Haemodynamic changes during beating heart coronary surgery with the 'Bristol Technique'.

OBJECTIVES: Optimal exposure and stabilization of the target coronary vessel is essential to allow the construction of a precise coronary anastomosis during off pump coronary surgery. However, this might be achieved at the expense of significant haemodynamic deterioration, particularly while grafting the circumflex and the posterior descending coronary arteries. The present study was designed to assess the haemodynamic changes with the beating heart positioned for grafting the three main coronaries. METHODS: Twenty-nine consecutive patients (21 male, mean age 62.6+/-7.1 years) undergoing off pump coronary surgery were enrolled in the study. Three different surgical settings of exposure and stabilization were used according to the site of anastomosis: left anterior descending (LAD - set-up 1; n=29), posterior descending (PDA - set-up 2; n=15), and circumflex (Cx - set-up 3; n=21) coronary arteries. Haemodynamic measurements were recorded before any cardiac manipulation (baseline) in set-ups 1, 2 and 3, and immediately after the completion of each distal anastomosis with the heart returned to its anatomical position. RESULTS: There were no marked changes in heart rate (HR) and systemic mean arterial pressure during the construction of the anastomoses for any of the three surgical settings. Set-up 1 (LAD) showed a decrease of 15.5% in stroke volume (SV) and an increase of 9% in pulmonary capillary wedge pressure (PCWP) compared to baseline (both P<0.05), with all the other haemodynamic parameters remaining unchanged. Set-up 2 (PDA) showed a marked decrease in SV and cardiac index (CI), and an increase in central venous pressure (CVP) when compared to baseline (all P<0.05). The most extensive changes were observed in set-up 3 (Cx) with a considerable reduction in SV and CI, and an increase in CVP, PCWP, pulmonary arterial pressure, and systemic vascular resistance index (all P<0.05). These haemodynamic changes were transient and totally recovered after the heart was returned to its anatomical position. CONCLUSIONS: Exposure and stabilization of the three main coronary arteries during beating heart surgery does not produce any appreciable change in systemic blood pressure and HR. The haemodynamic deterioration observed during the construction of the circumflex and posterior descending coronary arteries distal anastomoses is transient and well tolerated with no adverse clinical events.

Reduced cerebral embolic signals in beating heart coronary surgery detected by transcranial Doppler ultrasound.

Cerebral emboli detected by transcranial Doppler imaging were recorded in 20 patients undergoing multiple-vessel coronary artery bypass surgery, either with or without cardiopulmonary bypass, in a prospective unblinded comparative study. Emboli were recorded continuously from the time of pericardial incision until 10 min after the last aortic instrumentation. The numbers of coronary grafts and of aortic clampings were also documented. Patients undergoing revascularization with cardiopulmonary bypass had more emboli (median 79, range 38-876) per case compared with patients having off-pump surgery (median 3, range 0-18). No clinically detectable neurological deficits were seen in either group. Beating heart surgery is associated with fewer emboli than coronary surgery with cardiopulmonary bypass. Further research is necessary to determine whether a smaller number of emboli alters the incidence of neurological deficit after cardiac surgery.

Effect of cardiopulmonary bypass on pulmonary gas exchange: a prospective randomized study.

BACKGROUND: Conventional coronary artery bypass surgery is associated with postoperative pulmonary dysfunction. Inflammation due to cardiopulmonary bypass has been regarded as one of the main causes. In this study, we investigated the effect of coronary revascularization with or without cardiopulmonary bypass on pulmonary function. METHODS: Fifty-two patients (40 male, mean age 60.1 years) were prospectively randomized to undergo coronary revascularization via median sternotomy, with or without normothermic cardiopulmonary bypass. Alveolar-arterial oxygen gradients were measured before and after induction of anesthesia, postoperatively in the intensive care unit during mechanical ventilation and 6 hours after tracheal extubation. The techniques of anesthesia and mechanical ventilation were standardized throughout. RESULTS: Patient characteristics were similar in the two groups. The alveolar-arterial oxygen gradients increased progressively throughout the perioperative period, with no significant differences in the two groups at any time during the study. CONCLUSIONS: Myocardial revascularization with or without cardiopulmonary bypass caused a similar degree of pulmonary dysfunction, as assessed by alveolar-arterial oxygen gradient. Our study suggests that the deterioration in pulmonary gas exchange associated with cardiac surgery is due to factors other than the use of cardiopulmonary bypass.

Emergency transtracheal ventilation: assessment of breathing systems chosen by anaesthetists.

The choice of equipment for emergency transtracheal ventilation and the time taken to assemble it were surveyed in 39 anaesthetists. Thirty seven (95%) assembled a system in a median time of 104 s (interquartile range 54 s to 120 s). Systems specially constructed from oxygen tubing and connectors took longest to put together (p < 0.05). Consultants and senior registrars performed no better than senior house officers and registrars (p > 0.05). In the second part of the study we tested four anaesthetic systems which the survey revealed might be chosen for emergency transtracheal ventilation. These were: a simple length of oxygen tubing; a T-piece system; a Bain system; a jet injector. All had the appropriate connectors. The oxygen flow was measured through a 14 G venous "transtracheal' cannula on depression of the oxygen flush device on a standard Boyle's M anaesthetic machine. The jet injector was connected to the high pressure outlet. This device delivered the highest flow, 43 l.min-1 and was the only system capable of ventilating a trachea/lung model. The T-piece system, and the one constructed from oxygen tubing, delivered flows of 12.7 and 12.0 l.min-1, respectively, whereas the Bain system delivered only 4.7 l.min-1. We conclude that, except for jet ventilation, none of the systems chosen, using equipment available in the anaesthetic room, would be likely to achieve effective CO2 elimination; at best they would provide oxygenation.

Effects of PEEP on acinar gas transfer in healthy and lung-injured dogs.

We measured cardiorespiratory variables and 133xenon washout from a nonperfused lung region (XeW) in six anesthetized/paralyzed dogs, mechanically ventilated with 60% O2 at different positive end-expiratory pressures (PEEP). XeW in this technique represents directly measured acinar gas transfer (3). Measurements were repeated after induction of lung injury by lavaging the lungs 11 to 13 times with 600 ml saline. In control dogs, lung compliance (CL), alveolar ventilation (Valv), and XeW all decreased with increasing PEEP from 0 to 25 cm H2O (p < 0.05), while lung resistance (RL) did not change. After lavage, CL, Valv, and XeW below 15 cm H2O PEEP were all less than control values (p < 0.05), while RL was higher than control values. As PEEP increased from 0 to 20 cm H2O, Valv and XeW increased, but CL did not change; RL decreased only from 0 to 5 cm H2O. At 20 cm H2O PEEP, Valv and CL were not different from control values (p > 0.05), and XeW was higher than control values (p < 0.05). At estimated alveolar volumes above 400 ml, values for XeW before and after lavage were similar. We conclude that, during severe lung injury: (1) increasing PEEP to moderate levels will increase acinar gas transfer but, after a certain lung volume is reached, further increases in PEEP will have effects similar to the healthy condition; (2) overall mechanical properties of the lung do not reflect the responses to PEEP of the lung periphery.

In vitro oxyhaemoglobin saturation measurements in haemoglobin solutions using fibreoptic pulmonary artery catheters.

We compared in vitro oxyhaemoglobin saturations using two pulmonary artery catheters (catheter SO2), with oxyhaemoglobin saturations (SO2) measured by the IL282 co-oximeter and derived partial oxyhaemoglobin saturations (partial SO2) at different oxygen tensions (PO2) in six solutions: whole blood, 50:50 mixture of whole blood and Plasmalyte A (haemodiluted blood), 50:50 mixture of whole blood and 8% pyridoxylated haemoglobin-polyoxyethylene (PHP) conjugate (WB-PHP), 75:25 mixture of 8% PHP and Plasmalyte A solution (PHP66), 50:50 mixture of 8% PHP and Plasmalyte A solution (PHP44) and stroma-free haemoglobin solution (SFH). Calculated P50 values (PO2 vs SO2) were 3.79, 3.58, 3.49, 3.15, 3.04 and 2.07 kPa, respectively. However, if partial SO2 was used the curves were shifted to the left, reducing P50. Catheter SO2 correlated well with SO2 in whole blood (r2 > 0.99 for both catheters), haemodiluted blood (r2 > 0.98 for both catheters) and WB-PHP solution (r2 = 0.94 for both catheters). In PHP44 (r2 = 0.64 and r2 = 0.57), PHP66 (r2 = 0.40 for the Oximetrix and r2 = 0.25 for the Edwards catheter) and SFH solutions (r2 = 0.33 for the Oximetrix and r2 = 0.22 for the Edwards catheter) both catheters performed poorly. We conclude that mixed venous oxyhaemoglobin saturations measured by oximetric pulmonary artery catheters are inaccurate in the presence of haemoglobin solutions. For accuracy a multi-wavelength co-oximeter should be used if blood containing PHP or SFH is to be analysed.

Effect of lung volume on lung resistance and elastance in awake subjects measured during sinusoidal forcing.

BACKGROUND: Although lung volume may be changed by certain procedures during anesthesia and mechanical ventilation, dependence of the dynamic mechanical properties of the lungs on lung volume are not clear. Based on studies in dogs, the authors hypothesized that changes in lung mechanics caused by anesthesia in healthy humans could be accounted for by immediate changes in lung volume and that lung resistance will not be decreased by positive end-expiratory airway pressure if tidal volume and respiratory frequency are in the normal ranges. METHODS: Lung resistance and dynamic lung elastance were measured in six healthy, relaxed, seated subjects during sinusoidal volume oscillations at the mouth (5 mL/kg; 0.4 Hz) delivered at mean airway pressure from -9 to +25 cmH2O. Changes in lung volume from functional residual capacity were measured with inductance plethysmographic belts. RESULTS: Decreases in mean mean airway pressure that caused decreases in lung volume from functional residual capacity comparable to those typically observed during anesthesia were associated with significant increases in both dynamic lung elastance and lung resistance. Increases in mean mean airway pressure that caused increases in lung volume from functional residual capacity did not increase lung resistance and increased dynamic lung elastance only above about 15 cmH2O. CONCLUSIONS: Increases in dynamic lung elastance and lung resistance with anesthesia can be explained by the accompanying, acute decreases in lung volume, although other factors may be involved. Increasing lung volume by increasing mean airway pressure with positive end-expiratory pressure will decrease lung resistance only if the original lung volume is low compared to awake, seated functional residual capacity.

Intraosseous infusion for resuscitation.

An 11 week old infant who had a cardiac arrest secondary to gastrointestinal haemorrhage and was successfully treated using intraosseous infusion is reported. The child was discharged with no apparent neurological deficit.

Parents in the anaesthetic room. A questionnaire survey of parents' reactions.

One hundred and forty-one parents were asked to complete a questionnaire about their reactions after accompanying their child during induction of anaesthesia. Of 139 respondents, 99% believed that their presence was of benefit to their child, and 95% believed that they helped the anaesthetist. The degree of anxiety experienced by the parent did not significantly affect this view, nor was the degree of anxiety affected by the method of induction chosen by the anaesthetist.