Baroreceptor-mediated compensation for hemodynamic effects of positive end-expiratory pressure

Prediction of hypotension during the alveolar recruitment maneuver in spine surgery: a prospective observational study

BACKGROUND

Atelectasis can occur in many clinical practices. One way to prevent this complication is through the alveolar recruitment maneuver (ARM). However, hemodynamic compromise can accompany ARM. This study aims to predict ARM-induced hypotension using a non-invasive method.

METHODS

94 American Society of Anesthesiologists physical status I-II patients aged 19 to 75 with scheduled spinal surgery were enrolled. After anesthesia, we performed a stepwise ARM. Data on perfusion index, mean arterial pressure, heart rate, pleth variability index, cardiac index, and stroke volume variation was collected before induction of anesthesia (T0), just before ARM (T1), at the start of ARM (T2), 0.5 min (T3), 1 min (T4), 1.5 min (T5, end of ARM), and 2 min after the beginning of ARM (T6). Hypotension was defined as when the mean arterial pressure at T5 decreased by 20% or more compared to the baseline. The primary endpoint is that the perfusion index measuring before induction of anesthesia, which reflects the patients' own vascular tone, was correlated with hypotension during ARM.

RESULTS

Seventy-five patients (79.8%) patients developed hypotension during ARM. The pre-induction persufion index (Pi) (95% confidence interval) was 1.7(1.4-3.1) in the non-hypotension group and 3.4(2.4-3.9) in the hypotension group. (p < 0.004) The hypotension group showed considerably higher Pi than the non-hypotension group before induction. The decrease of Pi (%) [IQR] in the non-hypotensive group (52.8% [33.3-74.7]) was more significant than in the hypotensive group. (36% [17.6-53.7]) (p < 0.05) The area under the receiver operating characteristic curve of Pi for predicting hypotension during ARM was 0.718 (95% CI 0.615-0.806; p = 0.004), and the threshold value of the Pi was 2.4.

CONCLUSION

A higher perfusion index value measuring before induction of anesthesia can be used to predict the development of hypotension during ARM. Prophylactic management of the following hypotension during ARM could be considered in high baseline Pi patients.

Recruitment Maneuver in Elderly Patients with Different Peripheral Chemoreflex Sensitivity during Major Abdominal Surgery

The goal of the study was to evaluate the effect of a recruitment maneuver on respiratory biomechanics, oxygenation, and hemodynamics in patients suffering from chronic heart failure with different peripheral chemoreflex sensitivity. The study was conducted in 115 elderly patients which underwent major abdominal surgery under general/epidural surgery. Peripheral chemoreflex sensitivity (PCS) was evaluated with breath-holding duration (BHD) during breath-holding test. All patients were divided into two groups: group H had a high PCS (BHD = 38 seconds or less, n = 49); Group M had a middle PCS (BHD more than 38 seconds, n = 66). Recruitment maneuver improved oxygenation and respiratory biomechanics in all cases. However, cardiac output decreased by an average of 18%–31% in group H compared to 18%–28% in group M. SVR either remained unchanged or decreased by up to 14% of the initial value in group H, while, in group M, it had a tendency to increase, which was 24% of the initial value. So, recruitment maneuver is an effective method to improve oxygenation and biomechanical properties of the respiratory system but in patients with increased peripheral chemoreflex sensitivity it associates with the risk of hemodynamic disturbances.

Heterogenous haemodynamic effects of adaptive servoventilation therapy in sleeping patients with heart failure and Cheyne-Stokes respiration compared to healthy volunteers

This study investigated the haemodynamic effects of adaptive servoventilation (ASV) in heart failure (HF) patients with Cheyne-Stokes respiration (CSR) versus healthy controls. Twenty-seven HF patients with CSR and 15 volunteers were ventilated for 1 h using a new ASV device (PaceWave™). Haemodynamics were continuously and non-invasively recorded at baseline, during ASV and after ventilation. Prior to the actual study, a small validation study was performed to validate non-invasive measurement of Stroke volume index (SVI). Non-invasive measurement of SVI showed a marginal overall difference of -0.03 ± 0.41 L/min/m(2) compared to the current gold standard (Thermodilution-based measurement). Stroke volume index (SVI) increased during ASV in HF patients (29.7 ± 5 to 30.4 ± 6 to 28.7 ± 5 mL/m(2), p < 0.05) and decreased slightly in volunteers (50.7 ± 12 to 48.6 ± 11 to 47.9 ± 12 mL/m(2)). Simultaneously, 1 h of ASV was associated with a trend towards an increase in parasympathetic nervous activity (PNA) in HF patients and a trend towards an increase in sympathetic nervous activity (SNA) in healthy volunteers. Blood pressure (BP) and total peripheral resistance response increased significantly in both groups, despite marked inter-individual variation. Effects were independent of vigilance. Predictors of increased SVI during ASV in HF patients included preserved right ventricular function, normal resting BP, non-ischaemic HF aetiology, mitral regurgitation and increased left ventricular filling pressures. This study confirms favourable haemodynamic effects of ASV in HF patients with CSR presenting with mitral regurgitation and/or increased left ventricular filling pressures, but also identified a number of new predictors. This might be mediated by a shift towards more parasympathetic nervous activity in those patients.

Acute hemodynamic effects of recruitment maneuvers in patients with acute respiratory distress syndrome

BACKGROUND

The recruitment maneuver (RM) in acute respiratory distress syndrome (ARDS) can cause hemodynamic derangement. We evaluated circulatory and cardiac changes during RMs.

METHODS

We performed sustained inflation (SI) with a pressure of 40 cm H(2)O for 30 seconds as an RM on 22 patients with ARDS. Blood pressure (BP) and heart rate were recorded immediately before, every 10 seconds during, and 30 seconds after the RM. Ventricular dimensions were obtained simultaneously using M-mode echocardiography, and tissue Doppler imaging was performed on the left ventricular wall.

RESULTS

Mean, systolic, and diastolic BP decreased at 20 and 30 seconds during 30-second RMs (mean BP: 92 +/- 12 at baseline to 83 +/- 18 mm Hg at the end of the RM, P < .05) and subsequently recovered. Heart rate decreased at 10 and 20 seconds during the RM, and tended to increase afterward. Both ventricular dimensions decreased significantly during the RM. The left ventricular ejection fraction and peak velocity of the left ventricle during systole remained stable. The fractional changes in mean BP and left ventricular end-diastolic dimension during the RMs were correlated significantly with each other (r(s) = 0.59). Static compliance of the respiratory system (Crs) was lower in patients with mean BP change > or =15% than in patients in whom the change was <15% (P < .05).

CONCLUSIONS

A transient decrease in mean BP was observed during the RM, and its degree was correlated with the preload decrease, while cardiac contractility was maintained.

Heart rate variability and spontaneous baroreflex sequences in supine healthy volunteers subjected to nasal positive airway pressure

To determine the dynamic effects of short-term nasal positive airway pressure (nPAP) on cardiovascular autonomic control, continuous recordings of noninvasively obtained hemodynamic measurements and heart rate variability (HRV) were obtained in 10 healthy subjects during frequency-controlled breathing (between 0.20 and 0.24 Hz) in supine posture under different pressures of nPAP ranging from 3 to 20 cmH(2)O. HRV was assessed using spectral analysis of the R-R interval. The slope of the regression line between spontaneous systolic blood pressure and pulse interval changes was taken as an index of the sensitivity of arterial baroreflex modulation of heart rate (sequence method). Application of nPAP resulted in a pressure-dependent decrease of cardiac output and stroke volume (P < 0.05, ANOVA) and in an increase in total peripheral resistance (P < 0.03, ANOVA). Hemodynamic changes under increasing nPAP were accompanied by a decrease in total power of HRV despite mean R-R interval remaining unchanged. The overall decrease in HRV was accompanied by a reduction across all frequency bands when absolute units were used (P < 0.01). When the power of low frequency and high frequency was calculated in normalized units, a diminished high frequency and an increased low-to-high frequency ratio were observed (P < 0.05). Compared with low levels of nPAP, pressure levels of >10 cmH(2)O were associated with a significant decline in the mean slope of spontaneous baroreceptor sequences (P < 0.04). These findings indicate that short-term administration of nPAP in normal subjects exerts significant alterations in R-R interval variability and spontaneous baroreflex modulation of heart rate.

Heart rate variability and hemodynamic alterations in canines with normal cardiac function during exposure to pressure support, continuous positive airway pressure, and a combination of pressure support and continuous positive airway pressure

Variations in intrathoracic pressure generated by different ventilator weaning modes may significantly affect intrathoracic hemodynamics and cardiovascular stability. Although several investigators have attributed cardiovascular alterations during ventilator weaning to augmented sympathetic tone, there is limited investigation of changes in autonomic tone during ventilator weaning. Heart rate variability (HRV), the analysis of beat-to-beat changes in heart rate, is a noninvasive indicator of autonomic tone that might be useful in the identification of patients who are at risk for weaning difficulty due to underlying cardiac dysfunction. The authors describe HRV and hemodynamics in response to 3 ventilatory conditions: pressure support (PS) 10 cmH2O, continuous positive airway pressure (CPAP) 10 cmH2O, and a combination of PS 10 cmH2O and CPAP 10 cmH2O (PS + CPAP) in a group of canines with normal ventricular function. Six canines were studied in the laboratory. Continuous 3-lead electrocardiographic data were collected during baseline (controlled mechanical ventilation) and following transition to each of the ventilatory conditions (PS, CPAP, PS + CPAP) for analysis of HRV. HRV was evaluated using power spectral analysis to define the power under the curve in a very low frequency range (0.0033 to < 0.04 Hz, sympathetic tone), a low frequency range (0.04 to < 0.15 Hz, primarily sympathetic tone), and a high frequency range (0.15 to < 0.40 Hz, parasympathetic tone). A thermodilution pulmonary artery catheter measured cardiac output and right ventricular end-diastolic volume to describe global hemodynamics. There were significant increases in very low frequency power (sympathetic tone) with a concomitant significant reduction in high-frequency power (parasympathetic tone) with exposure to PS + CPAP. These alterations in HRV were associated with significantly increased heart rate and reduced right ventricular end-diastolic volume. Although there was a small but significant increase in cardiac output with exposure to PS, HRV was unchanged. These data indicate that there was a relative shift in autonomic balance to increased sympathetic and decreased parasympathetic tone with exposure to PS + CPAP. The increase in intrathoracic pressure reduced right ventricular end-diastolic volume (preload). This hemodynamic alteration generated a change in autonomic tone, so that cardiac output could be maintained. Individuals with autonomic and/or cardiovascular dysfunction may not be capable of this type of response and may fail to successfully wean from mechanical ventilation.