Decrease In Dynamic Compliance Research Articles

Comparison of volume-controlled ventilation, pressure-controlled ventilation and pressure-controlled ventilation-volume guaranteed in infants and young children in the prone position: A prospective randomized study

Study objectiveTo explore if the pressure-controlled ventilation (PCV) and pressure-controlled ventilation-volume guaranteed (PCV-VG) modes are superior to volume-controlled ventilation (VCV) in optimizing intraoperative respiratory mechanics in infants and young children in the prone position. DesignA single-center prospective randomized study. SettingChildren's Hospital, Zhejiang University School of Medicine. PatientsPediatric patients aged 1 month to 3 years undergoing elective spinal cord detethering surgery. InterventionsPatients were randomly allocated to the VCV group, PCV group and PCV-VG group. The target tidal volume (VT) was 8 mL/kg and the respiratory rate (RR) was adjusted to maintain a constant end tidal CO2. MeasurementsThe primary outcome was intraoperative peak airway pressure (Ppeak). Secondary outcomes included other respiratory and ventilation variables, gas exchange values, serum lung injury biomarkers concentration, hemodynamic parameters and postoperative respiratory complications. Main resultsA total of 120 patients were included in the final analysis (40 in each group). The VCV group showed higher Ppeak at T2 (10 min after prone positioning) and T3 (30 min after prone positioning) than the PCV and PCV-VG groups (T2: P = 0.015 and P = 0.002, respectively; T3: P = 0.007 and P = 0.009, respectively). The prone-related decrease in dynamic compliance was prevented by PCV and PCV-VG ventilation modalities at T2 and T3 than by VCV (T2: P = 0.008 and P = 0.015, respectively; T3: P = 0.015 and P = 0.014, respectively). Additionally, there were no significant differences in other secondary outcomes among the three groups. ConclusionIn infants and young children undergoing spinal cord detethering surgery in the prone position, PCV-VG may be a better ventilation mode due to its ability to mitigate the increase in Ppeak and decrease in Cdyn while maintaining consistent VT.

Effect of spine frame on the changes in respiratory dynamics in prone patients under general anaesthesia- a prospective, observational study.

The prone position is one of the common surgical positions used in clinical practice. Manoeuvring patients from supine to a prone position can impact respiratory dynamics and result in haemodynamic variations. This study included 64 patients and was conducted after obtaining approval from the ethics committee and registration of the trial. The primary objective was to evaluate the changes in peak inspiratory pressure (PIP), plateau pressure (Pplat) and mean airway pressure (MAP) in patients undergoing surgery under general anaesthesia in the prone position with (Group S) and without (Group P) spine frame. The secondary objective was to evaluate and compare the variations in heart rate and blood pressure. On turning the patient prone, there was statistically significant increase in median PIP (Group S 4 cmH2O vs. Group P 0.5 cmH2O, P < 0.001), Pplat (Group S 3.5 cmH2O vs. Group P 1 cmH2O, P = 0.004) and dynamic compliance (Group S -5.513 vs. Group P -2.78, P < 0.004). Our study found that prone positioning with a spine frame led to a significantly greater increase in airway pressures and a decrease in dynamic compliance when compared to patients positioned prone without the spine frame.

Comparative evaluation of airway dynamics in patients undergoing laparoscopic cholecystectomy under general anaesthesia with controlled ventilation using ProSeal laryngeal mask airway, I-Gel™ and Baska mask.

TheProSeal™ laryngeal mask airway (PLMA) and I-Gel™ are second-generation supraglottic airway devices (SADs). The Baska mask is a SAD having a non-inflatable cuff with a tendency to increase the perilaryngeal seal with an increase in airway pressures. This study compared the efficacy of I-Gel™, PLMA and Baska mask with respect to airway dynamics in patients scheduled for laparoscopic surgeries under general anaesthesia (GA). Ninety patients, of American Society of Anesthesiologists physical status I and II, aged 20-65 years scheduled for laparoscopic cholecystectomy under GA were enroled. The patients were randomised into three groups: Group P (n = 30): airway secured using PLMA, Group I (n = 30): airway secured using I-Gel™ and Group B (n = 30): airway secured using Baska mask. The primary outcome was the change in dynamic compliance, and the secondary outcomes included insertion time, changes in peak inspiratory pressure (PIP) and oropharyngeal leak pressure (OLP) at different time intervals. After insertion of the SADs, the dynamic compliance was highest in group B and least in the group I (p = 0.01). The maximum decrease in dynamic compliance was observed in group I. The insertion time for SAD placement was more in group P. The group B had least PIP as compared to groups P, I at insertion. After carboperitonium, groups P and B had comparable PIP, and group I had highest PIP (p = 0.001). OLP was highest in group B, whereas group I had least OLP. The airway dynamics are better maintained with Baska mask as compared to the PLMA and I-Gel™.

Early Metabolic Syndrome (MetS) in Chronic Rhesus Macaque Model of Human Allergic Asthma

Human asthma, obesity, MetS, overt Type 2 diabetes, and related sequelae such as cardiovascular diseases, account for much of the mortality and morbidity worldwide. The etiology and complex physiological mechanisms underlying these pathological states intersect within the human body – and within Rhesus macaques. Much like humans, these animals (in captivity) often develop spontaneous, age‐related obesity. Hence, these animals are ideally suited for investigations of obesity and metabolism, as well as chronic allergic asthma.In 2013, twenty animals were sensitized by i.p. injection of house dust mite antigen (HDM) adsorbed to alum; airway sensitization and maintenance were accomplished by exposure to aerosolized HDM (aeroHDM) at ≥ 2‐week intervals, to a dose that induced an acute asthmatic response: ≥ 100% increase in lung resistance, ≥ 40% decrease in dynamic compliance, and/or peripheral oxygen saturation ≤ 70%. Periodically, we assessed the late phase asthmatic response 24 hours after aeroHDM exposure: airway hyperreactivity was assessed by aerosolized methacholine challenge; pulmonary inflammation was assessed by bronchoalveolar lavage. Occasionally animals were also exposed to an experimental asthma therapeutic.In 2018, ten animals had developed obesity and were suspected to harbor other clinical manifestations of MetS. Retrospective analyses confirmed relative hypertension in animals that had robust responsiveness to aeroHDM and were &gt; 16 kg. Using archived frozen serum samples, we reconstructed the biochemical history of adiposity development and glucose metabolism ‐ a story that was evolving coincident with chronic exposures to both Diet A and aeroHDM (Fig. 1). By age 10 years, 4/5 of the largest animals (body weight, 21 ± 2 kg; waist circumference in lateral recumbency, 68 ± 5 cm; BMI using crown‐to‐rump length, 53 ± 3 kg/m2: values are mean ± SD) had insulin resistance (peak HOMA‐IR, 61 ± 29) associated with leptin &gt; 14 ng/ml and total adiponectin &lt; 3.5 μg/ml; 3/5 animals had dyslipidemia (Fig. 2); 1/5 animals had diabetes by age 8 years – 4 to 6 years earlier than would be expected based on non‐human primate literature. Biomarkers of inflammation and oxidative stress are outstanding.In July 2019, six months after switching to lower carbohydrate/higher protein Diet B, and &gt; 12 months since the last aeroHDM exposure: all animals lost weight coincident with larger animals resolving insulin resistance, dyslipidemia, and diabetes. As seen in some obese asthmatic humans, larger animals had higher pulmonary inflammation (especially neutrophilic) and higher airway hyperreactivity to aerosolized methacholine.We concluded that chronic allergic inflammation synergized with inflammation of developing adiposity, accelerating onset of MetS in susceptible animals. We hypothesize that resumption of chronic periodic aeroHDM exposure will trigger more rapid progression/re‐establishment of MetS, IR, and eventually overt Type 2 diabetes if we do not intervene.Historical event timeline.Figure 1Body weight and serum triglycerides of 5 largest animals (mean ± SD: n=3 to 5 for each time point). Gray vertical bar: gradual transition to lower carbohydrate/higher protein Diet B.Figure 2

The impact of bilateral vagotomy on the physostigmine-induced airway constriction in ferrets

Vagal innervations have a great role in the respiratory function and are the main route of signal transmission from respiratory neural centers into the trachea and others conducting airways.We have investigated the role of central mechanisms related to vagal neural pathways and the cholinergic outflow in tracheobronchial smooth muscle tone and lung mechanics parameters.Parameters of lung mechanics such as lung resistance (RL), dynamic compliance (Cdyn) and pressure in bypassed tracheal segment (Ptseg) were measured before and after vagotomy and asphyxia test. Before vagotomy (BV), the control measurements were obtained and physostigmine was administered systemically, in increasing dose 10, 40 and 100μg/kg body weight (bw) with 15min interval between doses. After vagotomy (AV), administration of physostigmine with the same doses as BV has been done and the asphyxia challenge was conducted as per study protocol. The values of Ptseg and RL after physostigmine administration, BV vs. AV, respectively, at maximal dose of 100μg/kg bw were 32.5±3.3cm H2O, and 10.6±1.5cm H2O (p<0.0001); 0.16±0.04cm H2O/mL/s, and 0.067±0.006cm H2O/mL/s AV (P<0.05). The Cydn values were affected after physostigmine administration only at the lowest dose of 10μg/kg bw, and BV was 0.75±0.05mL/cm H2O vs. 0.53±0.04mL/cm H2O AV (P<0.004).Cholinergic outflow produced increases in tracheal tone, lung resistance and a decrease in dynamic compliance before, but not after vagotomy. Our results show the high impact of central neuronal mechanism in parameters of lung mechanics and respiration.This study indicates that vagal nerves have a crucial role, in the transmission of impulses initiated from central nervous system, in regulating the respiration by contraction or relaxation of airway smooth muscle tone.

PPAR-α improves the recovery of lung function following acute respiratory distress syndrome by suppressing the level of TGF-β1.

Although peroxisome proliferator-activated receptor (PPAR)-α has been reported to be involved in preventing acute lung injury (ALI), the molecular regulation of post-ALI lung recovery remains to be fully elucidated. The aim of the present study was to characterize the mechanism by which PPAR-α prevents ALI and examine the role of PPAR-α in the recovery of lung function following acute respiratory distress syndrome (ARDS). Reverse transcription-quantitative-polymerase chain reaction and western blot analyses suggested that PPAR-α was effective in suppressing transforming growth factor (TGF)-β1 in HLF cells and RAW 264.7 cells. In an ALI mouse model, PPAR-α treatment prior to stimulation with lipopolysaccharide (LPS) resulted in a decrease in the expression of TGF-β1 in bronchoalveolar lavage fluid (BALF), peripheral blood and splenocytes. The injection of a virus expressing short hairpin PPAR-α into mice following LPS treatment resulted in a dose-dependent increase in lung resistance index and decrease in dynamic compliance, and a significant increase in BALF protein, which indicated PPAR-α was essential for the recovery of lung function following ALI. Of note, the serum expression of PPAR-α was inversely correlated with TGF-β1 and negatively correlated with disease severity in patients with ARDS. These data suggested that PPAR-α was essential for the recovery of lung function following ALI by the suppression of TGF-β1, which reveals a previously unappreciated mechanism controlling post-ALI lung recovery.

Vascular Endothelial-Cadherin Expression After Reperfusion Correlates With Lung Injury in Rat Lung Transplantation

Vascular endothelial-cadherin (VEC), composing the adherens junction of endothelial cells, has been shown to regulate vascular permeability. The aim of this study was to investigate VEC expression during cold ischemia (CI) and reperfusion and whether a dibutyryl cyclic adenosine 3',5'-monophosphate (db-cAMP) and nitroglycerin (NTG) additive to preservation solution can maintain VEC. Rat left lung transplantation after CI was performed, and reperfusion was done for 2 hours. The experimental groups were Control (n= 5), CI3 (n= 5), CI6 (n= 6), and CI6+AMP/NTG (n= 6) with minimum ischemic period, 3 hours and 6 hours of CI, respectively, and 6 hours of CI with db-cAMP and NTG additive to preservation solution, respectively. Lung mechanics, lung wet-to-dry weight ratio (W/D), and the histologic findings of the graft were evaluated. The expression of VEC was evaluated by Western blot analysis of the lung tissue lysates. The CI3 group showed a decrease in dynamic compliance with perivascular edema. Dynamic compliance, graft oxygenation, and W/D were substantially deteriorated, and intraalveolar edema with neutrophil infiltration was recognized in the CI6 group. They were improved in the CI6+AMP/NTG group. VEC expression was maintained during CI. After reperfusion, it reduced substantially in the CI6 group and was maintained in the CI6+AMP/NTG group. VEC expression was maintained during CI; however, it reduced early after reperfusion after 6 hours of CI, correlating with severe intraalveolar edema. db-cAMP/NTG additive to the preservation solution contributed to the maintenance of VEC expression after reperfusion.

OPTIMIZATION MECHANICAL VENTILATION BY STUDYING THE MECHANICAL PROPERTIES OF THE LUNGS IN NEWBORNS WITH THE SYNDROME OF INTRA-ABDOMINAL HYPERTENSION

Summary. The purpose of the study – optimization of mechanical ventilation by studying the mechanical properties of the lungs in newborns with viscero-abdominal disproportion and the syndrome of intra - abdominal hypertension in the perioperative period. Materials and methods. The study included 57 newborns with gastroschisis of them - 42 infants (73.7%) with omphalocele - 15 (2 (5.3%). All patients underwent intensive therapy, artificial lung ventilation apparatus «BearCub» modes (A / C, SIMV / PSV) with stable hemodynamic monitoring, respiratory mechanics (dynamic komplayns - Cdyn, resistance - Rpk, pressure-volumeloop, flow-volume using graphics monitor). Abdominal pressure measured by Crone . Results. The study found a link between abdominal pressure changes at different stages of research hand changes in respiratory rates in infants. All patients in the preoperative period was marked by the adaptation of newborn respiratory system. On the first day of the first phase correction viscero-abdominal imbalances observed a gradual decrease in dynamic compliance in both groups at 3.4 times, and marked increase in resistance with increase 2.42 times PIP to high numbers of 20-22 cm of water. c., and the maximum change indicators on the graphic display. Return performance mechanical properties of light to a relatively normal range is the end of 72 hours, stretching the skin-muscle flap of the anterior abdominal wall. Conclusion. Increased intra-abdominal pressure to high numbers leads to changes in respiratory mechanics and is very informative criterion for correction of parameters of ventilation. Also marked increase perioperative ICP (over 10-11 mm Hg. C) of the effect on the mechanical properties of the lungs in newborns with viscero-abdominal imbalances.

Absence of inflammatory lung injury in rabbits challenged intravascularly with complement-derived chemotactic factors.

Systemic activation of the complement system results in the generation of chemotactic factors that have been suggested to play a role in the pathogenesis of inflammatory pulmonary diseases such as the adult respiratory distress syndrome. This led us to ask whether systemic complement activation by cobra venom factor (CVF) or intravascularly administered zymosan-activated rabbit plasma (ZAP) or rabbit C5a would result in lung injury. As had been described previously for CVF and ZAP, intravenously administered rabbit C5a also caused an acute neutropenia along with sequestration of neutrophils within the pulmonary vasculature. However, no significant lung inflammation as measured by neutrophil emigration or increased vascular permeability occurred with any of the three stimuli. Only when these agents were combined with anesthesia, surgical manipulation, and intubation did significant neutrophil emigration into alveoli occur, but again without any change in vascular permeability. After administration of ZAP, a decrease in dynamic compliance and an increase in pulmonary resistance as well as a transient period of hypoxemia occurred that was not observed after CVF or rabbit C5a treatment. Thus, our studies suggest that changes in lung function after ZAP instillation may not represent changes from complement activation alone in that they are not reproduced with CVF or rabbit C5a. We conclude that complement activation, as an isolated event, may be an insufficient insult in the lung to produce significant lung injury.

Liver Reperfusion-Induced Decrease in Dynamic Compliance and Increase in Airway Resistance Are Ameliorated by Preischemic Treatment with Melatonin through Scavenging Hydroxyl Radicals in Rat Lungs

ObjectivesAcute lung injury is frequently observed in patients subsequent to liver ischemia and reperfusion (I/R) injury. However, the changes in pulmonary function, eg, lung dynamic compliance (Cdyn) and airway resistance (RI), are not well understood. We sought to study the alternations in pulmonary function during liver I/R and the protective effects of preischemic treatment with melatonin. MethodsAnimals were divided into 3 groups: sham-operated, liver I/R, and intraperitoneal (i.p.) pretreatment with melatonin (15 mg/kg). Liver I/R was performed by clamping the hepatic artery and portal vein for 30 minutes followed by releasing for 2 hours. The Cdyn and RI were studied at baseline and at 2 hours of reperfusion. We assessed the level of pulmonary hydroxyl radicals by methylguanidine (MG) content in the bronchoalveolar lavage fluid (BALF) as well as the liver damage using plasma levels of lactate dehydrogenase (LDH), glutamic oxaloacetic transaminase (GOT), and glutamic pyruvic transaminase (GPT). ResultsAfter 2 hours of liver reperfusion, Cdyn was reduced by ∼25%, while RI increased by ∼16% (P < .05). The decreased Cdyn and increased RI were markedly attenuated by melatonin pretreatment (P < .05). Melatonin pretreatment also protected the liver against I/R injury (P < .05), as seen by reduced LDH, GOT and GPT along with markedly reduced hydroxyl radicals (P < .05). ConclusionsPreischemic treatment with melatonin protected lung function against damage by liver I/R. The improvement in lung function was strongly associated with decreased hydroxyl radicals in the lungs.

Effects of preserved spontaneous breathing activity during mechanical ventilation in experimental intra-abdominal hypertension

Ventilation problems are common in critically ill patients with intra-abdominal hypertension. The aim of this study was to investigate the effects of preserved spontaneous breathing during mechanical ventilation on hemodynamics, gas exchange, respiratory function and lung injury in experimental intra-abdominal hypertension. Twenty anesthetized pigs were intubated and ventilated for 24 h with biphasic positive airway pressure without (BIPAP(PC)) or with additional, unsynchronized spontaneous breathing (BIPAP(SB)). In 12 animals, intra-abdominal pressure was increased to 30 mmHg for two 9 h periods followed by a 3 h pressure relief each. Eight animals served as controls and were ventilated for 24 h. Hemodynamics, gas exchange and respiratory mechanics were measured and lung injury was determined histologically. Intra-abdominal hypertension caused significant impairment of hemodynamics and respiratory mechanics in both modes. In the presence of intra-abdominal hypertension, BIPAP(SB) did not demonstrate superior respiratory mechanics and cardiovascular stability as compared to BIPAP(PC). Although the decrease of dynamic compliance and the increase of airway pressures were mitigated, BIPAP(SB) failed to lower pulmonary vascular resistance and caused increased dead space ventilation (p = 0.007). Blood pressures and cardiac output increased in BIPAP(SB), caused by an increase in heart rate (p < 0.001), but not in stroke volume (p = 0.06). BIPAP(SB) was associated with an increased breathing effort, decreased transpulmonary pressure during inspiration and lower lobe diffuse alveolar damage (p = 0.002). In the presence of severe intra-abdominal hypertension, the addition of unsupported spontaneous breaths to BIPAP did not improve hemodynamic and respiratory function and caused greater histopathologic damage to the lungs.

Changes in respiratory resistance and dynamic compliance induced by histamine in the guinea pig

Respiratory resistance and dynamic compliance in guinea pigs were measured by pulmonary mechanics analyzer Buxco Model 6. Changes induced by intravenous injection of histamine were studied. Administration of histamine caused dose-dependent increase in respiratory resistance and decrease in dynamic compliance in guinea pigs. The increase in respiratory resistance by repeated injections of the same dose of histamine was maintained at the same level 5 hours after the first injection. However, the decrease in dynamic compliance by histamine administration decreased significantly from 1 to 4 hours after the first injection. The baseline resistance increased from 1 to 5 hours after the first injection of histamine. The baseline compliance decreased from 1 to 5 hours after the first injection.

VTCO2 and dynamic compliance-guided lung recruitment in surfactant-depleted piglets: A computed tomography study

Using computed tomography (CT) as reference, our primary objectives were to test if maximal tidal elimination of carbon dioxide (VTCO2) could be used as a marker of "optimal recruitment," indicating maximal available lung tissue for gas exchange and if a decrease in dynamic compliance (Cdyn) indicated the beginning of lung collapse during a downward positive end-expiratory pressure (PEEP) titration. Prospective laboratory animal investigation. Clinical physiology research laboratory. Six piglets undergoing lung lavage. Saline-lavaged piglets were initially ventilated without PEEP at a tidal volume (VT) of 10 mL/kg followed by baseline ventilation at end-inspiratory pressure (EIP) 25 cm H2O and PEEP 6 cm H2O. PEEP was increased to 12 or 15 cm H2O. Then EIP was increased in steps of 5 cm H2O and the EIP where VTCO2 peaked or leveled off was assumed to define optimally recruited lungs. A downward PEEP titration followed from 12 or 15 to 4 cm H2O in steps of 1 cm H2O. First decline of Cdyn was assumed to define onset of lung collapse. VTCO2 and Cdyn were continuously recorded and CT scans iterated for each change of ventilation. "Open-lung PEEP" was set 2 cm H2O above PEEP at the first Cdyn decline and was used for a final period of "open-lung ventilation." CT images showed recruited lungs at peak VTCO2 and that a minimal amount of normally aerated lung was added by further increase in EIP. Cdyn declined just before CT scans indicated lung collapse. Compared with baseline, the target VT of 10 mL/kg was achieved at lower EIP and pressure amplitude (EIP-PEEP) during the final open-lung ventilation with more normally aerated and fewer collapsed lungs. Cdyn was doubled after recruitment. The lung recruitment maneuver was effective and lungs optimally recruited at maximal VTCO2. A fall in Cdyn indicated lung collapse during downward PEEP titration as confirmed by CT.

The Effects of Endotracheal Suctioning on the Accuracy of Oxygen Consumption and Carbon Dioxide Production Measurements and Pulmonary Mechanics Calculated by a Compact Metabolic Monitor

Open endotracheal suctioning (ETS), which is performed regularly in mechanically ventilated patients to remove obstructive secretions, can cause an immediate decrease in dynamic compliance and expired tidal volume and result in inadequate or inaccurate sidestream respiratory monitoring, necessitating prolonged periods of stabilization of connected metabolic monitors. We investigated the immediate effect of open ETS on the accuracy of oxygen consumption (VO2) and carbon dioxide production (VCO2) measurements and calculated lung mechanics, respiratory quotient, and resting energy expenditure in mechanically ventilated children without severe lung pathology, when using a compact modular metabolic monitor (E-COVX) continuously recording patient spirometry and gas exchange measurements. Open ETS was performed when clinically indicated in 11 children mechanically ventilated for sepsis or head injury. A total of 2800 pulmonary 1-min gas exchange measurements were recorded in 28 ETS instances for 50 consecutive minutes before and 50 min after the standardized procedure. Pulmonary mechanics and indirect calorimetry did not differ between pre- and postsuction sets of measurements. Pre- and postsuction VO2, VCO2, dynamic airway resistance, dynamic compliance, and expiratory minute ventilation remained stable from 5 to 55 min after tracheal suctioning and did not differ among different ventilatory modes. Average paired differences of sequential pre- and postsuction VO2, VCO2, respiratory quotient, and resting energy expenditure were -0.6%, -1%, -0.1%, and -0.3%. Ratio differences between the first and the second periods of measurements (1-25 vs 26-50 sets of 1-min measurements) did not differ in the two groups. Pulmonary mechanics and indirect calorimetry measurements are not influenced after uneventful open ETS in well-sedated patients. The E-COVX is able to reliably record spirometry and metabolic indices as early as 5 min after suctioning at different ventilator modes.

Commentary: Morrow B, Futter M, Argent A. (2006). Effect of endotracheal suction on lung dynamics in mechanically‐ventilated paediatric patients

AbstractEndotracheal suctioning is performed regularly in ventilated infants and children to remove obstructive secretions. The effect of suctioning on respiratory mechanics is not known. This study aimed to determine the immediate effect of endotracheal suctioning on dynamic lung compliance, tidal volume and airway resistance in mechanically ventilated paediatric patients by means of a prospective observational clinical study. Lung mechanics were recorded for 5 min before and 5 min after a standardized suctioning procedure in 78 patients intubated with endotracheal tubes of ≤4·0 mm internal diameter. Twenty‐four patients with endotracheal tube leaks ≥20% were excluded from analysis. There was a significant overall decrease in dynamic compliance (p &lt; 0·001) and mechanical expired tidal volume (p = 0·03) following suctioning with no change in the percentage of endotracheal tube leak (p = 0·41). The change in dynamic compliance was directly related to both endotracheal tube and catheter sizes. There was no significant change in expiratory or inspiratory airway resistance following suctioning (p &gt; 0·05). Although most of the patients (68·5%) experienced a drop in dynamic compliance following suctioning, dynamic compliance increased in 31·5% of patients after the procedure. This study demonstrates that endotracheal suctioning frequently causes an immediate drop in dynamic compliance and expired tidal volume in ventilated children with variable lung pathology, intubated with small endotracheal tubes, probably indicating loss of lung volume caused by the suctioning procedure. There is no evidence that suctioning reduces airway resistance. Abstract reprinted from the Australian Journal of Physiotherapy volume 52, Morrow B et al., ‘Effect of endotracheal suction on lung dynamics in mechanically‐ventilated paediatric patients’, pages 121–126. © 2006, reproduced with permission from the Australian Physiotherapy Association.

Effect of endotracheal suction on lung dynamics in mechanically-ventilated paediatric patients

Endotracheal suctioning is performed regularly in ventilated infants and children to remove obstructive secretions. The effect of suctioning on respiratory mechanics is not known. This study aimed to determine the immediate effect of endotracheal suctioning on dynamic lung compliance, tidal volume, and airway resistance in mechanically-ventilated paediatric patients by means of a prospective observational clinical study. Lung mechanics were recorded for five minutes before and five minutes after a standardised suctioning procedure in 78 patients intubated with endotracheal tubes < or = 4.0 mm internal diameter. Twenty-four patients with endotracheal tube leaks > or = 20% were excluded from analysis. There was a significant overall decrease in dynamic compliance (p < 0.001) and mechanical expired tidal volume (p = 0.03) following suctioning with no change in the percentage endotracheal tube leak (p = 0.41). The change in dynamic compliance was directly related to both endotracheal tube and catheter sizes. There was no significant change in expiratory or inspiratory airway resistance following suctioning (p > 0.05). Although the majority of patients (68.5%) experienced a drop in dynamic compliance following suctioning, dynamic compliance increased in 31.5% of patients after the procedure. This study demonstrates that endotracheal suctioning frequently causes an immediate drop in dynamic compliance and expired tidal volume in ventilated children with variable lung pathology, intubated with small endotracheal tubes, probably indicating loss of lung volume caused by the suctioning procedure. There is no evidence that suctioning reduces airway resistance.

Cardiopulmonary effects of dexmedetomidine in sevoflurane-anesthetized sheep with and without nitric oxide inhalation

To determine whether inhaled nitric oxide (NO) prevents pulmonary hypertension and improves oxygenation after i.v. administration of a bolus of dexmedetomidine in anesthetized sheep. 6 healthy adult sheep. In a crossover study, sevoflurane-anesthetized sheep received dexmedetomidine (2 microg/kg, i.v.) without NO (DEX treatment) or with inhaled NO (DEX-NO treatment). Cardiopulmonary variables, including respiratory mechanics, were measured before and for 120 minutes after bolus injection of dexmedetomidine. Dexmedetomidine induced a transient decrease in heart rate and cardiac output. A short-lived increase in mean arterial pressure (MAP) and systemic vascular resistance (SVR) was followed by a significant decrease in MAP and SVR for 90 minutes. Mean pulmonary arterial pressure (MPAP) and pulmonary vascular resistance increased transiently after dexmedetomidine injection. The Pao2 was significantly decreased 3 minutes after injection and reached a minimum of (mean +/- SEM) 13.3 +/- 78 kPa 10 minutes after injection. The decrease in Pao2 was accompanied by a sudden and prolonged decrease in dynamic compliance and a significant increase in airway resistance, shunt fraction, and alveolar dead space. Peak changes in MPAP did not differ between the 2 treatments. For the DEX-NO treatment, Pao2 was significantly lower and the shunt fraction significantly higher than for the DEX treatment. Inhalation of NO did not prevent increases in pulmonary arterial pressures induced by i.v. administration of dexmedetomidine. Preemptive inhalation of NO intensified oxygenation impairment, probably through increases in intrapulmonary shunting.

Subject index of volume 202

Pulmonary responses to ozone exposure (1.0 ppm) were investigated in mice sensitized to ovalbumin compared with control mice receiving saline. Pulmonary function parameters were measured by pneumotachography. Arterial blood gases and the concentrations of soluble intercellular adhesion molecule-1 (sICAM-1) and tumor necrosis factor-α (TNF-α) in bronchoalveolar lavage fluid were analyzed. Ozone exposure, when compared with filtered air exposure, caused significantly larger decreases in dynamic compliance (P<0.05) and minute ventilation (P<0.05) in ovalbumin-sensitized mice but not in control mice. Moreover, the decrease in minute ventilation in response to ozone exposure was significantly greater (P<0.01) in ovalbumin-sensitized mice than in control mice. Ozone exposure caused a significant decrease in PaO2 in ovalbumin-sensitized mice but not in control mice. PaO2 after ozone exposure tended to be smaller in ovalbumin-sensitized mice than in control mice. The concentration of sICAM-1 in bronchoalveolar lavage fluid increased in ovalbumin-sensitized mice, but effects of ozone exposure were not observed. These results indicated that sensitization of the immune system to ovalbumin might be a risk factor which aggravates the effects of ozone exposure on the respiratory system.

Mast cells and reactive oxygen species in citric acid-induced airway constriction.

The noncholinergic airway constriction is mediated by tachykinins, mainly neurokinin A and substance P, and this bronchoconstriction is usually enhanced during inflammatory episodes. We demonstrated previously that reactive oxygen species play an important role in capsaicin-, hyperventilation-, and citric acid (CA) inhalation-induced noncholinergic airway constriction. For understanding cellular involvement, we further investigated the relationship between mast cells, bradykinin (BK), reactive oxygen species, and noncholinergic airway constriction. Sixty-five guinea pigs were divided into seven groups: saline control; CA; BK + CA; cromolyn sodium (CS) + CA; BK + CS + CA; compound 48/80 + CA; and compound 48/80 + BK + CA. CS was used to stabilize mast cells, whereas a secretagogue, compound 48/80, was for the depletion of mast cells. Each animal was anesthetized, cannulated, paralyzed, and ventilated artificially. In control animals, CA aerosol inhalation caused decreases in dynamic compliance and forced expiratory parameters, indicating CA-induced noncholinergic airway constriction. Either CS or compound 48/80 significantly attenuated the CA-induced airway constriction. Also, we detected a significant increase in lucigenin-initiated chemiluminescence counts of the bronchoalveolar lavage sample in the BK + CA group. Furthermore, CA exposure caused an increase in bronchoalveolar lavage substance P level. Either CS or compound 48/80 prevented the above CA-induced increases in chemiluminescence and substance P. These results suggest that mast cells play an important role in CA aerosol inhalation-induced airway constriction via perhaps releasing constricting factors.

Use of the impulse oscillometry system for testing pulmonary function during methacholine bronchoprovocation in horses.

To compare sensitivity of the impulse oscillometry system (IOS) with that of the conventional reference technique (CRT; ie, esophageal balloon method) for pulmonary function testing in horses. 10 horses (4 healthy; 6 with recurrent airway obstruction [heaves] in remission). Healthy horses (group-A horses) and heaves-affected horses (group-B horses) were housed in a controlled environment. At each step of a methacholine bronchoprovocation test, threshold concentration (TC(2SD); results in a 2-fold increase in SD of a value) and sensitivity index (SI) were determined for respiratory tract system resistance (R(rs)) and respiratory tract system reactance (X(rs)) at 5 to 20 Hz by use of IOS and for total pulmonary resistance (RL) and dynamic lung compliance (C(dyn)), by use of CRT. Bronchoconstriction resulted in an increase in R(rs) at 5 Hz (R(5Hz)) and a decrease in X(rs) at all frequencies. Most sensitive parameters were X(rs) at 5 Hz (X(5Hz)), R(5Hz), and R(5Hz):R(10Hz) ratio; RL and the provocation concentration of methacholine resulting in a 35% decrease in dynamic compliance (PC(35)C(dyn)) were significantly less sensitive than these IOS parameters. The TC(2SD) for X(rs) at 5 and 10 Hz was significantly lower in group-B horses, compared with group-A horses. The lowest TC(2SD) was obtained for X(5Hz) in group-B horses and R(5Hz) in group-A horses. In contrast to CRT parameters, IOS parameters were significantly more sensitive for testing pulmonary function. The IOS provides a practical and noninvasive pulmonary function test that may be useful in assessing subclinical changes in horses.