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Biomedical subjects

M T Snider

Publications and source records attributed to M T Snider.

At least 37 records · Page 2Linked to original sources
PubMed1985

Accumulation of methane, acetone, and nitrogen in the inspired gas during closed-circuit anesthesia.

During closed-circuit anesthesia, the patient's inspired gas may become progressively contaminated by nonanesthetic gases. We studied the concentrations of methane, acetone, and nitrogen as nonanesthetic gas contaminants in the circuit gas of 16 cases during closed-circuit anesthesia. After a "short" period of denitrogenation (6-8 min), average nitrogen concentration in the closed circuit increased from 6.4 to 16.2%, methane from 4.3 to 22.4 ppm, and acetone from 0.3 to 2.2 ppm. After "long" denitrogenation (33 min), average nitrogen concentration in the closed circuit increased from 1.0 to 5.1%, methane from 3.7 to 17.9 ppm, and acetone from 1.3 to 5.9 ppm. It is concluded that gases stored in tissues or produced within the body can appear in the patient's expired gas during closed-circuit anesthesia. Intermittent flushing of the circuit with high flow gases is suggested to remove these contaminants.

Acetone↗
PubMed1983

High-frequency ventilation at rates of 375 to 1800 cycles per minute in four neonates with congenital diaphragmatic hernia.

Neonates with congenital diaphragmatic hernias (CDH) often die because of pulmonary hypoplasia and high pulmonary vascular resistance (PVR). Pulmonary hypertension and right-to-left shunting precedes progressive hypoxia and death. PVR is increased by acidosis and by high airway pressures. High-frequency oscillation (HFO) is a new technique which may improve the outcome for such infants. Gas exchange in HFO is achieved by directing rapid pulsations of small volumes of gas down the trachea, typically at rates greater than 200 cycles per minute, volumes less than 25% of dead space, and low airway pressures. Gas transport results from augmented diffusion, not from bulk flow. Four neonates with CDH deteriorated on conventional mechanical ventilation and required hand ventilation at rates above 200 per minute. HFO at frequencies from 375 to 1800 cycles per minute was then initiated using a flow-interrupter type of oscillator. A marked fall in PaCO2 and a rise in pH resulted. The elimination of CO2 was very efficient with low mean airway pressures (less than 15 mm Hg). The initial improvement during HFO probably resulted from a decrease in PVR due to reversal of the acidosis. However, all four babies died after 13 to 80 hours of HFO. Neonates with CDH who remain hypercapneic despite conventional mechanical ventilation can be successfully ventilated by HFO. Use of HFO produces respiratory alkalosis which may stabilize PVR in the normal range and improve survival rate.

Female↗
PubMed1981

Thermodilution right ventricular volume: a novel and better predictor of volume replacement in acute thermal injury.

Management of acutely burned patients requires intense but meticulous fluid therapy. Indicators of satisfactory resuscitation include: intravascular and arterial pressures and urine output. The usefulness of these parameters as a predictor of cardiac index (CI) has not been tested. Compared to central venous pressure, right ventricular end-diastolic volume (RVEDV) may give a closer approximation of the preload of the right ventricle. Modifying the pulmonary artery (PA) catheter and using the thermodilution technique we measured RVEDV and right ventricular ejection fraction (RVEF) as well as the classical parameters in 16 patients of mean age 39.3 years and of mean body surface area burn 75.2%. CI best correlated with RVEDV (r = 0.75). Mean PA pressure, wedge pressure, RV end-diastolic pressure, and urine output correlated poorly with CI (r = 0.36, 0.32, 0.27, and 0.26, respectively). Unlike atrial pressures the RVEDV and RVEF are unaffected by malpositioning of transducers, airway pressure, and compliance changes of the ventricle. The measurement of RVEDV is a useful clinical tool for the assessment of preload and when used in combination with RVEF may indicate the need for inotropy.

Adolescent↗
PubMed1980

Right ventricular dysfunction in acute thermal injury.

The elevated cardiac output (CO) and pulmonary artery hypertension (PAH) observed in thermal injury offers a unique opportunity to study the effects of a combined pressure-flow load on the right ventricle in previously healthy persons. Potential responses include a diminished right ventricular ejection fraction (RVEF), increased right ventricular end-diastolic volume index (RVEDVI), and augmented myocardial oxygen consumption because of increased systolic wall tension. We investigated these factors in 15 nonhypoxic patients without sepsis having 15--75% body surface area burns using flow directed catheters and the thermodilution technique. All patients increased their CO in response in fluid resuscitation, but six patients with an elevated mean pulmonary artery pressure (greater than 20 mmHG and increased pulmonary vascular resistance (greater than 1.2 mmHg/min/L) had right ventricular dysfunction as evidenced by an increase (188 +/- 15 ml/M2) in RVEDVI and a decreased (0.26 +/- 4 ml/M2) RVEF. Patients without PAH had a smaller RVEDVI (115 +/- 4 ML/M2) and larger RVEF (0.39 +/- 0.02). Patients with PAH and RV dysfunction were older, had larger body surface area burns, lower systemic diastolic artery pressures (63 +/- 4 mmHg) and higher heart rates (114 +/- 7 beats/min); RV end-diastolic pressures were minimally elevated (9.5 +/- 1.4 mmHg). The decrease in RVEF and increase in RVEDVI may limit the hemodynamic response to fluid volume replacement and survival.

Acute Disease↗
PubMed1980

Fetal cardiovascular and metabolic responses to simulated diving in the Weddell seal.

Fetal responses to normobaric diving simulated by submersion of the maternal head for 20 min were studied in four conscious Weddell seals near term. Microspheres injected into the maternal aorta were distributed to the placenta and kidneys in the ratio of 0.4 in the control period and 19.3 during diving, suggesting minimal placental vasoconstriction. Fetal heart rate fell during diving from a mean control value of 90 to 34 beats/min after 4 min. The onset of fetal bradycardia was not consistently associated with changes in blood gas tensions. Diving was associated with a fall in fetal arterial O2 tension from 24 to 9 Torr, arterial CO2 tension rose from 47 to 85 Torr, and arterial pH fell from 7.35 to 7.24. Fetal-maternal gradients for CO2 and H+ transport remained constant, whereas the gradient for O2 transport fell from 47 Torr before diving to 14 Torr at the end of diving. Blood lactate concentrations increased three- to fourfold during diving and reached peak values 10-15 min after diving ended. The similarity of the fetal and maternal heart rate responses to diving is consistent with the presence of physiological oxygen-conserving reflexes akin to the adult's.

Animals↗
PubMed1980

A comparison of continuous and discrete foreign gas VA/Q distributions.

Estimates of ventilation-perfusion ratio (VA/Q) distributions from foreign gas infusions have utilized a discrete lung model that constrains all alveoli to have 1 of 50 specified VA/Q. In contrast, distribution estimates based on a continuous model allow alveoli to have any VA/Q and can be derived directly from foreign gas data or by transforming distributions derived using the discrete model. We have compared analytically and empirically the properties of distributions based on these two models. Unlike the discrete model, the shape of distributions obtained from the continuous model are insensitive to changes in the VA/Q used in their calculation. Perfusion distributions found from the discrete model using VA/Q values evenly spaced on a logarithmic scale resemble ventilation distributions derived from the continuous model. In contrast, by use of VA/Q evenly spaced on a linear scale, perfusion distributions derived from either model have a similar shape. We concluded that physiological inferences derived from distribution shapes may vary according to the model employed. However, those based upon cumulative perfusion or distribution moments are invariant.

Humans↗
PubMed1979

Extracorporeal membrane oxygenation in severe acute respiratory failure. A randomized prospective study.

Nine medical centers collaborated in a prospective randomized study to evaluate prolonged extracorporeal membrane oxygenation (ECMO) as a therapy for severe acute respiratory failure (ARF). Ninety adult patients were selected by common criteria of arterial hypoxemia and treated with either conventional mechanical ventilation (48 patients) or mechanical ventilation supplemented with partial venoarterial bypass (42 patients). Four patients in each group survived. The majority of patients suffered acute bacterial or viral pneumonia (57%). All nine patients with pulmonary embolism and six patients with posttraumatic acute respiratory failure died. The majority of patients died of progressive reduction of transpulmonary gas exchange and decreased compliance due to diffuse pulmonary inflammation, necrosis, and fibrosis. We conclude that ECMO can support respiratory gas exchange but did not increase the probability of long-term survival in patients with severe ARF.

Acute Disease↗
PubMed1979

Regional blood flow during simulated diving in the conscious Weddell seal.

Changes in regional blood flow during simulated normobaric diving were studied in the conscious Antarctic Weddell seal (Leptonychotes weddelli) by injecting 25-microns radioactive microspheres into the left ventricle. Injections were performed before and 8--12 min after submersion of the head in iced seawater. Diving was associated with a fall in cardiac output from a mean control value of 39.8 +/- 10.2 to 5.6 +/- 3.4 l/min (mean +/- SD) and in heart rate from 52 +/- 15 to 15 +/- 4 beats/min. Blood flow to the splanchnic and peripheral vascular bed was reduced by more than 90%, cerebral blood flow was unchanged, right and left ventricular blood flow decreased by 85%, and adrenal blood flow decreased by 39%. The pulmonary fraction of the injected microsphere dose increased from 7.9 to 29.9% during diving. This may signify a large increase of peripheral arteriovenous shunting during the dive and/or increased bronchial artery blood flow. It is concluded that blood flow during diving is directed to organs and tissues according to their metabolic requirements.

Animals↗
PubMed1977

Pulmonary hypertension in severe acute respiratory failure.

We repeatedly assessed pulmonary and systemic hemodynamics in 30 patients undergoing therapy for severe acute respiratory failure of diverse causes. Pulmonary-artery hypertension and elevated pulmonar vascular resistance were observed in all patients after correction of systemic hypoxemia. Increasing pulmonary blood flow by isoproterenol infusion or decreasing pulmonary blood flow by partial bypass of the right side of the heart minimally altered pulmonary-artery pressure. Although neither elevated pulmonary vascular resistance nor low cardiac index reliably predicted death, survivors had preogressive decreases of pulmonary vascular resistance with time, whereas nonsurvivors tended to maintain or increase pulmonary vascular resistance. Right ventricular stroke-work index was markedly elevated in all patients. The work load imposed upon the right ventricle by elevation of pulmonary vascular resistance may be a factor limiting survival in severe acute respiratory failure.

Acute Disease↗
PubMed1975

Reaction to ketamine: anaphylactoid or anaphylactic?

A 3-year-old child developed extensive macular rash after ketamine. The mechanism of this reaction was investigated by the Prausnitz-Kutzner (P-K) test. It demonstrated that the histamine release was not the result of an anaphylactic reaction, but rather a direct pharmacological effect of the drug. The result suggests that this child can receive ketamine in the future without any severe manifestations. The mechanisms of histamine release are discussed and the treatment of its clinical manifestations is reviewed.

Anaphylaxis↗