Postoperative Cardiac Surgical Patients Research Articles

Growth hormone/insulin-like growth factors axis in children undergoing cardiac surgery.

To describe the sequential changes in the growth hormone (GH)/insulin-like growth factors axis and their relationship with nitrogen balance in children following cardiac surgery. Prospective, descriptive study. Pediatric intensive care unit of a university hospital. Twenty three postoperative cardiac surgical patients after bypass. Blood and urine samples were taken on days 1, 2, and 7 of pediatric intensive care unit admission. An intraanesthesia, presurgery sample was also obtained. Serum concentrations of insulin, insulin growth factor-I (IGF-I), insulin growth factor binding proteins 1 and 3 (IGFBP-1 and IGFBP-3), growth hormone binding protein (GHBP), and urinary concentrations of GH and free cortisol (UFC) were measured on days 1, 2, and 7 of the study period. C-reactive protein and prealbumin, were also measured in blood samples as conventional markers of inflammatory or nutritional status. Pediatric Risk of Mortality II score and UFC were used as indicators of acute stress. The nitrogen balance and urinary nitrogen urea excretion were used as markers of catabolic state. Urinary concentrations of GH were high from days 1 to 7. Plasma concentrations of IGF-I and GHBP were low and remained low throughout the study period. IGFBP-3 levels were below normal but without reaching statistical significance. The IGFBP-1 levels were initially high but descended progressively toward normal values. Urinary nitrogen urea production was persistently elevated and was associated with a negative nitrogen balance. No relationship was found between nitrogen balance and IGF-I, prealbumin, or C-reactive protein. A GH-resistant state is observed in postoperative children following cardiac surgery. Stress response is characterized by an elevation of growth hormone secretion that is not followed by the corresponding increment in IGF-I and IGFBP-3 concentrations. These hormonal changes may be permissive for the catabolic state of these patients. IGF-I and IGFBP-1 and -3 are not related to either nitrogen balance or urinary nitrogen urea excretion.

Differential effects of dopamine, dopexamine, and dobutamine on jejunal mucosal perfusion early after cardiac surgery

To evaluate the potential differential effects of dopamine, dopexamine, and dobutamine on jejunal mucosal perfusion, assessed by endoluminal laser Doppler flowmetry in uncomplicated postcardiac surgical patients. A prospective, blinded, randomized, crossover study. A cardiothoracic intensive care unit in a tertiary care center. A total of ten postoperative cardiac surgical patients were studied. Each patient received sequentially, randomly, and in a blinded fashion 2.7+/-0.2 microg x kg(-1) x min(-1) dopamine, 0.7+/-0.1 microg x kg(-1) x min(-1) dopexamine, and 2.7+/-0.1 microg x kg(-1) x min(-1) dobutamine. Each inotropic agent was titrated to increase cardiac output by 25% from baseline. Data on jejunal mucosal perfusion, splanchnic lactate, and oxygen extraction were obtained during a 5-min control period and a 5-min drug infusion period after the target cardiac output was reached. The procedure was sequentially repeated for each agent, and there was a 20- to 30-min washout period between each agent. Dopamine, dopexamine, and dobutamine increased jejunal mucosal perfusion by 27% (p < .01), 20% (p < .001), and 7% (p < .001), respectively. The increase in jejunal mucosal perfusion by dopamine and dopexamine were significantly more pronounced compared with dobutamine (p < .05 and p < .01, respectively), whereas there was no difference between dopamine and dopexamine. Splanchnic oxygen extraction decreased to the same extent with all three drugs. Splanchnic lactate extraction did not change for any of the drugs. The effects on central hemodynamics were similar for the three inotropic agents. Endoluminal laser Doppler flowmetry is a new tool for the detection of perfusion changes at the local intestinal mucosal level. Dopamine, dopexamine, and dobutamine have differential effects on jejunal mucosal perfusion probably because of their different receptor stimulating properties. These findings may be of clinical importance when the therapeutic goal is to improve gut mucosal perfusion.

The Use of Transesophageal Echocardiography for Preload Assessment in Critically Ill Patients

IV volume is often administered to patients in an intensive care unit (ICU) to improve cardiovascular function. We investigated the relationship between stroke volume (SV) and left ventricular (LV) size by using transesophageal echocardiography (TEE) in a population of 20 ICU patients and 21 postoperative cardiac surgical patients. We also examined whether LV end diastolic area (EDA), by TEE, could identify patients who increased SV by 20% or more (responders) after 500 mL of pentastarch administration. There was only a modest relationship (r = 0.60) between the EDA and the SV in all patients. No relationship could be found between the pulmonary capillary wedge pressure (PCWP) and the EDA in all patients. Both responder and nonresponder PCWP increased significantly after volume administration. Only responder EDA increased significantly after volume administration. Responders had significantly lower EDA (15.3 +/- 5.4 cm(2)) and PCWP (12.2 +/- 2.2 mm Hg) when compared with nonresponders (20.2 +/- 4.8 cm(2)) and 15.9 +/- 3.1 mm Hg, respectively). Few ICU patients and only those with a small EDA responded to volume administration. It was not possible to identify an overall optimal LV EDA below which most patients demonstrate volume-recruitable increases in SV. In a ventilated intensive care unit and cardiac surgical population, transesophageal echocardiography and pulmonary artery catheter are sensitive in detecting changes in preload after volume administration. Few patients demonstrate volume-recruitable increases in stroke volume when compared to cardiac surgical patients. It is not possible to establish an overall end diastolic threshold below which a large proportion of ventilated patients respond to volume administration.

Forced-air warming is no more effective than conventional methods for raising postoperative core temperature after cardiac surgery

Objective: To determine whether postoperative forced-air warming of cardiac bypass patients in the intensive care unit (ICU) results in faster rate of warming and improved outcomes compared with more conventional ICU warming methods. Design: Prospective randomized effectiveness study. Setting: Three hundred fifty—bed university-affiliated hospital. Participants: Sixty consenting randomized patients from a consecutive series of 84 patients undergoing routine adult cardiac surgery. Interventions: One group of patients received usual patient care, which includes warm blankets and overhead heat lamps. Patients in the other group were placed under forced-air warming devices on arrival in the ICU. Sixty consenting patients (30 in each group) were randomly assigned to one or the other method of warming. The remaining 24 patients refused randomization and self-selected a treatment group. Measurements and Main Results: Results are presented for the randomized groups. Core temperature, measured by pulmonary artery catheter thermistor, increased in both groups at the rate of 0.25°C per hour. No statistically or clinically significant differences were found between the group for whom the warming device was used and the standard care group in the incidence of postoperative cardiac arrhythmia, duration of time in the ICU, or any other clinical variable. Conclusions: There is no evidence from this study to warrant use of forced-air warming devices for the care of postoperative cardiac surgical patients in the ICU.

Semi-continuous versus injectate cardiac output measurement in intensive care patients after cardiac surgery.

Commercially available semi-continuous cardiac output (SCCO) monitoring systems are based on the pulsed warm thermodilution technique. There is evidence that SCCO fails to correlate with standard intermittent bolus cardiac output (ICO) in clinical situations with thermal instability in the pulmonary artery. Furthermore, ventilation may potentially influence thermodilution measurements by enhanced respiratory variations in pulmonary artery blood temperature and by cyclic changes in venous return. Therefore, we evaluated the correlation, accuracy and precision of SCCO versus ICO measurements before and after extubation. Prospective cohort study. Intensive care unit (ICU) of a university hospital. 22 cardiac surgical ICU patients. None. SCCO and ICO data were obtained at nine postoperative time points while the patients were on controlled mechanical ventilation. Further sets of measurements were taken during the weaning phase 20 min before extubation, and 5 min, 20 min and 1 h after extubation. SCCO and ICO measurements yielded 286 data pairs with a range of 1.8-9.9 l/min for SCCO and 1.9-9.8 l/min for ICO. The correlation between SCCO and ICO was highly significant (r = 0.92; p < 0.01), accompanied by a bias of -0.052 l/min and a precision of 0.56 l/min. Correlation, accuracy and precision were not influenced by the mode of respiration. Our results demonstrate excellent correlation, accuracy and precision between SCCO and ICO measurements in postoperative cardiac surgical ICU patients. We conclude that SCCO monitoring offers a reliable clinical method of cardiac output monitoring in ICU patients following cardiac surgery.

Semi-continuous versus injectate cardiac output measurement in intensive care patients after cardiac surgery

ObjectiveCommercially available semi-continuous cardiac output (SCCO) monitoring systems are based on the pulsed warm thermodilution technique. There is evidence that SCCO fails to correlate with standard intermittent bolus cardiac output (ICO) in clinical situations with thermal instability in the pulmonary artery. Furthermore, ventilation may potentially influence thermodilution measurements by enhanced respiratory variations in pulmonary artery blood temperature and by cyclic changes in venous return. Therefore, we evaluated the correlation, accuracy and precision of SCCO versus ICO measurements before and after extubation.DesignProspective cohort study.SettingIntensive care unit (ICU) of a university hospital.Patients and participants22 cardiac surgical ICU patients.InterventionsNone.Measurements and resultsSCCO and ICO data were obtained at nine postoperative time points while the patients were on controlled mechanical ventilation. Further sets of measurements were taken during the weaning phase 20 min before extubation, and 5 min, 20 min and 1 h after extubation. SCCO and ICO measurements yielded 286 data pairs with a range of 1.8–9.9 l/min for SCCO and 1.9–9.8 l/min for ICO. The correlation between SCCO and ICO was highly significant (r=0.92;p<0.01), accompanied by a bias of −0.052 l/min and a precision of 0.56 l/min. Correlation, accuracy and precision were not influenced by the mode of respiration.ConclusionsOur results demonstrate excellent correlation, accuracy and precision between SCCO and ICO measurements in postoperative cardiac surgical ICU patients. We conclude that SCCO monitoring offers a reliable clinical method of cardiac ouput monitoring in ICU patients following cardiac surgery.

Comparison of Pulmonary Artery Pressure Measurements in the Supine and 60° Lateral Positions: Leanne is continuing this research in her doctoral studies

Pulmonary artery pressure monitoring, with the patient in both the supine and lateral positions, is an essential element in the assessment of critically ill patients. Previous work offers conflicting results regarding the accuracy of measurements obtained with the patient in the lateral position. The purpose of this study was to determine if accurate pulmonary artery pressure measurements can be obtained in the cardiac surgical patient. Thirty-five patients underwent repositioning between the supine and both the left and right 60° lateral position while being mechanically ventilated and then breathing spontaneously. Pulmonary artery pressure measurements were recorded prior to, two minutes following and ten minutes following repositioning. Despite some variation in results the pulmonary capillary wedge pressure measurement was reliable ten minutes after repositioning in both the spontaneously breathing and mechanically ventilated patient. Other pulmonary artery pressure measurements were not so reliable in the lateral position. This study concludes that clinical practitioners can obtain accurate pulmonary capillary wedge pressure measurements in post-operative cardiac surgical patients positioned in either the left or right 60° lateral position. Further research is however required, with larger numbers from all sub-groups of the critical care population. Physiological and pathophysiological characteristics which preclude reliable pulmonary artery pressure measurements need to be identified.

Evaluation of Transesophageal Echocardiography as a Diagnostic and Therapeutic Aid in a Critical Care Setting

To assess the impact of transesophageal echocardiography (TEE) on therapeutic management in relation to pulmonary artery catheterization (PAC) in the ICU. Retrospective analysis of 108 consecutive TEE video and related patient files during a 7-month period. A 33-bed medical and surgical ICU. All critically ill patients with or without PAC in whom a TEE was performed, excluding postoperative cardiac surgical patients. Patients were divided in a cardiac and a septic group depending on the primary disease on admission to the ICU. The impact of TEE in relation to PAC on ICU management was evaluated in whether therapy changes were performed strictly on the basis of the TEE findings. Of 64% of patients with a PAC, 44% underwent therapy changes after TEE: 41% in the cardiac and 54% in the septic subgroup. In 41% of patients without a PAC, TEE led to a change in therapy. TEE results in altered therapeutic management in at least one third of our (noncardiac surgery) ICU patient population independent of the presence of a PAC.

Stressors perceived by cardiac surgical patients in the intensive care unit

Few studies have documented stressors experienced by patients recovering from cardiac surgery in the intensive care unit. Furthermore, research has indicated that nurses' predictions of stressors often are not accurate. Stressors frequently experienced by cardiac surgical patients in the intensive care unit must be clearly identified to enable nurses to predict them, plan interventions to minimize them, and help patients cope. To determine what stressors are perceived by cardiac surgical patients while in the intensive care unit. A descriptive survey design, employing the Intensive Care Unit Environmental Stressor Scale, was used. Patients completed the instrument while on a telemetry unit after transfer from the cardiac intensive care unit at a large regional hospital in the northwestern United States. A nonprobability convenience sample of 43 postoperative first-time cardiac surgical patients was used. Presence of oral and nasal tubes was rated as the primary stressor. Loss of control and missing one's spouse were the highest-rated psychological stressors. Overall mean scores for stressor items were low. Our results suggest that interventions reducing stressors enhance the recovery process for cardiac surgical patients.

Temporal patterns of heart rate and selected arrhythmias for 48 hours after cardiac surgery

To describe the temporal patterns of heart rate and arrhythmias in the immediate postoperative period following cardiac surgery. Six postoperative cardiac surgical patients with a mean age of 48.3 years were studied. Descriptive longitudinal design. Cardiac surgical ICU. Heart rate and arrhythmias were recorded continuously for 48 hours from a cardiac monitor using a Holter tape recorder. Environmental and treatment data were noted throughout data collection by trained nonparticipant observers. Mean heart rate and incidence of arrhythmias were different between the 2 study days; therefore, data were divided into two segments (A and B). These differences coincided with extubation in most cases. Individual subject cosinor analysis revealed 24-hour rhythms of heart rate in both segments in all subjects except segment B for one subject. Rhythms of shorter periods were also found. In segment A individual subjects' acrophases (peak times of fitted curves) occurred later than expected for subjects' prehospitalization sleep-wake schedule, whereas in segment B they occurred earlier. Cosinor analysis of arrhythmias revealed significant 24-hour rhythms in both segments in one of the three subjects with premature atrial complexes, two of the four subjects with premature ventricular complexes and both subjects with ventricular couplets. Four-hour rhythms were found in premature atrial complexes (n = 1), atrial tachycardia (n = 1) and premature ventricular complexes (n = 3). Acrophases for arrhythmias varied among patients. During segment B the 4-hour-rhythm acrophases in heart rate and arrhythmias were related to the timing of respiratory therapy. Temporal variations in heart rate could be identified in these six critically ill adults. Rhythm parameters changed during the first 48 hours after cardiac surgery. In those who had arrhythmias, some patients demonstrated temporal patterns in the incidence of selected arrhythmias. Further study is needed to describe the temporal patterns of heart rate and arrhythmias in varied groups of critically ill persons in a variety of settings.

Pulse Oximetry in the Postoperative Care of Cardiac Surgical Patients

Study objective To demonstrate the utility of pulse oximetry in detecting clinically unapparent episodes of arterial desaturation in postoperative cardiac surgical patients and to evaluate the effect of pulse oximetry on ordering arterial blood gas analyses. Design Prospective, randomized, partially blinded comparison. Setting Cardiothoracic surgical intensive care unit. Patients 35 patients following elective cardiac surgical procedures. Interventions All patients were monitored continuously with pulse oximetry throughout their ICU course. In group 1 patients, the SpO2 data were available at the bedside. In group 2 patients, the SpO2 data were masked at the bedside and monitored at a remote location. Measurements and results Utilization of pulse oximetry allowed a significant reduction in arterial blood gas utilization in group 1 (group 1: 12.4 ± 7.5 blood gas analyses per ICU admission vs group 2: 23.1 ±8.8; p = 0.0007) without adverse events. Clinically unapparent desaturations were detected in 7 of 15 patients in group 2. Conclusions Pulse oximetry improves patient safety through the detection of clinically unapparent episodes of desaturation and can allow a reduction in the number of blood gas analyses utilized without adverse effects to the patient. This may allow a potential cost savings to the patient. (Chest 1992; 102:1367-70)

Pulse Oximetry in the Postoperative Care of Cardiac Surgical Patients: A Randomized Controlled Trial

To demonstrate the utility of pulse oximetry in detecting clinically unapparent episodes of arterial desaturation in postoperative cardiac surgical patients and to evaluate the effect of pulse oximetry on ordering arterial blood gas analyses. Prospective, randomized, partially blinded comparison. Cardiothoracic surgical intensive care unit. 35 patients following elective cardiac surgical procedures. All patients were monitored continuously with pulse oximetry throughout their ICU course. In group 1 patients, the SpO2 data were available at the bedside. In group 2 patients, the SpO2 data were masked at the bedside and monitored at a remote location. Utilization of pulse oximetry allowed a significant reduction in arterial blood gas utilization in group 1 (group 1: 12.4 +/- 7.5 blood gas analyses per ICU admission vs group 2: 23.1 +/- 8.8; p = 0.0007) without adverse events. Clinically unapparent desaturations were detected in 7 of 15 patients in group 2. Pulse oximetry improves patient safety through the detection of clinically unapparent episodes of desaturation and can allow a reduction in the number of blood gas analyses utilized without adverse effects to the patient. This may allow a potential cost savings to the patient.

Pulmonary artery pressure measurement in patients with elevated pressures: effect of backrest elevation and method of measurement

To determine whether pulmonary artery pressure measurement is accurate if the head of the bed is elevated; to compare the end-expiratory graphic recording and digital monitor methods for pulmonary artery pressure measurement; to determine whether either mean arterial pressure or mixed venous oxygen saturation changes during backrest elevation. Nonrandomized clinical trial. A six-bed cardiac surgical intensive care unit of a 540-bed federal facility. Twenty-five postoperative cardiac surgical patients with elevated pulmonary artery pressures (systolic higher than 35 mm Hg). In supine patients pulmonary artery pressures were measured at each of the following backrest elevations: 0, 20, 30, 45 and again at 0 degrees. Measurements were obtained once during mechanical ventilation and once during normal breathing after extubation. End-expiratory graphic recording of pulmonary artery pressures; digital monitor values of pulmonary artery pressures; mean arterial pressure; and mixed venous oxygen saturation. No statistical difference was found in pulmonary artery pressures measured at each of the backrest elevations during mechanical ventilation or normal breathing after extubation. Pulmonary artery diastolic and pulmonary capillary wedge pressures obtained with the digital monitor method were significantly lower than the end expiratory graphic recording method during normal breathing after extubation but not during mechanical ventilation. No changes in mean arterial pressure or mixed venous oxygen saturation occurred during backrest elevation. These results show that pulmonary artery pressures can be measured accurately with the head of the bed in an elevated position. The data indicate that obtaining pulmonary artery pressure measurements from the digital display of the bedside monitor is accurate when respiratory wave form fluctuations are minimal but may lead to inaccurate values with prominent respiratory fluctuations. Further research is needed to validate this finding in different patient populations and with other models of monitoring equipment.

Bezold-Jarisch reflex in postoperative pediatric cardiac surgical patients

The Bezold-Jarisch reflex is an inhibitory reflex that originates from the heart, is mediated by the vagus nerve, and is manifested by hypotension and bradycardia. We present 4 pediatric cardiac surgical patients, aged 1 day to 9 months, who exhibited cardiovascular collapse in their early postoperative course. In each patient, cardiovascular deterioration was marked by an insidious decrease in arterial blood pressure without an associated change in heart rate, central venous pressure, or airway pressure. Bradycardiai followed the decrease in blood pressure. The Bezold-Jarisch reflex was suspected and atropine was administered, first as a bolus injection at 0.01 mg/kg, and later, as a continuous infusion at 0.01 mg · kg −1 · h −1. Atropine prevented recurrent episodes of hypotension and bradycardia. We believe the Bezold-Jarisch reflex is more prevalent than previously suspected in postoperative pediatric cardiac surgical patients.

Coronary haemo-dynamics and myocardial metabolism during weaning from mechanical ventilation in cardiac surgical patients

The present clinical study was undertaken to assess the alterations in myocardial metabolism and coronary haemodynamics during weaning from mechanical ventilation in postoperative cardiac surgical patients. Global and regional myocardial blood flow and metabolism were assessed using a dual port coronary sinus-great cardiac vein thermodilution catheter in 17 patients who had undergone coronary revascularization and who were being weaned from mechanical ventilation. Anaerobic myocardial metabolism, as demonstrated by the production of myocardial lactate, manifested in 8 of 17 patients during at least one of the weaning phases. There were no differences in coronary blood flow between patients who produced myocardial lactate and those who maintained aerobic cardiac metabolism. However, lactate producers exhibited larger changes in systemic vascular resistance and mean arterial pressure than the non-lactate producers. This metabolic manifestation of myocardial ischaemia was not accompanied by electrocardiographic changes of ischaemia, nor presence of chest pain, and may represent another form of silent ischaemia. We conclude that despite coronary revascularization, the myocardium may remain vulnerable to ischaemic anaerobic metabolism in the immediate postoperative period.

Lung glutamine flux following open heart surgery

Despite the attenuated skeletal muscle proteolysis that occurs following hypothermic anesthesia and open heart surgery, blood amino acid levels are maintained, suggesting enhanced amino acid release by another organ. To investigate the role of the lung in this response, we determined the release of glutamine (Gln) and alanine by the lung, since these two amino acids transport two-thirds of circulating amino acid nitrogen. Three groups of patients were studied: (a) preoperative non-stressed controls; (b) postoperative general surgical patients; and (c) postoperative cardiac surgical patients studied on Postoperative Day 1 following open heart surgery requiring cardiopulmonary bypass and hypothermic anesthesia. In preoperative controls the lung was an organ of glutamine and alanine balance. These exchange rates were unaffected by the stress of an abdominal surgical procedure despite a mild increase in pulmonary blood flow. However, lung Gln release in the cardiac surgical patients was significantly increased (−0.6 ± 1.2 μmole/kg/min in controls vs −6.5 ± 1.3 μmole/kg/min in postoperative hearts, P < 0.05) and was due exclusively to an increase in the pulmonary artery-systemic arterial concentration difference. Alanine release by the lungs was also increased in the postoperative cardiac surgical patients. The mechanism by which this augmented pulmonary glutamine release occurs following open heart surgery is unclear, but the lungs appear to play a central role in maintaining amino acid homeostasis. This metabolic role of the lungs following hypothermic anesthesia and cardiopulmonary bypass has not been previously described.

Temporary external DDD pacing after cardiac operations

Temporary atrial and ventricular pacing in the DVI, VVI, and AOO modes using atrioventricular sequential DVI devices is routinely used in cardiac operations. This study evaluated a new temporary external DDD pacemaker (Medtronic 5345 External Pulse Generator) capable of ten pacing modes. Thirty-nine devices have been applied to 38 adult patients (27 male, 11 female) after a variety of open heart procedures. Group 1 had atrial pacing wires placed 1.5 to 2.0 cm apart superiorly on the right atrium, group 2 had atrial wires placed 1.0 to 1.5 cm apart on the right atrial free wall, and group 3 had atrial wires placed on the right atrial free wall 0.8 cm apart, using a Silastic ring for fixation. Ventricular wires were placed on the free wall (group 1) or the diaphragmatic surface (groups 2 and 3) of the right ventricle. Postoperative atrial and ventricular sensing and pacing thresholds were obtained on return to the intensive care unit; analysis of variance demonstrated a significantly greater atrial sensing threshold in group 3. Four patients in group 1 permanently lost atrial sensing, 1 patient in group 2 intermittently lost atrial sensing at 24 hours with return at 36 hours postoperatively, and 1 patient in group 1 lost ventricular sensing capability. All other patients had adequate atrial and ventricular sensing capability documented until elective pacemaker removal (mean, 166 hours; range, 17 to 667.5 hours). Nineteen patients required some form of temporary pacing postoperatively; 11 patients demonstrated hemodynamic benefit from a pacing mode that is not available on the currently used DVI devices, and V of these required true DDD pacing capability. Six patients benefited front atrial pacing with adequate atrial sensing and simultaneous ventricular backup. Burst pacing with the device was used successfully to treat postoperative atrial flutter in 2 patients. We conclude that temporary external DDD pacing is feasible and effective in postoperative cardiac surgical patients. Atrial sensing is possible in most patients but electrode positioning is important for adequate thresholds. In some patients, hemodynamic as well as electrophysiologic improvement can be demonstrated with universal DDD pacing capability as compared with standard DVI pacing.

Intra-aortic balloon pump transducer study: 48 hours vs 72 hours transducer change comparison in post-operative cardiac surgical patients

Intra-aortic balloon pump transducer study: 48 hours vs 72 hours transducer change comparison in post-operative cardiac surgical patients

Use of patient controlled analgesia in postoperative cardiac surgical patients—a survey of ward staff attitudes

Staff who worked regularly on a postoperative cardiac surgical ward were asked to complete a questionnaire regarding the use of patient controlled analgesia, which had recently been introduced to the ward. Fifty-five per cent found that the machines reduced their workload, mainly by relieving them of the task of checking and administering controlled drugs. The benefits noted were increased patient confidence (noted by 74%) and improved analgesia (41%). However it was felt by 61% that some postoperative cardiac patients seemed reluctant to use the machines properly or did not fully understand the technique.

The renal effects of sodium nitroprusside in postoperative cardiac surgical patients.

Sodium nitroprusside (SNP) is frequently used to control hypertension and/or improve systemic blood flow following cardiac operations. Although SNP causes renal vasodilation when infused into isolated kidneys, the reported effects of SNP on renal vascular resistance and blood flow in intact animals and humans have varied. To define the effects of SNP in postoperative cardiac surgical patients, renal clearances and hemodynamics were measured in seven patients within 24 hours of coronary bypass grafting. Studies were delayed until patients were stabilized and had rewarmed following operation. Following baseline measurements (off SNP), SNP infusion was used to lower mean arterial pressure to 85 torr. Pulmonary wedge pressure was maintained by appropriate fluid therapy, and the measurements repeated 1 h later. SNP administration resulted in equivalent decreases in renal (-31 per cent), pulmonic (-29 per cent) and systemic (-33 percent) vascular resistance. Notwithstanding the decrease in arterial pressure (109 +/- 14 to 91 +/- 9 torr, P less than 0.01), renal blood flow increased by 20 per cent (653 +/- 193 to 792 +/- 210 ml . min-1 . 1.73 m-2, P less than 0.02), in direct proportion to the increase in cardiac index (2.5 +/- 0.4 to 3.0 +/- 0.3 1 . min-1 . m-2, P less than 0.01). Thus, in postoperative cardiac surgical patients, SNP administration can be expected to improve renal blood flow, so long as left atrial hypotension is avoided, and the decline in systemic arterial pressure is not excessive. The improvement in renal blood flow achievable with SNP may be critical for patients with severely depressed left ventricular function in whom severe depression of renal blood flow may occur as an antecedent to acute renal failure.