Evaluation of methods for indirect calorimetry with a ventilated lung model

A combined lung and ventilator model was built, validated and used to test commercial systems for indirect calorimetry. It simulates O₂ uptake and CO₂ excretion under ventilator treatment conditions. In the model inspiratory gases are diluted with N₂ and CO₂ to give the desired expiratory concentrations. Minute volume, F_I O ₂, ventilatory pressure, and consequently RQ can be altered to simulate the adult clinical situation. A selected respiratory pattern is maintained by the lung model. Equipment for indirect calorimetry can then be connected to it and the results compared. Reference values are derived from measurements with a mass spectrometer and a Godart spirometer. Three commercially available instruments (Beckman MMC, Horizon MMC and Engström MC) were evaluated with this system. The limits of agreement with the reference values under different conditions (F₁ O ₂ 0.4–0.7, ventilatory pressure 0–50 cmH₂O) were determined. Differences as high as 15% from the true values of and were observed. The pattern of mechanical ventilation and the intrinsic properties of the analyzers in the equipment used for indirect calorimetry influence measurements to a significant extent.This publication includes part of the thesis of J. Zundel and preliminary data were presented at the Workshop Salzburg 1986: Methodische Fragen zur indirekten Kalorimetrie.This publication includes part of the thesis of J. Zundel and preliminary data were presented at the Workshop Salzburg 1986: Methodische Fragen zur indirekten Kalorimetrie.     

Evaluation of a mobile unit for indirect calorimetry during spontaneous ventilation

Summary The Mijnhardt Oxycon-4 (OX-4), designed for measurements of gas exchange during exercise using a mouth-piece, was adapted for use in recumbant patients by the introduction of a transparent canopy and a suction device. This system was evaluated in laboratory models and in patients.     

婴幼儿密闭吸痰前提高吸氧浓度必要性的探讨

目的 研究机械通气下使用密闭式吸痰的婴幼儿吸痰前不常规提高吸氧浓度对患儿氧合的影响。 方法 通过对64例婴幼儿(192次吸痰操作),吸痰前不进行提高氧浓度的操作进行观察,分别记录患儿吸痰前平静时、吸痰中、吸痰后1min时患儿SpO₂的值和SpO₂恢复至平静时所需的时间。 结果 吸痰前不提高氧浓度,患儿在吸痰时及吸痰后SpO₂相对于吸痰前变化不明显。吸痰后SpO₂恢复至平静时的时间为18.00(5.25-30.00)s。 结论 吸痰前SpO₂稳定,并排除痉咳、心脏分流等原因的患儿,密闭式吸痰前没有必要常规给予提高吸氧浓度的操作。     

Effects of rapid permissive hypercapnia on hemodynamics,gas exchange,and oxygen transport and consumption during mechanical ventilation for the acute respiratory distress syndrome

Objective To measure the effects of rapid permissive hypercapnia on hemodynamics and gas exchange in patients with acute respiratory distress syndrome (ARDS).Design Prospective study.Setting: 18-bed, medical intensive care unit, university hospital.Patients 11 mechanically ventilated ARDS patients.Intervention Patients were sedated and ventilated in the controlled mode. Hypercapnia was induced over a 30–60 min period by decreasing tidal volume until pH decreased to 7.2 and/or P₅₀ increased by 7.5 mmHg. Settings were then maintained for 2 h.Results Minute ventilation was reduced from 13.5±6.1 to 8.2±4.1l/min (mean±SD), PaCO₂ increased (40.3±6.6 to 59.3±7.2 mmHg), pH decreased (7.40±0.05 to 7.26±0.05), and P₅₀ increased (26.3±2.02 to 31.1±2.2 mmHg) (p<0.05). Systemic vascular resistance decreased (865±454 to 648±265 dyne·s·cm^–5, and cardiac index (CI) increased (4±2.4 to 4.7±2.4 l/min/m²) (p<0.05). Mean systemic arterial pressure was unchanged. Pulmonary vascular resistance was unmodified, and mean pulmonary artery pressure (MPAP) increased (29±5 to 32±6 mmHg,p<0.05). PaO₂ remained unchanged, while saturation decreased (93±3 to 90±3%,p<0.05), requiring an increase in FIO₂ from 0.56 to 0.64 in order to maintain an SaO₂>90%. PvO₂ increased (36.5±5.7 to 43.2±6.1 mmHg,p<0.05), while saturation was unmodified. The arteriovenous O₂ content difference was unaltered. Oxygen transport (DO₂) increased (545±240 to 621±274 ml/min/m²,p<0.05), while the O₂ consumption and extraction ratio did not change significantly. Venous admixture (Q_va/Q_t) increased (26.3±12.3 to 32.8±13.2,p<0.05).Conclusions These data indicate that acute hypercapnia increases DO₂ and O₂ off-loading capacity in ARDS patients with normal plasma lactate, without increasing O₂ extraction. Whether this would be beneficial in patients with elevated lactate levels, indicating tissue hypoxia, remains to be determined. Furthermore, even though hypercapnia was well tolerated, the increase in Q_va/Q_t, CI, and MPAP should prompt caution in patients with severe hypoxemia, as well as in those with depressed cardiac function and/or severe pulmonary hypertension.     

An experimental randomized study of six different ventilatory modes in a piglet model with normal lungs

A randomized study of 6 ventilatory modes was made in 7 piglets with normal lungs. Using a Servo HFV 970 (prototype system) and a Servo ventilator 900 C the ventilatory modes examined were as follows: SV-20V, i.e. volume-controlled intermittent positive-pressure ventilation (IPPV); SV-20VIosc, i.e. volume-controlled ventilation (IPPV) with superimposed inspiratory oscillations; and SV-20VEf, i.e. volume-controlled ventilation (IPPV) with expiratory flush of fresh gas; HFV-60 denotes low-compressive high-frequency positive-pressure ventilation (HFPPV) and HVF-20 denotes low-compressive volume-controlled intermittent positive-pressure ventilation; and SV-20P denotes pressure-controlled intermittent positive-pressure ventilation. With all modes of ventilation a PEEP of 7.5 cm H₂O was used. In the abbreviations used, the number denotes the ventilatory frequency in breaths per minute (bpm). HFV indicates that all gas was delivered via the HFV 970 unit. The ventilatory modes described above were applied randomly for at least 30 min, aiming for a normoventilatory steady state. The HFV-60 and the HFV-20 modes gave lower peak airway pressures, 12–13 cm H₂O compared to approximately 17 cm H₂O for the other ventilatory modes. Also the mean airway pressures were lower with the HFV modes 8–9 cm H₂O compared to 11–14 cm H₂O for the other modes. The gas distibution was evaluated by N₂ washout and a modified lung clearance index. All modes showed N₂ wash-out according to a two-compartment model. The SV-20P mode had the fastest wash-out, but the HFV-60 and HFV-20 ventilatory modes also showed a faster N₂ wash-out than the others. Regarding the lung clearance index, the SV-20P, HFV-60 and HFV-20 modes showed better indices than the other modes. No relationship was found between the ventilatory mode and extravascular lung water, and there were no differences in the hemodynamic variables.This study was supported by the Swedish Medical Research Council (project 4252), Sweden     

Hydrogen peroxide ingestion associated with portal venousgas and treatment with hyperbaric oxygen: a case seriesand review of the literature

Introduction.?Ingestion of concentrated hydrogen peroxide (H₂O^₂) has been associated with venous and arterial gas embolic events, hemorrhagic gastritis, gastrointestinal bleeding, shock, and death. Although H^₂O^₂ is generally considered a benign ingestion in low concentrations, case reports have described serious toxicity following high concentration exposures. Hyperbaric oxygen (HBO) has been used with success in managing patients suffering from gas embolism with and without manifestations of ischemia.?Methods.?Poison center records were searched from July 1999 to January 2010 for patients with H^₂O^₂ exposure and HBO treatment. Cases were reviewed for the concentration of H₂O₂, symptoms, CT scan findings of portal gas embolism, HBO treatment, and outcome.?Results.?Eleven cases of portal gas embolism were found. Ages ranged from 4 to 89 years. All but one ingestion was accidental in nature. In 10 cases 35% H^₂O^₂ was ingested and in 1 case 12% H^₂O^₂ was ingested. All abdominal CT scans demonstrated portal venous gas embolism in all cases. Hyperbaric treatment was successful in completely resolving all portal venous gas bubbles in nine patients (80%) and nearly resolving them in two others. Ten patients were able to be discharged home within 1 day, and one patient had a 3.5-day length of stay.?Conclusions.?HBO was successful in resolving portal venous gas embolism from accidental concentrated H^₂O^₂ ingestions.     

Stimulus-induced Rotary Saturation (SIRS): a potential method for the detection of neuronal currents with MRI

Neuronal currents produce local transient and oscillatory magnetic fields that can be readily detected by MEG. Previous work attempting to detect these magnetic fields with MR focused on detecting local phase shifts and dephasing in T₂ or T₂-weighted images. For temporally biphasic and multi-phasic local currents the sensitivity of these methods can be reduced through the cancellation of the accrued phase induced by positive and negative episodes of the neuronal current. The magnitude of the phase shift is also dependent on the distribution of the current within the voxel. Since spins on one side of a current source develop an opposite phase shift relative to those on the other side, there is likely to be significant cancellation within the voxel.We introduce a potential method for detecting neuronal currents though their resonant T_1ρ saturation during a spin-lock preparation period. The method is insensitive to the temporal and spatial cancellation effects since it utilizes the multi-phasic nature of the neuronal currents and thus is not sensitive to the sign of the local field. To produce a T_1ρ reduction, the Larmor frequency in the rotating frame, which is set by γB_1lock (typically 20 Hz–5 kHz), must match the major frequency components of the stimulus-induced neuronal currents. We validate the method in MRI phantom studies. The rotary saturation spectra showed a sharp resonance when a current dipole within the phantom was driven at the Larmor frequency in the rotating frame. A 7 min block-design experiment was found to be sensitive to a current dipole strength of 56 nAm, an approximate magnetic field of 1 nT at 1.5 mm from the dipole. This dipole moment is similar to that seen using the phase shift method in a similar experimental setup by Konn et al. [Konn, D., Gowland, P., Bowtell, R., 2003. MRI detection of weak magnetic fields due to an extended current dipole in a conducting sphere: a model for direct detection of neuronal currents in the brain. Magn. Reson. Med. 50, 40–49], but is potentially less encumbered by temporal and spatial cancellation effects.     

The efficacy and safety of palonosetron compared with granisetron in preventing highly emetogenic chemotherapy-induced vomiting in the Chinese cancer patients: a phase II, multicenter, randomized, double-blind, parallel, comparative clinical trial

PURPOSE: This clinical trial was conducted to evaluate the efficacy and safety of Palonosetron in preventing chemotherapy-induced vomiting (CIV) among the Chinese cancer patients. PATIENTS AND METHODS: Two hundred and forty patients were scheduled to be enrolled and randomized to receive a single intravenous dose of palonosetron 0.25 mg, or granisetron 3 mg, 30 min before receiving highly emetogenic chemotherapy. The primary efficacy endpoint was the complete response (CR) rate for acute CIV (during the 0-24-h interval after chemotherapy). Secondary endpoints included the CR rates for delayed CIV (more than 24 h after chemotherapy). RESULTS: Two hundred and eight patients were accrued and received study medication. CR rates for acute CIV were 82.69% for palonosetron and 72.12% for granisetron, which demonstrated that palonosetron was not inferior to granisetron in preventing acute CIV. Comparisons of CR rates for delayed CIV yielded no statistical difference between palonosetron and granisetron groups and did not reveal non-inferiority of palonosetron to granisetron. Adverse events were mostly mild to moderate, with quite low rates among the two groups. CONCLUSIONS: A single dose (0.25 mg) of palonosetron is not inferior to a single dose (3 mg) of granisetron in preventing CIV and possesses an acceptable safety profile in the Chinese population.     

3:1 Compression to ventilation ratio versus continuous chest compression with asynchronous ventilation in a porcine model of neonatal resuscitation

Objective

In contrast to the resuscitation guidelines of children and adults, guidelines on neonatal resuscitation recommend synchronized 90 chest compressions with 30 manual inflations (3:1) per minute in newborn infants. The study aimed to determine if chest compression with asynchronous ventilation improves the recovery of bradycardic asphyxiated newborn piglets compared to 3:1 Compression:Ventilation cardiopulmonary resuscitation (CPR).

Intervention and measurements

Term newborn piglets (n = 8/group) were anesthetized, intubated, instrumented and exposed to 45-min normocapnic hypoxia followed by asphyxia. Protocolized resuscitation was initiated when heart rate decreased to 25% of baseline. Piglets were randomized to receive resuscitation with either 3:1 compressions to ventilations (3:1 C:V CPR group) or chest compressions with asynchronous ventilations (CCaV) or sham. Continuous respiratory parameters (Respironics NM3^®), cardiac output, mean systemic and pulmonary artery pressures, and regional blood flows were measured.

Main results

Piglets in 3:1 C:V CPR and CCaV CPR groups had similar time to return of spontaneous circulation, survival rates, hemodynamic and respiratory parameters during CPR. The systemic and regional hemodynamic recovery in the subsequent 4 h was similar in both groups and significantly lower compared to sham-operated piglets.

Conclusion

Newborn piglets resuscitated by CCaV had similar return of spontaneous circulation, survival, and hemodynamic recovery compared to those piglets resuscitated by 3:1 Compression:Ventilation ratio.     

The initial slope of the VCO<Subscript>2</Subscript>/VO<Subscript>2</Subscript>-curve (s1) in cardiopulmonary exercise testing is a strong and independent predictor of outcome in patients with previous myocardial infarction

Background  Detecting heart failure (HF) patients at risk is a relevant clinical problem. Our goal was to define associations of clinical HF-markers and exercise parameters with respect to their prognostic power in HF-patients. Methods  We performed cardiopulmonary exercise testing (CPET) in 103 ischemic HF-patients. CPET-parameters included peak VO₂, VO₂ at AT, peak oxygen pulse, minimal CO₂ and O₂ equivalents, VE/VCO₂ and s1, a motivation-independent and submaximal parameter representing the initial slope of the VCO₂/VO₂-curve that has not been described in HF-patients so far. Results  Median follow-up was 668 days. The combined endpoint of cardiovascular death and rehospitalization due to HF occurred in 14 patients. Patients with/without events differed significantly regarding their age, NYHA-class, LVEF and NT-proBNP serum-levels. Patients with events had significantly lower peak VO₂- and higher s1-values. NT-proBNP serum-levels, NYHA-class and LVEF were significantly correlated with peak VO₂. Only age, peak VO₂ and s1 were independent predictors of adverse events. Using multivariate analysis, s1 was a strong and independent parameter with good sensitivity and specificity. Conclusion  s1 is an independent and powerful predictor in HF-patients. Since s1 is independent of maximal exercise capacity, s1 might be more accurate for the evaluation of HF-patients not willing or unable to perform maximal exercise.     

Assessment of a new prototype hydrogel CO<Subscript><Emphasis Type="Bold">2</Emphasis></Subscript> sensor; comparison with air tonometry

Objective

Gastrointestinal ischemia is always accompanied by an increased luminal CO₂. Currently, air tonometry is used to measure luminal CO₂. To improve the response time a new sensor was developed, enabling continuous CO₂ measurement. It consists of a pH-sensitive hydrogel which swells and shrinks in response to luminal CO₂, which is measured by the pressure sensor. We evaluated the potential clinical value of the sensor during an in vitro and in vivo study.

Methods

The response time to immediate, and stepwise change in pCO₂ was determined between 5 and 15 kPa, as well as temperature sensitivity between 25 and 40 °C at two pCO₂ levels. Three sensors were compared to air tonometry (Tonocap^®) in healthy volunteers using a stepwise incremental exercise test, followed by a period of hyperventilation and an artificial CO₂-peak.

Results

The in vitro response time to CO₂ increase and decrease was mean 5.9 and 6.6 min. The bias, precision and reproducibility were +5%, 3% and 2%, resp. Increase of 1 °C at constant pCO₂ decreased sensor signal by 8%. In vivo tests: The relation with the Tonocap was poor during the exercise test. The response time of the sensor was 3 min during hyperventilation and the CO₂ peak.

Conclusion

The hydrogel carbon dioxide sensor enabled fast and accurate pCO₂ measurement in a controlled environment but is very temperature dependent. The current prototype hydrogel sensor is still too unstable for clinical use, and should therefore be improved.