Breathing pattern and gas exchange in emergency and elective abdominal surgical patients

The effect of non-invasive positive airway pressure therapy following thoracic surgical procedures: protocol for a systematic review

BACKGROUND

Thoracic surgical procedures impair respiratory function, decreasing ventilation and oxygenation and increasing the risk of acute respiratory failure and pulmonary complications. To prevent these clinical repercussions, positive airway pressure therapy is widely used to increase pulmonary ventilation, decrease muscle overload, and ensure adequate oxygenation; however, the benefit of this therapy remains unclear.

METHODS/DESIGN

A systematic search of the literature including PubMed, CINAHL, AMED, PsycINFO, LILACS, Scielo, Scopus, PEDro, and the Cochrane Library will identify the randomized and quasi-randomized trials that used CPAP, Bilevel, or IPPB compared with a control without intervention, a sham treatment or other lung expansion techniques following thoracic surgical procedures. From these trials, we will extract data on a predefined list of outcomes, including oxygenation, ventilation, respiratory failure, pulmonary complications, and time of resolution of the clinical condition. The methodological quality of each trial included will be assessed using the PEDro scale. The strength of the recommendations will be summarized using the GRADE scale. Meta-analyses will be performed, if appropriate.

DISCUSSION

This review aims to promote greater knowledge regarding the efficiency of the use of non-invasive positive airway pressure on recovery of respiratory function and on prevention of pulmonary complications following thoracic surgical procedures. This review could help health professionals improve the care for patients undergoing thoracic surgical procedures.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42015019004.

Ventilatory failure, ventilator support, and ventilator weaning

The development of acute ventilatory failure represents an inability of the respiratory control system to maintain a level of respiratory motor output to cope with the metabolic demands of the body. The level of respiratory motor output is also the main determinant of the degree of respiratory distress experienced by such patients. As ventilatory failure progresses and patient distress increases, mechanical ventilation is instituted to help the respiratory muscles cope with the heightened workload. While a patient is connected to a ventilator, a physician's ability to align the rhythm of the machine with the rhythm of the patient's respiratory centers becomes the primary determinant of the level of rest accorded to the respiratory muscles. Problems of alignment are manifested as failure to trigger, double triggering, an inflationary gas-flow that fails to match inspiratory demands, and an inflation phase that persists after a patient's respiratory centers have switched to expiration. With recovery from disorders that precipitated the initial bout of acute ventilatory failure, attempts are made to discontinue the ventilator (weaning). About 20% of weaning attempts fail, ultimately, because the respiratory controller is unable to sustain ventilation and this failure is signaled by development of rapid shallow breathing. Substantial advances in the medical management of acute ventilatory failure that requires ventilator assistance are most likely to result from research yielding novel insights into the operation of the respiratory control system.

The concentration-effect relationship of the respiratory depressant effects of alfentanil and fentanyl

The relative potencies of fentanyl and alfentanil for respiratory depression were determined in eight healthy male volunteers in a double-blinded, randomized study with a cross-over design. The drugs were delivered by computer-driven infusion with logarithmically ascending plasma concentrations until the respiratory rate reached 2/min and/or oxygen saturation decreased below 85% with subjects breathing room air. Ventilation was measured with respiratory inductive plethysmography, indirect calorimetry, and arterial blood gas analysis, and plasma drug concentrations were determined. Pharmacodynamic modeling was performed using a fractional E(max) model for minute volume and respiratory rate and the concentrations producing 50% depression (i.e., apparent 50% effective concentration [EC(50)] values) were determined. Both drugs decreased ventilation in a similar manner, and drug infusions were terminated at mean +/- SD measured plasma concentrations of 254 +/- 88 ng/mL and 5.1 +/- 1.7 ng/mL for alfentanil and fentanyl, respectively. Alfentanil decreased minute volume from baseline by 54% +/- 19% and respiratory rate by 40% +/- 11% with EC(50) values of 234 +/- 57 ng/mL and 195 +/- 101 ng/mL. The respective decreases for fentanyl were 50% +/- 11%, 41% +/- 15%, and the estimated EC(50) values were 6.1 +/- 1.4 ng/mL and 3.5 +/- 1.4 ng/mL, respectively. Using the apparent EC(50) values, the calculated potency ratio for alfentanil:fentanyl was (mean and 95% confidence interval) 1:39 (1:31-1:46) for minute volume and 1:51 (1:34-1:68) for respiratory rate. This is analogous to the analgesic effect studied earlier. The findings support the notion of parallel analgesic and respiratory depressant effects of alfentanil and fentanyl. Therefore equianalgesic concentrations of both drugs will lead to equally pronounced respiratory depression.

IMPLICATIONS

This double-blinded, randomized study evaluated the potency ratio of alfentanil and fentanyl-induced respiratory depression. The findings support the notion of parallel analgesic and respiratory depressant effects of alfentanil and fentanyl. Therefore equianalgesic concentrations of both drugs will lead to equally pronounced respiratory depression.

Morphine-induced cardiovascular stimulation: the effects of two doses on healthy subjects

In humans, morphine induces hypotension, probably because of histamine liberation. Earlier animal studies have, however, suggested that morphine can induce immediate cardiovascular stimulation when given as a sole medication. The aim of this study was to evaluate the initial effects of morphine on circulation, oxygen consumption, and plasma histamine and catecholamine concentrations. Oxycodone was used as a reference drug. Eight healthy volunteers received, in a random, cross-over, double-blinded fashion: 0.07 mg/kg morphine (M1); 0.14 mg/kg morphine (M2); 0.14 mg/kg oxycodone (O); and placebo (P) as a 2-min IV injection for pain. Mean arterial blood pressure (MAP), heart rate (HR), and oxygen consumption (VO(2)) were recorded. Plasma histamine and catecholamine concentrations were determined. Both M1 and M2 elicited an initial, but transient, increase in MAP from 84 +/- 5 to 96 +/- 9 mm Hg (P < 0.05) and from 83 +/- 8 to 100 +/- 10 mm Hg (P < 0.05), respectively. A parallel increase in HR was also seen after M1 (from 62 +/- 12 to 70 +/- 10 bpm, P < 0.05) and M2 (from 67 +/- 9 to 78 +/- 8 bpm, P < 0.05). After M2, this was accompanied by a simultaneous increase in VO(2) from 295 +/- 39 mL/min to 322 +/- 61 mL/min (P < 0.05). After O, as well as P, no increase in MAP or HR was detected. Plasma histamine and catecholamine concentrations were not clearly affected by any of the treatments. We conclude that the immediate effect of morphine on the hemodynamics of healthy volunteers was stimulation, not hypotension. This effect was not seen in conjunction with oxycodone, a morphine-like mu-receptor agonist.

IMPLICATIONS

In this double-blinded, randomized study, we evaluated whether morphine could induce immediate cardiovascular stimulation, as seen previously in animal studies. In healthy volunteers, during a painful stimulus, morphine caused an initial, transient hemodynamic stimulation, accompanied by increased oxygen consumption, without detectable release of histamine or catecholamines into the plasma. Oxycodone caused only minor hemodynamic alterations.

The effect of dopexamine on regional tissue oxygenation, systemic inflammation and amino acid exchange in major abdominal surgery

BACKGROUND

Beta-adrenergic agents are frequently used to improve cardiac performance in surgical and intensive care patients. Beta-adrenergic agents have metabolic and anti-inflammatory effects in addition to their cardiovascular effects. Splanchnic metabolic activity increases in response to surgery and inflammation. Dopexamine is believed to favor blood flow distribution to the splanchnic region.

METHODS

We investigated the effect of dopexamine, started before major abdominal surgery, on postoperative patterns of systemic and regional blood flow, metabolic response, and markers of inflammation. Twenty-one patients undergoing major abdominal surgery were studied. All patients were stabilized preoperatively to predefined hemodynamic endpoints with fluids. After preoperative measurement of systemic and splanchnic oxygen transport and splanchnic lactate, glutamine and alanine exchange and blood levels of tumor necrosis factor (TNF) and interleukin-6 (IL-6), the patients were randomized to receive an infusion of dopexamine at 0.5 microg kg(-1) min(-1) (group 1) or 2.0 microg kg(-1) min(-1) (group 2) or placebo. Measurements were repeated at 6 h and 24 h after the end of the operation and the blood levels of cytokines also at 36 h postoperatively.

RESULTS

Dopexamine evoked an increase in cardiac index preoperatively. Postoperatively, there was no difference between the groups in systemic and regional hemodynamics or oxygen transport: cardiac index, splanchnic blood flow and oxygen delivery increased similarly in each group. Accordingly, systemic oxygen extraction decreased. Glutamine, alanine and lactate exchange did not differ between the groups. The only metabolic change was an increased splanchnic uptake of alanine, which also was unaffected by dopexamine. There was no difference between the groups in TNF and IL-6 levels; TNF level did not change, while IL-6 level increased in response to surgery.

CONCLUSIONS

Dopexamine, when added to a preoperative stabilization protocol with fluids, did not augment the postoperative hemodynamic response, and had no effect on postoperative metabolic and inflammatory responses.

The effect of low-dose ketamine on fentanyl-induced respiratory depression

This study evaluated if adding low-dose ketamine to fentanyl could offer a haemodynamically stable drug combination with little respiratory side-effects. Eight healthy, consenting male volunteers received in a random, cross-over and double-blind fashion both fentanyl 2 micrograms.kg-1 + ketamine 0.25 mg.kg-1 and fentanyl 2 micrograms.kg-1 + placebo. The fentanyl and placebo reduced minute ventilation, alveolar ventilation and oxygen consumption (p < 0.05), with little effect on haemodynamics. After fentanyl and ketamine, the decrease in minute ventilation and alveolar ventilation was attenuated compared to the placebo-containing combination (p < 0.05), but with a simultaneous increase in oxygen consumption (p < 0.05) and stimulation of haemodynamics (p < 0.05). Both treatments decreased oxygen saturation and arterial oxygen pressure similarly. Ketamine thus attenuated the fentanyl-induced reduction in ventilation without preventing the decrease in blood oxygenation. In conclusion, combining low-dose ketamine to fentanyl offers no benefits in terms of preventing respiratory depression.