Neurohormonal responses during positive pressure mechanical ventilation

Early extubation after pediatric cardiac surgery

Early extubation after pediatric cardiac surgery has come full circle from being practiced in the early days of pediatric cardiac surgery, falling out of favor with opioid-heavy cardiostable anesthesia, and resurfacing again in more recent times as part of enhanced recovery after surgery practice. Early extubation is variably defined, but is mostly accepted as extubation that occurs within 6-8 h from the end of surgery. In recent years, the debate has shifted from early extubation in the intensive care unit to immediate extubation in the operating theatre. In this review, we examined the benefits and pitfalls of early and immediate extubation, factors that influence the success of early extubation, and potential guidelines for practice and implementation.

Cardiovascular function, pulmonary gas exchange and tissue oxygenation in isoflurane-anesthetized, mechanically ventilated Beagle dogs with four levels of positive end-expiratory pressure

OBJECTIVES

To compare pulmonary gas exchange, tissue oxygenation and cardiovascular effects of four levels of end-expiratory pressure: no positive end-expiratory pressure (ZEEP), positive end-expiratory pressure (PEEP) of maximal respiratory system compliance (PEEPmaxC_rs), PEEPmaxC_rs + 2 cmH₂O (PEEPmaxC_rs+2), PEEPmaxC_rs + 4 cmH₂O (PEEPmaxC_rs+4), in isoflurane-anesthetized dogs.

STUDY DESIGN

Prospective randomized crossover study.

ANIMALS

A total of seven healthy male Beagle dogs, aged 1 year and weighing 10.2 ± 0.7 kg (mean ± standard deviation).

METHODS

The dogs were administered acepromazine and anesthesia was induced with propofol and maintained with isoflurane. Ventilation was controlled for 4 hours with ZEEP, PEEPmaxC_rs, PEEPmaxC_rs+2 or PEEPmaxC_rs+4. Cardiovascular, pulmonary gas exchange and tissue oxygenation data were evaluated at 5, 60, 120, 180 and 240 minutes of ventilation and compared using a mixed-model anova followed by Bonferroni test. p < 0.05 was considered significant.

RESULTS

Cardiac index (CI) and mean arterial pressure (MAP) were lower in all PEEP treatments at 5 minutes when compared with ZEEP. CI persisted lower throughout the 4 hours only in PEEPmaxC_rs+4 with the lowest CI at 5 minutes (2.15 ± 0.70 versus 3.45 ± 0.94 L minute^-1 m^-2). At 180 and 240 minutes, MAP was lower in PEEPmaxC_rs+4 than in PEEPmaxC_rs, with the lowest value at 180 minutes (58 ± 7 versus 67 ± 7 mmHg). Oxygen delivery index (DO₂I) was lower in PEEPmaxC_rs+4 than in ZEEP at 5, 60, 120 and 180 minutes. Venous admixture was not different among treatments.

CONCLUSION AND CLINICAL RELEVANCE

The use of PEEP caused a transient decrease in MAP and CI in lung-healthy dogs anesthetized with isoflurane, which improved after 60 minutes of ventilation in all levels of PEEP except PEEPmaxC_rs+4. A clinically significant improvement in arterial oxygenation and DO₂I was not observed with PEEPmaxC_rs and PEEPmaxC_rs+2 in comparison with ZEEP, whereas PEEPmaxC_rs+4 decreased DO₂I.

Sodium Abnormalities in Cardiac Surgery With Cardiopulmonary Bypass in Adults: A Narrative Review

Perioperative sodium abnormalities or dysnatremia is not uncommon in patients presenting for cardiac surgery and is associated with increased morbidity and mortality. Both the disease process of heart failure and its treatment may contribute to abnormalities in serum sodium concentration. Serum sodium is the main determinant of serum osmolality, which in turn affects cell volume. Brain cells are particularly vulnerable to changes in serum osmolality because of the nondistensible cranium. The potentially catastrophic neurologic sequelae of rapidly correcting chronic dysnatremia and the time-sensitive nature of cardiac surgery can make the management of these patients challenging. The use of cardiopulmonary bypass to facilitate surgery adds another layer of complexity in the intraoperative management of sodium and water balance. This narrative review examines the definition and classification of dysnatremia. It also covers the etiology and pathophysiology of dysnatremia, implications during cardiac surgery requiring cardiopulmonary bypass, and the perioperative management of dysnatremia.

Complications and Pharmacologic Interventions of Invasive Positive Pressure Ventilation During Critical Illness

Objective: To review the fundamentals of invasive positive pressure ventilation (IPPV) and the common complications and associated pharmacotherapeutic management in order to provide opportunities for pharmacists to improve patient outcomes. Data Sources: A MEDLINE literature search (1950-December 2017) was performed using the key search terms invasive positive pressure ventilation, mechanical ventilation, pharmacist, respiratory failure, ventilator associated organ dysfunction, ventilator associated pneumonia, ventilator bundles, and ventilator liberation. Additional references were identified from a review of literature citations. Study Selection and Data Extraction: All English-language original research and review reports were evaluated. Data Synthesis: IPPV is a common supportive care measure for critically ill patients. While lifesaving, IPPV is associated with significant complications including ventilator-associated pneumonia, sinusitis, organ dysfunction, and hemodynamic alterations. Optimization of pain and sedation management provides an opportunity for pharmacists to directly affect IPPV exposure. A number of pharmacotherapeutic interventions are related directly to prophylaxis against IPPV-associated adverse events or aimed at reduction of duration of IPPV. Conclusions: Enhanced knowledge of the common complications, associated pharmacotherapy, and monitoring strategies facilitate the pharmacist's ability to provide increased pharmacotherapeutic insight in a multidisciplinary intensive care unit setting.

Inadvertent sodium loading with renal replacement therapy in critically ill patients

BACKGROUND

Inadvertent sodium (Na(+)) flux may occur during renal replacement therapy (RRT) in ICU. The objective of this study was to estimate sodium flux during RRT.

METHODS

Between September 2011 to December 2012 we studied 60 ICU patients receiving extended daily dialysis (EDD, Fresenius 4008S) or continuous renal replacement technique (CRRT, Aquarius 6.01). CRRT was categorized as dialysis with continuous veno-venous haemofiltration (CVVH) or haemodiafiltration (CVVHDF). Sodium balance was calculated as the difference between affluent and effluent fluid sodium concentration corrected for volume. The duration of study was either the duration of a single EDD session or 24 h of CRRT.

RESULTS

Both EDD and CRRT contributed to a positive Na(+) flux. Despite similar demographics, CRRT patients had a greater positive sodium flux (p < 0.001). At multivariate analysis, factors [exp(b) (SE), p] which significantly affected sodium flux in each mode of RRT were: (1) EDD (R(2) = 0.42): gradient between RRT Na(+) and serum Na(+) [20.9 (5.8), p < 0.02], and total litres of exchange [1.5 (0.68), p < 0.04]; (2) CVVH (R(2) = 0.77): gradient between RRT Na(+) and serum Na(+) [21.8 (4.7), p < 0.001], dialysis day [-20.9 (9.8), p < 0.05], and total litres of exchange [5.2 (0.96), p < 0.001]; (3) CVVHDF (R(2) = 0.73): gradient between RRT Na(+) and serum Na(+) [23.8 (3.7), p < 0.001], and total fluid removal [-18.5 (3.26), p < 0.001].

CONCLUSION

RRT may inadvertently contribute to sodium load in critically ill patients and is affected by multiple factors including gradient between RRT Na(+) and serum Na(+).

Autonomic tone in medical intensive care patients receiving mechanical ventilation and during a CPAP weaning trial

Mechanical ventilator support and the resumption of spontaneous ventilation or weaning create significant alterations in alveolar and intrathoracic pressure that influence thoracic blood volume and flow. Compensatory autonomic tone alterations occur to ensure adequate tissue oxygen delivery, but autonomic responses may produce cardiovascular dysfunction with subsequent weaning failure. The authors describe autonomic responses of critically ill patients (n = 43) during a 24-hr period of mechanical ventilatory support and during the 24 hr that included their initial spontaneous breathing trial using continuous positive airway pressure. Nearly two thirds of these patients demonstrated abnormal autonomic function and this dysfunction was more severe in those patients who were unable to sustain spontaneous ventilation (n = 15). With further systematic study, autonomic responses may be useful in the identification of patients who are likely to develop cardiac dysfunction with the resumption of spontaneous breathing.

Cardiovascular effects of mechanical ventilation and weaning

Because of their anatomic position in the closed thoracic cavity, the heart and lungs interact during each ventilation cycle. The application of mechanical ventilation and subsequent removal changes normal ventilatory mechanics and produces alterations in cardiac preload and afterload that influence global hemodynamic state and delivery of oxygen and nutrients. Adverse cardiovascular responses to mechanical ventilation and weaning from ventilation include hemodynamic alterations and instability, myocardial ischemia, autonomic dysfunction, and cardiac dysrhythmias. Clinicians must have a clear understanding of the cardiovascular effects of mechanical ventilation and weaning so they may anticipate, recognize, and effectively manage negative effects and improve patient outcomes.

Response of hypotensive dogs to dopamine hydrochloride and dobutamine hydrochloride during deep isoflurane anesthesia

OBJECTIVE

To evaluate the dose-related cardiovascular and urine output (UrO) effects of dopamine hydrochloride and dobutamine hydrochloride, administered individually and in combination at various ratios, and identify individual doses that achieve target mean arterial blood pressure (MAP; 70 mm Hg) and cardiac index (CI; 150 mL/kg/min) in dogs during deep isoflurane anesthesia.

ANIMALS

10 young clinically normal dogs.

PROCEDURES

Following isoflurane equilibration at a baseline MAP of 50 mm Hg on 3 occasions, dogs randomly received IV administration of dopamine (3, 7, 10, 15, and 20 microg/kg/min), dobutamine (1, 2, 4, 6, and 8 microg/kg/min), and dopamine-dobutamine combinations (3.5:1, 3.5:4, 7:2, 14:1, and 14:4 microg/kg/min) in a crossover study. Selected cardiovascular and UrO effects were determined following 20-minute infusions at each dose.

RESULTS

Dopamine caused significant dose-dependent responses and achieved target MAP and CI at 7 microg/kg/min; dobutamine at 2 microg/kg/min significantly affected only CI values. At any dose, dopamine significantly affected UrO, whereas dobutamine did not. Target MAP and CI values were achieved with a dopamine-dobutamine combination at 7:2 microg/kg/min; a dopamine-related dose response for MAP and dopamine- and dobutamine-related dose responses for CI were identified. Changes in UrO were associated with dopamine only.

CONCLUSIONS AND CLINICAL RELEVANCE

In isoflurane-anesthetized dogs, a guideline dose for dopamine of 7 microg/kg/min is suggested; dobutamine alone did not improve MAP. Data regarding cardiovascular and UrO effects indicated that the combination of dopamine and dobutamine did not provide greater benefit than use of dopamine alone in dogs.

Do intraoperative variables have an effect on the timing of tracheal extubation after coronary artery bypass graft surgery?

OBJECTIVE

The purpose of this study was to investigate whether any intraoperative variable had a significant effect on extubation time after coronary artery bypass graft surgery.

DESIGN

Study design was a retrospective study.

SETTING

Study took place in 1 cardiac center in the United Kingdom that had 1000 cases per year.

SUBJECTS

Eighty-nine patients had coronary artery bypass graft surgery in the first 6 months of 1998 performed by one consultant cardiac surgeon.

OUTCOME MEASURES

Study measures included intraoperative variables (number of vessels grafted, time on cardiopulmonary bypass [CPB], length of the operation, use of internal mammary artery) and extubation time.

RESULTS

Mean extubation time was 4.97 hours. On analysis via linear regression no intraoperative variables were found to be statistically significant (P = .05) to extubation time.

CONCLUSION

This study identified that early extubation can be achieved safely. Although no variable was found to have a significant effect on extubation time, the relationship between CPB and extubation may have been attributed to the low mean CPB time within the study (49.1 minutes). The relationship between cardiac status, ischemia, and the timing of extubation does warrant additional exploration.