Donald L. Clark

Prophylactic Nitroglycerin Infusions during Coronary Artery Bypass Surgery

The effects of prophylactic infusion of 1 µg · kg−1 · min−1 nitroglycerin (NTG) on the incidence of ischemia, hypertension, hypotension and perioperative myocardial infarction were studied in 81 patients during coronary artery bypass grafting (CABG). Forty-one patients (Group 1) received NTG and 40 patients (Group 2) received placebo. All patients received fentanyl for anesthesia and pancuronium. Mean arterial pressure (MAP), pulmonary capillary wedge pressure (PCWP), heart rate (HR), and cardiac output (CO) were measured before and after induction of anesthesia, after intubation, before and after chest incision, after sternotomy, after the pericardium was opened, and during normothermic cardiopulmonary bypass. Myocardial ischemia and infarction were diagnosed from the ECG, hypertension was denned as a 20% increase in MAP, and hypotension was defined as a 20% decrease in MAP compared with preinduction values. No significant differences between Groups 1 and 2 in HR, PCWP, or CO were seen. MAP was significantly lower in Group 1 than Group 2 (P < 0.05) before chest incision, but increased to levels equal to Group 2 after sternotomy. Hypertension occurred in 32 Group 2 patients and 25 Group 1 patients (0.05 < P < 0.1). Group 1 patients had 0.95 ± 0.14 episodes per patient of hypertension, while Group 2 patients had 2.10 ± 0.31 episodes (P < 0.05). Hypotension occurred in 20 Group 1 patients but only six Group 2 patients (P < 0.05). There was no difference in the incidence of ischemia. In Group 1, nine patients (22%) had ECG changes of ischemia, while 12 patients in Group 2 (30%) had ischemia. Three patients in each group (7%) had evidence of perioperative myocardial infarction. We conclude that prophylactic administration of 1 µg · kg−1 · min−1of NTG during fentanyl anesthesia in patients undergoing CABG did not prevent myocardial ischemia or reduce the incidence of perioperative myocardial infarction, but both lowered the incidence of hypertension, especially during intubation, and increased the incidence of hypotension (P < 0.05).

Effects of Colloid or Crystalloid Administration on Pulmonary Extravascular Water in the Postoperative Period After Coronary Artery Bypass Grafting

The effect of postoperative fluid management on pulmonary extravascular thermal volume (ETV1) as in index of pulmonary extravascular water after coronary artery bypass grafting was compared, using the thermal-dye technique, among five patients who received 5% albumin (group A), five patients who received 6% hydroxyethyl starch (group H), and five who received lactated Ringers solution (group C). lntraoperatively, all patients received lactated Ringers solution intravenously, and the cardiopulmonary bypass (CPB) circuit prime included 5% albumin. No statistically significant changes in ETV1 occurred postoperatively in any group, nor did ETV1 differ significantly between groups. After CPB, colloid osmotic pressure (COP) significantly decreased and pulmonary artery wedge pressure (WP) and the WP-COP gradient significantly increased in each group, implying an increase in transcapillary fluid flux. Cardiac index. changed variably. Pulmonary shunt fraction (Qsp/Qt) did not change in groups A and C but decreased during CPB in group H (from 0.22 ± 0.03 to 0.16 ± 0.11). Postoperatively, patients in the three groups received similar volumes of fluids and had similar perioperative weight gains. By the next morning (AM1), COP increased in all groups, returning to levels noted before CPB in group C, and exceeding these levels in groups A and H. Wedge pressure was similar in all three groups on AM1. PaO2 decreased significantly, and alveolar-arterial oxygen partial pressure difference increased significantly in all groups on AM1. In Group H, Qsp/Qt returned to levels observed before CPB by AM1 (0.27 ± 0.09). We conclude that in patients without postoperative increases in WP, ETV1 changes minimally during CPB and is not influenced by the type of fluid administered as the primary volume replacement in the postoperative period.

Neural Effects of Isoflurane (Forane) in Man

Neural effects of isoflurane, a structural isomer of enflurane, were studied in 12 volunteer subjects. In seven subjects who remained conscious while breathing isoflurane, sensory threshold, memory functions, ulnar nerve conduction, electroencephalogram (EEG), and somatosensory evoked responses (SERs) were measured. Five unconscious subjects provided data on ulnar nerve conduction, EEG, and SERs at anesthetic and subanesthetic concentrations of isoflurane at various Paco2 values. Isoflurane initially produced a low-amplitude EEG of 15–35 Hz which reverted to 5–9 Hz with arousal. With loss of consciousness, 12–14-Hz activity was superimposed on 2–6-Hz high-amplitude waves. At concentrations somewhat above the MAC this activity was interrupted by 6–10-µV, 6–8-Hz periods. Nonspecific activity in SERs was depressed in the conscious state. Initial specific positively was depressed by concentrations above MAC, while early negativity remained. Depression of initial positivity in the SERs and absence of seizure activity in the EEG differentiate the effects of isoflurane from those of enflurane. Structural isomerism in this case appears to produce different effects on cortical excitability.

Hemodynamic and Anesthetic Effects of Sufentanil as the Sole Anesthetic for Pediatric Cardiovascular Surgery

The efficacy, safety, and hemodynamic response to 5 μg/kg, 10 μg/kg, or 20 μg/kg of sufentanil and 0.1 mg/kg pancuronium was evaluated in children between 4 and 12 years of age scheduled for open heart surgery. Systolic time intervals, 2-D echocardiograms, systolic blood pressures (SBP), diastolic blood pressures (DBP), and heart rates (HR) were recorded before and after induction of anesthesia. Significant changes 10 min following induction of anesthesia but before intubation included increases in SBP in the 5 μg/kg group (P < 0.01) and in the ratio of preejection period to left ventricular ejection time in the 20 μg/kg group (P < 0.05). Instances of myoclonic jerking and coughing episodes were observed in all three study groups.Following intubation there were significant (P < 0.05) increases in SBP in all groups, in DBP in the 5 μg/kg group, and in HR in the 5 μg/kg and 10 μg/kg groups. Smaller increases in SBP, DBP, and HR were seen in all groups after skin incision and sternotomy. Mean plasma catecholamine levels showed nonsignificant increases following periods of intraoperative stimulation with wide patient variationsRecovery of responsiveness to command occurred in all groups within one hour from the end of surgery but extubation was impeded by shallow periodic breathing and hypercapnea. The authors conclude that for children undergoing open heart surgery use of sufentanil as a sole anesthetic in bolus form did not provide a reliable depth of anesthesia with any of the induction doses studied.

Effect of anesthetic drugs on time production and alpha rhythm

Ss produced time intervals before and during inhalation of low concentrations of anesthetic gases. The drugs increased time productions by raising the slope of the line representing produced against objective time. Alterations in time production were not accompanied by consistent changes in alpha rhythm, respiratory rate, heart rate, or body temperature. The findings argue against the’ alpha rhythm’s acting as the biological pendulum for the internal clock.

Effects of advanced age on extravascular lung water accumulation during coronary artery bypass surgery.

: Pulmonary extravascular thermal volume (ETVL) accumulation during aortocoronary bypass grafting (CABG) was compared between nine patients (group 1) aged 49 +/- 2 (SEM) yr and nine patients (group 2) aged 65 +/- 1.2 yr, using the thermal-dye technique. Before extracorporeal bypass (ECB), ETVL was significantly correlated with age and mean ETVL was significantly lower in group 1 (3.93 +/- 0.48 ml/kg body weight) than group 2 (5.93 +/- 0.38 ml/kg). During ECB, ETVL rose to 5.15 +/- 0.65 ml/kg in group 1 (p less than .05) and to 6.38 +/- 0.56 ml/kg in group 2. By the next morning, ETVL had returned to pre-ECB levels. Post-ECB, cardiac index decreased in group 1 and colloid osmotic pressure decreased in both groups, but all values returned to pre-ECB levels by the next morning. Although PaO2 had decreased and pulmonary shunt fraction had increased by this time, changes in these variables did not correlate with changes in ETVL. During ECB, ETVL increased transiently but returned to pre-ECB levels by the next morning.

Halothane metabolism in acyanotic and cyanotic patients undergoing open heart surgery.

The metabolism of halothane was examined in patients with acyanotic and cyanotic congenital heart disease undergoing open heart surgery. Statistically significant (P < 0.05) presurgical differences between acyanotic and cyanotic groups included pH (7.46 ± 0.02 vs 7.36 ± 0.02)PaO2 (277 ± 58 vs 51 ± 3 ion)O2 saturation (97 ± 1 vs 74 ± 4%)and hematocrit (45 ± 3 vs 58 ± 2%). Serum fluoride levels were significantly greater in cyanotic than in acyanotic groups 2–4 hours after initial exposure to halothane. Both groups had significant intragroup increases in serum levels of fluoride, bromide, and trifluoroacetic acid. Significant increases in serum levels of lactate dehydrogenase, creatinine phos- phokinase, and glutamic oxaloacetate transaminase were observed in both groups, whereas, the cyanotic patients had additional significant increases in blood urea nitrogen and direct bilirubin. The cyanotic group also had higher total and direct serum bilirubin levels than the acyanotic group. Therefore, patients with cyanotic congenital heart disease had greater reductive metabolism of halothane than acyanotics. However, cyanotic and acyanotic patients had essentially similar postoperative derangements in hepatic and renal function.

Hemodynamic Effects of Calcium Chloride in Adults with Regurgitant Valve Lesions

We evaluated the hemodynamic effects of 7 mg/kg intravenous calcium chloride (CaCl2) or placebo in 20 adults with regurgitant aortic and/or mitral valves before and after induction of anesthesia with fentanyl (50 μg/kg), followed by pancuronium (0.1 mg/kg) and 100% oxygen. CaCl2 produced no changes in mean systemic, pulmonary arterial, central venous, or pulmonary capillary wedge pressures or vascular resistances before or after induction of anesthesia. A significant increase in left ventricular stroke work index was seen 1 min after CaCl2 was administered after induction of anesthesia (from 31.29 ± 3.00 to 37.44 ± 3.81 g·m·M-2). Before induction, CaCl2 decreased heart rate from 93.9 ± 9.6 to 85.2 ± 8.7 beats/min (statistically significant 2.5 and 10 min after CaCl2) and after induction from 104.6 ± 8.4 to 89.3 ± 7.5 (significant at 1, 2.5, 5, and 10 min). These results suggest that CaCl2 is associated with an immediate increase in ventricular performance and that the subsequent decrease in heart rate is not sufficient to contraindicate use of CaCl2 as an inotrope in patients with chronic valvular regurgitation. The effects of CaCl2 injection in man on pulmonary shunt fraction (Qs/Qt) have not been described previously. We found no change in Qs/Qt, suggesting that CaCl2 has no direct effect on distribution of pulmonary blood flow.