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Biomedical subjects

C F Mackenzie

Publications and source records attributed to C F Mackenzie.

At least 55 records · Page 3Linked to original sources
PubMed1987

Collateral ventilation of obstructed lung during high-frequency oscillation in dogs and pigs.

To determine if collateral ventilation (CV) occurs in pigs and dogs during intermittent positive-pressure ventilation (IPPV) and high-frequency oscillation (HFO), seven pigs and seven dogs were studied by measuring Xenon 133 washout (XeW) from an occluded subsegmental bronchus. The rate constant/min (K) for Xe blood uptake (KXeb) was derived, and when subtracted from K for XeW (KXeW) gave K for removal of Xe by CV (KXecv). Pig XeW were single exponentials with mean KXew = 0.25/min during IPPV and 0.12/min with HFO. In pigs, mean K of XeW was no different from KXeb so that all XeW occurred by blood uptake and none by CV. XeW in dogs had two exponentials. Dogs had over 11 times greater mean KXeW than pigs during IPPV and over 24 times greater during HFO. In dogs, on average, 79% (IPPV) and 87% (HFO) of XeW occurred by CV. CV is a means of gas exchange during HFO and IPPV in dogs but not in pigs.

Animals↗
PubMed1987

Venous air embolism, hypotension, and end-tidal nitrogen.

The most sensitive method of venous air embolism (VAE) detection in clinical use is the precordial Doppler detector. Because the Doppler detector may provide false-positive and false-negative data, many clinicians rely on end-tidal gas measurements for verification of VAE in the operating room. End-tidal nitrogen (ETN2) increases soon after experimental VAE are small enough to cause minimal changes in blood pressure; however, decreases in end-tidal CO2 (ETCO2) are more sensitive. A large VAE causes hemodynamic instability, and the effect of low cardiac output on ETN2 has not been evaluated. This study was done to compare the changes in ETN2 and ETCO2 during large bolus and infusion VAE. Five mongrel dogs were anesthetized, intubated, and ventilated (FIO2 1.0, PaCO2 38 +/- 4 (SD) mm Hg). The animals were studied in the supine position; anesthesia and paralysis were maintained with a constant infusion of thiamylal and pancuronium. Maintenance fluids were administered at 5 ml kg-1 h-1. Mean arterial and pulmonary arterial pressures (PAP) and ETN2 and ETCO2 were displayed on a strip chart recorder. The dogs underwent both bolus and infusion VAE in separate experiments 10 to 14 days apart. The air emboli were given in random order by automated syringe over 1 minute (infusion) (1 to 2.5 ml kg-1 min-1) or by hand injection over 5 seconds (bolus) (1 to 2.5 ml kg-1). Changes in precordial Doppler sounds occurred in all animals at all doses. The peak increase in PAP and decrease in ETCO2 were significant after all air doses. ETN2 changes were biphasic. The peak increase was significant after all air doses; the peak decrease was significant in 37 of 40 bolus and infusion VAE episodes, occurred within 1 to 3 minutes, and lasted 20 to 30 minutes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Creatinine clearance of early detection of posttraumatic renal dysfunction.

Acute renal failure develops insidiously in the presence of normal urine output and vital signs. A prospective study was carried out to find whether renal impairment can be detected in the immediate postoperative period and to determine the renal function test best predicting the development of renal dysfunction. Forty patients with multiple trauma who required more than 10 units of blood and had a systolic blood pressure less than 80 mmHg on admission were studied. Creatinine clearance (Ccr), free-water clearance (CH2O), fractional excretion of Na+, blood urea nitrogen (BUN), urine flow rate, and vital signs were measured and compared in seven patients who developed renal dysfunction within a week of trauma (Group 1) and 33 patients who maintained normal renal function (Group 2). In all Group 1 patients Ccr remained less than 25 ml/min and CH2O greater than -15 ml/h for 6 h following surgery. None of the Group 2 patients had Ccr less than 25 ml/min for longer than 4 h following surgery. However, CH2O values were greater than -15 ml/h in 15 of the 33 Group 2 patients during the first 24 postoperative hours. Ccr values less than 25 ml/min were present, despite normal urine flow rate and blood pressure, in patients who subsequently developed renal dysfunction. Patients who have Ccr values less than 25 ml/min within 6 h following trauma and surgery may develop renal dysfunction, and some of them may proceed to acute renal failure. CH2O was not as good a predictor of development of renal dysfunction as Ccr.

Acute Kidney Injury↗
PubMed1985

Sensitivity of end-tidal nitrogen in venous air embolism detection in dogs.

Embolized nitrogen appears in alveolar gas during clinical and experimental venous air embolism (VAE). Since early detection of VAE is believed to reduce morbidity and mortality, this study was done to compare the sensitivity of end-tidal nitrogen (ETN2) monitoring with other detection methods in current clinical use--precordial Doppler (PD), end-tidal CO2 (ETCO2), and pulmonary artery pressure (PAP). Ten mongrel dogs (10-17 kg) were anesthetized, placed in the supine position, immobilized, and ventilated (FIO2 1.0; PaCO2 35-40 mmHg). Anesthesia and muscle relaxation were maintained with constant infusions of thiamylal and pancuronium. Maintenance fluids were administered at 5 ml X kg-1 X h-1. Mean arterial pressure (MAP), PAP, and ETN2 and ETCO2 (Medspec II mass spectrometer) were displayed on a strip chart recorder. The dogs were divided into two equal groups and given either a step-wise sequence of 1-min air infusions (0.1-1.5 ml X kg-1 X min-1) or 5-s bolus air injections (0.25-1.0 ml X kg-1). Changes in PD sounds occurred in all animals at all air doses. Changes in cardiovascular variables and PaO2 were minimal. The threshold dose for ETCO2 and ETN2 to reach significance was 0.1 and 0.25 ml X kg-1, respectively, while PAP increases were significant at greater than 0.5 ml X kg-1 air doses. The time to maximum change (delta max) ETN2 was 30-90 s earlier than delta max ETCO2 (P less than 0.05) and 6-105 s earlier than delta max PAP. The delta max for all variables was dose related and statistically significant except for the smallest infusion VAE, where only ETCO2 was significantly changed.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia↗
PubMed1985

Cardiorespiratory function before and after chest physiotherapy in mechanically ventilated patients with post-traumatic respiratory failure.

Chest physiotherapy (CPT) is used frequently in the ICU, but there is little available information that quantitates its effect on cardiac or respiratory function. Nineteen mechanically ventilated patients with post-traumatic respiratory failure were studied before, immediately after, and 2 h after CPT was used to manage secretion retention. Cardiac index was unchanged, but there was an immediate decrease in intrapulmonary shunt, followed 2 h later by an increase in lung/thorax compliance. We did not find the reduced cardiac output reported by others. The reasons for this may include use of different CPT techniques, a young patient population (mean age 32.4 yr), and mechanical ventilation with positive end-expiratory pressure. CPT did not produce the deleterious cardiopulmonary changes associated with bronchoscopy, and it reduced retained lung secretions without producing hypoxemia. Intrapulmonary shunt and lung/thorax compliance were significantly improved, but the long-term clinical effect of these changes is unknown.

Adult↗
PubMed1985

Assessment of cardiac and respiratory function during surgery on patients with acute quadriplegia.

Cardiorespiratory function was assessed in 22 mechanically ventilated patients who underwent surgery within an average of 4.8 days following traumatic spinal cord injury at C3-7. A fluid challenge technique was used to derive right and left ventricular function curves and to assist in choice of therapy from four possible outcome responses. Both right and left ventricular stroke work increased but left ventricular stroke work was still lower than normal in six (27%) of 22 patients despite elevation of cardiac filling pressures. Pulmonary vascular resistance fell, but systemic vascular resistance was unchanged following fluid challenge. Respiratory function, including intrapulmonary shunt, lung/thorax compliance, dead space, and arterial pO2 and pCO2, were unchanged by fluid administration averaging 520 ml of plasma protein fraction in 12 minutes. The Bainbridge reflex was inoperative. There was no correlation between anesthetic agent, level or type of neurological deficit, and cardiorespiratory function. Left ventricular function was impaired so the use of peripheral vasoconstrictors that elevate systemic vascular resistance should be avoided in the management of spinal shock. Instead, myocardial depressants should be reduced and fluid replacement used to optimize cardiac function. Elevation of central venous or pulmonary capillary wedge pressures to 18 mm Hg should be used to reverse hypotension, acidosis, low venous pO2, or oliguria before institution of centrally acting inotropic therapy in the management of acute spinal cord injury.

Adolescent↗
PubMed1980

Changes in total lung/thorax compliance following chest physiotherapy.

To quantitate and obtain objective assessment of the effect of secretion clearance following chest physiotherapy (CPT), total lung/thorax complicance (CT) was calculated immediately before and for 2 hours after one treatment with CPT. Forty-two patients who were mechanically ventilated because of respiratory failure were studied. Therapy averaged 57 minutes and included postural drainage, percussion, vibration, and endotracheal suctioning. The increase in CT following CPT was statistically significant (p less than 0.01) and remained so for at least 2 hours after CPT. There was no difference in the degree to which CT changed in patients with different indications for CPT or in patients ventilated with positive end-expiratory pressure. Largest mean values for CT were obtained 2 hours following CPT, the duration of our measurement of CT. Chest x-ray identification of affected areas of lung before CPT is necessary to allow the physiotherapist to produce the CT changes noted in this study. CT, which can be readily calculated from many recently designed ventilators, may be monitored during CPT to evaluate the efficacy of treatment and to quantitate the effect of secretion clearance following CPT. Duration of CPT should be determined by CT and auscultation.

Adolescent↗
PubMed1979

Two-year mortality in 760 patients transported by helicopter direct from the road accident scene.

Of 760 direct admissions to a specialized trauma center, 173 (22.7%) victims of motor vehicle accidents died. Excluding patients dead on arrival, the mortality rate was 14.5%. Autopsy reports were reviewed and showed that the major cause of death was head injury (49.7%). Uncontrollable hemorrhage from massive trauma was the next most common problem and usually proved fatal in the first 24 hours after admission. The incidence of sepsis and renal failure increased with prolongation of CCRU stay. Following admission, respiratory failure was not a common cause of death (3%). Because of direct helicopter rather than ambulance transport from the scene of the motor vehicle accident, earlier attention was paid to diagnosis of trauma and treatment of respiratory insufficiency with mechanical ventilation. Because of the early initiation of therapy, there was rapid restoration of circulating volume and tissue perfusion. This may account for the low mortality.

Accidents, Traffic↗
PubMed1979

Changing patterns of posttraumatic acute renal failure.

ARF will continue to occur as more severely traumatized patients survive with better resuscitation. The incidence of ARF, however, appears to be steadily decreasing and ARF occurs only in patients with severe injury and multiple organ failure. ARF developing for the past three years in MIEMS was a nonoliguric variety in the majority of patients. Management of ORF with dialysis has been disappointing. Prevention of oliguria in ARF appears possible and may be one of the most important steps to decrease the morbidity and fatality rate. Further investigation is required to find the cause and optimum management of NORF.

Acute Kidney Injury↗