Benchmarking a Canadian Anesthesiology Resident Research Program against national norms using a logic model framework: a quality improvement study

Background

Canadian specialty training programs are expected to deliver curriculum content and assess competencies related to the CanMEDS Scholar role. We evaluated our residency research program and benchmarked it against national norms for quality improvement purposes.

Methods

In 2021 we reviewed departmental curriculum documents and surveyed current and recently graduated residents. We applied a logic model framework to assess if our program's inputs, activities, and outputs addressed the relevant CanMeds Scholar competencies. We then descriptively benchmarked our results against a 2021 environmental scan of Canadian anesthesiology resident research programs.

Results

Local program content was successfully mapped to competencies. The local survey response rate was 40/55 (73%). In benchmarking, our program excelled in providing milestone-related assessments, research funding, administrative, supervisory, and methodologic support, and requiring a literature review, proposal presentation, and local abstract submission as output. Acceptable activities to meet research requirements vary greatly among programs. Balancing competing clinical and research responsibilities was a frequently reported challenge.

Conclusions

The logic model framework was easily applied and demonstrated our program benchmarked well against national norms. National level dialogue is needed to develop specific, consistent scholar role activities and competency assessments to bridge the gap between expected outcome standards and education practice.

Analgesic duration of interscalene block after outpatient arthroscopic shoulder surgery with intravenous dexamethasone, intravenous dexmedetomidine, or their combination: a randomized-controlled trial

PURPOSE

Both intravenous dexamethasone and dexmedetomidine prolong the analgesic duration of interscalene blocks (ISB) after arthroscopic shoulder surgery. This study compared their relative effectiveness and the benefit of their use in combination.

METHODS

This single-centre, double-blinded, parallel three-group superiority trial randomized 198 adult patients undergoing ambulatory arthroscopic shoulder surgery. Patients received preoperative ISB with 30 mL 0.5% bupivacaine and 50 µg dexmedetomidine or 4 mg dexamethasone or both of these agents as intravenous adjuncts. The primary outcome was analgesic block duration. Secondary outcomes included the quality of recovery 15 score (range: 0-150) on day 1 and postoperative neurologic symptoms in the surgical arm.

RESULTS

Block durations (n = 195) with dexamethasone (median [range], 24.5 [2.0-339.5] hr) and both adjuncts (24.0 [1.5-157.0] hr) were prolonged compared with dexmedetomidine (16.0 [1.5-154.0] hr). When analyzed by linear regression after an unplanned log transformation because of right-skewed data, the corresponding prolongations of block duration were 59% (95% confidence interval [CI], 28 to 97) and 46% (95% CI, 18 to 80), respectively (both P < 0.001). The combined adjuncts were not superior to dexamethasone alone (-8%; 95% CI, -26 to 14; P = 0.42). Median [IQR] quality of recovery 15 scores (n = 197) were significantly different only between dexamethasone (126 [79-149]) and dexmedetomidine (118.5 [41-150], P = 0.004), but by an amount less than the 8-point minimum clinically important difference.

CONCLUSION

Dexamethasone is superior to dexmedetomidine as an intravenous adjunct for prolongation of bupivacaine-based ISB analgesic duration. There was no additional benefit to using both adjuncts in combination.

TRIAL REGISTRATION

www.clinicaltrials.gov (NCT03270033); registered 1 September 2017.

Does eliminating the preoperative history and physical make a difference in low-risk cataract surgery patients? A before and after study of 30-day morbidity and mortality

OBJECTIVE

To evaluate the safety of omitting the conventional preoperative history and physical examination (H&P) for low-risk cataract surgery patients.

DESIGN

Comparison of outcomes before and after the January 1, 2015 system wide implementation of a program that eliminated the conventional preoperative H&P for low-risk patients as identified by a 12-item risk stratification questionnaire.

PARTICIPANTS

Two separate groups of Winnipeg residents who had cataract surgery at the city's sole ophthalmological referral centre between July 1 and December 31, 2014 (preimplementation reference group) or between October 1, 2015 and March 31, 2016 (postimplementation intervention group).

METHODS

A detailed chart review was completed for cataract surgery patients who experienced a postoperative medical event (a composite of death or hospital admission or emergency department visit, identified within administrative databases) within 30 days of surgery. Nonfatal events were captured for all 7 hospitals and urgent care centres in the city, including the ophthalmological referral centre.

RESULTS

Postoperative medical events occurred in 114 of 2981 (3.82%) intervention group surgeries and 125 of 3037 (4.12%) reference group surgeries (Relative risk 0.92, 95% confidence interval 0.72 to 1.19, p = 0.6 Fisher exact test). Subgroup analyses of major medical events and medical events by affected organ system yielded no significant differences between the 2 groups. In the opinion of the physician chart reviewers, none of the events among low-risk patients in the intervention group were related to the omission of a conventional preoperative H&P.

CONCLUSIONS

The risk of adverse medical events within 30 days of cataract surgery was not higher after the omission of the conventional preoperative H&P in patients screened to be low risk by a validated preoperative questionnaire.

End-Tidal Hypocapnia Under Anesthesia Predicts Postoperative Delirium

Background: Postoperative delirium (POD) might be associated with anesthetic management, but research has focused on choice or dosage of anesthetic drugs. We examined potential contributions of intraoperative ventilatory and hemodynamic management to POD.

Methods: This was a sub-study of the ENGAGES-Canada trial (NCT02692300) involving non-cardiac surgery patients enrolled in Winnipeg, Canada. Patients received preoperative psychiatric and cognitive assessments, and intraoperatively underwent high-fidelity data collection of blood pressure, end-tidal respiratory gases and anesthetic agent concentration. POD was assessed by peak and mean POD scores using the Confusion Assessment Method-Severity (CAM-S) tool. Bivariate and multiple linear regression models were constructed controlling for age, psychiatric illness, and cognitive dysfunction in the examination of deviations in intraoperative end-tidal carbon dioxide (areas over (AOC) and under the curve (AUC)) on POD severity scores.

Results: A total of 101 subjects [69 (6) years of age] were studied; 89 had comprehensive intraoperative hemodynamic and end-tidal gas measurements (data recorded at 1 Hz). The incidence of POD was 11.9% (12/101). Age, cognitive dysfunction, anxiety, depression, and intraoperative end-tidal CO₂ (AUC) were significant correlates of POD severity. In the multiple regression model, cognitive dysfunction and AUC end-tidal CO₂ (0.67 kPa below median intra-operative value) were the only independent significant predictors across both POD severity (mean and peak) scores. There was no association between cumulative anesthetic agent exposure and POD.

Conclusions: POD was associated with intraoperative ventilatory management, reflected by low end-tidal CO₂ concentrations, but not with cumulative anesthetic drug exposure. These findings suggest that maintenance of intraoperative normocapnia might benefit patients at risk of POD.

Perioperative implications of thoracic decortications: a retrospective cohort study

Purpose

An increasing number of thoracic decortications have been performed in Manitoba, from five in 2007 to 45 in 2014. The primary objective of this study was to define the epidemiology of decortications in Manitoba. The secondary objective was to compare patients who underwent decortication due to primary infectious vs non-infectious etiology with respect to their perioperative outcomes.

Methods

Data for this cohort study were extracted from consecutive charts of all adult patients who underwent a decortication in Manitoba from 2007-2014 inclusive.

Results

One hundred ninety-two patients underwent a decortication. The most frequent disease processes resulting in a decortication were pneumonia (60%), trauma (13%), malignancy (8%), and procedural complications (5%). The number of decortications due to complications of pneumonia rose at the greatest rate, from three cases in 2007 to 29 cases in 2014. Performing a decortication for an infectious vs a non-infectious etiology was associated with a higher rate of the composite postoperative outcome of myocardial infarction, acute kidney injury, need of vasopressors for > 12 hr, and mechanical ventilation for > 48 hr (44.4% vs 24.2%, respectively; relative risk, 1.83; 95% confidence interval, 1.1 to 2.9; P = 0.01).

Conclusion

There has been a ninefold increase in decortications over an eight-year period. Potential causes include an increase in the incidence of pneumonia, increased organism virulence, host changes, and changes in practice patterns. Patients undergoing decortication for infectious causes had an increased risk for adverse perioperative outcomes. Anesthesiologists need to be aware of the high perioperative morbidity of these patients and the potential need for postoperative admission to an intensive care unit.

Variable ventilation improves perioperative lung function in patients undergoing abdominal aortic aneurysmectomy

BACKGROUND

Optimizing perioperative mechanical ventilation remains a significant clinical challenge. Experimental models indicate that "noisy" or variable ventilation (VV)--return of physiologic variability to respiratory rate and tidal volume--improves lung function compared with monotonous control mode ventilation (CV). VV was compared with CV in patients undergoing abdominal aortic aneurysmectomy, a patient group known to be at risk of deteriorating lung function perioperatively.

METHODS

After baseline measurements under general anesthesia (CV with a tidal volume of 10 ml/kg and a respiratory rate of 10 breaths/min), patients were randomized to continue CV or switch to VV (computer control of the ventilator at the same minute ventilation but with 376 combinations of respiratory rate and tidal volume). Lung function was measured hourly for the next 6 h during surgery and recovery.

RESULTS

Forty-one patients for aneurysmectomy were studied. The characteristics of the patients in the two groups were similar. Repeated-measures analysis of variance (group x time interaction) revealed greater arterial oxygen partial pressure (P = 0.011), lower arterial carbon dioxide partial pressure (P = 0.012), lower dead space ventilation (P = 0.011), increased compliance (P = 0.049), and lower mean peak inspiratory pressure (P = 0.013) with VV.

CONCLUSIONS

The VV mode of ventilation significantly improved lung function over CV in patients undergoing abdominal aortic aneurysmectomy.

Effects of altered left atrial pressure on pulmonary vascular pressure-flow relationships

We studied the effects of changes in pulmonary capillary wedge pressure (PCWP) on the slope (incremental resistance) and the extrapolated pressure intercept (PI) of the mean pulmonary artery pressure (PAP)-cardiac output (CO) relationship. Multipoint plots of PAP against CO were obtained in intact anesthetized dogs. Group 1 consisted of six dogs entirely in West zone 3 and group 2 of four dogs with mixed West zone 2-3. The four conditions studied were the following: 1) fixed low PCWP, 2) fixed high PCWP, 3) variable PCWP, and 4) time-control repeat of condition 1. The PI significantly exceeded PCWP at fixed low PCWP (group 1, 9.3 vs. 11.1 mmHg, group 2, 6.6 vs. 3.9 mmHg). PI became identical to PCWP only at fixed high PCWP in group 1 (19 +/- 2.0 vs. 19 +/- 1.1 mmHg). Thus PCWP reflects the effective vascular outflow pressure when PCWP is fixed and high. For both groups of dogs in condition 3, when PCWP was varied with CO, the slope of the resulting PAP-CO plot was significantly greater than when PCWP was constant. Also in 9 of 10 dogs, PI was less than PCWP when PCWP was varied. These findings demonstrate that when changes in PCWP are allowed to occur during the generation of a pulmonary artery pressure-flow plot, the resulting slope and intercept, as defined by a Starling resistor model, do not accurately represent the incremental resistance and outflow pressure of the pulmonary vasculature.

Pulmonary vascular pressure-flow relationship in canine oleic acid pulmonary edema

We tested the hypothesis that the increased impedance to flow in canine oleic acid (OA) lung injury is predominantly due to an increase in effective downstream pressure (EDP), obtained by extrapolating to zero flow the linear portion of the pulmonary artery pressure (PAP)/flow (Q) relationship. PAP-Q coordinates were obtained in eight anesthetized, O2-ventilated dogs by varying Q through systemic arteriovenous fistulae. PAP-Q lines were obtained before and approximately 5 h after injection of OA. A second group of six dogs served as a time control (TC) group. There was a linear relationship between PAP and Q in both experimental and control groups (mean r value 0.948). The presence of pulmonary edema in the OA group caused the EDP to almost double, from 7 to 12 mmHg (P less than 0.01). In contrast, EDP remained constant in TCs. Incremental vascular conductance (IVC), slope of the PAP/Q line, decreased (P less than 0.05) a similar amount in both groups. The above findings are consistent with the modeling of the pulmonary circulation according to a Starling resistor in that large amounts of edema changed EDP but not incremental conductance.

Pulmonary vascular effects of hydralazine in a canine preparation of pulmonary thromboembolism

Pulmonary arterial pressure (PAP)-flow coordinates were obtained in 14 anesthetized dogs before and after pulmonary hypertension was induced with autologous blood clots. Cardiac output (CO) was altered by systemic arteriovenous fistulas. The PAP-CO coordinates were always rectilinear. Before emboli, the mean vascular closing or outflow pressure (the pressure intercept of the PAP-CO line) was 8.8 +/- 2.1 (SD) mm Hg. Emboli increased PAP (15.1 +/- 1.6 to 36.5 +/- 3.5 mm Hg; p less than .001) and decreased CO (3.8 +/- 0.6 to 2.4 +/- 0.8 liters X min-1; p less than .001). Incremental resistance (the slope of the PAP-CO line) only increased slightly. On the other hand, the marked increase in PAP was predominantly due to an increase in effective outflow pressure (from 8.8 +/- 2.1 to 28.6 +/- 3.6; p less than .001). Hydralazine was administered in a dose sufficient to double CO. This did not affect PAP and caused an inconsistent and small decrease in incremental resistance. However, a consistently significant decrease in effective outflow pressure, averaging 23%, was observed. In this canine preparation of pulmonary hypertension the predominant effect of hydralazine appears to be a decrease in the mean vascular closing or outflow pressure.

Hemodynamic management in clinical acute hypoxemic respiratory failure. Dopamine vs dobutamine

We investigated short-term hemodynamic effects of dopamine and dobutamine in eight patients with acute hypoxemic respiratory failure. We tested the hypothesis that for a similar increase in cardiac output, left ventricular filling pressure (pulmonary capillary wedge pressure [PCWP]) would increase with dopamine and decrease with dobutamine. Dopamine increased cardiac output (p less than 0.05), stroke volume (p less than 0.05), and PCWP (p less than 0.01). Cardiac output increased almost 20 percent when PCWP increased 50 percent with dopamine. In contrast, despite a mean 30 percent increase in cardiac output with dobutamine (p less than 0.01), PCWP decreased. In six of these patients, left ventricular end-diastolic volumes and end-systolic volumes were measured using scintigraphic techniques. In all patients, end-diastolic volume increased with dopamine (p less than 0.05); and in four of six, end-systolic volume increased. In contrast, with dobutamine, in five of six patients, end-diastolic volume decreased; and in all six patients, end-systolic volume decreased. There was a small increase in intrapulmonary shunt with both drugs. We conclude that if an inotropic agent is required to increase cardiac output in patients with acute hypoxemic respiratory failure, dobutamine is probably preferred over dopamine.

Treatment of canine permeability pulmonary edema: short-term effects of dobutamine, furosemide, and hydralazine

The effects of treatment of oleic acid pulmonary edema with dobutamine, furosemide, and hydralazine on cardiopulmonary function in 24 dogs were investigated. Pulmonary capillary wedge pressure (PCWP) was adjusted to approximately 7 mm Hg; 45 min after oleic acid (0.08 ml/kg), dogs were randomly divided into a control group, in which PCWP was maintained at approximately 7 mm Hg, and into treatment groups as described above. Mean time-averaged PCWP was 2.3 mm Hg in dogs treated with dobutamine, 4.1 mm Hg with furosemide, and 4.4 mm Hg with hydralazine. Four hours of treatment with dobutamine and furosemide significantly (p less than .01) reduced accumulation of lung water compared with the control and hydralazine groups. Qs/Qt was lower (p less than .05) with dobutamine and furosemide compared with the other groups. In dogs given hydralazine, cardiac output (CO) and systemic vascular resistance (SVR) remained constant over the 4 hr treatment interval. In contrast, in all other groups, SVR increased and CO decreased (both p less than .05). The short-term pulmonary effects of the above drugs are probably explained by differences in PCWP and/or by regional pulmonary vascular effects.

Acute cardiopulmonary effects of nitroglycerin in canine oleic acid pulmonary edema

In a canine model of acute respiratory failure, the authors investigated acute cardiopulmonary effects of nitroglycerin (TNG) and compared the results with those obtained after phlebotomy. Oleic acid increased intrapulmonary shunt (Qs/Qt) from 7.4 to 31% (P less than 0.001) and decreased (P less than 0.01) cardiac output (CO). In the presence of assumed low-pressure pulmonary edema, TNG was infused to decrease mean blood pressure (BP) by 40%; this was associated with a 26% decrease (P less than 0.05) in CO. Qs/Qt increased from 31 to 42% (P less than 0.01). There was a slight increase (P less than 0.01) in pulmonary vascular resistance (PVR) with TNG, and mean pulmonary artery pressure (PAP) decreased (P less than 0.05). In contrast, when CO was decreased by a similar amount with phlebotomy, mean Qs/Qt did not significantly change. There were similar changes in PVR and PAP and mixed venous O2 tension with TNG and phlebotomy. Accordingly, current results rule out increased flow, increased PVO2, and mechanical alterations in pulmonary vascular pressures as contributory to the increase in Qs/Qt with TNG. Alternatively, the increase in Qs/Qt with TNG may be explained by a direct pharmacologic decrease in pulmonary hypoxic vasoconstriction and/or by nonspecific pharmacologic effects.

Effects of vasodilators on canine cardiopulmonary function when a decrease in cardiac output complicates an increase in right ventricular afterload

In canine oleic acid pulmonary edema, we investigated acute cardiopulmonary effects of nitroprusside (NP) before (NP1), and after (NP2) pulmonary vascular resistance (PVR) was increased via glass bead embolization. In the setting of increased PVR and reduced cardiac output (CO), acute cardiopulmonary effects of NP and hydralazine were compared. Oleic acid increased (p less than 0.05) pulmonary shunt (Qs/Qt) from 15 to 24%, but did not alter PVR. Cardiac output decreased (p less than 0.01) 31% with oleic acid from 4.2 to 2.9 1 X min-1 and systemic vascular resistance (SVR) increased (p less than 0.01). When PVR was normal, NP reduced (p less than 0.05) blood pressure (BP) from 148 to 123 mmHg, decreased SVR 31%, and increased (p less than 0.05) CO and Qs/Qt. Glass bead embolization increased (p less than 0.001) PVR from 2.2 to 20 mgHg X 1-1 X min and reduced (p less than 0.01) CO 23%, from 2.6 to 2 L/min. The Qs/Qt did not increase with embolization. In contrast to effects of NP1, when RV afterload was increased, CO fell (p less than 0.05) with NP2 from 2 to 1.6 1 X min-1. Alternatively, hydralazine improved cardiopulmonary function. In the setting of increased RV afterload, SVR and PVR decreased (p less than 0.01) 48 and 29%, respectively, with hydralazine. Corresponding to the decrease in resistance, CO increased (p less than 0.001) 84% with hydralazine, from 1.9 to 3.5 1 X min-1. Also, BP and Qs/Qt remained constant and arterial O2 tension increased (p less than 0.05) with hydralazine, from 113 to 152 mmHg.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of reduced resistive afterload on left ventricular pressure-volume relationship

In seven anesthetized, beta-blocked dogs, we investigated the effects of a reduction in systemic vascular resistance (SVR) on left ventricular (LV) systolic mechanics. LV pressure and volumes (scintigraphic techniques) were measured in base-line condition, after opening one and then two arteriovenous fistulas (AVF). Volume was infused to maintain LV end-systolic pressure (LVESP). Despite a constant ESP, the mean end-systolic volume (LVESV) fell from 42 to 31 ml (P less than 0.025) when the SVR fell from 81 to 48 units (P less than 0.0025), and the LVESV fell further to 24 ml (P less than 0.0025) when the SVR was decreased to 30 units (P less than 0.025). In six similarly prepared dogs, aortic flow was measured, and when resistive afterload decreased, instantaneous flow increased. Since end-diastolic volume was not significantly changed when resistive afterload decreased, instantaneous LV volume decreased despite constant systolic LV pressure. In two of these dogs, LV pressure-volume (PV) trajectories were drawn for the ejection period. When SVR decreased there was a marked leftward shift of the PV trajectory as the end of ejection was approached. It is concluded that at a given contractile state and ventricular pressure, alterations in resistive load directly affect rate and extent of ventricular shortening.

Treatment of shock in a canine model of pulmonary embolism

Despite the high mortality (greater than 30%) associated with hypotension complicating pulmonary embolism, previous studies have not systematically investigated how best to treat shock resulting from pulmonary embolism. In 24 dogs, we measured relevant hemodynamic parameters before and after shock was produced by intravenously injected autologous blood clots. When systemic blood pressure fell to 70 mmHg, dogs were randomly divided into groups and treated blindly for 1 h. All control dogs and all dogs treated with volume and isoproterenol died. In contrast, all dogs treated with noradrenaline were resuscitated and remained hemodynamically stable for 1 h. This effect of noradrenaline was significant (p less than 0.01, Fisher's exact test). Noradrenaline improved right ventricular performance by increasing blood pressure and improving right ventricular perfusion and/or by a direct increase in contractility. We conclude that in a canine model of pulmonary embolism and shock, noradrenaline may be the drug of choice for acute resuscitation.

Direct effects of nitroprusside do not alter gas exchange in canine oleic acid edema

The authors investigated why intrapulmonary shunt (QS/QT) increases with sodium nitroprusside (SNP) in canine oleic acid pulmonary edema. To determine the effects of flow alone on QS/QT, a peripheral arteriovenous fistula with a variable resistor was employed to increase cardiac output (Q) 26 and 52% above base line in a stepwise fashion (P less than 0.01). To examine the direct effects of SNP, distinct from changes in flow, the drug was given to produce matched increments in Q in each dog (P less than 0.01). To control for time, base-line measurements were obtained before and after each intervention, the sequence of which was alternated. At each increment in Q, SNP and the arteriovenous fistula increased QS/QT a similar amount. The mixed venous O2 tension (P-vO2) followed Q similarly in each group. Pulmonary vascular resistance (PVR) fell more (P less than 0.01) with SNP than with the arteriovenous fistula at identical Q and P-vO2. The authors conclude that, in this model, a direct pharmacological effect of SNP does not contribute to the deterioration in QS/QT. In fact, SNP exerts a pulmonary vasoactive effect that does not adversely affect gas exchange.

Effects of dopamine on cardiopulmonary function and left ventricular volumes in patients with acute respiratory failure

We investigated cardiopulmonary effects of dopamine in patients with acute respiratory failure. Specifically, we wished to test the hypothesis that left ventricular filling pressure (Pcwp) would increase when cardiac output (CO) increased with dopamine. Dopamine (range, 5.5 to 20 micrograms/kg/min) increased blood pressure (BP) (p less than 0.001) Pcwp, CO, and stroke volume (SV) (p less than 0.005). Mean Pcwp increased (p less than 0.005) 45% with dopamine, from 11 to 16 mmHg. Qs/Qt increased with dopamine in association with an increase in mixed venous O2 tension, and arterial O2 tension remained constant. In 8 of these patients, left ventricular end-diastolic volume (LVEDV) and end-systolic volume (ESV) were measured using scintigraphic techniques. The LVEDV increased (p less than 0.01) in each patient after the administration of dopamine, and the mean change was from 134 to 163 ml. Although BP and LV afterload increased in each patient, there was no consistent change in LVESV after dopamine administration, i.e., ESV decreased in 1 patient, remained constant in 3, and increased in 4. Accordingly, because afterload increased in all patients and ESV did not, dopamine probably increased contractility. Because EDV increased in all patients, we concluded that the increase in SV with dopamine is explained by a combination of inotropic and peripheral vascular effects.

Effect of increased pulmonary vascular resistance on right ventricular systolic performance in dogs

We tested the possibility that for a given contractile state and right ventricular systolic pressure (RVSP), rate and extent of ventricular shortening would be reduced as resistance to ejection increased. In eight anesthetized, ventilated dogs, we measured RV and pulmonary artery pressure (Ppa), blood pressure, heart rate, cardiac output (CO), and RV dP/dt before (condition 1) and after (condition 2) pulmonary vascular resistance (PVR) was increased by injection of small (80 micron) glass beads. Glass beads caused a large increase (P less than 0.001) in Ppa and in RVSP and, despite increased RV end-diastolic pressure (EDP), CO and stroke volume (SV) were reduced. A third set of measurements was obtained following a further increase in resistance (condition 3). A comparison of condition 2 with condition 3, despite constant RVSP, constant mean Ppa, and increased EDP, showed a marked fall in CO and SV (P less than 0.001) when glass bead injection increased calculated resistance from 21 (condition 2) to 34 (condition 3) mmHg X 1(-1) X min. RV contractility, as assessed by Vmax and peak dP/dt was similar in both conditions. In five additional dogs, we measured the same parameters as before plus instantaneous pulmonary artery flow in all conditions. In a comparison of conditions 2 and 3, despite constant RVSP and increased EDP, peak and total flow (P less than 0.05) were reduced as resistance to RV ejection increased. We conclude that the right ventricle shortens more slowly and to a smaller extent against the same systolic pressure when its resistive afterload increases.

Volume expansion versus norepinephrine in treatment of a low cardiac output complicating an acute increase in right ventricular afterload in dogs

The authors investigated the effects of treatment on ventricular performance when cardiac output (CO) was reduced significantly because of an acute increase in pulmonary vascular resistance (PVR). In eight anesthetized, ventilated dogs, the effects of volume expansion (100 ml 6% dextran) on ventricular performance were determined before and after PVR was elevated. Resistance was increased by microembolization of the pulmonary vascular bed with glass beads (80-100 microns). When PVR was normal, volume expansion increased (P less than 0.05) stroke volume (SV) and mean blood pressure (BP). Alternatively, when RV afterload was increased, volume resulted in RV failure, i.e., decrease in SV (P less than 0.01) from 9.1 to 6.3 ml and a decrease (P less than 0.05) in mean BP from 97 to 65 mmHg, despite increased right ventricular end diastolic pressure (RVEDP) (P less than 0.05). Right ventricular dysfunction occurred with volume expansion, despite constant PVR and a decrease (P less than 0.01) in mean pulmonary artery pressure (PAP). In contrast to volume, norepinephrine infusion decreased biventricular filling pressures (P less than 0.01) and increased (P less than 0.01) SV from 6.2 to 11.3 ml. Accordingly, when RV afterload is increased significantly, even a relatively small increase in blood volume may result in RV dysfunction. Alternatively, inotropic agents with pressor effects may be the treatment of choice to increase CO when RV afterload is increased.

Treatment of canine low pressure pulmonary edema. Nitroprusside versus hydralazine

In canine oleic acid pulmonary edema, we investigated acute cardiopulmonary effects of different doses of nitroprusside and compared the results with those obtained after intravenously administered hydralazine. Oleic acid increased (p less than 0.05) intrapulmonary shunt (Qs/Qt), increased (p less than 0.01) systemic vascular resistance (SVR), and reduced (p less than 0.05) cardiac output (CO). In the presence of low-pressure pulmonary edema, low-dose nitroprusside (NP1) reduced (p less than 0.01) mean blood pressure (BP) approximately 8%, but with the exception of a small fall in ventricular filling pressure, other parameters remained constant. Compared with control values, a higher dose of nitroprusside (NP2) reduced mean BP 20%, and despite a fall (p less than 0.01) in pulmonary capillary wedge pressure, CO increased (p less than 0.05) 20%. Corresponding to the increase in flow, mean Qs/Qt increased (p less than 0.05) from 26 to 36% with NP2 and arterial O2 tension fell (186 to 166 mmHg, p less than 0.05). Compared with NP2, intravenously administered hydralazine caused a larger (p less than 0.01) change in CO. Despite increased CO and increased (p less than 0.01) mixed venous O2 tension, there was no deterioration in gas exchange with hydralazine. Mean Qs/Qt remained constant and arterial O2 tension, (PaO2) increased (p less than 0.05) from 174 mmHg to 217 mmHg. The increased CO with NP2 and hydralazine is probably explained by the large reduction in systemic vascular resistance. Because Qs/Qt remained constant with hydralazine, the increase in PaO2 is most likely due to the increase in PvO2, which increased because CO increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of hydralazine on cardiopulmonary function in canine low-pressure pulmonary edema

The authors investigated the acute cardiopulmonary effects of hydralazine in canine low-pressure pulmonary edema. Ninety minutes after oleic acid, right to left shunt (Qs/Qt) had increased from 16-46.7%, and arterial O2 tension decreased from 444-194 mmHg. In the presence of oleic acid pulmonary edema, hydralazine infusion increased cardiac output (CO) and stroke volume (SV) from 3.65-4.9 mmHg . 1 (-1) . min (P less than 0.001) and from 26-31 ml (P less than 0.005), respectively. These changes occurred despite reduced preload as mean pulmonary capillary wedge pressure (PCWP) decreased from 6.6-4.1 mmHg (P less than 0.005). These changes are most likely explained by a reduction in resistive afterload because hydralazine reduced systemic vascular resistance (SVR) from 29.1-20.8 mmHg . 1(-1) . min. Despite improved CO, Qs/Qt remained constant and arterial O2 tension increased (P less than 0.005) with hydralazine. Because Qs/Qt remained constant with hydralazine, the improvement in arterial O2 tension is explained most likely by the increased mixed venous oxygen tension secondary to the increase in CO. To the extent that canine oleic acid edema resembles low-pressure pulmonary edema in patients, hydralazine is a potential agent to reduce PCWP, increase CO and arterial O2 tension.