The Effects of Neuromuscular Paralysis on Systemic and Splanchnic Oxygen Utilization in Mechanically Ventilated Patients

doi:10.1378/chest.109.4.1038

Chest

Volume 109, Issue 4, April 1996, Pages 1038-1042

https://doi.org/10.1378/chest.109.4.1038 Get rights and content

Objective

To evaluate the effect of neuromuscular paralysis on systemic and splanchnic oxygen utilization in patients in respiratory failure during controlled mechanical ventilation.

Setting

A university-affiliated teaching hospital.

Intervention

Mechanically ventilated patients, who were undergoing hemodynamic monitoring and who had a gastric intramucosal pH (pHi) of less than 7.35, were studied. Prior to paralysis, the patients were sedated with lorazepam and morphine to standard end points, and the cardiac output and oxygenation were optimized. The patients were then paralyzed with doxacurium and the ventilator rate adjusted to keep the PaCO₂ at baseline value. The hemodynamic and oxygenation profile and pHi were determined prior to paralysis and repeated 2 to 2.5 h later.

Results

Eight patients were studied; their mean age was 63±8 years and acute physiology and chronic health evaluation II score was 22±4. The mean fraction of inspired oxygen, positive end-expiratory pressure, and venous admixture ratio prior to the study was 0.7±0.14, 11.8±2.4 cm H₂O, and 26±9%, respectively. Prior to paralysis, the mean set assist controlled ventilation rate was 15± 2 breaths/min and the patient rate was 23±5 breaths/min. With neuromuscular paralysis, the cardiac index fell from 4.6±2.2 to 4.3±2.4 L/min/m² (p=0.1), the oxygen delivery fell from 537±129 to 471±95 mL/min/m² (p=0.03), and the oxygen consumption and extraction ratio fell from 200±77 to 149±35 mL/min/m² (p=0.03) and 36±5 to 31±10, respectively (p=0.2). The pHi increased from 7.21±0.16 to 7.29±0.1 (p=0.02).

Conclusion

In critically ill patients in respiratory failure, neuromuscular paralysis decreases whole body oxygen consumption and increases pHi. Presumably, by eliminating the work of breathing, there is a redistribution of blood flow from the respiratory muscles to the splanchnic and other nonvital vascular beds.

Section snippets

Materials and Methods

This study was conducted in the Medical and Surgical ICUs at St. Vincent Hospital, a university-affiliated teaching hospital in Worcester, Mass. Approval to conduct this study was obtained from our Institutional Review Board.
During the study period, all patients admitted to our ICUs with the sepsis syndrome¹⁸ and acute respiratory failure, who had a pulmonary artery catheter in situ and required neuromuscular blockade to facilitate mechanical ventilation, were screened for inclusion into this

Results

Eight patients were studied: three men and five women. The mean age of the patients was 63±8 years. The patients' clinical characteristics are listed in Table 1. The patients were all seriously ill, with a mean acute physiology and chronic health evaluation II score of 22 ±4. All patients had significant lung injury requiring a mean fraction of inspired oxygen of 0.7±0.14 and positive end-expiratory pressure of 11.8±2.4 cm H₂O to maintain adequate oxygenation (arterial oxygen saturation >90%).

Discussion

In this study, we have demonstrated that neuromuscular paralysis will decrease total body oxygen consumption and increase pHi in critically ill patients with evidence of splanchnic ischemia, during assisted, volume-cycled mechanical ventilation. Presumably, by eliminating the work of breathing during AC ventilation, there is a redistribution of blood from the respiratory muscles to the splanchnic and other nonvital vascular beds.

The results of this study are supported by both clinical and

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While lactic acid has been associated with increased mortality in trauma and burn patients [9], respiratory oxygen uptake's impact on survival has not been studied. While patients in our study had multiple reasons to have decreased oxygen extraction including sedation, paralysis, hypo nutrition, mechanical ventilation, and sepsis, [10] [11] currently there is no evidence to support that respiratory uptake of oxygen correlates with the oxygen extraction ratio in circulating blood. Since 55% of our cohort died from sepsis, it is possible that decreased respiratory uptake is an early marker of sepsis.
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.
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.
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In sedated patients, body temperature may be the main determinant of energy expenditure [17]. Some studies have found a reduction in Vo2 after application of NMB [18-23]. MacCall et al [23] showed that NMB in severe head-injured patients decreased energy expenditure to PEE levels, independent of morphine use, body temperature, and feeding.
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.
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.
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.
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Chest

Clinical Investigations in Critical CareThe Effects of Neuromuscular Paralysis on Systemic and Splanchnic Oxygen Utilization in Mechanically Ventilated Patients

Objective

Setting

Intervention

Results

Conclusion

Section snippets

Materials and Methods

Results

Discussion

Surg Clin North Am

Chest

Chest

Chest

Chest

Lancet

Am J Cardiol

J Crit Care

Prognosis in acute organ-system failure

Ann Surg

Use of survivors cardiorespiratory values as therapeutic goals in septic shock

Crit Care Med

Hemodynamic and oxygen transport patterns in surviving and non-surviving postoperative patients

Crit Care Med

Oxygen transport in adult respiratory distress syndrome and other acute circulatory problems: relationship of oxygen deliveiy and oxygen consumption

Crit Care Med

Septic shock in humans: advances in understanding of pathogenesis, cardiovascular dysfunction and therapy

Ann Intern Med

The oxygen cost of breathing in patients with cardiopulmonary disease

Am Rev Respir Dis

The inspiratory workload of patients-initiated mechanical ventilation

Am Rev Respir Dis

External work output and force generation during synchronized intermittent mechanical ventilation: effect of machine assistance on breathing effort

Am Rev Respir Dis

Regional blood flow distribution in dog during induced hypotension and low cardiac output: spontaneous breathing versus artificial ventilation

J Clin Invest

Clinical Investigations in Critical Care
The Effects of Neuromuscular Paralysis on Systemic and Splanchnic Oxygen Utilization in Mechanically Ventilated Patients