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Biomedical subjects

R J Byrick

Publications and source records attributed to R J Byrick.

68 records · Page 4Linked to original sources
PubMed1980

Respiratory compensation during spontaneous ventilation with the Bain circuit.

The volume of carbon dioxide rebreathed by spontaneously breathing patients under halothane anaesthesia at various fresh gas flow rates (FGF) with the Bain modification of the Mapleson "D" breathing circuit is measured. The effect of rebreathing on a heterogeneous patient population is shown to be unpredictable hypercapnia in those patients who cannot respond adequately to this carbon dioxide challenge. All adults rebreathe significant volumes of carbon dioxide at a FGF rate of 100 ml . kg-1 . min-1. This carbon dioxide load is a potential risk to every patient and this hypercapnia is preventable by using high FGF rates. Rebreathing occurs because the inspired carbon dioxide load is unpredictable in a given patient and the patient's response is uncontrolled. Patients respond to this carbon dioxide challenge by increasing inspiratory flow rate (Vt/Ti), which results in increased rebreathing of carbon dioxide from the expiratory limb of the circuit. To prevent potentially dangerous rebreathing of carbon dioxide in all patients the fresh gas flow rate must be much higher than presently recommended.

Adult↗
PubMed1980

Respiratory waveform and rebreathing in T-piece circuits: a comparison of enflurane and halothane waveforms.

The effects of respiratory waveform on rebreathing in a modified Mapleson D circuit were studied in 18 healthy adult patients anesthetized with either enflurane or halothane. At high fresh gas flow (FGF) rate, when no rebreathing of CO2 occurred, the duration of inspiration (Ti) with enflurane was 41 per cent greater than that with halothane. With enflurane there was a characteristic long end-expiratory pause, 0.69 s, whereas with halothane it was only 0.196 s. The mean inspiratory flow rate (Vt/Ti) was higher (224 ml/s) when halothane was used than with enflurane (187 ml/s). When the FGF rate was reduced to 100 ml/kg/min in the modified Mapleson D circuit, patients breathing halothane had increases in minute volumes (VE) in response to increases of 53-75 per cent in inspired volumes of CO2. The increases in VE resulted fro increases in Vt/Ti of 34-38 per cent. The volume of CO2 inspired when enflurane was used did not increase until FGF rate was as low as 70 ml/kg/min. The reduced rebreathing was related to the respiratory waveform. The advantage of reduced rebreathing with enflurane is counter-balanced by the more profound respiratory depression it causes. The FGF needed to abolish rebreathing of CO2 is highly variable, and is dependent on respiratory waveform.

Adult↗
PubMed1980

Cost-effectiveness of intensive care for respiratory failure patients.

Fifty-eight consecutive patients admitted to the ICU requiring ventilatory support for respiratory failure were studied. The Therapeutic Intervention Scoring System (TISS) was used daily as an objective measure of the severity of critical illness in each patient. Patients who survived (27 of 58) 8-10 months after admission to the ICU were interviewed in their homes to assess the outcome of their illness. Most survivors were functioning at or above their premorbid level with respect to their activities of self care and community living. Survivors had minimal recall of the pain and anguish of their ICU experience. The financial cost of care was estimated. Of the total ICU cost, 40% was expended on the 27 survivors. The TISS alone could not distinguish survivors from nonsurvivors in this patient population. The major factor determining the outcome of the illness was the age of the patient. More information on the outcome of critical illness in elderly patients is needed.

Cost-Benefit Analysis↗
PubMed1978

Influence of elevated pulmonary vascular resistance on the relationship between central venous pressure and pulmonary artery occluded pressure following cardiopulmonary bypass.

This study has demonstrated that CVP measurement is an unreliable index of left ventricular filling pressure in unselected patients undergoing A-C bypass procedures. The influence of altered PVR on the disparity between right and left ventricular filling pressures is not of prime importance. The inconsistent relationship between CVP and PAo is primarily a result of ventricular dysfunction and not altered PVR. This suggests that following A-C bypass surgery patients cannot be grouped with respect to altered PVR as the variable which determines whether CVP will be a reliable guide to changes in left atrial pressure. Routine use of Swan-Ganz catheters would improve the precision of monitoring and fluid administration in all patients following CPB. However, it would also increase the cost and complexity of routine care and add a very low incidence of complications to all patients having cardiac surgery. At present, we monitor high risk patients from the time of surgery and advocate early insertion of Swan-Ganz catheters in low risk patients if they are not responding to appropriate management.

Blood Pressure↗
PubMed1978

Postperfusion lung syndrome. Comparison of Travenol bubble and membrane oxygenators.

To examine the role of the oxygenator in the postperfusion lung syndrome, we studied 16 patients undergoing aorta-coronary bypass with a bubble oxygenator and 14 similar patients with a membrane oxygenator both before and for 2 days after the operation. To maintain the same pulmonary artery occluded pressure and hemoglobin level at the end of the surgical procedure, significantly more blood was required in the bubble than in the membrane group. Postoperative pulmonary dysfunction in the bubble group was characterized by increased pulmonary vascular resistance (PVR) and lung water. The increase in lung water was present after bubble oxygenation on three successive measurements, whereas there was no increase in lung water above control value at any measurement time in the membrane group. The bubble group had a significantly greater increase in PVR at the immediate postoperative study time than did the membrane group. PVR returned to control value for the duration of study. These differences in lung water and PVR measurements may be related to greater blood component trauma with a Travenol bubble oxygenator than with a membrane lung.

Blood↗
PubMed1977

Extravascular lung water accumulation in patients following coronary artery surgery.

We studied patients undergoing A-C Bypass with haemodilution. The bubble oxygenator was primed with either two units of plasma and lactated Ringer's solution (PLASMA) or with lactated Ringer's solution (RINGER'S) alone. We found no difference in pulmonary function or lung water determinations between the Ringer's and the Plasma groups. When all patients were grouped together we found no significant increase in lung water (ETVL)5 immediately post-operatively. This suggests lung water did not increase during cardiopulmonary bypass. By the following morning there was a highly significant increase in lung water which was related to changes in the balance between hydrostatic pressure and colloid osmotic pressure and which continued through the second post-operative day. Pulmonary dysfunction, as measured by gas exchange, was not a major problem except in one patient whose lung water increase exceeded 3 ml H2O/kg of total body weight (52 per cent increase) and in whom there was increased shunting. We consider the increase in lung water important, since it may reduce lung compliance and further lung water accumulation. Since the increased lung water was associated with a change in the balance of Starling's forces (PMV - COPMV), treatment designed to reduce that balance should reduce lung water accumulation.

Adult↗