Susan Garwood

Mannitol and dopamine in patients undergoing cardiopulmonary bypass: a randomized clinical trial.

In this prospective, randomized, placebo-controlled, double-blinded study, we determined the effects of two commonly used adjuncts, mannitol and dopamine, on &bgr;2-microglobulin (&bgr;2M) excretion rates in patients undergoing coronary artery bypass graft surgery with cardiopulmonary bypass (CPB). &bgr;2M excretion rate has been described as a sensitive marker of proximal renal tubular function. One-hundred patients with a preoperative serum creatinine level ≤1.5 mg/dL were prospectively randomized into 4 groups: 1) placebo, 2) mannitol 1 g/kg added to the CPB prime, 3) dopamine 2 &mgr;g · kg−1 · min−1 from the induction of anesthesia to 1 h post-CPB, or 4) mannitol plus dopamine. The primary outcome measure was &bgr;2M excretion rate at 1 h post-CPB. Secondary outcome measures included &bgr;2M excretion rate at 6 and 24 h post-CPB; urinary flow rate and creatinine clearance at 1, 6, and 24 h post-CPB; and the highest postoperative serum creatinine level. Length of intensive care stay and hospitalization, as well as adverse events, were also considered secondary outcomes. Dopamine significantly increased &bgr;2M excretion rate at 1 h post-CPB (2.48 ± 3.61 &mgr;g/min) compared with placebo (0.59 ± 1.04 &mgr;g/min; P = 0.001). This effect was not ameliorated by the addition of mannitol (&bgr;2M excretion rate, 2.05 ± 2.77 &mgr;g/min; P = 0.007 compared with placebo). &bgr;2M excretion rate was similar in patients given placebo or mannitol alone (P = 0.831). Rather than being a protective drug in the setting of CPB, dopamine alone or in combination with mannitol increases &bgr;2M excretion rate, which may be a measure of renal tubular dysfunction. The clinical implications of this increase and whether it is also seen in patients with established renal dysfunction undergoing CPB require additional investigation.

Adverse gastrointestinal complications after cardiopulmonary bypass: can outcome be predicted from preoperative risk factors?

Adverse gastrointestinal (GI) outcome after cardiac surgery is an infrequent event but is a clinically important health care problem because of associated increased morbidity and mortality. The ability to identify patients at greatest risk before surgery may be helpful in planning appropriate perioperative management strategies. We examined the pre- and intraoperative characteristics of 2417 patients from 24 diverse United States medical centers enrolled in the Multicenter Study of Perioperative Ischemia Study who were undergoing cardiac surgery using cardiopulmonary bypass as predictors for adverse GI outcome. Resource utilization was evaluated for patients with and without adverse GI outcomes. Adverse GI outcomes occurred in 5.5% of patients (133 of 2417), increased in-hospital mortality 6.5-fold, prolonged the mean intensive care unit length of stay by 1 wk, and more than doubled the mean postoperative hospital stay (P < 0.0001). Predictors of adverse GI outcome included decreased left ventricular function, hyperbilirubinemia, thrombocytopenia, prolonged partial thromboplastin time, prior cardiovascular surgery, combined coronary artery bypass graft surgery and intracardiac or proximal aortic surgery, pharmacological cardiovascular support, and intraoperative transfusion. The literature suggests that adverse GI outcome after cardiac surgery is secondary to poor splanchnic perfusion, which many of these risk factors may predict. Therefore, patients deemed to be at risk before surgery may benefit from tightly controlled hemodynamic management and other strategies that optimize perioperative organ perfusion.

Transesophageal echocardiography interpretation: A comparative analysis between cardiac anesthesiologists and primary echocardiographers

Diagnostic interpretation of intraoperative transesophageal echocardiography (TEE) examinations may vary, particularly when the echocardiographer is also the anesthesiologist. We therefore evaluated the concordance of TEE interpretation as part of a process of continuous quality improvement (CQI). Ten cardiac anesthesiologists participating in a CQI program conducted 154 comprehensive TEE examinations, each consisting of 16 major fields describing cardiac anatomy and function. These examinations were subsequently interpreted off-line by two primary echocardiographers (a radiologist and a cardiologist). Agreement was assessed using the &kgr; coefficient and percent agreement. Overall &kgr; and percent agreement were 0.58 and 83% for anesthesiologists versus radiologist, 0.57 and 80% for anesthesiologists versus cardiologist, and 0.60 and 82% for radiologist versus cardiologist. Anesthesiologists with longer than 5 yr of TEE experience had higher levels of agreement with the radiologist when assessing the aorta, right atrium, pulmonary vein flow, transmitral flow, and fractional area change. Cardiac anesthesiologists supported by a CQI program interpret TEE examinations at a level comparable with physicians whose primary practice is echocardiography. Thus, the anesthesiologist and the intraoperative echocardiographer need not be mutually exclusive.

Measuring renal blood flow with the intraoperative transesophageal echocardiography probe.

Susan Garwood, MB, ChB In 2007, an international organization endorsed by the American Society of Nephrology and the Society of Critical Care Medicine convened to draft consensus statements regarding the pathophysiology and treatment of acute kidney injury (AKI) in cardiac surgery. Six general pathophysiological processes were concluded to contribute to AKI: exogenous and endogenous toxins, metabolic factors, ischemia-reperfusion, neurohormonal activation, inflammation, and oxidative stress. It was proposed that they are most likely interrelated and probably synergistic. Isolation of a single factor in the clinical setting was not considered feasible, rendering proof of causation unlikely. Given the complexity of cardiac surgeryassociated AKI and a current lack of preemptive interventions or proven treatment strategies, only limited recommendations could be made in the consensus statements. Of particular interest to readers of the journal, one of the recommendations was “maintenance of adequate renal perfusion.” Therein lies the difficulty for the clinician participating in the care of patients undergoing cardiac surgery. Renal autoregulation is incomplete during anesthesia in surgical patients and is complicated by the addition of hemodilution and hypothermia. In general surgery patients, renal plasma flow, as measured by standard clearance methods, is significantly reduced after the induction of anesthesia. This occurs despite a stable mean arterial blood pressure or cardiac output, decreasing by as much as 40%. With the addition of normovolemic hemodilution, renal blood flow (RBF) may be even further reduced. In the rat model, initially there is an increase in RBF at a hematocrit of 25% due to the reduced viscosity, but this is accompanied by a halving of the baseline parenchymal oxygen tension. Hematocrits below 15% are associated with a significant decrease in RBF and an even more precipitous decrease in oxygen tension. Although animal models demonstrate that hypothermia is associated with a 50% reduction of RBF, invasive measurements in cardiac surgery patients suggest that the transition from normothermic to hypothermic bypass at the same flow rate is not accompanied by a reduced RBF. Nevertheless, RBF passively follows pump flow during cardiopulmonary bypass and is on average 60% of the prebypass level in the presence of typical mean arterial blood pressures and pump flows encountered during hypothermic bypass. Promoting “maintenance of adequate renal perfusion” would imply that we should be able to measure it. There is no practical method of accomplishing this intraoperatively. Investigations during cardiac surgery have been difficult to conduct. Techniques have included insertion of a renal vein retrograde thermodilution catheter guided by fluoroscopy and iodinated contrast venography or the measurement of effective renal plasma flow with I-hippuran clearance, which is problematic in patients with significant tubular dysfunction or during hypothermia. Outside the operating room, transabdominal renal Doppler ultrasonography is a primary modality for assessing RBF. With this technique, two-dimensional scanning of the main renal arteries is followed by analysis of renal artery velocities by Doppler. An anterior approach (patient supine, transducer applied to the midline of the abdomen) or From the Department of Anesthesiology, Yale University School of Medicine, New Haven, Connecticut. Accepted for publication January 26, 2009. Address correspondence and reprint requests to Susan Garwood, MB, ChB, Department of Anesthesiology, Yale University School of Medicine, 333 Cedar St., Tompkins no. 3, PO Box 208051, New Haven, CT 065120-8051. Address e-mail to susan. garwood@yale.edu. Copyright

Retrograde Fiberoptic Intubation

A 49-yr-old obese Caucasian man presented to our emergency room after suffering traumatic injury to the head and abdomen. Due to progressive obtundation, apnea, and oxyhemoglobin desaturation, direct laryngoscopy and tracheal intubation were attempted but were unsuccessful. A surgical airway was then performed and proved to be technically challenging. A 6.0-mm inner diameter cuffed endotracheal tube (ETT) was successfully placed through the cricothyroid membrane, and intubation was confirmed by auscultation. The patient was transferred to the operating room where he underwent a “damage control” laparotomy (7,8), a splenectomy, and repair of a renal laceration. Intraoperative attempts at revision of the cricothyroidectomy were abandoned because of hemodynamic instability. The patient was taken to the surgical intensive care unit with the plan of returning him to the operating room in 24-48 h for repeat laparotomy. After 48 h in the surgical intensive care unit, the patient was hemodynamically stable, but airway management had become increasingly difficult because of mechanical obstruction (due to kinking and pulmonary secretions) of the 6.0 ETT, causing high peak inspiratory airway pressures and frequent oxyhemoglobin desaturations. The patient was returned to the operating room for abdominal wall closure and airway stabilization. During the surgical procedure, rigid-direct and fiberoptic laryngoscopies were attempted, but the laryngeal structures could not be identified because of significant soft tissue swelling. After completion of the abdominal surgical procedure, a retrograde fiberoptic, guidewire-assisted intubation was planned. The tracheal stoma and 6.0 ETT were cleansed