.02) with changes in breathing comfort. CONCLUSIONS: In chronic obstructive pulmonary disease patients with hypercapnic acute respiratory failure, NIV-PAV was able to unload inspiratory muscles similarly to NIV-PSV but may be more comfortable than NIV-PSV.

Acute Disease↗
PubMed2001

Frequency of change of ventilator circuit in premature infants: Impact on ventilator-associated pneumonia.

OBJECTIVE: Ventilator-associated pneumonia (VAP) is associated with substantial mortality. The frequency of changing the ventilator circuit (VC) might influence the occurrence rate of VAP. In premature infants receiving ventilatory support, the question regarding the frequency of changing VC is as yet unsettled. DESIGN: A prospective, randomized, and controlled trial in 60 premature neonates receiving ventilatory support. INTERVENTIONS: We investigated the impact of two VC change regimens on VAP in premature infants, either every 24 hrs or every 72 hrs. In each patient, the humidifier, inspiratory tube, and expiratory tube were changed and cultured at the assigned intervals along with cultures of tracheal aspirates. Blood cultures were obtained whenever there was clinical evidence of pneumonia or sepsis. MEASUREMENTS AND MAIN RESULTS: The two study groups did not differ significantly in gestational age, birth weight, gender, duration of mechanical ventilatory support, surfactant therapy, duration of hospitalization, mortality rate, rate of bloodstream infection, or rate of colonization of tracheal aspirate, humidifier, and expiratory tube by microbes. The inspiratory tube was significantly less colonized in the 72-hr group as compared to the 24-hr group (p <.05). The rate of VAP per 1000 ventilator days was not higher in the 72-hr group, compared with the 24-hr group (23.3 vs. 37.7; not significant). Switching from a 24-hr to a 72-hr change policy would save our neonatal intensive care unit a yearly sum of $14,000 (US). CONCLUSIONS: Extending the VC-change interval in premature infants from 24 hrs to 72 hrs is safe and cost-effective.

Journal Article↗
PubMed1985

Controlled ventilation in dental outpatients. Controlled ventilation with atracurium and alfentanil analgesia compared with halothane.

This study compares anaesthesia with controlled ventilation of the lungs with atracurium and alfentanil analgesia with halothane anaesthesia. Recovery time, the incidence of dysrhythmias and postoperative morbidity were evaluated. Anaesthesia with controlled ventilation was found to reduce significantly the incidence of cardiac dysrhythmias during dental surgery, and to produce a significantly more rapid recovery than halothane anaesthesia. The incidence of subjective postoperative complications is similar. It is concluded that controlled ventilation with atracurium and alfentanil is a suitable outpatient dental technique.

Adjuvants, Anesthesia↗
PubMed1995

Does dead space ventilation always alleviate hypocapnia? Long-term ventilation with plain tracheostomy tubes.

Long-term tracheostomy-ventilated patients have better speech with a cuffless tracheostomy tube and a large tidal volume. Moderate day time hyperventilation from a pressure-limited ventilator is necessary in these patients to avoid hypoxia during sleep due to the variable insufflation leak. This study sought to confirm whether a dead space of 3 ml.kg-1 could help to provide normocapnic hyperventilation during waking time without causing hypercapnia and hypoxaemia during sleep. Transcutaneous blood gas studies were performed on 11 patients with high tetraplegia undergoing pressure-limited pulmonary ventilation with room air. Recordings were made for 120 min each when awake and asleep, with and without dead space. The mean derived arterial PCO2 without the dead space was 2.95 kPa awake and 3.21 kPa asleep, whilst the corresponding tensions with dead space were 3.39 kPa and 3.79 kPa. These small increases associated with the dead space, both awake and asleep, were statistically significant. There was a statistically, though not clinically significant decrease in oxygen tension when the patients without dead space went to sleep. The fact that the carbon dioxide tension was higher during sleep when dead space was in situ indicates that, despite the insufflation leak in these patients, there is significant rebreathing back through the dead space. Amelioration of hypocapnia during waking and sleeping is achievable using a dead space extension in these patients.

Blood Gas Monitoring, Transcutaneous↗
PubMed1995

Mathematical model for a new mode of artificial ventilation: volume assisted pressure supported ventilation: a comparative study.

The patient submitted to artificial ventilation generally is connected to a high impedance flow source with controlled respiratory cycles to assure volume requirements or to a low impedance pressure source with spontaneous cycles to allow synchronization between his effort and system flow delivery. These two types of cycles represent the initial and final stages of artificial ventilation. The patient who needs a volume guarantee and at the same time presents unstable or insufficient inspiratory effort is difficult to manage with assisted cycles which are analogous to the controlled presence of a high impedance flow source. This paper presents a new approach where the respiratory cycles are obtained by the combination of flow and pressure sources using mathematical modeling. These cycles, named volume assisted pressure supported (VAPS) cycles, are compared with conventional assisted cycles showing a decrease in the patient work of breathing (WOB) during assisted ventilation. The theoretical results have been confirmed by clinical trials.

Humans↗
PubMed1998

Core guidelines for the discharge home of the child on long-term assisted ventilation in the United Kingdom. UK Working Party on Paediatric Long Term Ventilation.

Paediatric home ventilation is a feasible option and can be successful in a wide range of conditions and ages. Advances in ventilator technology and an ethos of optimism for home care has increased the possibilities for discharging chronically ventilated children from intensive care units and acute medical beds. With careful planning the process can succeed, but difficulties often thwart the responsible team, especially when attempting discharge for the first time. These core guidelines aim to assist a smooth, swift and successful transfer. They were developed by a working party of interested professionals spanning a wide range of health care disciplines and represent a synthesis of views accumulated from the experiences of individual teams throughout the UK. Three case scenarios provide further illustrative detail and guidance.

Caregivers↗
PubMed1992

Functional residual capacity and ventilation homogeneity in mechanically ventilated small neonates.

A modification of a computerized tracer gas (SF6) washout method was designed for serial measurements of functional residual capacity (FRC) and ventilation homogeneity in mechanically ventilated very-low-birth-weight infants with tidal volumes down to 4 ml. The method, which can be used regardless of the inspired O2 concentration, gave accurate and reproducible results in a lung model and good agreement compared with He dilution in rabbits. FRC was measured during 2-4 cmH2O of positive end-expiratory pressure (PEEP) in 15 neonates (700-1,950 g), most of them with mild-to-moderate respiratory distress syndrome. FRC increased with body weight and decreased (P less than 0.05) with increasing O2 requirement. Change to zero end-expiratory pressure caused an immediate decrease in FRC by 29% (P less than 0.01) and gave FRC (ml) = -1.4 + 17 x weight (kg) (r = 0.83). Five minutes after PEEP was discontinued (n = 12), FRC had decreased by a further 16% (P less than 0.01). The washout curves indicated a near-normal ventilation homogeneity not related to changes in PEEP. This was interpreted as evidence against the presence of large volumes of trapped alveolar gas.

Body Weight↗
PubMed1993

Normal values for the hypercapnic ventilation response: effects of age and the ability to ventilate.

Normal values reported for the hypercapnic ventilation response (HCVR) vary considerably, but the reported normal values have come from studies containing small sample sizes and/or the subjects were young or of unidentified age. We speculated that age has a major effect on HCVR due to the generally lower maximal ventilation (VEmax) of elderly subjects. Therefore, we performed a large study to more accurately define the normal range and to reveal any effects which age and sex might have on HCVR. We studied 181 normal subjects (69 males, 112 females) between the ages of 20 and 93 years. Prior to measuring HCVR we measured forced expired volume in 1 s (FEV1) and forced vital capacity to establish whether lung function was normal and to obtain an estimate of VEmax. Results for the entire group revealed a significant correlation between FEV1 and HCVR [HCVR = 0.51 + (0.33 FEV1), r = 0.43, p < 0.001], so it is clear that the ability to ventilate can influence HCVR. We also found a significant correlation between age and HCVR [HCVR = 2.08-(0.01.age), r = 0.34, p < 0.001]. The mean HCVR for our male group (1.86 +/- 0.54 l/min.mm Hg) was significantly higher (p < 0.001) than that for the females (1.37 +/- 0.60) even though their mean ages were similar (41.3 vs. 41.7 years, respectively). We expect that this difference in HCVR was due to the higher FEV1 in males compared to females (3.82 vs. 2.83 liter, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1981

Ventilation, respiratory center output, and contribution of the rib cage and abdominal components to ventilation during CO2 rebreathing in children with cystic fibrosis.

Although there has been extensive research into the control of breathing in adults with chronic obstructive lung diseases, there is little information in this area in children with cystic fibrosis (CF). The purpose of this study was to investigate the respiratory response of children with CF to CO2 under hyperoxic conditions. Using a standard CO2 rebreathing technique, we studied 14 children with CF. We evaluated their response to CO2 in terms of ventilation (VE), mean inspiratory flow rate (VT/TI), and the pressure generated at the mouth after 0.1 s of an inspiratory effort against an occlusion (P0.1). In order to understand the contributions of the rib cage and abdominal components to ventilation, we assessed the volume change in each compartment by attaching magnetometers to the chest and abdomen. Overall changes in lung volume were assessed in a volume displacement plethysmograph. We found that, when corrected for the height of the child, the slope of VE versus end tidal CO2 (PETCO2), as well as the slope of VT/TI versus PETCO2 correlated significantly with the degree of airway obstruction as expressed by the forced expiratory flow between 25 and 75% of vital capacity. The values for P0.1 were all within the normal range and showed no correlation with the degree of airway obstruction. The contribution of the rib cage and abdomen to ventilation during rebreathing was similar to that previously reported for adults. No changes were observed in functional residual capacity during rebreathing. We showed that tests involving a mechanical response to CO2 correlated with the degree of airway obstruction, but there was no evidence that the neuromuscular drive was abnormal.

Adolescent↗
PubMed2005

Comparison of oxygen cost of breathing between pressure-support ventilation and airway pressure release ventilation.

We compared the oxygen cost of breathing between pressure-support ventilation (PSV) and airway pressure release ventilation (APRV). This prospective, randomized, crossover study was conducted in a mixed ICU of a university hospital. Twenty clinically stable and spontaneously breathing patients after long-term mechanical ventilation were included. The patients were randomized to start on either PSV or APRV mode and measurements were obtained after an adaptation period of 30 minutes with a PaCO2 between 35-45 mmHg and PaO2 above 60 mmHg. Patients were then switched to the other mode and the same measurements were repeated. Indirect calorimetry was performed during each ventilatory mode for a period of 30 minutes. Oxygen consumption, energy expenditure, CO2 production, and respiratory quotient were measured. The parameters did not differ significantly between the two ventilatory modes, regardless of the patient's randomization. There were no statistically significant differences with regard to respiratory rate, minute volume, and blood gas analysis. All patients tolerated both ventilatory modes without signs of discomfort. PSV and APRV produced similar results in terms of oxygen cost of breathing and other metabolic variables.

Blood Gas Analysis↗
PubMed1996

Stomach as a source of colonization of the respiratory tract during mechanical ventilation: association with ventilator-associated pneumonia.

The aetiopathogenesis of ventilator-associated pneumonia (VAP) requires abnormal oropharyngeal and gastric colonization and the further aspiration of their contents to the lower airways. VAP develops easily if aspiration or inoculation of microorganisms occur in patients with artificial airways, in whom mechanical, cellular and/or humoral defences are altered. Well-known risk factors for gastric colonization include: alterations in gastric juice secretion; alkalinization of gastric contents; administration of enteral nutrition; and the presence of bilirubin. However, the role of the colonized gastric reservoir in the development of VAP remains debatable. Evidence in favour of the role of the stomach in the development of VAP comes mainly from randomized, controlled trials of selective gut decontamination and stress ulcer prophylaxis in the intensive care unit (ICU), in which reducing the bacterial burden of the stomach decreases the incidence of nosocomial respiratory infections. However, at least three studies of flora have found an absence of stomach origin of pneumonia occurring during mechanical ventilation. Prophylactic measures suggested to prevent VAP in relation to the gastric reservoir include: treatment for stress ulcers with sucralfate; prevention of duodenal reflux with metoclopramide; reduction of gastric burden and bacterial translocation by selective digestive decontamination; acidification of enteral feeding; and jejunal feeding. Gastro-oesophageal reflux can be prevented by using small bore nasogastric tubes and jejunal feeding. The aspiration of gastric contents can be reduced by positioning patients in a semirecumbent position, checking the patency of the tube cuff, and aspiration of subglottic secretions. The role of the stomach as a reservoir for microorganisms causing ventilator-associated pneumonia is still controversial but despite the debate, there is major evidence in the literature in favour of the gastric origin of part of these pulmonary infections.

Colony Count, Microbial↗
PubMed2002

Effects of short-term pressure-controlled ventilation on gas exchange, airway pressures, and gas distribution in patients with acute lung injury/ARDS: comparison with volume-controlled ventilation.

STUDY OBJECTIVES: The potential clinical benefits of pressure-controlled ventilation (PCV) over volume-controlled ventilation (VCV) in patients with acute lung injury (ALI) or ARDS still remain debated. We compared PCV with VCV in patients with ALI/ARDS with respect to the following physiologic end points: (1) gas exchange and airway pressures, and (2) CT scan intrapulmonary gas distribution at end-expiration. DESIGN: Prospective, observational study. SETTING: A multidisciplinary ICU in a nonuniversity, acute-care hospital. PATIENTS: Ten patients with ALI or ARDS (9 men and 1 woman; age range, 17 to 80 years). INTERVENTIONS: Sequential ventilation in PCV and VCV with a constant inspiratory/expiratory ratio, tidal volume, respiratory rate, and total positive end-expiratory pressure; measurement of gas exchange and airway pressures; and achievement of CT sections at lung base, hilum, and apex for the quantitative analysis of lung densities and of aerated vs nonaerated zones. RESULTS: PaO(2), PaCO(2), and PaO(2)/fraction of inspired oxygen ratio levels did not differ between PCV and VCV. Peak airway pressure (Ppeak) was significantly lower in PCV compared with VCV (26 +/- 2 cm H(2)O vs 31 +/- 2 cm H(2)O; p < 0.001; mean +/- SEM). The surface areas of the nonaerated zones as well as the total areas at each section level were unchanged in PCV compared with VCV, except at the apex level, where there was a significantly greater nonaerated area in VCV (11 +/- 2 cm(2) vs 9 +/- 2 cm(2); p < 0.05). The total mean CT number of each lung (20 lungs from 10 patients) was similar in the two modes, as were the density values at the basal and apical levels; the hilum mean CT number was - 442 +/- 28 Hounsfield units (HU) in VCV and - 430 +/- 26 HU in PCV (p < 0.005). CONCLUSIONS: These data show that PCV allows the generation of lower Ppeaks through the precise titration of the lung distending pressure, and might be applied to avoid regional overdistension by means of a more homogeneous gas distribution.

Adolescent↗
PubMed1988

Cardiovascular effects of conventional positive pressure ventilation and airway pressure release ventilation.

The hemodynamic sequelae of conventional positive pressure ventilation (CPPV), airway pressure release ventilation (APRV), and spontaneous breathing were compared with continuous positive airway pressure (CPAP) in ten anesthetized dogs who had ventilatory failure with and without parenchymal lung injury. The APRV corrected respiratory acidosis without significantly effecting arterial blood oxygenation, venous admixture, cardiovascular function, or tissue oxygen utilization. Application of CPPV precipitated marked depressions in blood pressure, stroke volume, and cardiac output. A concomitant decrease in venous admixture did not compensate for these adverse cardiovascular effects. Deterioration of tissue oxygen delivery resulted in oxygen supply-demand imbalance during CPPV. The results of this experimental study indicate that if ventilatory augmentation of subjects who require CPAP is desired, APRV will enhance alveolar ventilation without compromising circulatory function and tissue oxygen balance, whereas CPPV will impair cardiovascular function significantly.

Animals↗