The effects of neuromuscular paralysis on systemic and splanchnic oxygen utilization in mechanically ventilated patients

Neuromuscular Blockade in the Pre- and COVID-19 ARDS Patients

Acute respiratory distress syndrome (ARDS) accounts for a quarter of mechanically ventilated patients, while during the pandemic, it overwhelmed the capacity of intensive care units (ICUs). Lung protective ventilation (low tidal volume, positive-end expiratory pressure titrated to lung mechanics and oxygenation, permissive hypercapnia) is a non-pharmacological approach that is the gold standard of management. Among the pharmacological treatments, the use of neuromuscular blocking agents (NMBAs), although extensively studied, has not yet been well clarified. The rationale is to minimize the risk for lung damage progression, in the already-injured pulmonary parenchyma. By abolishing rigorous spontaneous efforts, NMBAs may decrease the generation of high transpulmonary pressures that could aggravate patients’ self-inflicted lung injury. Moreover, NMBAs can harmonize the patient–ventilator interaction. Recent randomized controlled trials reported contradictory results and changed the clinical practice in a bidirectional way. NMBAs have not been documented to improve long-term survival; thus, the current guidance suggests their use only in patients in whom a lung protective ventilation protocol cannot be applied, due to asynchrony or increased respiratory efforts. In the present review, we discuss the published data and additionally the clinical practice in the “war” conditions of the COVID-19 pandemic, concerning NMBA use in the management of patients with ARDS.

Advances in Ventilator Management for Patients with Acute Respiratory Distress Syndrome

The ventilatory care of patients with acute respiratory distress syndrome (ARDS) is evolving as our understanding of physiologic mechanisms of respiratory failure improves. Despite several decades of research, the mortality rate for ARDS remains high. Over the years, we continue to expand strategies to identify and mitigate ventilator-induced lung injury. This now includes a greater understanding of the benefits and harms associated with spontaneous breathing.

Acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is an acute respiratory illness characterised by bilateral chest radiographical opacities with severe hypoxaemia due to non-cardiogenic pulmonary oedema. The COVID-19 pandemic has caused an increase in ARDS and highlighted challenges associated with this syndrome, including its unacceptably high mortality and the lack of effective pharmacotherapy. In this Seminar, we summarise current knowledge regarding ARDS epidemiology and risk factors, differential diagnosis, and evidence-based clinical management of both mechanical ventilation and supportive care, and discuss areas of controversy and ongoing research. Although the Seminar focuses on ARDS due to any cause, we also consider commonalities and distinctions of COVID-19-associated ARDS compared with ARDS from other causes.

Resuscitation of the Critically Ill Older Adult

In 30 years, adults 65 and older will represent 20% of the US population, with increased medical comorbidities leading to higher rates of critical illness and mortality. Despite significant acute illness, presenting symptoms and vital sign abnormalities may be subtle. Resuscitative guidelines are a helpful starting point but appropriate diagnostics, bedside ultrasound, and frequent reassessments are needed to avoid procrustean care that may worsen outcomes. Baseline functional status is as important as underlying comorbid conditions when prognosticating, and the patient's personal wishes should be sought early and throughout care with clear communication regarding prospects for immediate survival and overall recovery.

Myorelaxants in ARDS patients

Neuromuscular blocking agents (NMBAs) inhibit patient-initiated active breath and the risk of high tidal volumes and consequent high transpulmonary pressure swings, and minimize patient/ ventilator asynchrony in acute respiratory distress syndrome (ARDS). Minimization of volutrauma and ventilator-induced lung injury (VILI) results in a lower incidence of barotrauma, improved oxygenation and a decrease in circulating proinflammatory markers. Recent randomized clinical trials did not reveal harmful muscular effects during a short course of NMBAs. The use of NMBAs should be considered during the early phase of severe ARDS for patients to facilitate lung protective ventilation or prone positioning only after optimising mechanical ventilation and sedation. The use of NMBAs should be integrated in a global strategy including the reduction of tidal volume, the rational use of PEEP, prone positioning and the use of a ventilatory mode allowing spontaneous ventilation as soon as possible. Partial neuromuscular blockade should be evaluated in future trials.

Transfusion-free treatment strategies for acute anemia in critical care

Acute anemia is a frequently encountered diagnosis in critically ill patients, and can be a challenge if blood products are not readily available or if patients refuse these products on the basis of their religious beliefs. This article discusses the goals of anemia management and summarizes several alternatives to blood transfusions that can be used to prevent and treat acute anemia.

Respiratory oxygen uptake is associated with survival in a cohort of ventilated trauma and burn patients

BACKGROUND

Little data is available in the literature about the role of end tidal oxygen in critically ill patients. We sought to identify the association between the level of respiratory oxygen and clinical outcomes in critically-ill ventilated trauma and burn patients.

METHODS

A retrospective cohort of 55 trauma and burn patients from 2010 to 2016 was collected. Exposures of interest included a) expiratory end tidal oxygen (ETO2) and b) the difference between FiO₂ and ETO2 (uptake). Associations of clinical characteristics with ETO2 and oxygen uptake were examined using a Spearman correlation. The relationships between discharge status, demographics, injury type, severity, and clinical characteristics were examined using chi-square (or Fisher's exact) tests and two-sample t-tests. Multivariable analyses using linear and logistic regression were performed to determine whether expiratory end tidal oxygen or oxygen uptake was an independent predictor of clinical outcomes.

RESULTS

Mean age for the patients was 46.3±18.2years with 41 (74.6%) male and 34 (61.8%) white. In the cohort, 27 (49.1%) of patients had burns and 28 (50.9%) blunt trauma. Oxygen uptake was negatively correlated with lactic acid, minute ventilation, total ICU days, and ventilator days (p<0.05). Patients who died demonstrated lower oxygen uptake than those alive, oxygen uptake remained significantly associated with discharge status after adjusting for potential confounders (p=0.028).

CONCLUSION

A narrowed difference between ETO₂ and inspiratory oxygen is associated with increased mortality in a cohort of ventilated trauma and burn patients. Future research is needed to further elucidate the role of respiratory oxygen level in larger, prospective studies.

Effect of muscle relaxation on the oxygenation of human skeletal muscle: a prospective in-vivo experiment using an isolated forearm technique

Background

Total oxygen consumption has been found to be reduced under deep neuromuscular blockade due to a lower rate of metabolism of skeletal muscles. However, the magnitude of this effect in individual muscles has not been investigated. Thus the aim of this study was to compare the oxygenation of paralyzed versus non-paralyzed forearm muscle under tourniquet-provoked ischemia.

Methods

After ethics approval and written informed consent, 30 patients scheduled for elective hand and wrist surgery were included. Ischemia was provoked by inflation of bilateral upper arm tourniquets and muscle relaxation was achieved via intravenous administration of rocuronium 0.9 mg/kg. Bilateral tourniquets were applied to both upper arms before induction of anesthesia and near infrared spectrometry (NIRS) electrodes applied on both forearms. Muscular ischemia in an isolated (= non-paralyzed, NP) as well as a paralyzed forearm (P) was created by sequential inflation of both tourniquets before and after intravenous administration of rocuronium. Muscle oxygen saturations (S_mO₂) of NIRS in both forearms and their changes were determined and compared.

Results

Data of 30 patients (15 male, 15 female; 41.8 ± 14.7 years) were analyzed. The speed of S_mO₂ decrease (50% decrease of S_mO₂ from baseline (median [percentiles]: NP 210 s [180/480s] vs. P 180 [180/300]) as well as the maximum decrease in S_mO₂ (minimum S_mO₂ in % (median [percentiles]: NP 20 [19/24] vs. P 21 [19/28]) were not significantly affected by neuromuscular paralysis.

Conclusions

No significant effect of muscle relaxation on NIRS-assessed muscle oxygenation under tourniquet-induced ischemia was found in human forearm muscles.

Energy expenditure in patients with severe head injury: controlled normothermia with sedation and neuromuscular blockade

OBJECTIVES

Providing optimal caloric intake is important for patients with severe traumatic brain injury. Insufficient nutrition worsens prognosis, and excessive nutrition may lead to complications such as weaning delay from mechanical ventilation. However, using controlled normothermia with sedation and neuromuscular blockade for patients with anticipated severe brain edema, the optimal caloric intake is still unclear.

METHODS

Ten patients with severe traumatic brain injury were studied. All patients received midazolam and vecuronium or pancuronium to control body temperature to 36.0°C. Energy expenditure was measured using indirect calorimetry. Age, body height, body weight, heart rate, blood pressure, body temperature, and minute ventilation volume were evaluated at the time of the study. Differences between the mean measured energy expenditures (MEEs) and predicted basal energy expenditures (PEEs from the Harris-Benedict equation) were analyzed using paired t test. Furthermore, the relationships between these variables and MEEs were analyzed with multiple regression analysis.

RESULTS

The result of MEE was 1279±244 kcal/d. When compared with PEE, MEE/PEE was 87.2% ± 10%. Multiple regression analysis showed that age, body height, body weight, heart rate, and minute ventilation volume were related with MEE.

CONCLUSIONS

Energy expenditure in patients with severe traumatic brain injury who need mechanical ventilation and have received controlled normothermia with sedation and neuromuscular blockade was 13% less than predicted basal levels. Energy expenditure might be obtained from age, body height, body weight, heart rate, and minute ventilation.

Neuromuscular blockade with rocuronium bromide increases the tolerance of acute normovolemic anemia in anesthetized pigs

BACKGROUND

The patient's individual anemia tolerance is pivotal when blood transfusions become necessary, but are not feasible for some reason. To date, the effects of neuromuscular blockade (NMB) on anemia tolerance have not been investigated.

METHODS

14 anesthetized and mechanically ventilated pigs were randomly assigned to the Roc group (3.78 mg/kg rocuronium bromide followed by continuous infusion of 1 mg/kg/min, n = 7) or to the Sal group (administration of the corresponding volume of normal saline, n = 7). Subsequently, acute normovolemic anemia was induced by simultaneous exchange of whole blood for a 6% hydroxyethyl starch solution (130/0.4) until a sudden decrease of total body O(2) consumption (VO(2)) indicated a critical limitation of O(2) transport capacity. The Hb concentration quantified at this time point (Hb(crit)) was the primary endpoint of the protocol. Secondary endpoints were parameters of hemodynamics, O(2) transport and tissue oxygenation.

RESULTS

Hb(crit) was significantly lower in the Roc group (2.4 ± 0.5 vs. 3.2 ± 0.7 g/dl) reflecting increased anemia tolerance. NMB with rocuronium bromide reduced skeletal muscular VO(2) and total body O(2) extraction rate. As the cardiac index increased simultaneously, total body VO(2) only decreased marginally in the Roc group (change of VO(2) relative to baseline -1.7 ± 0.8 vs. 3.2 ± 1.9% in the Sal group, p < 0.05).

CONCLUSION

Deep NMB with rocuronium bromide increases the tolerance of acute normovolemic anemia. The underlying mechanism most likely involves a reduction of skeletal muscular VO(2). During acellular treatment of an acute blood loss, NMB might play an adjuvant role in situations where profound stages of normovolemic anemia have to be tolerated (e.g. bridging an unexpected blood loss until blood products become available for transfusion).

Spontaneously regulated vs. controlled ventilation of acute lung injury/acute respiratory distress syndrome

PURPOSE OF REVIEW

To present an updated discussion of those aspects of controlled positive pressure breathing and retained spontaneous regulation of breathing that impact the management of patients whose tissue oxygenation is compromised by acute lung injury.

RECENT FINDINGS

The recent introduction of ventilation techniques geared toward integrating natural breathing rhythms into even the earliest phase of acute respiratory distress syndrome support (e.g., airway pressure release, proportional assist ventilation, and neurally adjusted ventilatory assist), has stimulated a burst of new investigations.

SUMMARY

Optimizing gas exchange, avoiding lung injury, and preserving respiratory muscle strength and endurance are vital therapeutic objectives for managing acute lung injury. Accordingly, comparing the physiology and consequences of breathing patterns that preserve and eliminate breathing effort has been a theme of persisting investigative interest throughout the several decades over which it has been possible to sustain cardiopulmonary life support outside the operating theater.

Emergency subtotal colectomy in a Jehovah's Witness with massive lower gastrointestinal bleeding: challenges encountered and lessons learned

A 66-year-old woman who was a Jehovah's Witness had massive lower gastrointestinal bleeding and subsequent hypovolemic shock, necessitating a subtotal colectomy. During the postoperative period, her hemoglobin level decreased to a low of 2.6 g/dL, prolonging her dependence on mechanical ventilation. Prudent perioperative care resulted in a successful outcome. Blood-conserving techniques are indispensable in the management of Jehovah's Witnesses who have massive blood loss. Maximizing oxygen transport, minimizing blood loss, using a cell saver when permissible, providing optimal ventilatory support, performing tracheostomy early if prolonged mechanical ventilation is expected, and augmenting hemoglobin production with administration of iron and erythropoietin are techniques that can facilitate successful outcome in patients who refuse blood transfusion.

[Effects of sedative agents on metabolic demand]

Literature about the effects of sedative drugs on the metabolic demand of critically ill patients is relatively old and of relatively poor quality. Most are experimental or observational studies. Level of evidence is therefore relatively low corresponding to "expert opinion". The effects of analgesics and hypnotics on tissue metabolic demand associated remain difficult to be adequately quantified. They are essentially related to a decreased neuro-humoral response to stress. This response involves principally the sympathetic system, which could be effectively blocked by most of the anesthetic agents. Other factors could participate to the observed reduction in tissue metabolic demand, as a decrease in spontaneous muscular activity, a reduction in work of breathing and/or a decrease in body temperature. The relative contribution of these different factors will depend on the clinical situation of the patient. Proper effects of anesthetic agents on cellular metabolism are limited as they can only decrease the functional component of this metabolism especially at the level of the heart and to some extent, at the level of the brain. Although the control of the sympathetic activity may be beneficial in critically ill patient, complete sympathetic blockade could be detrimental. Indeed, when oxygen transport to the tissues is acutely reduced, the sympathetic system plays an important role in the redistribution of blood flow according of local metabolic demand. The complete blunting of the neuro-humoral response to stress and therefore of the sympathetic system alters this physiological mechanism and results in a decrease in tissue oxygen extraction capabilities. An imbalance between tissue oxygen demand and delivery could appear with the development of cellular hypoxia. The institution of sedation in a critically ill patient requires careful evaluation of the sedation level using an appropriate scale. In patients in whom a reduction in metabolic demand is specifically requested, but also in patients with limited oxygen transport, the effects of sedative agents on the oxygen consumption-oxygen delivery relationship must also be monitored. The choice of the different agents to be administered will depend on the predefined objectives. As far as intravenous agents are concerned, there is no evidence than one association is more efficient in reducing patient's metabolic demand.

[Indications and uses of neuromuscular blocking agents in the ICU]

Although many questions are still debated, some recommendations can be formulated regarding the use of neuromuscular blocking agents in the ICU. A transient curarization can be used during brief diagnostic or therapeutic procedures in order to avoid haemodynamic consequences of deep sedation. A volume controlled ventilation has to be used during the procedure. In ARDS patients, a prolonged curarization of 48 h or more is beneficial regarding systemic oxygenation, even in patients well adapted to their ventilator. The use of cisatracurium should be recommended in this context. The depth of curarization has to be checked by using a train of four stimulation at the corugator supercilii with an endpoint of 2/4 responses. A recovery from curarization should be daily envisaged if possible, in order to check the depth of the underlying sedation. In brain injured patients, a curarization can be envisaged if adaptation to the ventilator remains difficult or if normothermia or moderate hypothermia, if indicated, cannot be obtained. However, these attitudes are not based on specific data at the present time.

[Sedation an acute respiratory distress syndrome]

AIM

To assess the role of sedation and myorelaxant agents in acute respiratory distress syndrome (ARDS) and to propose an updated management according to recent literature. EXTRACTION OF DATA: From Medline and Cochrane database of English and French language articles. Keywords were: acute respiratory distress syndrome, acute lung injury, general anaesthetics, inhalation, intravenous anaesthetics and intensive care. Selection of original articles, reviews and expert reports. Case reports have been included.

TOPIC

ARDS is a clinical picture in which respiratory constraints are major because of hypoxemia. To insure correct haematosis, mechanical ventilation has to be considered. It constitutes, then, the most frequent indication of sedation in the intensive care unit. The objectives are to help the ventilation of lungs and to improve gas exchange, by controlling agitation, fight against ventilation and to reduce mechanical ventilation associated injuries. In this situation, use of myorelaxant agents is aimed at facilitating synchronization of the patient with his/her ventilator and serves to improve oxygenation during the early inflammatory phase of ARDS. Several mechanisms may enflame this improvement of oxygenation. One of the most probable effect on optimization is the possibility of optimize protective ventilation at the cares phase of ARDS and to reduce mechanical ventilation-associated injuries.

CONCLUSION

With regard to benefits and inconvenient, sedation is considered as a treatment of ARDS. Its goals are the well being of patient and his/her adaptation to ventilator, but also the prevention on mechanical ventilation associated injuries. Hence, most authors suggest using a deep sedation at the early phase of ARDS. In this contact, use of myorelaxant agent is an intersecting adjuvant if sedation is not enough. The benefit is terms of survival and outcome remains to show.

Nonventilatory interventions in the acute respiratory distress syndrome

Acute respiratory distress syndrome was first described in 1967. Acute respiratory distress syndrome and acute lung injury are diseases the busy intensivist treats almost daily. The etiologies of acute respiratory distress syndrome are many. A significant distinction is based on whether the insult to the lung was direct, such as in pneumonia, or indirect, such as trauma or sepsis. Strategies for managing patients with acute respiratory distress syndrome/acute lung injury can be subdivided into 2 large groups, those based in manipulation of mechanical ventilation and those based in nonventilatory modalities. This review focuses on the nonventlilatory strategies and includes fluid restriction, exogenous surfactant, inhaled nitric oxide, manipulation of production, or administration of eicosanoids, neuromuscular blocking agents, prone position ventilation, glucocorticoids, extracorporeal membrane oxygenation, and administration of beta-agonists. Most of these therapies either have not been studied in large trials or have failed to show a benefit in terms of long-term patient mortality. Many of these therapies have shown promise in terms of improved oxygenation and may therefore be beneficial as rescue therapy for severely hypoxic patients. Recommendations regarding the use of each of these strategies are made, and an algorithm for implementing these strategies is suggested.

Severe sepsis and septic shock: review of the literature and emergency department management guidelines

Severe sepsis and septic shock are as common and lethal as other acute life-threatening conditions that emergency physicians routinely confront such as acute myocardial infarction, stroke, and trauma. Recent studies have led to a better understanding of the pathogenic mechanisms and the development of new or newly applied therapies. These therapies place early and aggressive management of severe sepsis and septic shock as integral to improving outcome. This independent review of the literature examines the recent pathogenic, diagnostic, and therapeutic advances in severe sepsis and septic shock for adults, with particular relevance to emergency practice. Recommendations are provided for therapies that have been shown to improve outcomes, including early goal-directed therapy, early and appropriate antimicrobials, source control, recombinant human activated protein C, corticosteroids, and low tidal volume mechanical ventilation.

Severe autoimmune hemolytic anemia treated by paralysis, induced hypothermia, and splenic embolization

Autoimmune hemolytic anemia (AIHA) is the clinical condition in which IgG antibodies bind to RBC surface antigens and initiate RBC destruction via the complement and reticuloendothelial system. AIHA is commonly treated with transfusions, corticosteroids, and splenectomy. We present a case of an adult with life-threatening AIHA secondary to ulcerative colitis emergently managed with neuromuscular paralysis, induced hypothermia, and splenic embolization.

Gastric intramucosal pH and intraluminal PCO2 during weaning from mechanical ventilation

OBJECTIVE

To study the value of gastric intramucosal pH and gastric intraluminal PCO2 measurements to predict weaning outcome from mechanical ventilation.

DESIGN

Prospective clinical study.

SETTING

Intensive care medicine department of a university hospital.

PATIENTS

Nineteen adult critically ill patients who were mechanically ventilated because of acute respiratory failure and were considered ready to be weaned.

INTERVENTIONS

The patients were weaned with: synchronized intermittent mandatory ventilation plus positive end-expiratory pressure (SIMV+PEEP) or continuous positive airway pressure with pressure support ventilation (CPAP+PSV). A gastric tonometer was placed in all the patients. Tonometric, respiratory, and hemodynamic variables were measured during the weaning process.

MEASUREMENTS

Hemodynamic variables, respiratory mechanics, pulmonary gas exchange, respiratory muscle force, spontaneous pattern of breathing, and the central control of breathing were recorded. Simultaneously, the intramucosal pH and gastric intraluminal PCO2 were measured.

MAIN RESULTS

Eleven patients were successfully extubated and eight failed. The patients who failed showed higher values of mouth occlusion pressure, respiratory rate, and effective inspiratory impedance (mouth occlusion pressure/mean inspiratory flow). The intramucosal pH was initially 7.19 +/- 0.22 and decreased to 7.10 +/- 0.16 during the weaning process in patients who failed (p < .05). At the same time, the intramucosal pH showed a nonsignificant change from 7.36 +/- 0.07 to 7.32 +/- 0.07 in the patients who were successfully extubated. The intramucosal pH was statistically different when both groups were compared during the initial and the final evaluations (p < .05). For the initial evaluation, the sensitivity and specificity to predict weaning failure when the intramucosal pH was < or =7.30 were 0.88 (95% confidence interval [CI], 0.66-1) and 0.82 (95% CI, 0.59-1), respectively. The gastric intraluminal PCO2 was higher in patients who failed (p < .05). When gastric intraluminal PCO2 was . or =40 torr during the initial evaluation, weaning failure occurred with a sensitivity of 1 (95% CI, 0.31-1) and a specificity of 0.55 (95% CI, 0.26-0.84).

CONCLUSIONS

Weaning failure was associated with gastric intramucosal acidosis. The intramucosal pH and gastric intraluminal PCO2 may be helpful to predict weaning outcome. Further controlled clinical trials in a larger group of patients are needed.

Anesthetics, sedatives, and paralytics. Understanding their use in the intensive care unit

This article reviews the use of inhalational, intravenous, and epidural agents used in the operating room and ICU. An emphasis is placed on the rationale for their selection. Additionally, the side effects and expected complications are discussed. By developing expertise with one's own repertoire of sedatives, narcotics, and neuromuscular blocking agents, one may decrease postoperative complications and lengths of stay.

Effect of neuromuscular blockade on oxygen consumption and energy expenditure in sedated, mechanically ventilated children

OBJECTIVE

To quantify the effects of neuromuscular blockade (NMB) on energy expenditure for intubated, mechanically ventilated, critically ill children.

DESIGN

A prospective, unblinded clinical study. Each subject was studied twice, before and after establishment of NMB.

SETTING

A tertiary care pediatric intensive care unit.

PATIENTS

Critically ill children undergoing mechanical ventilation and receiving ongoing sedation were eligible, if they had a cuffed endotracheal tube and were physiologically stable.

INTERVENTIONS

A total of 20 children (age, 1 to 15 yrs) were studied in an unblinded, crossover fashion. All were mechanically ventilated via a cuffed endotracheal tube, with ventilator rate and tidal volume adequate to provide complete ventilation, and F(IO2) <0.6. Absence of gas leak around the endotracheal tube was assured, and all patients were sedated using continuous infusions of midazolam and/or fentanyl; no changes in ventilator settings, nutritional input, or inotropic drug dose were permitted during the study period. Each patient underwent indirect calorimetry immediately before establishment of NMB. NMB was then induced, and indirect calorimetry was repeated. Complete blockade was verified using a peripheral nerve stimulator. In each case, the two sets of measurements were completed within a 1-hr period.

MEASUREMENTS AND MAIN RESULTS

Data analyzed included identifying and diagnostic information, oxygen consumption, and carbon dioxide production. Energy expenditure was calculated using standard formulas. Oxygen consumption and energy expenditure values obtained before and after the establishment of NMB were compared by using paired Student's t-test. NMB reduced oxygen consumption from 6.54+/-0.49 mL/kg/min to 5.90+/-0.40 ml/kg/min, and energy expenditure was reduced from 46.5+/-3.7 kcal/kg/24 hrs to 41.0+/-2.8 kcal/kg/24 hrs (p < .001 in each case). The reduction in oxygen consumption was 8.7+/-1.7%, and that in energy expenditure 10.3+/-1.8%, of pre-NMB values, respectively.

CONCLUSION

NMB significantly reduces oxygen consumption and energy expenditure in critically ill children who are sedated and mechanically ventilated; the degree of reduction is small.

Energy expenditure in acetaminophen-induced fulminant hepatic failure

OBJECTIVE

To determine energy expenditure in critically ill patients suffering from acetaminophen-induced fulminant hepatic failure and compare it with values obtained in matched, healthy control subjects and in patients studied during the anhepatic period of elective liver transplantation.

DESIGN

Prospective, controlled, observational study.

SETTING

A ten-bed intensive therapy unit and a liver transplant unit at a University teaching hospital.

PATIENTS AND SUBJECTS

Sixteen patients suffering from acetaminophen-induced fulminant hepatic failure who were sedated, paralyzed, and mechanically ventilated; 16 age-, gender-, and weight-matched, awake, healthy control subjects; and 16 patients with chronic liver disease, undergoing elective liver transplantation, who were studied during the anhepatic period of surgery.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The mean energy expenditure was calculated in each case for a 30-min period, using indirect calorimetry. In the patients undergoing liver transplantation, measurements were performed after clamping the hepatic veins and recipient hepatectomy. Energy expenditure was markedly increased in the fulminant hepatic failure group (mean energy expenditure, 4.05 [SD 0.52] kJ x kg(-1) x hr(-1)), in comparison with healthy control subjects (mean, 3.44 [0.27] kJ x kg(-1) x hr(-1); mean difference, 18%; p < .001) and in comparison with patients during the anhepatic period of liver transplantation (mean, 3.15 [0.61] kJ x kg(-1) x hr(-1); mean difference, 29%; p < .001). These differences were even more pronounced when a correction factor for differences in core temperature was included in the calculation. Harris-Benedict predictions of energy expenditure were unreliable in the patients with acute liver failure. No correlations were found among energy expenditure and hemodynamic variables, the requirement for vasoconstrictors, or the presence of renal failure.

CONCLUSIONS

Despite the loss of functioning liver cell mass, the metabolic rate is substantially increased in patients with acetaminophen-induced fulminant hepatic failure. This finding is consistent with the marked systemic inflammatory response, which accompanies acute hepatic failure. The Harris-Benedict equation is unreliable when an estimation of energy expenditure is required in patients with this condition.

Influence of mechanical ventilation on blood lactate in patients with acute respiratory failure

OBJECTIVES

To determine whether mechanical ventilation (MV) may affect blood lactate concentration in patients with acute respiratory failure.

DESIGN

Prospective observational study with follow-up to hospital discharge.

SETTING

A 17-bed medical and coronary intensive care unit in a 650-bed general hospital.

PATIENTS

55 adult patients mechanically ventilated for acute respiratory failure between May 1996 and April 1997 were recruited.

MEASUREMENTS AND RESULTS

Arterial blood samples for determination of plasma lactate and blood gas analysis were taken just before tracheal intubation on spontaneous breathing, and 20 and 60 min after the initiation of controlled MV. Cuff systemic arterial pressure was measured before tracheal intubation and every 10 min during the first h of MV. Hyperlactatemia (arterial blood lactate > or = 2 mmol/l) was present in 21 of the 55 patients studied. After 20 min of MV, there was a decrease in blood lactate from 4.74 +/- 1.78 to 3.07 +/- 1.69 mmol/l (p < 0.01); 40 min later there was a further decrease to 2.63 +/- 1.35 mmol/l (p < 0.05). The decrease in blood lactate was also observed in those patients who after starting MV developed systemic arterial hypotension (p < 0.01). In patients with a normal lactate concentration at the entry to the study, lactate remained the same after 60 min on MV (NS).

CONCLUSIONS

Controlled MV decreases substantially the severity of hyperlactatemia in patients with acute respiratory failure, and any adverse circulatory effects of MV do not alter this beneficial outcome.

Acute withdrawal syndrome related to the administration of analgesic and sedative medications in adult intensive care unit patients

OBJECTIVES

To estimate the frequency of acute withdrawal syndrome related to the administration of analgesic and sedative medications in mechanically ventilated adult intensive care unit (ICU) patients; to identify associated clinical factors.

DESIGN

Retrospective review of medical records.

SETTING

An adult trauma/surgical ICU in an urban Level I trauma center.

PATIENTS

Twenty-eight mechanically ventilated adult trauma/ surgical ICU patients requiring >7 days of ICU care.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Daily doses of all opioid, sedative, hypnotic, and major tranquilizer drugs administered to each patient were measured, as was duration of ICU stay, duration of mechanical ventilation, and duration of the administration of analgesic, sedative, and neuromuscular blocking agents (NMBAs) for each patient. All opioids and benzodiazepines were converted to their respective fentanyl and lorazepam equivalent units based on potency and bioavailability. Calculation of the weaning rate for each patient during tapering from opioid and benzodiazepine medications was performed. The presence or absence of acute withdrawal syndrome was identified for each patient. Nine (32.1%) patients developed acute withdrawal syndrome potentially related to the administration of analgesic or sedative medications. Patients in the withdrawal group received significantly higher mean daily (p = .049) and peak (p = .032) doses of fentanyl equivalents, as well as higher mean daily lorazepam equivalents (p = .049) compared with patients not experiencing withdrawal. Patients in the withdrawal group were also significantly more likely to have received neuromuscular blocking agents (p = .004) or propofol (p =.026) for >1 day during ICU admission compared with patients not experiencing withdrawal. Duration of mechanical ventilation (p = .049), benzodiazepine therapy (p = .048), and propofol therapy (p = .049) was also significantly longer in the group experiencing withdrawal. Withdrawal patients received a significantly lower mean daily dose of haloperidol (p = .026). There was a significant association between the development of withdrawal syndrome and the presence of ARDS (p = .017). Finally, the slopes of the lines representing opioid and benzodiazepine drug weaning were more steep for the withdrawal group, although these results did not achieve statistical significance.

CONCLUSIONS

These results suggest that mechanically ventilated adult patients with extended ICU care (> or =7 days) who receive large doses of analgesic and sedative medications are at risk for acute withdrawal syndromes during drug weaning. The association between ARDS and withdrawal syndrome, combined with the observation that withdrawal syndromes were also associated with the use of neuromuscular blocking agents and prolonged mechanical ventilation, suggests that patients with ARDS may be more likely to receive high doses of analgesic and sedative medications, and are therefore at increased risk for withdrawal syndrome.