Alternative modes of ventilation. Part I. Disadvantages of controlled mechanical ventilation: intermittent mandatory ventilation.

Controlled mechanical ventilation is an accepted therapy for acute respiratory failure but by virtue of the increase in intrathoracic pressure has a large number of disadvantages. It is to overcome these disadvantages that alternative modes of ventilation have been introduced. These aim to reduce the effects of abnormally high airway pressure on the lung whilst recruiting solid alveoli and at the same time maintaining effective blood volume. Intermittent mandatory ventilation is a mode of ventilation first introduced to aid weaning which may reduce the need for sedation, permit better tolerance of high levels of PEEP and maintain urine osmolar output. High frequency ventilation utilising low airway pressures can maintain pulmonary gas exchange whilst reducing the effects of stretch on the lung. Its major role would seem to be in cases of bronchopleural fistula and necrotising pneumonia where a low mean airway pressure is essential. Low frequency positive pressure ventilation with extra corporeal CO2 removal, whilst a very labour intensive technique, has produced a favourable outcome in patients with terminal respiratory failure. Use of PEEP is associated with further deleterious haemodynamic effects which are largely overcome with use of continuous positive airway pressure during spontaneous respiration. PEEP is widely used. Its effect on pulmonary compliance, dead space and oxygen delivery are unpredictable making haemodynamic monitoring mandatory. Inversed ratio ventilation requires further evaluation whereas differential lung ventilation is logical, complicated but very valuable where the time constants for each lung are significantly different.

Electrolyte measurement by clinicians.

The development of automated techniques for the measurement of electrolytes using ion-selective electrode technology has resulted in the availability of such machines for use by clinicians. A study is described which compares values obtained for plasma sodium and potassium by interested clinicians using a Beckman Electrolyte 2 analyser, with results obtained by laboratory staff using a Beckman E2A autoanalyser. A total of 14 estimations each for sodium and potassium were made on 96 samples of venous blood from patients on an intensive care unit. Comparisons were made using the coefficient of variation and analysis of variance (ANOVA). Seventy-three percent of observations of sodium and 87% of observations of potassium made by clinicians lie within 2 mmol l-1 and 0.2 mmol l-1 respectively, of observations made by laboratory staff. Observations outside these ranges are examined. The authors conclude that the results obtained by interested clinicians lie well within acceptable limits for medical usefulness, that inappropriate therapy based on such results is unlikely, and that such estimations would appear to be safe and acceptably accurate.

Isoflurane for prolonged sedation in the intensive care unit; efficacy and safety.

OBJECTIVE: To compare isoflurane with midazolam for prolonged sedation in ventilated patients. DESIGN: Randomised controlled study. SETTING: General intensive care unit in university teaching hospital. PATIENTS: Sixty patients aged 17-80 years who required mechanical ventilation for more than 24 h. INTERVENTIONS: Sedation with either 0.1-0.6% isoflurane in an air-oxygen mixture (30 patients) or a continuous infusion of midazolam 0.02-0.20 mg/kg/h (30 patients). Sedation was assessed initially and hourly thereafter on a six point scale. The trial sedative was stopped when the patient was ready for weaning from ventilatory support. MEASUREMENTS AND RESULTS: Measurements were made of haemodynamic, respiratory and biochemical variables regularly during the period of sedation and for a week after stopping the sedative agent. There was no difference in any of the physiological or biochemical variables recorded between the two groups. Patients sedated with isoflurane recovered more rapidly and were weaned from mechanical ventilation sooner than those sedated with midazolam. CONCLUSIONS: Isoflurane is a useful agent for prolonged sedation of ventilated patients and does not have any adverse effect on the cardiorespiratory system or on hepatic, renal or adrenal function.

Sweet's syndrome associated with systemic inflammatory response syndrome.

Septic shock is characterised by infection causing a systemic inflammatory response, end-organ failure and acute circulatory collapse. Treatment consists of antimicrobial therapy and the supportive management of multi-organ failure. We report a case of what we believed to be septic shock due to pyelonephritis in a patient whose condition continued to deteriorate despite conventional treatment until the diagnosis of Sweet's syndrome was made. Once she was started on high dose steroids, her condition improved and she made a full recovery. We believe this to be the first case of a severe systemic inflammatory response syndrome associated with Sweet's syndrome.

Plasma catecholamine concentration during sedation in ventilated patients requiring intensive therapy.

The effects of isoflurane and midazolam sedation on the catecholamine responses of ventilated patients were studied over a 24-h period. Sixty ventilated patients admitted to our intensive therapy unit were allocated randomly to receive either isoflurane or midazolam sedation. Arterial blood samples for plasma catecholamine concentrations were taken at baseline, 6 h after starting sedation and at the end of the study period. Patients sedated with isoflurane showed a progressive reduction in both adrenaline and noradrenaline concentrations during the period of sedation which reached statistical significance for adrenaline at 6 h (p less than 0.02) and at the end of the study (p less than 0.001). Patients sedated with midazolam showed no significant changes of adrenaline or noradrenaline concentrations. Overall, a more satisfactory degree of sedation was achieved with isoflurane.

An outbreak of aspergillosis in a general ITU.

Over a 5-month period, six patients in a general intensive therapy unit became colonized by Aspergillus species including Aspergillus fumigatus, and invasive infection occurred in at least two of them. Broncho-alveolar lavage was unhelpful in discriminating between infection and colonization. The source of infection was presumed to be disturbance of an accumulation of spores in fibrous insulation material above the perforated metal ceiling. Patients in such units without clearly identifiable defects of defence against infection may be at risk from aspergillosis. The risk can be reduced by improved hospital design, satisfactory ventilation and thorough regular cleaning of environmental surfaces.

APACHE II scoring system on a general intensive care unit: audit of daily APACHE II scores and 6-month survival of 691 patients admitted to a general intensive care unit between May 1990 and December 1991.

In this paper we present a detailed analysis of the use of the APACHE II (acute physiological and chronic health evaluation) scoring system on all of the patients admitted to the general intensive care unit at the Bristol Royal Infirmary over a 20-month period. The 6-month survival of 691 adult medical and surgical patients following intensive care was recorded and this data was analysed with admission and daily APACHE II scores using a relational database. Our data confirms the relationship between admission APACHE II scores and outcome, with mean scores decreasing as duration of survival increases. We also demonstrate that the best day one scores are approximately 50% less than the admission score, irrespective of outcome, indicating the benefit of intensive care. By contrast, however, the scores on day one have either not improved or have worsened since admission, reflecting the importance of the pre-morbid health status of the patient in determining outcome from intensive care.

Isoflurane compared with midazolam for sedation in the intensive care unit.

OBJECTIVE: To compare isoflurane with midazolam for sedation of ventilated patients. DESIGN: Randomised control study. Setting--Intensive care unit in university teaching hospital. PATIENTS: Sixty patients aged 18-76 who required mechanical ventilation. INTERVENTIONS: Sedation with either 0.1-0.6% isoflurane in an air-oxygen mixture (30 patients) or a continuous intravenous infusion of midazolam 0.01-0.20 mg/kg/h (30 patients). Sedation was assessed initially and hourly thereafter on a six point scale. Incremental intravenous doses of morphine 0.05 mg/kg were given for analgesia as required. The trial sedative was stopped when the patient was judged ready for weaning from ventilatory support or at 24 hours (whichever was earlier). END POINT: Achievement of a predetermined level of sedation for as much of the time as possible. MAIN RESULTS: Isoflurane produced satisfactory sedation for a greater proportion of time (86%) than midazolam (64%), and patients sedated with isoflurane recovered more rapidly from sedation. CONCLUSION: Isoflurane is a promising alternative technique for sedation of ventilated patients in the intensive care unit.

Elective ventilation of potential organ donors.

Elective ventilation describes the procedure of transferring selected patients dying from rapidly progressive intracranial haemorrhage from general medical wards to intensive care units for a brief period of ventilation before confirmation of brain stem death and harvesting of organs. This approach in Exeter has led to a rate of kidney retrieval and transplant higher than has been achieved elsewhere in the United Kingdom, with a stabilisation of numbers on patients on dialysis. Recently doubt has been cast on the legality of our practice of elective ventilation on the grounds that relatives are not permitted to consent to treatment of an incompetent person when that treatment is not in the patient's best interests. We are thus faced with the dilemma of a protocol that is ethical, practical, and operates for the greater good but which may be illegal. This article explores various objections to the protocol and calls for public, medical, and legal debate on the issues.

Fluid and electrolyte disorders. Water.

It is very rare for disturbances of water balance to occur as isolated phenomena. More commonly, mixed electrolyte abnormalities present. However, to permit the logical application of therapy an understanding of basic water balance in health and disease is essential.

Malignant hyperthermia susceptibility. Management during pregnancy and labour.

A case of pregnancy complicated by malignant hyperthermia susceptibility is reported. Serum CPK and electrolyte concentrations were measured during pregnancy and labour. Labour and delivery were managed successfully under epidural analgesia using plain bupivacaine 0.5%.

Paranasal sinusitis: a complication of nasotracheal intubation. Two case reports.

Reports are presented on two patients who developed severe paranasal sinusitis in association with prolonged nasotracheal intubation. The likely predisposing factors are discussed.