Neuromuscular blockade significantly decreases systemic oxygen consumption during hypothermic cardiopulmonary bypass

The effects of general anaesthesia on oxygen consumption: A meta-analysis guiding future studies on perioperative oxygen transport

BACKGROUND

Increased oxygen extraction, the ratio of consumption to delivery, has been associated with poor outcome after surgery. Oxygen consumption (VO2) can change in several ways in the perioperative period, but is seldom monitored directly in routine care. This study investigates the effects of general anaesthesia on VO2.

METHODS

We searched PubMed, EMBASE, and Cochrane Library 1946-2018 for studies including VO2 measurements before and after anaesthesia induction. Quality was assessed by Cochrane risk of bias tool and NIH Quality Assessment tool for before-and-after studies. Changes in VO2 after anaesthesia induction were pooled in a random effects model meta-analysis with standardized mean differences transformed to absolute changes of VO2. Changes in VO2 after surgical incision and after recovery from anaesthesia were analysed as secondary outcomes in the included studies.

RESULTS

Twenty-four studies including 453 patients were analysed for VO2 changes induced by anaesthesia. Studies were published during 1969-2000 and mean age of patients ranged 28-70 years. VO2 decreased after anaesthesia induction by -65 (-75; -55, 95% CI) mL min^-1 and indexed VO2 (VO2I) by -33 (-38; -28, 95% CI) mL min^-1  m^-2 . After surgical incision and in the post-operative period VO2 increased again. Heterogeneity was considerable among the studies and the overall quality of evidence was very low.

CONCLUSIONS

General anaesthesia probably reduces oxygen consumption but the effect estimate is uncertain. Given the limited generalizability and low quality of the available evidence, new studies in modern perioperative settings and in today's older high-risk surgical patient populations are needed.

Deep Hypothermia and Circulatory Arrest in Adults

Brain protection during cardiopulmonary bypass has been the subject of intense research. Deep hypothermic circulatory arrest (DHCA) continues to be used for that goal during complex aortic arch and large intracranial aneurysm surgeries. The anesthetic management for adult patients undergoing these types of procedures requires specific knowledge and expertise. Based on our experience and review of the current literature, the authors highlight the key areas of the anesthetic plan, discussing the risk factors associated with adverse neurologic outcome as well as the rationale for decisions regarding specific monitors and medications. In the conclusion an anesthetic protocol for adult patients undergoing DHCA is suggested.

A case of severe perioperative hypoxia in uncorrected tetralogy of fallot: Anesthetic management

Tetralogy of fallot (TOF) is one of the most common congenital heart disease (CHD) in children. With the development of pediatric surgery and intensive care units, increasing number of grown-up CHD patients are presenting for non-cardiac surgeries. Non-operated TOF patients suffer from chronic hypoxia and decreased pulmonary blood flow resulting in considerable alteration in the physiology. The optimal management of these patients, therefore, require a thorough understanding of the pathophysiology of the uncorrected TOF. We hereby report a case of successful management of a 10-year-old child with an uncorrected TOF posted for tibial external fixation device.

Tissue microcirculation measured by vascular occlusion test during anesthesia induction

Tissue microcirculation measured by vascular occlusion test is impaired during septic shock. However, it has not been investigated extensively during anesthesia induction. The aim of the study is to evaluate tissue microcirculation during anesthesia induction. We hypothesized that during anesthesia induction, tissue microcirculation measured by vascular occlusion test might be enhanced with peripheral vasodilation during anesthesia induction. We conducted a prospective observational study of 50 adult patients undergoing cardiac surgery. During anesthesia induction, we measured and analyzed tissue oxygen saturation, vascular occlusion test, cerebral oximetry, forearm-minus-fingertip skin temperature gradients and hemodynamic data in order to evaluate microcirculation as related to alterations in peripheral vasodilation as reflected by increased Tforearm-finger thermal gradients. During anesthesia induction, recovery slope during vascular occlusion test and cerebral oxygen saturation increased from 4.0 (1.5) to 4.7 (1.3) % s(-1) (p = 0.02) and 64.0 (10.2) to 74.2 (9.2) % (p < 0.001), respectively. Forearm-minus-fingertip skin temperature gradients decreased from 1.9 (2.9) to -1.4 (2.2) °C (p < 0.001). There was an inverse correlation between changes in the skin temperature gradients and changes in cerebral oximetry (r = 0.33; p = 0.02). During anesthesia induction, blood pressure and forearm-minus-fingertip skin temperature gradients decrease while cerebral oximetry and vascular occlusion test recovery slope increase. These findings suggest that anesthesia induction increases tissue microcirculation with peripheral vasodilation.

[Successful treatment of extreme metabolic acidosis and profound hypothermia]

A case of extreme metabolic acidosis (pH 6.6) and severe hypothermia (27.3 degrees C) is reported. The patient's anamnesis and medical examination led to the assumption of ketoacidosis. Pronounced ketoacidosis is not unusual in juvenile diabetics type 1 and the incidence in Europe is reported to be between 15 and 70% for all type 1 diabetics. The case describes the targeted therapy of controlled re-warming to avoid neurological damage.

Full recovery of an avalanche victim with profound hypothermia and prolonged cardiac arrest treated by extracorporeal re-warming

Survival of hypothermic avalanche victims with cardiac arrest is rare. This report describes full recovery of a 29-year-old backcountry skier completely buried for 100 min at 3.0m (9.8 ft) depth. On extrication he was unconscious, but breathing spontaneously into an air pocket; core body temperature measured 22.0 degrees C (71.6 degrees F). He was intubated and ventilated on site. Ventricular fibrillation commenced during helicopter transportation, whereby chest compression was lacking for 15 min. At the nearest hospital continuous cardiopulmonary resuscitation was initiated, but defibrillation failed. Tympanic core body temperature measurement confirmed life-threatening hypothermia of 21.7 degrees C (71.1 degrees F) and serum K(+) was 4.3 mmol/l, necessitating transferral to a hospital with cardiopulmonary bypass facilities. Defibrillation finally succeeded following re-warming, by femoral veno-arterial bypass, to 34.5 degrees C (94.1 degrees F). Total duration of cardiac arrest was 150 min. The patient developed pulmonary oedema, treated by extracorporeal membrane oxygenation, but progressed well and was discharged from hospital on day 17, fit to resume professional and social activities. Follow-up cerebral magnetic resonance imaging 2 years after avalanche burial demonstrated only minimal changes attributable to unrelated, prior cranial trauma. Extensive neurological and psychological investigations gave excellent results. This report confirms previous literature that an air pocket with patent airways is essential for survival of a completely buried avalanche victim after 35 min and endorses the recommended management strategies of the International Commission for Mountain Emergency Medicine ICAR MEDCOM. In particular, all hypothermic victims extricated with an air pocket and free airways must be treated optimistically, even despite prolonged cardiac arrest. This remarkable case documents the fastest drop in core temperature ever recorded during snow burial, namely 9.0 degrees C (16.2 degrees F)/h, and the second-lowest reversible core temperature in avalanche literature.

Muscle relaxation does not influence venous oxygen saturation during cardiopulmonary bypass

STUDY OBJECTIVE

To examine whether the omission of neuromuscular blocking drugs during cardiopulmonary bypass (CPB) is associated with increased anesthetic requirements, higher frequency of intraoperative movements, and lower venous oxygen saturation (SvO(2)).

DESIGN

Prospective, randomized study.

SETTING

Large community hospital.

PATIENTS

30 ASA physical status III and IV patients scheduled for cardiac surgery.

INTERVENTIONS

Patients were randomized to one of two groups: group 1 (n = 15) received a 3xED(95) bolus dose of cisatracurium at induction and thereafter no more neuromuscular blocking drug; group 2 (n = 15) received a continuous infusion of cisatracurium during the entire procedure.

INTERVENTIONS

Both groups received a standardized anesthetic with bispectral index-guided propofol target-controlled infusion and a remifentanil infusion steered by hemodynamic changes. Venous oxygen saturation was continuously determined during CPB.

MEASUREMENTS AND MAIN RESULTS

Propofol consumption was 5.4 +/- 1.7 and 4.4 +/- 1.0 mg/(kg/h) in groups 1 and 2, respectively (P = 0.07). Remifentanil consumption was 0.15 +/- 0.05 and 0.17 +/- 0.05 mug/(kg/min) in groups 1 and 2, respectively (P = 0.19). In groups 1 and 2, no patient recalled any intraoperative phenomena; none moved or had diaphragmatic contractions. During CPB, SvO(2) was 81.3 +/- 3.2% (76%-85%) in group 1 and 80.6 +/- 3.1% (73%-85%) in group 2 (P = 0.53).

CONCLUSIONS

Omitting the continuous administration of neuromuscular blocking drugs during CPB did not increase anesthetic requirements. No intraoperative movements occurred, nor was there decreased SvO(2).

Impairment of mitochondrial respiratory chain enzyme activities in tetralogy of Fallot

BACKGROUND

During the last decade, disorders of the respiratory chain, so-called mitochondrial disorders, have emerged as a major clinical entity. Tetralogy of fallot (TOF) children>2 month of age are at risk for postoperative myocardial contractile failure. Myocardial ischemia is associated with a reduction in mitochondrial enzyme activity and have impaired metabolism resulting in decreased postoperative myocardial adenosine triphosphate (ATP) concentrations and increased lactate levels. With this in view, we measured the mitochondrial energy system (respiration and OXPHOS) and to study morphological changes from the right ventricular outflow tract (RVOT) muscle of patients with TOF.

METHODS

30 infants with TOF were studied with age-matched control group consisted of 12 normal patients who died due to extracardiac causes. Mitochondrial respiratory chain complexes, OXPHOS, cytochrome content and ATPase activity were measured by documented standard procedure. Morphological changes examined with a transmission electron microscope.

RESULTS

In the presence of glutamate and succinate as substrates, the rate of mitochondrial oxygen consumption was significantly lower in RVOT muscles (p<0.001) by using with and without addition of ADP. The ADP/O ratio indices for glutamate and succinate were not significantly affected. The activities of rotenone-sensitive NADH cytochrome c reductase (complexes I+III), cytochrome c oxidase (complex IV) and the ratio of I and III to II and III complexes (complex I) were significantly lower in TOF (p<0.001). A significant reduction of total cytochrome content and ATPase activity (p<0.001) was noted in study group. Morphological changes were also seen in study group as compared with control.

CONCLUSIONS

OXPHOS, mitochondrial respiratory chain complex I, I+III and IV, cytochrome content and ATPase activity are more impaired in RVOT muscles in patients with TOF.

An anaesthetic protocol in the young domestic pig allowing neuromuscular blockade for studies of cardiac function following cardioplegic arrest and cardiopulmonary bypass

BACKGROUND

Neuromuscular blockade should, for ethical reasons, not be allowed in animal experiments unless the use is strongly motivated. Beforehand, the anaesthetic protocol must be documented without muscle relaxation in the species studied. Documentation is difficult to obtain from the scientific literature. When focusing on cardiac function over time, in particular, the ideal anaesthetic protocol should cause no or minor alterations in cardiac variables.

METHODS

We intended to document an anaesthetic protocol involving ventilation with N(2)O combined with loading doses and continuous infusions of pentobarbital, fentanyl and midazolam in seven pigs by applying potentially painful stimuli every 15 min for 7 h. Subsequently, left ventricular global and regional function was studied with conductance catheter and strain rate imaging by echocardiography in eight pigs with pancuronium included.

RESULTS

Pigs without pancuronium were completely immobilized and unresponsive to potentially painful stimuli and sternotomy, with no accumulation or degradation of anaesthetic agents. With pancuronium included, left ventricular preload gradually decreased together with reduction of cardiac index from 3.52 +/- 0.14 at 2 h to 2.84 +/- 0.11 L min(-1). m(-2) (+/-SEM) after 7 h of observation. Preload recruitable stroke work decreased after 7 h, whereas peak systolic strain in the anterior left ventricular wall and load-independent indices of diastolic function were not significantly altered.

CONCLUSION

In specific experimental protocols, the anaesthetic protocol described could allow the use of muscular paralysis in young domestic pigs, for instance when involving hypothermic cardiopulmonary bypass, cardioplegic arrest and reperfusion.

[Anaphylaxis after rocuronium: advantage of blood tests for early diagnosis]

A 56-year-old patient was scheduled for coronary artery bypass surgery, because of a severe coronary artery disease. Soon after induction of anaesthesia, he rapidly developed a cardiovascular collapse with bronchospasm and rash. Specific immunoglobulin E and tryptase measurements supported the diagnosis of grade III anaphylactic shock due to rocuronium bromide. A few days later, a general anaesthesia was administered without muscle relaxant and was uneventful.

Oxygen consumption, carbon dioxide production and lactic acid during normothermic cardiopulmonary bypass

The objective of this study was to measure oxygen consumption, carbon dioxide production and lactic acid levels during normothermic cardiopulmonary bypass. A prospective study was undertaken in a tertiary care community hospital, involving 20 adults undergoing cardiopulmonary bypass with prolonged (>65 min) crossclamping of the aorta. O2 consumption, CO2 production, hemoglobin and lactic acid levels were measured 5, 35 and 65 min after crossclamping of the aorta. O2 consumption was 79.7 +/- 14.5, 78.8 +/- 15.4 and 81.5 +/- 14.1 ml/min/m2 at 5, 35 and 65 min after crossclamping the aorta. CO2 production was 61.8 +/- 42.9, 60.6 +/- 26.3 and 62.2 +/- 35.9 ml/min/m2 at the same times. Lactic acid levels were 1.6 +/- 0.5 mM/dl at all three times and did not correlate with O2 consumption or CO2 production. In conclusion, although oxygen consumption was low, there was no evidence of abnormal lactate or anaerobic metabolism to suggest tissue ischemia.

A nomogram to evaluate the arterial mixed venous oxygen saturation difference during cardiopulmonary bypass

A nomogram providing the arterial mixed venous haemoglobin saturation difference (S(a-v)O2) corresponding to normal oxygen consumption (VO2) during cardiopulmonary bypass (CPB) was produced. Normal VO2 during CPB (95.8 +/- 20.1 ml/min/m2 at 37 degrees C) was obtained from the literature. The nomogram computes the S(a-v)O2 from the body surface, pump flow, blood haemoglobin and patient temperature; a table is also presented which supplies the S(a-v)O2 ranges corresponding to VO2 mean +/-1 and +/-2SD. The nomogram was tested on 10 subjects undergoing CPB for myocardial revascularization. S(a-v)O2 was determined by arterial and mixed venous blood oximetry 5, 20, and 35 min after the start of CPB. The measured S(a-v)O2 was 27.1 +/- 7.2% while S(a-v)O2 obtained from the nomogram was 24.9 +/- 4.0%, the difference was not statistically significant. Eighteen values (60%) were within the range corresponding to VO2 mean +/-1SD. One value was lower than the S(a-v)O2 value corresponding to VO2 mean - 2SD and was associated with the lowest value of blood haemoglobin. Two values were higher than the S(a-v)O2 value corresponding to VO2 mean + 2SD and were associated with inadequate muscle relaxation. By comparing measured S(a-v)O2 values with those obtained by the nomogram and the table, anaesthesiologists and perfusionists can easily detect patients presenting abnormally low or high VO2 values.

The relationship between systemic oxygen uptake and delivery during moderate hypothermic cardiopulmonary bypass: critical values and effects of vasodilation by hydralazine

The relationship between oxygen delivery (DO2) and uptake (VO2) has been studied during moderately hypothermic cardiopulmonary bypass (CPB) in 15 patients undergoing myocardial revascularization. As soon as nasopharyngeal temperature was lowered to 32 degrees C, blood flow was decreased from 2.4 to 2.0 l/min/m2. Arterial and mixed venous blood gas analyses were performed five and eight minutes later and DO2 and VO2 were calculated; VO2 stabilized in five minutes after changing blood flow and neither DO2 nor VO2 values changed three minutes later (DO2: 217 +/- 19 versus 215 +/- 17 ml/min/m2; VO2: 63 +/- 12 versus 66 +/- 14 ml/min/m2). Blood flow then was increased to 2.3 l/min/m2 and DO2 and VO2 were determined again, five minutes later; they both increased significantly, to 243 +/- 20 and 74 +/- 13 ml/min/m2, respectively. However, a further blood flow increase to 2.6 l/min/m2 which caused DO2 to increase to 277 +/- 24 ml/min/m2, did not affect VO2 which was unchanged five minutes later (76 +/- 13 ml/min/m2); VO2 dependence on DO2 values higher than 243 +/- 20 ml/min/m2 was consequently ruled out. Ten patients, having a mean arterial pressure higher than 80 mmHg, were eventually vasodilated with hydralazine, 0.1 mg/kg intravenously, and DO2 and VO2 were determined after five and ten minutes. As blood flow did not change, DO2 was unaffected while a slight increase in VO2 mean values was observed which was not statistically significant (prior to hydralazine: 78 +/- 15 ml/min/m2; five minutes later: 82 +/- 17 ml/min/m2; 10 minutes later: 76 +/- 18 ml/min/m2). In conclusion, during hypothermic CPB at 32 degrees C, VO2 plateau ranges between 48 and 102 ml/min/m2 (mean +/- 2 SD) in 95% of patients, corresponding to 66 and 141 ml/min/m2 at 37 degrees C; this finding closely matches other literature reports. Consequently, lower VO2 values suggest inadequate oxygen supply to tissues. Critical DO2 at 32 degrees C is lower than 283 ml/min/m2 in 97.5% of patients. Finally, arterial vasoconstriction does not seem to play a significant role in tissue hypoperfusion.

Pancuronium does not decrease oxygen consumption during hypothermic or normothermic cardiopulmonary bypass

Muscle relaxation reportedly reduces systemic oxygen consumption 30% during hypothermic cardiopulmonary bypass. A potential mechanism is inhibition of hypothermia-induced subclinical muscle tone ("microshivering"). Accordingly, we tested the hypothesis that pancuronium administration would decrease systemic oxygen consumption during hypothermic cardiopulmonary bypass, but not during normothermic bypass. We studied 20 patients undergoing normothermic cardiopulmonary bypass at a nasopharyngeal temperature of 37.6 +/- 0.8 degrees C (mean +/- SD) and 15 patients undergoing hypothermic bypass at a nasopharyngeal temperature of 28.2 +/- 1.2 degrees C. Oxygen consumption during bypass was determined, using the Fick principle, before and after administration of pancuronium 0.15 mg/kg. Morphometric characteristics and anesthetic management were similar in the two groups. Oxygen consumption averaged 93 +/- 28 mL.min-1.m-2 in the normothermic patients and 43 +/- 10 mL.min-1.m-2 in the hypothermic group. Administration of pancuronium decreased oxygen consumption only 2% in the normothermic patients. However, muscle relaxation also decreased oxygen consumption only 2% in the hypothermic patients. We were thus unable to confirm our hypothesis because muscle relaxation induced by administration of pancuronium did not significantly reduce oxygen consumption in either group.

Isoflurane and hypothermic cardiopulmonary bypass: vasodilation without metabolic effects

During cardiopulmonary bypass, isoflurane may have beneficial effects on systemic oxygen uptake and vascular resistance. For this reason, the effects of isoflurane during low-flow (1.6 L/min/m2), hypothermic (27 degrees to 29 degrees C) cardiopulmonary bypass on systemic hemodynamics and oxygen uptake were studied in 20 patients in a cross-over experiment. Mean arterial and central venous pressures were measured during two consecutive periods of 10 minutes' duration. Blood samples were aspirated at the end of each period from the arterial and venous lines and analyzed for oxygen content. The concentration of isoflurane in the arterial samples was also determined. Systemic oxygen uptake and vascular resistance were calculated. Isoflurane had no significant effect on systemic oxygen uptake. Significant inverse relationships between blood isoflurane concentration and both mean arterial pressure and systemic vascular resistance were found. It is concluded that isoflurane is a vasodilator under the abnormal conditions of hypothermic cardiopulmonary bypass, but has no effect on systemic oxygen uptake.