Nutritional status of multiple sclerosis (MS) patients attending Kasr Alainy MS unit: an exploratory cross-sectional study

BACKGROUND

Nutrition was claimed to be a factor in MS causation, course, complications, and management. Several studies were conducted to assess the nutritional status of MS patients; however, few studies were conducted to assess this problem in Egypt. Therefore, the purpose of the current study was to assess the nutritional status of a sample of MS patients.

METHODS

The researchers conducted an exploratory cross-sectional study among 76 relapsing-remitting MS (RRMS) patients attending Kasr Alainy Multiple Sclerosis Unit (KAMSU) from October 2018 to January 2019 to assess the nutritional status of a sample of MS patients. Data were collected using a structured interview questionnaire including an inquiry about the socioeconomic status, and nutritional status using anthropometric measurements, patient-generated subjective global assessment (PG-SGA), semi-quantitative food frequency questionnaires (SQFFQ), and hemoglobin level measurement. Assessment of fatigue was done using the Modified Fatigue Impact Scale 5-items version.

RESULTS

The mean age of the study participants was 30 ± 6 years. The disease duration ranged from 2 to 264 months. Malnutrition was prevalent among 67.1% (27.6 % overweight, 36.8% obese, and 2.6% underweight). Half of the investigated patients were anemic. According to the PG-SGA, more than half of the studied patients (53.9%) were classified as moderately or suspected malnourished. The unhealthy dietary habits such as taking only a few meals, junk food intake and skipping breakfast were observed in considerable proportions of the group. The SQFFQ revealed overconsumption of energy and fat, and less than acceptable consumption of dietary fibers by most of the studied patients.

CONCLUSIONS

Overweight, obesity, anemia, and unhealthy dietary habits were prevalent among the RRMS patients attending the KAMSU. Nutrition care service is extremely needed for this group of patients.

Clinical and epidemiologic features of psoriasis patients in an Egyptian medical center

Background

Identification of epidemiologic and phenotypic variations of psoriasis among different ethnic groups can further our understanding of this perplexing disease, aiming at better management of patients worldwide.

Objective

To provide a descriptive analysis of psoriasis patients registered at Kasr Al-Ainy Psoriasis Unit Disease Registry.

Methods

This retrospective single-center registry study included patient records between November 2015 and November 2018 (2534 patients). Sociodemographic and phenotypic data were analyzed.

Results

The mean age of the registered patients was 39.3 years and 56.3% were men. Stress was the main precipitating factor (48.3%), whereas the most common symptom reported was itching (82.4%). The median body mass index was 27.5, and the median percentage of body surface area involved was 10.0. The mean Psoriasis Area Severity Index score was 8.7, and the mean Psoriasis Disability Index score was 13.0. Both parameters correlated positively, and both showed significantly higher means in smokers.

Limitations

Despite that the study was performed at a highly specialized tertiary care center with a high flow of patients, this was still a single-center registry.

Conclusions

This work shows that the characteristics of Egyptian patients with psoriasis are comparable to those of other studied ethnic groups, with minor differences.

Effect of an educational intervention on breastfeeding knowledge and attitude among interns at Cairo University Hospital

BACKGROUND

Professional advice provided to mothers has an effective role on the prevalence and duration of breastfeeding. Previous studies showed that health care providers had defective knowledge and skills necessary to promote and support breastfeeding.

AIM

To assess breastfeeding-related knowledge and attitude among interns at Cairo University Hospital, before and after the provision of breastfeeding educational training sessions.

MATERIALS AND METHODS

The first phase was a cross-sectional study, conducted in Cairo University Hospital (Kasr Al Ainy) among 137 interns. The second phase was a pre-post interventional design. A pretested self-administered questionnaire was used to explore breastfeeding-related knowledge and attitude before, immediately after, and 3 months after breastfeeding educational sessions.

RESULTS

Participants' mean age was 23.7 ± 0.81, (range 22-27 years), with equally distributed males and females. The median total knowledge percent score was 56.4 (45.2-64.5). The highest median subtotal knowledge percent score was for effective feeding 100 (100-100), and the least median was for breast milk expression 20 (0:40). Participants' knowledge improved after the educational intervention: The subtotal knowledge scores showed a statistically significant improvement immediately after and 3 months after the intervention in the following items: advantages for the baby, colostrum, duration, complementary feeding, and breast milk expression. The median total attitude percent score was 80 (74.1-83.5) and significantly improved immediately after the intervention.

CONCLUSION

Baseline knowledge and attitude scores among interns significantly improved after the intervention. Therefore, adoption of different curricular and extracurricular activities to improve breastfeeding knowledge and skills is required.

Tracheal intubating conditions and apnoea time after small-dose succinylcholine are not modified by the choice of induction agent

BACKGROUND

In a randomized, double-blind clinical trial, we studied the effect of different i.v. induction drugs on tracheal intubation conditions and apnoea time after small-dose (0.6 mg kg(-1)) succinylcholine used to facilitate orotracheal intubation at an urban, university-affiliated community medical centre.

METHODS

One hundred and seventy-five ASA I and II adult patients scheduled to undergo surgical procedures requiring general anaesthesia and tracheal intubation were allocated to one of five groups according to i.v. anaesthetic induction drug used. General anaesthesia was induced by i.v. administration of lidocaine 30 mg and propofol 2.5 mg kg(-1) (Group 1), thiopental 5 mg kg(-1) (Group 2), lidocaine 30 mg and thiopental 5 mg kg(-1) (Group 3), etomidate 0.3 mg kg(-1) (Group 4), or lidocaine 30 mg and etomidate 0.3 mg kg(-1) (Group 5). After loss of consciousness, succinylcholine 0.6 mg kg(-1) was given i.v. followed by direct laryngoscopy and tracheal intubation after 60 s. Measurements included intubation conditions recorded during laryngoscopy 60 s after succinylcholine administration, and apnoea time.

RESULTS

Overall, clinically acceptable intubation conditions were met in 168 out of the 175 patients studied (96%). They were met in 35/35 patients in Group 1, 33/35 patients in Group 2, 34/35 patients in Group 3, 33/35 patients in Group 4, and 33/35 patients in Group 5. Mean (SD) apnoea time was 4.0 (0.4), 4.2 (0.3), 4.2 (0.6), 4.1 (0.2) and 4.1 (0.2) min respectively in Groups 1-5. There were no differences in the intubation conditions or apnoea times between the groups.

CONCLUSIONS

The use of succinylcholine 0.6 mg kg(-1) produced the same favourable intubation conditions and a short apnoea time regardless of the induction drug used.

Verification of endotracheal tube position

The goals of tracheal intubation are to place the tube in the trachea and to position the tube at an appropriate depth inside the trachea. Various clinical signs and technical aids are described to verify tracheal intubation and to diagnose esophageal intubation. Many of these methods fail under certain circumstances. Not all these methods can be applied in every intubation, but it is essential that the clinician involved in tracheal intubation have the necessary airway management skills, perform these tests accurately, and interpret the results correctly. Prioritization of these tests depends on many factors, including familiarity, availability of monitors, and the location of intubation. Viewing the tube passing between the cords during direct laryngoscopy and visualization of the tracheal rings and carinae with a fiberoptic scope after intubation are the only fullproof methods of confirming tracheal intubation. In the nonarrested patient, carbon dioxide monitoring quickly can differentiate tracheal from esophageal intubation. In the arrested patient, however, carbon dioxide monitoring can be unreliable, although it can be useful as a prognostic indicator of the efficacy of resuscitation. Devices such as [figure: see text] the self-inflating bulb and esophageal detector device may be more useful in patients with cardiac arrest, but they also can yield false results. Placing the distal tip of the tube in the middle of the trachea can be accomplished by positioning the upper end of the cuff 2 cm below the cords during direct laryngoscopy or by placing the distal tip of the tube 4 cm above the carinae with the aid of a fiberoptic scope. The position of the tube always should be verified by clinical assessment (e.g., auscultation). If direct visualization cannot be done, referencing the marks on the tube, transillumination techniques, or cuff maneuvers can be helpful. In the emergency and critical care settings, a chest radiograph easily can detect malpositioned tracheal tubes that may not be detected by routine clinical assessment. Other techniques (e.g., use of fiberoptic scopes, cuff maneuvers, transillumination) can decrease the need for frequent chest radiographs. Based on available information, two algorithms are proposed: one for emergency intubation (Fig. 9) and the other for verification of tracheal tube position in elective intubation (Fig. 10). These algorithms are designed [figure: see text] to assist the clinician and should not be substituted for clinical judgment. Under no circumstances should clinical signs be ignored in the presence of conflicting information from monitors and technical aids.

Preoxygenation with tidal volume and deep breathing techniques: the impact of duration of breathing and fresh gas flow

Various techniques of "preoxygenation" before anesthetic induction have been advocated, including tidal volume breathing (TVB) for 3-5 min, four deep breaths (DB) in 0.5 min, and eight DB in 1 min. However, no study has compared the effectiveness of these techniques, assessed extending deep breathing beyond 1 min, or investigated the influence of fresh gas flow (FGF) in the same subjects using a circle absorber system. In 24 healthy adult volunteers breathing oxygen from a circle absorber system by tight-fitting mask, we compared TVB/5 min and deep breathing at a rate of 4 DB/0.5 min for 2 min at 5, 7, and 10 L/min FGF. Inspired and end-tidal respiratory gases were measured at 0.5-min intervals. During TVB, end-tidal oxygen (ETO2) increased rapidly and plateaued by 2.5 min at 86%, 88%, and 88% with 5, 7 and 10 L/min FGF, respectively. ETO2 values of > or =90% were attained between 3 and 4 min. Four DB/0.5 min increased ETO2 to 75%, 77%, and 80% at 5, 7, and 10 L/min FGF. Eight DB/min resulted in ETO2 values of 82% and 87% at 7 and 10 L/min, respectively. Extending deep breathing to 1.5 and 2 min with 10 L/min FGF increased ETO2 by > or =90%, although a decrease in ETCo(2) was noted. We concluded that TVB/3-5 min was effective in achieving maximal "preoxygenation" whereas 4 DB/0.5 min resulted in submaximal "preoxygenation," and thus should be used only when time is limited. Increasing FGF from 5 to 10 L/min does not enhance "preoxygenation" with either TVB or 4 DB/0.5 min. Deep breathing yields maximal "preoxygenation" when extended to 1.5 or 2 min, and only when high (10 L/min) FGF is used.

IMPLICATIONS

Using a circle absorber system, normal breathing of oxygen for 3-5 min achieves optimal oxygenation of the lungs; whereas 4 deep breaths in 30 s does not. However, extending deep breathing to 1.5-2 min and using a high flow of oxygen improves oxygenation of the lungs to the same degree as normal breathing for 3-5 min. This may have important implications for patient safety.

Efficacy of preoxygenation with tidal volume breathing. Comparison of breathing systems

BACKGROUND

Preoxygenation before tracheal intubation is intended to increase oxygen reserves and delay the onset of hypoxemia during apnea. Various systems are used for preoxygenation. Designed specifically for preoxygenation, the NasOral system uses a small nasal mask for inspiration and a mouthpiece for exhalation. One-way valves in the nasal mask and the mouthpiece ensure unidirectional flow. This investigation compares the efficacy of preoxygenation using the standard circle system with the NasOral system and five different resuscitation bags.

METHODS

Twenty consenting, healthy volunteers were studied in the supine position for 5-min periods of tidal volume breathing using the circle absorber system, the NasOral system, and five resuscitation bags in a randomized order. Data were collected during room air breathing and at 30-s intervals during 5 min of oxygen administration. Inspired oxygen, end-tidal oxygen, and end-tidal nitrogen were measured by mass spectrometry.

RESULTS

At 2. 5 min of oxygenation, end-tidal oxygen plateaued at 88.1 +/- 4.8 and 89.3 +/- 6.4% (mean +/- SD) for the circle absorber and NasOral systems, respectively. This was associated with inverse decreases in end-tidal nitrogen. At no time did these end-tidal oxygen or nitrogen values differ from each other. Three of the resuscitation bags (one disk type and two duck-bill type with one-way exhalation valves) delivered inspired oxygen more than 90%, and the end-tidal oxygen plateaued between 77 and 89% at 2 min of tidal volume breathing. The other two resuscitation bags (both duck-bill bags without exhalation valves) delivered inspired oxygen less than 40%, and the end-tidal oxygen values ranged between 21.8 +/- 5.0 and 31.9 +/- 8.7%.

CONCLUSIONS

The circle absorber and NasOral systems were equally effective in achieving maximal preoxygenation during tidal volume breathing. Resuscitation bags differed markedly in effectiveness during preoxygenation; those with duck-bill valves without one-way exhalation valves were the least effective. Thus, the use of these bags should be avoided for preoxygenation.

Direct coronary vasomotor effects of sevoflurane and desflurane in in situ canine hearts

BACKGROUND

An extracorporeal system was used to investigate the direct coronary vasomotor effects of sevoflurane and desflurane in vivo. The role of the adenosine triphosphate-sensitive potassium channels (KATP channels) in these effects was evaluated.

METHODS

Twenty-one open-chest, anesthetized (fentanyl-midazolam) dogs were studied. The left anterior descending coronary artery was perfused at controlled pressure (80 mmHg) with normal arterial blood or arterial blood equilibrated with either sevoflurane or desflurane. Series 1 (n = 16) was divided into two groups of equal size on the basis of whether sevoflurane (1.2, 2.4, and 4.8%) or desflurane (3.6, 7.2, and 14.4%) was studied. The concentrations for the anesthetics corresponded to 0.5, 1.0, and 2.0 minimum alveolar concentration (MAC), respectively. Coronary blood flow (CBF) was measured with an ultrasonic, transit-time transducer. Local coronary venous samples were obtained and used to evaluate changes in myocardial oxygen extraction (EO2). In series 2 (n = 5), changes in CBF by 1 MAC sevoflurane and desflurane were assessed before and during intracoronary infusion of the KATP channel inhibitor glibenclamide (100 microg/min).

RESULTS

Intracoronary sevoflurane and desflurane caused concentration-dependent increases in CBF (and decreases in EO2) that were comparable. Glibenclamide blunted significantly the anesthetic-induced increases in CBF.

CONCLUSIONS

Sevoflurane and desflurane have comparable coronary vasodilative effects in in situ canine hearts. The KATP channels play a prominent role in these effects. When compared with data obtained previously in the same model, the coronary vasodilative effects of sevoflurane and desflurane are similar to those of enflurane and halothane but considerably smaller than that of isoflurane.

Nitric oxide does not modulate whole body oxygen consumption in anesthetized dogs

The effects of the NO synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) and the NO donor sodium nitroprusside (SNP) on whole body O2 consumption (VO2) were assessed in 16 dogs anesthetized with fentanyl or isoflurane. Cardiac output (CO) and mean arterial pressure (MAP) were measured with standard methods and were used to calculate VO2 and systemic vascular resistance (SVR). Data were obtained in each dog under the following conditions: 1) Control 1, 2) SNP (30 microg. kg-1. min-1 iv) 3) Control 2, 4) L-NAME (10 mg/kg iv), and 5) SNP and adenosine (30 and 600 microg. kg-1. min-1 iv, respectively) after L-NAME. SNP reduced MAP by 29 +/- 3% and SVR by 47 +/- 3%, while it increased CO by 39 +/- 9%. L-NAME had opposite effects; it increased MAP and SVR by 24 +/- 4% and 103 +/- 11%, respectively, and it decreased CO by 37 +/- 3%. Neither agent changed VO2 from the baseline value of 4.3 +/- 0.2 ml. min-1. kg-1, since the changes in CO were offset by changes in the arteriovenous O2 difference. Both SNP and adenosine returned CO to pre-L-NAME values, but VO2 was unaffected. We conclude that 1) basally released endogenous NO had a tonic systemic vasodilator effect, but it had no influence on VO2; 2) SNP did not alter VO2 before or after inhibition of endogenous NO production; 3) the inability of L-NAME to increase VO2 was not because CO, i.e., O2 supply, was reduced below the critical level.

Isoflurane-induced dilation of porcine coronary arterioles is mediated by ATP-sensitive potassium channels

BACKGROUND

Isoflurane causes increases in coronary blood flow in vivo, which are mediated by the adenosine triphosphate (ATP)-sensitive potassium channels, but the role of the arterioles (resistance vessels) in these responses is controversial.

METHODS

Medium porcine coronary arterioles (internal diameter, 172 +/- 51 [SD] microm) were placed in a chamber supplied with Kreb's buffer, pressurized (40 mmHg), and preconstricted with acetylcholine (10(-8)-10(-6) M). Vascular diameter (VD) was assessed using an optical density video-detection system. Isoflurane (in 95% oxygen and 5% carbon dioxide) was added to buffer using a membrane oxygenator supplied by a calibrated vaporizer. In series 1 (n = 14), 2% isoflurane was administered according to an abrupt (ISO-A) and gradual (ISO-G) protocol. In series 2 (n = 13) and 3 (n = 6), ISO-A (1.5%) was assessed before and after glibenclamide (an ATP-sensitive potassium channel antagonist) or 8-phenyltheophylline (a nonselective adenosine receptor antagonist), respectively. In series 4 (n = 5), validation studies were performed using sodium nitroprusside and adenosine diphosphate to verify that the vascular smooth muscle and endothelium of the vessels were functionally intact. In series 5 (n = 6), ISO-A (0.75 and 1.5%) was compared during preconstriction with acetylcholine and the thromboxane analog U46619 (10(-6) M).

RESULTS

ISO-G caused essentially concentration-dependent increases in VD. At 2% isoflurane, the increases in VD were greater during ISO-A than ISO-G. Glibenclamide, but not 8-phenyltheophylline, attenuated isoflurane-induced increases in VD. Both sodium nitroprusside and adenosine diphosphate caused dose-dependent increases in VD. Isoflurane caused equivalent concentration-dependent increases in VD during acetylcholine and U46619.

CONCLUSIONS

Isoflurane is a concentration-dependent dilator of porcine coronary arterioles preconstricted with acetylcholine or U46619. This effect is blunted by gradual administration, suggesting that the vessels may adapt to the relaxing effects of isoflurane. Isoflurane-induced dilation of coronary arterioles is mediated by the ATP-sensitive potassium channels but not by the adenosine receptors.

Is calcium a coronary vasoconstrictor in vivo?

BACKGROUND

Calcium produces constriction in isolated coronary vessels and in the coronary circulation of isolated hearts, but the importance of this mechanism in vivo remains controversial.

METHODS

The left anterior descending coronary arteries of 20 anesthetized dogs whose chests had been opened were perfused at 80 mmHg. Myocardial segmental shortening was measured with ultrasonic crystals and coronary blood flow with a Doppler flow transducer. The coronary arteriovenous oxygen difference was determined and used to calculate myocardial oxygen consumption and the myocardial oxygen extraction ratio. The myocardial oxygen extraction ratio served as an index of effectiveness of metabolic vasodilation. Data were obtained during intracoronary infusions of CaCl2 (5, 10, and 15 mg/min) and compared with those during intracoronary infusions of dobutamine (2.5, 5.0, and 10.0 microg/min).

RESULTS

CaCl2 caused dose-dependent increases in segmental shortening, accompanied by proportional increases in myocardial oxygen consumption. Although CaCl2 also increased coronary blood flow, these increases were less than proportional to those in myocardial oxygen consumption, and therefore the myocardial oxygen extraction ratio increased. Dobutamine caused dose-dependent increases in segmental shortening and myocardial oxygen consumption that were similar in magnitude to those caused by CaCl2. In contrast to CaCl2, however, the accompanying increases in coronary blood flow were proportional to the increases in myocardial oxygen consumption, with the result that the myocardial oxygen extraction ratio remained constant.

CONCLUSIONS

Calcium has a coronary vasoconstricting effect and a positive inotropic effect in vivo. This vasoconstricting effect impairs coupling of coronary blood flow to the augmented myocardial oxygen demand by metabolic vascular control mechanisms. Dobutamine is an inotropic agent with no apparent direct action on coronary resistance vessels in vivo.

Efficacy of the self-inflating bulb in differentiating esophageal from tracheal intubation in the parturient undergoing cesarean section

We studied the efficacy of the self-inflating bulb (SIB) in differentiating tracheal from esophageal intubation in 40 parturients undergoing elective cesarean section under general anesthesia. After induction and muscle relaxation, the trachea was intubated under direct vision with cuffed tube. In 20 parturients, the esophagus was also intubated with an identical tube. Before ventilation was initiated, an independent anesthesiologist checked tube positions with the SIB using two techniques. In one technique (T1), the SIB was compressed before connection to the tube; in the other technique (T2), the SIB was first connected to the tube and then compressed. The speed of reinflation was graded as rapid, delayed, and none. Tracheal tube position was reassessed immediately before and after delivery. Before initiation of controlled ventilation, the incidence of false negative results was 47.5% with T1 and 27.5% with T2 but significantly decreased to 17.5% with T1 and 7.5% with T2 when retested before delivery. After delivery, no false negative results occurred. The incidence of false positive results immediately after induction was 30% with T1 and 35% with T2. The mechanism of false negative responses may be attributed to decreased functional residual capacity leading to reduced caliber of intrathoracic airways and terminal airway closure; whereas false positive responses may be related to an incompetent gastroesophageal junction. We conclude that the SIB is unreliable for differentiating tracheal from esophageal intubation in the parturient undergoing cesarean section.

Role of adenosine triphosphate-sensitive potassium channels in coronary vasodilation by halothane, isoflurane, and enflurane

BACKGROUND

Halothane, isoflurane, and enflurane cause coronary vasodilation and cardiac depression. This study was performed to assess the role of adenosine triphosphate (ATP)-sensitive potassium channels (KATP channels) in these effects.

METHODS

Twenty-five thoracotomized dogs were anesthetized with fentanyl and midazolam. The left anterior descending coronary artery was perfused via either of two pressurized (80 mmHg) reservoirs. One reservoir was supplied with arterial blood free of a volatile anesthetic, and the second reservoir was supplied with arterial blood equilibrated in an oxygenator with a 1 minimum alveolar concentration of either halothane (0.9%, n = 10), isoflurane (1.4%, n = 8), or enflurane (2.2%, n = 7). Coronary blood flow (CBF) was measured using a Doppler flow transducer, and segmental shortening (SS) was measured with ultrasonic crystals. Responses to the volatile anesthetics were assessed under control conditions, during intracoronary infusion of the KATP channel inhibitor glibenclamide (100 micrograms/min), and after cessation of glibenclamide (recovery). The effectiveness of glibenclamide was verified from inhibition of coronary vasodilator responses to the KATP channel opener cromakalim without effect on those to the KATP channel-independent vasodilators, sodium nitroprusside and acetylcholine.

RESULTS

Under control conditions, the volatile anesthetics caused pronounced increases in CBF (isoflurane > halothane = enflurane), and decreases in SS (enflurane > halothane = isoflurane). Glibenclamide blunted significantly (and reversibly) the increases in CBF, but it had no effect on the decreases in SS.

CONCLUSIONS

The KATP channels play an important role in coronary vasodilation but apparently are not involved in cardiac depression caused by halothane, isoflurane, and enflurane in canine hearts in situ.

Investigations into the mechanisms of coronary vasodilation by contrast media in dogs

RATIONALE AND OBJECTIVES

The study was performed to clarify the mechanisms underlying contrast-induced coronary vasodilation.

METHODS

The left anterior descending coronary artery of 14 open-chest dogs was perfused at constant pressure. Coronary blood flow (CBF) was measured electromagnetically and used to calculate myocardial oxygen consumption (MVO2). Responses were evaluated during intracoronary infusions (2 mL/ minute) of the ionic contrast medium, Hypaque-76, and the nonionic contrast medium, Isovue-370, and compared with those caused by hypertonic saline solutions with comparable osmolarities. Studies also were conducted using Isovist-300, which is a new nonionic and iso-osmolar contrast medium.

RESULTS

Hypaque-76 and Isovue-370 caused initial peak increases in CBF (reflecting decreases in coronary vascular resistance), which waned rapidly to achieve more modest steady-state increases within 2 to 3 minutes. Both the peak and steady-state increases in CBF were greater during Hypaque-76 than during Isovue-370. The increases in CBF caused by the contrast medium were greater than those caused by the corresponding saline solution. Neither Hypaque-76 nor Isovue-370 changed MVO2-Isovist-300 had no effect on CBF or MVO2.

CONCLUSIONS

The coronary vasodilation by contrast media is the result of a direct vasorelaxing effect rather than secondary to a metabolic mechanism. Hyperosmolarity can account only in part for contrast-induced coronary vasodilation.

Efficacy of the self-inflating bulb in confirming tracheal intubation in the morbidly obese

BACKGROUND

This study was designed to determine the incidence of false-negative and false-positive results when the self-inflating bulb (SIB) is used to differentiate tracheal from esophageal intubation in morbidly obese patients using two techniques. In technique 1, the SIB is compressed before it is connected to the tube; in technique 2, the SIB is compressed after connection to the tube.

METHODS

With institutional review board approval, 54 consenting adult morbidly obese patients (body mass index > 35) undergoing elective surgical procedures were included in the study. After anesthetic induction and muscle relaxation, both the trachea and esophagus were intubated under direct vision with identical cuffed tubes. The efficacy of the SIB in verifying the position of both tubes was tested by a second anesthesiologist. The speed of reinflation was graded as rapid ( < 4 s) or none ( > 4 s), using both techniques. In the case of tracheal intubation, the absence of reinflation was recorded as a false-negative, whereas in cases of esophageal intubation, rapid reinflation was recorded as a false-positive. Identification of tube location by the second anesthesiologist was based on SIB reinflation results from techniques 1 and 2, as well as the presence of a flatuslike sound elicited by technique 2 in esophageally placed tubes. All patients were retested by the SIB after receiving three breaths of 400-500 ml each. In all patients exhibiting false-negative results, six obese patients exhibiting true-positive results, and four nonobese patients exhibiting true-positive results, tracheal responses to the SIB maneuvers were observed directly by a flexible fiberoptic bronchoscope incorporating an airtight system, 15-20 min after mechanical ventilation was instituted.

RESULTS

The incidence of false-negative results was initially 30% with technique 1 and 11% with technique 2, but decreased to 4% when technique 2 was used after the delivery of three breaths. The second anesthesiologist initially identified tube location in 92.5% of patients correctly. After the delivery of three breaths, tube location was correctly identified in 96.3% of patients. Fiberoptic bronchoscopic examination of the patients exhibiting false-negative results revealed exaggerated inward bulging of the posterior tracheal membrane during reinflation of the SIB when technique 1 was used.

CONCLUSIONS

Contrary to previous investigations in healthy patients, the current study demonstrates a high incidence of false-negative results when the SIB is used to confirm tracheal intubation in morbidly obese patients. If the SIB is used, the technique should include compression of the SIB after connection to the tube and should be used in conjunction with other clinical signs and technical aids. The mechanism of false-negative results in these patients seems to be related to reduction of caliber of airways secondary to a marked decrease in functional residual capacity, and collapse of large airways due to invagination of the posterior tracheal wall when sub-atmospheric pressure is generated by the SIB.

The direct effects of enflurane on coronary blood flow, myocardial oxygen consumption, and myocardial segmental shortening in in situ canine hearts

This study evaluated changes in coronary blood flow (CBF), myocardial oxygen consumption (MVo2), and myocardial segmental shortening (SS) during intracoronary administrations of enflurane in in situ canine hearts. The left anterior descending coronary artery (LAD) of 11 anesthetized and mechanically ventilated dogs was perfused at constant perfusion pressure (80 mm Hg) with enflurane-free blood or with blood equilibrated in an extracorporeal oxygenator with enflurane (1.1%, 2.2%, 4.4%). CBF (measured with a Doppler flow transducer) was multiplied by the local arteriovenous (A-V) O2 difference to calculate MVo2. SS was measured with ultrasonic crystals. Myocardial lactate uptake was assessed. Peak CBF responses during enflurane were compared with those during maximum coronary vasodilation with adenosine. Enflurane caused concentration-dependent increases in CBF, and decreases in MVo2 and SS. The greatest increase in CBF during enflurane (4.4%) was similar to that achievable with adenosine. Myocardial lactate uptake was not affected by enflurane. In conclusion, enflurane has a direct coronary vasodilating effect. The potency of this effect is underscored by the ability of enflurane to cause marked increases in CBF, while appreciably reducing myocardial O2 demand. Since the enflurane-induced reduction in myocardial contractility was not due to ischemia, it likely reflected a direct negative inotropic effect. When the direct effects of enflurane are compared with those of equianesthetic concentrations of halothane and isoflurane previously shown in the same model, enflurane has a coronary vasodilating effect similar to that of halothane but less than that of isoflurane, and it has a negative inotropic effect greater than that of both isoflurane and halothane.

Isoflurane-induced coronary vasodilation is preserved in reperfused myocardium

Isoflurane causes vasodilation in the coronary circulation. The present study evaluated whether this action is preserved after a brief coronary occlusion followed by reperfusion. Fourteen open-chest dogs anesthetized with fentanyl and midazolam were studied. The left anterior descending coronary artery was perfused via an extracorporeal system with normal arterial blood or with arterial blood equilibrated with 1.4% (1 minimum alveolar anesthetic concentration [MAC]) isoflurane. Coronary perfusion pressure was maintained at 90 mm Hg. Coronary blood flow (CBF) was measured with a Doppler flow transducer. Steady-state changes in CBF during isoflurane, and during intracoronary infusions of acetylcholine (Ach; 20 micrograms/min), an endothelium-dependent vasodilator, and sodium nitroprusside (SNP; 80 micrograms/min), an endothelium-independent vasodilator, were compared in normal myocardium and in myocardium subjected to 15 min of ischemia (due to cessation of perfusion) followed by 30 min of reperfusion. Ischemia-reperfusion had no significant effect on the increases in CBF by isoflurane (421% +/- 88% vs 388% +/- 84%) or SNP (115% +/- 18% vs 135% +/- 19%), whereas it attenuated these increases in CBF by Ach (232% +/- 38% vs 143% +/- 21%). In conclusion, a brief period of myocardial ischemia followed by reperfusion did not affect the coronary vasodilating effects of isoflurane and SNP, although it blunted these effects of Ach. The present findings provide further evidence suggesting that the ability of isoflurane to relax coronary vascular smooth muscle is independent of the nitric oxide-cyclic guanosine monophosphate pathway.

Preoperative pregnancy testing in ambulatory surgery. Incidence and impact of positive results

BACKGROUND

The incidence of unrecognized early pregnancy and its influence on the surgical and anesthetic course in patients presenting for elective ambulatory surgery have not been previously determined. The current study was designed to determine the incidence of unrecognized pregnancy in women presenting for ambulatory surgery. In addition, it examined how discovery of the pregnancy altered the anesthetic or surgical course.

METHODS

In a prospective study over a 1-yr period, all women of childbearing potential (defined as menstruating women without prior hysterectomy or tubal ligation) were preoperatively evaluated and tested for urine or serum human chorionic gonadotropin, to determine unrecognized pregnancy. If a pregnancy was detected, the disposition of the surgical procedure and the effect on the surgical and anesthetic management was recorded.

RESULTS

Of 2,056 women of childbearing potential presenting for ambulatory surgery, testing revealed 7 previously unrecognized pregnancies, an incidence of 0.3%. Included among these patients were two patients scheduled to undergo fertility procedures. On learning the test result and even before being advised of available options, all patients elected to cancel or postpone the surgical procedure.

CONCLUSIONS

The incidence of previously unrecognized pregnancy in menstruating women presenting for ambulatory, nonobstetric surgery was 0.3%. The knowledge of a positive test resulted in cancellation or postponement of the operative procedure. Patient desire for cancellation was the main determining factor in each case.

Hemodilution impairs hypocapnia-induced vasoconstrictor responses in the brain and spinal cord in dogs

Despite the increasing use of plasma expanders in the perioperative period, there have been few studies of cerebrovascular responsiveness during hemodilution. The present study was performed to evaluate the influence of isovolemic hemodilution on vasoconstrictor responses in the brain and spinal cord during hypocapnia. Sixteen mechanically ventilated, halothane-anesthetized dogs were randomly divided into two equal groups: Group 1, control group (hematocrit [Hct], 42% +/- 2%); Group 2, isovolemic hemodilution with 5% dextran 40 (Hct, 19% +/- 2%). Hypocapnia (22 +/- 1 mm Hg) was induced in both groups by removal of dead space tubing without altering mechanical ventilation. Regional blood flow in the brain and spinal cord was measured with 15-microns radioactive microspheres and used to calculate regional vascular resistance (RVR). In Group 1, hypocapnia caused increases in RVR (ranging from 44% +/- 10% in the cerebral cortex to 93% +/- 17% in the thoracic spinal cord). In Group 2, hemodilution itself decreased RVR relatively uniformly throughout the brain and spinal cord. After hemodilution, hypocapnia had no significant effect on RVR in the cerebral cortex, cerebellum, pons, and medulla, and caused less pronounced increases in RVR within the spinal cord. We conclude that hemodilution either attenuated or completely abolished vasoconstrictor responses within the brain and spinal cord during hypocapnia. Furthermore, the present findings suggest that induced hypocapnia may be less effective as a clinical maneuver to reduce increased intracranial pressure during hemodilution.

Coronary vasodilation by isoflurane. Abrupt versus gradual administration

BACKGROUND

Under certain circumstances, isoflurane is associated with coronary artery vasodilation. The objective of the current study was to ascertain whether the rate of administration of isoflurane influences its vasodilating effect in the coronary circulation.

METHODS

Seven open-chest dogs anesthetized with fentanyl and midazolam were studied. The left anterior descending coronary artery was perfused via either of two pressurized (80 mmHg) reservoirs; reservoir 1 (control) was supplied with arterial blood free of isoflurane, and reservoir 2 was supplied with blood from an extracorporeal oxygenator, which was provided with 95% O2/5% CO2 gas that passed through calibrated vaporizer. Coronary blood flow (CBF) was measured with Doppler flow transducer. In each dog, isoflurane was administered according to two protocols; abrupt (isoflurane-A) or gradual (isoflurane-G). In isoflurane-A, the left anterior descending coronary artery was switched from reservoir 1 to reservoir 2 after the latter was filled with blood previously equilibrated with 1.4% (1 MAC) isoflurane. In isoflurane-G, the left anterior descending coronary artery was switched to reservoir 2 with vaporizer set at 0% isoflurane; then the vaporizer was adjusted to 1.4% isoflurane, which produced a gradual increase in isoflurane concentration within reservoir 2 that reached a level equivalent to that in isoflurane-A (as evaluated by gas chromatography) by 30 min. CBF during maximally dilating, intracoronary infusion of adenosine served as a reference to assess effects of isoflurane.

RESULTS

Isoflurane-A caused marked increases in CBF, which, at constant perfusion pressure, reflected pronounced reductions in vascular resistance. These increases in CBF were 80% of those with adenosine. Although isoflurane-G also caused increases in CBF, the increases were only 45% of those caused by isoflurane-A.

CONCLUSIONS

The current findings demonstrate that the extent of coronary vasodilation by isoflurane was not dependent only on its blood concentration but also on the rate at which this blood concentration was achieved; a gradual increase in blood concentration blunted the vasodilator effect. Differences in the rate of administration of isoflurane likely contributed to its widely variable coronary vasodilating effects in previous studies.

Direct effects of halothane on coronary blood flow, myocardial oxygen consumption, and myocardial segmental shortening in in situ canine hearts

Previous in vivo studies of the coronary vascular effects of halothane (HAL) were complicated by varying hemodynamic conditions and global cardiac work demands. Accordingly, the current study evaluated changes in coronary blood flow (CBF) and associated variables during selective intracoronary administrations of HAL in in situ canine hearts using an extracorporeal-controlled pressure perfusion system. Findings during HAL were compared to those during isoflurane (ISO). The left anterior descending coronary artery (LAD) of 8 open-chest dogs anesthetized with fentanyl and midazolam was perfused at constant pressure (109 +/- 2 mm Hg) with HAL-free arterial blood or with blood equilibrated in an extracorporeal oxygenator with HAL (0.5%, 1.0%, 2.0% in 95% O2-5.0% CO2). In the LAD bed, measurements of CBF were obtained with an electromagnetic flowmeter and used to calculate myocardial oxygen consumption (MVO2). Percent segmental shortening (%SS) was measured with ultrasonic crystals. Changes in CBF by HAL were compared to those during maximal vasodilation with adenosine. Separate studies (n = 5) were performed using 1.4% [1 minimum alveolar anesthetic concentration (MAC)] ISO and the findings compared to those during an equianesthetic (1.0%) concentration of HAL. HAL caused concentration-dependent increases in CBF, and decreases in MVO2 and %SS. With 2.0% HAL, the level of CBF was 50% of the maximal adenosine-induced response. At equianesthetic concentrations, HAL caused increases in CBF that were one-third of those caused by ISO, while the decreases in MVO2 and %SS caused by the drugs were not significantly different.(ABSTRACT TRUNCATED AT 250 WORDS)

Effectiveness of the self-inflating bulb for verification of proper placement of the Esophageal Tracheal Combitube

The esophageal tracheal Combitube (ETC; Sheridan Catheter Corporation, Argyle, NY) is a twin-lumen tube used to establish emergency ventilation. After blind placement, ventilation is performed via the proximal lumen if it is in the esophagus or via the distal lumen if it is in the trachea. This investigation was designed to test the reliability of the self-inflating bulb (SIB) in identifying the location of the ETC and facilitating its proper positioning in anesthetized patients. In Group 1 (n = 26), the ETC was introduced blindly. In Group 2 (n = 20), the tube was placed in the trachea (eight patients) or once in the trachea and once in the esophagus, randomly (12 patients) under direct vision rigid laryngoscopy by the anesthesiologist performing the intubation. In both groups, the efficacy of the SIB in identifying the location of the ETC was tested by a second blinded anesthesiologist. In Group 1, blind insertion of the ETC resulted in esophageal placement in all patients, and in each case was correctly identified. The second anesthesiologist reported no reinflation when the compressed SIB was connected to the distal lumen. When the compressed SIB was connected to the proximal lumen, instantaneous reinflation was observed in 23 patients, delayed reinflation (2-4 s) in two and no reinflation (> 4 s) in one patient. Instantaneous reinflation occurred in these three patients after repositioning of the ETC. In Group 2, the second anesthesiologist correctly identified the location of the ETC in all cases. The results confirm previous findings that blind introduction of the ETC leads to esophageal placement and yields adequate ventilation.(ABSTRACT TRUNCATED AT 250 WORDS)

Contribution of nitric oxide to coronary vasodilation during hypercapnic acidosis

The present study was performed to evaluate the role of nitric oxide (NO) in coronary vasodilation during hypercapnic acidosis (HC). The left anterior descending coronary arteries of 17 anesthetized, open-chest dogs were perfused with normal arterial blood or with arterial blood equilibrated in an extracorporeal circuit with 90% O2-10% CO2 [arterial carbon dioxide tension (PaCO2) 72 +/- 3 mmHg, arterial pH 7.16 +/- 0.02]. Coronary perfusion pressure (CPP) was initially set at 100 mmHg. Coronary blood flow (CBF) was measured with a Doppler transducer. Studies were conducted under constant-pressure (variable CBF; n = 13) and constant-flow (variable CPP) conditions (n = 4). Steady-state changes in CBF (or CPP) during HC and during intracoronary infusions of acetylcholine (ACh, 20 micrograms/min), an endothelium-dependent vasodilator, and sodium nitroprusside (SNP, 80 micrograms/min), an endothelium-independent vasodilator, were compared before and after intracoronary infusion of a NO synthase inhibitor, either NG-nitro-L-arginine methyl ester (L-NAME, 4.5 mg) or NG-monomethyl-L-arginine (L-NMMA, 30 mg). Under constant pressure, L-NAME blunted increases in CBF by HC (274 +/- 32 vs. 113 +/- 24%) and ACh (400 +/- 43 vs. 68 +/- 17%), whereas increases in CBF by SNP were not significantly affected (207 +/- 34 vs. 186 +/- 18%). Results with L-NMMA were similar. Under constant flow, L-NAME attenuated decreases in CPP by HC and ACh, whereas it had no significant effect on decreases in CPP by SNP. In conclusion, HC elicits release of NO from coronary vascular endothelium via a direct effect rather than secondary to an increased flow rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of intracoronary infusions of amrinone and dobutamine on segment shortening, blood flow, and oxygen consumption in in situ canine hearts

Previous in vivo studies assessing the effects of amrinone on myocardial contractility used intravenous infusions, and thus were complicated by varying cardiac loading conditions. Accordingly, the present study was performed in 15 open-chest, anesthetized (fentanyl and midazolam) dogs using infusions of amrinone and dobutamine directly into the left anterior descending artery (LAD). In the LAD bed, percentage of segment shortening (%SS), an index of local myocardial contractility, was assessed with ultrasonic crystals. Coronary blood flow was measured electromagnetically and used to calculate myocardial oxygen consumption and infused drug concentrations. Amrinone and dobutamine were infused separately into the LAD at rates yielding calculated arterial blood concentrations in the clinical range (100, 150, and 200 micrograms/min, and 2.5, 5.0, and 7.5 micrograms/min, respectively). A mixture of amrinone and dobutamine was also infused into LAD and changes in %SS compared with the sum of the their individual effects. In six of the dogs, an extracorporeal system was used to maintain constant coronary blood flow during amrinone infusions. Amrinone and dobutamine caused individually increases in %SS that were comparable (range, 20%-45%). Myocardial oxygen consumption increased in parallel with %SS for both amrinone and dobutamine. For amrinone, coronary blood flow increased more than myocardial oxygen consumption, resulting in a modest (at highest dose approximately 10%) decrease in oxygen extraction; whereas for dobutamine, coronary blood flow increased in proportion to myocardial oxygen consumption, resulting in no change in oxygen extraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitric oxide does not mediate coronary vasodilation by isoflurane

BACKGROUND

Isoflurane causes vasodilation in the coronary circulation. The current study employed a canine model permitting selective intracoronary administrations of isoflurane (1) to test the hypothesis that coronary vasodilation by isoflurane is mediated by nitric oxide and (2) to evaluate the persistence of coronary vasodilation during an extended exposure to isoflurane.

METHODS

Open-chest dogs anesthetized with fentanyl and midazolam were studied. The left anterior descending coronary artery (LAD) was perfused via extracorporeal system with normal arterial blood or with arterial blood equilibrated with 1.4% (1 MAC) isoflurane. In the LAD bed, coronary blood flow (CBF) was measured with an electromagnetic flowmeter and used to calculate myocardial oxygen consumption (MVO2). In series 1, performed at constant coronary perfusion pressure (CPP), the LAD was exposed to 3 h of isoflurane in two groups of eight dogs: control group, normal coronary endothelium; and experimental group, intracoronary infusion of the nitric oxide synthase inhibitor L-NAME (0.15 mg/min for 30 min). Series 2 was performed with CBF constant; thus, CPP varied directly with coronary vascular resistance. In this series, initial steady-state changes in CPP by isoflurane were evaluated in the same four dogs before and after L-NAME.

RESULTS

In the control group of series 1, isoflurane caused a maximal, initial increase in CBF of 444%; however, CBF decreased progressively reaching a value not significantly different from baseline after 3 h of isoflurane. Isoflurane caused a significant (approximately 35%) decrease in MVO2, which persisted during the 3-h administration. Findings after L-NAME (experimental group) were not significantly different from those in control group. In series 2, isoflurane caused significant decreases in CPP that were not affected by L-NAME.

CONCLUSIONS

The lack of effect of L-NAME on isoflurane-induced coronary vasodilation suggests that nitric oxide does not mediate this response. The increase in CBF during prolonged isoflurane waned over time, perhaps because of tachyphylaxis or emergence of a competitive vasoconstrictor mechanism, e.g., metabolic factors secondary to reduced oxygen demands.

Efficacy of the self-inflating bulb in detecting esophageal intubation. Does the presence of a nasogastric tube or cuff deflation make a difference?

BACKGROUND

The principle underlying the use of the self-inflating bulb in differentiating esophageal from tracheal intubation is that the trachea is held open by rigid cartilaginous rings, whereas the esophagus collapses when a negative pressure is applied to its lumen. This investigation was designed to test the efficacy of the bulb in detecting esophageal intubation in the presence of a nasogastric tube and after tracheal tube cuff deflation.

METHODS

In anesthetized patients, the trachea and esophagus were intubated with identical tubes. The efficacy of the bulb was tested after a nasogastric tube was placed (group 1, n = 70) and after cuff deflation (group 2, n = 60) by a second anesthesiologist.

RESULTS

In patients with nasogastric tubes (group 1), the anesthesiologists reported no reinflation of the compressed bulbs connected to tubes placed in the esophagus and immediate reinflation when connected to tracheally placed tubes in every case. In group 2, the determination of tube placement was correct in every case after cuff deflation. Mean (+/- SEM) negative pressures generated when compressed bulbs were connected to esophageally placed tubes were 57.8 +/- 0.48 mmHg (group 1) and 55.3 +/- 0.52 mmHg (group 2) and remained unchanged after the introduction of nasogastric tubes or after cuff deflation.

CONCLUSIONS

These results confirm that a nasogastric tube or cuff deflation does not interfere with the reliability of the self-inflating bulb in detecting esophageal intubation and thus does not contribute to false positive results. Confirmation of tracheal tube placement by this simple method makes it ideal for use with other recognized methods both in and outside the operating rooms and enables physicians and emergency personnel to proceed with other resuscitative measures.

Effects of hypertonic saline solutions in the coronary circulation

The use of small-volume injections of hypertonic saline solutions (HSS) in resuscitation from hemorrhagic shock is accompanied by well-maintained and pronounced increases in coronary blood flow (CBF) and by increases in myocardial contractility. The present study was performed in open-chest, anesthetized dogs to evaluate the contribution of direct coronary vasodilator and positive inotropic effects of HSS to these therapeutic responses. The left anterior descending coronary artery (LAD) was cannulated and perfused at constant pressure (100 mm Hg) with normal arterial blood. CBF in LAD was measured electromagnetically, and used to calculate myocardial oxygen consumption (MVO2) and coronary arterial plasma osmolality. Percent segmental shortening in LAD bed (% SS) was evaluated with ultrasonic crystals. Measurements were obtained during infusion into LAD of 2.5, 5.0, and 7.5% HSS at 2 ml/min. These HSS solutions yielded calculated plasma osmolalities of 329 +/- 3, 361 +/- 8, and 378 +/- 10 mOsm/kg, respectively. The increases in plasma osmolality by 2.5% HSS were in the therapeutic range, whereas those by 5.0 and 7.5% HSS were supertherapeutic. HSS caused initial peak increases in CBF (reflecting decreases in coronary vascular resistance), which waned rapidly to achieve modest steady-state increases within 2-3 min. The magnitude of the peak and steady-state increases in CBF by HSS correlated to osmolality. The 2.5% HSS had no effect on MVO2 and % SS, whereas the 5.0% and 7.5% HSS increased these variables in an osmolality-dependent manner.

CONCLUSIONS

(1) intracoronary infusions of HSS caused modest steady-state coronary vasodilation, (2) Supertherapeutic elevations of plasma osmolality by HSS were required for direct positive inotropic effects, and (3) the present findings suggest that the direct cardiac actions of HSS contribute minimally to the increases in coronary blood flow and myocardial contractility that follow the use of these solutions for resuscitation from hemorrhagic shock.

Use of the self-inflating bulb for detecting esophageal intubation after "esophageal ventilation"

This present investigation tests the efficacy of the self-inflating bulb for detecting esophageal intubation after intentional "esophageal ventilation" to mimic gastric insufflation after bag-and-mask ventilation. In 72 anesthetized patients, the trachea and esophagus were intubated with identical tubes. The efficacy of the bulb was tested by a second anesthesiologist before and after the delivery of three breaths at a tidal volume of 300-350 mL each. The pressures generated by the bulb connected to esophageally placed tubes were measured in 10 patients. In all patients, the second anesthesiologist reported no reinflation of the bulbs when connected to esophageally placed tubes and instantaneous reinflation when connected to tracheally placed tubes, thus correctly identifying the location of each tube. The mean negative pressure generated when compressed bulbs were connected to esophageally placed tubes was 55.4 +/- 1.2 mm Hg before esophageal ventilation and 59.0 +/- 0.68 mm Hg after esophageal ventilation. We conclude that insufflation of the stomach as a result of esophageal ventilation, to the extent demonstrated in this study, does not interfere with the effectiveness of the bulb in differentiating esophageal from tracheal intubation.

Right and left ventricular O2 uptake during hemodilution and beta-adrenergic stimulation

Myocardial O2 uptake (MVO2) and related variables were compared in right and left ventricles (RV and LV, respectively) during isovolemic hemodilution (HD) alone and combined with isoproterenol (Iso) infusion in 13 isoflurane-anesthetized open-chest dogs. Measurements of myocardial blood flow (MBF) obtained with radioactive microspheres were used to calculate MVO2. Lactate extraction (Lacext) was determined. The study consisted of two experimental series: 1) graded HD (dextran) to hematocrit (Hct) of 10% and 2) Iso (0.1 microgram.kg-1.min-1 iv) during moderate HD (Hct = 18 +/- 1%). In series 1, arteriovenous O2 content difference in both ventricles decreased in parallel with reduced arterial O2 content caused by HD, i.e., percent O2 extraction was constant; MVO2 was maintained by proportional increases in MBF. In series 2, Iso during moderate HD raised MVO2 (RV, +156%; LV, +80%). Higher MVO2 was satisfied by combination of increased MBF and O2 extraction in RV and by increased MBF alone in LV. Lacext remained consistent with adequate myocardial O2 delivery throughout study. Conclusions were that 1) both RV and LV tolerated extreme HD (Hct = 10%) because blood flow reserves were sufficient to fully compensate for reduced arterial O2 content; 2) significant cardiac reserve was evident during HD, which could be recruited Iso; and 3) because increase in MVO2 in RV caused by Iso in presence of HD was partially satisfied by increased O2 extraction, the absence of augmented O2 extraction during HD alone was not due to impaired release of O2 from diluted red blood cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Direct effects of propofol on myocardial contractility in in situ canine hearts

The pronounced decrease in arterial blood pressure evident during anesthetic induction with propofol has raised the possibility that propofol has a direct negative inotropic effect. Previous attempts to evaluate this mechanism in vivo have been inconclusive because of confounding variables associated with intravenous administration of propofol. Accordingly, in the current study, steady-state changes in myocardial contractility and related hemodynamic parameters were assessed during intracoronary infusions of propofol in seven open-chest dogs anesthetized with fentanyl and midazolam. The left anterior descending coronary artery (LAD) was cannulated and perfused at controlled pressure (100 mmHg) with normal arterial blood. In LAD-perfused myocardium, contractility was evaluated from measurements of percent segmental shortening (%SS) obtained with ultrasonic crystals. Coronary blood flow in LAD was measured electromagnetically and used to calculate myocardial oxygen consumption (MVO2; Fick principle) and coronary propofol concentration. Propofol was infused into the LAD at 150, 300, 600, and 1,200 micrograms/min (P-150, P-300, P-600, P-1,200). These infusion rates yielded calculated blood concentrations of 7 +/- 1, 15 +/- 1, 26 +/- 2, and 50 +/- 5 micrograms.ml-1, respectively. The calculated blood concentrations at P-150 were in the clinical range, whereas those at P-300, P-600, and P-1,200 were supratherapeutic. P-150 had no effect on %SS, whereas higher infusion rates caused decreases in %SS. Changes in MVO2 by propofol generally paralleled changes in %SS. At P-150 and P-300, coronary blood flow was proportional to MVO2, whereas at P-600 and P-1,200, coronary blood flow was in excess of the prevailing MVO2, resulting in increased coronary venous oxygen tension.(ABSTRACT TRUNCATED AT 250 WORDS)

Phenylephrine does not limit myocardial blood flow or oxygen delivery during isoflurane-induced hypotension in dogs

Experiments were performed on seven fentanyl-pentobarbital-anesthetized, open-chest dogs to determine whether stimulation of coronary alpha 1-adrenergic receptors by phenylephrine causes coronary vasoconstriction and impaired myocardial oxygen delivery when phenylephrine is infused to correct isoflurane-induced hypotension. Myocardial blood flow was measured with radioactive microspheres, and myocardial oxygen and lactate extraction were determined. The Fick equation was used to calculate myocardial oxygen consumption. Measurements were obtained (a) under control conditions, (b) after a 30-min inhalation of isoflurane sufficient to decrease mean aortic pressure by 30%, and (c) while maintaining administration of isoflurane, 5-10 min after restoration of mean aortic pressure by intravenous infusion of phenylephrine. Isoflurane-induced hypotension was accompanied by a baroreceptor-mediated increase in heart rate and by a decrease in myocardial oxygen consumption; however, myocardial blood flow was maintained, resulting in decreased oxygen extraction and increased coronary sinus PO2, thus implying a direct coronary vasodilating effect for isoflurane. Lactate extraction was unaffected. Phenylephrine infusion during inhalation of isoflurane returned mean aortic pressure and heart rate to their respective control values, and it did not change myocardial oxygen consumption, myocardial blood flow, myocardial oxygen extraction, coronary sinus PO2, or lactate extraction from values obtained during isoflurane alone. These latter findings are consistent with undiminished coronary vasodilation by isoflurane in the presence of phenylephrine. In conclusion, infused phenylephrine to restore aortic pressure during isoflurane administration had no vasoconstrictor effect in the coronary circulation and did not impair myocardial oxygen delivery. Apparently, the direct coronary vasodilating action of isoflurane completely nullified phenylephrine-induced vasoconstriction via local alpha 1-adrenergic receptors.

Oxygen extraction ratio: a valid indicator of transfusion need in limited coronary vascular reserve?

We have described whole body oxygen (O2) extraction ratio (ER) as a reliable indicator of transfusion need in acute normovolemic anemia. In normal hearts, myocardial lactate production (-LACT), indicating anaerobic metabolism, does not occur until the ER greater than 50% and Hct less than 10%. It is not known if the ER is valid in the setting of limited coronary vascular reserve. This study assesses the effect of a critical left anterior descending (LAD) coronary stenosis on the compensation to acute blood loss anemia. Adult dogs were anesthetized, paralyzed, and mechanically ventilated. A critical LAD stenosis was created in seven animals (STEN). There were seven controls (CON). Animals underwent isovolemic exchange transfusion with 6% HES until cardiac failure (CF). Catheters were placed in the aorta, pulmonary artery, and anterior interventricular coronary vein. Cardiac failure occurred at Hct = 8.6% +/- 0.4% in the CON and 17.0% +/- 0.5% in the STEN animals. Cardiac output increased in the CON, but not in the STEN animals. Blood flow in the LAD increased in the CON but not the STEN animals. -LACT began in the CON and STEN animals at Hct less than 20% and coincided with an ER greater than 50% in both groups. We conclude that CF occurs at a higher hematocrit with a critical LAD stenosis. The whole body ER greater than 50% remains a valid indicator of myocardial metabolism in anemia in the presence of limited coronary vascular reserve. The ER may be a useful guide to transfusion therapy.

Hemodynamic responses to endotracheal extubation after coronary artery bypass grafting

After coronary artery bypass grafting (CABG) surgery, patients may remain at risk for myocardial ischemia and infarction and ventricular dysrhythmias. The hemodynamic responses to endotracheal extubation and the efficacy of intravenous lidocaine pretreatment were studied after CABG surgery and overnight mechanical ventilation. Twenty-five patients were divided into two groups: group 1 (n = 13) patients who had tracheal extubation after pretreatment with a placebo; group 2 patients who received lidocaine (1 mg/kg IV) before tracheal extubation. Hemodynamic data, electrocardiographic tracings, and arterial blood gases were obtained before tracheal extubation, during suctioning, and 1, 5, and 20 min after tracheal extubation. Group 1 patients displayed significant increases in heart rate, arterial blood pressure, rate-pressure product, right atrial pressure, and cardiac index during suctioning and within 1 min of tracheal extubation, returning to preextubation level by 5 min. There were no significant changes in pulmonary and systemic resistance indices. Hemodynamic changes in group 2 patients were similar to those in group 1. Both in the absence and presence of lidocaine, tracheal extubation caused hemodynamic responses that were small in magnitude and brief in duration. These responses were not associated with electrocardiographic or enzymatic evidence of myocardial ischemia or infarction, or with ventricular dysrhythmias. Compared with the well-documented hemodynamic responses to tracheal intubation, we found that extubation of the trachea after CABG surgery was associated with less pronounced responses. This may be related to avoidance of laryngoscopy and possibly accommodation to the endo-tracheal tube. These modest hemodynamic responses of extubation of the trachea after CABG surgery were not modified by intravenous lidocaine.