Chemical regulation of ventilation during isoflurane sedation and anaesthesia in humans

To assess the effects of isoflurane on chemical regulation of ventilation, we studied the ventilatory responses to (1) hyperoxic hypercarbia, (2) isocapnic hypoxaemia, and (3) a single half vital capacity breath of carbon dioxide. 20 per cent in oxygen in 12 human subjects, awake and sedated or anaesthetized with isoflurane, 0.1 or 1.1 MAC. Sedation did not alter ventilation nor the ventilatory response to hypercarbia but reduced the responses to hypoxaemia and to the half vital capacity breath of CO₂. Anaesthesia reduced ventilation and the response to hypercarbia and nearly abolished the responses to hypoxaemia and to the breath of CO₂. The results indicate that isoflurane reduces ventilatory responses to several chemical drives and that it selectively impairs those responses mediated by peripheral chemoreceptors. In these respects, isoflurane is similar to halothane and enflurane.     

Enflurane requirement and ventilatory response to carbon dioxide during lidocaine infusion in dogs.

Arterial plasma lidocaine concentration of 1 to 3.5 microgram/ml produced dose-related decreases in enflurane requirement (MAC) ranging from 15 to 37 per cent in dogs. The ventilatory responses to carbon dioxide at comparable depths of anesthesia with enflurane alone and the enflurane-lidocaine combination were measured in each animal and compared. With both anesthetic regimens there were increases in resting arterial carbon dioxide tension (mean maximal increase = 18 torr) and a 69 per cent decrease in the slope of the ventilatory response as depth of anesthesia increased. The effect of the drug interaction appears to be additive, since the ventilatory depression produced by the enflurane-lidocaine combination was no greater than that produced by enflurane alone at equivalent levels of anesthesia.     

Effects of caudal block with mepivacaine on resting ventilation and ventilatory response to carbon dioxide in sedated children

We examined the effects of caudal anaesthesia using 10 mg.kg-1 of one or two per cent mepivacaine without epinephrine on resting ventilation, arterial blood gas tensions and the ventilatory response to carbon dioxide in 27 sedated children. Expired minute volume and respiratory frequency decreased significantly after the caudal blocks in both groups. PaO2 and PaCO2 remained unchanged in both groups. The slope of the CO2 response curve increased significantly in both groups. The mean plasma mepivacaine levels were 4.6 +/- 1.6 (SD) and 4.6 +/- 1.0 micrograms.ml-1 20 minutes after the caudal blocks with one and two per cent mepivacaine, respectively. These results demonstrate that resting ventilation is impaired but the ventilatory response to carbon dioxide is improved similarly by caudal block with one or two per cent mepivacaine.     

Lung function, breathing pattern, and gas exchange in interstitial lung disease.

BACKGROUND: The aim of this study was to determine the relation between the severity of abnormalities in ventilatory function tests and tidal breathing pattern and gas exchange indices in interstitial lung disease. METHODS: Pulmonary function, ventilation, carbon dioxide production, oxygen consumption, arterial blood gas tensions, and pH were measured during resting steady state conditions in 60 patients with proved interstitial lung disease. Patients were categorised by forced vital capacity (FVC) (percentage of predicted values) as having a mild, moderate, or severe restrictive defect with means (SD) of 71% (4%), 57% (4%), and 41% (7%) of predicted values, respectively. RESULTS: FVC varied from 29% to 79% of predicted values and from 0.99 l to 4.32 l. The two measurements of FVC correlated strongly with most static lung volumes and with transfer factor for carbon monoxide. Mean respiratory rates (per minute) and tidal volumes (ml) were 17 (4) and 484 (131), 20 (4) and 460 (139), and 23 (5) and 377 (109) in mild, moderate, and severe restrictive defects, respectively. FVC correlated negatively with respiratory rate and positively with tidal volume. Arterial carbon dioxide tension ranged from 30 to 49 mm Hg; only two patients were hypercapnic. Mean arterial oxygen tensions were not significantly different among the three groups, and there were no significant correlations between forced expiratory volume in one second or FVC and arterial carbon dioxide tension or carbon dioxide production. CONCLUSION: Low values of FVC were associated with increased respiratory rate and decreased tidal volume; this pattern of breathing mimics external elastic loading, suggesting that mechanoreceptors may contribute to the rapid and shallow pattern of breathing in interstitial lung disease. Hypercapnia seems to be rare in interstitial lung disease even when functional impairment is severe and tidal volume is small. The increased respiratory rate is important in maintaining adequate ventilation. In the face of a severe restrictive defect carbon dioxide production did not increase, which also contributed to the maintenance of eucapnia.     

Postoperative hypoxaemia: oesophagectomy with gastric replacement

Pre- and postoperative arterial blood samples were analysed for oxygen partial pressure (PaO2) and carbon dioxide partial pressure (PaCO2) in a consecutive series of 21 patients subjected to two- or three-stage oesophagectomy for carcinoma of the oesophagus. The forced vital capacity (FVC) was measured at the same time. On the second postoperative day the PaO2 showed a fall to 65 per cent of the preoperative value followed by a gradual recovery to 78 per cent on the tenth postoperative day. After 13 weeks the PaO2 had recovered to 95 per cent of the preoperative value. The PaCO2 decreased in the early postoperative period but had returned to the preoperative level by the tenth day. The FVC showed a trend similar to the PaO2 with a reduction to 33 per cent of the preoperative value on the second postoperative day, 52 per cent on the tenth day and 85 per cent after 13 weeks.     

Correlation between integrated evoked EMG and respiratory function following atracurium administration in unanaesthetized humans

In six healthy volunteers, integrated evoked electromyography (IEEMG) measured in response to ulnar nerve stimulation was correlated with respiratory function-tidal volume (VT), forced vital capacity (FVC), forced expiratory volume in one second (FEV1), maximum negative inspiratory pressure (NIP), hand grip (HG) and head-lift during steady-state infusion of subparalytic doses of atracurium. Studies were carried out at train-of-four T4/T1 = 0.2 and T4/T1 = 0.6. When T4/T1 = 0.2, all subjects had difficulty with swallowing and phonation, none could sustain any head-lift and HG was 26 per cent of control. However, VT was normal, FVC was 80 per cent, FEV1 was 82 per cent, and NIP was 50 per cent of control. AT T4/T1 = 0.6, all assessments of peripheral strength were normal, and all respiratory measurements were not significantly different from control, except for NIP which was 73 per cent of control (P less than 0.05). We conclude that an IEEMG of 0.6, recorded from the hypothenar muscles, in unanaesthetized subjects is consistent with near normal respiratory function.     

Treatment of ununited fractures of the scaphoid by iliac bone grafts and Kirschner-wire fixation

Of 151 ununited fractures of the scaphoid that were treated with iliac bone grafts and Kirschner-wire fixation through a volar approach, all but four (97 per cent) healed in an average of seventeen weeks, Three of the four failures resulted from obvious technical errors. Neither the preoperative existence of necrosis of the proximal fragment nor the location of the fracture affected the results. When there was mild radiocarpal arthritis preoperatively, it did not progress postoperatively; if there was moderate radiocarpal arthritis preoperatively, progression seldom was seen if a radial styloidectomy was done. Displaced and unstable ununited fractures healed even if the deformity was not corrected completely. The principal benefit of the procedure was relief of pain rather than an increase either in motion of the wrist or in strength of grip.     

Assessment of fitness in patients with cystic fibrosis and mild lung disease

BACKGROUND: Maximal exercise testing is used in patients with cystic fibrosis to assess functional status and prognosis. The lactate threshold is an index of aerobic fitness with significant advantages over maximal exercise tests. This study was undertaken to determine if the lactate threshold might be identified, non-invasively, in adult patients with cystic fibrosis and mild lung disease by measurement of ventilatory and gas exchange parameters. METHODS: Ten subjects with mild cystic fibrosis (forced vital capacity (FVC) > 70% predicted) and 10 healthy controls undertook an incremental exercise test on a bicycle ergometer. Ventilation and gas exchange parameters were measured continually and arterialised venous blood pH, carbon dioxide tension (PCO2), and lactate concentrations were measured at intervals throughout the tests. RESULTS: In subjects with cystic fibrosis there was no significant difference between the mean gas exchange and lactate thresholds (mean difference 1.0 (95% confidence interval (CI) of the mean -1.5 to 3.44) ml/kg/min). In contrast, there was a significant difference between the mean ventilatory and lactate thresholds (3.8 (95% CI 0.9 to 6.7) ml/kg/min). Arterialised venous PCO2 increased significantly during the exercise tests. In healthy subjects the mean differences between these thresholds were not significantly different from zero and PCO2 fell significantly during the tests. CONCLUSIONS: The ventilatory threshold significantly overestimates the lactate threshold in subjects with cystic fibrosis induced lung disease because of impaired carbon dioxide excretion during exercise. However, the gas exchange threshold may be used to determine the lactate threshold in this patient group.


     

Delayed diaphragm recovery in 12 patients after high cervical spinal cord injury. A retrospective review of the diaphragm status of 107 patients ventilated after acute spinal cord injury

STUDY DESIGN: The functional outcome of the diaphragm after acute spinal cord injury was reviewed over a 16 year period for 107 patients who had required assisted ventilation in the acute phase. OBJECTIVES: To quantify the incidence of recovery of diaphragm function which occurred beyond the period of acute oedema; to produce a time-related profile of this as a guide to clinicians considering phrenic nerve pacing; and to assess the value of phrenic nerve testing in predicting recovery. SETTING: The Southport Regional Spinal Injuries Centre, Southport, England. METHODS: Bilateral phrenic nerve and diaphragm integrity was assessed clinically, by spirometry, and by fluoroscopy without and with phrenic nerve stimulation. RESULTS: Thirty-one per cent of all the ventilated patients (33 cases), with a level of injury between C1 and C4 (Scale A in ASIA Impairment Scale), had diaphragmatic paralysis at the time of respiratory failure. The subsequent diaphragm recovery which appeared in seven of these patients, between 40 and 393 days (mean 143), permitted weaning from ventilatory support at 93 to 430 days (mean 246) after the acute injury, with a vital capacity of over 15 ml kg(-1) at that stage. The diaphragm recovery in a further five patients, whose vital capacity remained below 10 ml kg(-1) and who could not be fully weaned, occurred significantly later, between 84 and 569 days (mean 290), P=0.053. Negative phrenic nerve tests were followed by weaning at a later interval in several cases. By contrast, one patient with an early positive phrenic stimulation test and subsequent diaphragm activity could not be weaned from the ventilator. CONCLUSION: Twenty-one per cent of the patients with initial diaphragm paralysis were ultimately able to breathe independently after 4 and 14 months, whilst a further 15% had some diaphragm recovery. Phrenic nerve testing should be repeated at 3 monthly intervals for the first year after high tetraplegia.     

Two-stage flexor-tendon reconstruction. Ten-year experience

One hundred and fifty fingers in 136 patients were treated by a two-stage flexor-tendon reconstruction and followed for an average of 2.4 years. A salvage procedure such as this was needed for most of these fingers since 81 per cent of the injuries were in Zone 2 and 45 per cent were Grade 5 in severity. Before reconstruction, the mean total active motion (all joints combined) for each finger was 102 degrees and the mean grip strength was 20 per cent of normal. At final follow-up, the mean total active motion of these fingers was 176 degrees and the mean grip strength was 79 per cent of normal. Three months after tendon-grafting, the results had reached a plateau, and no significant change occurred thereafter. Complications were a flexion contracture of varying degree in 41 per cent of the fingers, especially when a contracture was present preoperatively (40 per cent); rupture of the tendon graft in 14 per cent; and infection in 4 per cent. This review reaffirmed the usefulness of two-stage flexor-tendon reconstruction as a salvage procedure to restore function of flexor tendons.     

Pulmonary function in adolescents with mild idiopathic scoliosis.

Spirometric indices, lung volumes, maximum voluntary ventilation, and maximum inspiratory and expiratory pressures were measured in 44 adolescents with mild idiopathic scoliosis (spinal curvature less than 30 degrees). All were symptom free, but six (13.6%) showed a restrictive defect with forced vital capacity less than 80% of predicted. In 12 subjects (27.3%) maximum voluntary ventilation was reduced to less than 80% of predicted normal. Forced vital capacity was significantly correlated with maximum inspiratory pressure and with maximum expiratory pressure, measures of respiratory muscle strength, but was not related to the degree of thoracic curvature. When maximum inspiratory pressure and forced vital capacity were corrected for differences in body size these variables remained positively correlated, most significantly in the girls. These data indicate that ventilatory function may be impaired in mild, idiopathic scoliosis and that the force developed by the respiratory muscles is a more important determinant of this impairment than the radiologically determined degree of spinal curvature.     

The effects of carbon dioxide on pulmonary mechanics in hyperventilating, normal volunteers.

Transpulmonary pressure, air flow, and end-tidal carbon dioxide levels were measured in normal human volunteers during hypocapnic, eucapnic, and hypercapnic hyperventilation. Respiratory rate and tidal volumes were well matched at a minute ventilation of 52 L. on three inspired gas mixtures: 21 per cent oxygen and 79 per cent nitrogen; 5 per cent carbon dioxide, 21 per cent oxygen and 74 per cent nitrogen; and 12 per cent carbon dioxide, 21 per cent oxygen and 67 per cent nitrogen. Respiratory rate, tidal volume, lung compliance, resistance, and resistive work per liter were calculated with a digital computer. In 13 experiments in 7 normal volunteers, no net bronchoconstriction or bronchodilatation was observed when eucapnic hyperventilation was compared to hypocapnic or hypercapnic hyperventilation. During hyperventilation of this degree, a change in bronchomotor tone owing to alteration in arterial or alveolar PCO2 either does not occur or else is masked by other reflexes or mechanical factors acting on the bronchi.     

Effect of doxapram on control of breathing in cats.

The effects of doxapram infusion (0.25 mg.kg-1. min-1) were studied in cats anaesthetized with pentobarbitone (35 mg . kg-1 intraperitoneally). Cats were studied breathing 50 per cent oxygen and the responses to two concentrations of inspired carbon dioxide were measured. Doxapram infusion increased pulmonary ventilation by increasing both tidal volume and respiratory frequency, and also caused increases in the volume inspired in the first 0.5 second after the onset of an inspiration (V0.5) and the pressure generated in the airway 0.5 second after the onset of an inspiration when the airway had been occluded (P degrees 0.5). V 0.5, P degrees 0.5 and the mean inspiratory flow rate (VT/VI) were essentially equivalent indices of inspiratory drive. Doxapram infusion did not alter the effective impedance of the respiratory system (P degrees 0.5/V 0.5). Doxapram infusion increased the ventilatory response to carbon dioxide. The slope of the ventilatory response to carbon dioxide was increased and the response line was shifted to the left. We conclude that the increase in pulmonary ventilation caused by doxapram infusion is due almost entirely to increased inspiratory neuromuscular drive (P degrees 0.5).     

Respiratory depression following diazepam: reversal with high-dose naloxone

The authors compared the effects of naloxone and saline solution on the respiratory changes following diazepam in a double-blind crossover trial in six subjects. Following baseline measurements of respiration, each subject was given diazepam, 15 mg, intravenously. Sixty and ninety-five minutes later each subject received either two doses of naloxone, 15 mg, intravenously, or two doses of the equivalent volume of saline solution. Forty-five minutes after diazepam administration the slopes of the curves of the ventilatory responses to rebreathing carbon dioxide (VE/PETCO2) were depressed to 53 per cent of control (P < 0.05). Following the two doses of naloxone, the slopes of VE/PETCO2 recovered, until, 120 minutes after the second dose of naloxone, slopes had returned to control values. After saline solution, however, slopes remained depressed at 68 per cent of control (P < 0.05). A similar recovery following naloxone was observed in the PETCO2 intercept of the VE/PETCO2 response curve and in the slope of the mouth-occlusion-pressure response curve to rebreathing carbon dioxide. End-tidal carbon dioxide during quiet breathing and during inspiratory resistive-loaded breathing (80 cm H2O/l/s) showed small increases after diazepam, which were not significantly reduced by naloxone. The results of this study show that diazepam produces respiratory depression, and that this may be relieved by large doses of naloxone.     

Low-level laser therapy with a wrist splint to treat carpal tunnel syndrome: a double-blinded randomized controlled trial

The efficacy of low-level laser therapy (LLLT) was evaluated in a total of 66 patients with mild to moderate carpal tunnel syndrome (CTS) with a double-blinded randomized controlled study. The patients were randomly assigned into two groups. Group I received 15 sessions of a gallium-aluminum-arsenide laser treatment at a dosage of 18 J per session over the carpal tunnel area with neutral wrist splint. Group II received placebo laser therapy with neutral wrist splint. The patients were evaluated with the following parameters: (1) clinical parameters which consisted of visual analog scale, symptom severity scale, functional status scale, and pinch strength and grip strength before the treatment and at 5- and 12-week follow-ups and (2) electroneurophysiological parameters from nerve conduction study which were evaluated before the treatment and at 12-week follow-up. Fifty nine patients (112 hands: unilateral CTS?=?6 hands and bilateral CTS?=?106 hands) completed the study. Both groups I and II had n?=?56 hands. Improvements were significantly more pronounced in the LLLT-treated group than the placebo group especially for grip strength at 5- and 12-week follow-ups. At 12-week follow-up, distal motor latency of the median nerve was significantly improved in the LLLT group than the placebo group (p?<?0.05). LLLT therapy, as an alternative for a conservative treatment, is effective for treating mild to moderate CTS patients. It can improve hand grip strength and electroneurophysiological parameter with a carry-over effect up to 3 months after treatment for grip strength of the affected hands.     

SOME RESPIRATORY EFFECTS OF A MODIFIED KNEE-ELBOW POSITION DURING ANAESTHESIA

A modified knee-elbow position which facilitates the repairof vesico-vaginal fistulae is described. Some respiratory effectsconsequent on the assumption of this position were investigated.In twenty-seven conscious male subjects the vital capacity wasreduced by an average of 16.3 per cent on assuming the position.In twelve patients under light anaesthesia with halothane therewas no difference in mean values for respiratory rate, minutevolume, arterial carbon dioxide tension and oxygen saturationobtained in the modified knee-elbow and in the supine position.It is concluded that the use of this position in patients withhealthy lungs does not increase the hazards of the operationif respiratory muscle function is not impaired by deep anaesthesiaor the injudicious use of muscle relaxants.     

The detection of feigned hand weakness using the five position grip strength test.

This study assessed the sensitivity and specificity of the five-position grip strength test (5PGST) for detecting feigned hand weakness in healthy volunteers. The 5PGST reliably detected feigned hand weakness in only 15% of cases. Thirty-three per cent of volunteers demonstrated an entirely normal pattern of grip strength when feigning weakness.     

Respiratory muscle and pulmonary function in polymyositis and other proximal myopathies

We studied 53 patients with proximal myopathy to determine at what level of muscle weakness hypercapnic respiratory failure is likely, and which tests of pulmonary function or respiratory muscle strength would best suggest this development. Respiratory muscle strength was determined from maximal static efforts and in half the patients, both inspiratory and expiratory muscle strengths were less than 50% of normal. In the 37 patients without lung disease respiratory muscle weakness was accompanied by significant decreases in vital capacity, total lung capacity, and maximum voluntary ventilation; by significant increases in residual volume and arterial carbon dioxide tension (PaCO2); and greater likelihood of dependence on ventilators, atelectasis, and pneumonia. Hypercapnia was particularly likely when respiratory muscle strength was less than 30% of normal in uncomplicated myopathy, and when vital capacity was less than 55% of the predicted value in any patient.     

Results of compression-plating of closed Galeazzi fractures

Diaphyseal fractures of the distal third of the radius that are associated with disruption of the distal radio-ulnar joint accounted for eighty-four (6.8 per cent) of 1236 fractures in the forearm that were treated during a five-year period at the Los Angeles County-University of Southern California Medical Center. Thirty-six closed Galeazzi fractures, twenty-eight in male and eight in female patients, were followed for 1.5 to seven years after treatment using standard AO-compression plates with four to seven holes. Complications included seven injuries to the sensory or dorsal interosseous branch of the radial nerve, two infections, two non-unions, two re-fractures after plate removal, and shortening of the radius of five millimeters in one patient. The complication rate was 39 per cent. The average grip strength at follow-up was 71 per cent of the calculated normal value. The loss of strength was not related to use of a volar or dorsal surgical approach, the patient's age, or a delay of surgery for more than ten days after injury. The average loss of grip strength in the seven upper extremities with restricted motion of the wrist and forearm was 48 per cent, compared with an average loss of 29 per cent in the whole group. Of the twelve patients who were operated on more than ten days after injury, six had loss of motion at follow-up, compared with three who had such a loss among the twenty-four patients who were operated on within ten days after injury.(ABSTRACT TRUNCATED AT 250 WORDS)     

Herbert screw: results of a single-centre trial.

We report the results of a single-centre trial of the Herbert screw in the treatment of acute fractures, fracture-dislocations and non-unions of the carpal scaphoid. In the trial, 22 patients were studied with a maximum follow-up of 2.5 years. Of the patients, 84 per cent had minimal or no pain, and 94 per cent were happy with their result or significantly improved. There was an average loss of 34 per cent of radial deviation of the wrist and of 10 per cent in cylinder grip strength. On radiographic examination, 86 per cent achieved satisfactory union. However, only 73 per cent of type D2 fractures united. Overall, the subjective and objective clinical results achieved were more satisfactory than the radiographic results would suggest.