Intrahospital transport of critically ill patients: complications and difficulties.

An audit of 97 intrahospital transports of critically ill patients was undertaken within Westmead Hospital. The aims of this audit were to assess all factors that may lead to problems during intrahospital transports. At the completion of a transport medical staff were asked to provide information about their patient and their treatment, as well as any difficulties they may have encountered. Overall, 62% of transports reported some difficulty or complication. Of these, 31% were patient-related and 45% were related to equipment or the transport environment. (15% encountered problems in both areas). Many of the difficulties were preventable with adequate pre-transport communication and planning. Other problems were directly related to the increased severity of illness in these patients.

Barriers to hepatitis C transmission within breathing systems: efficacy of a pleated hydrophobic filter.

It has been suggested that breathing circuits contaminated with body fluids may provide a route of nosocomial patient-to-patient transmission of the hepatitis C virus. Thus, a number of authorities have recommended the use of breathing circuit filters to minimize such risks. The present study sought to simulate a humidified breathing circuit and evaluate two different designs of breathing circuit filters to determine their efficacy in preventing passage of the hepatitis C virus. A hydrophobic pleated-membrane filter consistently prevented the passage of hepatitis C virus while a large-pore "electret" filter design was ineffective. We conclude that not all filter types are equally suited to preventing the passage of viruses and we therefore consider it essential that, if filters are intended to prevent the passage of named pathogens in a humidified breathing circuit, they should be evaluated in a similar experimental system to that described in order to prove their efficacy.

Arteriovenous fistula following lumbar disc surgery--the use of total cardiopulmonary bypass during repair.

Arteriovenous fistula is a rare complication of lumbar disc surgery and there is often a delay in diagnosis. A patient who developed multi-system failure associated with an aortocaval fistula, which occurred following a lumbar disc operation, is presented in this study. Surgical repair was facilitated by the use of total cardiopulmonary bypass which enabled a degree of safety and control that would have been difficult to obtain with standard methods.

Evaluation of the transcutaneous electrical nerve stimulator for postoperative analgesia following cardiac surgery.

The effectiveness of transcutaneous electrical nerve stimulation (TENS) in postoperative pain relief was assessed in this prospective randomised controlled study of 31 patients during the first 72 hours after cardiac surgery. Fourteen patients were given functioning TENS units, and seventeen patients were given non-functioning units. Postoperative pulmonary function tests, analgesic requirements and the incidence of atelectasis were compared in the two groups. Morphine requirement was significantly reduced on the second postoperative day and peak expiratory flow rates (PEFR) were significantly improved for the first two postoperative days in patients with functioning TENS units. The forced vital capacity (FVC) was significantly larger with functioning TENS units on the second postoperative day, but there were no other significant differences in forced expiratory volume in one second (FEV1) or forced vital capacity (FVC) values between the two groups. A questionnaire given to patients assessing their opinions of the effectiveness of the TENS unit for analgesia showed a placebo effect in some patients with non-functioning units. In summary, this study suggests that TENS may be of benefit in postoperative pain relief after cardiac surgery, especially on the second postoperative day.

Intraoperative diagnosis of rate-dependent bundle branch block.

Rate-dependent left bundle branch block (LBBB) occasionally occurs during anaesthesia when the heart rate exceeds a critical value. While it is usually a benign disorder, it may mask the electrocardiographic manifestations of myocardial ischaemia and the ST-T wave pattern associated with LBBB may be mistaken for those of ischaemia. This case report presents two cases in which rate-dependent LBBB was clearly documented during the perioperative period. It demonstrates the use of pharmacologic agents (e.g., atropine and neostigmine) and physiologic manipulations (e.g., carotid sinus massage) to alter the heart rate and confirm the diagnosis of benign rate-dependent LBBB in the operating room. These interventions should be used with caution in patients who have hypertension, angina, cerebrovascular, or AV node disease or in the setting of myocardial ischaemia or severe bundle branch disease.

Low-dose fentanyl blunts circulatory responses to tracheal intubation.

The effect of fentanyl, 8 micrograms/kg, used as an adjunct to thiopental for induction of anesthesia, on the circulatory response to tracheal intubation was investigated in 36 patients undergoing major vascular surgery. Patients were randomly assigned to receive either thiopental, 6 mg/kg, alone (N = 18), or thiopental, 3 mg/kg, along with fentanyl, 8 micrograms/kg (N = 18), for induction of anesthesia. The electrocardiogram, arterial pressure, pulmonary capillary wedge pressure, cardiac output, and central venous pressure were measured during induction of anesthesia, laryngoscopy, and intubation. Mean arterial blood pressure increased more following intubation in patients given thiopental than in patients given fentanyl-thiopental, reaching a peak value of 144 +/- 4 torr in patients receiving thiopental only, compared with 108 +/- 6 torr in those receiving fentanyl and thiopental (p less than 0.0001). Increases in systolic blood pressure, diastolic blood pressure, and pulmonary capillary wedge pressure with intubation were also significantly greater following administration of thiopental than following fentanyl-thiopental. Doses of fentanyl that are low enough to cause little postoperative respiratory depression significantly blunt postintubation hypertension when used as an adjunct to thiopental.

Pulmonary mechanics and gas exchange in seated normal men with chest restriction.

Lung volumes, static pressure-volume curves, maximal expiratory flow-volume curves, right-to-left intrapulmonary shunts (Qs/Qt), and distributions of ventilation and perfusion relative to the alveolar ventilation and perfusion ration (VA/Q) were determined in seated normal men before chest strapping while breathing air (Cair) and during chest strapping while breathing air (Sair) or 100% oxygen (So2). With Sair and So2, mean vital capacity was reduced by 44% from control. Elastic recoil pressure [Pst(L)] of the lung at 50% control total lung capacity (TLC) increased significantly (P less than 0.05) from 4.64 +/- 0.39 cmH2O (mean +/- SE) to 7.00 +/- 0.47 cmH2O with Sair and to 7.24 +/- 0.70 cmH2O with So2. Maximal expiratory flow at 50% of control TLC increased significantly (P less than 0.05) from 3.22 to 0.25 l/s (mean +/- SE) to 5.84 +/- 0.69 l/s with Sair and to 5.50 +/- 0.68 l/s with So2. With Sair, no significant increase in Qs/Qt from control was observed. With So2, mean Qs/Qt increased significantly (P less than 0.05) from 0 to 2.2 +/- 0.9% of the cardiac output. It is therefore unlikely that the development of atelectasis, as indicated by an increase in Qs/Qt, accounts for the increase in Pst (L) with Sair and So2. Current evidence suggests that either change in alveolar surface compliance or distortion of the lung or both are responsible for the increased recoil pressure but that neither mechanism alone appears to explain it totally.

Hypoxemia and general anesthesia: an analysis of distribution of ventilation and perfusion.

There is now overwhelming evidence that anesthesia with and without muscle paralysis is associated with an increased inefficiency of gas exchange, with abnormal oxygenation and CO2 elimination. There is great variation in the degree of this change from individual to individual; it results from increased right-to-left intrapulmonary shunting, increased alveolar dead space, increased dispersion of VA/Q ratios, altered cardiac output, and changes of the ODC. In normal subjects the abnormality can be largely explained by mismatch of ventilation and perfusion. Distribution of perfusion is determined by right ventricular output, the distribution of pulmonary vascular impedance, and their mutual interaction. This interaction is specifically influenced by gravity, right heart dynamics, systemic hemodynamics, particularly via the left atrium, and lung inflation. General anesthesia modifies the distribution of perfusion, largely to the extent that the above determinants are changed by: the particular anesthetic agents used; the posture adopted (gravity); the type and extent of ventilation employed; hypoxic pulmonary vasoconstriction; and any accompanying special techniques such as deliberate hypotension. Ventilation distribution is dependent on the posture of the subject and changes of the lung volumes and mechanics, which probably result from altered chest wall and diaphragm mechanics. These changes occur soon after induction of anesthesia and do not appear to be progressive. They can persist, however, well into the postoperative period. Alterations of pulmonary function during anesthesia and surgery are rarely life threatening in the operating room. Awareness of the problems of hypoxemia during general anesthesia and an appropriate response by the anesthesiologist, however, is a prerequisite of good medical practice.

Inert gas a-A differences: a direct reflection of V/Q distribution.

A computer model was developed to study the relationship between ventilation-to-perfusion (V/Q) mismatch and the development of inert gas arterial-to-alveolar partial pressure differences (a-A differences). Increasing inhomogeneity of V/Q ratio is revealed directly as an increase in the a-A difference of each gas. The quantitative relationships between the Q vs. V/Q distribution and the fractional a-A difference solubility plot (a-A difference plot) were studied and described. These studies demonstrated that for log normally distributed V/Q ratios, the area under the a-A difference plot is linearly related to the log variance of the V/Q distribution and can be estimated directly from the values obtained from six gases. The maximum a-A difference occurs for a gas whose solubility is numerically equal to the mean V/Q. The effects of departure from log normality and multimodality are discussed. We conclude from these studies that quantitative information regarding the degree of inhomogeneity of V/Q for log normal distribution is available from direct calculations of inert gas retention and excretion data. Qualitative information is also available indicating the departure from log normality and the region toward which the distribution is skewed.

A portable, low cost ventilation system for transportation of patients with severe acute respiratory failure.

As part of the development of a life support stretcher for transportation of critically ill patients, a portable ventilation system was developed. This system was used successfully during transportation of 6 of 11 patients who required ventilatory assistance and who were being considered for extracorporeal membrane oxygenator support. Immediately after transportation, PaCO2 values were significantly lower (p less than 0.05) in patients ventilated with this system, when compared to PaCO2 values of the remaining 5 patients in whom ventilation was assisted with a 2-liter anesthesia bag (PaCO2 = 58.7 +/- 3.6). This system offers significant advantages over other presently manufactured systems, including low cost, portability, and efficiency in terms of oxygen utilization. (Manual ventilation is supplied so that no auxiliary electrical power supply is necessary.) Positive end-expiratory pressure (PEEP) can be varied by 2.5 cm H2O increments using a commercially available, weighted ball valve. In addition, it has been useful for transporting patients with acute respiratory failure within the hospital for therapeutic maneuvers or diagnostic studies.

Effects of Intersept micropore filtration of blood on microaggregates and other constituents.

Micropore filtration (Intersept) of whole, stored blood was examined in two studies. In Study A, 1 unit of 14-day-old blood flowed by gravity across the filter. In Study B, the filter was preloaded by passage of 2 units of blood, and the effects on a third, consisting of 21-day-old blood, flowing under 150 mm Hg pressure, were examined. Filtration did not significantly alter erythrocyte count, total hemoglobin, plasma hemoglobin, erythrocyte fragility, plasma sodium, potassium, albumin, or globulin in either study, although some platelets and leukocytes were removed. Microaggregates, assessed by Coulter counting, screen filtration pressure, total screen proteins, wet and dry weights of material retained, and scanning electron microscopy, were satisfactorily removed over the whole range of particle sizes. Comparison with the Bentley PFS-127, Fenwal 4C2417, Pall Ultipore, and Swank IL200 filters led to the conclusion that the Intersept is the most efficient filter available at the present time for removing microaggregates during massive blood transfusion.