Thomas E. Reilley

Experience with phenylephrine as a component of the pharmacologic support of septic shock.

ObjectiveTo evaluate the use of the selective α1-adrenergic receptor agonist phenylephrine in the hemodynamic support of patients with septic shock. DesignRetrospective analysis of clinical use of phenylephrine. SettingSurgical ICU in a university hospital. PatientsThirteen patients with septic shock (diagnosed by defined criteria) requiring pharmacologie support for the treatment of hypotension. Interventions and Main ResultsAll patients underwent invasive hemodynamic monitoring followed by volume resuscitation and inotropic support to reverse flow-dependent oxygen consumption and lactic acidosis. Patients with persistent hypotension (mean arterial pressure [MAP] <65 mm Hg) and vasodilation (systemic vascular resistance index [SVRI] <1500 dyne-sec/cm5-m2 received phenylephrine at iv infusion rates of 0.5 to 9 μg/kg·min to maintain MAP >70 mm Hg. MAP, SVRI, left ventricular stroke work index, and stroke volume index were significantly (p < .05) increased after phenylephrine administration and at the time of highest oxygen consumption (&OV0312;o2). Cardiac index was unchanged initially but increased at the time of highest &OV0312;o2 (p < .05). Pulmonary artery occlusion pressure and heart rate were unchanged. Average baseline &OV0312;o2 increased from 145 to 200 mL/min·m2 and oxygen delivery (&U1E0A;o2) increased from 447 to 597 mL/min-m2 during phenylephrine treatment (p < .05). Blood lactate concentrations decreased and urine output increased significantly (p < .05), while serum creatinine concentrations remained unchanged during phenylephrine therapy. ConclusionsTreatment with phenylephrine was associated with beneficial hemodynamic effects when used to maintain perfusion, while increasing &U1E0A;o2 and &OV0312;o2 in patients with septic shock.

Analysis of risk factors for postoperative pulmonary complications in head and neck surgery

Preoperative pulmonary function tests (PFTs) are unproven in their predictive value for postoperative pulmonary complications. There is a lack of prospective outcome studies upon which to form an opinion, particularly regarding noncavitary surgery.1 Seventy‐three head and neck surgery patients were prospectively evaluated with preoperative PFTs, arterial blood gas analysis (ABG), medical history, and physical examination. Age, anesthesia duration, forced expiratory volume in 1 second (FEV1), peak flow (PF), PaO2, Roizen class, and pack years of smoking were significantly correlated with postoperative pulmonary complications. As similar studies in head and neck surgery patients have not been previously taken, it is hoped that these results will serve as a basis for future endeavors.

Comparison of effects of lidocaine hydrochloride, buffered lidocaine, diphenhydramine, and normal saline after intradermal injection

STUDY OBJECTIVE To evaluate pain and the spread of analgesia when local anesthetics are given as an intradermal injection into the dorsal aspect of the hand. DESIGN Randomized, double-blinded, placebo-controlled study. SETTING University medical center. PATIENTS 40 consenting adult volunteers. INTERVENTIONS Volunteers were randomly assigned to receive a 0.25-mL injection of either lidocaine hydrochloride (1%), buffered lidocaine, diphenhydramine (1%), or placebo (0.9% sodium chloride solution) into the dorsal aspect of both hands. MEASUREMENTS The volunteers used a visual analog scale to compare the pain of needle insertion and solution injection. Then at 1, 2, 5, 10, 20, and 30 minutes after intradermal injection, the extent of the analgesic area was marked on a strip of tape placed horizontally across the hand. Then at 32 minutes after intradermal injection, the extent of the analgesic area was marked on a strip of tape placed vertically across the hand. The volunteers were called each day and asked the duration of their numbness or hyperesthesia until their hands were no longer numb or sore. MAIN RESULTS Buffered lidocaine during intradermal infiltration was found to be significantly (p < 0.05) less painful than either lidocaine hydrochloride or diphenhydramine and equivalent to placebo. Diphenhydramine and lidocaine hydrochloride during intradermal infiltration induced significantly (p < 0.05) more pain than buffered lidocaine or placebo. Lidocaine hydrochloride displayed a significantly (p < 0.05) larger diameter of analgesia than placebo by 1 minute after the injection, buffered lidocaine by 2 minutes after injection, and diphenhydramine by 5 minutes after injection. By 20 minutes after injection, diphenhydramine diameter of analgesia was significantly (p < 0.05) larger than placebo but significantly less than buffered lidocaine. By 30 minutes after injection, diphenhydramine diameter of analgesia was equivalent to placebo whereas buffered lidocaine and lidocaine diameters were still significantly (p < 0.05) larger than placebo. Diphenhydramine injection resulted in numbness that lasted significantly (p < 0.05) longer than other study solutions whereas buffered lidocaine and lidocaine injections resulted in numbness that lasted significantly longer than placebo. Diphenhydramine injection resulted in hyperesthesia that lasted for 2 or more days in 12 of the volunteers. CONCLUSION There is a reduction of infiltration pain using buffered lidocaine as opposed to lidocaine and diphenhydramine. Although lidocaine injection resulted in a slightly faster spread of analgesic diameter, buffered lidocaine was equivalent to lidocaine from minute 2 until minute 30. Therefore, to obtain optimal anesthetic conditions, we recommend that buffered lidocaine be given 2 minutes before performing catheterization, whereas diphenhydramine should be given 5 minutes before catheterization, but only when buffered lidocaine cannot be used.

Evaluation of collateral circulation of the hand.

In 1929, Edgar V. Allen described a noninvasive evaluation of the patency of the arterial supply to the hand of patients with thromboangitis obliterans (Am J Med Sci 1929;178:237). In the early 1950s, Allens test was modified (Wright I. Vascular diseases in clinical practice. Chicago: Year Book Medical Publishers, 1952) for use as a test of collateral circulation prior to arterial cannulation. This test involves the examiner occluding the patients ulnar and radial arteries while the patient makes a fist, causing the hand to blanch. The patient is then asked to extend the fingers. After the hand is open, the examiner releases the ulnar artery while continuing to maintain pressure on the radial artery. Adequate collateral circulation is felt to be indicated by return of normal color to the hand. The patient is instructed not to hyperextend the fingers when opening the hand. Hyperextension may cause a decrease in perfusion to the arch, possibly resulting in a false interpretation of the Allen test (Anesthesiology 1972;37:356). The modified Allens test can be performed quickly and easily, but it is susceptible to error. (With Allens original test, both hands were tested simultaneously. The patient clenched both fists tightly for 1 minute while the examiner compressed one artery of each hand. This method helps diagnose complete occlusion, just as Allen intended. The test was later modified, however, to evaluate the adequacy of collateral circulation. To perform the modified Allens test, the examiner compresses both arteries while the patients fists are clenched. The patient then opens the hand, and the adequacy of circulation is evaluated when the examiner releases one of the arteries.) This study was designed to combine the modified Allens test with the sensitivity of oximetry and plethysmography to provide a quantifiable and reproducible evaluation of the palmar collateral circulation with or without the subjects cooperation. Superficial palmar arches of 90 normal volunteers (aged 22–45 years) were evaluated with the modified Allens test. These results were compared with the flow patterns demonstrated by plethysmography and pulse oximetry. All of the modified Allens tests were normal, with the palmar blush occurring in an average of 2.3 seconds (range, 2–5 s). Results were recorded independently by two observers, with agreement in all cases. Four of the 90 (4.4%) palmar arches were found to have abnormal circulatory patterns. Plethysmography clearly demonstrated the dominant arterial supply to the hand and, in appropriate cases, indicated the existence of an incomplete arch. The four abnormal circulatory patterns (two incomplete palmar arches and two other aberrant arterial communications) were clearly shown by plethysmography. Pulse oximetry was found to be too sensitive. Significant changes in flow did not result in a decrease in saturation. Only the incomplete superficial palmar arches resulted in a change in saturation. The two abnormal arterial communications were not detected by pulse oximetry. Pulse oximetry also could not show dominant flow patterns. Our findings indicate that plethysmography can be used to demonstrate palmar collateral circulation, but that pulse oximetry cannot.

Variability in dobutamine pharmacokinetics in unstable critically ill surgical patients

Objective: To delineate the variability in the pharmacokinetics of dobutamine over time in an unstable critically ill adult surgical patient population concurrently receiving therapeutic interventions to optimize oxygen delivery and consumption variables. Design: Prospective study. Setting: University hospital adult surgical intensive care unit. Patients: Sixteen hemodynamically unstable adults (aged 18 to 84 yrs) requiring dobutamine for inotropic support. Interventions: None. Measurements and Main Results: Samples for dobutamine serum concentration determination were collected at selected times during therapy, following at least 30 mins of a constant infusion rate and measured using high‐performance liquid chromatography. Clearance and changes in clearance were calculated. A first‐order pharmacokinetic model was validated by lack of dependence of dose on clearance and an established graphical method. Mean ± SD infusion rate of dobutamine was 8.2 ± 5.7 &mgr;g/kg/min (range 1.7 to 22.3), which resulted in a mean serum concentration of 214 ± 183 ng/mL (range 15 to 759). The correlation between infusion rate and steady‐state dobutamine concentration was r2 = .67. Variability in steady‐state dobutamine concentration at various infusion rates was large. Clearance at initial pharmacokinetic analysis averaged 58.4 ± 33.3 mL/kg/min (range 19 to 120). The percent change in calculated clearance varies from a 72% decrease to an 88% increase, with the greatest variability in clearance occurring during the first 24 hrs of therapy. There was little correlation between initial dobutamine clearance and weight (r2 = .10), net cumulative fluid balance before initiation of dobutamine (r2 < .01), age (r2 = .20), and estimated creatinine clearance (r2 = .09). Conclusions: Dobutamine pharmacokinetics in adult critically ill patients is best described by a first‐order model. Pathophysiologic factors may have an effect on the pharmacokinetics of dobutamine which appears to change over time. Both inter‐ and intrapatient variability in infusion rate administered and resultant serum concentrations were wide, suggesting that infusion rate should be guided by clinical end points rather than by predetermined values. (Crit Care Med 1994; 22:1926–1932)

Effect of positive end-expiratory pressure on extravascular lung water in porcine acute respiratory failure.

Recent studies of acute respiratory failure suggest that PEEP causes increased pulmonary interstitial fluid collection and therefore increased extravascular lung water (EVLW). We examined the effect of increasing levels of PEEP on EVLW in 20 to 25-kg pigs with acute respiratory failure induced by continuous infusion of live Pseudomonas aeruginosa (2 X 10(8) organisms/20 kg.min). Animals were intubated, paralyzed, and ventilated at 15 ml/kg tidal volume and an FIO2 of 0.4. Pigs in group 1 were given 4 ml/kg.h of iv fluid (lactated Ringers solution) with no PEEP administered. Animals in groups 2 through 5 were given 0, 4, 17, and 44 ml/kg.h of lactated Ringers solution, respectively, and PEEP was added at 5-cm H2O increments per half-hour, starting one hour after beginning P. aeruginosa infusion. EVLW in PEEP animals was less than or equal to that in controls despite variation in the administration of lactated Ringers solution. This suggests that PEEP may slow EVLW accumulation over time and provide a protective effect that allows increased amounts of crystalloid fluids to be administered.

Improvement in cardiac output during airway pressure release ventilation

Positive-pressure ventilation is known to affect cardiac output and hemodynamic stability (1). Minimizing the number of positive-pressure breaths and allowing more spontaneous ventilation increase cardiac output by augmenting venous return (2, 3). Airway pressure release ventilation (APRV) is different from other positive-pressure modes of mechanical ventilation. It allows spontaneous ventilation and, by alternating between high and low continuous positive airway pressure levels, causes changes in the functional residual capacity, which augments CO2 elimination (4). This method of ventilation results in lower peak airway pressures and has a minimal effect on cardiac output in animal studies (5). We present a case in which a change in the mode of mechanical ventilation from intermittent mandatory ventilation (IMV) with continuous positive airway pressure to APRV resulted in improvement in the cardiac output of a patient requiring mechanical ventilatory support.

Comparison of digital blood pressure, plethysmography, and the modified Allen's test as means of evaluating the collateral circulation to the hand

The collateral circulation to the hand was evaluated on 70 hands of healthy volunteers. Comparisons were made between the results of the modified Allens test alone and the Allens test combined with either plethysmography or digital blood pressure. The modified Allens test requires patient cooperation and the results can be subjective. Plethysmography does not require patient cooperation and produces a signal that varies directly with flow; however, this is not a quantifiable signal. Digital blood pressure (measured by the 2300 Finapres noninvasive blood pressure monitor, Ohmeda, Englewood, CO, USA) also requires no patient cooperation. The values produced are of clinical value and reproducible. Both the plethysmograph and digital blood pressure monitors were able to demonstrate the dominant arterial vessel of the hand. The digital blood pressure monitor produces an objective recordable numerical value, an accepted clinical parameter, and it does not require patient cooperation. The use of a digital blood pressure monitor may prove to be an acceptable alternative to the traditional Allens test.

Loss of nitroglycerin to cardiopulmonary bypass apparatus.

An in vitro model of a cardiopulmonary bypass (CPB) circuit using a bubble oxygenator was developed to assess the potential of this system to extract nitroglycerin (NTG). A NTG solution (100 ng/ml) was circulated through a CPB circuit at 5 L/min for 60 min. Samples obtained for NTG analysis revealed a significant loss of drug to the circuit. By 60 min, only 18% of the initial NTG concentration was present. In a separate experiment, the bubble oxygenator was shown to be the major source of drug extraction because less than 15% of the drug concentration infused directly into the oxygenator appeared in the arterial outlet. These results indicate that patients may not receive the expected dose of NTG during CPB even if caution is taken to administer the drug through nonadsorbing iv tubing.

Postoperative course after sufentanil or fentanyl anesthesia for coronary artery surgery

Postoperative hemodynamic effects were compared in 50 patients randomly selected to receive either sufentanil, 25 micrograms/kg, or fentanyl, 100 micrograms/kg, anesthesia for coronary artery bypass grafting. The two groups exhibited similar patient demographics; dose of premedicants and muscle relaxants; and use of inhalation agents. Values for 15 hemodynamic variables were recorded at baseline and at six postoperative times. The times to awakening, response to verbal commands, and extubation were also noted. Patients who received sufentanil had a more stable course, with higher cardiac outputs, lower systemic vascular resistances, and a lower incidence of hypertension. Postoperatively, the two groups had similar values for time to awakening, response to verbal commands, and extubation. Elimination half-lives differed significantly: 554 +/- 91 minutes (fentanyl) versus 277 +/- 60 minutes (sufentanil). Serum concentrations of both decreased linearly. The added advantages of postoperative hemodynamic stability could be important in the choice of anesthetic.