Respiratory muscle fatigue: a cause of ventilatory failure in septic shock

Abstract

The effect of endotoxic shock on the respiratory muscle performance was studied in spontaneously breathing dogs given Escherichia coli endotoxin (Difco Laboratories, 10 mg/kg). Diaphragmatic (Edi) and parasternal intercostal (Eic) electromyograms were recorded using fishhook electrodes. The recorded signals were then rectified and electrically integrated. Pleural, abdominal, and transdiaphragmatic (Pdi) pressures were recorded by a balloon-catheter system. After a short control period, the endotoxin was administered slowly intravenously (within 5 min). Death was secondary to respiratory arrest in all animals. All animals died within 150-270 min after the onset of endotoxic shock. Within 45-80 min of the endotoxin administration, mean blood pressure and cardiac output dropped to 42.1 +/- 4.1 and 40.1 +/- 6.0% (mean +/- SE) of control values, respectively, with little change afterward. Mean inspiratory flow rate and Pdi increased from control values of 0.27 +/- 0.03 l X s-1 and 5.75 +/- 0.7 cmH2O to mean values of 0.44 +/- 0.3 l X s-1 and 8.70 +/- 1.05 cmH2O and then decreased to 0.17 +/- 0.03 l X s-1 and 3.90 +/- 0.30 cmH2O before the death of the animals. There were no major changes in the mechanics of the respiratory system. Edi and Eic increased progressively to mean values of 360 +/- 21 and 263 +/- 22% of control, respectively, before the death of the animals. None of the dogs were hypoxic. Arterial PCO2 decreased from a control value of 42.9 +/- 1.7 Torr to a mean value of 29.9 +/- 2.8 Torr and then increased to 51 +/- 4.3 Torr before the death of the animals.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of poor nutrition on the necessity of mechanical ventilation among children admitted to the Pediatric Intensive Care Unit

“…Por outro lado, a respiração nos primeiros anos de vida é primordialmente mantida pela função diafragmática, de forma que as crianças, quando admitidas por insuficiência respiratória associada à desnutrição, estarão mais propensas a desenvolver fadiga respiratória ou descompensação de seu quadro respiratório, como o observado em nosso estudo 1,2,[5][6][7][8]14,19,20 . Assim, não é de se surpreender que a desnutrição tenha sido um fator de risco decisivo para a necessidade de ventilação mecânica, quando associada à admissão na UTI por falência respiratória, ou em crianças menores de um ano de vida.…”

“…Em estudos de saúde pública, a desnutrição tem sido identificada como um fator decisivo, que infui tanto na prevalência como na magnitude da insuficiência respirató-ria 11,12 . Entretanto, nos poucos estudos realizados em terapia intensiva pediátrica, existem dados conflitantes acerca da influência da desnutrição na necessidade de suporte ventilatório e na mortalidade desses pacientes [13][14][15][16][17] .…”

Respiratory muscles and weaning failure

“…9) Sepsis and endotoxic shock: pose a potentially great threat to respiratory muscle contractility, as is convincingly evident from animal models [61][62][63][64]. This is especially important for mechanically-ventilated patients, since mechanical ventilation, per se, greatly increases the risk of infection and/or sepsis, thus potentially initiating a vicious circle.…”

“…expiration for the inspiratory muscles, the increased duty cycle fraction increases the time that the compressive effect is exerted, thus diminishing the blood flow. During states of decreased cardiac output in animal models with cardiogenic [69] or septic shock [62,63], blood flow to the inspiratory muscles remained relatively high representing a substantial percentage of cardiac output. However, the amount of blood flow was smaller than that required, leading eventually to fatigue of the respiratory muscles and inability to sustain spontaneous breathing.…”

“…When dogs with cardiogenic or septic shock [62,63,69,82] were mechanically ventilated, only 3% of their CO was directed to their respiratory muscles. On the contrary, when these dogs were allowed to breathe spontaneously their respiratory muscles received up to 20% of the CO, stealing blood from other organs, such as the brain, liver or other muscles.…”