Critical care medicine
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Several recent articles have suggested the use of mean airway pressure (Paw) as an index of the physiological effect of ventilating pressures. To facilitate the understanding of this parameter, operational formulas are derived by applying the explicit, mathematical definition of Paw to several clinically relevant pressure waveforms. These formulas are then generalized to apply to any wave shape. It is shown that any pressure waveform can be characterized by a waveform constant K, knowledge of which permits the estimation of Paw using information from either airway pressure recordings or the control settings and pressure gauges on conventional ventilators.
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Critical care medicine · Apr 1982
Comparative StudyHemoglobin solution in the treatment of hemorrhagic shock.
The major physiological effects of hemorrhage are hypovolemia and anemia. The administration of an oxygen-carrying plasma expander, such as crystalline hemoglobin solution (CHb), can restore both of these deficits while avoiding many of the logistical problems entailed in the use of blood. The authors have used Chb to treat severe hypovolemia and anemia in separate canine models and found it to be highly effective. ⋯ Hemodynamic responses to low P50 CHb, however, suggest that oxygen offloading at the tissue level is compromised by the high oxygen affinity of unmodified CHb. Whereas such oxygen offloading deficits may be compensated for in the chronic situation, they may be of crucial importance in severe trauma where oxygen transport is often limited by arterial desaturation, low cardiac output, maldistribution of perfusion and interstitial water overload. The development of a lower-affinity CHb is, therefore, of the essence.
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The ventilatory response in acute lactic acidosis was assessed in 39 patients. In 18 patients, the acidosis was associated with phenformin ingestion and in 21, with other causes such as shock and sepsis, but not pulmonary edema. ⋯ Only 1 lactic acidotic patient had a triflingly lower CO2 tension. Shock was present in 8 of the 9 lactic acidotic patients whose CO2 tensions were more than 2 torr above the 95% confidence band.
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Critical care medicine · Mar 1982
Comparative StudyTracheal tube forces on the posterior larynx: index of laryngeal loading.
Most tracheal tubes sold today are arcuate in shape while the human airway is S-shaped. In situ, the tubes exert different forces on the posterior larynx, depending on their stiffness. Laryngeal damage after prolonged intubation is recognized as the result of these forces. ⋯ The airway model and test procedure can be utilized by manufactures, designers, and others to provide valuable information on tracheal tube performance and to develop improved tracheal tubes in the future. The results indicate that the polyvinylchloride tubes (PVC) and the silicone rubber tubes had the lowest index of laryngeal loading after long-term conditioning and would be preferable for prolonged intubation. The red rubber tube had the highest index of laryngeal loading after long-term conditioning, yet its stiffness would facilitate intubation.
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Critical care medicine · Mar 1982
Colloid osmotic pressure and fluid resuscitation with hetastarch, albumin, and saline solutions.
The effects of fluid resuscitation with 6% hetastarch, 5% albumin, or 0.9% saline solutions on plasma colloid osmotic pressure (COP) were examined in 26 patients with hypovolemic circulatory shock. One liter of hetastarch produced a 36% increase in COP compared to an 11% increase after 1 L of albumin (p less than 0.001). One liter of saline resulted in a 12% decrease in COP (p less than 0.05). ⋯ These changes persisted from 2-5 days after resuscitation. Saline resuscitation required significantly larger amounts of fluid. The authors conclude that fluid resuscitation of circulatory shock with colloid solutions increases COP and requires less volume of resuscitative fluid.