Arterial Blood Gas Tensions Research Articles

The effects of epidural anesthesia on ventilatory response to hypercapnia and hypoxia in elderly patients.

Epidural anesthesia may impair pulmonary ventilation in elderly people. We examined the effects of lumbar or thoracic epidural anesthesia on resting ventilation, arterial blood gas tensions, the ventilatory response to hypercapnia, and progressive isocapnic hypoxia in elderly patients. Two groups of eight unpremedicated elderly patients, aged 65 yr or older, undergoing lower or upper abdominal surgery, respectively, were studied twice before and 20 min after the lumbar or thoracic administration of 10 mL of 2% lidocaine. Lumbar epidural anesthesia had no significant effect on resting ventilation, whereas thoracic epidural caused a significant 13% decrease in minute ventilation and a 14% decrease in tidal volume (P < 0.05). The ventilatory response to hypercapnia was significantly increased after lumbar epidural anesthesia, but no change was observed after thoracic epidural anesthesia. The slope of the hypoxic response curve did not show any change in either group, but minute ventilation at a Spo2 of 90% significantly increased after lumbar epidural anesthesia (P < 0.05). We conclude that neither lumbar nor thoracic epidural anesthesia per se impairs the ventilatory response to hypercapnia and hypoxia, despite slight impairment in resting ventilation by thoracic epidural anesthesia, in elderly patients.

The Effects of Epidural Anesthesia on Ventilatory Response to Hypercapnia and Hypoxia in Elderly Patients

Epidural anesthesia may impair pulmonary ventilation in elderly people.We examined the effects of lumbar or thoracic epidural anesthesia on resting ventilation, arterial blood gas tensions, the ventilatory response to hypercapnia, and progressive isocapnic hypoxia in elderly patients. Two groups of eight unpremedicated elderly patients, aged 65 yr or older, undergoing lower or upper abdominal surgery, respectively, were studied twice before and 20 min after the lumbar or thoracic administration of 10 mL of 2% lidocaine. Lumbar epidural anesthesia had no significant effect on resting ventilation, whereas thoracic epidural caused a significant 13% decrease in minute ventilation and a 14% decrease in tidal volume (P < 0.05). The ventilatory response to hypercapnia was significantly increased after lumbar epidural anesthesia, but no change was observed after thoracic epidural anesthesia. The slope of the hypoxic response curve did not show any change in either group, but minute ventilation at a SpO2 of 90% significantly increased after lumbar epidural anesthesia (P < 0.05). We conclude that neither lumbar nor thoracic epidural anesthesia per se impairs the ventilatory response to hypercapnia and hypoxia, despite slight impairment in resting ventilation by thoracic epidural anesthesia, in elderly patients. (Anesth Analg 1996;82:306-11)

Lesson of the Week: Nephrotic syndrome in childhood complicated by life threatening pulmonary oedema

A consensus statement on nephrotic syndrome from the British Association for Paediatric Nephrology has recently recommended intravenous 20% albumin for the management of hypovolaemia in this condition.1 The suggested dose is 1 g/kg over one to two hours followed by frusemide. Caution is required with this treatment, however, as considerable fluid shift may occur.2 We describe three children who were transferred to our paediatric intensive care unit because they had developed life threatening fluid overload and pulmonary oedema after receiving an excessive dose or too rapid infusion of 20% albumin. Beware of infusing too much 20% albumin too quickly in children with nephrotic syndrome A 4 year old girl presented to her local hospital with a 10 day history of periorbital and lower limb oedema, a three day history of diarrhoea and vomiting, and oliguria for the past 24 hours. Urine analysis showed heavy proteinuria. The plasma albumin concentration was 15 g/l, urea concentration 11.6 mmol/l, creatinine concentration 41 μmol/l, haemoglobin concentration 120 g/l, and urinary sodium concentration 11 mmol/l. Nephrotic syndrome was diagnosed, and oral prednisolone was started. Oliguria persisted and her weight increased. There was no response to intravenous frusemide. She was given 20% albumin at a dose of 3.5 g/kg ideal body weight over four hours. During the infusion she became breathless, cyanosed, and had a generalised seizure followed by respiratory arrest. At intubation pink frothy sputum welled from the trachea. Initial arterial blood gas tensions when she was ventilated with 100% oxygen were pH 6.87, Pco2 8.7 kPa, Po2 5.9 kPa, base excess -24.6. Central venous pressure was +20 cm H2O. …

中高年層での呼吸機能と動脈血液ガス分析値に対する喫煙の影響

中高年層での呼吸機能と動脈血液ガス分析値に対する喫煙の影響

Peritoneal ventilation in rabbits: augmentation of gas exchange with cisapride.

Peritoneal ventilation has been shown to be effective in achieving extrapulmonary oxygenation and carbon dioxide elimination in an animal model of severe adult respiratory distress syndrome (ARDS). Cisapride is a "prokinetic" agent (increases gastric emptying), that may increase the splanchnic circulation and thus favourably affect gas exchange in peritoneal ventilation. Using Doppler ultrasound the effect of cisapride on the portal venous circulation was examined in eight spontaneously breathing rabbits and the effect of cisapride on gas exchange in five rabbits spontaneously breathing room air was compared with that of a control group who did not receive cisapride. Its effect on gas exchange in five rabbits with ARDS being treated with mechanical lung and peritoneal ventilation was compared with that of a control group, and its effect on gas exchange in five rabbits with ARDS treated with conventional ventilation was also compared with that of a control group. Enteral administration of cisapride increased portal venous blood velocity, as measured ultrasonographically, by a mean of 188% one hour after receiving the drug. In rabbits with ARDS being treated with both peritoneal ventilation and mechanical ventilation to the lungs, those receiving cisapride had arterial oxygen tensions 1.5-3 times that of controls. Cisapride had no effect on arterial blood gas tensions in rabbits who were spontaneously breathing room air, nor in rabbits with ARDS who received only conventional mechanical lung ventilation. Cisapride increases arterial oxygenation in rabbits with severe ARDS treated with peritoneal ventilation, probably due to its ability to increase splanchnic circulation. It should be considered as an adjuvant medication to peritoneal ventilation.

Long term effect of erythromycin therapy in patients with chronic Pseudomonas aeruginosa infection.

Diffuse panbronchiolitis is a chronic infection of the lower respiratory tract common among the Japanese people, with a persistent Pseudomonas aeruginosa infection in the late stage and sustained neutrophil retention in the airways. The long term effect of erythromycin was examined retrospectively in a group of patients with diffuse panbronchiolitis, with and without P aeruginosa infection, and the relationship between drug-induced bacterial clearance and clinical improvement was investigated. The history, daily volume of sputum, type of organisms in sputum cultures, pulmonary function tests, arterial blood gas tensions, and chest radiographs were compared in 16 patients with diffuse panbronchiolitis with P aeruginosa infection and 12 without. The total and differential cell counts in the bronchoalveolar lavage (BAL) fluid were compared in 14 of the 28 patients (five of whom were infected with P aeruginosa) before and after 1-12 months of treatment with erythromycin (600 mg/day). The outcome of treatment in patients showing clearance of organisms on repeated sputum cultures was compared with that in those demonstrating persistence of bacteria in the sputum and patients with normal flora. Erythromycin improved respiratory function and arterial blood gas tensions irrespective of the presence or absence of P aeruginosa in the sputum. Treatment also resulted in a reduction in the BAL fluid total cell count and the percentage of neutrophils in both groups of patients. There were no differences between patients in whom the bacteria cleared and those with persistent bacteria or patients with a normal flora with regard to the degree of improvement of respiratory function, arterial blood gas tensions, and BAL fluid cell composition. The results suggest that the efficacy of erythromycin in diffuse pan-bronchiolitis may be due to anti-inflammatory effect, independent of P aeruginosa infection or bacterial clearance.

Toluene diisocyanate induction of airway hyperresponsiveness at the threshold limit value (10 ppb) in rabbits.

Induction of acute lung injury and the development of airway hyperresponsiveness (AHR) by toluene diisocyanate (TDI) exposure was studied in a new rabbit model of occupational lung diseases. TDI in the range of the threshold limit value (TLV) of 10 ppb, as well as at 5 and 30 ppb, administered four times over a period of 1 h to three groups of eight rabbits, did not significantly alter airway resistance (RI), dynamic elastance (Edyn), slope of inspiratory pressure generation (delta Pes/tI), arterial pressure (Pa) or arterial blood gas tensions (PaO2, PaCO2). Airway responsiveness (AR) to aerosols of 2% acetylcholine (ACH) was measured before and after each TDI exposure. After TDI inhalation of 10 ppb over 4 h, the amplitude of the ACH-induced airway constrictor response indicated by the changes in Edyn rose significantly to almost twice the control response value (p < 0.005). Similar changes in the amplitude of RI and in the slope of delta Pes/tI were obtained. After inhalation of 5 ppb TDI, no changes in airway reactivity were observed. The responses of respiratory mechanical parameters to ACH rose to three to four times the control responses after exposure to 30 ppb TDI. In a control group of eight animals not undergoing TDI exposure, no significant changes of respiratory responses were obtained after inhalation of 0.2% ACH for 1 min. In summary, TDI atmospheres in the range of TLV increased AR to ACH within 4 h of exposure in this rabbit model. This augmented AR may indicate an increased risk for the development of isocyanate-induced obstructive lung diseases.

Effect of hemidiaphragmatic paresis caused by interscalene brachial plexus block on breathing pattern, chest wall mechanics, and arterial blood gases.

We investigated the effects of hemidiaphragmatic paresis caused by interscalene brachial plexus block on breathing patterns, chest wall mechanics, and arterial blood gas tensions using respiratory inductive plethysmography. Ten healthy patients received interscalene block with 20-40 mL 1.5% lidocaine with epinephrine. Rib cage contribution to tidal volume (%RC) increased from 28.9% +/- 9.7% to 50.0% +/- 8.3% (P < 0.01), respiratory frequency (f) increased from 14.6 +/- 3.2/min to 16.3 +/- 2.4/min (P < 0.05), and PaO2 decreased from 84.7 +/- 7.3 mm Hg to 78.0 +/- 9.5 mm Hg (P < 0.05). No significant changes were observed in tidal volume (VT), minute volume (VE), or PaCO2. These results indicated that VT, VE, and PaCO2 were maintained after interscalene block, apparently by increases in f and %RC to compensate for hemidiaphragmatic paresis caused by interscalene block. Nevertheless, PaO2 was reduced, presumably due to increased ventilation-perfusion mismatching. Recognizing that we studied healthy patients, the decrease in PaO2 may be more in patients with cardiopulmonary disease.

Effect of Hemidiaphragmatic Paresis Caused by Interscalene Brachial Plexus Block on Breathing Pattern, Chest Wall Mechanics, and Arterial Blood Gases

We investigated the effects of hemidiaphragmatic paresis caused by interscalene brachial plexus block on breathing patterns, chest wall mechanics, and arterial blood gas tensions using respiratory inductive plethysmography.Ten healthy patients received interscalene block with 20-40 mL 1.5% lidocaine with epinephrine. Rib cage contribution to tidal volume (%RC) increased from 28.9% +/- 9.7% to 50.0% +/- 8.3% (P <0.01), respiratory frequency (f) increased from 14.6 +/- 3.2/min to 16.3 +/- 2.4/min (P <0.05), and PaO2 decreased from 84.7 +/- 7.3 mm Hg to 78.0 +/- 9.5 mm Hg (P <0.05). No significant changes were observed in tidal volume (VT), minute volume (VE), or PaCO2. These results indicated that VT, VE, and PaCO2 were maintained after interscalene block, apparently by increases in f and %RC to compensate for hemidiaphragmatic paresis caused by interscalene block. Nevertheless, PaO2 was reduced, presumably due to increased ventilation-perfusion mismatching. Recognizing that we studied healthy patients, the decrease in PaO2 may be more in patients with cardiopulmonary disease. (Anesth Analg 1995;81:962-6)

Ventilatory and arterial blood gas tension adjustments to strenuous exercise in Standardbreds

SUMMARY Five healthy, fit Standardbreds (mean ± sem, 490.4 ± 15.0 kg, 4.0 ± 0.5 years) were studied during a standardized test carried out on a treadmill. The test consisted of an 8-minute warm-up and a 9-minute exercise period (1 minute at 1.7, 4, 7, 8, 9, and 10 m/s; 2 minutes at 4 m/s; and a 1-minute walk at a 6% slope). Respiratory airflow, tidal volume (Vt), and respiratory frequency (f) were continuously recorded, using 2 ultrasonic pneumotachographs connected to a face mask and mass spectrometer. Oxygen uptake, carbon dioxide output, and expired minute volume (V˙e) were obtained on a breath-by-breath basis. Arterial blood was tested at the end of each step for O2 and CO2 partial pressures. Heart rate was continuously recorded, using a heart rate recording system. Stride frequency was measured at each step, and the stride frequency-to-f ratio was calculated. Venous blood was tested for plasma lactate concentration before and 2 minutes after completion of the test. Some horses had a locomotion-respiration coupling (lrc), but this coupling was occasional and intermittent. The f was lower and Vt was higher than values reported for Thoroughbreds working under similar experimental conditions. Nevertheless, maximal V˙e did not overshoot maximal V˙e reported in Thoroughbreds. All horses were hypoxemic and hypercapnic, but there was wide variability between subjects. The horses with the highest oxygen uptake and the lowest plasma lactate concentration were more hypoxemic and hypercapnic. The Standardbreds, studied under our laboratory conditions, did not have constant lrc and had lower f with higher Vt than did Thoroughbreds under similar experimental conditions. Despite these differences in breathing strategy, the Standardbreds did not have higher V˙e than did Thoroughbreds, and they were hypoxemic and hypercapnic. The fact that these Standardbreds, which obviously freely selected their breathing strategy, were unable or unwilling to adopt compensatory hyperventilation reinforces the hypothesis that, in strenuous exercising horses, there could be a physiologic limit to ventilation, most probably related to mechanical factors, but independent of any lrc.

Control of breathing in patients with limb girdle dystrophy: a controlled study.

In patients with limb girdle dystrophy the relative contribution of peripheral factors (respiratory muscle weakness, and lung and/or airway involvement) and central factors (blunted and/or inadequate chemoresponsiveness) in respiratory insufficiency has not yet been established. To resolve this, lung volumes, arterial blood gas tensions, respiratory muscle strength, breathing pattern and neural respiratory drive were investigated in a group of 15 patients with limb girdle dystrophy. An age-matched normal group was studied as a control. Respiratory muscle strength was assessed as an arithmetic mean of maximal inspiratory (MIP) and expiratory (MEP) pressures. Breathing pattern was evaluated in terms of volume (ventilation VE, tidal volume VT) and time (respiratory frequency Rf, inspiratory time TI, expiratory time TE) components of the respiratory cycle. Neural respiratory drive was assessed as the mean inspiratory flow (VT/TI), mouth occlusion pressure (P0.1) and electromyographic activity (EMG) of the diaphragm (EMGd) and the intercostal parasternal (EMGp) muscles. In 10 of the 15 patients the responses to carbon dioxide (PCO2) stimulation were also evaluated. Most patients exhibited a moderate decrease in vital capacity (VC) (range 37-87% of predicted), MIP (range 23-84% of predicted), and/or MEP (range 13-41% of predicted). The arterial carbon dioxide tension (PaCO2) was increased in three patients breathing room air, while PaO2 was normal in all. Compared with the control group Rf was higher, and VT, TI and TE were lower in the patients. EMGd and EMGp were higher whilst VT/TI and P0.1 were normal in the patients. Respiratory muscle strength was inversely related to EMGd and EMGp. PaCO2 was found to relate primarily to VC and duration of illness, but not to respiratory muscle strength. During hypercapnic rebreathing delta VE/delta PCO2, delta VT/delta PCO2, and delta P0.1/delta PCO2 were lower than normal, whilst delta EMGd/delta PCO2 and delta EMGp/delta PCO2 were normal in most patients. A direct relation between respiratory muscle strength and delta VT/delta PCO2 was found. The respiratory muscles, especially expiratory ones, are weak in patients with limb girdle dystrophy. Reductions in respiratory muscle strength are associated with increased neural drive and decreased ventilatory output (delta VT/delta PCO2). The decrease in VC, together with the duration of disease, influence PaCO2. VC is a more useful test than respiratory muscle strength for following the course of limb girdle dystrophy.

Effect of fentanyl on the minimum alveolar concentration of isoflurane in swine.

Fentanyl is used in anesthetic protocols for swine, but there are no reports on its potency in this species. This study measured the extent to which fentanyl reduces the minimum alveolar concentration of isoflurane (MACISO) in swine. Sixteen swine were randomly assigned to four groups. For each group, baseline MACISO was determined, and three groups received two of three fentanyl infusions as follows: 50 micrograms.kg-1.h-1 intravenously followed by 100 micrograms.kg-1.h-1, 50 micrograms.kg-1.h-1 followed by 200 micrograms.kg-1.h-1, or 100 micrograms.kg-1.h-1 followed by 200 micrograms.kg-1.h-1 (n = 8 for each dosage). A loading dose of fentanyl preceded each infusion. Each infusion was maintained for 60 min before initiating minimum alveolar concentration determination. The infusions were maintained throughout the period of minimum alveolar concentration determination. Plasma fentanyl samples were obtained after 30 min of each infusion, and plasma fentanyl and hemodynamic parameters were obtained immediately before stimulating swine for the final isoflurane concentration used in determining minimum alveolar concentration. A fourth group, control animals, received saline infusions. After each infusion, the MACISO was redetermined. Minimum alveolar concentration was determined using incremental changes in isoflurane concentrations until gross purposeful movement resulted when using a hemostat stimulus applied for 1 min to a rear dewclaw. MACISO for controls was 2.19 +/- 0.17% (mean +/- SEM) and changed minimally over time (-0.13 +/- 4.77%). MACISO decreased significantly (P < or = 0.01) 24.5 +/- 3.2%, 29.9 +/- 4.8%, and 45.9 +/- 5.5% with fentanyl dosages of 50, 100, and 200 micrograms.kg-1.h-1, respectively. Corresponding plasma fentanyl concentrations were 14 +/- 1 ng/ml, 26 +/- 3 ng/ml, and 59 +/- 5 ng/ml, respectively. A ceiling effect on reduction of MACISO was not observed. Changes over time or between groups were not observed for arterial blood gas tensions, blood pressure, heart and respiratory rate, or body temperature. These fentanyl dosages are larger than those commonly used in humans and other species. Anesthetic protocols using fentanyl for swine should be designed with the knowledge that a fentanyl infusion of 200 micrograms.kg-1.h-1 contributes approximately a 50% MACISO equivalent.

Evaluation of pulmonary function and analgesia in dogs after intercostal thoracotomy and use of morphine administered intramuscularly or intrapleurally and bupivacaine administered intrapleurally

SUMMARY Eighteen dogs undergoing lateral thoracotomy at the left fifth intercostal space were randomly assigned to 1 of 3 postoperative analgesic treatment groups of 6 dogs each as follows: group A, morphine, 1.0 mg/kg of body weight, im; group B, 0.5% bupivacaine, 1.5 mg/kg given interpleurally; and group C, morphine, 1.0 mg/kg given interpleurally. Heart rate, respiratory rate, arterial blood pressure, arterial blood gas tensions, alveolar-arterial oxygen differences, rectal temperature, pain score, and pulmonary mechanics were recorded hourly for the first 8 hours after surgery, and at postoperative hours 12, 24, and 48. These values were compared with preoperative (control) values for each dog. Serum morphine and cortisol concentrations were measured at 10, 20, and 30 minutes, hours 1 to 8, and 12 hours after treatment administration. All dogs had significant decreases in pHa, PaO2, and oxygen saturation of hemoglobin, and significant increases in PaCO2 and alveolar-arterial oxygen differences in the postoperative period, but these changes were less severe in group-B dogs. Decreases of 50% in lung compliance, and increases of 100 to 200% in work of breathing and of 185 to 383% in pulmonary resistance were observed in all dogs after surgery. Increases in work of breathing were lower, and returned to preoperative values earlier in group-B dogs. The inspiratory time-to-total respiratory time ratio was significantly higher in group-B dogs during post-operative hours 5 to 8, suggesting improved analgesia. Blood pressure was significantly lower in group-A dogs for the first postoperative hour. Significant decreases in rectal temperature were observed in all dogs after surgery, and hypothermia was prolonged in dogs of groups A and C. Significant differences in pain score were not observed between treatment groups. Cortisol concentration was high in all dogs after anesthesia and surgery, and was significantly increased in group-B dogs at hours 4 and 8. Significant differences in serum morphine concentration between groups A and C were only observed 10 minutes after treatment administration. In general, significant differences in physiologic variables between groups A and C were not observed. Results of the study indicate that anesthesia and thoracotomy are associated with significant alterations in pulmonary function and lung mechanics. Interpleurally administered bupivacaine appears to be associated with fewer blood gas alterations and earlier return to normal of certain pulmonary function values. Interpleural administration of morphine does not appear to provide any advantages, in terms of analgesia or pulmonary function, compared with its im administration.

Microdialyzed adenosine in nucleus tractus solitarii and ventilatory response to hypoxia in piglets.

Levels of adenosine, inosine, and hypoxanthine from the interstitial space at the nucleus tractus solitarii were measured by microdialysis in eight 20- to 25-day-old anesthetized spontaneously breathing piglets. Microdialyzed samples were collected every 30 min for 2 h after the insertion of the probe to ensure stability of purine levels and then during 30 min each of normoxia, hypoxia (10% O2-90% N2), and normoxia. The purines were separated by high-pressure liquid chromatography with ultraviolet detection and quantified at 254-nm wavelength. Tidal volume, breathing frequency, minute ventilation, mean arterial blood pressure, pH, and gas tensions were measured. Compared with control, adenosine levels during hypoxia increased by 40.7 +/- 5.5% and then tended to decline during the recovery from hypoxia, but the levels remained higher than in control. Ventilatory measures exhibited a modest biphasic pattern during hypoxia and resumed control values by 10 min after the removal of the hypoxia. The increased adenosine release during hypoxia provides additional evidence for the possible participation of adenosine in the central suppression of breathing during hypoxia.

Postnatal maturation of the blood-brain barrier for unbound bilirubin in newborn piglets

The postnatal maturation of the blood-brain barrier (BBB) for unbound bilirubin was studied in 2-day- and 2-week-old piglets. Hyperbilirubinemia was induced by bolus infusion of bilirubin at 25 mg/kg followed by continuous infusion of 20 mg/kg/h for 3 h. During the study period, arterial blood pH and blood gas tensions, serum osmolarity, and mean arterial blood pressures were within the physiologic range. Brain bilirubin content and the brain/blood distribution ratio for bilirubin were higher in the 2-day-old than in the 2-week-old piglets. In both age groups, regional brain bilirubin concentration and brain/blood ratios were higher in subcortical regions (cerebellum and brainstem) than in the cerebral cortex. We conclude that in the newborn piglets the blood-brain barrier for unbound bilirubin matures with increasing postnatal age and that irrespective of maturity the relative permeability of the BBB for bilirubin appears higher in subcortical than in cortical regions.

Nocturnal saturation and respiratory muscle function in patients with chronic obstructive pulmonary disease.

Nocturnal desaturations, mainly caused by hypoventilation, occur frequently in patients with chronic obstructive pulmonary disease (COPD). Daytime arterial oxygen and carbon dioxide tensions (PaO2 and PaCO2) appear to predict which patients will desaturate at night. It is unknown if respiratory muscle strength, which may be decreased in these patients, plays an additional part. Polysomnography, maximal respiratory pressures, lung function, and arterial blood gas tensions were measured in 34 patients with COPD (mean (SD) forced expiratory volume in one second (FEV1) 41.7 (19.9)% pred). Significant correlations were found between the mean nocturnal arterial oxygen saturation and maximal inspiratory mouth pressure (r = 0.65), maximal inspiratory transdiaphragmatic pressure (r = 0.53), FEV1 (r = 0.61), transfer coefficient (KCO) (r = 0.38), arterial oxygen saturation (SaO2) (r = 0.75), and PaCO2 (r = -0.44). Multiple regression analysis showed that 75% of the variance in nocturnal SaO2 (70%) and FEV1 (5%). Inspiratory muscle strength and nocturnal saturation data are correlated, but daytime SaO2 and FEV1 remain the most important predictors of nocturnal saturation.

Outcome of domiciliary nasal intermittent positive pressure ventilation in restrictive and obstructive disorders.

Nasal intermittent positive pressure ventilation (NIPPV) is a new technique which has rapidly supplanted other non-invasive methods of ventilation over the last 5-10 years. Data on its effectiveness are limited. The outcome of long term domiciliary NIPPV has been analysed in 180 patients with hypercapnic respiratory failure predominantly due to chest wall restriction, neuromuscular disorders, or chronic obstructive lung disease. One hundred and thirty eight patients were started on NIPPV electively, and 42 following an acute hypercapnic exacerbation. Outcome measures were survival (five year probability of continuing NIPPV), pulmonary function, and health status. A crossover study from negative pressure ventilation to NIPPV was carried out in a subgroup of patients. Five year acturial probability of continuing NIPPV for individuals with early onset scoliosis (n = 47), previous poliomyelitis (n = 30), following tuberculous lung disease (n = 20), general neuromuscular disorders (n = 29), and chronic obstructive pulmonary disease (n = 33) was 79% (95% CI 66 to 92), 100%, 94% (95% CI 83 to 100), 81% (95% CI 61 to 100), 43% (95% CI 6 to 80), respectively. Most of the patients with bronchiectasis died within two years. One year after starting NIPPV electively the mean (SD) PaO2 compared with the pretreatment value was +1.8 (1.9) kPa, mean PaCO2 -1.4 (1.3) kPa in patients with extrapulmonary restrictive disorders, and PaO2 +0.8 (1.0) kPa, PaCO2 -0.9 (0.8) kPa in patients with obstructive lung disease. Arterial blood gas tensions improved in patients transferred from negative pressure ventilation to NIPPV. Health status was ranked highest in patients with early onset scoliosis, previous poliomyelitis, and following tuberculous lung disease. In the group as a whole health perception was comparable to outpatients with other chronic disorders. The long term outcome of domiciliary NIPPV in patients with chronic respiratory failure due to scoliosis, previous poliomyelitis, and chest wall and pulmonary disease secondary to tuberculosis is encouraging. The results of NIPPV in patients with COPD and progressive neuromuscular disorders show benefit in some subgroups. The outcome in end stage bronchiectasis is poor.

Indices of exercise capacity in horses presented for poor racing performance

SummaryWe examined 106 Thoroughbred (TB) and 51 Standardbred (SB) racehorses that were presented because of poor performance. All horses were in training and had raced within 2 weeks of presentation. Horses were acclimatised (2–4 runs) and tested on a treadmill set at a 10% slope. The exercise test consisted of 3 min at 4 m/s, 2 min at 6 m/s, then 1 min steps at 8, 10, 11, 12 and 13 m/s or until the horse could not maintain pace with the treadmill. At the end of each speed, arterial blood and expired gas samples were collected and heart rate recorded. Measurements during the test included: arterial blood gas tensions, plasma lactate concentration [LA], V̇O2, V̇CO2, O2 pulse (V̇O2/HR), heart rate, maximum stride length (SLmax), post exercise haematocrit (PCVPE), total red cell volume (CV) and total run time. The TB ran longer than SB (522 vs. 477 s) and had higher values for CV, PCVPE, V̇O2max, V̇O2‐200, maximum O2 pulse, V200, VHRmax, post exercise [LA] ([LAPE]) and SLmax. There were no breed differences for VLA4 and PaO2 at 10 m/s. In the TB, significant correlations (Spearman's rank order) (P&lt;0.01) were found for treadmill run time with: PCVPE, V̇O2max, V̇O2–200, peak O2 pulse, PaO2 at 10 m/s, PaCO2 at 10 m/s, V200, VLA4, [LAPE], VHRmax, maximum blood temperature and SLmax. In the SB significant but lower correlations (P&lt;0.05) were found for treadmill run time with: PCVPE, V̇O2max, V200, VLA4, [LAPE], VHRmax, maximum blood temperature and SLmax. While these results may not be applicable to normal racehorses, the indices which correlated best with treadmill run time were generally those indicating a high capacity for oxygen transport.

Cardiovascular effects after epidural injection of xylazine in isoflurane-anesthetized dogs.

The cardiovascular effects following epidural injection of xylazine or isotonic saline during isoflurane anesthesia were assessed in six healthy dogs. Dogs were anesthetized with isoflurane in O2 and maintained at 2.0% end-tidal concentration. Ventilation was controlled to maintain PaCO2 at 35 to 45 mm Hg. The dorsal pedal artery was cannulated for measurement of arterial blood pressure (AP)(systolic AP, mean AP, diastolic AP) and for blood sample collection. Arterial pH and blood gas tensions (PaO2 and PaCO2) were determined. Cardiac output was measured by thermodilution. The electrocardiogram (ECG), heart rate (HR), core body temperature, central venous pressure (CVP), mean pulmonary AP, and end-tidal isoflurane concentration (ETISO) and CO2 tension (ETCO2) were monitored. Systemic vascular resistance (SVR), arterial HCO2 concentration, base balance, and cardiac index (CI) were calculated. After baseline measurements were taken, either xylazine (0.2 mg/kg) in 5 mL isotonic saline or 5 mL of isotonic saline was injected into the lumbosacral epidural space. Data were then recorded at 5, 15, 30, 45, 60, 75, 90, 105, and 120 minutes after epidural injection. Data were analyzed by two-way analysis of variance (ANOVA) for repeated measures. When significant differences were encountered, mean values were compared using Bonferroni's test. The level of significance was set at P < .05. Mean values for diastolic AP decreased at 90 and 120 minutes compared with the mean value at 15 minutes after epidural injection of xylazine. No differences were detected at any time or between treatments for HR, systolic AP, mean AP, CVP, CI, SVR, mean pulmonary AP, temperature, ETCO2, ETISO, arterial pH, PaCO2, PaO2, plasma bicarbonate concentration, or base balance.(ABSTRACT TRUNCATED AT 250 WORDS)

Ventilation‐perfusion relationships during graded exercise in the Standardbred trotter

SummaryThe aim of this study was to evaluate pulmonary function in Standardbred trotters during graded exercise. The exercise test consisted of 4 work loads corresponding to 10%, 42%, 70% and 96% of the individual V̇O2max. Oxygen uptake was detected from an open bias flow system without valves. Cardiovascular and haemodynamic data were recorded at walk and during steady state exercise in 7 horses. Pulmonary gas exchange was assessed by conventional blood gas variables (arterial and mixed venous blood gas tensions) and the ventilation‐perfusion distribution V̇A|Q̇ as estimated by the multiple inert gas elimination technique. The dispersion of perfusion and ventilation distribution respectively (SDQ) and the difference between measured PaO2 and that predicted on the basis of amount of ventilation‐perfusion mismatching and shunt that was observed (predicted‐measured), were determined. The latter reflects mostly diffusion limitation. At the highest work load the PaCO2 increased to 50.3 torr. V̇A|Q̇ inequality increased significantly with exercise [mean log = 0.32 ± 0.03 (walk) and 0.46 ± 0.06 (heavy exercise), P &lt; 0.01]. Alveolar‐capillary diffusion limitation of oxygen was evident at and above exercise at 70% of V̇O2max. The arterial hypoxaemia seen during the highest work load was a result of a) hypoventilation, accounting for 4%, b) increase in V̇A|Q̇ mismatch, accounting for 41% and c) considerable diffusion limitation of oxygen, accounting for 55%.